Controlling Centre-to-Selvedge Colour Variation in Sheet Dyeing of Denim

In denim manufacturing, colour variation is one of the most visible and commercially sensitive problems. A small shade difference that may look harmless on dyed yarn can become very obvious after weaving, garment washing and finishing.

Among the different types of shade variation, one important problem in sheet dyeing or slasher dyeing is centre-to-selvedge colour variation. This happens when the yarns in the centre of the warp sheet dye slightly differently from the yarns near the two selvedges.

After weaving, this may show as darker or lighter bands running lengthwise in the denim fabric. In garment form, it may further become visible as panel-to-panel shade difference, side shading, streakiness or inconsistent washing response.

The problem is not caused by one factor alone. In sheet dyeing, centre-to-selvedge variation is usually born at the intersection of three controls: liquor pick-up, warp-sheet mechanics and indigo bath chemistry.

Central idea: In sheet dyeing, shade is not controlled only by the dye recipe. Shade is controlled by the complete process — yarn preparation, liquor pick-up, nip pressure, tension, oxidation, washing and monitoring.

Table of Contents

1. What is centre-to-selvedge colour variation?
2. Why sheet dyeing is sensitive to this problem
3. Main causes of centre-to-selvedge shade variation
4. How to control centre-to-selvedge variation
5. Practical troubleshooting table
6. A practical control plan for mills
7. Conclusion
8. General disclaimer

What is centre-to-selvedge colour variation?

In sheet dyeing, warp yarns are spread side-by-side in open sheet form and pass through dye boxes, squeeze rollers, oxidation zones and sizing units. Ideally, every yarn from the left selvedge to the right selvedge should receive the same dyeing treatment.

In practice, the centre yarns and edge yarns may not behave exactly alike. Centre-to-selvedge variation means that the yarns near the centre of the sheet show a different depth, tone or brightness compared with the yarns near the selvedges.

The difference may be visible immediately after dyeing, but sometimes it becomes clearer only after weaving, finishing or garment washing. This is especially important in denim because washing partly removes and modifies the indigo surface, making earlier shade differences more visible.

Denim is a highly visual fabric. The indigo shade is not only a colour; it is part of the identity of the fabric. Buyers expect a controlled blue, black, grey, sulphur-bottom or topping shade. Any side-to-side difference reduces the acceptability of the fabric.

Why sheet dyeing is sensitive to this problem

In rope dyeing, warp yarns are gathered into ropes, dyed, oxidised and later opened during long-chain beaming. Because the yarns are rearranged during subsequent processing, some shade variation may get distributed.

In sheet dyeing, however, yarns remain in sheet form. The position of the yarn across the width is more directly related to its final position in the fabric. This makes sheet dyeing efficient and compact, but it also makes it more sensitive to width-wise variation.

If the left edge, centre and right edge do not receive the same liquor pick-up, pressure, tension, immersion or oxidation, the variation can directly appear in the woven denim. In simple words, sheet dyeing gives less room to hide width-wise mistakes.

Main causes of centre-to-selvedge shade variation

1. Uneven nip pressure across the width

The padding or squeezing system is one of the most important areas to examine. When yarns come out of the dye box, the squeeze rollers control how much dye liquor remains on the yarn. If nip pressure is not uniform across the full width, liquor pick-up will also not be uniform.

If the centre pressure is higher, the centre yarns may carry less liquor. If the edge pressure is higher, the selvedge yarns may carry less liquor. In both cases, the shade can change across the width.

This may happen because of roller deflection, roller hardness variation, poor roller grinding, incorrect loading, worn bearings, improper alignment or uneven pneumatic or hydraulic pressure. The problem may become more serious on wider machines because roller deflection becomes more difficult to control.

The first rule of centre-to-selvedge control is therefore simple: do not blame the dye before checking the padder or squeeze roller.

2. Variation in liquor pick-up

In indigo sheet dyeing, liquor pick-up determines how much reduced indigo solution is carried by the yarn before oxidation. Any variation in pick-up becomes a variation in available dye.

Liquor pick-up can vary due to nip pressure, yarn absorbency, yarn tension, bath level, viscosity, wetting, foam, contamination or uneven yarn sheet density. Even if the dye bath recipe is correct, poor pick-up control can still produce shade variation.

Liquor pick-up may be expressed as:

\[ \text{Liquor Pick-up \%} = \frac{\text{Wet Weight} - \text{Dry Weight}}{\text{Dry Weight}} \times 100 \]

A practical mill should not depend only on visual judgement. Width-wise pick-up should be checked at the left selvedge, left-middle, centre, right-middle and right selvedge. If the values are not consistent, shade variation is almost expected.

3. Uneven warp tension across the sheet

Warp-sheet tension is another major factor. If some sections of the sheet are tighter than others, the yarns may pass through the bath, squeeze rollers and oxidation zone differently.

Higher tension may flatten the yarn, reduce penetration, alter squeeze-out and change the way the yarn opens during oxidation. Lower tension may allow the yarn to carry more liquor or behave differently at the nip.

Uneven tension can also create small differences in yarn path, contact angle and residence time. Centre-to-selvedge variation should therefore be investigated together with tension variation.

The sheet should enter the dye box evenly and should not show slack edges, tight centre, uneven spreading, crowding or bowing.

