Saturday, 24 May 2008
The botanical name of cotton is Gossypium. It has four varieties
a. G. Arboreum, G. Herbaccum- Old world cotton, native of Asia and India- Low yield - fibers are also short and coarse.
b. G. Hirsutum, G. Barbadense- America and Carribeans- High yield- fibres long and fine
Classification of Cottons
1. Primary Parmaters- Fibre length, length uniformity, fineness, maturity and bundle strength at 0 guage and 3.2 mm guage length.
2. secondary- Trash content, honey dew content and color
1.1 Fibre length and uniformity- Most important quality parameter that decides the price of cotton-Long staple cottons are used to spin finer counts and hence fetch higher prices
Uniformity ratio= (50% span length x 100)/ 2.5% span length
1.2 Fibre fineness: Indian cotton particularly long and extra long staple varities and hybrids show low micronaire values as compared to cottons of similar staple length grown in USA, Egypt and Sudan.This is due to lower maturity levels of Indian cottons.
1.3 Fibre Maturity
Maturity Coefficient = (Mature+0.6xHalf Mature+0.4xImmature)/100
Poor fibre maturity results in nappiness of the yarn and also leads to problems in even dyeing of fabric. Generally, lack of moisture and nutrients and incidence of insects and pests during cotton boll developments results in low fibre maturity
1.4 Fiber Strength
In the OE rotor system, it is fibre bundle strength, that is assigned the highest importance. Fibre bundle strength is determined by using the stelometer at zero guage. and 1/8 inch (3.2mm) guage length. It is well known that fibre strength decreases when guage length is increased. Also it is observed that yarn strength is correlated well with fibre tenacity at 3.2 mm guage length. Hence the ratio of strength at zero to that of 3.2mm is known as strength uniformity ratio.
2.1 Trash including other contaminants
Cut Seeds- during ginning
Trash and other extraneous matter. General carelessness in picking, sorting, handling and transportation of Kapas at all stages upto and including ginning.
2.2 Honey dew and Color of cotton.
Honey dew consists of sugar secreted by sucking insects that harbour on the cotton plants. Presence leads to roller lapping.
Color is more important in USA, where cotton is picked by machines and doing so gets rubbed against plant parts and thus gets contaminated.
Assessment of Spinning Performance
Where L= 50% span length
S= Bundle strength at 3.2 mm guage
M= maturity coefficient
F= Micronaire Value
FQI can be used to arrive at yarn CSP for a given count by using empirical equations.
Friday, 23 May 2008
-Dark Blue Indigo color
-High Dissolved Solids ( Decomposed products of hydro)
-High Chemical Oxygen Demand (COD)
-Chlorides and Sulphates of Suspended matter
Characteristics of Effluent
Appearance: Dark Blue
Suspended Solids: 250ppm
Dissolved Solids: 3500-5000 ppm
BOD ( 5 days, 20 deg C): 160-350 ppm
COD: 570-1100 ppm
Alkalinity (pH): 400 ppm
,,,,,,,,,,,,,,,,,(MO): 1700 ppm
Total Hardness: 220 ppm
Chlorides: 210-480 ppm
Sulphates ( SO4): 1200 ppm
Calcium: 15 ppm
Magnesium: 45 ppm
Ammonical Nitrogen: 2.5 ppm
Color (pt.Co): 250
Effluent is characterized by “high strength low volume”, as most of the most contaminated (“high strength”) effluent come from comparatively small quantity ( “low volume”) of wash waters used for rinse after yarn dyeing with indigo. Major contaminant is Indigo.
Permissible Limits for Cotton/ Synthetic Textile Industry (India) Effluent
Suspended Solids= 100 ppm
Oil and Grease= 10 ppm
BOD= 30 ppm
COD= 100 ppm
Hexavalent chromium: 0.1 ppm
Total Chromium= 2.0 ppm
Phenolic Compunds= 5 ppm
Sodium absorption ratio= 26
Sulphides= 2.0 ppm
color ( pt.Co.Scale) = 100
Bioassay test= 90% survival of fish after 9 hours in 100% effluent.
Effluent Treatment Scheme
Equalization tank in two compartments. Retention time of at least 7-8 hours.
2. Flash Mixing
Equalisation Tank flash mixer ( to adjust pH) clarifloculator Unit ( Alum/Poly Aluminium Chloride) for coagulation/segmentation
( it is a physico chemical process with 35-40% COD removal, 25-30% BOD and 70-80% color removal, also >95% color removal is possible if PAC and polymer dosage increased) overflow rate at CFU < 20 m^3/day
The sludge withdrawal should not be too less or too large ( can take place in lamella unit also )
Effluent after CFU aeration process ( time > 18 hours) ( New recent aerators use injectors which produce very fine bubble resulting in a large air/water interface. Waste water is used as pressure water fro the operations of injection. Water +air stream are subjected at the bottom of the tower to prevent any possible sedimentation. Gas bubble rise to full height of the tower long resident time. Good utilization of oxygen upto 80% is possible.
Effluent from aeration clarifier ( resident time 3-4 hours) activated sludge recalculated from clarifier to aeration tank sludge thickened centrifugal decanter filtrate is then discharged to another tank.
Clarified Effluent deficient in dissolved oxyen (DO)( for bioassay parameters) DO make uptank ( 2 hours resident time) – the output is expected to meet the criteria.
Process for filtration of particles >5 n meters, from feed water made to flow at low pressure through membrane having pore size of 4-5 nm.
Useful for elimination of high molecular weight organic compounds. By using this ( the original indigo concentration in rinse water is 0.05%) fully usable 5% dispersion of indigo dye is obtained.
