GREY DEPARTMENT:
It is the first and the most important department of a wet processing mill. It plays an important role in further processing. With the help of 100% inspection the fabric fault are counted and grading of fabric is done and this grading helps us in fabric selection for a particular task. From this department the sample of fabric is send to the laboratory for checking the following parameters:
1 Construction
2 Weight
3 Count
4 Weight/m
5 Blend ratio
6 % Of size
Material enters in mill through this department and the flow of material here is as follows:
It is the first and the most important department of a wet processing mill. It plays an important role in further processing. With the help of 100% inspection the fabric fault are counted and grading of fabric is done and this grading helps us in fabric selection for a particular task. From this department the sample of fabric is send to the laboratory for checking the following parameters:
1 Construction
2 Weight
3 Count
4 Weight/m
5 Blend ratio
6 % Of size
Material enters in mill through this department and the flow of material here is as follows:
FUNCTIONS OF GREY DEPARTMENT:
Following are the main functions of grey department.
To inspect, mend & grade the fabric.
Supply the Grey for further processing.
To keep the record of store fabric.
The rejected fabric is sent back to the respected Mill.
INITIAL STORAGE:
When Grey is unloaded, the 10% inspection is done at the initial stage, which includes testing of counts end and pick & meters of fabric. Then whole delivery is sent for 100% checking, if failed then sent to non-conforming area or rejection area.
MENDING:
This is the portion of the grey department where the faults are removed .The lots after clearing the 10% inspection is sent in mending department for 100% inspection in which the defect are identified and counted and some are mended, according to them grading of fabric done.
The grading criterion is:
A Grade 6-7% defect
B Grade 10% defect /m
C Grade 12-14% defect /m
NP Grade not printable
R Grade Rejected
The faults, which are present at this stage in a fabric, are of three types.
a) Weaving faults.
b) Mending faults.
c) Washable faults.
a) WEAVING FAULTS: -
They are the faults, which cannot be removed during mending process. These include:
JALA: - It is due to the entanglement of warp & weft & their breakage during weaving. It cannot be removed because of breakage of yarn.
CRACK: It is basically the breakage of weft in the middle i.e. lining in the weft direction.
PATTI: It is due to the stoppage of m/c .Its in the direction of weft
DOUBLE PICK: They produce if somehow weft is inserted twice.
BROKEN PICK: It is due to the breakage of pick.(weft)
MISS PICK: When weft is missing then this is produce.
STARTING MARK: This is the line, which is produced in weft direction due to changing of beam.
REED MARK: It is usually produce throughout the length of fabric. It is due to the presence of dent in the reed as gap is producing b/w the warp in this case.
TEMPLE MARK: It is a weaving fault, which arises due to the non-movement of ball & pins of the temple in the loom.
CONTAMINATION: The embossed yarn due to uneven twists and appears over surface as a dot.
b) MENDING DEFECTS
: They are known as mending because they can be removed during mending process by combing (snarls, mis comb and slubs), cutting (h/threads, hole and torn) & application of petrol or emrolex (for the removal of stains). The mending defects include:
SNARLS: It is basically the collection of threads at the surface of fabric. This defect arises by the slow movement of projectile.
H/THREADS: Hanging thread is the piece of yarn attached to the Grey cloth. This fault is removed by cutting.
SLUBS: The fibers are in bunch form at the fabric.
MISS COMB: It is the entanglement of the warp & weft, which appears as disturbance over the surface of fabric.
c) WASHABLE DEFECTS:
These include the following:
1. Oily weft
2. Oil stains
3. Rusty stains
4. Emrolex stains: It is the chemical, which is used to remove the above-mentioned stains, & if a stain remains as a white spot over the fabric, it can be removed by scouring.
DETAIL OF THE DEFECTS:
The number of defects and the type of defects are noted on a chart, which is attached here.
FOLDING AND STORAGE BIN:
The fabric after mending process is folded mechanically under the supervision of usually two workers. There are four folding machines and piles are of one meter. Then the fabric is sent to the storage bin that is divided into different segments according to the quality (grading) of the fabric.
QUALITY ASSURANCE:
In Gul Ahmad after 100% mending, the fabric is rechecked and a quality assurance team does this, which inspects 5% of the total lots. The standards for printed and dyed grey cloth according to the quality assurance department are mentioned in the table, which is attached. Grey department itself before sending the fabric for further processing also checks the quality of the fabric. (10% inspection is done to check the previous inspection).
· If pass then send for singeing
· If fails then sent for 100% inspection.
STICHING SECTION:
Suppose (x) meters of fabric are issued from the grey department then it is sent to the stitching section where the lots are stitched by means of jockey machine.
LOOMS: Mostly the defects created in the fabrics are due to the loom. Different % of defects and different looms are as follows:
1. SHUTTLELESS LOOMS: The fabric has fewer defects and the selvages are large in width. Due to less number of defects the fabric is of ‘A’ and ‘B’ quality.
There are usually 10-12 faults per meter, 2-3 jala permitted. A pair of workers inspects 2500m of fabric in 8 hours.
2. AUTO LOOMS: The fabric made by auto looms has more defects than the shuttle less looms. There are usually 18 defects found per meter of fabric with 4-5 jalas. In 8 hours, a pair of worker can inspect 1600m of fabric.
3.POWER LOOMS: The fabric of power loom has more defects than any other loom, there are mostly 25 defects per meter of fabric including 4-5 jalas and fabric is of ‘B’ and ‘C’ quality. Due to increase in number of faults, only 1000m of fabric is inspected in 8 hours.
GREY ACCESSORIES:
INSPECTION TABLE: for inspection purpose, tube lights are fixed behind the glass. This is used to highlight the defects.
FOLDING MACHINE: There are 4 folding machines and piles are made of 1m, only the one end is fixed while the whole folding is automatically done. Four persons were working at 1 folding machine.
TROLLEY: The trolley is capable of carrying 3000-4000 of fabric. It is moved with the help of a jack.
STITCHING MACHINE: There were 4 jockey machines in stitching section.
FORK LIFTER: the fork lifter is used for carrying bales, rollers and other things and its weighing capacity is 2.5-3 tons.
COMPUTER SYSTEM FOR DATA COLLECTION:
7. FIRE FIGHTING SYSTEM
EXHAUST SYSTEM
PICK GLASS
WEIGHT OF FABRIC CALCULATION
CALCULATION OF FABRIC CONSTRUCTION:
1. 60x50/22x22 = 60x 25.7/22 + 56x 25.7/22 = 135 gm
Similarly:
2. 76x68/30x30 = 76x 25.7/30 + 68x 25.7/ 30 = 65.106 + 58.25 = 123.359 gm
MANAGEMENT INCHARGE:
Mr. Rizwan
Total workers: 200 Pair of workers: 37
Clerks: 03 Head checker: 10
Computer operator: 01 Supervisor: 01
OSTHOFF SINGEING MACHINE (1995)
SINGEING:
Singeing is the process applied to both yarn and fabric to produce an even surface by burning off projecting fibers, yarn ends and fuzz.
OBJECTS OF SINGEING: Following are the main objects of singeing:
Surface hairs help to trap the air in the fabric when it is immersed in water. This means that it takes longer time for water to enter the fabric since it must first displace the air. Singeing, therefore, helps to increase the fabric wet ability.
It creates a smooth surface for printing on. It may be possible to print fine details on hairy surface but once the hair move again after printing the details will become fuzzy.
To emphasize the woven structure of the fabric if that is considered essential.
It prevents frosty appearance after dyeing a hairy fabric who has been dyed may have somewhat a cloudy appearance.
To minimize or prevents the tendency of blend fibers composed of cellulose and synthetic fibers to form pills.
MACHINARIES USED IN SINGEING PROCESS
The machines that are used in singeing process are:
Plate Singeing Machine
Roller Singeing Machine
Gas Singeing Machine.
In case of plate singeing machine a plate is red hot and the fabric is passed at a specific distance and hence the pills reduces. But the draw back is this when fabric passes continuously the plates get cooled and uneven results occur and hence gas-singeing machines are commonly used in almost all the mills.
DRAW BACKS OF ROLLER AND PLATE SINGEING MACHINES
Local cooling
Groove formation as the fabric remains in contact with the plates
Proper maintenance is required
The process is very slow (speed is 60 m/min)
Only single face of the fabric is singed (not in case of roller singeing)
GAS SINGEING MACHINE:
It has the following advantages;
Fabric face and back singe at the same time
Efficient process
No local cooling
Even singeing
There are 2 types of gas singeing machines:
DIRECT HEATING SYSTEM: In this system the fabric is exposed directly against flame. It is mostly used in industries.
INDIRECT HEATING SYSTEM: In this system the fabric is introduced in a heating chamber against infrared radiation. This system is efficient in case of lightweight fabric.
DESIZING (STEEPING):
As looming process involve stretching so fabric strength should be improved by applying certain sizing adhesives. These adhesives may be gum, cellulose based compounds or synthetic sizing agents. Industries do not prefer synthetic thickeners because they are expensive and use natural thickeners, that is, starch. To remove the effect of sizing desizing is done. Main object of desizing is to attain absorbency of fabric.
TYPES OF DESIZING: The four types of desizing are:
Rot desizing
Acid desizing
Oxidative desizing
Enzymatic desizing
ROT DESIZING: In this fabric is soaked in water for 24 hours at room temperature. This is a time consuming process and requires large vats. The results may be uneven from where the fabric is not completely dipped in water. Mildew may be developed because of long time dipping in water.
ACID DESIZING: This is a quicker process and starch easily degrades by acid. The fabric is soaked in oxalic acid for 3-4 hours. The draw back of this process is cellulose degradation that is, hydro cellulose formation occurs and hence strength of fabric decreases.
OXIDATIVE DESIZING: Different oxidizing agents for e.g. Hydrogen peroxide, chlorides, bromides are used. Oxidative desizing is preferred when scouring, bleaching and desizing are done at a time.
ENZYMATIC DESIZING: Enzymes are the catalysts, which do not participate and takes the reaction to completion without any increase in temperature. Enzymes are proteinic nature compounds .At very high temperature the enzyme becomes dead and non-reactive but the strength of the fabric is not affected and this is the main advantage of this process and therefore, this is commonly used in industries. The sources of enzymes are malt, bacterial and pancreatic. In case of bacterial enzymes the pH range is 5.5 to 7 and temperature of 50 to 70C can be beard therefore these enzymes are preferred in industries.
IMPORATNT PARTS OF MACHINE:
There are 3 singeing machines in Gul Ahmed, which consists of the following parts:
GUIDE ROLLERS: These are used to guide the fabric in open width form to the machine.
BOWING ROLLERS: These are used to make the irregular yarn regular that is, for weft straightening.
DRYING CYLINDERS: These are used to remove the moisture from the fabric, thus drying it completely so that dust, attaching impurities and hanging threads are easily removed which is not possible in case of moist fabric.
BRUSHING ROLLERS: Two brushes move opposite to the fabric and perform the following functions:
To remove attached or stick fiber from the fabric.
Dust particles and other impurities are also removed.
It is done to avoid hard black residue form on surface of fabric.
Hairs are raised by brushing and thus easily burned.
5. BURNERS: This is the most important part of a singeing machine. It is a direct heating system that is; the fabric is exposed to flame directly at a high speed.
SPECIFICATIONS:
Flame colour: blue (oxidative flame is used)
Following are the main functions of grey department.
To inspect, mend & grade the fabric.
Supply the Grey for further processing.
To keep the record of store fabric.
The rejected fabric is sent back to the respected Mill.
INITIAL STORAGE:
When Grey is unloaded, the 10% inspection is done at the initial stage, which includes testing of counts end and pick & meters of fabric. Then whole delivery is sent for 100% checking, if failed then sent to non-conforming area or rejection area.
MENDING:
This is the portion of the grey department where the faults are removed .The lots after clearing the 10% inspection is sent in mending department for 100% inspection in which the defect are identified and counted and some are mended, according to them grading of fabric done.
The grading criterion is:
A Grade 6-7% defect
B Grade 10% defect /m
C Grade 12-14% defect /m
NP Grade not printable
R Grade Rejected
The faults, which are present at this stage in a fabric, are of three types.
a) Weaving faults.
b) Mending faults.
c) Washable faults.
a) WEAVING FAULTS: -
They are the faults, which cannot be removed during mending process. These include:
JALA: - It is due to the entanglement of warp & weft & their breakage during weaving. It cannot be removed because of breakage of yarn.
CRACK: It is basically the breakage of weft in the middle i.e. lining in the weft direction.
PATTI: It is due to the stoppage of m/c .Its in the direction of weft
DOUBLE PICK: They produce if somehow weft is inserted twice.
BROKEN PICK: It is due to the breakage of pick.(weft)
MISS PICK: When weft is missing then this is produce.
STARTING MARK: This is the line, which is produced in weft direction due to changing of beam.
REED MARK: It is usually produce throughout the length of fabric. It is due to the presence of dent in the reed as gap is producing b/w the warp in this case.
TEMPLE MARK: It is a weaving fault, which arises due to the non-movement of ball & pins of the temple in the loom.
CONTAMINATION: The embossed yarn due to uneven twists and appears over surface as a dot.
b) MENDING DEFECTS
: They are known as mending because they can be removed during mending process by combing (snarls, mis comb and slubs), cutting (h/threads, hole and torn) & application of petrol or emrolex (for the removal of stains). The mending defects include:
SNARLS: It is basically the collection of threads at the surface of fabric. This defect arises by the slow movement of projectile.
H/THREADS: Hanging thread is the piece of yarn attached to the Grey cloth. This fault is removed by cutting.
SLUBS: The fibers are in bunch form at the fabric.
MISS COMB: It is the entanglement of the warp & weft, which appears as disturbance over the surface of fabric.
c) WASHABLE DEFECTS:
These include the following:
1. Oily weft
2. Oil stains
3. Rusty stains
4. Emrolex stains: It is the chemical, which is used to remove the above-mentioned stains, & if a stain remains as a white spot over the fabric, it can be removed by scouring.
DETAIL OF THE DEFECTS:
The number of defects and the type of defects are noted on a chart, which is attached here.
FOLDING AND STORAGE BIN:
The fabric after mending process is folded mechanically under the supervision of usually two workers. There are four folding machines and piles are of one meter. Then the fabric is sent to the storage bin that is divided into different segments according to the quality (grading) of the fabric.
QUALITY ASSURANCE:
In Gul Ahmad after 100% mending, the fabric is rechecked and a quality assurance team does this, which inspects 5% of the total lots. The standards for printed and dyed grey cloth according to the quality assurance department are mentioned in the table, which is attached. Grey department itself before sending the fabric for further processing also checks the quality of the fabric. (10% inspection is done to check the previous inspection).
· If pass then send for singeing
· If fails then sent for 100% inspection.
STICHING SECTION:
Suppose (x) meters of fabric are issued from the grey department then it is sent to the stitching section where the lots are stitched by means of jockey machine.
LOOMS: Mostly the defects created in the fabrics are due to the loom. Different % of defects and different looms are as follows:
1. SHUTTLELESS LOOMS: The fabric has fewer defects and the selvages are large in width. Due to less number of defects the fabric is of ‘A’ and ‘B’ quality.
There are usually 10-12 faults per meter, 2-3 jala permitted. A pair of workers inspects 2500m of fabric in 8 hours.
2. AUTO LOOMS: The fabric made by auto looms has more defects than the shuttle less looms. There are usually 18 defects found per meter of fabric with 4-5 jalas. In 8 hours, a pair of worker can inspect 1600m of fabric.
3.POWER LOOMS: The fabric of power loom has more defects than any other loom, there are mostly 25 defects per meter of fabric including 4-5 jalas and fabric is of ‘B’ and ‘C’ quality. Due to increase in number of faults, only 1000m of fabric is inspected in 8 hours.
GREY ACCESSORIES:
INSPECTION TABLE: for inspection purpose, tube lights are fixed behind the glass. This is used to highlight the defects.
FOLDING MACHINE: There are 4 folding machines and piles are made of 1m, only the one end is fixed while the whole folding is automatically done. Four persons were working at 1 folding machine.
TROLLEY: The trolley is capable of carrying 3000-4000 of fabric. It is moved with the help of a jack.
STITCHING MACHINE: There were 4 jockey machines in stitching section.
FORK LIFTER: the fork lifter is used for carrying bales, rollers and other things and its weighing capacity is 2.5-3 tons.
COMPUTER SYSTEM FOR DATA COLLECTION:
7. FIRE FIGHTING SYSTEM
EXHAUST SYSTEM
PICK GLASS
WEIGHT OF FABRIC CALCULATION
CALCULATION OF FABRIC CONSTRUCTION:
1. 60x50/22x22 = 60x 25.7/22 + 56x 25.7/22 = 135 gm
Similarly:
2. 76x68/30x30 = 76x 25.7/30 + 68x 25.7/ 30 = 65.106 + 58.25 = 123.359 gm
MANAGEMENT INCHARGE:
Mr. Rizwan
Total workers: 200 Pair of workers: 37
Clerks: 03 Head checker: 10
Computer operator: 01 Supervisor: 01
OSTHOFF SINGEING MACHINE (1995)
SINGEING:
Singeing is the process applied to both yarn and fabric to produce an even surface by burning off projecting fibers, yarn ends and fuzz.
OBJECTS OF SINGEING: Following are the main objects of singeing:
Surface hairs help to trap the air in the fabric when it is immersed in water. This means that it takes longer time for water to enter the fabric since it must first displace the air. Singeing, therefore, helps to increase the fabric wet ability.
It creates a smooth surface for printing on. It may be possible to print fine details on hairy surface but once the hair move again after printing the details will become fuzzy.
To emphasize the woven structure of the fabric if that is considered essential.
It prevents frosty appearance after dyeing a hairy fabric who has been dyed may have somewhat a cloudy appearance.
To minimize or prevents the tendency of blend fibers composed of cellulose and synthetic fibers to form pills.
MACHINARIES USED IN SINGEING PROCESS
The machines that are used in singeing process are:
Plate Singeing Machine
Roller Singeing Machine
Gas Singeing Machine.
In case of plate singeing machine a plate is red hot and the fabric is passed at a specific distance and hence the pills reduces. But the draw back is this when fabric passes continuously the plates get cooled and uneven results occur and hence gas-singeing machines are commonly used in almost all the mills.
DRAW BACKS OF ROLLER AND PLATE SINGEING MACHINES
Local cooling
Groove formation as the fabric remains in contact with the plates
Proper maintenance is required
The process is very slow (speed is 60 m/min)
Only single face of the fabric is singed (not in case of roller singeing)
GAS SINGEING MACHINE:
It has the following advantages;
Fabric face and back singe at the same time
Efficient process
No local cooling
Even singeing
There are 2 types of gas singeing machines:
DIRECT HEATING SYSTEM: In this system the fabric is exposed directly against flame. It is mostly used in industries.
INDIRECT HEATING SYSTEM: In this system the fabric is introduced in a heating chamber against infrared radiation. This system is efficient in case of lightweight fabric.
DESIZING (STEEPING):
As looming process involve stretching so fabric strength should be improved by applying certain sizing adhesives. These adhesives may be gum, cellulose based compounds or synthetic sizing agents. Industries do not prefer synthetic thickeners because they are expensive and use natural thickeners, that is, starch. To remove the effect of sizing desizing is done. Main object of desizing is to attain absorbency of fabric.
TYPES OF DESIZING: The four types of desizing are:
Rot desizing
Acid desizing
Oxidative desizing
Enzymatic desizing
ROT DESIZING: In this fabric is soaked in water for 24 hours at room temperature. This is a time consuming process and requires large vats. The results may be uneven from where the fabric is not completely dipped in water. Mildew may be developed because of long time dipping in water.
ACID DESIZING: This is a quicker process and starch easily degrades by acid. The fabric is soaked in oxalic acid for 3-4 hours. The draw back of this process is cellulose degradation that is, hydro cellulose formation occurs and hence strength of fabric decreases.
OXIDATIVE DESIZING: Different oxidizing agents for e.g. Hydrogen peroxide, chlorides, bromides are used. Oxidative desizing is preferred when scouring, bleaching and desizing are done at a time.
ENZYMATIC DESIZING: Enzymes are the catalysts, which do not participate and takes the reaction to completion without any increase in temperature. Enzymes are proteinic nature compounds .At very high temperature the enzyme becomes dead and non-reactive but the strength of the fabric is not affected and this is the main advantage of this process and therefore, this is commonly used in industries. The sources of enzymes are malt, bacterial and pancreatic. In case of bacterial enzymes the pH range is 5.5 to 7 and temperature of 50 to 70C can be beard therefore these enzymes are preferred in industries.
IMPORATNT PARTS OF MACHINE:
There are 3 singeing machines in Gul Ahmed, which consists of the following parts:
GUIDE ROLLERS: These are used to guide the fabric in open width form to the machine.
BOWING ROLLERS: These are used to make the irregular yarn regular that is, for weft straightening.
DRYING CYLINDERS: These are used to remove the moisture from the fabric, thus drying it completely so that dust, attaching impurities and hanging threads are easily removed which is not possible in case of moist fabric.
BRUSHING ROLLERS: Two brushes move opposite to the fabric and perform the following functions:
To remove attached or stick fiber from the fabric.
Dust particles and other impurities are also removed.
It is done to avoid hard black residue form on surface of fabric.
Hairs are raised by brushing and thus easily burned.
5. BURNERS: This is the most important part of a singeing machine. It is a direct heating system that is; the fabric is exposed to flame directly at a high speed.
SPECIFICATIONS:
Flame colour: blue (oxidative flame is used)
Fabric speed: 120m/min (also depends on quality)
Burner's temperature: 400-500C
Pressure on compensators: 2-3 bars
Burner angle: 180 when fabric is moving at high speed. As the speed of fabric
Decreases (upto 50m/min) the angle becomes 90
Width of fabric: 120 inches
Gas consumption: 240-250 cm3 per day
Two rows of burners are provided so that the fabric can be singed from face and back. Water circulation is also provided in the rollers for their cooling.
COMPENSATORS: They are used to maintain the tension over the running fabric and they work with the help of pneumatic pressure. They maintain the tension over the fabric by charging and discharging. Charging is defines as:
DESIZING BATH: It is tank containing desizing liquor for the removal of size so that the fabric becomes absorbent for further processing. It consists of 8 pair of rollers so that the fabric remains in contact with the liquor for 5 min. Squeezing rollers are provided after this tank that removes the extra liquor from the fabric, which comes again into the tank through a tray.
SPECIFICATIONS:
Temperature of the tank: 70C
CHEMICALS:
For PC: NaOH (It acts a s a surfactant)
Imrolex (It destroys the size)
For Cotton: Oxalic acid
Sandozen MRN (It acts as a surfactant and wetting agent)
The capacity of this tank is 1000 liters, which is usually used to treat 3000m of fabric.
8. MACHINE UTILITIES: the machine utilities are current, water, gas and air.
GOLLER SCOURING AND BLEACHING MACHINE
SCOURING:
All natural impurities in textile fibers other than coloring matter are removed by means of scouring. The ultimate aim of scouring is to make the material uniformly and highly absorbent in a cost-effective manner so that there are no difficulties in the later processes of dyeing, printing and finishing.
Natural impurities include:
a. Mineral matters
Oils and waxes
Leaf particles
Coloring pigments
Dust
Pectates
a. MINERAL MATTERS:
These are salts of calcium and magnesium present in soil. These are water-soluble and can be removed easily. If these are not removed from the fabric, spotting occurs on fabric.
b. OILS AND WAXES: There are two types of oils: Edible oil and Non edible oil
- Edible oils can be removed by sponification that is, they are converted into water-soluble component with the help of alkali.
- Non-edible or lubricating oils are dispersed into fine droplets and remain in suspension and the process is called emulsification. These oils can also be removed by extraction with organic solvents.
c. COLOURING PIGMENTS: These are the nitrogen containing compounds (azo group) and these cannot be removed in scouring but in bleaching.
d. LEAF PARTICLES: These are removed in ginning but if not removed completely they are dissolved with the help of alkali.
e. DUST: Dust comes from atmosphere and can be removed easily. Dust must be in suspension form otherwise the removal will not be 100% .So dust removing agents are added which makes the sand (dust) in suspension.
f. PECTATES: These are long chain carbohydrates, insoluble in water and soluble in alkalis. Yellowing tint is present on the fabric due to the presence of pectates and also the problem of absorbency occurs.
BLEACHING:
Scouring removes almost all the impurities of cotton fibers except husk and natural coloring matters that are ultimately removed by oxidizing agents. The oxidation treatment or bleaching is necessary for producing white goods as finished products or for dyeing pastel shades. Even for dark shades, bleaching improves the brilliance and evenness of shade. Bleaching may be Oxidative or Reductive.
OXIDATIVE BLEACHING: In case of this type of bleaching the process is irreversible that is, whiteness for always. Oxidative bleaching is done with the help of following bleaching agents. CHLORINE CONTAINING: Sodium hypovchlorite, calcium hypochlorite and sodium chlorite. OXYGEN CONTAINING: Hydrogen peroxide, sodium peroxide and barium peroxide.
Chlorine containing agents gives more whiteness as compared to oxygen containing but problem in this is chlorine retention that is, chlorine can not be removed 100% and chlorates forms on the fabric and yellowness appears that is why oxygen containing bleaching agents are preferred.
REDUCTIVE BLEACHING: In case of reductive bleaching the process is reversible that is the fabric again gets yellow on exposure to air due to the oxygen present in the atmosphere. Reductive bleaching agents are sulfur dioxide, sodium thio-sulphite and Na2S2O8.
For effective bleaching pH, temperature, time, concentration and impurities are to be controlled. For bleaching the compound must be present in unstable form that is, ionizes easily. Market form is stable form so the bleach must be converted into unstable form for the process. It is to be checked what is the stable form of bleach. If it is stable in acidic medium then alkali is added for instability and vice versa.
SCOURING & BLEACHING: In our project CONTINUOS SCOURING &BLEACHING (one step) is carried out for following purposes;
· For A High Degree Of Whiteness
· Complete Degrading Of Seeds & Removal Of All Impurities
· Outstanding &Even Absorbency
· Low Fiber Damage
· Improved Hand Of The Fabric
· Reproducibility Of Finishing Result
· High Efficiency
· Short Amortization Time
PARTS OF A MACHINE:
PRE WASHING: It is done with pure water at a temperature of 98C to remove the chemicals, which are applied in the desizing bath. This washing both contains 22m of fabric hover and 8 pairs of rollers.
VACO SET: This arrangement is mounted over the machine and is used for sucking extra fluff from the surface of fabric with the help of vacuum. The vacuum is created by a separate motor and pump arrangement by maintaining a pressure of –150m bar. It consists of a rectangular ceramic piece having slots in its center throughout the length from where the suction is done. A wire is provided over the slot and fabric passes between the wire and ceramic piece. The function of the wire is to block the slot upto the portion other than the width of fabric.
SQUEEZING ROLLERS: Expander is provided before the squeezing rollers. Its function is to remove the creases from the fabric if present. After passing through it, the fabric squeezes by means of squeezing rollers. The pressure over squeezing rollers is up to 2-3 bars and the pick up is 65%, but these can be varied according to the type of the fabric. Then the fabric passes over the bowing roller, its function is to straighten the weft, it is a curved rubber roller, which gets the drive from the friction of the fabric.