4. Uneven wetting and pre-treatment

Before indigo dyeing, cotton warp yarn must be properly prepared. Cotton contains natural waxes, pectins, oils, size residues and other impurities. If these are not removed uniformly, the yarn will not absorb dye liquor uniformly.

Poor wetting is especially dangerous in sheet dyeing. If the centre yarns wet more slowly than the selvedge yarns, or if the selvedge yarns contain more residual wax or size, the dye uptake will differ.

Trapped air in yarns can also reduce liquor contact and create uneven dyeing. Good pre-scouring, wetting-agent control, washing and yarn absorbency testing are therefore essential.

In many mills, the dyeing department tries to correct shade variation that actually started in preparation.

5. Indigo bath instability

Indigo is not applied like many other dyes. It must first be reduced into a soluble leuco form so that it can enter or deposit on the cotton yarn. After dipping, the yarn is exposed to air, where the reduced indigo oxidises back to its insoluble blue form.

Because of this chemistry, the final shade is affected by several variables: indigo concentration, caustic level, reducing-agent level, pH, oxidation-reduction potential, temperature, immersion time, number of dips, oxidation time and wetting agent.

If the bath is unstable, the shade may vary over time. But if bath circulation is poor across the width, or if chemical distribution is not uniform, width-wise variation can also appear.

In a good denim range, indigo bath control should not be based only on recipe addition. The mill should monitor pH, redox condition, temperature, circulation, bath level and concentration at regular intervals.

6. Non-uniform oxidation or skying

After each dip, indigo needs controlled oxidation. Oxidation develops the blue colour and influences brightness, tone and fastness. If oxidation is incomplete or uneven, the shade will vary.

In sheet dyeing, the centre and edge portions of the sheet must receive similar exposure to air. Variation in airflow, sheet spreading, roller path, moisture level or dwell time can create width-wise differences.

If the centre portion remains wetter or less exposed, oxidation may be different from the selvedge portions. Indigo dyeing is not only a dipping process; it is a repeated dip-and-oxidise process.

7. Edge effects and selvedge behaviour

The selvedge side of the warp sheet often behaves differently from the centre. Edge yarns may experience different airflow, drying, tension, guiding pressure or contact with machine elements.

They may also be more exposed to side evaporation, splash, dripping or mechanical disturbance. In some cases, the selvedge becomes lighter because it carries less liquor or oxidises differently.

In other cases, it becomes darker because of higher liquor retention or local accumulation. The exact direction of shade difference depends on the process condition.

Therefore, the question should not be only “Why is the selvedge lighter?” or “Why is the centre darker?” The better question is: Which width-wise process variable is different at that position?

How to control centre-to-selvedge variation

1. Start with width-wise measurement

The first correction is measurement. The mill should build a habit of checking left, centre and right positions. Ideally, five positions should be used: left selvedge, left-middle, centre, right-middle and right selvedge.

At each position, the mill can check shade, liquor pick-up, pH, moisture, tension and yarn appearance. For shade, visual assessment should be supported by spectrophotometer readings wherever possible.

A small colour difference may become commercially significant after garment washing. The colour difference can be expressed using \(\Delta E\), where:

\[ \Delta E = \sqrt{(\Delta L^*)^2 + (\Delta a^*)^2 + (\Delta b^*)^2} \]

Here, \(L^*\) represents lightness, \(a^*\) represents the red-green axis and \(b^*\) represents the yellow-blue axis. Without width-wise data, the discussion remains subjective.

2. Check padder and squeeze roller condition

The padder or squeeze roller system should be checked for uniformity across the width. Important checks include roller hardness, roller surface condition, roller grinding accuracy, nip impression, pressure balance, loading system, bearing condition and roller parallelism.

A simple carbon paper or nip impression test can sometimes reveal what the eye cannot see during running. If the nip is not uniform, the shade cannot be expected to remain uniform.

For wider machines, deflection-controlled or specially designed padders are especially useful because normal rollers may bend under pressure, creating different squeezing behaviour at the centre and edges.

3. Standardise liquor pick-up

Liquor pick-up should be treated as a critical process parameter. It should be measured and recorded, not assumed. If the target pick-up is 70%, the left, centre and right should not show large deviations.

Pick-up control depends on nip pressure, machine speed, yarn absorbency, bath temperature, wetting-agent level, yarn tension, bath level and roller condition. Whenever centre-to-selvedge variation is noticed, pick-up testing should be one of the first diagnostic steps.

4. Maintain uniform warp-sheet tension

The warp sheet should run flat, straight and evenly spread. The machine operator should check whether the sheet is tighter at the centre, looser at the edges, or unstable during running.

Important controls include uniform let-off tension, correct guiding, proper sheet spreading, avoidance of slack selvedges, equal loading across beams, proper alignment of guide rollers and avoidance of yarn crowding or overlapping.

If the sheet itself is mechanically unstable, dyeing uniformity becomes difficult.

5. Improve pre-treatment and wetting

Before dyeing, the yarn should be uniformly absorbent. A simple drop test or absorbency test across width can reveal whether the preparation is consistent.

Good preparation includes removal of wax and impurities, removal or control of previous sizing materials, proper wetting, control of water hardness, effective washing, avoidance of oil or grease contamination and prevention of trapped air.

If yarns do not wet evenly, they cannot dye evenly.

6. Control indigo bath chemistry

The indigo bath should be controlled for concentration, pH, caustic, reducing agent, redox potential, temperature and bath circulation. Operators should avoid large corrections made only after shade variation becomes visible.