There are two types of membranes available. 1. Organic 2. Mineral – resistant to pH 0-14, resistant to mechanical and thermal conditions and are unaffected by solvents.
Burning of waste
Major threat to possible health
Destruction of resources
8. Sludge Disposal
85% of the waste is biodegradable. Can be used for compost. Lime sludge has agricultural value as it is free from pathogenic microorganisms
Bugs convert dyes into colorless substances
Microorganisms ( Geotrichum Candidum filament fungus isolated from soil) can decompose 18 different kinds of dyes in to colorless substances. Preferred pH for them is 4-7 at a temperature of 20-30 deg C. Can destroy dye in two days ( at a concentration of 12 g/lit). They can eat indigo also.
Process Control for Effluent
Usually 10% of the applied indigo is washed off in rinses. Indigo fixation of yarn could be improved by:
-Slightly lower pH- can reduce indigo consumption for a given visual depth of shade
-Use of pre reduced indigo and indigo dyeing under nitrogen blanket. Can cut hydro consumption
-Use of prereduced sulpher dye and maintain reduction potential with hydrol ( glucose + other oligomeric reducing agent) instead of sod. Sulphide.
Effluent volume can be reduced through water conservation
-Washing in counter current type
-Decrease size of wash tanks
-Use Na2CO3 (Sod. Bicarbonate) in first rinse tank
-Use Co2 for neutralization of alkali
-Use as many nips as possible during washing to squeeze out alkali to maximum ( squeezed liquor should not drop back into bath)
-Relying more on spray rather than immersion into the bath
-Create enough stir in wash tank for best washing efficiency.
Thursday, 22 May 2008
Preshrinking of Textile Fabrics- or compressive shrinkage
Shrinkage can be
- Natural Wash shrinkage- When the fibres swell in the presence of water and tensions induced during Spinning, weaving and processing of fabrics
- Compressive or Mechanical Shrinkage
It can be compared to the action of press. The effectiveness of ironing depends upon:
Temperature of the press
Amount of Moisture present in the fabrics
Amount of Physical Pressure Applied
Time duration of application of press.
In case of pressing, the new memory is set by drying, in compressive shrinking, it is the palmer unit which dries the fabric, thereby setting its new memory
Amount of preshrinkage left in the fabric is adjusted by varying the relative speed of the palmer to that of the rubber belt unit.
The temperature affects in the following way the various components of the palmer/ compressive shrinkage unit
- Rubber Belt Cylinder
o Lower Temperature- Fabric appearance is affected- Sharp crease
o Higher temperature- rubber belt life is shortened
- Palmer Cylinder
o If lower temperature: No dry Stuff; Elongation of preshrunk fabric- also stretching of inspection and rolling operation.
o The purpose of palmer cylinder is to dry a fabric to a level of about 4% relative humidity. If there is higher temperature, there is elongation with natural moisture regain.
- Temperature of fabric as it enters rubber belt unit
If properly controlled, then high production. Most fabrics will shrink more easily if heated before entering the rubber belt unit.
- 100% cotton denim may require as much as 14% moisture to permit effective pre shrinkage
- Moisture must be uniform thoroughout the length, width, and depth of fabric
How to ensure moisture uniformity
- Use of heated cans
- Apply needed moisture of fabric vial cooling water applied to rubber belt surface. But it also depends upon the condition of the rubber belt. Freshly grinded rubber belt carry more water à water removal roll of the rubber belt unit
Penetration of moisture applied to the fabric is very important. If insufficient moistureà Innermost dry layers of yarn will act like spring and cause the fabric to elongate.
Maximum amount of rubber belt compression should not be greater than 25% of the actual belt thickness.
More heavy the fabric, more potential, more compression will it need
If above three factors are maintained and we have a sufficiently large palmer unit, we can compress durably a fabric to its ‘zero’ potential.
Its important to use cooling cans at the exit of the palmer
Fabric Scray: Use of exit scray allows additional time for fabric cooling as it is impossible to roll fabrics without the use of lengthwise tension.
Guider: The function of the guider is to keep the fabric to its full width.
Skyer: It is a sort of time delay device allowing time for moisture to penetrate into the fabric without the need to increase the machine length.
Heated Can: purpose: it is to drive the surface moisture into the fabric and to preheat the fabric.
Dry the fabric and set shrinkage
Adjust the shrinkage
To compare incoming and outgoing fabric tension and determine fabric shrinkage
Less dense the felt, greater is the drying capacity
- To relax and cool;
- To prevent hot stop marks. It increases the rubber belt life
- To facilitate shrink environment
Why Wet Finishing for Denim
- Moisture doesn’t penetrate in the core- in foam finishing
- Its better to shrink fabric with a low moisture content than those which are bone dried
In integrated Machine
- squeezing the moisture
- application of heat
Once it is shrunk the fabric is thoroughly dried by palmer
- Hand can be adjusted in padder use of starch, lubricant
- Width can be controlled by adjusting tension between the padder and dry can
- Higher speed
- Even ness of the moisture content- Residual moisture after leaving palmer should be 4%
Drying depends upon the pressure of the steam, m/c speed, size of palmer , construction of felt
Rubber Belts: 36-40 deg. Shore
Harder- crack and lesser shrinkage capacity
Softer- require replacement frequently
Thicker- more grinding
- more wear and tear to machine parts
- energy consumption
Rubber belt: Inside circumference- 3.962m
- Rubber surface width should exceed fabric width by at least 6” and preferably 8”
How to increase the life of the Rubber belt
- Nip pressure used on rubber belt should be optimum
- Over tension in the rubber belt should be avoided
- Belt should be run with sufficient cooling water in its interior and exterior surface
- Belt should be run with lowest possible operating temperature 115 deg- 140deg
- Frequency of grinding of the rubber belt should be optimum ie should be enough and at sufficient depth.