COMPENSATOR: It serves the following three functions:
1: CREASE REMOVAL: Creases are removed by the weight of the compensating roller that is equal to 25kg. For heavy weight we can even increase the tension by applying the pressure from 1bar to 4bar. This is called as charging position, where as for lightweight fabric we can reduce the tension by applying the negative pressure, which range between 17-12 bars. This is known as discharge.
2.SYNCHRONIZATION: If the compensator is down, then the speed of the processes following increases automatically and vice versa.
3: AUTOMATIC STOP: It provides an automatic stop to the machine if the fabric torn out.
Total number of compensators used in this machine is 12.
DIP SET#01: This is a tank like arrangement in which we apply the chemical for scouring over the fabric, that’s why it is also known as scouring chemical bath.
CONSTRUCTION OF DIP SET: It has a special arrangement for the feeding of the chemical that consists of a narrow tray over which the feeding pipe is provided. When the tray over flow, the chemical falls over the fast moving fabric through out the width. This is done to prevent staining of the chemical over the fabric. After impregnation of the fabric in the chemical, it passes between the doctor rolls, they have blade like structures on two sides. This helps to squeeze the excess liquor.
FEEDING MECHANISM OF DIP SET: The solution of chemical according to the type of fabric is made in the main or mother tank. From there it is fed to the dip set according to the speed of the fabric. To keep the concentration constant, the chemical from the dip set is continuously removed and mixed with the solution in the mother tank along with fresh chemicals.
STEAMER# 1: Fabric containing the chemical from the dip set enters into the steamer for the completion of the reaction. Here the fabric stays for 15min and the temperature is maintained at102C.
CONSTRUCTION OF STEAMER: It consists of two parts. The upper portion has roller arrangement while the lower is consists of a roller bed. The fabric after passing through the roller, stay over the roller bed. Below the roller bed, sump is provided which contains water. Super heated steam is injected in it, thus water evaporates and saturated steam passes through the roller bed and finally over the fabric. In this way, the temperature of the steamer is maintained at 102C. At the end of the roller bed, mechanical sensors are provided which is star shaped. The function of the mechanical sensor is that, it touches the roller bed, thus stopping the feeding of fabric in the steamer.
INTERMEDIATE WASHING: Just after scouring steamer, two intermediate washing baths are provided to remove the scouring chemical. Here the washing is done with plane water at 98C.
DIP SET # 02: This is also a chemical tank where the chemicals for bleaching are provided. Its construction and feeding mechanism are same as of dip set 01.
STEAMER# 02: The function is same as mentioned in steamer 01, the only difference is dwell time i.e here the fabric remains for 30min and another difference is the type of the sensor i.e here we use photo cell instead of mechanical sensor.
WASHING TANK: After bleaching 5 washing tanks are provided. The capacity of the4 tanks is 22m fabrics each and the washing in them is done with water at 98C. The 5th tank treats the fabric with acid to get the neutral pH and then do the washing with plain water. Its capacity is 25m fabric. In between each washing tank, expander, squeezing roller, bowing roller and compensator is provided and their functions are same as mentioned above.
DRYING ARRANGEMENT: 22 drums containing steam are provided in3 rows for the drying mechanism. After passing through them, fabric comes in to J shaped tray. Just above the J shaped tray we have moisture meter over the roller, which is in contact with the fabric and measures the moisture, which is usually, maintained at6%. One compensator before drying drums and one before the J shaped tray is provided to control the speed of the fabric through the machine.
BATCH MAKING: The fabric after drying is stored over the batcher, which can then be sending for further processing.
IMPORTANT ASPECTS OF THIS MACHINE:
HEAT RECOVERY SYSTEM: The water in the pre wash is at 98C. It is not wasted but with the help of the heat recovery system, it is used to increase the temperature of feeding water unto 70C. This system is consist of a drum having filler to remove the impurities and the used water then comes in the large diameter long pipe having pipes of small diameter in it. It carries fresh feeding water & by the transfer of heat it gets the temperature of about 65-70C, where as the used water after loosing the heat is disposed off.
WATER RECOVERY SYSTEM: The dirty water is disposed off and the fresh water is feeded to each washing tank separately. But there is also a special arrangement by means of which the water is transferred, if it is in the condition to be used, from 7th washing to 6th and then to 5th and so on by piping system.
MOTOR ARRANGEMENT: There are 22 AC motors provided in the machine these are of two types: main motors and auxiliary motors. Main motors are with chain and auxiliary motors have belts.
RUBBER ROLLERS: Main motors drive all rubber rollers. A separate main motor drives each.
STEEL ROLLER (TOP): auxiliary motors drive these. Many steel rollers are driven by one single motor.
STEEL ROLLER (BOTTOM): These are driven frictionally by fabric.
BED ROLLS: All are driven by one single main motor.
GOLLER BLEACH SPECIFICATIONS:
PH =7-8
ABSORBANCY: (for printing) 30-40mm.
(For dyeing) above 60mm
WHITENESS: PC (both dyeing and printing) above 70
Cotton (for printing) 65-70
Cotton (for white) 75
Cotton (for dyeing) 65-70
PROCESS: Desize to bleach wt. Reduction is 12%
SHRINKAGE: Cotton 17-19%
PC stain 4-5%
PC 7-8%
ELONGATION: Cotton 3-5%
PC 1-1.5%
MERCERIZE SHRINKAGE: cotton 2%
MACHINE UTILITIES:
1: The machine requires 5 workers during operations.
2: The length of running fabric in it is 500m
3: The time of insertion of running fabric is 8 hrs.
4: For about 100000m of fabric
Water needed =275m3
Electricity=1078kwh
Steam=44tons
CHEMICALS:
For scouring: NaOH liquid 48 Be
Sandozin MRN (wetting agent)
For bleaching: hydrogen peroxide 50%
NaOH liquid 48 Be
Stablical A (stablizer)
Sandozin MRN
Sirrix 2UD (sequestering agent)
J-BOX
This machine is used for scouring and bleaching in rope forms. In J box the fabric is feeded in piled form and stored. The J box is well insulated to retain the heat and is lined with steel. It is used in Gul Ahmad for local dyeing.
ROPE FORM: It can be
1: scour bleach (in old J box)
2: solomatic (new J box)
SCOUR BLEACH (hot boiling) this is also known as boiling off or boil bleach. It includes scouring and bleaching of the fabric and is done in old J box. The flow of the material through this machine is attached in flow chart.
PARTS:
GREY PITS: The fabric from Osthoff singing machine is stored in grey pits for the completion of the reaction. There are total 12 chambers in which 8000-10000m of narrow width fabric and 5000m of wider width fabric can be stored.
PRE WASHING: This is done with hot water i.e at a temperature of 70C. It consists of 6 pairs of rollers and about 80-100m of fabric remains in it. After washing, fabric enters in to saturator by passing through padder rollers.
SATURATOR (scouring tank): This is the portion of the machine where scouring takes place and all the natural impurities are removed. NaOH is fed from the mother tank whose capacity is 1000m where as other chemicals are fed from a separate drum of 500lites. 3-4m of fabric remains in contact with the chemical for about 3-4 min.
STEAMER# 01: It is a 20 ft high J shaped box whose capacity is about 1200kg and the fabric remains under 100C for about 2-2.5 hours. The maintenance of J box is done if in any case staining occurs on the fabric. For this purpose two openings one at the top and other at the bottom are provided and this maintenance normally takes 8 hrs. From the steamer, the fabric enters into mid washer.
MID WASHER: This consists of two chambers one is for hot washing 70C and other is for cold washing 30C. This is done to remove the chemicals from the fabric. The problem of dissociation of hydrogen peroxide can arise at the temperature of 70C so cold washing is provided to keep the fabric at room temp. The capacity of this washing chamber is 102m.
SATURATOR (bleaching tank): Here the pre mixed chemicals from the mother tank by means of motor and a pump. The fabric is impregnated in the chemicals for about 3-4min. After it, the fabric passes through the padder roller to the steamer. The pick up of the fabric depends on the quality but it is normally 90%.
STEAMER #02: This is the second J box and the fabric remains in it for about 1.5-2 hrs so that the bleaching reaction completes. The capacity of this J box is about 800kg and the temp here is 100C.
FINAL WASHING: The final washing also consists of hot and cold wash. From here the fabric is stored in white pits. There are total 9 white pits these are called as white pits because the fabric comes here after bleaching.
SOLOMATIC PROCESS:
This is done in new J box. This process involves only bleaching of the fabric. The flow of the material in this process is given as:
Pre washing--------à saturator------------àsteamer----------à final wash--------à white pits.
PARTS:
PRE WASHING: It consists of six pairs of rollers and has the capacity of holding 120m of fabric at a time. First hot washing at 70-90C and then cold washing at 30-35C takes place. This is done to cool down the fabric because the heated fabric is sent to the saturator then due to the increase in temp, hydrogen peroxide dissociates so in normal practice we provide a cold wash to the fabric so that the reaction takes place at room temperature.
SATURATOR (bleaching tank): The fabric us treated with hydrogen peroxide and NaOH. 3-4m of fabric remains in contact with the chemical for3-4min.
STEAMER: Here the fabric remains for 1.5hrs under 100C and its capacity is 2600kg. The steam is provided from bottom, mid and top of the J box. There are 3 pressure gauges indicating the steam pressure and also a temperature indicator, which indicates the temp of steam in the J box.
FINAL WASHING: It also consists of hot and cold washing and is done top removed the remaining impurities or chemicals after bleaching. Their are4 hot chambers and 2 cold chambers. After this the fabric gets stored in white pits.
WATER MANGLE
Textile materials require drying after washing that is carried out in two stages. First water is removed mechanically and then by application of heat. Evaporation of water by heat is expensive and so maximum quantity of water is extracted by mechanical means, which are
(a). Centrifuging,
(b) Mangling and
(c) Suction methods.
Mangling is the most economical of all the three methods of extraction and its cost is about half of centrifuging and one third of suction method. Here in Gul Ahmad, there are 2 water mangles. They are distinguished by:
OLD WATER MANGLES NEW WATER MANGLES
This is for narrow width this is for wider width
In this machine only batch formation is possible Pilot as well as batch can be made
The speed is about 50-70m/min its speed is usually 1/3 of the speed Of J box
In this there is no arrangement for neutralization here a trough for the acid is
of the fabric. Provided for neutralization.
The flow of the material through water mangle is attached.
WORKING:
The fabric from the white pits enters here through the guide rolls in the form of a rope. At the beginning of the mangle there is beater rope opener arrangement that helps to open the rope by continuous rotations. Just after it, expanders are present which will open the fabric width wise and remove the crease upto some extent. This whole arrangement is repeated twice. After passing through the roller the fabric is dipped in acid then in water trough to maintain the pH. After passing through bowing, squeezing and finally guide rollers, the fabric moves towards the drying drums and finally wounded over the batcher or can be stored over pilot.
MERCERIZATION
(GOLLER MERCERIZATION MACHINE)
Mercerization is a very important operation in the cotton wet processing industry and by virtue of the resultant effects it may be considered both a pre treatment and a finishing process. Mercerization is the treatment of the fabric with strong caustic soda solution of about 20% strength. The changes appear on cotton after the treatment is as follows:
1. Shrinkage in area of fabric and length of yarn.
2. Increase in moisture absorption.
3. Great increase in dye up take.
4. Increase in chemical reactivity.
5. Increase in tensile strength of the material.
TYPES OF MERCERIZATION MACHINE: These are of two types:
1. Chain type
2. Chainless type.
Chainless machines are normally used in all mills. The differences between the two are as follows:
CHAIN MACHINES:
a. The chain machine gives a better tension control or better mercerization in both the warp and weft direction and imparts a comparatively better luster to the heavier weight fabrics.
b. The maintenance of the chains is high because these cannot be lubricated and so wears off rapidly.
CHAINLESS MACHINES:
g. These have a lower capital cost per unit production
h. These machines are more efficient in use of caustic soda and there is a less possibility of physical damage to the delicate fabrics.
i. Chainless machines have also higher productivity because two or more layers of fabric can be mercerized simultaneously by placing these side by side or by superimposing one on the other.
IMPORANT PARTS OF MACHINE:
1: CREELING: The fabric is fed in batch form that comes from continuous bleaching and scouring machine. The fabric passes through the tension rolls and the series of bowing rollers. There are total 9 bowing rollers for straightening of the weft because the mercerization the fabric has to swell.
2. MERCERIZATION CHAMBERS: There are three chambers for mercerization containing a strong lye of 30 Be(299 gm/liter). Here the fabric passes between two rollers in which top one is of rubber and bottom one is of grooved steel. NaOH softens the fabric where as grooved steel rollers straightens the fabric. There are 4 pairs of rollers in each chamber and each chamber contains 7m of fabric .The fabric passes through these chambers in 45 seconds at room temperature.
3.SQUEEZING ROLLERS: There are 4 squeezing rollers having 75% pick up and the pressure applied on these rollers is 4 bars.
4.STABLIZATION CHAMBER: There are 4 stabilization chambers containing weak lye of 7-8 Be and the dip time is 60 seconds. This is done for permanent straightening of the fabric. Here also 7m of fabric are present in each chamber and the temperature of the chamber is 85C. After this the fabric passes through squeezing rollers (5 bar pressure and pick up=80%) to the batcher and then to the washing pad steam water mangle.
There are 2 mercerization machines in Gul Ahmed .One (new model 1999) is for wider width (3.2m) and the other (old model 1965) is for narrow width (1.6m). The old machine also contains the washing chambers whereas the new one does not.
LYE PREPARATION:
Strong lye (NaOH) is feeded from a mother tank (1000liters) to a bottom dip tank of 2500 liters from where the lye is pumped to the mercerization chamber. The concentration of caustic soda is controlled automatically. For filtration of caustic, a round filter is provided. To prepare weal lye for stabilization chamber 4.5 liters/kg of water is provided before the second set of squeezing rollers so that the concentration decreases upto 7-8 Be and then pumped by means of 16 pumps to the stabilization chamber.
CAUSTIC RECOVERY UNIT (CRU)
During the process of mercerization we use a large amount of caustic whose initial concentration is 30 Be and is reduced to 7-8 Be in the stabilization chamber. For reduction of concentration we add a large amount of water i.e 4.5lit/kg. If this dilute solution is wasted directly to the sewage then a large amount of caustic will waste. To overcome this problem we use CRU.
It is a unit where caustic is recovered by a simple process of evaporation.
WORKING:
Caustic from mercerization chamber is pumped to the pre filter that is made of nylon and then enters into buffer tank for storage. After reaching a certain level caustic passes to the heat exchanger where it is heated by exchanging heat with hot water and then comes into evaporator. Steam is supplied in first evaporator for evaporation. In evaporator the caustic circulates in pipes where as steam is in surrounding. When caustic begins to evaporate it passes to the separator where the vapors being lighter goes up where as caustic enters into second evaporator. This evaporator is heated by means of paper present in separator. This process is repeated one more time so that the water separates completely. Then the required concentration of caustic is obtained i.e 30Bu (specific gravity 1.26) the caustic enters into the lye cooler above which a heat exchanger is provided in which cold water circulates and hence the caustic cools down.
A sensor called lye measurement sensor (LMS) controls the conc. of caustic. After reaching a certain level in lye cooler caustic is stored in concentrate tank. From here the caustic again passé to the mercerization tank.
OSTHOFF SINGEING MACHINE (1995)
SINGEING:
Singeing is the process applied to both yarn and fabric to produce an even surface by burning off projecting fibers, yarn ends and fuzz.
OBJECTS OF SINGEING: Following are the main objects of singeing:
Surface hairs help to trap the air in the fabric when it is immersed in water. This means that it takes longer time for water to enter the fabric since it must first displace the air. Singeing, therefore, helps to increase the fabric wet ability.
It creates a smooth surface for printing on. It may be possible to print fine details on hairy surface but once the hair move again after printing the details will become fuzzy.
To emphasize the woven structure of the fabric if that is considered essential.
It prevents frosty appearance after dyeing a hairy fabric who has been dyed may have somewhat a cloudy appearance.
To minimize or prevents the tendency of blend fibers composed of cellulose and synthetic fibers to form pills.
MACHINARIES USED IN SINGEING PROCESS
The machines that are used in singeing process are:
Plate Singeing Machine
Roller Singeing Machine
Gas Singeing Machine.
In case of plate singeing machine a plate is red hot and the fabric is passed at a specific distance and hence the pills reduces. But the draw back is this when fabric passes continuously the plates get cooled and uneven results occur and hence gas-singeing machines are commonly used in almost all the mills.
DRAW BACKS OF ROLLER AND PLATE SINGEING MACHINES
Local cooling
Groove formation as the fabric remains in contact with the plates
Proper maintenance is required
The process is very slow (speed is 60 m/min)
Only single face of the fabric is singed (not in case of roller singeing)
GAS SINGEING MACHINE:
It has the following advantages;
Fabric face and back singe at the same time
Efficient process
No local cooling
Even singeing
There are 2 types of gas singeing machines:
DIRECT HEATING SYSTEM: In this system the fabric is exposed directly against flame. It is mostly used in industries.
INDIRECT HEATING SYSTEM: In this system the fabric is introduced in a heating chamber against infrared radiation. This system is efficient in case of lightweight fabric.
DESIZING (STEEPING):
As looming process involve stretching so fabric strength should be improved by applying certain sizing adhesives. These adhesives may be gum, cellulose based compounds or synthetic sizing agents. Industries do not prefer synthetic thickeners because they are expensive and use natural thickeners, that is, starch. To remove the effect of sizing desizing is done. Main object of desizing is to attain absorbency of fabric.
TYPES OF DESIZING: The four types of desizing are:
Rot desizing
Acid desizing
Oxidative desizing
Enzymatic desizing
ROT DESIZING: In this fabric is soaked in water for 24 hours at room temperature. This is a time consuming process and requires large vats. The results may be uneven from where the fabric is not completely dipped in water. Mildew may be developed because of long time dipping in water.
ACID DESIZING: This is a quicker process and starch easily degrades by acid. The fabric is soaked in oxalic acid for 3-4 hours. The draw back of this process is cellulose degradation that is, hydro cellulose formation occurs and hence strength of fabric decreases.
OXIDATIVE DESIZING: Different oxidizing agents for e.g. Hydrogen peroxide, chlorides, bromides are used. Oxidative desizing is preferred when scouring, bleaching and desizing are done at a time.
ENZYMATIC DESIZING: Enzymes are the catalysts, which do not participate and takes the reaction to completion without any increase in temperature. Enzymes are proteinic nature compounds .At very high temperature the enzyme becomes dead and non-reactive but the strength of the fabric is not affected and this is the main advantage of this process and therefore, this is commonly used in industries. The sources of enzymes are malt, bacterial and pancreatic. In case of bacterial enzymes the pH range is 5.5 to 7 and temperature of 50 to 70C can be beard therefore these enzymes are preferred in industries.
IMPORATNT PARTS OF MACHINE:
There are 3 singeing machines in Gul Ahmed, which consists of the following parts:
GUIDE ROLLERS: These are used to guide the fabric in open width form to the machine.
BOWING ROLLERS: These are used to make the irregular yarn regular that is, for weft straightening.
DRYING CYLINDERS: These are used to remove the moisture from the fabric, thus drying it completely so that dust, attaching impurities and hanging threads are easily removed which is not possible in case of moist fabric.
BRUSHING ROLLERS: Two brushes move opposite to the fabric and perform the following functions:
To remove attached or stick fiber from the fabric.
Dust particles and other impurities are also removed.
It is done to avoid hard black residue form on surface of fabric.
Hairs are raised by brushing and thus easily burned.
5. BURNERS: This is the most important part of a singeing machine. It is a direct heating system that is; the fabric is exposed to flame directly at a high speed.
SPECIFICATIONS:
Flame colour: blue (oxidative flame is used)
Fabric speed: 120m/min (also depends on quality)
Burner's temperature: 400-500C
Pressure on compensators: 2-3 bars
Burner angle: 180 when fabric is moving at high speed. As the speed of fabric
Decreases (upto 50m/min) the angle becomes 90
Width of fabric: 120 inches
Gas consumption: 240-250 cm3 per day
Two rows of burners are provided so that the fabric can be singed from face and back. Water circulation is also provided in the rollers for their cooling.
COMPENSATORS: They are used to maintain the tension over the running fabric and they work with the help of pneumatic pressure. They maintain the tension over the fabric by charging and discharging. Charging is defines as:
DESIZING BATH: It is tank containing desizing liquor for the removal of size so that the fabric becomes absorbent for further processing. It consists of 8 pair of rollers so that the fabric remains in contact with the liquor for 5 min. Squeezing rollers are provided after this tank that removes the extra liquor from the fabric, which comes again into the tank through a tray.
SPECIFICATIONS:
Temperature of the tank: 70C
CHEMICALS:
For PC: NaOH (It acts a s a surfactant)
Imrolex (It destroys the size)
For Cotton: Oxalic acid
Sandozen MRN (It acts as a surfactant and wetting agent)
The capacity of this tank is 1000 liters, which is usually used to treat 3000m of fabric.
8. MACHINE UTILITIES: the machine utilities are current, water, gas and air.
GOLLER SCOURING AND BLEACHING MACHINE
SCOURING:
All natural impurities in textile fibers other than coloring matter are removed by means of scouring. The ultimate aim of scouring is to make the material uniformly and highly absorbent in a cost-effective manner so that there are no difficulties in the later processes of dyeing, printing and finishing.
Natural impurities include:
a. Mineral matters
Oils and waxes
Leaf particles
Coloring pigments
Dust
Pectates
a. MINERAL MATTERS:
These are salts of calcium and magnesium present in soil. These are water-soluble and can be removed easily. If these are not removed from the fabric, spotting occurs on fabric.
b. OILS AND WAXES: There are two types of oils: Edible oil and Non edible oil
- Edible oils can be removed by sponification that is, they are converted into water-soluble component with the help of alkali.
- Non-edible or lubricating oils are dispersed into fine droplets and remain in suspension and the process is called emulsification. These oils can also be removed by extraction with organic solvents.
c. COLOURING PIGMENTS: These are the nitrogen containing compounds (azo group) and these cannot be removed in scouring but in bleaching.
d. LEAF PARTICLES: These are removed in ginning but if not removed completely they are dissolved with the help of alkali.
e. DUST: Dust comes from atmosphere and can be removed easily. Dust must be in suspension form otherwise the removal will not be 100% .So dust removing agents are added which makes the sand (dust) in suspension.
f. PECTATES: These are long chain carbohydrates, insoluble in water and soluble in alkalis. Yellowing tint is present on the fabric due to the presence of pectates and also the problem of absorbency occurs.
BLEACHING:
Scouring removes almost all the impurities of cotton fibers except husk and natural coloring matters that are ultimately removed by oxidizing agents. The oxidation treatment or bleaching is necessary for producing white goods as finished products or for dyeing pastel shades. Even for dark shades, bleaching improves the brilliance and evenness of shade. Bleaching may be Oxidative or Reductive.
OXIDATIVE BLEACHING: In case of this type of bleaching the process is irreversible that is, whiteness for always. Oxidative bleaching is done with the help of following bleaching agents. CHLORINE CONTAINING: Sodium hypovchlorite, calcium hypochlorite and sodium chlorite. OXYGEN CONTAINING: Hydrogen peroxide, sodium peroxide and barium peroxide.
Chlorine containing agents gives more whiteness as compared to oxygen containing but problem in this is chlorine retention that is, chlorine can not be removed 100% and chlorates forms on the fabric and yellowness appears that is why oxygen containing bleaching agents are preferred.
REDUCTIVE BLEACHING: In case of reductive bleaching the process is reversible that is the fabric again gets yellow on exposure to air due to the oxygen present in the atmosphere. Reductive bleaching agents are sulfur dioxide, sodium thio-sulphite and Na2S2O8.
For effective bleaching pH, temperature, time, concentration and impurities are to be controlled. For bleaching the compound must be present in unstable form that is, ionizes easily. Market form is stable form so the bleach must be converted into unstable form for the process. It is to be checked what is the stable form of bleach. If it is stable in acidic medium then alkali is added for instability and vice versa.
SCOURING & BLEACHING: In our project CONTINUOS SCOURING &BLEACHING (one step) is carried out for following purposes;
· For A High Degree Of Whiteness
· Complete Degrading Of Seeds & Removal Of All Impurities
· Outstanding &Even Absorbency
· Low Fiber Damage
· Improved Hand Of The Fabric
· Reproducibility Of Finishing Result
· High Efficiency
· Short Amortization Time
PARTS OF A MACHINE:
PRE WASHING: It is done with pure water at a temperature of 98C to remove the chemicals, which are applied in the desizing bath. This washing both contains 22m of fabric hover and 8 pairs of rollers.
VACO SET: This arrangement is mounted over the machine and is used for sucking extra fluff from the surface of fabric with the help of vacuum. The vacuum is created by a separate motor and pump arrangement by maintaining a pressure of –150m bar. It consists of a rectangular ceramic piece having slots in its center throughout the length from where the suction is done. A wire is provided over the slot and fabric passes between the wire and ceramic piece. The function of the wire is to block the slot upto the portion other than the width of fabric.
SQUEEZING ROLLERS: Expander is provided before the squeezing rollers. Its function is to remove the creases from the fabric if present. After passing through it, the fabric squeezes by means of squeezing rollers. The pressure over squeezing rollers is up to 2-3 bars and the pick up is 65%, but these can be varied according to the type of the fabric. Then the fabric passes over the bowing roller, its function is to straighten the weft, it is a curved rubber roller, which gets the drive from the friction of the fabric.
COMPENSATOR: It serves the following three functions:
1: CREASE REMOVAL: Creases are removed by the weight of the compensating roller that is equal to 25kg. For heavy weight we can even increase the tension by applying the pressure from 1bar to 4bar. This is called as charging position, where as for lightweight fabric we can reduce the tension by applying the negative pressure, which range between 17-12 bars. This is known as discharge.
2.SYNCHRONIZATION: If the compensator is down, then the speed of the processes following increases automatically and vice versa.
3: AUTOMATIC STOP: It provides an automatic stop to the machine if the fabric torn out.
Total number of compensators used in this machine is 12.
DIP SET#01: This is a tank like arrangement in which we apply the chemical for scouring over the fabric, that’s why it is also known as scouring chemical bath.
CONSTRUCTION OF DIP SET: It has a special arrangement for the feeding of the chemical that consists of a narrow tray over which the feeding pipe is provided. When the tray over flow, the chemical falls over the fast moving fabric through out the width. This is done to prevent staining of the chemical over the fabric. After impregnation of the fabric in the chemical, it passes between the doctor rolls, they have blade like structures on two sides. This helps to squeeze the excess liquor.
FEEDING MECHANISM OF DIP SET: The solution of chemical according to the type of fabric is made in the main or mother tank. From there it is fed to the dip set according to the speed of the fabric. To keep the concentration constant, the chemical from the dip set is continuously removed and mixed with the solution in the mother tank along with fresh chemicals.
STEAMER# 1: Fabric containing the chemical from the dip set enters into the steamer for the completion of the reaction. Here the fabric stays for 15min and the temperature is maintained at102C.