A stable bath gives the process a stable base. But stability should mean both length-wise and width-wise stability. The bath should be well circulated, and chemical additions should be properly mixed before they affect the yarn sheet.

Important controls include regular pH checking, ORP monitoring, indigo concentration control, hydrosulphite or reducing-agent control, caustic control, temperature control, foam control, bath level control, filtration and circulation.

7. Ensure uniform oxidation

Oxidation should be uniform across the full sheet width. The yarns should not be crowded, stuck together or unevenly spread during skying. Air movement should not favour one side of the sheet.

Important checks include adequate skying length, uniform airflow, proper yarn separation, consistent machine speed, avoidance of wet patches, no side dripping and stable roller path.

The shade after indigo dyeing is not created inside the dye box alone. It is created by repeated dipping and oxidation. If oxidation is uneven, the shade will also be uneven.

8. Use left-centre-right shade control after washing

Indigo shade should be assessed after proper washing and drying, not only in the wet state. Wet yarns and wet fabric can mislead the eye.

A proper comparison should be done under standard light conditions after the sample reaches a stable state. For better control, mills may maintain a record of left-centre-right shade reading, \(\Delta E\), K/S value, pick-up percentage, bath pH, ORP value, machine speed, nip pressure, oxidation length, lot number and beam number.

Practical troubleshooting table

Observed problem	Possible cause	What to check first	Corrective action
Centre darker than selvedge	Higher pick-up at centre or lower squeeze pressure at centre	Nip impression and pick-up test	Correct roller pressure, alignment or deflection
Selvedge darker than centre	Higher pick-up at edges or edge liquor accumulation	Edge yarn wetness and squeeze condition	Check edge pressure, dripping and guiding
One side darker than the other	Left-right pressure imbalance or poor machine alignment	Left vs right nip and tension	Balance pressure and align rollers
Shade changes after every few hundred metres	Bath instability or poor chemical dosing	pH, ORP, indigo concentration	Stabilise dosing and circulation
Variation increases after washing	Uneven ring dyeing or oxidation	Oxidation and washing uniformity	Improve skying and washing control
Random bands across width	Yarn preparation or absorbency variation	Width-wise absorbency test	Improve scouring and wetting
Thick counts show more variation	Poor penetration and higher sensitivity to tension or pick-up	Count-wise process settings	Adjust dip time, wetting, pressure and speed

A practical control plan for mills

A mill can control centre-to-selvedge variation through a simple but disciplined routine. First, check the machine. The padder, squeeze rollers, guide rollers and tension system should be mechanically sound.

Second, check the yarn sheet. The sheet should run evenly from left to right. There should be no crowding, slack edges, tight centre, broken yarn disturbance or uneven spreading.

Third, check liquor pick-up. Measure it across the width. Do not assume that the centre and selvedge are carrying the same amount of dye liquor.

Fourth, check bath chemistry. Maintain pH, reducing condition, temperature, dye concentration and circulation within the required range.

Fifth, check oxidation. Ensure that the yarn sheet gets uniform exposure to air after every dip.

Sixth, check shade with data. Use left-centre-right readings, \(\Delta E\), K/S values and proper production records.

Related Reading on Dyeing, Cotton Yarn Quality and Textile Processing

• Direct Dyeing vs Reactive Dyeing: A Technical, Economic and Ecological Comparison
• Optimising Cotton Yarn Quality Through Raw Material Parameters
• Mercerization: The Midas Touch That Makes Cotton Shine
• Textile Finishing

References and Further Reading

1. Xin, J. H., Chong, C. L., & Tu, T. M. (2000). Colour variation in the dyeing of denim yarn with indigo. Coloration Technology, 116, 260–265. View source
2. Cotton Incorporated. Open Width Pad-Batch Dyeing of Cotton Fabrics, Technical Bulletin TRI 3007. View source
3. EFI Mezzera. Indigo Dyeing and Finishing Ranges / Denim Line Brochure. View source
4. Textile Commissioner, Government of India. Semi-continuous Openwidth Dyeing Machines. View source
5. Paul, R. (Ed.). (2015). Denim: Manufacture, Finishing and Applications. Woodhead Publishing / Elsevier. View source

Conclusion

Centre-to-selvedge colour variation in denim sheet dyeing is not a mysterious defect. It is usually the visible result of invisible process differences across the width of the warp sheet.

The most important causes are uneven nip pressure, unequal liquor pick-up, non-uniform tension, poor wetting, unstable indigo chemistry and uneven oxidation. Among these, nip pressure and liquor pick-up deserve special attention because they directly decide how much dye liquor each yarn carries.

In sheet dyeing, the yarns remain spread in open-width form. This gives the process speed, compactness and flexibility, but it also makes width-wise control critical. A well-controlled sheet dyeing range must therefore be managed not only from lot to lot, but also from selvedge to centre to selvedge.

The best approach is not to correct shade variation after it appears, but to prevent it through systematic control of machine condition, yarn preparation, bath chemistry, oxidation and left-centre-right monitoring. In denim, shade is not only a recipe. Shade is a result of the whole process.

General Disclaimer

This article is for educational and general textile knowledge purposes only. Actual denim dyeing results depend on yarn quality, cotton fibre properties, machine design, indigo chemistry, reducing system, process route, water quality, operator skill, maintenance condition, testing method and buyer requirements.