- Grind when density of belt surface has varied by 10% of its original hardness
- Water removal roll pressure adjustment is very important to insure max. belt life. Water acts not only to cool the rubber, but is also a lubricant
- Product machine stops or “hot stops” should be avoided to the maximum extent possible. One of the best ways to eliminate is to install scrays at the entrance and exit of the shrinking machine.
- Foreign objects should be avoided. Knot size for joining fabrics should be smaller.
- Regular cleaning and inspection of rubber belt.
- Use correct belt width
- Be careful during installation and maintenance of rubber belt, avoid use of chemicals.
Function of Felt Palmer
- It is required to maintain the preshrunk fabrics in intimate uniform contact with the surface of the heated cylinder in order to ensure uniform smooth drying of the fabricà new dimensionally stable memory.
- Fabric drying depends upon, palmer cylinder temperature, shrinking machine speed and permeability of the drying felt.
- It helps in precise fabric shrinking adjustment. It acts as a fabric puller to precisely control tension on the fabric
- Provides a pressing and calendaring effect on the preshrunk fabric
Wednesday, 21 May 2008
1. Vat Indigo dye
2. NaoH--> flake, lye
4. Dispersing Agent
5. Wetting Agent
6. Potessium persulphate
7. Thin boiling Starch
9. Mutton Tallow- or equivalent
10. Acrylic Polymer
11. Hessian Cloth- a. 45"width, 10 oz./linear yard, b. 45"width, 14 oz. per linear yard
12. High Molecular high density polyethylene: 65" guage x 44 "width, 65" guage x 50" width
13. Spiral Built Paper a. 51mm ID x 60-60.5 mm OD x 60" long
For 7s count
Evaluated at the end of 6 months
>1900=4, 1800-1899=3, 1700-1799=2, 1600-1699=1, <1599=0>Count CV
a. Thin places
0-2=5, 3-10=2, >10=0
b. Thick Places
0-2=5, 3-6=2, >6=0
a. Analysis for total faults
<10=4, 30="2," 50="1,">50=0
b. Analysis for Objectionable Faults(A4, B4, C3, C4, D3, D4)
0-2=4, 3-4=2, >4 =0
Weightage in Quality
CSP=20%, Count CV=20%, Imperfections( Thin=10%, Thick=10%, Neps=10%), Classimate ( Total Faults=10%, Objectionable Faults=20%)
II. Delivery Schedule
100% Compliance=5, 90-99%=4, 80-89%=3, 70-79%=2, 60-69%==1, <60%=0
They are determined on a 5-point basis.
>3.8--> Excellent, 3.0-3.8-->Good, 2.0-3.0-->Average, <2-->Poor
Vendors are evaluate quartly on the basis of the quality of material supplied while at the end of year, other parameters are also taken into consideration.
The number of lots whose sample test reports show total conformance to the standard parameters of strength, micronaire and staple length will be determined, then a rating is given as:
A. % of accepted but non-conforming lots
B. Non Conforming lots rejected
Sum Total will give the overall rating
V. poor--> <2
Annual Evaluation Procedure
1. Quality-->60% weightage
2. Delivery --> 15% weightage
1. Quality with respect to Standard Parameters
A. % of lots above
0-10=1, 10-20=2, 20-30=3, >30=4
B. % of lots adhering
0-25=1, 25-50=2, 50-60=3, 60-70=4, 70-80=5, 80-90=6, >90=7
C. % of Lots below
0-10=1, 10-20=2, 20-30=3, >30=4
Total Score= A+B-C
2. Delivery Schedule
100% compliance-->5, 90-99%-->4, 80-89%-->3, 70-79%-->2, 60-69%-->1, <60%=>
3. Price: 1-5 scale basis
4. Service: 5 point scale
Excellent=6.4-7.4, Good=4.4-6.3, Average= 3.4-4.3, Poor= 7.4-3.3, V. Poor= <2.3
Tuesday, 20 May 2008
Monday, 19 May 2008
In a tank of 1000 liters:
a. take 400 litres of water (soft)
b. add setamol ws--> 4 g/l (stirring) ( dispersing solution)
c. Add 100 kg of Indigo ( at 1.8 % shade -see the indigo calculations- stirring)
d. add caustic soda --> stirring ( for solubilising and pH)
e. allow to cool it for 2/3 hours
f. Add hydrosulphide ( As reducing agent)
g. Make the solution to 1000 l by adding water.
If pH is fluctuating, if it is > 11.7 then hydro is added (2-3 kg), if (<11.2) then caustic is added.
For 100 kg of Indigo,
Caustic Required= 90 kg
Hydro Required= 80 kg
For 12 ropes, at 24 m/min, of 344 ends of 14000 m length of 7s count.
wt of yarn = (12*344*14000*100*453.6)/(7*840*36*2.54*1000) kg= 5000 kg
at 24 m/min, a lot of 14000 m will be completed in 14000/24 = 583.3 min
at 1.8% shade
100 kg of yarn needs--> 1.8 kg of Indigo
5000 kg of yarn needs --> 90 kg of dye
at 100 gpl
100 gms of dye = 1 lit of solution
90 kg of dye = 900 litres
900 litres should be completed in 583.3 min
1 litre would be completed in = 583.3/900= 38.8 seconds
so flow rate will be 38.8 seconds / litre
Similarly flow rate of caustic and hydro can be determined
Hydro is taken around 100 gpl
caustic is taken around 90 to 100 gpl
1. Concentration of Hydrosulphite
It is measured by vatometer. It should be from 1.5 gpl to 2.5gpl , or by redox potential of dye bath which should be from -730 mV to -860 mV.