CONSTRUCTION OF STEAMER: It consists of two parts. The upper portion has roller arrangement while the lower is consists of a roller bed. The fabric after passing through the roller, stay over the roller bed. Below the roller bed, sump is provided which contains water. Super heated steam is injected in it, thus water evaporates and saturated steam passes through the roller bed and finally over the fabric. In this way, the temperature of the steamer is maintained at 102C. At the end of the roller bed, mechanical sensors are provided which is star shaped. The function of the mechanical sensor is that, it touches the roller bed, thus stopping the feeding of fabric in the steamer.
INTERMEDIATE WASHING: Just after scouring steamer, two intermediate washing baths are provided to remove the scouring chemical. Here the washing is done with plane water at 98C.
DIP SET # 02: This is also a chemical tank where the chemicals for bleaching are provided. Its construction and feeding mechanism are same as of dip set 01.
STEAMER# 02: The function is same as mentioned in steamer 01, the only difference is dwell time i.e here the fabric remains for 30min and another difference is the type of the sensor i.e here we use photo cell instead of mechanical sensor.
WASHING TANK: After bleaching 5 washing tanks are provided. The capacity of the4 tanks is 22m fabrics each and the washing in them is done with water at 98C. The 5th tank treats the fabric with acid to get the neutral pH and then do the washing with plain water. Its capacity is 25m fabric. In between each washing tank, expander, squeezing roller, bowing roller and compensator is provided and their functions are same as mentioned above.
DRYING ARRANGEMENT: 22 drums containing steam are provided in3 rows for the drying mechanism. After passing through them, fabric comes in to J shaped tray. Just above the J shaped tray we have moisture meter over the roller, which is in contact with the fabric and measures the moisture, which is usually, maintained at6%. One compensator before drying drums and one before the J shaped tray is provided to control the speed of the fabric through the machine.
BATCH MAKING: The fabric after drying is stored over the batcher, which can then be sending for further processing.
IMPORTANT ASPECTS OF THIS MACHINE:
HEAT RECOVERY SYSTEM: The water in the pre wash is at 98C. It is not wasted but with the help of the heat recovery system, it is used to increase the temperature of feeding water unto 70C. This system is consist of a drum having filler to remove the impurities and the used water then comes in the large diameter long pipe having pipes of small diameter in it. It carries fresh feeding water & by the transfer of heat it gets the temperature of about 65-70C, where as the used water after loosing the heat is disposed off.
WATER RECOVERY SYSTEM: The dirty water is disposed off and the fresh water is feeded to each washing tank separately. But there is also a special arrangement by means of which the water is transferred, if it is in the condition to be used, from 7th washing to 6th and then to 5th and so on by piping system.
MOTOR ARRANGEMENT: There are 22 AC motors provided in the machine these are of two types: main motors and auxiliary motors. Main motors are with chain and auxiliary motors have belts.
RUBBER ROLLERS: Main motors drive all rubber rollers. A separate main motor drives each.
STEEL ROLLER (TOP): auxiliary motors drive these. Many steel rollers are driven by one single motor.
STEEL ROLLER (BOTTOM): These are driven frictionally by fabric.
BED ROLLS: All are driven by one single main motor.
GOLLER BLEACH SPECIFICATIONS:
PH =7-8
ABSORBANCY: (for printing) 30-40mm.
(For dyeing) above 60mm
WHITENESS: PC (both dyeing and printing) above 70
Cotton (for printing) 65-70
Cotton (for white) 75
Cotton (for dyeing) 65-70
PROCESS: Desize to bleach wt. Reduction is 12%
SHRINKAGE: Cotton 17-19%
PC stain 4-5%
PC 7-8%
ELONGATION: Cotton 3-5%
PC 1-1.5%
MERCERIZE SHRINKAGE: cotton 2%
MACHINE UTILITIES:
1: The machine requires 5 workers during operations.
2: The length of running fabric in it is 500m
3: The time of insertion of running fabric is 8 hrs.
4: For about 100000m of fabric
Water needed =275m3
Electricity=1078kwh
Steam=44tons
CHEMICALS:
For scouring: NaOH liquid 48 Be
Sandozin MRN (wetting agent)
For bleaching: hydrogen peroxide 50%
NaOH liquid 48 Be
Stablical A (stablizer)
Sandozin MRN
Sirrix 2UD (sequestering agent)
J-BOX
This machine is used for scouring and bleaching in rope forms. In J box the fabric is feeded in piled form and stored. The J box is well insulated to retain the heat and is lined with steel. It is used in Gul Ahmad for local dyeing.
ROPE FORM: It can be
1: scour bleach (in old J box)
2: solomatic (new J box)
SCOUR BLEACH (hot boiling) this is also known as boiling off or boil bleach. It includes scouring and bleaching of the fabric and is done in old J box. The flow of the material through this machine is attached in flow chart.
PARTS:
GREY PITS: The fabric from Osthoff singing machine is stored in grey pits for the completion of the reaction. There are total 12 chambers in which 8000-10000m of narrow width fabric and 5000m of wider width fabric can be stored.
PRE WASHING: This is done with hot water i.e at a temperature of 70C. It consists of 6 pairs of rollers and about 80-100m of fabric remains in it. After washing, fabric enters in to saturator by passing through padder rollers.
SATURATOR (scouring tank): This is the portion of the machine where scouring takes place and all the natural impurities are removed. NaOH is fed from the mother tank whose capacity is 1000m where as other chemicals are fed from a separate drum of 500lites. 3-4m of fabric remains in contact with the chemical for about 3-4 min.
STEAMER# 01: It is a 20 ft high J shaped box whose capacity is about 1200kg and the fabric remains under 100C for about 2-2.5 hours. The maintenance of J box is done if in any case staining occurs on the fabric. For this purpose two openings one at the top and other at the bottom are provided and this maintenance normally takes 8 hrs. From the steamer, the fabric enters into mid washer.
MID WASHER: This consists of two chambers one is for hot washing 70C and other is for cold washing 30C. This is done to remove the chemicals from the fabric. The problem of dissociation of hydrogen peroxide can arise at the temperature of 70C so cold washing is provided to keep the fabric at room temp. The capacity of this washing chamber is 102m.
SATURATOR (bleaching tank): Here the pre mixed chemicals from the mother tank by means of motor and a pump. The fabric is impregnated in the chemicals for about 3-4min. After it, the fabric passes through the padder roller to the steamer. The pick up of the fabric depends on the quality but it is normally 90%.
STEAMER #02: This is the second J box and the fabric remains in it for about 1.5-2 hrs so that the bleaching reaction completes. The capacity of this J box is about 800kg and the temp here is 100C.
FINAL WASHING: The final washing also consists of hot and cold wash. From here the fabric is stored in white pits. There are total 9 white pits these are called as white pits because the fabric comes here after bleaching.
SOLOMATIC PROCESS:
This is done in new J box. This process involves only bleaching of the fabric. The flow of the material in this process is given as:
Pre washing--------à saturator------------àsteamer----------à final wash--------à white pits.
PARTS:
PRE WASHING: It consists of six pairs of rollers and has the capacity of holding 120m of fabric at a time. First hot washing at 70-90C and then cold washing at 30-35C takes place. This is done to cool down the fabric because the heated fabric is sent to the saturator then due to the increase in temp, hydrogen peroxide dissociates so in normal practice we provide a cold wash to the fabric so that the reaction takes place at room temperature.
SATURATOR (bleaching tank): The fabric us treated with hydrogen peroxide and NaOH. 3-4m of fabric remains in contact with the chemical for3-4min.
STEAMER: Here the fabric remains for 1.5hrs under 100C and its capacity is 2600kg. The steam is provided from bottom, mid and top of the J box. There are 3 pressure gauges indicating the steam pressure and also a temperature indicator, which indicates the temp of steam in the J box.
FINAL WASHING: It also consists of hot and cold washing and is done top removed the remaining impurities or chemicals after bleaching. Their are4 hot chambers and 2 cold chambers. After this the fabric gets stored in white pits.
WATER MANGLE
Textile materials require drying after washing that is carried out in two stages. First water is removed mechanically and then by application of heat. Evaporation of water by heat is expensive and so maximum quantity of water is extracted by mechanical means, which are
(a). Centrifuging,
(b) Mangling and
(c) Suction methods.
Mangling is the most economical of all the three methods of extraction and its cost is about half of centrifuging and one third of suction method. Here in Gul Ahmad, there are 2 water mangles. They are distinguished by:
OLD WATER MANGLES NEW WATER MANGLES
This is for narrow width this is for wider width
In this machine only batch formation is possible Pilot as well as batch can be made
The speed is about 50-70m/min its speed is usually 1/3 of the speed Of J box
In this there is no arrangement for neutralization here a trough for the acid is
of the fabric. Provided for neutralization.
The flow of the material through water mangle is attached.
WORKING:
The fabric from the white pits enters here through the guide rolls in the form of a rope. At the beginning of the mangle there is beater rope opener arrangement that helps to open the rope by continuous rotations. Just after it, expanders are present which will open the fabric width wise and remove the crease upto some extent. This whole arrangement is repeated twice. After passing through the roller the fabric is dipped in acid then in water trough to maintain the pH. After passing through bowing, squeezing and finally guide rollers, the fabric moves towards the drying drums and finally wounded over the batcher or can be stored over pilot.
MERCERIZATION
(GOLLER MERCERIZATION MACHINE)
Mercerization is a very important operation in the cotton wet processing industry and by virtue of the resultant effects it may be considered both a pre treatment and a finishing process. Mercerization is the treatment of the fabric with strong caustic soda solution of about 20% strength. The changes appear on cotton after the treatment is as follows:
1. Shrinkage in area of fabric and length of yarn.
2. Increase in moisture absorption.
3. Great increase in dye up take.
4. Increase in chemical reactivity.
5. Increase in tensile strength of the material.
TYPES OF MERCERIZATION MACHINE: These are of two types:
1. Chain type
2. Chainless type.
Chainless machines are normally used in all mills. The differences between the two are as follows:
CHAIN MACHINES:
a. The chain machine gives a better tension control or better mercerization in both the warp and weft direction and imparts a comparatively better luster to the heavier weight fabrics.
b. The maintenance of the chains is high because these cannot be lubricated and so wears off rapidly.
CHAINLESS MACHINES:
g. These have a lower capital cost per unit production
h. These machines are more efficient in use of caustic soda and there is a less possibility of physical damage to the delicate fabrics.
i. Chainless machines have also higher productivity because two or more layers of fabric can be mercerized simultaneously by placing these side by side or by superimposing one on the other.
IMPORANT PARTS OF MACHINE:
1: CREELING: The fabric is fed in batch form that comes from continuous bleaching and scouring machine. The fabric passes through the tension rolls and the series of bowing rollers. There are total 9 bowing rollers for straightening of the weft because the mercerization the fabric has to swell.
2. MERCERIZATION CHAMBERS: There are three chambers for mercerization containing a strong lye of 30 Be(299 gm/liter). Here the fabric passes between two rollers in which top one is of rubber and bottom one is of grooved steel. NaOH softens the fabric where as grooved steel rollers straightens the fabric. There are 4 pairs of rollers in each chamber and each chamber contains 7m of fabric .The fabric passes through these chambers in 45 seconds at room temperature.
3.SQUEEZING ROLLERS: There are 4 squeezing rollers having 75% pick up and the pressure applied on these rollers is 4 bars.
4.STABLIZATION CHAMBER: There are 4 stabilization chambers containing weak lye of 7-8 Be and the dip time is 60 seconds. This is done for permanent straightening of the fabric. Here also 7m of fabric are present in each chamber and the temperature of the chamber is 85C. After this the fabric passes through squeezing rollers (5 bar pressure and pick up=80%) to the batcher and then to the washing pad steam water mangle.
There are 2 mercerization machines in Gul Ahmed .One (new model 1999) is for wider width (3.2m) and the other (old model 1965) is for narrow width (1.6m). The old machine also contains the washing chambers whereas the new one does not.
LYE PREPARATION:
Strong lye (NaOH) is feeded from a mother tank (1000liters) to a bottom dip tank of 2500 liters from where the lye is pumped to the mercerization chamber. The concentration of caustic soda is controlled automatically. For filtration of caustic, a round filter is provided. To prepare weal lye for stabilization chamber 4.5 liters/kg of water is provided before the second set of squeezing rollers so that the concentration decreases upto 7-8 Be and then pumped by means of 16 pumps to the stabilization chamber.
CAUSTIC RECOVERY UNIT (CRU)
During the process of mercerization we use a large amount of caustic whose initial concentration is 30 Be and is reduced to 7-8 Be in the stabilization chamber. For reduction of concentration we add a large amount of water i.e 4.5lit/kg. If this dilute solution is wasted directly to the sewage then a large amount of caustic will waste. To overcome this problem we use CRU.
It is a unit where caustic is recovered by a simple process of evaporation.
WORKING:
Caustic from mercerization chamber is pumped to the pre filter that is made of nylon and then enters into buffer tank for storage. After reaching a certain level caustic passes to the heat exchanger where it is heated by exchanging heat with hot water and then comes into evaporator. Steam is supplied in first evaporator for evaporation. In evaporator the caustic circulates in pipes where as steam is in surrounding. When caustic begins to evaporate it passes to the separator where the vapors being lighter goes up where as caustic enters into second evaporator. This evaporator is heated by means of paper present in separator. This process is repeated one more time so that the water separates completely. Then the required concentration of caustic is obtained i.e 30Bu (specific gravity 1.26) the caustic enters into the lye cooler above which a heat exchanger is provided in which cold water circulates and hence the caustic cools down.
A sensor called lye measurement sensor (LMS) controls the conc. of caustic. After reaching a certain level in lye cooler caustic is stored in concentrate tank. From here the caustic again passé to the mercerization tank.
DYEING
Dye: They are the organic compounds, which produce psychological sensation when the light of certain wavelength reaches the eye.
Dyeing: It is the process, which produces chemical or physical change in a substance so that the reflection of light appears colored.
Dye Stuff: The substance, which produces such change in a substance, is known as dyestuff.
Basic Functions of Dyeing: There are 3 basic functions of dyeing they are:
I. Dye.
II. Medium.
III. Substrate.
Dye consists of 2 important parts. They are Chromogen and Solublising Group.
Chromogen:
The organic compound-carrying group that is chromophore is known as Chromogen. This word is drive from a Greek words, “Chroma” means Color And “Gen” means Generating. This itself can be divided into two. Auxochrome and Chromophore.
Auxochrome:
It is the auxiliary of chroma. This auxiliary is one that help in brightening the color or to enhance the color, but itself is unable to produce the color. It is also drive from Greek words “Auxein” means to increase and Chroma means color. Every dye must have one auxochrome and one chromophore. They convert a color compound into a dye that must fix permanently in a fabric. Generally colorless chromogens become colored when an auxochrome is introduced into it. They may be acidic of basic, and on the basis of depth they may be Bathochomic (deepens the color) and Hypschromic (fade the color).
Chromophore:
It is color-bearing group of dye, it is also drive from Greek word Chroma and Phore, means color bearing. Different chromophores have different power of developing color. They can be arrange in descending order as: C = C, C º N, C = O, N = N, C = S.
The General Theory of Dyeing.
Dyeing is the process of coloring textile materials by immersing them in and aqueous solution of dye, called dye liquor. Normally the dye liquor consists of dye, water and an auxiliary. To improve the effectiveness of dying, heat s usually applied to the dye liquor.
The theory of aqueous dyeing is modified when an organic solvent is substituted for water.
The general theory explains the interaction between dye, fabric, water, and dye auxiliary. More specifically, it explains:
1. Forces of repulsion which are developed between the dye molecule and water; and
2. Forces of attraction, which are developed between the dye molecule and fibers.
These forces are responsible for the dye molecules leaving the aqueous dye liquor and entering and attaching themselves to the palymers of the fabric.
DYEING MACHINARIES: (EXPORT)
PAD THERMOSOL: (Monfort’s thermex)
It is a continuos dyeing machine and is used for vat, disperse reactive and pigment dyeing in which fixation of the dye is done by means of heat. All types of shades can be dyed on this machine but we usually dye dark shades. In Gul Alhmad this machine is used mainly for polyester dyeing.
DYEING TROUGH:
The fabric is unfolded from batcher and with the help of guiding rolls and tension rollers enter into the trough having 4 rollers. In trough the liqour temp is kept at low i.e 25-30C. In trough, dyes migration inhibitors alkali (to maintain ph) and wetting agents (for heavy fabric) are used. After trough fabric is passed through padders to remove excess of dyeing and chemical solution by applying 1.5 bar pressure. The pick up is about 65-70% (depends on the quality of fabric).
AIRING ZONE:
There are six pairs of steel rollers in this zone fabric pass through these rollers under atmospheric pressure and temp for the proper penetration of the dye.
INFRA RED CHAMBER:
In padding polyester and PC fabrics, the dye solution is not fully absorbed like in 100% cotton fabrics and rubs off on coming in contact with a hot metal guide roller. The PC fabrics pick about 50% of liquor but if moisture level could be brought down to 30%, the dye migration is avoided. Therefore for this purpose there are two infrared zones in this machine for removing 30-40% of moisture from the fabric. It works as a dye migration inhibitor so that’s why direct drying is avoided and prevent uneven dying. Infra red radiation has higher wavelength and lower energy and that’s why they evaporates water only, dye molecules being bigger in size than water molecules and hence are not disturbed by infrared radiation. The temp of infrared radiation is 400-500C.
The IR heaters are mounted in banks and are either heated electrically or by gas. The IR radiation selected is of 3 micrometers wavelength as textile fibers preferentially absorb this. To monitor moisture content and subsequently speed of padding, microwave sensors are fitted that absorb the wave energy according to the moisture content in the fabric and alter speed of motor of the padder. At the bottom of the heater battery, warm air is blown that travel upwards and helps in removal of the steam away from the fabric. In case of an accidental stoppage of the fabric during working of the IR radiators, the fabric is protected from the intense heat by automatic cut off system for gas or electric supply as well as by dropping a metal shutter in front of the heaters.
DRYING CHAMBERS:
There are 3 chambers. First one is drying chamber having a temperature of 120C and 35m of fabric remains in it for 1 min. The 2nd chamber is pre curing chamber here the temp=150C and the fabric passes through it in30seconds. This chamber is for removing the moisture from the fabric completely so that no problem occurs in curing i.e to prepare the fabric for fixation.
3rd chamber is curing chamber here the temp=190C and 35m of fabric passes in 1min. This is for fixation of the dye. Total 91m of cloth is in 3 chambers.
GOLLER PAD STEAM DYEING MACHINE:
Continuous roller steamer is used for diffusion of reactive, vat, sulphur and direct dyes into cellulosic fibers in an atmosphere of heat and moisture that is created by saturated steam injected into the steamer. The fabric is moved in open width around rollers in top and bottom horizontal banks in a heat insulated steel chamber like a hot flue dryer. This is an ideal machine for Reactive dyeing. Light, pale and medium shades can be dyed in this machine. Here wet on wet dyeing is done.
PURPOSES OF THE MACHINE: It is a multi purpose m/c and serves the following purposes:
1. It can be used as a pad batch for reactive dyeing in which batch is left for 12-18 hours for the completion of the reaction. For time saving the fabric passes through the steamer for 1 minute and the reaction is completed.
2. It can also be used for reduction clearance (RC) in which we treat PC fabric with caustic and sod. Hydrosulphide to remove the disperse dye from cotton.
3. Stripping of the fabric can also be done on this machine that is, colour can be removed completely by adding higher amount of caustic and sod.hydrosulphide.
4. It can be used for the development of Vat dyes.
5. The dyed fabric can be washed in this machine.
The flow of the fabric through different parts of machine is as follows:
CREELING=èPADDING TROUGH=èSTEAMER=èACID TROUGH=èAIRING ZONE=èWASHERS=èDRYERS=èBATCHER
PADDING TROUGH:
The fabric enters into padding trough by passing trough different tension and guide rollers. There are 4 rolls in this trough. The trough contains the dye and other auxiliaries according to the dye to be used. To remove the excess amount of dyeing liquor from the fabric padding rollers are provided on which 1.5 bar pressure is applied at the center and 2.1 bar at the sides. This pressure is pneumatic and is supplied by means of compressors. The pick up on the padding rolls is normally 75%.
STEAMER:
There are 3 chambers in the steamer in which 8 pairs of rollers are present in two chambers and 6 pairs in the third one. Sensors are provided when the fabric enters from one chamber to another to control the speed or if the fabrics get rolled on to the rollers. The temperature of the steamer is 106Cand 75m of fabric remains in it for 1 minute. Sensor is provided here indicating the steamer temp. To maintain the temp constant throughout the steamer, small pieces of stainless steel are placed in the roof so that they remain hot for long time and do not allow condensation of the steam. The entrance of the steamer is known as LIP in which two pipes are provided adjacent to each other from which steam is supplied. To avoid foaming problem steam is supplied to third chamber and from third to second and from second to first. Steam can be provided to steamer by two means. First, by means of Sump (tray). Dry heated steam comes to the sump and becomes saturated when entered to the steamer. The other way of providing steam is by means of Gatra.
WATER SEAL:
The temp here is 40-45C and it serves the following purposes:
1 to cool the fabric
2 Remove excess dye from surface.
3 It condenses the steam that comes along the fabric
ACID TROUGH:
Acetic acid and HCl are added in this trough. Acetic acid is used to control pH where as HCl is used to clean NaOH i.e remove the alkaline effect.
AIRING ZONE:
There are two portions in this zone and a ceramic sensor is present at the end of each portion that maintains the tension of the fabric. There are 23 pairs of rollers in this zone. The fabric is allowed to pass these rollers under fresh air for good color fixation.
WASHING TANKS:
There are 9 washing tanks. Washing #1,2, 8 and 9 contains fresh water where as the others is fed from these tanks. The capacity of each washing tank is about 950-1300liters.
NORMAL WASH:
This wash is for printed fabrics the temp is kept at 50-60C.
MERCERIZED WASH:
In this only hot washing is done. The temp in washing 1 is 50 C and from washing 2 –8 is 98C and last one has 70C.
DYED WASH:
This is used for dyed fabrics and in this we add soap (RSK), dispergator, Cibapon R for washing. For light shades only soap is added where as for dark shades soda ash is also added with soap which decreases the depth of color and improve rubbing fastness. The temp in 1st and 2nd tank is room temp and from 3rd –8th is 98C where as in the last one is 50C. The tem-p in washing tanks is controlled by a PT temp sensor.
DRYING CYLINDERS:
There are 11 pairs of drying cylinders that are arranged horizontally and steam is injected by means of syfon pipes. After these cylinders 2 cooling cylinders are provided for cooling the fabric at room temp.
BATCHER:
The fabric from drying cylinders passes through some tension rolls and also from anti static rods which absorbs the charge from the fabric. This rod has 5 KV voltages and 1800-18000A of current after passing through this fabric is winded on the batcher.
PAD BATCH KUSTER PADDER (BLIND DYEING)
It is a semi continuous method of dyeing & is used incase of reactive dyes only.
DYE PADDER:
The padding operation consists of two parts: first immersion of the fabric in dye liquor in a trough and second passing the fabric b/w two rollers to force dye liquor in and to squeeze excess liquor back to trough. Padder is the most sensitive component of the continuous dyeing system and any fault developed at the padding stage will not be corrected later. Padder may have 2 or 3 rolls: the latter having 2 dips and 2 nips. Normally the 2-roll padder is preferred for most types of fabrics and the 3 roll one is used only for heavy weight fabrics.
Both the rollers should have exactly the same hardness otherwise there will be a color difference in the face and backsides of the fabric. The material of the rubber should be chemically resistant to dye liquor and auxiliary products. Speed of this m/c is 50m/min and 6-7 m of fabric is present in this m/c at a time.
PADDING TROUGH:
The padding trough is generally considered to be just a container for the dye liquor and its importance in obtaining constant shade and dye economy is not fully realized by the dyers. The trough is placed below and in front of the padder and consists of a u or v shaped box with one or more free running guide rollers of about 10 cm dia. Dye liquor is fed in through a perforated pipe running across the entire length of tank with perforations pointing away from fabric.
Ideally a trough should contain a minimum quantity of dye liquor consistent with adequate pick up so as to reduce wastage of un-used dye at the end of the process and more importantly to have a high liquor replacement value. Small liquor volume and minimum distance b/w top of trough and nip of pad rolls are necessary to reduce the effect of preferential pick up of dye or water by fabric and thus minimize tailing effect.
The troughs are double walled so that hot or cold water could be circulated through the jacket to maintain dye liquor at constant and optimum temperature. To ensure constancy of fabric immersion time through out it’s running in trough the dye liquor is kept at same level by automatic controls.
COLOR MIXING:
The colors and chemicals i.e. alkalis are put in separate tank and are mixed by a diaphragm at a ratio of 4:1. The diaphragm feed these mixed chemicals to the trough by means of pipes.
WORKING:
The fabric is feeded in this machine in the form of batcher, which after passing through certain tension rollers and guide rollers enters into the dyeing trough. In this trough the dyes and chemicals are showered on the fabric. There is a tube attached with the trough indicating the level of mixture in the trough. Padders are provided after trough having the pressure of 2 bars and pick up of 75%, they squeeze the excess liquor. Finally the fabric passes through some rollers and winded on a batcher. The batcher should rotate continuously for about 12-18 hrs for fixation of the color. From this m/c fabric goes to washing m/c and then to the drying cylinders.
HOT FLUE: 1976
This m/c is used for local dyeing (exhaust process). This is a semi thermosol m/c but do not have curing chamber like thermosol. When vat dyeing is done in this machine then only padding and drying is done. After this the pad is taken to the jigger for development.
WORKING:
The fabric after mercerization is feeded by means of tension and guide rolls to the padding trough. In this trough there are 3 rollers and dye and leveling agents are added. Hydraulic pressure of 2.5 bar in center and 1.6 bars at side is applied on padder rollers.
COMPENSATOR:
The compensator in this m/c is mechanical based; it controls the speed of m/c. It is connected through a chain to a sensor (rod). When the speed increases the tension applied on compensator increases due to which it moves up and hence the chain also moves as a result of this movement the sensor rod moves downward since it is connected with the opposite side of chain. Electric sensors provide the limit if the rod touches it the m/c stops automatically.
DRYING CHAMBERS:
There are 2 drawing chambers where drying is done with the help of steam. In each chamber there are 7 pairs of rollers. The top rollers are driven by means of rope, which gets drive by a chain from main motor, and bottom rollers are frictionally driven by fabric i.e. they are free running. In first dryer the temp is 140 ‘C & in second dryer is 150’C. The length of fabric from padded and drying chamber is 75m. The exhaust of moist air and fluff is through a duct at the top. After drying the fabric is winded either on batcher or it is piled.
LOCAL DYEING MACHINARIES:
PAD STEAM CONTINUOUS DYEING MACHINE
This machine is used for dyeing narrow width fabric. It can also be used only for washing. The speed of this machine is about 40m/minand about 180m of fabric is present on the machine at a time. The flow of the material through different parts of machine is as follows:
CREEL=èDYEINGTROUGH=èSTEAMER=èACIDTROUGH=èAIRING=èWASHER=èDRYERS=èBATCHER
IMPORTANT PARTS OF MACHINE:
DYEING TROUGH:
The dye is prepared in a tank of 500 liters and pumped to another tank from where it is feeded to the dyeing trough. The dyeing trough has the capacity of 25 liters and about 80m of fabric (lawn) can be dyed by this. After this the fabric passes through 3 padders that has the pick up of 68-70% and 1-2 bar pressure is applied.