Mills should validate all process changes through laboratory trials, pilot runs and controlled bulk trials before implementing them in commercial production. The author does not accept responsibility for production losses, shade rejections or process failures arising from direct application of this educational material without mill-specific technical verification.

Buy my books at Amazon.com

Some Notes on Denim Washing

There are four main processes in the Denim washing

- Pretreatment

- Stone or Enzyme Wash- To adjust the surface effect

- Bleaching- To adjust the color

- Finishing- To adjust the handfeel of the garment

Pretreatment involves removal of impurities from the garments and desizing the garment. It also involves prevention of creases in the garment. Wetting Dispersing agent is used in desizing process. It should be able to rapidly wet the jeans so that it can prevent white lines of creases and prevents back staining. Back staining is the redeposition of indigo dyed short fibers, or loose indigo, removed during desizing, stone-washing or enzyme washing. Backstaining reduces the contrast of warp and undyed weft. It also stains pockets and labels and it is more prone ot ozone and yellowing. An anticrease agent is added to prevent crease formation during the washing process. 

Enzyme in garment Industry

Enzyme is a kind of protein. They help the chemical reaction but themselves do not take part in chemical reaction. The starting molecule in a reation is called substrate and the yield molecule is called substate. Enzymes and substrate work like lock-key model so only one enzyme is useful for one type of substrate. Enzymes are better than chemical catalyst because they act in mild conditions such as room temperature. They are also biodegradable. Many enzymes are used in garment washing. An enzyme called Amylase is used in removing starch in desizing. Celullase is used in breaking and removing cellulose fibers. Laccase is used in biobleaching and catalase is used as an anti peroxide. 

Stone and Enzyme Wash

Cellulase weaken the surface fibers which are then mechanically torn off during processing, taking with them indigo. However, they need mechanical action to work. Hence they are used with stones. Cellulase is also used in biopoloshing, which removes surface fibers and make the surface smooth. 

Bleach 

Laccase enzyme decolorises indigo without using bleach. It provides very good contrast and since it attacks only indigo dye and not the fiber so it gives excellent tensile strength. 

Yellowing

The discolouration of textiles, i.e. a change of shade or loss of whiteness, giving a yellow tint, is commonly known as YELLOWING.Yellowing is due to many reasons. Cotton, yellows with age. However aging cannot make severe yellowing happen. Certain lubricants used in weaving and knitting can cause yellowing. The Anti oxidants present in these oils can cause a type of yellowing called as phenolic yellowing. The anti oxidants are also present in packaging materials and silicon softeners. Also temperature of drying and curing during processing can scorch the fibers and cause yellowing. 

Indigo dyed fabrics are more prone to yellowing. Indigo when exposed to NOx or Ozone can produce yellow colored compounds. Indigo itself through simple oxidation can transform into yellow colored compounds. 

There are specialised anti-yellowing softeners available. This work by either forming a protective filem, or by reacting the pollutants to form colorless compounds.

The source of these notes this presentation. This also contains images and chemical reactions. You can also view images of various denim washes here. One more resource is here.

Now that you've finished reading this post, what are you going to do? You should join the Forum.

Denim Produced from Your Torn Jeans

There is a patent document which claims that the denim fabric can be produced from waste denim yarn. In this fabric 40%-100% of waste fiber is used. To reclaim the waste fiber, the fabric is subjected to garnetting and low tension carding, before spinning it in the form of yarn and using it to weave fabric.

The only thing remains to be seen is the techno-commercial viability of such product. Garnetted fibers produce problems in carding, drawframe and posisbly in high speed weaving. Though it is claimed that such a denim will have adequate strength, it will remain a challange. It is suggested that some virgin fiber should be added in the garnetted fiber or it is subjected to some lubrication before spinning. All this will lead to increase in process cost.

Neverthless, this is a good news for your torn denim jeans which can now be recycled into a new one without damaging the environment. Just give your jeans to the local rag picker and it will eventually find itself into a new jeans. However, if you don't want to part away with your jeans, here are the instructions what you can do with them. Of course, there are 25 other ways to make use of your old jeans.

Worldwise, concerns are growing reagarding using the denim waste. A project making the use of denim shoddy is one of such cases. It is being used in myriad ways including its use in oil filters. Successful attempts have been made to make paper out of denim wastes.

Note: Garnetting is a process by which material such as threads, rags, woven cloth scraps, and the like are broken up and returned to a substantial fluffy, fibrous condition simulating the original condition of the fiber. This is done by first chopping the material to small pieces (e.g. two to six inches) and then running the pieces through a series of high speed cylinders which can be covered with wire (e.g. saw wire), steel spikes, or the like. The treatment breaks up the material into individual fibers typically having a length of one and one-eighth inches or less.