2. Caustic Soda or pH value
Should be from 11.5-12.5
3. Dye concentration in Dye bath
it is measured by spectrophotometer. It should be in g/l
High Indigo Concentration --> Shade is greener and lighter
Low Indigo Concentration --> Shade is dull and Red.
High pH or Caustic Concentration --> Redder and lighter
Low pH or caustic concentration --> greener and darker
Longer the dipping time, better will be the penetration and lesser will be the ring dyeing effect. It varies from 15-22 seconds.
High pressure will lead to lower wet pick up and result in lesser color and better penetration. At rope dyeing, squeeze pressure is 5-10 tonnes, ie. wet pick up is as low as 60%. Hardness of squeeze roller is about 70-75 deg. shores. It sqeeze rolls are too hard then there are chances of slippage and uneven yarn tension.. If squeeze rollers are too soft then shading will occur. Surface of the squeeze rolls should be ground twice a year.
It should be 60-75 seconds. Longer airing time results in high tension on the yarn and subsequent processes will become difficult.
Insufficient or unevenly dried yarns will result in poor rebeaming
Calculation of Replenishing Dye feed/min
Conc. of stock vat is g/l= 90
range speed in yards/min=25
count = 7s
totoal ends = 4100
Wt of yarn dyed /min= (4100*25*1000)/(7*840*202)= 7924 gms
shade desired = 2%
Amount of dye to be replenished/min= 158.5 gms
Effect of pH
At pH of 10.5 to 11.5, there will be formation of more monophenolate ions, which lead to higher color yield, as strike rate of the dye to the yarn bundle is very high, and wash down activities will be very good.
At pH higher than this, dye penetration will be less and wash down characteristics are also poor.
1. Alkalanity in Dye Bath Liquor
Pipet 10.0 ml of vat liquor into 100ml of distilled water in a 150 ml beaker. place under continuous agitation and insert the electrodes of a pH meter caliberated at pH 7.0 with standard buffer solution.
Titrate with tenth normal HCl ( 0.1 HCl) to pH 7.0 (ml = A)
g/l of NaOH = A *0.40
2. Hydro in Dye bath Liquor
Add 2 ml of 37% HCHO to 150 ml beaker. Add 2 ml of dye range liquor . Add 6 ml of 25% glacial acetic acid solution prepared by diluting 1 part acid with 3 parts water. Add 2 ml of starch/KI indicator. Add ml of water. Titrate with 0.046 N ( prepared by diluting 460 ml of 0.1 N Iodine to one liter ) solution until the color changes from emarald green to bluish purple.
G/l of hydro= mo fo 0.046N of Iodine
Importance of High Concentration of Free Hydrosulphite
The clearest shades with minimum reddish streaks are observed at by relatively high conc. of hydrosulphite. On the other side, with lack of hydrosulphite, the leuco indigo is less dissolved and thereby adheres to a greater extent to the fibres. With lack of hydrosulphite furthermore, the amount of unreduced dyestuff by oxidation at the upper level of the liquor and through activiation of unfixed dyestuff, gets separated from the fibrous material would constantly rise as the reducing agent for creating leucoform would be missing. Under these circumstances a reddish bronze like shade results due to dispersion of not reduced dyestuff in the yarn. The min. proportion of hydrosulphite should be around 1.3 to 1.5 gpl in case of rope dyeing and 3-4 gpl in case of sheet dyeing. Also to avoid the lack of hydrosulphite or Indigo at certain places in the immersion, vat, the whole quantity of the liquor should be circulated 2-3 times every hour.
At very short reaction time, an adequate liquor exchange ( i.e. the amount of chemicals consumed and replaced by fresh addition of reduced indigo) is not assured. This has a negative influence on dyeing and depth of dye penetration. In addition to this the time available for diffusion of dyestuff until oxidation commences is too short. To ensure an even and good depth of dye penetration by dyeing in several passages, the reaction time should be 20-30 sec. for each vat (eg. at a speed of 20m/min for a reaciton time of 10 seconds, the immersion path should be maximum 3.3 meters).
A reaction time exceeding 60 seconds should be avoided as the amount of dyestuff again get reduced and released may again supersede that of additionally take up dye stuff, resulting in higher shades.
Softening Agent: 8 g/lit
Drying: Rest humidity should be 30% and then sized.
Addition of chemicals
1. Red Tinge: reduce addition of NaOH, increase slightly Na2S2O3
2. Darkish Red: increase Hydro
3. Light Greenish: decrease Hydro
4. Dark Green: Increase Caustic
For further information you can read this article
Saturday, 17 May 2008
Notes on Yarn for Rope Dyeing
* Yarn faces stress and stretch at ball warping, rope dyeing, rebeaming, sizing and loom shed so elongation of yarn should be more than stretch at (ball warping + Robe Dyeing+ Rebeaming + Sizing )= (2-3%) + Loom shed (about 5%)
* Tension at Ball warping should be less by 7-8% of single yarn strength.
* Strength CV should be within limits as it may give rise to weak points
* The tendency of yarn to migrate at rope dyeing can be countered by less micronaire of yarn ( should be around 3.8-4.2)
* More dropping of short fibers at long chain beaming is good
*The sensitivity settings for neps is set at +280 for rotor spun yarn and not +200 as in case of ring spun yarn. The reason for this is that the structure of rotor spun yarn is intrinsically different from that of conventional ring spun yarn. Neps in rotor yarn tend to be spun into the solid yarn body rather than remaining on the yarn surface, which is typical of ring spun yarns. Although embedded in the yarn core, these neps still represent a short mass defect and will therefore trigger the imperfection counter upon exceeding the preset value. However, compared to neps that are attached to the yarn surface, fully embedded neps are barely perceptible for the human eye. Thus, in order to balance the typical visual appearance of rotor spun yarn with the imperfection counts, +280 sensitivity setting is a common convention for rotor spun yarns.