STEAMER:
It has 2 chambers and each chamber has 7 pair of rollers. The temperature in the steamer is about 102C and 36m of fabric passes through it in 1 minute.
ACID TROUGH:
This trough is used for oxidation of soluble vat dyes by means of sulphuric acid. This acid is feeded to the trough from a tank having a capacity of 200 liters. In case of reactive dye this trough contains water only. The capacity of acid trough is about 50 liters.
AIRING ZONE:
This zone has 7 pair of rollers. It is used when soluble vat dye is oxidized, therefore, for giving reaction time the fabric is exposed to fresh air for 2-2.5 minutes.
WASHING TANKS:
There are 7 washing tanks. In case of dyeing the first two tanks contains cold water only and have 5 pair of rollers, third tank contains soap (MRN) and the temperature here is 85C.5gm/litsoap is added. If the pH of fabric is less than 7 then soda ash is also added along with the soap. Fourth to sixth washing tanks are for hot wash and the temperature here is 85Cand these tanks contain 4 pair of rollers. Last tank is for cold wash. In case of only washing off the fabric the first and the last tanks are for cold wash whereas others are for hot wash. Water can be transferred from one tank to other by means of a pipe. Since the third tank contains soap so it is drained out after washing. Compensators are provided after every washing tank that is mechanical based that is, they maintain the tension with the help of the weight attached with them. Bowing rollers are also provided along with compensator.
DRYING CYLINDERS:
Two expanders are present before these cylinders for crease removal. There are 20 drying cylinders, arranged vertically, which are heated by means of steam. A moisture meter is used to indicate the amount of moisture in the fabric. If the amount is higher then the steam will automatically injected into these cylinders. The fabric after passing through these cylinders and also through different tension rollers is finally winded on the batcher.
DRAWBACKS OF THIS MACHINE:
Jigger machine is the best replacement of this machine because it has the following drawbacks:
The cost of the chemicals and dyes are higher in this machine.
Only light shades of soluble vat dyes can be dyed.
In using vat dyes in pad steam, the depth of penetration is less.
In pad steam sulphur dyes can be used for dyeing but it will cause colour contamination over the rollers that will be difficult to wash off, therefore are not suitable for sulphur dyeing. This problem is not present in Jiggers.
The quality produced by jigger is better than that of pad steam.
JIGGER
For batch processing of cotton cloth in open width, jigger or jig is the oldest and still frequently used dyeing machine. In the past, jiggers were mainly used for dyeing medium and heavy weight fabrics b/c of excessive longitudinal tension imposed on the fabric. However, modern versions cause very little tension and so light weight fabrics may also dye now. A jigger consists of a V shaped trough or vat containing dye solution through which fabric, batched as a roll, moves and is wound on another roller. After the second roll is full, movement of cloth is reversed. Each batching on a roller is called a pass or an end.
MAIN PURPOSES:
Jigger is a multi-purpose m/c and it serves as follows;
1- Vat developing
2- Reactive dyeing
3- Bleaching
To ensure even dyeing there are 2 rounds of fabric in cold water.
CHEMICALS:
Incase of reactive dyes fixation, salt and NaHCO3 are used. For development of vat dyes (local), sodium hydro sulphide Na2S2O4 is added in small portions for even fixation and caustic (liquid) 38’be is used. Caustic either increases depth of color or decreases. As we don’t want to decrease color so we add dye in cold water and the fabric is allowed to complete 2 rounds. Then the chemicals are added in hot water (65’C). If water is not heated then the chemical will burst the dye molecule and not even color results. In order to avoid oxidation by air we keep fabric in center by a lever. Incase of bleaching in jigger, a squeezer roll is provided which is adjusted by a handle. So that the roller presses fabric and squeezes the bleaching chemicals. In development of vat dyes & bleaching we provide direct steam through holes provided in beneath of trough. But for reactive dyeing we provide indirect steam i.e. the steel pipes provided in trough are heated by circulating steam in coils of pipes.
As only a few meters of fabric are immersed in dye bath at a time, a very low liquor ratio of 4 to 5 can be achieved. Normal size jiggers store about 700 to 1000m of fabric and fabric generally moves at a rate of 60 to 100 m/min depending upon its unit weight. After 4 rounds of chemical the fabric takes 1 round of hot wash with soap MRN and in case of development of vat soda ash is also added to remove H2O2, Acetic acid etc and than 1 round of cold water. For unloading of fabric from jigger a steel rod is provided and fabric is unwound from batcher and winded on this roll.
From here the fabric is to water mangle where initially 2 washing tanks are provided and finally dried and piled.
WINCH
The winch m/c is one of the oldest dyeing m/c (for reactive and direct dyeing) & is still popular b/c of low capital cost, simplicity in operation and versatility in use for different types of fabrics & operations. Principle of winch is to circulate a no. of fabric loops that are lying in a dye bath but are continuously pulled out & returned to it with the help of a circular or elliptical winch.
Compared to the jigger, the winch dyeing causes less lengthwise tension in fabric. As the winches are suffering from deficiencies of long liquor ratio, non-uniform temp of dye bath, formation of creases in fabric and excessive mans power requirements. So jets are replacing winches.
In Gull Ahmed, the winches are used only for washing purpose. For washing of printed fabrics like lawn having dark shades. Linen which is 100% viscose is preferred washed in rope form otherwise due o a little elongation it deteriorates.
WASHING METHOD:
Usually 1000 liters of water is taken in the stainless steel vat having a depth of 2.5m, height of 1m and length varying b/w 2 to 4 m. The backside of vat is not vertical but it is sloping at an angle of 45’ so as to facilitate the sliding of ropes and also to reduce volume of processing liquor. To avoid entanglement, a peg rail fitted below a jockey roller in front of m/c, separates the fabric ropes. The fabric rotates at a speed of 60 to 70 m/min. A salting box is provided in front of m/c by interposing a perforated steel sheet at a distance of 30cm from the front of dye bath. Water & steam pipes and a drain valve are also provided in this compartment. Fabric pieces are loaded manually but are unloaded with the help of a mobile set of squeeze rollers after tying together different ropes of fabric into a continuous length. The liquor goods ratio of winches varies from 12 to 20.
In 1000lit of water, soap and soda ash are added at a temp of 100’C. Firstly, fabric is given a cold wash for 15mins then with chemicals fabric is washed for 45mins. Washing of reactive dyes are done only in winch.
JET DYEING MACHINE
This m/c is mainly used for dyeing (Disperse) Polyester fabric since polyester dyeing requires very high temp about 130’C in the acidic medium of ph 3-5 otherwise the dye will not fix in fabric. Dyeing at this temperature yields rapid, better penetrated and more level dyeing that really makes an economic sense. In Gull Ahmed there are 4 jet-dyeing machines, 2 are small having capacity about 1000lit & 2 are big with capacity 1500lit. In big jet dyeing m/c two narrow width fabrics may load together. The liquor ratio of 1:10 is maintained in this m/c.
WORKING:
This m/c is based on the principle of using a jet of dye liquor to transport fabric in m/c. In this system, the fabric is rotate at a very high speed through a circular tube with the help of circulating dye liquor. The liquor is collected from bottom of m/c, passed through a heat exchanger and then a high volume centrifugal pump and injected at the top of m/c along with fabric through the tube.
For 15mins the fabric is circulated in cold water then the acid and leveling agents are added in water through the mother tank, this feeding of chemicals takes only 5 to 10 seconds then a filter closes the mouth of tank. The fabric is run for 10 to 15mins in these chemicals. The dye is added in the liquor of m/c and fabric is allowed to run for 10 to 15mins at room temperature. Then gradually the temperature is raise until it reaches 130’C, this temp is indicated on a temperature indicator fixed at the top of m/c. The fabric is allowed to circulate in the dyeing liquor according to the shades of fabric i.e. for light shades 1/2 hr, for medium shades 45mins, for dark shades 1 to 1 1/2hrs. When the temperature reaches to 100’C the shades are checked. There is speed, temperature
SAMPLING.
LOCAL SAMPLING:
Black and white paper print design from design department comes into sampling department incases of local printing. Then usually no color ways are made here for each print. These color ways are made by table printing with flat screen and then are sent to the marketing department. Designers of marketing dept select 5 or 6 color ways normally out of 20 and then selected ones are sent again to the sampling department. Now the workers here convert the recipe of dyes for the bulk and sample usually of one repeat is made over the rotor printing m/c. They are again sent to the marketing for final selection and then bulk production starts.
FLOW CHART: -
DESIGN-àCOLOR SELECTION-àMARKETING DEPT-àPRINTING M/C-àMARKETING-àBULK PRODUCTION.
EXPORT SAMPLING:
For export purpose the design are provided by the customer as well as the by design dept his design could be over the paper or fabric. Customer and marketing will first of all discuss the design and then sampling starts.
It includes C.P.S, which stands for color physics system. It identifies the colors of design by the spectrophotometer and gives the recipe. The color mixing is done and colors are dispensing out. Gammets are made over the F.A.M m/c for checking of color shades. If the shades are matched then sample of 5-10m is made by K.D.M firstly usually small screens are used. After printing in K.D.M fabric is dyed, cures and washed to get the final sample. This is sent to the marketing dept where meeting b/w dept and customer is arranged and if design is selected then it is again sent to sampling dept. This time same design is made but with bigger screen and in this case screen and design proofing is done over K.D.M. This design is matched with first sample and if selected then design is sent for bulk production.
FLOW CHART: -
CUSTOMER-àMARKETING-àDESIGNING-àPAPER PRINT-àSCREEN MAKING-àSAMPLING-à-àCPL-àCOLOR MIXING-àFAM-àKDM-àDRYING-àCURING-àWASHING-àFINISHING-àMARKETING-àSTRIKE OFF-àKDM-àPROOFING-àBULK PRODUCTION.
FAM: - It is used for producing gammets following coverage percentage.
1) 100%
2) 59%
3) 25%
4) 10%
These gammets help designer for selection of color.
1-WORKING MECHANISM: - The magnetic force of attraction is created electrically below the FAM table, which moves the rod along the length of table, by which table, by which gametes are formed.
2-KNURLING ON THE ROD: - The rod used for printing and producing gametes is usually knurled so that color penetration is even on whole design.
K.D.M: - It is used for producing samples for local and export customers. Usually 5-20m of sample is produced. It is also used for screen proofing purpose, which means the checking of screen before running in production. If the design running on m/c have some problem in screen or old design are needed again then this m/c is used for screen proofing that they are producing same effect or not.
MACHINE DESCRIPTION:
GLUING SYSTEM: -The fabric is stick on the blanket by means of glue or adhesive material so that it does not shrink during printing. Dipping the fabric in the glue-carrying trough provided in front of KDM.
TYPES OF SCREEN: -The screens are used for rotary printing is made of nickel screen of 3200mm in length. The screen length can be adjusted according to the width of fabric, which ranges from 1280, 1620, 1850, 2400 and 2800mm in length. The screen circumstances are 641, 840 and 914mm. There is only two screens drive in KDM.
ROD: -The rods used for printing are of following diameters.8, 10(this rod is used for producing effects), 12, 15, 20mm
DRIVING MECHANIM OF BLANKET AND SCREEN: -Screen head is drive by means of gearbox and roller drive is used for blanket.
BLANKET WASHING: -
BLANKETàSHOWERINGàSCRAPERàSHOWERINGàSCRAPING.
Blanket washing time is about 10-30min.
FLUX SELECTION: -Flux is selected by seeing two things 1) rod size 2) design type
PRINTING SEQUENCE:
- Dark shades first then light shades.
- White paste should be first applied incase of reactive, for pigment it is lastly applied.
- Golden, silver paints should be applied in last so that they cannot stick to screen of other colors if applied first.
- More coverage and dark shades the dia will be increasing otherwise the magnet flux will increase.
PRINTING FAULTS: -
- Rod selection
- Pressure and flux variations
- Viscosity variations
- Checking of screen
- Setting of screen
- Due to dust particles
Color kitchen supplies color to KDM.
DESIGN ENGRAVING.
DESIGNING: The design department of Gull Ahmed is totally a separate dept having skilled designers who are working manually and as well as on computers. The customers either provides the designs or customers select the design prepared by Gull Ahmed’s designers.
The design, which is selected, is first of all scanned directly if it is on paper & is solid where as if it is complicated, delicate and on fabric than it is traced by hand on plastic sheets and than they are scanned. After scanning color separation is done on computers and then coloration is done i.e. same design with different colors are made & finally texture mapping takes place i.e. designing is done according to end use. At this stage design is discussed with customer then it is saved in CD and sent to engraving dept.
ENGRAVING: This is the process of copying design over the different screens according to the number of design colors. Screens are made of Nickel having mesh size 60, 80, 125 normally. They are imported from Holland & can be reuse 3 or 4 times but this also depends on handling. Their length can vary 2800, 1280 mm. The diameter of screen can be 640 & 914 mm. Engraving can be of following type:
1- Ultraviolet
2- Wax
3- Laser
Wax and laser are used here.
LASER ENGRAVING: -
Firstly the screen is coated with a emulsion SCR100. This makes a thin layer over screen & blocks all mesh then screen is dried. This whole procedure takes about 1/2hr. Then this screen is sent to polymerization chamber so that emulsion becomes hard. Here heating is done at 150’C for 2hrs. The polymerization chamber can store 8 – 10 screens at a time. Then screen is fitted over laser m/c. the design is feed to computer, dia & length of screen & repetition of design is also feed to computer. The laser rays are provided by combining Helium, Nitrogen & Carbon & then are bombarded by moving head over the rotated screen according to compute program. This usually takes 1hr for 2800mm long screen and 15mins for 1280mm but this time also depends on type of design. In laser actually the burning of emulsion occurs so it does not give very sharp results so for delicate design wax engraving is used.
WAX ENGRAVING: -
Here wax is used for copying design. It is different from laser in a way that after screens are coated and dried, they are not polymerized but they are sent to wax engraving m/c. As white or sun light can harden the coated layer of emulsion so yellow light is provided in the room having this m/c. Wax and ink are fixed in a fixed ratio by computer, in which the design is feeded and the head moves according to the program. The head of wax engraving m/c has two portions one has 64 nozzles, which spray the mixture over the rotating screens acc to design and the other chamber have Halogen light produced at 5000volts. When spraying is completed the screen is exposed to this light so that emulsion on screen other than wax portion becomes hard and then it is washed with simple water to remove paste from its surface and for final hardening screen is sent to polymerization chamber at temp 150’C for 2hrs. After this end rings are glued at the screen ends so that they can be fixed in gears of printing m/c.
If comparison is done b/w two m/c at this stage than we can conclude that wax engraving is used to show each and every fine detail of design whereas laser is used commonly for solid designs. The combination of both machines may also use in printing machine.
The General Theory of Printing.
The printing of textile materials is the application of color according to a predetermined Design.
The printing paste that is applied to textile material consists of dye, water, thickener and hydrocarbon solvent or oil, after the printing paste is applied, the textile material is usually steamed. This is to enable the dye molecules to migrate from the surface to the fibres and to enter the fibre polymer system. Steaming swells the fibres and ensures better penetration of the dye and improved color fastness properties of the textile material.
The general theory of printing explains the interaction between the dye, fibre, water, thickener and hydrocarbon solver. More specifically, it explains how within the printing paste:
1. forces of repulsion are developed between the dye molecules and the constituents of the printing paste; and
2. Forces of attraction are developed between the dye molecules and the fibres of the textile material to be printed.
The Role of the Thickener.
The purpose of the thickener is to produce a medium for the dye paste and the resultant product is called the printing paste. The printing paste is an emulsion of the thickener and hydrocarbon, such as white sprit or Very light hydrocarbon oil, plus a surface-active agent. This surface-active agent enables the emulsification of the thickener with the hydrocarbon to form a printing paste of uniform consistency. The uniform consistency of the printing paste is referred to as its viscosity (the ease with which the paste will flow). The viscosity of the printing paste is very important as it influences the clarity and appearance of the printed pattern.
PRINTING DEPT OF GULL AHMED
a- For export quality here pigments are used.
b- For local quality here reactive dyes are used.
Two methods of printing used here are
a- Screen printing
b- Roller or rotary printing.
SCREEN PRINTING:
This section is utilized for the printing of local goods and some exports. It is usually used for printing the dupatta and shirting material and panel design like Mickey Mouse etc. The printing table used is 200mm in length and 102inch in width. The table is heated by steam at temp of 70-90’C. The glue is first applied on table so that fabric sticks on table. After which the printing is done in following sequence:
For cotton goods: -
- First the dark shade screen is used having less coverage so that the fabric is not shrink and then move towards the lighter shades.
- The white should be first applied on the fabric so it gets the time to dry. The fabric is then aged, washed and finished.
ROTARY PRINTING:
- Rotary screen-printing has been developed a fully continuous screen proofing techniques to rival and in fact take over from the engraved roller printing.
- Rotary screen-printing uses seamless cylindrical screen, which are composed of nickel mesh with end rings, soldered on the cylinder to prevent collapsed. Each rotary screen is positioned across the fabric and it is independently drive at one end.
- As the screen rotates, it is feed internally with print paste, which is forced through the open mesh area by the stationary squeegee may be either a convention rubber polymeric blade i.e. doctor blade or metallic rod held against the rod by stationary electromagnetic beneath the printing table.
- In modern conveyor fabric is dry by passing through a hot air dryer.
The rotary m/c installed in Gull Ahmed are
a- RD 2
b- RD 4
c- RD 5 (RD4 2800)
d- RD W
The basic working principle of all m/c is same. Their differences and description is therefore given in the form of chart.
DESCRIPTION OF M/C:
The material is feeded to all of them in form of batch. RD 5 and RD W have scary Arrangement this will save the time of batch changing (without stopping m/c). After feeding in different arrangements are provided for removal of lint from fabric.
LINT REMOVAL METHOD: -
LINT:
The loose cotton thread and fluff are on the fabric surface. These are all unwanted material and may damage the design of printing. To remove them following methods are used in printing m/c.
EVAC METHOD:
The material is removed by suction. A turbo rotary blower produces a high vacuum. The fabric is passed through a slot. The clearance of slot should not be more than 3mm.
LOBACIN METHOD:
Lobacin is the name of a milking chemical having high sticking properties. This chemical is applied on a roll, which is passed with a little touching contact. The unwanted material sticks to roll and blade scraps it. This method is only used on printing m/c cleaning the printing face only. This system is found in RD 4 and RD 5 machines.
CYCLONE METHOD:
This consists of a brushing roll and sucking system. The brushes remove the lint from surface of fabric and then sucking system sucks it. A separate motor is provided for its control. It runs at same speed as of blanket of RD.
HEATING TRAYS: -
After this cleaning arrangement heating tray is provided. It works in case of polyester fabric, as it cannot stick over blanket when it gets wet with glue it is heated and special rubber coating is made over whole blanket over which heated polyester fabric gets stick.
GLUE TROUGH: -
For cotton fabric a glue tray is provided below the blanket. The blanket is dipped into it and extra glue is removed from it through scrapper and fabric from heating tray presses over it by pressing roll so that it gets stick there and do not move over blanket.
SQUEEGEE: -
Color in screen is provided by it. Normally three types of squeegee are used for printing.
1- Metallic rod having knurled
2- Doctor blade
3- Airflow squeegee.
COLOR FEED PUMP: -
Electrically driven reversible colors feed pumps are located under catwalk that is extended on both sides of printing head. Print paste level in screen is maintained as required.
WASHING EQUIPMENT: -
Washing system is provided at the end of the blanket frame below blanket. First it is washed by reuse water and foam fixed there. Then it passes over brushes with water and then from foams again but with fresh water. After this scrappers are provided to make them dry before entering into glue trough.
DRYERS: -
The printed fabrics leaves rubber blanket after last printing section and is transported on the carrier blanket in specially designed high efficiency three pass drier that ensures drying of printing material at high speed. The speed of conveyor is synchronized with speed of fabric being printed. The drying is done hot air produced by gas heating or by convection mechanism through oil.
AIR CIRCULATION: -
The fans are driven by V-belt and are mounted over both sides of dryers. The fan bearings are equipped with air-cooling system. Uniform drying over entire width of fabric is ensured by arrangement of nozzles sets on upper and lower side of cloth.
COLOUR KITCHEN
This is the most important department as far as printing is concerned because this is the place where shades are made. CPS separates the shades in the design, which is sent by the customer or by the design department.
COLOUR PHYSICS SYSTEM (CPS):
Here a spectrophotometer is provided which senses the colour shade by the wavelength measurement. If the reflectance % is more it means shade is light and vice versa. CPS then provides the shade recipe. After determining the recipe costing is done to check which is suitable for processing and fulfilling the fastness (both light and washing) according to the demand of the customer.
METHODS OF COLOUR SELECTION:
There are two methods of colour selection:
Fixed Triangle
Free Triangle
FIXED TRIANGLE:
The colours in this case are selected from the database according to the shade. This colour could be a single or combination of two or three. But in case of fixed triangle any colour of the recipe cannot be replaced.
FREE TRIANGLE:
In this case any of the colour of the combination is causing metameric effect or resulting poor washing or light fastness can be replaced with alternative. The recipe, which is selected from the CPS, is directly transferred to the IPS, where colour checking and screen groups are made. After this it is send to the dispensing unit.
ITEGRATED PASTE PREPARATION SYSTEM (IPS):
The recipe that is feeded here from CPS is converted from 1kg to bulk that is, 60 or 80kg as required. All calculations are done automatically and then are sending to the dispensing unit. In IPS 4 status are made. First one is for feeding of recipe that is, colour ways, screen group etc. Second is for calculation, third is correction and last one is send to the dispensing unit for getting the colour.
DISPENSING UNIT:
It is an automatic unit in which pigments are feeded and calculated weight dispenses out automatically. It consists of feeded drum connected to the dispense nozzle by pumps and filters. The material stored in drums is filtered after every 5 minutes and circulated automatically to avoid any blockage. It is capable of storing 24 dyes in it. Speed of dosing is controlled by electrical mechanism, depending on the material to be feeded. Pneumatic pistons control the dosing.
PRINTING PASTE MAKING:
The colours in the calculated amount according to the recipe are dispensed in container and then pigment paste is added to it. Pigment paste consists of water, urea=2% (as it is of hygroscopic nature and is added to avoid mesh clogging), ammonia =0.5% and antifoaming agents (2kg in about 1500kg).
The pigment pastes used here are of two types.
P1 = only chemicals with very little amount of thickener
P2 = chemicals and 35% thickener
These are of two different types because the bacteria can change the viscosity, which is usually maintained between 50-60 decipoise so we use P1 along with P2 to get the required thickness, and P1 is used first since its viscosity may vary. Fixing agent is also added manually in liquid form. Here fixation is done with the help of sodium bicarbonate since it is a weak alkali.
After mixing of all chemicals the paste is mixed with stirrer and then filtered to remove any impurity that may damage the screen.
FINISHING:
Textile finishing is the term used for a series of processes to which all bleached, dyed, printed and certain grey fabrics are subjected before they are put on the market.
This is the most important department of a textile industry as it involves the activity of the fabric in many major steps. The aim of textile finishing is to render textile goods fit for their purpose or endues. Finishing processes are carried out to improve the natural properties or attractiveness of the fabric and to increase its service ability.
The techniques of finishing depends on the following:
Nature of the fabric tat is, chemical composition state, weave etc. this determines the appearance i.e. transparency, luster, fullness, weight, whiteness etc
The physical properties of the fabric i.e. feel, softness, stiffness, tensile strength, elongation, shrinkage property
The endues of the material i.e. non shrinkage, non creasing (good crease recovery), crease retention draping, stiffening, resistance to abrasion, non soiling nature etc
Receptivity of the fabric to various finishing operation i.e. eater proofing, g flame proofing, rot proofing etc
Susceptibility to chemical modification.
The finishing operation differs according to the properties to be imparted to the material
Improving the appearance luster, whiteness etc
Improving the feel, which depends on the handle of the material and its softness, suppleness, fullness etc
Weaving qualities, non soiling, anti crease, anti shrink, comfort etc
Special properties required for particular uses water proofing, flame proofing etc
Covering of fault in the original cloth
Increasing the weight of the cloth.
In finishing, the department controls the design deviation (slewing and bowing), vigils the quality control, checks the softness, stiffness or shining and colour fastness is visually analyzed to match the original flapper. When the first time the fabric arrives in the finishing department after bleaching, it is equalized (stretched in accordance to the required width) to be sent for dyeing or printing.
The fabric is equalized for:
Dyeing
Printing
Mercerizing
The finishing department also does the heat setting of the fabric before it goes to the dyeing department.
The second time the fabric returns to the finishing department after dyeing and printing. There are two processes left for finishing department:
Chemical finish
Mechanical finish
The chemical finish is done on stenters whereas the mechanical finish is done on calendars.
CALENDARING
Calendaring is an operation carried out on a fabric to improve its aesthetics. Purpose of calendaring is:
To upgrade the fabric hand and to impart a smooth silky touch to the fabric.
To improve the opacity of the fabric
To compress the fabric and reduce its thickness.
To impart different degree of luster to the fabric.
To reduce yarn slippage.
The mechanical finish is done for softness and shining of the fabric or stiffness according to the nature of the chemical, this process is done after the chemical finishing as per buyer requirement.
In calendaring the threads of the fabric are close to give it a gloss or the seal required. An ordinary calendar consists of series of hard (steel) and soft (cotton) bowls placed in a definite order. The sequence of the roller is that no two hard rollers are in contact with each other. The pressure and the heat applied in calendaring depend upon the type of finish required. The calendaring effect produced depends on the moisture content of the fabric, the number of bowls of the calendar used, the composition of the bowls (steel cotton, cotton steel, steel paper, cotton plastic), bowl arrangement, temperature, pressure and speed.
CONSTRUCTION OF HARD BOWL:
The hard bowl consists of mild steel and a cast iron shell of linear diameter. The shell is heated when it expands and in this state it slip to the core and chilled when it contracts and grip the core tightly. The iron bowl are made with a highly polished hard surface and heated inside by steam.
COTTON BOWL:
The compressible material bowls are made either of cotton or wool paper, linen paper or flax paper.
In Gul Ahmed following types of calendars are used:
7 bowls calendar
5 bowls calendar
3 bowls nipco calendar
7 bowls calendar
TECHNICAL SPECIFICATIONS:
SPECIFICATION 7BOWLS 5BOWLS NIPCO 7BOWLS
KOYOTA
Daily production 24000m/shift 16000 m/shift 35000m/shift 24000m/s
Pressure at steel roll upto 350N/mm
Pressure at cotton roll upto 350N/mm
Pressure at systhetic bowl upto 150 bar
Length of cylinder 138 inches
Speed 65m/mi 40-50m/min upto 150m/min 50-60m/mi
Pressure system mechanical mechanical hydraulic mechanical
Heating system steam steam hot oil steam
Pressure 55kp/cm2 25kp/cm2 50 kp/cm2
Temperature 70-80C 50-70C 70-180C 70-80C
Bowl arrangement vertical vertical L shaped vertical
For soft finish the fabric is passed through cotton bowl. For satin fabric the pressure at cotton bowl is less than the pressure at steel bowl.