Tsudakoma ZAX- Settings for standard Denim

Tsudakoma-ZAX Loom Settings for 14.5 Oz/Sq yd OE/OE Denim (EPI x PPI = 64 x 37) count (6s x 7s)


Back Rest- 125 mm (vertical)
-16th mark ( horizontal)

Dropper Box- 100 mm (vertical)
- 50 mm (vertical)

Shedding Amount

1st Frame- 99 mm
2nd Frame-91mm
3rd Frame- 83 mm
4th Frame- 75 mm

Heald Frame Height:

1st Frame - 43 mm
2nd Frame-41mm
3rd Frame-39mm
4th Frame- 37mm

Shed Crossing Timing- 290 deg

Leno Crossing Timing- 290 deg ( LH Side), 0 deg ( RH side)

Temple- 15 rings- Medium Type

Sub Nozzle angle- 4 deg
Sub nozzle height- 3rd Mark
Machine Pulley- 220 mm
Motor Pulley- 113 mm for 760 rpm

iboard Settings

Tension- 280 kgf
Upper Limit- 560 kgf
Lower Limit- 0 kgf
Pick Density- 37 pick
Turns/Pick- 4
Arrvial setting - 240 deg
Filling insertion timing- 80 deg
No. of Sub groups- 5

Timing

Feeler H1- 200 deg to 290 deg
H2- 200 deg to 310 deg
Forward- 350 deg
Rev (others)- 180 deg/320 d eg
(Filling)- 290 deg
WBS- 240deg-300deg

SENSOR/TROUBLE
Dropper Setting: 10 th Volume
Sensor- on
Feeler-on
Timing

Pin: 50deg-200 deg
Main: 50deg-200deg
AUX Main: 60deg-100deg
80deg

Auxiliary Nozzle- 76 deg-176 deg
1st Pick- 86 deg

Sub Nozzle

64deg-170 deg
100deg-190deg
130deg-220deg
150deg-230deg
170deg-250deg

Stretch Nozzle- 200deg-300deg

STOP MARK Data

1. F Kick ( Filling) - 0 upto 7 steps
2. F Kick (Others)- 0 upto 7 steps
3. R Kick ( Filling)- 0 upto 7 steps
4. R Kick (Others) - 0 upto 7 steps
5. Kick Back Speed- 1. Low 2, Medium 3, High On
6. Kickback order- on 1

1. Rev to Forward
2. Forward to Rev

7. Down time- 5 min
8. Fell Control-8
9. Dia Comp-48
10. Let Off Avg-2
11. F-Gain-0
12. R.Gain- 0

13. Gain -1
1. Low
2. Medium
3. High

14. Rush Torque- 1200%
15. change Picks-2
16. Change timing- 30 deg
17. 1 pick insertion- On
18. Autolevelling- On

Critical Process Parameters- Denim Manufacturing

Critical Process Parameters- Denim Manufacturing

Warping:

Machine Speed m/min= 600+-50
Tension on individual thread ( cN) 90+-30
Warping breaks ( Avg/10000m/400 ends) < = 0.2

Dyeing-cum-Sizing

1. Machine Speed = 30+-2
2. Size Viscosity ( Flow seconds) = 6+-1
3. Size Add on ( %)= 6+-2
4. Breaking Force (gf) sized yarn = >=1100
5. Tenacity ( cN/tex) ( sized yarn) = >13
6. Elongation ( %) of sized yarn >= 4.5

Finishing

Quality	7 x 6	7 x 6	7 x 7	7 x 9	7 x 6
Width(cm)	151+-1	149+-1	151+-1	151+-1	151+-1
Shrinkage ( %)	15+-1	14.5+-1	15.5+-1	16+-1	14+-1
Skew ( %)	5-11	5-11	5-11	5-11	5-11

Finished Properties of some Common Denim Fabrics

Finished Properties of Common Denim Fabrics: Understanding Weight, Yarn Count, Construction and Fastness

Denim is one of the most widely used fabrics in garments, especially for jeans, jackets, skirts, children’s wear and casual apparel. Although denim is often identified by its appearance, shade and wash effect, the real performance of denim depends on measurable fabric properties such as weight, yarn count, ends per inch, picks per inch, rubbing fastness and laundering fastness.

The original note listed finished properties for three common denim fabrics with ideal weights of 14.5 oz/sq yd, 13.75 oz/sq yd and 12.5 oz/sq yd. These values are useful because denim is often commercially discussed by weight category, but weight alone does not tell the full story. A merchandiser, fabric buyer or production person must also understand the relation between yarn count, fabric construction and finished performance.

Table of Contents

• Why Finished Denim Properties Matter
• Comparative Finished Properties of Common Denim Fabrics
• Understanding Fabric Weight in Denim
• Role of Warp and Weft Count
• EPI and PPI: Fabric Construction
• Rubbing Fastness and Laundering Fastness
• Practical Notes for Merchandisers
• Common Mistakes in Reading Denim Specifications
• Conclusion

Why Finished Denim Properties Matter

In denim manufacturing, the fabric that comes out of weaving is not the same as the fabric finally used in garments. Denim passes through finishing operations such as singeing, desizing, washing, sanforizing, softening, skew correction and sometimes special chemical or mechanical treatments. These processes change the fabric’s handle, dimensions, shrinkage, shade appearance and apparent fabric weight.

Therefore, when we say that a denim fabric is 14.5 oz, 13.75 oz or 12.5 oz, we should be clear whether we are talking about greige weight, finished weight or washed weight. Finished properties are especially important because the garment buyer and consumer experience the fabric after finishing, not at the loom stage.

Visual 1: Denim fabric properties map showing how weight, count, construction and fastness affect final performance.