Friday, 16 May 2008
* A four point system can be adopted, with 9 qualities ( from 9 to 1).
The point distribution is as follows:
upto 3"= 1 point
3-6"= 2 point
6-9"= 3 points
9" and above= 4 points
Any defect across full width = 4 point
All the above defects may be length or width wise.
Length wise one course or fine ends/ up to one meter=4
Starting mark (across the width)=4
- continuous slub or slubbing weft
- thinck end more than one meter
- major shade variation
- blanket impression
-Jala-jerky-chira-wrong drawn- float-snarls-missing ends- more warp breaks- patti-holes-cuts-sever temple mark- more pick findings in short length, double pick
-Slack and tight ends >1m
* From qualities 3-9, only 2 pieces in a single roll are allowed and no piece should be less than 30 meters.
The qualities Criterian can be defineds as follows:
9--> 2 shades allowed, allow 20 points per linear meter which no greater than 2 to 3 4 points defects
8--> 3 shades are allowed, allow 36 points per linear meter no greater than 4, 4 point defects
7--> same as 8 but here we allow upto 5 shades
6--> Allow 72 points per linear meter, upto 3 shades -no greater than 5 to 6 , 4 point defects
5--> same as 6, but 5 shades are allowed.
4--> points should not be greater than 72, any number of shades, any number of 4 point defects. We do not allow patta ( width wide strips)
3--> Same as 4, we can allow patta
2--> same as 3, 5 pieces are allowed ( every piece 10-30 meters each)
1--> any continuous defect is allowed ( pack the piece less than 1 meter)
Shade gradation can be
Dark Shade--> D+
Normal Shade --> D
Light Shade --> D-
Relation between Manual and "l a b" grading system
l, a, b values
D- = 554,654,655
Tolerance for l a b values--> L = +-0.5, a = +/- 0.5, b= +/- 0.5
Voile, Cambric, Terry voile, shiffon, long cloth, classical oxford, pin-point oxford, Chief Value Cotton
It is a doubled yarn, highly twisted with count range >60s. It has an square and open construction. The fabric made from it is light weight, transparent, crispy and granular feel. It can be either cotton or P/C. Its trade name is 2 x2 Rubia. 72 epi and 72 ppi.
It is a single yarn, rest properties are same as voile.
It is name of voile with 2/81 high twisted fabric in 67:33 blend which is later carborised to get a 100% polyester fabric.
Count is 62s. Here weft is highly twisted (1400-1500 tpm) polyester filamnet and textured and warp is p/c. 67:33
It is a plain fabric with special kind of finish which remains for some times even after normal washing.
Poplin Broad Cloth
A tightly woven, subtle variation on a plain-weave fabric, characterised by a very high thread count- 100 to 200 tpi- produces a thin, but relatively opaque fabric with a crisp, hard finishing. Also characteristics of the fabric is its fine horizontal ribbing, produced by the lengthwise warp threads being packed more densly than the crossing weft threads. The ribbing is scarcely noticeable but makes any on-grain stripes very clear and appear solid in color, and it also adds a little shine on the fabric. If the cotton fiber itself has any shine, it will enhance the shine of ribbing and produces a very dressy effect. It comes in solid colors, stripes, plaids and checks.
Chambray: It looks solid color but is a plain worked with two colors of yarns, usually a white warp and a colored weft or vice-versa. They are woven in all weights. It can be poplin, or twill or dobby chambray
It is like chambray, but in contrast to a chambrays plain weave, oxford cloth is woven in a basket weave. It produces the fabric's soft bulkiness.
Warp is Dyed and weft grey
warp --> 2/40s, Weft --> 2/30s
Pin Point Oxford
When worked in a fine weave, oxford cloth is called a pinpoint oxford.
both warp and weft 2/80s, 144 ends/inch in grey and 60-62 ppi.
Chief Value Cotton
60% cotton, 40% polyester
Enzyme treatment. Here fabric gets very good lustre and feel. Also we do a process called weight reduction process ( weight is reduced by 4-5%, so bulkiness in the fabric is given.
3/1 twill with 2/40s * 2/30s. When single yarn is used it is called Drill.
with 2/40s * 2/30s
1. Process of dyeing of sulphur color:
1st Wash tank: mercerisation by taking 22% NaOH ie. 250 gpl
2nd Wash Tank: Hot Wash
3rd Wash Tank: Cold Wash
2. In 1st and 2nd dye bath take sulphur color 6-8% on the weight of the yarn sheet. Temperature 90 deg. cel. The solution contains the following:
1. solubalised sulphur color: 150 gpl
2. Na2S--> reducing agent: It is added to increase its reducing power
3. Caustinc Soda --> 10 gpl--> reducing agent
4. Wetting agent--> 2gpl
5. Antioxident Sulphide ( Glucose paste--> 5gpl). This is added to prevent the oxidation of of Sulphide solution. It will always remain in reduced form
( Alos if the shade is slightly greyish, one can add tiny tinge of sulpher blue--> 20gpl)
in III, IV and V dye bath--> cold wash
in 6th dye bath. We take H2O2(30%)+Acetic Acid(2:1 by weight). H2O2 acts as an oxidising agent. But as it acts on neutral pH (=7) and after cold bath the solution is slightly alkaline, to make it neutral wil add acetic acid. Acs in alkaline pH, oxidising action of H2O2 will be similar to the bleaching action, which may cause tendering in the fabric.