NIPCO CALENDAR:
Nipco calendar or L calendar has deflection compensation roll and precision width control. It has three bowls:
Steel bowl
Nipco bowl racolan sleeve (highly elastic polyamide base)
Cotton bowl
STEEL BOWL:
This bowl is heated by means of hot oil that is, the temperature can be raised up to 210C and also high pressure up to 250 N/mm2 can be given. Because of this the three rolls produces better results, in spite of less contact area, than 5 or 7 bowl calendars. Element system is also present in steel bowl that is, the bowl is heated only up to the required width of the fabric.
NIPCO BOWL:
This bowl is 3.6m in length. The sleeve rotates by means of hydrostatic oil film that pressurize only the desired area by means of hydrostatic bearing.
COTTON BOWL:
The temperature is applied by the hydraulic oil circulation and by means of heat exchangers. The medium inside the tube of cotton bowl has temperature of hydraulic oil. T (in)=230C and T(out)= 80C. The medium outside the tube chilled water temperature T(in) = 15C and T(out)= 35C. Flow rate of hydraulic oil is 52-m3/ hour.
Flow rate of chilled water = 5m3/ hour. The hydraulics oil used in napco calendar is Mobil gear 630 or Aral Degol BG 200.
DIMENSIONS OF NIPCO BOWL:
- Outer dia of sleeve 500mm
- Inner dia of sleeve 400mm
- Length of sleeve 4000mm
- Working length 3.6m
- Web width (min) 800mm
- Web width (max) 3.6m
- Web speed (min) 10m /min
- Web speed (max) 100m/min
- Line force (min) 50 N/mm
- Line force (max) 250 N/mm
- Lifting of sleeve + - 10mm
TYPES OF FINISHING EFFECTS:
SHINING EFFECT: Fabric passes through nip pf nipco and steel roll giving smooth and luster effect.
HIGH GLOSS EFFECT: fabric runs with steel roll and nipco roll then with nipco roll and cotton roll giving smooth and matt effect.
DULL EFFECT: Between nipco and cotton roll.
The fabric after mechanical finish or chemical finish is sent to the lab for testing to be approved for the folding department and for stitching and then is forwarded fro shipment.
STENTER
Stenter is the most expensive and important m/c in a dye house and besides the dye fixation; it is used to control the finished length and width of fabric. The stenting process has thus an effect on handle, appearance and final finish of fabric. In chemical finish the stenter m/c acts to soften or harden the fabric by the application or deposition of chemical.
WORKING: -
The chemical in stenter is applied over the fabric by passing it through the chemical trough. Fabric after the chemical trough goes into the padder and then into the weft straightner (Bianco or Mahlo system). After this process the fabric goes over the chain and enters into the drying chambers. If required the fabric is further mechanically processed or it goes to lab for testing.
IMPORTANT PARTS OF MONFORTS MONTEX M/C:
CHEMICAL THROUGH:
The fabric from the in feed system enters into it, where the chemicals are applied to get required effects. The chemicals that are usually used for finishing are;
SOFTNERS: -
They are of two types.
1- Cationic (they are temporary softners)
2- Silicon (they are permanent softners)
They are in liquid form and have soapy touch, when applied to fabric it gives slippery effect so fabric feels soft. Silicon softners are of two types; micro and macro. Micro is permanent finish as it enters into intermolecular spaces of fabric whereas macro’s finish will remove after some washes.
POLY VINYL ACETATE: -
PVA is a type of thickeners used to stiffen the fabric. It fills the inter spaces of warp and weft and hence increases the weight of fabric.
RESINS: -
They are applied only on pure cotton and are used as crease recovery or easy crease. They also control the shrinkage and dimensional stability. They polymerize with the cotton fibers so are considered as permanent finish. Catalyst is also added with resigns to increase the rate of reaction. Due to resigns the fabric lose its strength so we always use Calonine L (softener) with it to maintain the strength.
BINDERS: -
It is used to improve the rubbing fastness of printed or pigment dyed fabric. It is also used to reduce pilling as it makes a layer over the fabric.
OPTICAL BRIGHTNERS: -
They are used for whitening effect of fabric. They actually convert the ultra violet light into visible range. 1gm/lit of it increases 40 to 50% whiteness of fabric.
DRYING CYLINDERS: -
They are provided after the chemical trough. Steam is provided here so that fabric after squeezing when passes through these cylinders then fabric gets heated and we can run m/c at higher speed. They are used only incase of dyeing for even results.
EVAC SYSTEM: -
This system is used for removal of fluff, unbounded moisture and loose thread suction. Turbo rotary blower used to produce a high vacuum. The fabric is passes through a slot that should not be more than 3mm.
WEFT STRAIGHNERS: -
In stenters clips or pins automatically grip the required amount of salvages in running condition, which maintain the width along the whole length. The bainco system is used for controlling, skewing and bowing of the fabric along the whole length of stenter chamber. The system also shows the percentage of skewing and bowing of cloth. It is seen that the fabric, which is produced by goller bleach, has 0 – 3 % skewing and bowing property while the fabric produced by the J/box has irregular width.
In mahlo system skewing and bowing is controlled manually that is by means of applying pressure or force mechanically. Skew and bow rolls are arranged in a pattern in order to control the skewing and bowing process.
DRYING CHAMBERS: -
10 drying chambers are provided here for drying. They have 5 burners and 20 motors for circulation fans. The length of fabric in chamber is about 55-60m.
STAR JET NOZZLE BODIES:
These are the perforated holes in nozzle body, which showers hot air on the fabric from both sides. Small holes are 10mm in dia for showering the gas and 100mm holes are used for exhaust opening.
Air circulation system in dryer:
Fresh air is taken from the atmosphere at standard temperature and pressure to help burning in burning chambers using methane gas. This hot gas is forced to pass through the star jet bodies by circulating fans. The star jet nozzle bodies shower the hot air on the fabric and used air is re-circulated and passed through the burner. If no fresh air is taken, a time will come that the re-circulated gas will get saturated and will be having no more tendencies to absorb moisture from the wet fabric.
Cooling zone:
At the exit of drying chamber cooling jet nozzle bodies or cooling drums are used to reduce the temperature of out coming fabric.
SANFORISING MACHINE
Sanforising is a mechanical of treating the textile fabrics to prevent the normal dimension alterations of warp weft, which occur in the finishing operation; especially those carried on in laundering &allied operations.
The process involves:
Precise determination of changes that occur in dimension when subjected to full laundry wash producing the finished effect to enhanced commercial value.
The sanforizing, which used in PDT, is of EVASET mechanical range (monforts)
Specification is:
Max. Cloth width 55inch
Compression 16%
Speed 90yards/min
Note: keeps half-inch width extra to help compensate for the inevitable slight extension of the fabric during the shrinking process
MECHANICAL COMPRESSIVE SHRINKAGE: -
The fabric is compressed by the contraction of the conveyor surfaces on which the fabric has been made to adhere. The conveyor takes the form of a rubber belt or sleeve. The outer end expands as it passes over a roller and at this point the fabric is applied. The surface contracts with it, expansion and contraction are controlled, precise and predetermined length can be obtained, hence the process is positive.
EVASET PRINCIPLE a specially made rubber sleeve is tensioned b/w roller 2 and 3. A driving roll on the outside of sleeve and deflects the upper run of sleeve into a reverse curvature, the driving roller 1 is steam heated.
The outer surface of rubber sleeve is expanded as it moves round the tension roller. The driving roller nips the fabric into contact with the expanded surface contract on taking up the reverse curvature around the driving roller.
CAUSE & CONTROL OF SHRINKAGE
LOOM:
When the fabric is woven, vertically the yarn stretches along the warp wise direction so the fabric is made under the constant tension condition.
IN PROCESSING:
Finishing process stretches yarn, during the commercial bleaching, dyeing, mercerization and other finishing processes. Both the warp and weft yarn are subjected to the stretching.
Complete shrinked yarn is fully relaxed, when fabrics are damped; all yarns become wavy and shorter i.e. their shrinkage occurs. The compressive shrinkage process is the most dependable and accurate method of shrinking fabric.
EFFECT OF SHRINKAGE
The fabric is improved, after shrinking there are more threads per inch both in the warp and weft direction. As a result, the shrinked fabrics have greater wearing qualities and improved hand.
WHY FABRIS SHRINKS
. Because the yarn it self swells in water and because of restricting effects of twist tends to contract.
. Because process tension are shed when a fabric is washed in water. In the process of manufacturing and finishing in continuous length fabrics are in elastically stretched. They tend to become longer and narrow. When washed such fabrics will expend in weft and contract in warp.
. The readjustment is referred to generally as shrinkage.
MAIN STEPS OF SHRINKAGE PROCESS
- DAMPING
- STENTERING
- SHHRINKING
- FINISHING
LABORATORY
This is the most advanced and most important department as fabric after every process comes here for testing. It is the key to the efficient working of all the department of the processing unit. Instruments used in the lab are according to the requirements and must be modern enough so that any test can be performed. A lab consist of following departments:
1. Application service 2. Quality control
1.Application service:
Works are:
1. Color matching
2. Research and development
3. Trouble shooting
4. External service
2. Quality control:
Fabric Testing Section Raw Material Testing
In Process Finished Product
Quality Control Quality Control
APS section:
· There work includes selection of the dyestuff, process, costing and fastness checking according to the end used of product.
· It also tests the new market products.
THE TESTS CONDUCTED IN LAB ARE: -
IN APPLICATION SERVICES:
1- Test for color matching
2- To check the metameric effect of fabric
3- To check the properties of new product before purchase and make the cost analysis
4- To find out the cause and effect of any problem arises during the bulk production.
IN RAW MATERIAL SECTION:
1- To check the whiteness of optical brightening agents.
2- To test for fixing agent
3- To determine the PH for chemical
4- Test for stiffness/softness
5- Determination of viscosity
6- Test for desizer
7- Test for stablizer and sequestering agent
8- Checking of white paste
9- Analysis of water
10- To check purity of different chemicals by finding their melting and boiling points.
IN FABRIC TESTING SECTION:
FOR GREY FABRIC:
1-To find out ends and picks
2-calculate the count
3-to check the size percentage
4-blend ratio
5-width
6-weight/m2
IN PROCESS QUALITY CONTROL:( IPQC)
AFTER BLEACHING.
1-PH
2-Absorbancy
3-Tegawa (degree of desize)
4-Whiteness
5-Width
6-Width drop %
7-Pilling
AFTER EQUALISING.
1-Whiteness
2-Skew and bow %
3-Width
4-Weight per m2
AFTER CURING. (BEFORE FINISHING)
1-Rubbing action (dry and wet)
2-Washing fastness
3-brushing fastness
4-PH (it is checked after dyeing)
IN FINISHED PRODUCT QUALITY CONTROL (FPQC)
1-Width
2-Weight/m2
3-Shrinkage of warp and weft
4-Pilling
5-Tensile strength
6-Flamability
7-Whiteness
8-Washing fastness
9-Crocking (dry and wet)
10-Brushing
11-Light fastness
12-Formaldehyde content
13-PH
14-Finish construction (ends and picks)
15-Finish content
16-Skew and bow %
17-Design deviation %.
Burner's temperature: 400-500C
Pressure on compensators: 2-3 bars
Burner angle: 180 when fabric is moving at high speed. As the speed of fabric
Decreases (upto 50m/min) the angle becomes 90
Width of fabric: 120 inches
Gas consumption: 240-250 cm3 per day
Two rows of burners are provided so that the fabric can be singed from face and back. Water circulation is also provided in the rollers for their cooling.
COMPENSATORS: They are used to maintain the tension over the running fabric and they work with the help of pneumatic pressure. They maintain the tension over the fabric by charging and discharging. Charging is defines as:
DESIZING BATH: It is tank containing desizing liquor for the removal of size so that the fabric becomes absorbent for further processing. It consists of 8 pair of rollers so that the fabric remains in contact with the liquor for 5 min. Squeezing rollers are provided after this tank that removes the extra liquor from the fabric, which comes again into the tank through a tray.
SPECIFICATIONS:
Temperature of the tank: 70C
CHEMICALS:
For PC: NaOH (It acts a s a surfactant)
Imrolex (It destroys the size)
For Cotton: Oxalic acid
Sandozen MRN (It acts as a surfactant and wetting agent)
The capacity of this tank is 1000 liters, which is usually used to treat 3000m of fabric.
8. MACHINE UTILITIES: the machine utilities are current, water, gas and air.
GOLLER SCOURING AND BLEACHING MACHINE
SCOURING:
All natural impurities in textile fibers other than coloring matter are removed by means of scouring. The ultimate aim of scouring is to make the material uniformly and highly absorbent in a cost-effective manner so that there are no difficulties in the later processes of dyeing, printing and finishing.
Natural impurities include:
a. Mineral matters
Oils and waxes
Leaf particles
Coloring pigments
Dust
Pectates
a. MINERAL MATTERS:
These are salts of calcium and magnesium present in soil. These are water-soluble and can be removed easily. If these are not removed from the fabric, spotting occurs on fabric.
b. OILS AND WAXES: There are two types of oils: Edible oil and Non edible oil
- Edible oils can be removed by sponification that is, they are converted into water-soluble component with the help of alkali.
- Non-edible or lubricating oils are dispersed into fine droplets and remain in suspension and the process is called emulsification. These oils can also be removed by extraction with organic solvents.
c. COLOURING PIGMENTS: These are the nitrogen containing compounds (azo group) and these cannot be removed in scouring but in bleaching.
d. LEAF PARTICLES: These are removed in ginning but if not removed completely they are dissolved with the help of alkali.
e. DUST: Dust comes from atmosphere and can be removed easily. Dust must be in suspension form otherwise the removal will not be 100% .So dust removing agents are added which makes the sand (dust) in suspension.
f. PECTATES: These are long chain carbohydrates, insoluble in water and soluble in alkalis. Yellowing tint is present on the fabric due to the presence of pectates and also the problem of absorbency occurs.
BLEACHING:
Scouring removes almost all the impurities of cotton fibers except husk and natural coloring matters that are ultimately removed by oxidizing agents. The oxidation treatment or bleaching is necessary for producing white goods as finished products or for dyeing pastel shades. Even for dark shades, bleaching improves the brilliance and evenness of shade. Bleaching may be Oxidative or Reductive.
OXIDATIVE BLEACHING: In case of this type of bleaching the process is irreversible that is, whiteness for always. Oxidative bleaching is done with the help of following bleaching agents. CHLORINE CONTAINING: Sodium hypovchlorite, calcium hypochlorite and sodium chlorite. OXYGEN CONTAINING: Hydrogen peroxide, sodium peroxide and barium peroxide.
Chlorine containing agents gives more whiteness as compared to oxygen containing but problem in this is chlorine retention that is, chlorine can not be removed 100% and chlorates forms on the fabric and yellowness appears that is why oxygen containing bleaching agents are preferred.
REDUCTIVE BLEACHING: In case of reductive bleaching the process is reversible that is the fabric again gets yellow on exposure to air due to the oxygen present in the atmosphere. Reductive bleaching agents are sulfur dioxide, sodium thio-sulphite and Na2S2O8.
For effective bleaching pH, temperature, time, concentration and impurities are to be controlled. For bleaching the compound must be present in unstable form that is, ionizes easily. Market form is stable form so the bleach must be converted into unstable form for the process. It is to be checked what is the stable form of bleach. If it is stable in acidic medium then alkali is added for instability and vice versa.
SCOURING & BLEACHING: In our project CONTINUOS SCOURING &BLEACHING (one step) is carried out for following purposes;
· For A High Degree Of Whiteness
· Complete Degrading Of Seeds & Removal Of All Impurities
· Outstanding &Even Absorbency
· Low Fiber Damage
· Improved Hand Of The Fabric
· Reproducibility Of Finishing Result
· High Efficiency
· Short Amortization Time
PARTS OF A MACHINE:
PRE WASHING: It is done with pure water at a temperature of 98C to remove the chemicals, which are applied in the desizing bath. This washing both contains 22m of fabric hover and 8 pairs of rollers.
VACO SET: This arrangement is mounted over the machine and is used for sucking extra fluff from the surface of fabric with the help of vacuum. The vacuum is created by a separate motor and pump arrangement by maintaining a pressure of –150m bar. It consists of a rectangular ceramic piece having slots in its center throughout the length from where the suction is done. A wire is provided over the slot and fabric passes between the wire and ceramic piece. The function of the wire is to block the slot upto the portion other than the width of fabric.
SQUEEZING ROLLERS: Expander is provided before the squeezing rollers. Its function is to remove the creases from the fabric if present. After passing through it, the fabric squeezes by means of squeezing rollers. The pressure over squeezing rollers is up to 2-3 bars and the pick up is 65%, but these can be varied according to the type of the fabric. Then the fabric passes over the bowing roller, its function is to straighten the weft, it is a curved rubber roller, which gets the drive from the friction of the fabric.
COMPENSATOR: It serves the following three functions:
1: CREASE REMOVAL: Creases are removed by the weight of the compensating roller that is equal to 25kg. For heavy weight we can even increase the tension by applying the pressure from 1bar to 4bar. This is called as charging position, where as for lightweight fabric we can reduce the tension by applying the negative pressure, which range between 17-12 bars. This is known as discharge.
2.SYNCHRONIZATION: If the compensator is down, then the speed of the processes following increases automatically and vice versa.
3: AUTOMATIC STOP: It provides an automatic stop to the machine if the fabric torn out.
Total number of compensators used in this machine is 12.
DIP SET#01: This is a tank like arrangement in which we apply the chemical for scouring over the fabric, that’s why it is also known as scouring chemical bath.
CONSTRUCTION OF DIP SET: It has a special arrangement for the feeding of the chemical that consists of a narrow tray over which the feeding pipe is provided. When the tray over flow, the chemical falls over the fast moving fabric through out the width. This is done to prevent staining of the chemical over the fabric. After impregnation of the fabric in the chemical, it passes between the doctor rolls, they have blade like structures on two sides. This helps to squeeze the excess liquor.
FEEDING MECHANISM OF DIP SET: The solution of chemical according to the type of fabric is made in the main or mother tank. From there it is fed to the dip set according to the speed of the fabric. To keep the concentration constant, the chemical from the dip set is continuously removed and mixed with the solution in the mother tank along with fresh chemicals.
STEAMER# 1: Fabric containing the chemical from the dip set enters into the steamer for the completion of the reaction. Here the fabric stays for 15min and the temperature is maintained at102C.
CONSTRUCTION OF STEAMER: It consists of two parts. The upper portion has roller arrangement while the lower is consists of a roller bed. The fabric after passing through the roller, stay over the roller bed. Below the roller bed, sump is provided which contains water. Super heated steam is injected in it, thus water evaporates and saturated steam passes through the roller bed and finally over the fabric. In this way, the temperature of the steamer is maintained at 102C. At the end of the roller bed, mechanical sensors are provided which is star shaped. The function of the mechanical sensor is that, it touches the roller bed, thus stopping the feeding of fabric in the steamer.
INTERMEDIATE WASHING: Just after scouring steamer, two intermediate washing baths are provided to remove the scouring chemical. Here the washing is done with plane water at 98C.
DIP SET # 02: This is also a chemical tank where the chemicals for bleaching are provided. Its construction and feeding mechanism are same as of dip set 01.
STEAMER# 02: The function is same as mentioned in steamer 01, the only difference is dwell time i.e here the fabric remains for 30min and another difference is the type of the sensor i.e here we use photo cell instead of mechanical sensor.
WASHING TANK: After bleaching 5 washing tanks are provided. The capacity of the4 tanks is 22m fabrics each and the washing in them is done with water at 98C. The 5th tank treats the fabric with acid to get the neutral pH and then do the washing with plain water. Its capacity is 25m fabric. In between each washing tank, expander, squeezing roller, bowing roller and compensator is provided and their functions are same as mentioned above.
DRYING ARRANGEMENT: 22 drums containing steam are provided in3 rows for the drying mechanism. After passing through them, fabric comes in to J shaped tray. Just above the J shaped tray we have moisture meter over the roller, which is in contact with the fabric and measures the moisture, which is usually, maintained at6%. One compensator before drying drums and one before the J shaped tray is provided to control the speed of the fabric through the machine.
BATCH MAKING: The fabric after drying is stored over the batcher, which can then be sending for further processing.
IMPORTANT ASPECTS OF THIS MACHINE:
HEAT RECOVERY SYSTEM: The water in the pre wash is at 98C. It is not wasted but with the help of the heat recovery system, it is used to increase the temperature of feeding water unto 70C. This system is consist of a drum having filler to remove the impurities and the used water then comes in the large diameter long pipe having pipes of small diameter in it. It carries fresh feeding water & by the transfer of heat it gets the temperature of about 65-70C, where as the used water after loosing the heat is disposed off.
WATER RECOVERY SYSTEM: The dirty water is disposed off and the fresh water is feeded to each washing tank separately. But there is also a special arrangement by means of which the water is transferred, if it is in the condition to be used, from 7th washing to 6th and then to 5th and so on by piping system.
MOTOR ARRANGEMENT: There are 22 AC motors provided in the machine these are of two types: main motors and auxiliary motors. Main motors are with chain and auxiliary motors have belts.
RUBBER ROLLERS: Main motors drive all rubber rollers. A separate main motor drives each.
STEEL ROLLER (TOP): auxiliary motors drive these. Many steel rollers are driven by one single motor.
STEEL ROLLER (BOTTOM): These are driven frictionally by fabric.
BED ROLLS: All are driven by one single main motor.
GOLLER BLEACH SPECIFICATIONS:
PH =7-8
ABSORBANCY: (for printing) 30-40mm.
(For dyeing) above 60mm
WHITENESS: PC (both dyeing and printing) above 70
Cotton (for printing) 65-70
Cotton (for white) 75
Cotton (for dyeing) 65-70
PROCESS: Desize to bleach wt. Reduction is 12%
SHRINKAGE: Cotton 17-19%
PC stain 4-5%
PC 7-8%
ELONGATION: Cotton 3-5%
PC 1-1.5%
MERCERIZE SHRINKAGE: cotton 2%
MACHINE UTILITIES:
1: The machine requires 5 workers during operations.
2: The length of running fabric in it is 500m
3: The time of insertion of running fabric is 8 hrs.
4: For about 100000m of fabric
Water needed =275m3
Electricity=1078kwh
Steam=44tons
CHEMICALS:
For scouring: NaOH liquid 48 Be
Sandozin MRN (wetting agent)
For bleaching: hydrogen peroxide 50%
NaOH liquid 48 Be
Stablical A (stablizer)
Sandozin MRN
Sirrix 2UD (sequestering agent)
J-BOX
This machine is used for scouring and bleaching in rope forms. In J box the fabric is feeded in piled form and stored. The J box is well insulated to retain the heat and is lined with steel. It is used in Gul Ahmad for local dyeing.
ROPE FORM: It can be
1: scour bleach (in old J box)
2: solomatic (new J box)
SCOUR BLEACH (hot boiling) this is also known as boiling off or boil bleach. It includes scouring and bleaching of the fabric and is done in old J box. The flow of the material through this machine is attached in flow chart.
PARTS:
GREY PITS: The fabric from Osthoff singing machine is stored in grey pits for the completion of the reaction. There are total 12 chambers in which 8000-10000m of narrow width fabric and 5000m of wider width fabric can be stored.
PRE WASHING: This is done with hot water i.e at a temperature of 70C. It consists of 6 pairs of rollers and about 80-100m of fabric remains in it. After washing, fabric enters in to saturator by passing through padder rollers.
SATURATOR (scouring tank): This is the portion of the machine where scouring takes place and all the natural impurities are removed. NaOH is fed from the mother tank whose capacity is 1000m where as other chemicals are fed from a separate drum of 500lites. 3-4m of fabric remains in contact with the chemical for about 3-4 min.
STEAMER# 01: It is a 20 ft high J shaped box whose capacity is about 1200kg and the fabric remains under 100C for about 2-2.5 hours. The maintenance of J box is done if in any case staining occurs on the fabric. For this purpose two openings one at the top and other at the bottom are provided and this maintenance normally takes 8 hrs. From the steamer, the fabric enters into mid washer.
MID WASHER: This consists of two chambers one is for hot washing 70C and other is for cold washing 30C. This is done to remove the chemicals from the fabric. The problem of dissociation of hydrogen peroxide can arise at the temperature of 70C so cold washing is provided to keep the fabric at room temp. The capacity of this washing chamber is 102m.
SATURATOR (bleaching tank): Here the pre mixed chemicals from the mother tank by means of motor and a pump. The fabric is impregnated in the chemicals for about 3-4min. After it, the fabric passes through the padder roller to the steamer. The pick up of the fabric depends on the quality but it is normally 90%.
STEAMER #02: This is the second J box and the fabric remains in it for about 1.5-2 hrs so that the bleaching reaction completes. The capacity of this J box is about 800kg and the temp here is 100C.
FINAL WASHING: The final washing also consists of hot and cold wash. From here the fabric is stored in white pits. There are total 9 white pits these are called as white pits because the fabric comes here after bleaching.
SOLOMATIC PROCESS:
This is done in new J box. This process involves only bleaching of the fabric. The flow of the material in this process is given as:
Pre washing--------à saturator------------àsteamer----------à final wash--------à white pits.
PARTS:
PRE WASHING: It consists of six pairs of rollers and has the capacity of holding 120m of fabric at a time. First hot washing at 70-90C and then cold washing at 30-35C takes place. This is done to cool down the fabric because the heated fabric is sent to the saturator then due to the increase in temp, hydrogen peroxide dissociates so in normal practice we provide a cold wash to the fabric so that the reaction takes place at room temperature.
SATURATOR (bleaching tank): The fabric us treated with hydrogen peroxide and NaOH. 3-4m of fabric remains in contact with the chemical for3-4min.
STEAMER: Here the fabric remains for 1.5hrs under 100C and its capacity is 2600kg. The steam is provided from bottom, mid and top of the J box. There are 3 pressure gauges indicating the steam pressure and also a temperature indicator, which indicates the temp of steam in the J box.
FINAL WASHING: It also consists of hot and cold washing and is done top removed the remaining impurities or chemicals after bleaching. Their are4 hot chambers and 2 cold chambers. After this the fabric gets stored in white pits.
WATER MANGLE
Textile materials require drying after washing that is carried out in two stages. First water is removed mechanically and then by application of heat. Evaporation of water by heat is expensive and so maximum quantity of water is extracted by mechanical means, which are
(a). Centrifuging,
(b) Mangling and
(c) Suction methods.
Mangling is the most economical of all the three methods of extraction and its cost is about half of centrifuging and one third of suction method. Here in Gul Ahmad, there are 2 water mangles. They are distinguished by:
OLD WATER MANGLES NEW WATER MANGLES
This is for narrow width this is for wider width
In this machine only batch formation is possible Pilot as well as batch can be made
The speed is about 50-70m/min its speed is usually 1/3 of the speed Of J box
In this there is no arrangement for neutralization here a trough for the acid is
of the fabric. Provided for neutralization.
The flow of the material through water mangle is attached.
WORKING:
The fabric from the white pits enters here through the guide rolls in the form of a rope. At the beginning of the mangle there is beater rope opener arrangement that helps to open the rope by continuous rotations. Just after it, expanders are present which will open the fabric width wise and remove the crease upto some extent. This whole arrangement is repeated twice. After passing through the roller the fabric is dipped in acid then in water trough to maintain the pH. After passing through bowing, squeezing and finally guide rollers, the fabric moves towards the drying drums and finally wounded over the batcher or can be stored over pilot.