Comparative Finished Properties of Common Denim Fabrics

Property	Heavy Denim	Medium-Heavy Denim	Medium Denim
Ideal Weight	14.5 oz/sq yd	13.75 oz/sq yd	12.5 oz/sq yd
Warp Count, Washed	6.9 ± 0.6	6.9 ± 0.5	6.9 ± 0.5
Weft Count, Washed	6.0 ± 0.4	6.9 ± 0.5	9.0 ± 0.5
EPI, Unwashed	70 ± 2	70 ± 2	70 ± 2
PPI, Unwashed	43 ± 2	43 ± 2	43 ± 2
Actual Weight	14.2 oz/sq yd	13.4 oz/sq yd	12.2 oz/sq yd
Rubbing Fastness, Dry	2–3	2–3	2–3
Fastness to Laundering	2	2	2

This small table contains an important technical lesson. The three fabrics have almost the same warp count, EPI and PPI, but the weft count changes. This means that the weight difference is mainly controlled through the weft yarn, while the face character of the fabric is kept broadly similar.

Understanding Fabric Weight in Denim

Fabric weight in denim is commonly expressed in ounces per square yard. Heavier denim generally feels thicker, stronger and more rigid, while lighter denim feels softer, more flexible and easier to wear in warm conditions. A 14.5 oz denim is usually perceived as a heavy and rugged fabric, while a 12.5 oz denim is closer to a medium-weight commercial denim.

Denim Weight	Practical Meaning	Typical Use
Around 14.5 oz	Heavy denim	Rugged jeans, workwear-inspired garments, structured bottoms
Around 13.75 oz	Medium-heavy denim	Regular jeans, casual bottoms, durable apparel
Around 12.5 oz	Medium denim	Comfortable jeans, fashion denim, lighter casual wear

In the data, the actual finished weights are slightly lower than the ideal weights. For example, the 14.5 oz fabric shows an actual weight of 14.2 oz/sq yd, while the 12.5 oz fabric shows 12.2 oz/sq yd. Such differences can occur because of yarn variation, weaving tension, finishing loss, moisture content and process conditions.

Role of Warp and Weft Count

The warp yarn count remains nearly the same in all three fabrics, around 6.9 Ne. This suggests that the main difference between the three denim qualities is not coming from the warp yarn, but from the weft yarn. The weft count changes from 6.0 Ne in the heavier fabric to 9.0 Ne in the lighter fabric.

In the English cotton count system, a lower count number means a coarser yarn. Therefore, 6s weft is coarser than 9s weft. This explains the weight difference clearly:

\( \text{Coarser weft yarn} \Rightarrow \text{more yarn mass per unit area} \Rightarrow \text{heavier denim} \)

\( \text{Finer weft yarn} \Rightarrow \text{less yarn mass per unit area} \Rightarrow \text{lighter denim} \)

This is a useful point for merchandisers. If EPI and PPI remain almost constant, but fabric weight changes, the change is often due to yarn count, especially weft count.

Visual 2: Relationship between weft count and denim weight, showing why coarser weft gives heavier fabric.

EPI and PPI: Fabric Construction

The construction shown in all three fabrics is approximately 70 × 43. This means that the fabric has about 70 ends per inch in the warp direction and about 43 picks per inch in the weft direction. Since EPI and PPI are the same across all three fabrics, the construction density remains largely unchanged.

EPI stands for ends per inch, or the number of warp yarns in one inch of fabric width. PPI stands for picks per inch, or the number of weft yarns in one inch of fabric length. In the given case:

\( \text{EPI} = 70 \pm 2 \)

\( \text{PPI} = 43 \pm 2 \)

This is a good example of how fabric properties should be read together. Looking only at fabric weight may not explain the reason for the difference. Looking at weight, yarn count and construction together gives a much clearer technical understanding.

Why Warp Count is Similar but Weft Count Changes

In conventional denim, the warp yarn is usually indigo dyed, while the weft yarn is generally undyed or lightly coloured. The warp gives denim its characteristic blue appearance, while the weft contributes strongly to weight, handle and body.

Keeping the warp count similar helps maintain a consistent denim appearance and surface character. Changing the weft count allows the manufacturer to create different weights without drastically changing the face appearance of the fabric. This is why three fabrics can look similar at first glance but behave differently in hand feel, stiffness and garment comfort.

Rubbing Fastness and Laundering Fastness

The dry rubbing fastness given for all three fabrics is 2–3. This indicates that colour transfer during rubbing is a concern. In denim, this is especially important because indigo dye is mainly present on the surface of the yarn rather than deeply penetrating the fibre.

A dry rubbing fastness rating of 2–3 means that some colour transfer may occur when the fabric rubs against another surface. This may appear as blue staining on light-coloured shirts, shoes, bags, upholstery or inner pocketing. For the merchandiser, this means care instructions and buyer expectations should be handled carefully.

The laundering fastness is shown as 2 for all three fabrics. This means that the fabric is likely to lose shade during washing. In denim, this is not always considered a defect because fading is often part of the desired denim character. However, from a quality-control perspective, this rating must be interpreted according to the buyer’s requirement.

Visual 3: Denim fastness performance map showing rubbing fastness, laundering fastness and consumer risk points.

Relationship Between Weight, Comfort and Durability

Heavier denim usually gives better body and ruggedness, but it may feel stiff and warm. Lighter denim gives better comfort and flexibility, but may not have the same rugged appeal. Medium-weight denim often becomes the commercial balance between durability and wearability.