7th and 8th Dye Bath: Cold Wash
Wash Box Number 4: Here washing is done with detergent and soda ash at 60-70 deg.c
5th and 6th Wash Box: Hot Wash
7th wash Box: Here softner is added at 25 gpl. It is cationic softener with pH 4.5 to 6.5. As during oxidation of sulphur, strength is reduced by 10%. On a yarn sulphur is of two types :
1. Free Sulphur
2. Reacted Sulphur.
The free sulphur will react with moisture in the atmosphere to form:
H2O + S --> H2SO4
Which tenders the yarn. Now at acidic pH reaction is much faster. So we add only a small amount of softener (25 gpl) as against that in indigo which is 100gpl.
Over all during sulphur dyeing and storing, the yarn strength is reduced by 15% as compared to Indigo.
If ball formation takes place of sulphur dyed warp at loom shed, then we can taken in 4th dye bath little Na2S+Caustic to reduce the free sulphur.
Thursday, 15 May 2008
Practical Considerations in Rope Dyeing for Indigo dyed Denim.
The passage of yarn in rope dyeing is as follows:
Pre-scouring -->hot wash-->cold wash --> Dye baths--> hot wash-->cold wash--> application of softener
lets discuss these processes one by one:
1. The objectives of pre-scouring are the removal of wax content from cotton, removal of trapped air from cotton yarn and Making yarn wet
2. This is done at 90 o C
3. We use the following ingredients at pre-scouring stage:
Caustic Soda: Its quantity depends upon the quality of cotton fibres used in the mixing. Generally we take 2-4% of caustic soda. It removes the wax by the action of soapanification.
Wetting agent: It is anionic in nature
Sequestering Agent: Even with the use of water softening, it is very difficult to find the desired softness in water ( about 2-3 ppm) . So we use the agent to make the water soft.
4. Why Trapped Air should be removed. The reason for this can be understood as follows:
In 1 kg of yarn, there is approximately 2 litres of air. 1 litre of air decomposes 1.8 litres of Sodium Hydrosulphide. It will cause uneven dyeing and more consumption of Sodium Hydrosulphide ( hydro).
5. Absorbency of yarn may be checked after scouring.
As some caustic is carried by the yarn after pre-scouring, so hot water is given at 70-800C. If this is not done, this yarn will go into the dye-bath which will change the pH of the dye-bath.
After hot wash, yarn temperature is more. To bring it back to its room temperature, cold wash is given to it.
1. Indigo is not a perfect vat color. It may be called a trash vat color. The constant of substantivity for other colors is 30, for indigo it is only 2.7. So there is a need of 5 to 6 dye baths and make the use of multi-dip and multi-nip facility to increase the penetration.
2. The dyeing is done at room temperature as indigo belongs to Ik class of vat dyes, where dyeing is done at room temperature and oxidation is done by air only and not by chemicals. If oxidizing agents are used, they will cause stripping of colors.
3. Indigo is not soluble in water. So it is reduced with Sodium Hydrosulphide. Then caustic soda is added to make sodium salt of vat colors to make it soluble. To reduce 1 kg of Indigo, 700 gms of sodium hydrosulphide is required. However some extra SHS needs to be taken to avoid some decomposition of SHS.
Practically it is prepared in the following sequence
-Then reducing agent
4. When caustic is added to indigo, it is an exothermic reaction. It is allowed to cool down, then before sending it to feeder, sodium hydro-sulphide is added. Reducing agent is not added first as it will be decomposed first, so consumption of it will increase. It is also not advisable to take solubalised vat, as offered by some companies due to the following reasons:
a. If it is used after 6 months, there will be a decomposition of sod. Hydrosulphide. It will become partially soluble. Then to make it soluble again, more SHS has to be added.
b. Transportation is difficult
c. Cost is more
5. Feeding System
Rat of flow of yarn is given by
((No of ropes x no of ends x speed of machine)/ count x 1.693 x 1000)
in kg of yarn / minute
So we can determine the rate of feed of indigo. It is very important that replenishment of indigo is there as any variation will result in the change of shade and also if level is more, there is a problem of over-flow.
6. If total capacity of dye bath for example is 15000 litres, then circulation must be 3 times the volume. If it is less then there are 100% chances of getting a lighter shade.
7. Core and ring dyeing effect
This effect is obtained by multidip-multinip facility
8. pH of the Dye bath should be kept in between 10.5-11.5. At this pH , sodium salt of Indigo is mono phenolic form. At this form, the strike rate of dye is very high. So after washing, there will be a better dye effect. At pH 11.5 to 11.7, at this affinity is less, so dye effect will be less prominent.
pH is controlled by the addition of caustic soda.
9. Testing of Hydro
We take 10 ml of indio with SHS in 30-35 ml of water. It is set for one minute and shaken. As air will decompose SHS. So vacuum created will fetch the water from above. If 3 ml of water is required, then concentration of hydro is 3 gpl. As a thumb rule, concentration of total hydro should be min. 1.5 gpl.
It is the hydro that is used for the reduction of Indigo. It should be around 0.7 ( 1000 kg of Indigo needs 700 kg of hydro to reduce it). For testing we take 10 ml of dye solution and 30 ml of water and 5-6 drops of 40% formaldehyde and shake it for one minute. The water that goes gives the readings of the reduced hydro.
Total Hydro- Reduced Hydro = free hydro
If Total hydro is min. 1.5 gm/lit. then free hydro must be min. 0.5 gms/ litre which acts as buffer
10. Also hydro reduction capacity is measured by mV meter which measures the Redox Potential.
It should be around 760-800
Through the day, the redox potential should be +- 20 mV of the norm. If it is more then the process control is a failure.