MERCERIZATION
(GOLLER MERCERIZATION MACHINE)
Mercerization is a very important operation in the cotton wet processing industry and by virtue of the resultant effects it may be considered both a pre treatment and a finishing process. Mercerization is the treatment of the fabric with strong caustic soda solution of about 20% strength. The changes appear on cotton after the treatment is as follows:
1. Shrinkage in area of fabric and length of yarn.
2. Increase in moisture absorption.
3. Great increase in dye up take.
4. Increase in chemical reactivity.
5. Increase in tensile strength of the material.
TYPES OF MERCERIZATION MACHINE: These are of two types:
1. Chain type
2. Chainless type.
Chainless machines are normally used in all mills. The differences between the two are as follows:
CHAIN MACHINES:
a. The chain machine gives a better tension control or better mercerization in both the warp and weft direction and imparts a comparatively better luster to the heavier weight fabrics.
b. The maintenance of the chains is high because these cannot be lubricated and so wears off rapidly.
CHAINLESS MACHINES:
g. These have a lower capital cost per unit production
h. These machines are more efficient in use of caustic soda and there is a less possibility of physical damage to the delicate fabrics.
i. Chainless machines have also higher productivity because two or more layers of fabric can be mercerized simultaneously by placing these side by side or by superimposing one on the other.
IMPORANT PARTS OF MACHINE:
1: CREELING: The fabric is fed in batch form that comes from continuous bleaching and scouring machine. The fabric passes through the tension rolls and the series of bowing rollers. There are total 9 bowing rollers for straightening of the weft because the mercerization the fabric has to swell.
2. MERCERIZATION CHAMBERS: There are three chambers for mercerization containing a strong lye of 30 Be(299 gm/liter). Here the fabric passes between two rollers in which top one is of rubber and bottom one is of grooved steel. NaOH softens the fabric where as grooved steel rollers straightens the fabric. There are 4 pairs of rollers in each chamber and each chamber contains 7m of fabric .The fabric passes through these chambers in 45 seconds at room temperature.
3.SQUEEZING ROLLERS: There are 4 squeezing rollers having 75% pick up and the pressure applied on these rollers is 4 bars.
4.STABLIZATION CHAMBER: There are 4 stabilization chambers containing weak lye of 7-8 Be and the dip time is 60 seconds. This is done for permanent straightening of the fabric. Here also 7m of fabric are present in each chamber and the temperature of the chamber is 85C. After this the fabric passes through squeezing rollers (5 bar pressure and pick up=80%) to the batcher and then to the washing pad steam water mangle.
There are 2 mercerization machines in Gul Ahmed .One (new model 1999) is for wider width (3.2m) and the other (old model 1965) is for narrow width (1.6m). The old machine also contains the washing chambers whereas the new one does not.
LYE PREPARATION:
Strong lye (NaOH) is feeded from a mother tank (1000liters) to a bottom dip tank of 2500 liters from where the lye is pumped to the mercerization chamber. The concentration of caustic soda is controlled automatically. For filtration of caustic, a round filter is provided. To prepare weal lye for stabilization chamber 4.5 liters/kg of water is provided before the second set of squeezing rollers so that the concentration decreases upto 7-8 Be and then pumped by means of 16 pumps to the stabilization chamber.
CAUSTIC RECOVERY UNIT (CRU)
During the process of mercerization we use a large amount of caustic whose initial concentration is 30 Be and is reduced to 7-8 Be in the stabilization chamber. For reduction of concentration we add a large amount of water i.e 4.5lit/kg. If this dilute solution is wasted directly to the sewage then a large amount of caustic will waste. To overcome this problem we use CRU.
It is a unit where caustic is recovered by a simple process of evaporation.
WORKING:
Caustic from mercerization chamber is pumped to the pre filter that is made of nylon and then enters into buffer tank for storage. After reaching a certain level caustic passes to the heat exchanger where it is heated by exchanging heat with hot water and then comes into evaporator. Steam is supplied in first evaporator for evaporation. In evaporator the caustic circulates in pipes where as steam is in surrounding. When caustic begins to evaporate it passes to the separator where the vapors being lighter goes up where as caustic enters into second evaporator. This evaporator is heated by means of paper present in separator. This process is repeated one more time so that the water separates completely. Then the required concentration of caustic is obtained i.e 30Bu (specific gravity 1.26) the caustic enters into the lye cooler above which a heat exchanger is provided in which cold water circulates and hence the caustic cools down.
A sensor called lye measurement sensor (LMS) controls the conc. of caustic. After reaching a certain level in lye cooler caustic is stored in concentrate tank. From here the caustic again passé to the mercerization tank.
OSTHOFF SINGEING MACHINE (1995)
SINGEING:
Singeing is the process applied to both yarn and fabric to produce an even surface by burning off projecting fibers, yarn ends and fuzz.
OBJECTS OF SINGEING: Following are the main objects of singeing:
Surface hairs help to trap the air in the fabric when it is immersed in water. This means that it takes longer time for water to enter the fabric since it must first displace the air. Singeing, therefore, helps to increase the fabric wet ability.
It creates a smooth surface for printing on. It may be possible to print fine details on hairy surface but once the hair move again after printing the details will become fuzzy.
To emphasize the woven structure of the fabric if that is considered essential.
It prevents frosty appearance after dyeing a hairy fabric who has been dyed may have somewhat a cloudy appearance.
To minimize or prevents the tendency of blend fibers composed of cellulose and synthetic fibers to form pills.
MACHINARIES USED IN SINGEING PROCESS
The machines that are used in singeing process are:
Plate Singeing Machine
Roller Singeing Machine
Gas Singeing Machine.
In case of plate singeing machine a plate is red hot and the fabric is passed at a specific distance and hence the pills reduces. But the draw back is this when fabric passes continuously the plates get cooled and uneven results occur and hence gas-singeing machines are commonly used in almost all the mills.
DRAW BACKS OF ROLLER AND PLATE SINGEING MACHINES
Local cooling
Groove formation as the fabric remains in contact with the plates
Proper maintenance is required
The process is very slow (speed is 60 m/min)
Only single face of the fabric is singed (not in case of roller singeing)
GAS SINGEING MACHINE:
It has the following advantages;
Fabric face and back singe at the same time
Efficient process
No local cooling
Even singeing
There are 2 types of gas singeing machines:
DIRECT HEATING SYSTEM: In this system the fabric is exposed directly against flame. It is mostly used in industries.
INDIRECT HEATING SYSTEM: In this system the fabric is introduced in a heating chamber against infrared radiation. This system is efficient in case of lightweight fabric.
DESIZING (STEEPING):
As looming process involve stretching so fabric strength should be improved by applying certain sizing adhesives. These adhesives may be gum, cellulose based compounds or synthetic sizing agents. Industries do not prefer synthetic thickeners because they are expensive and use natural thickeners, that is, starch. To remove the effect of sizing desizing is done. Main object of desizing is to attain absorbency of fabric.
TYPES OF DESIZING: The four types of desizing are:
Rot desizing
Acid desizing
Oxidative desizing
Enzymatic desizing
ROT DESIZING: In this fabric is soaked in water for 24 hours at room temperature. This is a time consuming process and requires large vats. The results may be uneven from where the fabric is not completely dipped in water. Mildew may be developed because of long time dipping in water.
ACID DESIZING: This is a quicker process and starch easily degrades by acid. The fabric is soaked in oxalic acid for 3-4 hours. The draw back of this process is cellulose degradation that is, hydro cellulose formation occurs and hence strength of fabric decreases.
OXIDATIVE DESIZING: Different oxidizing agents for e.g. Hydrogen peroxide, chlorides, bromides are used. Oxidative desizing is preferred when scouring, bleaching and desizing are done at a time.
ENZYMATIC DESIZING: Enzymes are the catalysts, which do not participate and takes the reaction to completion without any increase in temperature. Enzymes are proteinic nature compounds .At very high temperature the enzyme becomes dead and non-reactive but the strength of the fabric is not affected and this is the main advantage of this process and therefore, this is commonly used in industries. The sources of enzymes are malt, bacterial and pancreatic. In case of bacterial enzymes the pH range is 5.5 to 7 and temperature of 50 to 70C can be beard therefore these enzymes are preferred in industries.
IMPORATNT PARTS OF MACHINE:
There are 3 singeing machines in Gul Ahmed, which consists of the following parts:
GUIDE ROLLERS: These are used to guide the fabric in open width form to the machine.
BOWING ROLLERS: These are used to make the irregular yarn regular that is, for weft straightening.
DRYING CYLINDERS: These are used to remove the moisture from the fabric, thus drying it completely so that dust, attaching impurities and hanging threads are easily removed which is not possible in case of moist fabric.
BRUSHING ROLLERS: Two brushes move opposite to the fabric and perform the following functions:
To remove attached or stick fiber from the fabric.
Dust particles and other impurities are also removed.
It is done to avoid hard black residue form on surface of fabric.
Hairs are raised by brushing and thus easily burned.
5. BURNERS: This is the most important part of a singeing machine. It is a direct heating system that is; the fabric is exposed to flame directly at a high speed.
SPECIFICATIONS:
Flame colour: blue (oxidative flame is used)
Fabric speed: 120m/min (also depends on quality)
Burner's temperature: 400-500C
Pressure on compensators: 2-3 bars
Burner angle: 180 when fabric is moving at high speed. As the speed of fabric
Decreases (upto 50m/min) the angle becomes 90
Width of fabric: 120 inches
Gas consumption: 240-250 cm3 per day
Two rows of burners are provided so that the fabric can be singed from face and back. Water circulation is also provided in the rollers for their cooling.
COMPENSATORS: They are used to maintain the tension over the running fabric and they work with the help of pneumatic pressure. They maintain the tension over the fabric by charging and discharging. Charging is defines as:
DESIZING BATH: It is tank containing desizing liquor for the removal of size so that the fabric becomes absorbent for further processing. It consists of 8 pair of rollers so that the fabric remains in contact with the liquor for 5 min. Squeezing rollers are provided after this tank that removes the extra liquor from the fabric, which comes again into the tank through a tray.
SPECIFICATIONS:
Temperature of the tank: 70C
CHEMICALS:
For PC: NaOH (It acts a s a surfactant)
Imrolex (It destroys the size)
For Cotton: Oxalic acid
Sandozen MRN (It acts as a surfactant and wetting agent)
The capacity of this tank is 1000 liters, which is usually used to treat 3000m of fabric.
8. MACHINE UTILITIES: the machine utilities are current, water, gas and air.
GOLLER SCOURING AND BLEACHING MACHINE
SCOURING:
All natural impurities in textile fibers other than coloring matter are removed by means of scouring. The ultimate aim of scouring is to make the material uniformly and highly absorbent in a cost-effective manner so that there are no difficulties in the later processes of dyeing, printing and finishing.
Natural impurities include:
a. Mineral matters
Oils and waxes
Leaf particles
Coloring pigments
Dust
Pectates
a. MINERAL MATTERS:
These are salts of calcium and magnesium present in soil. These are water-soluble and can be removed easily. If these are not removed from the fabric, spotting occurs on fabric.
b. OILS AND WAXES: There are two types of oils: Edible oil and Non edible oil
- Edible oils can be removed by sponification that is, they are converted into water-soluble component with the help of alkali.
- Non-edible or lubricating oils are dispersed into fine droplets and remain in suspension and the process is called emulsification. These oils can also be removed by extraction with organic solvents.
c. COLOURING PIGMENTS: These are the nitrogen containing compounds (azo group) and these cannot be removed in scouring but in bleaching.
d. LEAF PARTICLES: These are removed in ginning but if not removed completely they are dissolved with the help of alkali.
e. DUST: Dust comes from atmosphere and can be removed easily. Dust must be in suspension form otherwise the removal will not be 100% .So dust removing agents are added which makes the sand (dust) in suspension.
f. PECTATES: These are long chain carbohydrates, insoluble in water and soluble in alkalis. Yellowing tint is present on the fabric due to the presence of pectates and also the problem of absorbency occurs.
BLEACHING:
Scouring removes almost all the impurities of cotton fibers except husk and natural coloring matters that are ultimately removed by oxidizing agents. The oxidation treatment or bleaching is necessary for producing white goods as finished products or for dyeing pastel shades. Even for dark shades, bleaching improves the brilliance and evenness of shade. Bleaching may be Oxidative or Reductive.
OXIDATIVE BLEACHING: In case of this type of bleaching the process is irreversible that is, whiteness for always. Oxidative bleaching is done with the help of following bleaching agents. CHLORINE CONTAINING: Sodium hypovchlorite, calcium hypochlorite and sodium chlorite. OXYGEN CONTAINING: Hydrogen peroxide, sodium peroxide and barium peroxide.
Chlorine containing agents gives more whiteness as compared to oxygen containing but problem in this is chlorine retention that is, chlorine can not be removed 100% and chlorates forms on the fabric and yellowness appears that is why oxygen containing bleaching agents are preferred.
REDUCTIVE BLEACHING: In case of reductive bleaching the process is reversible that is the fabric again gets yellow on exposure to air due to the oxygen present in the atmosphere. Reductive bleaching agents are sulfur dioxide, sodium thio-sulphite and Na2S2O8.
For effective bleaching pH, temperature, time, concentration and impurities are to be controlled. For bleaching the compound must be present in unstable form that is, ionizes easily. Market form is stable form so the bleach must be converted into unstable form for the process. It is to be checked what is the stable form of bleach. If it is stable in acidic medium then alkali is added for instability and vice versa.
SCOURING & BLEACHING: In our project CONTINUOS SCOURING &BLEACHING (one step) is carried out for following purposes;
· For A High Degree Of Whiteness
· Complete Degrading Of Seeds & Removal Of All Impurities
· Outstanding &Even Absorbency
· Low Fiber Damage
· Improved Hand Of The Fabric
· Reproducibility Of Finishing Result
· High Efficiency
· Short Amortization Time
PARTS OF A MACHINE:
PRE WASHING: It is done with pure water at a temperature of 98C to remove the chemicals, which are applied in the desizing bath. This washing both contains 22m of fabric hover and 8 pairs of rollers.
VACO SET: This arrangement is mounted over the machine and is used for sucking extra fluff from the surface of fabric with the help of vacuum. The vacuum is created by a separate motor and pump arrangement by maintaining a pressure of –150m bar. It consists of a rectangular ceramic piece having slots in its center throughout the length from where the suction is done. A wire is provided over the slot and fabric passes between the wire and ceramic piece. The function of the wire is to block the slot upto the portion other than the width of fabric.
SQUEEZING ROLLERS: Expander is provided before the squeezing rollers. Its function is to remove the creases from the fabric if present. After passing through it, the fabric squeezes by means of squeezing rollers. The pressure over squeezing rollers is up to 2-3 bars and the pick up is 65%, but these can be varied according to the type of the fabric. Then the fabric passes over the bowing roller, its function is to straighten the weft, it is a curved rubber roller, which gets the drive from the friction of the fabric.
COMPENSATOR: It serves the following three functions:
1: CREASE REMOVAL: Creases are removed by the weight of the compensating roller that is equal to 25kg. For heavy weight we can even increase the tension by applying the pressure from 1bar to 4bar. This is called as charging position, where as for lightweight fabric we can reduce the tension by applying the negative pressure, which range between 17-12 bars. This is known as discharge.
2.SYNCHRONIZATION: If the compensator is down, then the speed of the processes following increases automatically and vice versa.
3: AUTOMATIC STOP: It provides an automatic stop to the machine if the fabric torn out.
Total number of compensators used in this machine is 12.
DIP SET#01: This is a tank like arrangement in which we apply the chemical for scouring over the fabric, that’s why it is also known as scouring chemical bath.
CONSTRUCTION OF DIP SET: It has a special arrangement for the feeding of the chemical that consists of a narrow tray over which the feeding pipe is provided. When the tray over flow, the chemical falls over the fast moving fabric through out the width. This is done to prevent staining of the chemical over the fabric. After impregnation of the fabric in the chemical, it passes between the doctor rolls, they have blade like structures on two sides. This helps to squeeze the excess liquor.
FEEDING MECHANISM OF DIP SET: The solution of chemical according to the type of fabric is made in the main or mother tank. From there it is fed to the dip set according to the speed of the fabric. To keep the concentration constant, the chemical from the dip set is continuously removed and mixed with the solution in the mother tank along with fresh chemicals.
STEAMER# 1: Fabric containing the chemical from the dip set enters into the steamer for the completion of the reaction. Here the fabric stays for 15min and the temperature is maintained at102C.
CONSTRUCTION OF STEAMER: It consists of two parts. The upper portion has roller arrangement while the lower is consists of a roller bed. The fabric after passing through the roller, stay over the roller bed. Below the roller bed, sump is provided which contains water. Super heated steam is injected in it, thus water evaporates and saturated steam passes through the roller bed and finally over the fabric. In this way, the temperature of the steamer is maintained at 102C. At the end of the roller bed, mechanical sensors are provided which is star shaped. The function of the mechanical sensor is that, it touches the roller bed, thus stopping the feeding of fabric in the steamer.
INTERMEDIATE WASHING: Just after scouring steamer, two intermediate washing baths are provided to remove the scouring chemical. Here the washing is done with plane water at 98C.
DIP SET # 02: This is also a chemical tank where the chemicals for bleaching are provided. Its construction and feeding mechanism are same as of dip set 01.
STEAMER# 02: The function is same as mentioned in steamer 01, the only difference is dwell time i.e here the fabric remains for 30min and another difference is the type of the sensor i.e here we use photo cell instead of mechanical sensor.
WASHING TANK: After bleaching 5 washing tanks are provided. The capacity of the4 tanks is 22m fabrics each and the washing in them is done with water at 98C. The 5th tank treats the fabric with acid to get the neutral pH and then do the washing with plain water. Its capacity is 25m fabric. In between each washing tank, expander, squeezing roller, bowing roller and compensator is provided and their functions are same as mentioned above.
DRYING ARRANGEMENT: 22 drums containing steam are provided in3 rows for the drying mechanism. After passing through them, fabric comes in to J shaped tray. Just above the J shaped tray we have moisture meter over the roller, which is in contact with the fabric and measures the moisture, which is usually, maintained at6%. One compensator before drying drums and one before the J shaped tray is provided to control the speed of the fabric through the machine.
BATCH MAKING: The fabric after drying is stored over the batcher, which can then be sending for further processing.
IMPORTANT ASPECTS OF THIS MACHINE:
HEAT RECOVERY SYSTEM: The water in the pre wash is at 98C. It is not wasted but with the help of the heat recovery system, it is used to increase the temperature of feeding water unto 70C. This system is consist of a drum having filler to remove the impurities and the used water then comes in the large diameter long pipe having pipes of small diameter in it. It carries fresh feeding water & by the transfer of heat it gets the temperature of about 65-70C, where as the used water after loosing the heat is disposed off.
WATER RECOVERY SYSTEM: The dirty water is disposed off and the fresh water is feeded to each washing tank separately. But there is also a special arrangement by means of which the water is transferred, if it is in the condition to be used, from 7th washing to 6th and then to 5th and so on by piping system.
MOTOR ARRANGEMENT: There are 22 AC motors provided in the machine these are of two types: main motors and auxiliary motors. Main motors are with chain and auxiliary motors have belts.
RUBBER ROLLERS: Main motors drive all rubber rollers. A separate main motor drives each.
STEEL ROLLER (TOP): auxiliary motors drive these. Many steel rollers are driven by one single motor.
STEEL ROLLER (BOTTOM): These are driven frictionally by fabric.
BED ROLLS: All are driven by one single main motor.
GOLLER BLEACH SPECIFICATIONS:
PH =7-8
ABSORBANCY: (for printing) 30-40mm.
(For dyeing) above 60mm
WHITENESS: PC (both dyeing and printing) above 70
Cotton (for printing) 65-70
Cotton (for white) 75
Cotton (for dyeing) 65-70
PROCESS: Desize to bleach wt. Reduction is 12%
SHRINKAGE: Cotton 17-19%
PC stain 4-5%
PC 7-8%
ELONGATION: Cotton 3-5%
PC 1-1.5%
MERCERIZE SHRINKAGE: cotton 2%
MACHINE UTILITIES:
1: The machine requires 5 workers during operations.
2: The length of running fabric in it is 500m
3: The time of insertion of running fabric is 8 hrs.
4: For about 100000m of fabric
Water needed =275m3
Electricity=1078kwh
Steam=44tons
CHEMICALS:
For scouring: NaOH liquid 48 Be
Sandozin MRN (wetting agent)
For bleaching: hydrogen peroxide 50%
NaOH liquid 48 Be
Stablical A (stablizer)
Sandozin MRN
Sirrix 2UD (sequestering agent)
J-BOX
This machine is used for scouring and bleaching in rope forms. In J box the fabric is feeded in piled form and stored. The J box is well insulated to retain the heat and is lined with steel. It is used in Gul Ahmad for local dyeing.
ROPE FORM: It can be
1: scour bleach (in old J box)
2: solomatic (new J box)
SCOUR BLEACH (hot boiling) this is also known as boiling off or boil bleach. It includes scouring and bleaching of the fabric and is done in old J box. The flow of the material through this machine is attached in flow chart.
PARTS:
GREY PITS: The fabric from Osthoff singing machine is stored in grey pits for the completion of the reaction. There are total 12 chambers in which 8000-10000m of narrow width fabric and 5000m of wider width fabric can be stored.
PRE WASHING: This is done with hot water i.e at a temperature of 70C. It consists of 6 pairs of rollers and about 80-100m of fabric remains in it. After washing, fabric enters in to saturator by passing through padder rollers.
SATURATOR (scouring tank): This is the portion of the machine where scouring takes place and all the natural impurities are removed. NaOH is fed from the mother tank whose capacity is 1000m where as other chemicals are fed from a separate drum of 500lites. 3-4m of fabric remains in contact with the chemical for about 3-4 min.
STEAMER# 01: It is a 20 ft high J shaped box whose capacity is about 1200kg and the fabric remains under 100C for about 2-2.5 hours. The maintenance of J box is done if in any case staining occurs on the fabric. For this purpose two openings one at the top and other at the bottom are provided and this maintenance normally takes 8 hrs. From the steamer, the fabric enters into mid washer.
MID WASHER: This consists of two chambers one is for hot washing 70C and other is for cold washing 30C. This is done to remove the chemicals from the fabric. The problem of dissociation of hydrogen peroxide can arise at the temperature of 70C so cold washing is provided to keep the fabric at room temp. The capacity of this washing chamber is 102m.
SATURATOR (bleaching tank): Here the pre mixed chemicals from the mother tank by means of motor and a pump. The fabric is impregnated in the chemicals for about 3-4min. After it, the fabric passes through the padder roller to the steamer. The pick up of the fabric depends on the quality but it is normally 90%.
STEAMER #02: This is the second J box and the fabric remains in it for about 1.5-2 hrs so that the bleaching reaction completes. The capacity of this J box is about 800kg and the temp here is 100C.
FINAL WASHING: The final washing also consists of hot and cold wash. From here the fabric is stored in white pits. There are total 9 white pits these are called as white pits because the fabric comes here after bleaching.
SOLOMATIC PROCESS:
This is done in new J box. This process involves only bleaching of the fabric. The flow of the material in this process is given as:
Pre washing--------à saturator------------àsteamer----------à final wash--------à white pits.
PARTS:
PRE WASHING: It consists of six pairs of rollers and has the capacity of holding 120m of fabric at a time. First hot washing at 70-90C and then cold washing at 30-35C takes place. This is done to cool down the fabric because the heated fabric is sent to the saturator then due to the increase in temp, hydrogen peroxide dissociates so in normal practice we provide a cold wash to the fabric so that the reaction takes place at room temperature.
SATURATOR (bleaching tank): The fabric us treated with hydrogen peroxide and NaOH. 3-4m of fabric remains in contact with the chemical for3-4min.
STEAMER: Here the fabric remains for 1.5hrs under 100C and its capacity is 2600kg. The steam is provided from bottom, mid and top of the J box. There are 3 pressure gauges indicating the steam pressure and also a temperature indicator, which indicates the temp of steam in the J box.
FINAL WASHING: It also consists of hot and cold washing and is done top removed the remaining impurities or chemicals after bleaching. Their are4 hot chambers and 2 cold chambers. After this the fabric gets stored in white pits.
WATER MANGLE
Textile materials require drying after washing that is carried out in two stages. First water is removed mechanically and then by application of heat. Evaporation of water by heat is expensive and so maximum quantity of water is extracted by mechanical means, which are
(a). Centrifuging,
(b) Mangling and
(c) Suction methods.
Mangling is the most economical of all the three methods of extraction and its cost is about half of centrifuging and one third of suction method. Here in Gul Ahmad, there are 2 water mangles. They are distinguished by:
OLD WATER MANGLES NEW WATER MANGLES
This is for narrow width this is for wider width
In this machine only batch formation is possible Pilot as well as batch can be made
The speed is about 50-70m/min its speed is usually 1/3 of the speed Of J box
In this there is no arrangement for neutralization here a trough for the acid is
of the fabric. Provided for neutralization.
The flow of the material through water mangle is attached.
WORKING:
The fabric from the white pits enters here through the guide rolls in the form of a rope. At the beginning of the mangle there is beater rope opener arrangement that helps to open the rope by continuous rotations. Just after it, expanders are present which will open the fabric width wise and remove the crease upto some extent. This whole arrangement is repeated twice. After passing through the roller the fabric is dipped in acid then in water trough to maintain the pH. After passing through bowing, squeezing and finally guide rollers, the fabric moves towards the drying drums and finally wounded over the batcher or can be stored over pilot.
MERCERIZATION
(GOLLER MERCERIZATION MACHINE)
Mercerization is a very important operation in the cotton wet processing industry and by virtue of the resultant effects it may be considered both a pre treatment and a finishing process. Mercerization is the treatment of the fabric with strong caustic soda solution of about 20% strength. The changes appear on cotton after the treatment is as follows:
1. Shrinkage in area of fabric and length of yarn.
2. Increase in moisture absorption.
3. Great increase in dye up take.
4. Increase in chemical reactivity.
5. Increase in tensile strength of the material.
TYPES OF MERCERIZATION MACHINE: These are of two types:
1. Chain type
2. Chainless type.
Chainless machines are normally used in all mills. The differences between the two are as follows:
CHAIN MACHINES:
a. The chain machine gives a better tension control or better mercerization in both the warp and weft direction and imparts a comparatively better luster to the heavier weight fabrics.
b. The maintenance of the chains is high because these cannot be lubricated and so wears off rapidly.
CHAINLESS MACHINES:
g. These have a lower capital cost per unit production
h. These machines are more efficient in use of caustic soda and there is a less possibility of physical damage to the delicate fabrics.
i. Chainless machines have also higher productivity because two or more layers of fabric can be mercerized simultaneously by placing these side by side or by superimposing one on the other.
IMPORANT PARTS OF MACHINE:
1: CREELING: The fabric is fed in batch form that comes from continuous bleaching and scouring machine. The fabric passes through the tension rolls and the series of bowing rollers. There are total 9 bowing rollers for straightening of the weft because the mercerization the fabric has to swell.
2. MERCERIZATION CHAMBERS: There are three chambers for mercerization containing a strong lye of 30 Be(299 gm/liter). Here the fabric passes between two rollers in which top one is of rubber and bottom one is of grooved steel. NaOH softens the fabric where as grooved steel rollers straightens the fabric. There are 4 pairs of rollers in each chamber and each chamber contains 7m of fabric .The fabric passes through these chambers in 45 seconds at room temperature.