Fabric Weight	Advantages	Possible Limitations
Heavy denim	Strong body, rugged look, durable feel	Stiffer, warmer, slower to break in
Medium-heavy denim	Good balance of strength and comfort	May still feel firm before washing
Medium denim	Softer, easier to wear, better drape	Less rugged appearance than heavy denim

Simple Weight Calculation Concept

A simplified fabric weight relationship can be understood as:

\( \text{Fabric Weight} \propto \text{Yarn Linear Density} \times \text{Fabric Density} \)

In practical terms:

\( \text{Weight} \approx f(\text{Warp Count}, \text{Weft Count}, \text{EPI}, \text{PPI}, \text{Crimp}, \text{Finishing}) \)

This means that the final denim weight is influenced by both yarn size and construction. In the present example, because EPI and PPI are constant, the difference in weight is largely explained by the difference in weft count.

Practical Notes for Merchandisers

A merchandiser should not approve denim only by looking at the weight. Two denim fabrics with the same weight can behave differently if the yarn count, twist, fibre quality, weave compactness, finishing route or shrinkage control is different.

Checkpoint	Why It Matters
Finished weight	Determines body, feel and product category
Warp and weft count	Explains yarn thickness and fabric mass
EPI and PPI	Indicates fabric density and construction stability
Rubbing fastness	Shows risk of colour transfer
Laundering fastness	Shows expected wash-down behaviour
Shrinkage	Critical for garment fit
Skew and bow	Important for leg twisting in jeans
Handle and stiffness	Affects consumer comfort
Shade consistency	Critical for bulk approval

Common Mistakes in Reading Denim Specifications

One common mistake is to assume that heavier denim is always better. This is not true. Heavy denim may be unsuitable for hot climates, fashion silhouettes or comfort products. Another mistake is to compare denim fabrics only by ounce weight without checking construction.

A third mistake is ignoring rubbing fastness. Denim may pass visual inspection but still create complaints if it stains other garments or accessories. Similarly, laundering fastness must be understood according to the intended wash effect. In denim, fading can be either a defect or a design feature, depending on the product brief.

Buyer’s Interpretation of the Given Data

The data suggests that the three denim fabrics are constructed with a similar warp system and similar fabric density. The main adjustment is in the weft yarn count, which changes the fabric weight. The heaviest fabric uses the coarsest weft yarn, while the lightest fabric uses the finest weft yarn.

The fastness ratings are similar across all three fabrics, which means that changing the weight has not significantly improved or reduced rubbing and laundering fastness. This is important because fastness depends more on dyeing, washing and finishing conditions than on weight alone.

Knowledge Nugget

In denim, the blue character comes mainly from the warp, but the body of the fabric is strongly influenced by the weft. Therefore, two denim qualities can have a similar face appearance but different weight and handle because of the weft yarn.

Conclusion

The original table is small, but it contains a useful technical lesson. Denim weight is not an isolated property. It is connected with yarn count, fabric construction and finishing. In the given examples, all three fabrics have nearly the same EPI, PPI and warp count, while the weft count changes. This change in weft count explains the difference between heavier and lighter denim fabrics.

For a merchandiser, this type of specification is very valuable. It helps in understanding why a fabric feels heavier, why one denim quality may feel more rigid, and why fastness ratings must be checked even when the construction looks acceptable. A good denim evaluation should always combine measurable data with hand feel, shade behaviour, washing performance and final garment requirement.

Related Reading on Denim, Fabric Construction and Finishing

• Some Notes on Denim Washing
• Critical Process Parameters- Denim Manufacturing
• Manufacturing Process of Denim
• How to calculate the weight of Fabric
• Count, Construction and Width of common Cotton Fabrics

General Disclaimer

This article is intended for educational and practical understanding of textile and denim concepts. Actual fabric properties may vary depending on fibre quality, yarn type, spinning method, weaving conditions, dyeing process, finishing route, testing method and buyer specification. Readers should verify production decisions with mill technologists, testing laboratories, buyer standards and applicable textile testing methods before applying these values commercially.

Denim of Polyester Cotton Blend

In such denims, the polyester used in warp is kept low about 20-25%, because the blend is harder to dye than cotton . Polyester can be used in much higher percentage in filling. It has the advantage of being strong, durable and even in appearance.

Receipes for different shades of Denim

Receipes For Different Shades on Denim


A) Black-on-Black
Black-on-Blue

Recipe

Liquid Sulphast Black= 200 gpl
Sodium Sulphide= 20 gpl
Sandozol HSI = 10 gpl
Soda Ash= 10 gpl

B) Blue-on- Blue

Receipe

Liquid Sulphar Navy Blue = 100 gpl
Liquid Sulphast Black= 50 gpl
Sodium Sulphide= 20 gpl
Sandozol HSI= 10 gpl
Soda Ash= 10 gpl

C) Reactive Series

Receipe

01) Ramazol Turquoise Blue G = 110 gpl
Urea= 100 gpl
Swanic 6L= 10 gpl

02) Sodium Silicate= 250 gpl
Caustic Soda = 10 gpl

Ratio of 01) and 02) = 3:1

D) Ramazol Coffee Brown G

Receipe
01) Coffee Brown G = 100gpl
Urea = 100 gpl
Swanic 6L= 10 gpl

02) Sodium Silicate = 250 gpl
Caustic Soda= 10 gpl

Ratio of 01) and 02) = 3:1

E) Ramazol Parrot Green

Receipe
01) Ramazol Turquoise Blue G = 90 gpl
Ramazol Yellow FG = 40 gpl
Urea= 100 gpl
Swanic 6L= 10 gpl