Caustic--> It is around 0.4 to 0.5 times the hydro used.
Rubbing fastness of indigo is very important. On a scale of (1-4), it is 2. Washing is done to improve the rubbing fastness.
Wash at 60 deg.--> Wash at 60 deg.--> Wash at room temperature--> wash with softener
1. The rope is going to be opened at Long Chain Beamer. It the softener is not used, opening will be hampered.
2. It is generally 1.2% of the weight of the yarn. It is a cationic softener. It is always having pH in the range of 4 to 55. Softening is done at room temperature. If high temperature is used there is always some chance of tendering of yarn.
3. Concept of Buffer pH is given by Virkler USA, they say by addition of this, there is 40% less consumption of Indigo for same shade depth.
4. Metering Consumption
If solution is of 900 litres
10% Indigo-->90 litres
Hydro--> 90*.7 = 63 kg
Caustic--> 63*0.445= 28 kg.
Here are some of the common fabric defects and their troubleshooting as observed on Denim weaving Airjet looms. I have included the damages observed on Tsudakoma looms, but I am sure the principles can be applied on other airjet looms also:
a. Bent Pick
1. Check catch cord drawing in and its position
2. Air pressure of all nozzles
3. Heald Frame height and shed crossing
4. Check stretch nozzle timing and position
5. Reed dent gap opposite to stretch nozzle.
6. Check condition and position of weft rubber stopper.
7. H1 Feeler head condition to check for any damage etc.
8. Heald frame side play to check
9. Binding of Leno Yarn
b. Weft Patti
1. Check pressure of AGS
2. Check AGS piston
3. Check beam gear and beam drive pinion
4. Check beam bearing bush, clamper condition and beam bearing
5. Check ELO timing
7. Check tension lever rod freeness and shock absorber position
8. Check take up gear and take up belt condition
9. Check press roll spring tension
10. The machine should not be stopped for long duration
11. Train workmen to follow work instructions for first pick insertion
c. Weft Float
1. Check Air pressure
2. Check leakage of air pipes
3. Check nozzle jet timing
4. Check catch cord end drawing in position
5. Check stretch nozzle position against reed dent gap.
6. Check heald frame height and shed crossing timing
7. Check fringe length
8. Check LHS cutter timing
9. Check position and condition of rubber stopper
10. Check proper winding of weft turn on FDP
11. Check individual subnozzles for blowing
12. Check all warp ends are tight enough
13. RH/LH selvedge should run on last ring of the temple.
d. Missing End / Chira
1. Check all serrated bars are not in loose contact at the clamp
2. Serrated bars should be thoroughly cleaned with petrol/thinner
3. Dropper sensitivity to be checked
4. Electric connection at the cable with clamp should be checked.
5. Remove fluff from the serrated bars
6. Ensure that each warp end is attached with one drop pin.
e. Torn or Hole at the Temple
1. Check that temple cover is face to face with temple bracket
2. Ensure that temple bracket are fitted firmly on temple bar
3. Check heald frame height and shed crossing timing.
4. Check warp tension
5. Check bottom guide bar setting
6. Check press roll spring tension
f. Abrasion Mark
1. Check position of warp stop motion separator
2. check cross ends
3. Check freeness of heald wires.
4. Check emery roll for any cuts etc.
5. Check freeness of temple rings
6. Check smoothness of temple covers
7. Bottom guide bar position and condition to be checked
8. Check reed-dent spacing
g. Nozzle Mark
1. check sub nozzle angle and height
2. Check scratches at tip of sub nozzle
3. Sub nozzles should be parallel
4. Check Reed dents
h. Jirky/ Missing Pick
1. Check working of H1/ H2 feeler
2. Check feeler timing in I-board
3. Check setting of FU-203 (sensitivity of H1 and H2 feelers)
4. Clean H1 and H2 Feeler head
i. Tight Ends
1. Check that ends should be parallel
2. Remove entanglement of warp ends
3. Check that sticky ends of selvedge should not run in the body.
j. Oil Daghi
1. Check that no oily fluff is stuck to the warp sheet
2. Check that no oily fluff is stuck to the emery roll or pressure roll.
k. Bad selvedge
1. Check leno stop motion
2. check proper RH cutter setting
3. Check continous working of batching winder
Friday, 9 May 2008
Thursday, 8 May 2008
Wednesday, 7 May 2008
Sunday, 4 May 2008
For manufacturing Denim and Grey Fabric, the process is same up to the level of weaving, but in case of Denim Fabric, dyeing is done at the stage of sizing where as for Grey Fabric it depends upon the finished product. The details of each process are given below:
1. Fabric Weaving
a. Grey Yarn on ConesNormally yarns received for weaving in cone forms are either from ring spinning or from open end spinning in single or double fold as required. For weaving, yarn used is categorised into:
o Warp yarn
o Weft yarn
Normally for Weaving, yarn used as warp should be sufficiently strong to withstand stress and strains exerted during weaving operations. Hence they are having Count Strength Product(CSP) and further sized to increase its strength. The weft yarn is directly used on weaving machines and in some cases, if required, is rewound also so as to enhance its performance in weaving.
b. Warping on Sectional/ Direct Warping
The warp yarn is required to be fed into a sheet form to the weaving machines. At warping, the individual cones are put into the creel (the number of cones depends upon fabric construction) and yarn from individual cones is pulled together in sheet form, wound on a barrel called warping beams (for Direct warping) or on weaving beams (for Sectional Warping). Normally if warp sheet is with patterns of different coloured yarns it is processed on sectional warping machine.
c. Sizing of yarn in Set/ Beam to Beam Position
The object of Sizing is to improve the strength of yarn by chemically binding the fibres with each other and also improve upon its friction resistance capacity by chemically coating the surface of yarn/fibres. Further, number of threads in warpers beam sheet is very less against number of threads required in whole width of fabric. Hence multiplication of sheets by drawing yarns together from many warp beams and again making one sheet is also performed on sizing machine. On sizing, normally, 8-12 % size material on warp thread is applied. This improvement in strength and frictional resistance characteristic of warp yarn is essential because during weaving, yarn has to undergo severe strain & stress as well as frictional operations.