3.SQUEEZING ROLLERS: There are 4 squeezing rollers having 75% pick up and the pressure applied on these rollers is 4 bars.
4.STABLIZATION CHAMBER: There are 4 stabilization chambers containing weak lye of 7-8 Be and the dip time is 60 seconds. This is done for permanent straightening of the fabric. Here also 7m of fabric are present in each chamber and the temperature of the chamber is 85C. After this the fabric passes through squeezing rollers (5 bar pressure and pick up=80%) to the batcher and then to the washing pad steam water mangle.
There are 2 mercerization machines in Gul Ahmed .One (new model 1999) is for wider width (3.2m) and the other (old model 1965) is for narrow width (1.6m). The old machine also contains the washing chambers whereas the new one does not.
LYE PREPARATION:
Strong lye (NaOH) is feeded from a mother tank (1000liters) to a bottom dip tank of 2500 liters from where the lye is pumped to the mercerization chamber. The concentration of caustic soda is controlled automatically. For filtration of caustic, a round filter is provided. To prepare weal lye for stabilization chamber 4.5 liters/kg of water is provided before the second set of squeezing rollers so that the concentration decreases upto 7-8 Be and then pumped by means of 16 pumps to the stabilization chamber.
CAUSTIC RECOVERY UNIT (CRU)
During the process of mercerization we use a large amount of caustic whose initial concentration is 30 Be and is reduced to 7-8 Be in the stabilization chamber. For reduction of concentration we add a large amount of water i.e 4.5lit/kg. If this dilute solution is wasted directly to the sewage then a large amount of caustic will waste. To overcome this problem we use CRU.
It is a unit where caustic is recovered by a simple process of evaporation.
WORKING:
Caustic from mercerization chamber is pumped to the pre filter that is made of nylon and then enters into buffer tank for storage. After reaching a certain level caustic passes to the heat exchanger where it is heated by exchanging heat with hot water and then comes into evaporator. Steam is supplied in first evaporator for evaporation. In evaporator the caustic circulates in pipes where as steam is in surrounding. When caustic begins to evaporate it passes to the separator where the vapors being lighter goes up where as caustic enters into second evaporator. This evaporator is heated by means of paper present in separator. This process is repeated one more time so that the water separates completely. Then the required concentration of caustic is obtained i.e 30Bu (specific gravity 1.26) the caustic enters into the lye cooler above which a heat exchanger is provided in which cold water circulates and hence the caustic cools down.
A sensor called lye measurement sensor (LMS) controls the conc. of caustic. After reaching a certain level in lye cooler caustic is stored in concentrate tank. From here the caustic again passé to the mercerization tank.
DYEING
Dye: They are the organic compounds, which produce psychological sensation when the light of certain wavelength reaches the eye.
Dyeing: It is the process, which produces chemical or physical change in a substance so that the reflection of light appears colored.
Dye Stuff: The substance, which produces such change in a substance, is known as dyestuff.
Basic Functions of Dyeing: There are 3 basic functions of dyeing they are:
I. Dye.
II. Medium.
III. Substrate.
Dye consists of 2 important parts. They are Chromogen and Solublising Group.
Chromogen:
The organic compound-carrying group that is chromophore is known as Chromogen. This word is drive from a Greek words, “Chroma” means Color And “Gen” means Generating. This itself can be divided into two. Auxochrome and Chromophore.
Auxochrome:
It is the auxiliary of chroma. This auxiliary is one that help in brightening the color or to enhance the color, but itself is unable to produce the color. It is also drive from Greek words “Auxein” means to increase and Chroma means color. Every dye must have one auxochrome and one chromophore. They convert a color compound into a dye that must fix permanently in a fabric. Generally colorless chromogens become colored when an auxochrome is introduced into it. They may be acidic of basic, and on the basis of depth they may be Bathochomic (deepens the color) and Hypschromic (fade the color).
Chromophore:
It is color-bearing group of dye, it is also drive from Greek word Chroma and Phore, means color bearing. Different chromophores have different power of developing color. They can be arrange in descending order as: C = C, C º N, C = O, N = N, C = S.
The General Theory of Dyeing.
Dyeing is the process of coloring textile materials by immersing them in and aqueous solution of dye, called dye liquor. Normally the dye liquor consists of dye, water and an auxiliary. To improve the effectiveness of dying, heat s usually applied to the dye liquor.
The theory of aqueous dyeing is modified when an organic solvent is substituted for water.
The general theory explains the interaction between dye, fabric, water, and dye auxiliary. More specifically, it explains:
1. Forces of repulsion which are developed between the dye molecule and water; and
2. Forces of attraction, which are developed between the dye molecule and fibers.
These forces are responsible for the dye molecules leaving the aqueous dye liquor and entering and attaching themselves to the palymers of the fabric.
DYEING MACHINARIES: (EXPORT)
PAD THERMOSOL: (Monfort’s thermex)
It is a continuos dyeing machine and is used for vat, disperse reactive and pigment dyeing in which fixation of the dye is done by means of heat. All types of shades can be dyed on this machine but we usually dye dark shades. In Gul Alhmad this machine is used mainly for polyester dyeing.
DYEING TROUGH:
The fabric is unfolded from batcher and with the help of guiding rolls and tension rollers enter into the trough having 4 rollers. In trough the liqour temp is kept at low i.e 25-30C. In trough, dyes migration inhibitors alkali (to maintain ph) and wetting agents (for heavy fabric) are used. After trough fabric is passed through padders to remove excess of dyeing and chemical solution by applying 1.5 bar pressure. The pick up is about 65-70% (depends on the quality of fabric).
AIRING ZONE:
There are six pairs of steel rollers in this zone fabric pass through these rollers under atmospheric pressure and temp for the proper penetration of the dye.
INFRA RED CHAMBER:
In padding polyester and PC fabrics, the dye solution is not fully absorbed like in 100% cotton fabrics and rubs off on coming in contact with a hot metal guide roller. The PC fabrics pick about 50% of liquor but if moisture level could be brought down to 30%, the dye migration is avoided. Therefore for this purpose there are two infrared zones in this machine for removing 30-40% of moisture from the fabric. It works as a dye migration inhibitor so that’s why direct drying is avoided and prevent uneven dying. Infra red radiation has higher wavelength and lower energy and that’s why they evaporates water only, dye molecules being bigger in size than water molecules and hence are not disturbed by infrared radiation. The temp of infrared radiation is 400-500C.
The IR heaters are mounted in banks and are either heated electrically or by gas. The IR radiation selected is of 3 micrometers wavelength as textile fibers preferentially absorb this. To monitor moisture content and subsequently speed of padding, microwave sensors are fitted that absorb the wave energy according to the moisture content in the fabric and alter speed of motor of the padder. At the bottom of the heater battery, warm air is blown that travel upwards and helps in removal of the steam away from the fabric. In case of an accidental stoppage of the fabric during working of the IR radiators, the fabric is protected from the intense heat by automatic cut off system for gas or electric supply as well as by dropping a metal shutter in front of the heaters.
DRYING CHAMBERS:
There are 3 chambers. First one is drying chamber having a temperature of 120C and 35m of fabric remains in it for 1 min. The 2nd chamber is pre curing chamber here the temp=150C and the fabric passes through it in30seconds. This chamber is for removing the moisture from the fabric completely so that no problem occurs in curing i.e to prepare the fabric for fixation.
3rd chamber is curing chamber here the temp=190C and 35m of fabric passes in 1min. This is for fixation of the dye. Total 91m of cloth is in 3 chambers.
GOLLER PAD STEAM DYEING MACHINE:
Continuous roller steamer is used for diffusion of reactive, vat, sulphur and direct dyes into cellulosic fibers in an atmosphere of heat and moisture that is created by saturated steam injected into the steamer. The fabric is moved in open width around rollers in top and bottom horizontal banks in a heat insulated steel chamber like a hot flue dryer. This is an ideal machine for Reactive dyeing. Light, pale and medium shades can be dyed in this machine. Here wet on wet dyeing is done.
PURPOSES OF THE MACHINE: It is a multi purpose m/c and serves the following purposes:
1. It can be used as a pad batch for reactive dyeing in which batch is left for 12-18 hours for the completion of the reaction. For time saving the fabric passes through the steamer for 1 minute and the reaction is completed.
2. It can also be used for reduction clearance (RC) in which we treat PC fabric with caustic and sod. Hydrosulphide to remove the disperse dye from cotton.
3. Stripping of the fabric can also be done on this machine that is, colour can be removed completely by adding higher amount of caustic and sod.hydrosulphide.
4. It can be used for the development of Vat dyes.
5. The dyed fabric can be washed in this machine.
The flow of the fabric through different parts of machine is as follows:
CREELING=èPADDING TROUGH=èSTEAMER=èACID TROUGH=èAIRING ZONE=èWASHERS=èDRYERS=èBATCHER
PADDING TROUGH:
The fabric enters into padding trough by passing trough different tension and guide rollers. There are 4 rolls in this trough. The trough contains the dye and other auxiliaries according to the dye to be used. To remove the excess amount of dyeing liquor from the fabric padding rollers are provided on which 1.5 bar pressure is applied at the center and 2.1 bar at the sides. This pressure is pneumatic and is supplied by means of compressors. The pick up on the padding rolls is normally 75%.
STEAMER:
There are 3 chambers in the steamer in which 8 pairs of rollers are present in two chambers and 6 pairs in the third one. Sensors are provided when the fabric enters from one chamber to another to control the speed or if the fabrics get rolled on to the rollers. The temperature of the steamer is 106Cand 75m of fabric remains in it for 1 minute. Sensor is provided here indicating the steamer temp. To maintain the temp constant throughout the steamer, small pieces of stainless steel are placed in the roof so that they remain hot for long time and do not allow condensation of the steam. The entrance of the steamer is known as LIP in which two pipes are provided adjacent to each other from which steam is supplied. To avoid foaming problem steam is supplied to third chamber and from third to second and from second to first. Steam can be provided to steamer by two means. First, by means of Sump (tray). Dry heated steam comes to the sump and becomes saturated when entered to the steamer. The other way of providing steam is by means of Gatra.
WATER SEAL:
The temp here is 40-45C and it serves the following purposes:
1 to cool the fabric
2 Remove excess dye from surface.
3 It condenses the steam that comes along the fabric
ACID TROUGH:
Acetic acid and HCl are added in this trough. Acetic acid is used to control pH where as HCl is used to clean NaOH i.e remove the alkaline effect.
AIRING ZONE:
There are two portions in this zone and a ceramic sensor is present at the end of each portion that maintains the tension of the fabric. There are 23 pairs of rollers in this zone. The fabric is allowed to pass these rollers under fresh air for good color fixation.
WASHING TANKS:
There are 9 washing tanks. Washing #1,2, 8 and 9 contains fresh water where as the others is fed from these tanks. The capacity of each washing tank is about 950-1300liters.
NORMAL WASH:
This wash is for printed fabrics the temp is kept at 50-60C.
MERCERIZED WASH:
In this only hot washing is done. The temp in washing 1 is 50 C and from washing 2 –8 is 98C and last one has 70C.
DYED WASH:
This is used for dyed fabrics and in this we add soap (RSK), dispergator, Cibapon R for washing. For light shades only soap is added where as for dark shades soda ash is also added with soap which decreases the depth of color and improve rubbing fastness. The temp in 1st and 2nd tank is room temp and from 3rd –8th is 98C where as in the last one is 50C. The tem-p in washing tanks is controlled by a PT temp sensor.
DRYING CYLINDERS:
There are 11 pairs of drying cylinders that are arranged horizontally and steam is injected by means of syfon pipes. After these cylinders 2 cooling cylinders are provided for cooling the fabric at room temp.
BATCHER:
The fabric from drying cylinders passes through some tension rolls and also from anti static rods which absorbs the charge from the fabric. This rod has 5 KV voltages and 1800-18000A of current after passing through this fabric is winded on the batcher.
PAD BATCH KUSTER PADDER (BLIND DYEING)
It is a semi continuous method of dyeing & is used incase of reactive dyes only.
DYE PADDER:
The padding operation consists of two parts: first immersion of the fabric in dye liquor in a trough and second passing the fabric b/w two rollers to force dye liquor in and to squeeze excess liquor back to trough. Padder is the most sensitive component of the continuous dyeing system and any fault developed at the padding stage will not be corrected later. Padder may have 2 or 3 rolls: the latter having 2 dips and 2 nips. Normally the 2-roll padder is preferred for most types of fabrics and the 3 roll one is used only for heavy weight fabrics.
Both the rollers should have exactly the same hardness otherwise there will be a color difference in the face and backsides of the fabric. The material of the rubber should be chemically resistant to dye liquor and auxiliary products. Speed of this m/c is 50m/min and 6-7 m of fabric is present in this m/c at a time.
PADDING TROUGH:
The padding trough is generally considered to be just a container for the dye liquor and its importance in obtaining constant shade and dye economy is not fully realized by the dyers. The trough is placed below and in front of the padder and consists of a u or v shaped box with one or more free running guide rollers of about 10 cm dia. Dye liquor is fed in through a perforated pipe running across the entire length of tank with perforations pointing away from fabric.
Ideally a trough should contain a minimum quantity of dye liquor consistent with adequate pick up so as to reduce wastage of un-used dye at the end of the process and more importantly to have a high liquor replacement value. Small liquor volume and minimum distance b/w top of trough and nip of pad rolls are necessary to reduce the effect of preferential pick up of dye or water by fabric and thus minimize tailing effect.
The troughs are double walled so that hot or cold water could be circulated through the jacket to maintain dye liquor at constant and optimum temperature. To ensure constancy of fabric immersion time through out it’s running in trough the dye liquor is kept at same level by automatic controls.
COLOR MIXING:
The colors and chemicals i.e. alkalis are put in separate tank and are mixed by a diaphragm at a ratio of 4:1. The diaphragm feed these mixed chemicals to the trough by means of pipes.
WORKING:
The fabric is feeded in this machine in the form of batcher, which after passing through certain tension rollers and guide rollers enters into the dyeing trough. In this trough the dyes and chemicals are showered on the fabric. There is a tube attached with the trough indicating the level of mixture in the trough. Padders are provided after trough having the pressure of 2 bars and pick up of 75%, they squeeze the excess liquor. Finally the fabric passes through some rollers and winded on a batcher. The batcher should rotate continuously for about 12-18 hrs for fixation of the color. From this m/c fabric goes to washing m/c and then to the drying cylinders.
HOT FLUE: 1976
This m/c is used for local dyeing (exhaust process). This is a semi thermosol m/c but do not have curing chamber like thermosol. When vat dyeing is done in this machine then only padding and drying is done. After this the pad is taken to the jigger for development.
WORKING:
The fabric after mercerization is feeded by means of tension and guide rolls to the padding trough. In this trough there are 3 rollers and dye and leveling agents are added. Hydraulic pressure of 2.5 bar in center and 1.6 bars at side is applied on padder rollers.
COMPENSATOR:
The compensator in this m/c is mechanical based; it controls the speed of m/c. It is connected through a chain to a sensor (rod). When the speed increases the tension applied on compensator increases due to which it moves up and hence the chain also moves as a result of this movement the sensor rod moves downward since it is connected with the opposite side of chain. Electric sensors provide the limit if the rod touches it the m/c stops automatically.
DRYING CHAMBERS:
There are 2 drawing chambers where drying is done with the help of steam. In each chamber there are 7 pairs of rollers. The top rollers are driven by means of rope, which gets drive by a chain from main motor, and bottom rollers are frictionally driven by fabric i.e. they are free running. In first dryer the temp is 140 ‘C & in second dryer is 150’C. The length of fabric from padded and drying chamber is 75m. The exhaust of moist air and fluff is through a duct at the top. After drying the fabric is winded either on batcher or it is piled.
LOCAL DYEING MACHINARIES:
PAD STEAM CONTINUOUS DYEING MACHINE
This machine is used for dyeing narrow width fabric. It can also be used only for washing. The speed of this machine is about 40m/minand about 180m of fabric is present on the machine at a time. The flow of the material through different parts of machine is as follows:
CREEL=èDYEINGTROUGH=èSTEAMER=èACIDTROUGH=èAIRING=èWASHER=èDRYERS=èBATCHER
IMPORTANT PARTS OF MACHINE:
DYEING TROUGH:
The dye is prepared in a tank of 500 liters and pumped to another tank from where it is feeded to the dyeing trough. The dyeing trough has the capacity of 25 liters and about 80m of fabric (lawn) can be dyed by this. After this the fabric passes through 3 padders that has the pick up of 68-70% and 1-2 bar pressure is applied.
STEAMER:
It has 2 chambers and each chamber has 7 pair of rollers. The temperature in the steamer is about 102C and 36m of fabric passes through it in 1 minute.
ACID TROUGH:
This trough is used for oxidation of soluble vat dyes by means of sulphuric acid. This acid is feeded to the trough from a tank having a capacity of 200 liters. In case of reactive dye this trough contains water only. The capacity of acid trough is about 50 liters.
AIRING ZONE:
This zone has 7 pair of rollers. It is used when soluble vat dye is oxidized, therefore, for giving reaction time the fabric is exposed to fresh air for 2-2.5 minutes.
WASHING TANKS:
There are 7 washing tanks. In case of dyeing the first two tanks contains cold water only and have 5 pair of rollers, third tank contains soap (MRN) and the temperature here is 85C.5gm/litsoap is added. If the pH of fabric is less than 7 then soda ash is also added along with the soap. Fourth to sixth washing tanks are for hot wash and the temperature here is 85Cand these tanks contain 4 pair of rollers. Last tank is for cold wash. In case of only washing off the fabric the first and the last tanks are for cold wash whereas others are for hot wash. Water can be transferred from one tank to other by means of a pipe. Since the third tank contains soap so it is drained out after washing. Compensators are provided after every washing tank that is mechanical based that is, they maintain the tension with the help of the weight attached with them. Bowing rollers are also provided along with compensator.
DRYING CYLINDERS:
Two expanders are present before these cylinders for crease removal. There are 20 drying cylinders, arranged vertically, which are heated by means of steam. A moisture meter is used to indicate the amount of moisture in the fabric. If the amount is higher then the steam will automatically injected into these cylinders. The fabric after passing through these cylinders and also through different tension rollers is finally winded on the batcher.
DRAWBACKS OF THIS MACHINE:
Jigger machine is the best replacement of this machine because it has the following drawbacks:
The cost of the chemicals and dyes are higher in this machine.
Only light shades of soluble vat dyes can be dyed.
In using vat dyes in pad steam, the depth of penetration is less.
In pad steam sulphur dyes can be used for dyeing but it will cause colour contamination over the rollers that will be difficult to wash off, therefore are not suitable for sulphur dyeing. This problem is not present in Jiggers.
The quality produced by jigger is better than that of pad steam.
JIGGER
For batch processing of cotton cloth in open width, jigger or jig is the oldest and still frequently used dyeing machine. In the past, jiggers were mainly used for dyeing medium and heavy weight fabrics b/c of excessive longitudinal tension imposed on the fabric. However, modern versions cause very little tension and so light weight fabrics may also dye now. A jigger consists of a V shaped trough or vat containing dye solution through which fabric, batched as a roll, moves and is wound on another roller. After the second roll is full, movement of cloth is reversed. Each batching on a roller is called a pass or an end.
MAIN PURPOSES:
Jigger is a multi-purpose m/c and it serves as follows;
1- Vat developing
2- Reactive dyeing
3- Bleaching
To ensure even dyeing there are 2 rounds of fabric in cold water.
CHEMICALS:
Incase of reactive dyes fixation, salt and NaHCO3 are used. For development of vat dyes (local), sodium hydro sulphide Na2S2O4 is added in small portions for even fixation and caustic (liquid) 38’be is used. Caustic either increases depth of color or decreases. As we don’t want to decrease color so we add dye in cold water and the fabric is allowed to complete 2 rounds. Then the chemicals are added in hot water (65’C). If water is not heated then the chemical will burst the dye molecule and not even color results. In order to avoid oxidation by air we keep fabric in center by a lever. Incase of bleaching in jigger, a squeezer roll is provided which is adjusted by a handle. So that the roller presses fabric and squeezes the bleaching chemicals. In development of vat dyes & bleaching we provide direct steam through holes provided in beneath of trough. But for reactive dyeing we provide indirect steam i.e. the steel pipes provided in trough are heated by circulating steam in coils of pipes.
As only a few meters of fabric are immersed in dye bath at a time, a very low liquor ratio of 4 to 5 can be achieved. Normal size jiggers store about 700 to 1000m of fabric and fabric generally moves at a rate of 60 to 100 m/min depending upon its unit weight. After 4 rounds of chemical the fabric takes 1 round of hot wash with soap MRN and in case of development of vat soda ash is also added to remove H2O2, Acetic acid etc and than 1 round of cold water. For unloading of fabric from jigger a steel rod is provided and fabric is unwound from batcher and winded on this roll.
From here the fabric is to water mangle where initially 2 washing tanks are provided and finally dried and piled.
WINCH
The winch m/c is one of the oldest dyeing m/c (for reactive and direct dyeing) & is still popular b/c of low capital cost, simplicity in operation and versatility in use for different types of fabrics & operations. Principle of winch is to circulate a no. of fabric loops that are lying in a dye bath but are continuously pulled out & returned to it with the help of a circular or elliptical winch.
Compared to the jigger, the winch dyeing causes less lengthwise tension in fabric. As the winches are suffering from deficiencies of long liquor ratio, non-uniform temp of dye bath, formation of creases in fabric and excessive mans power requirements. So jets are replacing winches.
In Gull Ahmed, the winches are used only for washing purpose. For washing of printed fabrics like lawn having dark shades. Linen which is 100% viscose is preferred washed in rope form otherwise due o a little elongation it deteriorates.
WASHING METHOD:
Usually 1000 liters of water is taken in the stainless steel vat having a depth of 2.5m, height of 1m and length varying b/w 2 to 4 m. The backside of vat is not vertical but it is sloping at an angle of 45’ so as to facilitate the sliding of ropes and also to reduce volume of processing liquor. To avoid entanglement, a peg rail fitted below a jockey roller in front of m/c, separates the fabric ropes. The fabric rotates at a speed of 60 to 70 m/min. A salting box is provided in front of m/c by interposing a perforated steel sheet at a distance of 30cm from the front of dye bath. Water & steam pipes and a drain valve are also provided in this compartment. Fabric pieces are loaded manually but are unloaded with the help of a mobile set of squeeze rollers after tying together different ropes of fabric into a continuous length. The liquor goods ratio of winches varies from 12 to 20.
In 1000lit of water, soap and soda ash are added at a temp of 100’C. Firstly, fabric is given a cold wash for 15mins then with chemicals fabric is washed for 45mins. Washing of reactive dyes are done only in winch.
JET DYEING MACHINE
This m/c is mainly used for dyeing (Disperse) Polyester fabric since polyester dyeing requires very high temp about 130’C in the acidic medium of ph 3-5 otherwise the dye will not fix in fabric. Dyeing at this temperature yields rapid, better penetrated and more level dyeing that really makes an economic sense. In Gull Ahmed there are 4 jet-dyeing machines, 2 are small having capacity about 1000lit & 2 are big with capacity 1500lit. In big jet dyeing m/c two narrow width fabrics may load together. The liquor ratio of 1:10 is maintained in this m/c.
WORKING:
This m/c is based on the principle of using a jet of dye liquor to transport fabric in m/c. In this system, the fabric is rotate at a very high speed through a circular tube with the help of circulating dye liquor. The liquor is collected from bottom of m/c, passed through a heat exchanger and then a high volume centrifugal pump and injected at the top of m/c along with fabric through the tube.
For 15mins the fabric is circulated in cold water then the acid and leveling agents are added in water through the mother tank, this feeding of chemicals takes only 5 to 10 seconds then a filter closes the mouth of tank. The fabric is run for 10 to 15mins in these chemicals. The dye is added in the liquor of m/c and fabric is allowed to run for 10 to 15mins at room temperature. Then gradually the temperature is raise until it reaches 130’C, this temp is indicated on a temperature indicator fixed at the top of m/c. The fabric is allowed to circulate in the dyeing liquor according to the shades of fabric i.e. for light shades 1/2 hr, for medium shades 45mins, for dark shades 1 to 1 1/2hrs. When the temperature reaches to 100’C the shades are checked. There is speed, temperature
SAMPLING.
LOCAL SAMPLING:
Black and white paper print design from design department comes into sampling department incases of local printing. Then usually no color ways are made here for each print. These color ways are made by table printing with flat screen and then are sent to the marketing department. Designers of marketing dept select 5 or 6 color ways normally out of 20 and then selected ones are sent again to the sampling department. Now the workers here convert the recipe of dyes for the bulk and sample usually of one repeat is made over the rotor printing m/c. They are again sent to the marketing for final selection and then bulk production starts.
FLOW CHART: -
DESIGN-àCOLOR SELECTION-àMARKETING DEPT-àPRINTING M/C-àMARKETING-àBULK PRODUCTION.
EXPORT SAMPLING:
For export purpose the design are provided by the customer as well as the by design dept his design could be over the paper or fabric. Customer and marketing will first of all discuss the design and then sampling starts.
It includes C.P.S, which stands for color physics system. It identifies the colors of design by the spectrophotometer and gives the recipe. The color mixing is done and colors are dispensing out. Gammets are made over the F.A.M m/c for checking of color shades. If the shades are matched then sample of 5-10m is made by K.D.M firstly usually small screens are used. After printing in K.D.M fabric is dyed, cures and washed to get the final sample. This is sent to the marketing dept where meeting b/w dept and customer is arranged and if design is selected then it is again sent to sampling dept. This time same design is made but with bigger screen and in this case screen and design proofing is done over K.D.M. This design is matched with first sample and if selected then design is sent for bulk production.
FLOW CHART: -
CUSTOMER-àMARKETING-àDESIGNING-àPAPER PRINT-àSCREEN MAKING-àSAMPLING-à-àCPL-àCOLOR MIXING-àFAM-àKDM-àDRYING-àCURING-àWASHING-àFINISHING-àMARKETING-àSTRIKE OFF-àKDM-àPROOFING-àBULK PRODUCTION.
FAM: - It is used for producing gammets following coverage percentage.
1) 100%
2) 59%
3) 25%
4) 10%
These gammets help designer for selection of color.
1-WORKING MECHANISM: - The magnetic force of attraction is created electrically below the FAM table, which moves the rod along the length of table, by which table, by which gametes are formed.
2-KNURLING ON THE ROD: - The rod used for printing and producing gametes is usually knurled so that color penetration is even on whole design.
K.D.M: - It is used for producing samples for local and export customers. Usually 5-20m of sample is produced. It is also used for screen proofing purpose, which means the checking of screen before running in production. If the design running on m/c have some problem in screen or old design are needed again then this m/c is used for screen proofing that they are producing same effect or not.
MACHINE DESCRIPTION:
GLUING SYSTEM: -The fabric is stick on the blanket by means of glue or adhesive material so that it does not shrink during printing. Dipping the fabric in the glue-carrying trough provided in front of KDM.
TYPES OF SCREEN: -The screens are used for rotary printing is made of nickel screen of 3200mm in length. The screen length can be adjusted according to the width of fabric, which ranges from 1280, 1620, 1850, 2400 and 2800mm in length. The screen circumstances are 641, 840 and 914mm. There is only two screens drive in KDM.