02) Sodium Silicate = 250 gpl
Caustic Soda = 10 gpl

Ratio of 01) and 02) = 3:1

F) Ramazol Blue

Receipe
01) Ramazol Black B = 70 gpl
Urea = 100 gpl
Swanic 6L = 10 gpl

02) Sodium Silicate = 250 gpl
Caustic Soda = 10 gpl

Ratio of 01) and 02) = 3:1

shrinkage norms for 14.5 oz. denim

Length wise shrinkage--> after 3rd wash---> -1.2% to -2.8%
Width wise shrinkage --> after 3rd wash--> -2.5% to -3.5%

Hard waste % in denim industry

Hard Waste % in Denim Industry

Warping--> 0.7%
Unsized Yarn--> 0.4%
Sized Yarn--> 0.6%
Fringe--> 1.7%

All these  above are percentage of Hacoba Production

Knotting + Reknotting waste --. 0.7%
Extra ends--> 0.7%

All the above are as percentage of loom shed production

Total Hard Waste= 4.8%

warp preparation for rope dyeing-1

Warp Preparation Requirements for Rope Dyeing

Ball Warping: Equipment required to form the rope of yarn. It involves creeling multiple ends of yarn ( Between 350-500 ends) and collecting them into an untwisted rope for dyeing. the rope is wound onto a long cylinder called a log on a machine called as a ball warper.

Some Notes

1. Packages of yarn are preconditioned before ball warping
2. Packages are loaded into the creel ( larger lots- magine transefer creeL0 and smaller lots- swing gate or truck creel
3. Packages are placed on adapters. An adapter support the package of yarn and ensure that the package remains aligned to the tensioning devices. Wooden plug type adapter are most effective as they require least amount of exertion to remove the empty package.

Next Step is threading the tensioner located at each yarn package

1. Post and Disk tensioner. It has two posts mounted onto a flat base. two round disk are placed onto each post. The yarn is threaded between the disk and wrapped around the post. One of the parts is movable so that the angle of wrap can be varied. More tension can be added to the yarn by adding round weights onto the top disk.

Advantages are 1. Inexpnsive 2. does Marginally adequate job of maintaining yarn tension 3. Simple to thread up 4. Low maintenance requirements.

Disadvantages are 1. Yarn has a tendency to jump out from between the disks at the rear of the creel. 2. It is labour intensive- when different tension levels are required. 3. There is more frequency of cleaning up 4. It doesnt control tension well at higher speed.

2. The driven disk tensioner

It also uses twin disk arrangement, however the disks are supported from below- there are no posts. Tension is applied from above- there are weights or spring loaded.
A gear under each pair of disks is matched to another gear mounted on a continuous shaft which runs the length of the vertical tension post. This shaft is connected to a 4 rpm motor which rotates the disk.

Advantage of disk rotation are 1. Thread cutting prevention 2. Dampens out variation due to ballooning action of yarn. There is mor uniform tension 4. Less effor required to change tension levels.

Disadvantages are 1. It is more difficult to thread up, there is more maintenance due to electric motor used and at high speed the tension control is not well.

cotton Characteristics

Cotton

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

FQI= LSW/F

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.

Denim Specification Sheet

Effluent treatment in denim industry

Denim Effluent
Characteristics
-Dark Blue Indigo color
-High Dissolved Solids ( Decomposed products of hydro)
-High Chemical Oxygen Demand (COD)
-High pH
-Chlorides and Sulphates of Suspended matter

Characteristics of Effluent
Appearance: Dark Blue
pH: 9-10
Suspended Solids: 250ppm
Dissolved Solids: 3500-5000 ppm
Oil/Grease: Traces
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
pH= 5.5-9.0
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

1. Equalization
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

3. flocculation
( 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 )

4. Aeration
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.

5. Clarification
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.

Dissolving Oxygen
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.

6. Ultrafilteration
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.

7. Incineration
Burning of waste
Major threat to possible health
Destruction of resources
Expensive
Generate toxins

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.

Integrated Finishing for Denim- my Notes

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.

Temperature

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.
Moisture

- 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.

Pressure

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

d. Duration

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.

Palmer

Function

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

Exit Scary
- 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

Padder- wetting
- 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
Thickness- 67mm

Thicker- more grinding
- cracking
- 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

Balancing of a spinning line for denim Manufacturing

Critical Consumable Item List in Denim Industry

1. Vat Indigo dye
2. NaoH--> flake, lye
3. Na2SO4
4. Dispersing Agent
5. Wetting Agent
6. Potessium persulphate
7. Thin boiling Starch
8. PVA
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

Vendor Rating for Yarn Supplier for Denim

For 7s count

Evaluated at the end of 6 months

Weightage



Quality=50%,Price=30%,Delivery= 20%


I. Quality

CSP
>1900=4, 1800-1899=3, 1700-1799=2, 1600-1699=1, <1599=0>Count CV
0-2.5=2, >2.5=0,

Imperfections( /1000m)

a. Thin places
0-2=5, 3-10=2, >10=0

b. Thick Places
<10=5, 40="2,">40=0

c. Neps
0-2=5, 3-6=2, >6=0

Classimate Results

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

III. Prices

They are determined on a 5-point basis.

Total

>3.8--> Excellent, 3.0-3.8-->Good, 2.0-3.0-->Average, <2-->Poor