Weaving is basically interlacement of two sets i.e. warp and weft threads in desired sequence and pattern. To obtain this interlacement, warp yarn sheet is bifurcated & opened in the form of two layers/ sheet and weft thread is inserted between so opened two warp sheets. This operation is called shedding. to perform shedding the warp yarn needs to be passed through heald eyes of the heald shafts, this operation is called as drawing-in.
e. Beam Gaiting or Knotting on Loom
The drawn weavers beams are fixed on weaving machines, threads are tied and heald shafts are coupled. This operation is called Beam Gaiting. If undrawn warp threads are directly knotted to the threads of finished beams, it is called Knotting. These operations are essential because normally weavers beam can carry only certain length of warp sheet on it and when so woven, whole length is converted to the fabric by weaving machine. Further warp length is required to be fed which can be done by knotting or gaiting other beams on weaving machine.
As stated earlier, weaving is interlacing two sets of yarn and making fabric. One set is called warp thread which is in sheet form, the other one is called weft thread which is inserted between two layers of warp sheet by means of a suitable carrier i.e. Shuttle, Projectile, Rapier, Air current, Water current, etc. Depending upon the type of the weaving machines. The different types of technologies available for weaving machines are briefly explained as below:
o Conventional Shuttle Weaving System by Ordinary Looms or Automatic Looms.
o Shuttle less Weaving System by Airjet /Waterjet/Rapier/Projectile
Shuttle loom is a conventional Technology with much less production on account of slow speed and excessive wear and tear of machinery. This shuttle loom technology has now become obsolete. Denim is woven through Shuttle less Weaving System by using 96 ZAX-e Type Tsodakoma Corporation’s Airjet looms or rapier looms or projectile looms. These looms are distinguished by weft insertion method, which is briefly discussed hereunder.
These types of looms adopt the latest development in Weaving Technology where weft insertion is done with the help of compressed air. A very high weft insertion rate up to 1800 metre per minute is achieved. Compared to rapier and projectile looms, these looms are less versatile but are economical and are used in mass textile production unit like denim.
a. Grey Fabric
The finally woven fabric or Grey Fabric, as it is popularly called, wound on a cloth roll is taken out from weaving machines at certain intervals and checked on inspection machines for possibilities of any weaving fault. If such faults are seen anywhere in fabric during inspection, certain corrective steps are taken at weaving, warping, sizing, etc so that they can be minimised in subsequent product. This is a quality control exercise.
b. Denim Fabric
Denim Fabrics woven of 100% cotton would be very strong and durable.
Traditionally Blue Denim is warp faced cotton fabric with 3 x 1 twill construction with warp being dyed in a solid colour and weft left un-dyed. The look and quality of the Denim Fabric shall improve after dyeing, the process of which differs from plant to plant. Normally the process of dyeing dictates the technology of Denim manufacturing.
The dyeing for Denim Fabric happens at the sizing stage. Generally there are two most popular methods of dyeing Denim Fabric. They are:
o Rope Dyeing
o Sheet Dyeing
A company can adopt any of the methods. In countries like India Sheet Dyeing Method is commonly used for manufacture of its Denim Fabrics, which has following advantages over Rope Dyeing Method:
o The technology is less capital intensive.
o The technology is a proven one.
o The cost of production is lower.
o The process time is lower.
o The Sheet Dyeing machines are very easy to operate.
c. Sheet Dyeing Process
This process eliminates a few intermediate processes of the rope dyeing. The yarn sheet is washed with chemicals such as caustic and washing soda and after squeezing the excess water; the yarn sheet is allowed to pass through Dyeing Troughs one time for oxidation and development of dye on yarn. After dyeing, the dyed yarn is washed again with fresh water for two-three times and finalIy squeezed before allowing it to pass through six drying cylinders. The dyed yarn enters the starching device and sizing is done. After sizing, the sized warp beam goes for weaving. After weaving, the woven Denim Fabrics goes for various finishing processes consisting of brushing, singeing, washing, impregnation for dressing and drying. Brushing and singeing should eliminate impurities and help to even the surface of the fabric. Dressing regulates the hand and rigidity of the fabric while compressive shrinking regulates its dimensional stability.
Even today Denim Fabric without Indigo Dyeing is not called authentic Denim. Initially when Denim Fabric entered the fashion market, Denim manufacturers were using Natural Indigo Dye, which was costly and giving a natural finish. Though Synthetic Indigo Dye has gradually replaced Natural Indigo Dye, some unorganised manufacturers still prefer the latter and attract premium after branding them “Natural Dye Used”.
Weaving of fabrics on such multi sizes is not economical, hence a standard width fabrics is then sent to making up. Fabrics are cut into the desired width as per size required on this machine. Denim Fabric and Grey Fabric are thoroughly checked for various types of defects such as:
o Weaving Defects
· Uneven Dyeing
o Bleaching and Dyeing Defect
o Oil Stain
Here the final product is categorised quality-wise. The products then found okay are segregated and sent to packaging department whereas defective ones are sent for correction. After inspection, the sets are wrapped with polythene covers and sent for despatch as per buyer’s specifications.
Rolls and sets so formed and packed as per buyers’ requirements are then sent for final despatches.