ROD: -The rods used for printing are of following diameters.8, 10(this rod is used for producing effects), 12, 15, 20mm
DRIVING MECHANIM OF BLANKET AND SCREEN: -Screen head is drive by means of gearbox and roller drive is used for blanket.
BLANKET WASHING: -
BLANKETàSHOWERINGàSCRAPERàSHOWERINGàSCRAPING.
Blanket washing time is about 10-30min.
FLUX SELECTION: -Flux is selected by seeing two things 1) rod size 2) design type
PRINTING SEQUENCE:
- Dark shades first then light shades.
- White paste should be first applied incase of reactive, for pigment it is lastly applied.
- Golden, silver paints should be applied in last so that they cannot stick to screen of other colors if applied first.
- More coverage and dark shades the dia will be increasing otherwise the magnet flux will increase.
PRINTING FAULTS: -
- Rod selection
- Pressure and flux variations
- Viscosity variations
- Checking of screen
- Setting of screen
- Due to dust particles
Color kitchen supplies color to KDM.
DESIGN ENGRAVING.
DESIGNING: The design department of Gull Ahmed is totally a separate dept having skilled designers who are working manually and as well as on computers. The customers either provides the designs or customers select the design prepared by Gull Ahmed’s designers.
The design, which is selected, is first of all scanned directly if it is on paper & is solid where as if it is complicated, delicate and on fabric than it is traced by hand on plastic sheets and than they are scanned. After scanning color separation is done on computers and then coloration is done i.e. same design with different colors are made & finally texture mapping takes place i.e. designing is done according to end use. At this stage design is discussed with customer then it is saved in CD and sent to engraving dept.
ENGRAVING: This is the process of copying design over the different screens according to the number of design colors. Screens are made of Nickel having mesh size 60, 80, 125 normally. They are imported from Holland & can be reuse 3 or 4 times but this also depends on handling. Their length can vary 2800, 1280 mm. The diameter of screen can be 640 & 914 mm. Engraving can be of following type:
1- Ultraviolet
2- Wax
3- Laser
Wax and laser are used here.
LASER ENGRAVING: -
Firstly the screen is coated with a emulsion SCR100. This makes a thin layer over screen & blocks all mesh then screen is dried. This whole procedure takes about 1/2hr. Then this screen is sent to polymerization chamber so that emulsion becomes hard. Here heating is done at 150’C for 2hrs. The polymerization chamber can store 8 – 10 screens at a time. Then screen is fitted over laser m/c. the design is feed to computer, dia & length of screen & repetition of design is also feed to computer. The laser rays are provided by combining Helium, Nitrogen & Carbon & then are bombarded by moving head over the rotated screen according to compute program. This usually takes 1hr for 2800mm long screen and 15mins for 1280mm but this time also depends on type of design. In laser actually the burning of emulsion occurs so it does not give very sharp results so for delicate design wax engraving is used.
WAX ENGRAVING: -
Here wax is used for copying design. It is different from laser in a way that after screens are coated and dried, they are not polymerized but they are sent to wax engraving m/c. As white or sun light can harden the coated layer of emulsion so yellow light is provided in the room having this m/c. Wax and ink are fixed in a fixed ratio by computer, in which the design is feeded and the head moves according to the program. The head of wax engraving m/c has two portions one has 64 nozzles, which spray the mixture over the rotating screens acc to design and the other chamber have Halogen light produced at 5000volts. When spraying is completed the screen is exposed to this light so that emulsion on screen other than wax portion becomes hard and then it is washed with simple water to remove paste from its surface and for final hardening screen is sent to polymerization chamber at temp 150’C for 2hrs. After this end rings are glued at the screen ends so that they can be fixed in gears of printing m/c.
If comparison is done b/w two m/c at this stage than we can conclude that wax engraving is used to show each and every fine detail of design whereas laser is used commonly for solid designs. The combination of both machines may also use in printing machine.
The General Theory of Printing.
The printing of textile materials is the application of color according to a predetermined Design.
The printing paste that is applied to textile material consists of dye, water, thickener and hydrocarbon solvent or oil, after the printing paste is applied, the textile material is usually steamed. This is to enable the dye molecules to migrate from the surface to the fibres and to enter the fibre polymer system. Steaming swells the fibres and ensures better penetration of the dye and improved color fastness properties of the textile material.
The general theory of printing explains the interaction between the dye, fibre, water, thickener and hydrocarbon solver. More specifically, it explains how within the printing paste:
1. forces of repulsion are developed between the dye molecules and the constituents of the printing paste; and
2. Forces of attraction are developed between the dye molecules and the fibres of the textile material to be printed.
The Role of the Thickener.
The purpose of the thickener is to produce a medium for the dye paste and the resultant product is called the printing paste. The printing paste is an emulsion of the thickener and hydrocarbon, such as white sprit or Very light hydrocarbon oil, plus a surface-active agent. This surface-active agent enables the emulsification of the thickener with the hydrocarbon to form a printing paste of uniform consistency. The uniform consistency of the printing paste is referred to as its viscosity (the ease with which the paste will flow). The viscosity of the printing paste is very important as it influences the clarity and appearance of the printed pattern.
PRINTING DEPT OF GULL AHMED
a- For export quality here pigments are used.
b- For local quality here reactive dyes are used.
Two methods of printing used here are
a- Screen printing
b- Roller or rotary printing.
SCREEN PRINTING:
This section is utilized for the printing of local goods and some exports. It is usually used for printing the dupatta and shirting material and panel design like Mickey Mouse etc. The printing table used is 200mm in length and 102inch in width. The table is heated by steam at temp of 70-90’C. The glue is first applied on table so that fabric sticks on table. After which the printing is done in following sequence:
For cotton goods: -
- First the dark shade screen is used having less coverage so that the fabric is not shrink and then move towards the lighter shades.
- The white should be first applied on the fabric so it gets the time to dry. The fabric is then aged, washed and finished.
ROTARY PRINTING:
- Rotary screen-printing has been developed a fully continuous screen proofing techniques to rival and in fact take over from the engraved roller printing.
- Rotary screen-printing uses seamless cylindrical screen, which are composed of nickel mesh with end rings, soldered on the cylinder to prevent collapsed. Each rotary screen is positioned across the fabric and it is independently drive at one end.
- As the screen rotates, it is feed internally with print paste, which is forced through the open mesh area by the stationary squeegee may be either a convention rubber polymeric blade i.e. doctor blade or metallic rod held against the rod by stationary electromagnetic beneath the printing table.
- In modern conveyor fabric is dry by passing through a hot air dryer.
The rotary m/c installed in Gull Ahmed are
a- RD 2
b- RD 4
c- RD 5 (RD4 2800)
d- RD W
The basic working principle of all m/c is same. Their differences and description is therefore given in the form of chart.
DESCRIPTION OF M/C:
The material is feeded to all of them in form of batch. RD 5 and RD W have scary Arrangement this will save the time of batch changing (without stopping m/c). After feeding in different arrangements are provided for removal of lint from fabric.
LINT REMOVAL METHOD: -
LINT:
The loose cotton thread and fluff are on the fabric surface. These are all unwanted material and may damage the design of printing. To remove them following methods are used in printing m/c.
EVAC METHOD:
The material is removed by suction. A turbo rotary blower produces a high vacuum. The fabric is passed through a slot. The clearance of slot should not be more than 3mm.
LOBACIN METHOD:
Lobacin is the name of a milking chemical having high sticking properties. This chemical is applied on a roll, which is passed with a little touching contact. The unwanted material sticks to roll and blade scraps it. This method is only used on printing m/c cleaning the printing face only. This system is found in RD 4 and RD 5 machines.
CYCLONE METHOD:
This consists of a brushing roll and sucking system. The brushes remove the lint from surface of fabric and then sucking system sucks it. A separate motor is provided for its control. It runs at same speed as of blanket of RD.
HEATING TRAYS: -
After this cleaning arrangement heating tray is provided. It works in case of polyester fabric, as it cannot stick over blanket when it gets wet with glue it is heated and special rubber coating is made over whole blanket over which heated polyester fabric gets stick.
GLUE TROUGH: -
For cotton fabric a glue tray is provided below the blanket. The blanket is dipped into it and extra glue is removed from it through scrapper and fabric from heating tray presses over it by pressing roll so that it gets stick there and do not move over blanket.
SQUEEGEE: -
Color in screen is provided by it. Normally three types of squeegee are used for printing.
1- Metallic rod having knurled
2- Doctor blade
3- Airflow squeegee.
COLOR FEED PUMP: -
Electrically driven reversible colors feed pumps are located under catwalk that is extended on both sides of printing head. Print paste level in screen is maintained as required.
WASHING EQUIPMENT: -
Washing system is provided at the end of the blanket frame below blanket. First it is washed by reuse water and foam fixed there. Then it passes over brushes with water and then from foams again but with fresh water. After this scrappers are provided to make them dry before entering into glue trough.
DRYERS: -
The printed fabrics leaves rubber blanket after last printing section and is transported on the carrier blanket in specially designed high efficiency three pass drier that ensures drying of printing material at high speed. The speed of conveyor is synchronized with speed of fabric being printed. The drying is done hot air produced by gas heating or by convection mechanism through oil.
AIR CIRCULATION: -
The fans are driven by V-belt and are mounted over both sides of dryers. The fan bearings are equipped with air-cooling system. Uniform drying over entire width of fabric is ensured by arrangement of nozzles sets on upper and lower side of cloth.
COLOUR KITCHEN
This is the most important department as far as printing is concerned because this is the place where shades are made. CPS separates the shades in the design, which is sent by the customer or by the design department.
COLOUR PHYSICS SYSTEM (CPS):
Here a spectrophotometer is provided which senses the colour shade by the wavelength measurement. If the reflectance % is more it means shade is light and vice versa. CPS then provides the shade recipe. After determining the recipe costing is done to check which is suitable for processing and fulfilling the fastness (both light and washing) according to the demand of the customer.
METHODS OF COLOUR SELECTION:
There are two methods of colour selection:
Fixed Triangle
Free Triangle
FIXED TRIANGLE:
The colours in this case are selected from the database according to the shade. This colour could be a single or combination of two or three. But in case of fixed triangle any colour of the recipe cannot be replaced.
FREE TRIANGLE:
In this case any of the colour of the combination is causing metameric effect or resulting poor washing or light fastness can be replaced with alternative. The recipe, which is selected from the CPS, is directly transferred to the IPS, where colour checking and screen groups are made. After this it is send to the dispensing unit.
ITEGRATED PASTE PREPARATION SYSTEM (IPS):
The recipe that is feeded here from CPS is converted from 1kg to bulk that is, 60 or 80kg as required. All calculations are done automatically and then are sending to the dispensing unit. In IPS 4 status are made. First one is for feeding of recipe that is, colour ways, screen group etc. Second is for calculation, third is correction and last one is send to the dispensing unit for getting the colour.
DISPENSING UNIT:
It is an automatic unit in which pigments are feeded and calculated weight dispenses out automatically. It consists of feeded drum connected to the dispense nozzle by pumps and filters. The material stored in drums is filtered after every 5 minutes and circulated automatically to avoid any blockage. It is capable of storing 24 dyes in it. Speed of dosing is controlled by electrical mechanism, depending on the material to be feeded. Pneumatic pistons control the dosing.
PRINTING PASTE MAKING:
The colours in the calculated amount according to the recipe are dispensed in container and then pigment paste is added to it. Pigment paste consists of water, urea=2% (as it is of hygroscopic nature and is added to avoid mesh clogging), ammonia =0.5% and antifoaming agents (2kg in about 1500kg).
The pigment pastes used here are of two types.
P1 = only chemicals with very little amount of thickener
P2 = chemicals and 35% thickener
These are of two different types because the bacteria can change the viscosity, which is usually maintained between 50-60 decipoise so we use P1 along with P2 to get the required thickness, and P1 is used first since its viscosity may vary. Fixing agent is also added manually in liquid form. Here fixation is done with the help of sodium bicarbonate since it is a weak alkali.
After mixing of all chemicals the paste is mixed with stirrer and then filtered to remove any impurity that may damage the screen.
FINISHING:
Textile finishing is the term used for a series of processes to which all bleached, dyed, printed and certain grey fabrics are subjected before they are put on the market.
This is the most important department of a textile industry as it involves the activity of the fabric in many major steps. The aim of textile finishing is to render textile goods fit for their purpose or endues. Finishing processes are carried out to improve the natural properties or attractiveness of the fabric and to increase its service ability.
The techniques of finishing depends on the following:
Nature of the fabric tat is, chemical composition state, weave etc. this determines the appearance i.e. transparency, luster, fullness, weight, whiteness etc
The physical properties of the fabric i.e. feel, softness, stiffness, tensile strength, elongation, shrinkage property
The endues of the material i.e. non shrinkage, non creasing (good crease recovery), crease retention draping, stiffening, resistance to abrasion, non soiling nature etc
Receptivity of the fabric to various finishing operation i.e. eater proofing, g flame proofing, rot proofing etc
Susceptibility to chemical modification.
The finishing operation differs according to the properties to be imparted to the material
Improving the appearance luster, whiteness etc
Improving the feel, which depends on the handle of the material and its softness, suppleness, fullness etc
Weaving qualities, non soiling, anti crease, anti shrink, comfort etc
Special properties required for particular uses water proofing, flame proofing etc
Covering of fault in the original cloth
Increasing the weight of the cloth.
In finishing, the department controls the design deviation (slewing and bowing), vigils the quality control, checks the softness, stiffness or shining and colour fastness is visually analyzed to match the original flapper. When the first time the fabric arrives in the finishing department after bleaching, it is equalized (stretched in accordance to the required width) to be sent for dyeing or printing.
The fabric is equalized for:
Dyeing
Printing
Mercerizing
The finishing department also does the heat setting of the fabric before it goes to the dyeing department.
The second time the fabric returns to the finishing department after dyeing and printing. There are two processes left for finishing department:
Chemical finish
Mechanical finish
The chemical finish is done on stenters whereas the mechanical finish is done on calendars.
CALENDARING
Calendaring is an operation carried out on a fabric to improve its aesthetics. Purpose of calendaring is:
To upgrade the fabric hand and to impart a smooth silky touch to the fabric.
To improve the opacity of the fabric
To compress the fabric and reduce its thickness.
To impart different degree of luster to the fabric.
To reduce yarn slippage.
The mechanical finish is done for softness and shining of the fabric or stiffness according to the nature of the chemical, this process is done after the chemical finishing as per buyer requirement.
In calendaring the threads of the fabric are close to give it a gloss or the seal required. An ordinary calendar consists of series of hard (steel) and soft (cotton) bowls placed in a definite order. The sequence of the roller is that no two hard rollers are in contact with each other. The pressure and the heat applied in calendaring depend upon the type of finish required. The calendaring effect produced depends on the moisture content of the fabric, the number of bowls of the calendar used, the composition of the bowls (steel cotton, cotton steel, steel paper, cotton plastic), bowl arrangement, temperature, pressure and speed.
CONSTRUCTION OF HARD BOWL:
The hard bowl consists of mild steel and a cast iron shell of linear diameter. The shell is heated when it expands and in this state it slip to the core and chilled when it contracts and grip the core tightly. The iron bowl are made with a highly polished hard surface and heated inside by steam.
COTTON BOWL:
The compressible material bowls are made either of cotton or wool paper, linen paper or flax paper.
In Gul Ahmed following types of calendars are used:
7 bowls calendar
5 bowls calendar
3 bowls nipco calendar
7 bowls calendar
TECHNICAL SPECIFICATIONS:
SPECIFICATION 7BOWLS 5BOWLS NIPCO 7BOWLS
KOYOTA
Daily production 24000m/shift 16000 m/shift 35000m/shift 24000m/s
Pressure at steel roll upto 350N/mm
Pressure at cotton roll upto 350N/mm
Pressure at systhetic bowl upto 150 bar
Length of cylinder 138 inches
Speed 65m/mi 40-50m/min upto 150m/min 50-60m/mi
Pressure system mechanical mechanical hydraulic mechanical
Heating system steam steam hot oil steam
Pressure 55kp/cm2 25kp/cm2 50 kp/cm2
Temperature 70-80C 50-70C 70-180C 70-80C
Bowl arrangement vertical vertical L shaped vertical
For soft finish the fabric is passed through cotton bowl. For satin fabric the pressure at cotton bowl is less than the pressure at steel bowl.
NIPCO CALENDAR:
Nipco calendar or L calendar has deflection compensation roll and precision width control. It has three bowls:
Steel bowl
Nipco bowl racolan sleeve (highly elastic polyamide base)
Cotton bowl
STEEL BOWL:
This bowl is heated by means of hot oil that is, the temperature can be raised up to 210C and also high pressure up to 250 N/mm2 can be given. Because of this the three rolls produces better results, in spite of less contact area, than 5 or 7 bowl calendars. Element system is also present in steel bowl that is, the bowl is heated only up to the required width of the fabric.
NIPCO BOWL:
This bowl is 3.6m in length. The sleeve rotates by means of hydrostatic oil film that pressurize only the desired area by means of hydrostatic bearing.
COTTON BOWL:
The temperature is applied by the hydraulic oil circulation and by means of heat exchangers. The medium inside the tube of cotton bowl has temperature of hydraulic oil. T (in)=230C and T(out)= 80C. The medium outside the tube chilled water temperature T(in) = 15C and T(out)= 35C. Flow rate of hydraulic oil is 52-m3/ hour.
Flow rate of chilled water = 5m3/ hour. The hydraulics oil used in napco calendar is Mobil gear 630 or Aral Degol BG 200.
DIMENSIONS OF NIPCO BOWL:
- Outer dia of sleeve 500mm
- Inner dia of sleeve 400mm
- Length of sleeve 4000mm
- Working length 3.6m
- Web width (min) 800mm
- Web width (max) 3.6m
- Web speed (min) 10m /min
- Web speed (max) 100m/min
- Line force (min) 50 N/mm
- Line force (max) 250 N/mm
- Lifting of sleeve + - 10mm
TYPES OF FINISHING EFFECTS:
SHINING EFFECT: Fabric passes through nip pf nipco and steel roll giving smooth and luster effect.
HIGH GLOSS EFFECT: fabric runs with steel roll and nipco roll then with nipco roll and cotton roll giving smooth and matt effect.
DULL EFFECT: Between nipco and cotton roll.
The fabric after mechanical finish or chemical finish is sent to the lab for testing to be approved for the folding department and for stitching and then is forwarded fro shipment.
STENTER
Stenter is the most expensive and important m/c in a dye house and besides the dye fixation; it is used to control the finished length and width of fabric. The stenting process has thus an effect on handle, appearance and final finish of fabric. In chemical finish the stenter m/c acts to soften or harden the fabric by the application or deposition of chemical.
WORKING: -
The chemical in stenter is applied over the fabric by passing it through the chemical trough. Fabric after the chemical trough goes into the padder and then into the weft straightner (Bianco or Mahlo system). After this process the fabric goes over the chain and enters into the drying chambers. If required the fabric is further mechanically processed or it goes to lab for testing.
IMPORTANT PARTS OF MONFORTS MONTEX M/C:
CHEMICAL THROUGH:
The fabric from the in feed system enters into it, where the chemicals are applied to get required effects. The chemicals that are usually used for finishing are;
SOFTNERS: -
They are of two types.
1- Cationic (they are temporary softners)
2- Silicon (they are permanent softners)
They are in liquid form and have soapy touch, when applied to fabric it gives slippery effect so fabric feels soft. Silicon softners are of two types; micro and macro. Micro is permanent finish as it enters into intermolecular spaces of fabric whereas macro’s finish will remove after some washes.
POLY VINYL ACETATE: -
PVA is a type of thickeners used to stiffen the fabric. It fills the inter spaces of warp and weft and hence increases the weight of fabric.
RESINS: -
They are applied only on pure cotton and are used as crease recovery or easy crease. They also control the shrinkage and dimensional stability. They polymerize with the cotton fibers so are considered as permanent finish. Catalyst is also added with resigns to increase the rate of reaction. Due to resigns the fabric lose its strength so we always use Calonine L (softener) with it to maintain the strength.
BINDERS: -
It is used to improve the rubbing fastness of printed or pigment dyed fabric. It is also used to reduce pilling as it makes a layer over the fabric.
OPTICAL BRIGHTNERS: -
They are used for whitening effect of fabric. They actually convert the ultra violet light into visible range. 1gm/lit of it increases 40 to 50% whiteness of fabric.
DRYING CYLINDERS: -
They are provided after the chemical trough. Steam is provided here so that fabric after squeezing when passes through these cylinders then fabric gets heated and we can run m/c at higher speed. They are used only incase of dyeing for even results.
EVAC SYSTEM: -
This system is used for removal of fluff, unbounded moisture and loose thread suction. Turbo rotary blower used to produce a high vacuum. The fabric is passes through a slot that should not be more than 3mm.
WEFT STRAIGHNERS: -
In stenters clips or pins automatically grip the required amount of salvages in running condition, which maintain the width along the whole length. The bainco system is used for controlling, skewing and bowing of the fabric along the whole length of stenter chamber. The system also shows the percentage of skewing and bowing of cloth. It is seen that the fabric, which is produced by goller bleach, has 0 – 3 % skewing and bowing property while the fabric produced by the J/box has irregular width.
In mahlo system skewing and bowing is controlled manually that is by means of applying pressure or force mechanically. Skew and bow rolls are arranged in a pattern in order to control the skewing and bowing process.
DRYING CHAMBERS: -
10 drying chambers are provided here for drying. They have 5 burners and 20 motors for circulation fans. The length of fabric in chamber is about 55-60m.
STAR JET NOZZLE BODIES:
These are the perforated holes in nozzle body, which showers hot air on the fabric from both sides. Small holes are 10mm in dia for showering the gas and 100mm holes are used for exhaust opening.
Air circulation system in dryer:
Fresh air is taken from the atmosphere at standard temperature and pressure to help burning in burning chambers using methane gas. This hot gas is forced to pass through the star jet bodies by circulating fans. The star jet nozzle bodies shower the hot air on the fabric and used air is re-circulated and passed through the burner. If no fresh air is taken, a time will come that the re-circulated gas will get saturated and will be having no more tendencies to absorb moisture from the wet fabric.
Cooling zone:
At the exit of drying chamber cooling jet nozzle bodies or cooling drums are used to reduce the temperature of out coming fabric.
SANFORISING MACHINE
Sanforising is a mechanical of treating the textile fabrics to prevent the normal dimension alterations of warp weft, which occur in the finishing operation; especially those carried on in laundering &allied operations.
The process involves:
Precise determination of changes that occur in dimension when subjected to full laundry wash producing the finished effect to enhanced commercial value.
The sanforizing, which used in PDT, is of EVASET mechanical range (monforts)
Specification is:
Max. Cloth width 55inch
Compression 16%
Speed 90yards/min
Note: keeps half-inch width extra to help compensate for the inevitable slight extension of the fabric during the shrinking process
MECHANICAL COMPRESSIVE SHRINKAGE: -
The fabric is compressed by the contraction of the conveyor surfaces on which the fabric has been made to adhere. The conveyor takes the form of a rubber belt or sleeve. The outer end expands as it passes over a roller and at this point the fabric is applied. The surface contracts with it, expansion and contraction are controlled, precise and predetermined length can be obtained, hence the process is positive.
EVASET PRINCIPLE a specially made rubber sleeve is tensioned b/w roller 2 and 3. A driving roll on the outside of sleeve and deflects the upper run of sleeve into a reverse curvature, the driving roller 1 is steam heated.
The outer surface of rubber sleeve is expanded as it moves round the tension roller. The driving roller nips the fabric into contact with the expanded surface contract on taking up the reverse curvature around the driving roller.
CAUSE & CONTROL OF SHRINKAGE
LOOM:
When the fabric is woven, vertically the yarn stretches along the warp wise direction so the fabric is made under the constant tension condition.
IN PROCESSING:
Finishing process stretches yarn, during the commercial bleaching, dyeing, mercerization and other finishing processes. Both the warp and weft yarn are subjected to the stretching.
Complete shrinked yarn is fully relaxed, when fabrics are damped; all yarns become wavy and shorter i.e. their shrinkage occurs. The compressive shrinkage process is the most dependable and accurate method of shrinking fabric.
EFFECT OF SHRINKAGE
The fabric is improved, after shrinking there are more threads per inch both in the warp and weft direction. As a result, the shrinked fabrics have greater wearing qualities and improved hand.
WHY FABRIS SHRINKS
. Because the yarn it self swells in water and because of restricting effects of twist tends to contract.
. Because process tension are shed when a fabric is washed in water. In the process of manufacturing and finishing in continuous length fabrics are in elastically stretched. They tend to become longer and narrow. When washed such fabrics will expend in weft and contract in warp.
. The readjustment is referred to generally as shrinkage.
MAIN STEPS OF SHRINKAGE PROCESS
- DAMPING
- STENTERING
- SHHRINKING
- FINISHING
LABORATORY
This is the most advanced and most important department as fabric after every process comes here for testing. It is the key to the efficient working of all the department of the processing unit. Instruments used in the lab are according to the requirements and must be modern enough so that any test can be performed. A lab consist of following departments:
1. Application service 2. Quality control
1.Application service:
Works are:
1. Color matching
2. Research and development
3. Trouble shooting
4. External service
2. Quality control:
Fabric Testing Section Raw Material Testing
In Process Finished Product
Quality Control Quality Control
APS section:
· There work includes selection of the dyestuff, process, costing and fastness checking according to the end used of product.
· It also tests the new market products.
THE TESTS CONDUCTED IN LAB ARE: -
IN APPLICATION SERVICES:
1- Test for color matching
2- To check the metameric effect of fabric
3- To check the properties of new product before purchase and make the cost analysis
4- To find out the cause and effect of any problem arises during the bulk production.
IN RAW MATERIAL SECTION:
1- To check the whiteness of optical brightening agents.
2- To test for fixing agent
3- To determine the PH for chemical
4- Test for stiffness/softness
5- Determination of viscosity
6- Test for desizer
7- Test for stablizer and sequestering agent
8- Checking of white paste
9- Analysis of water
10- To check purity of different chemicals by finding their melting and boiling points.
IN FABRIC TESTING SECTION:
FOR GREY FABRIC:
1-To find out ends and picks
2-calculate the count
3-to check the size percentage
4-blend ratio
5-width
6-weight/m2
IN PROCESS QUALITY CONTROL:( IPQC)
AFTER BLEACHING.
1-PH
2-Absorbancy
3-Tegawa (degree of desize)
4-Whiteness
5-Width
6-Width drop %
7-Pilling
AFTER EQUALISING.
1-Whiteness
2-Skew and bow %
3-Width
4-Weight per m2
AFTER CURING. (BEFORE FINISHING)
1-Rubbing action (dry and wet)
2-Washing fastness
3-brushing fastness
4-PH (it is checked after dyeing)
IN FINISHED PRODUCT QUALITY CONTROL (FPQC)
1-Width
2-Weight/m2
3-Shrinkage of warp and weft
4-Pilling
5-Tensile strength
6-Flamability
7-Whiteness
8-Washing fastness
9-Crocking (dry and wet)
10-Brushing
11-Light fastness
12-Formaldehyde content
13-PH
14-Finish construction (ends and picks)
15-Finish content
16-Skew and bow %
17-Design deviation %.