1. Management of Quality in Finishing Part 2: Practical Considerations
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2. Define Objectives It is important to distinguish between
Performance Targets
Finishing Control Targets
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3. Performance Targets Are what the customer demands
Fabric weight per unit area
Fabric width
Maximum shrinkage levels
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4. Finishing Control Targets
Are what the finisher has to control in order to guarantee performance
as few as possible
can be measured on-line
Not necessarily the same properties as the performance targets
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5. Choice of Control Targets
Shrinkages can not be monitored directly
Weight is difficult to monitor accurately
Practical control targets are
Fabric Length (course density)
Fabric Width (wale density)
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6. Rule One
It is not practical to control all of the performance targets at the same time
Select two fabric properties - one for length and one for width - and concentrate on them
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7. Confirm Shrinkage Targets
Check customer’s definition of shrinkage
Average or maximum
Line dry or Tumble dry
Expected level of variation
Control can only be in terms of the average
To know the maximum, we need to know the Standard Deviation
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8. Tubular or Open Width?
Experience shows that TUBULAR processing usually gives a better chance of hitting finishing targets
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9. Achieving the Targets
Drying and compacting is where the Finished Dimensions are achieved
Machinery and Technique are decisive
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10. Length Stretching During Knitting
Plain Jersey, Ne 18 to Ne 50 30 25 20
Stretching % 15 10 5 12 13 14 15 16 17 18
Knitted Tightness Factor
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11. Width Stretching During Knitting
Plain Jersey, Ne 18 to Ne 50 30 25 20
Stretching % 15 10 5 12 13 14 15 16 17 18
Knitted Tightness Factor
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12. Fabric Stretching During Preparation
Plain Jersey, Ne 18 to Ne 50 25 20 15 10
Stretching Percent 5 -5
-10 12 13 14 15 16 17 18
Knitted Tightness Factor
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13. Rule Two
After preparation and dyeing the fabric will be highly stretched
Therefore Equalize length and width tensions
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14. Tubular Wet Spreading
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15. Tubular Wet Spreading Width stretched to greater than Target
plain jersey: 15 – 25%
1 x 1 rib : ~ 40%
NB: - not close to a squeeze mangle - preferably before a relax dryer
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16. Relax Dryers Attempt to imitate tumble drying vibrating carriers
perforated drums
staggered, opposed air jets
NB: proper overfeed and space between belts
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17. Relax Dryer Interior
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18. Shrinkage During Tumble Drying
Bleached Interlock 16 12
Length Shrinkage % 8 4
Dry
Wet 20 40 60 80
100
Moisture Regain after Tumbling
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19. Rule Three
Mechanical action will induce relaxation only when the fabric contains less than about 35% moisture
A technique used with very difficult fabrics, such as brushed fleece, is to spray on 40% of water directly in front of a relax dryer
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20. Weko Rotor Spray: Principle
Belt drive
Fabric
Liquor
Rotors
Baffles
Liquor delivery according to fabric weight and speed
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21. Weko Rotor Spray: Implementation
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22. Tumble drying can cause an increase in fabric THICKNESS of up to 40%
Consolidation
Tumble drying can cause an increase in fabric THICKNESS of up to 40%
Low-shrink fabrics must have maximum thickness
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23. Develop and Maintain Fabric Thickness
Rule Four
Develop and Maintain Fabric Thickness
Effect of calenders is to reduce thickness and increase length
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24. Compressive Shrinking
Compacting forcibly reduces fabric length
rubber belts
felt blankets
polished steel shoe
Moisture and frictional conditions are important
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25. Compressive Shrinking: Principle
Belt is stretched
Smooth heated
cylinder runs slightly
faster than the belt
Fabric
Fabric is compressed
Steam
Rubber
belt
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26. Steam Condensation: Theory
Specific heat of dry cellulose ~ 0.3 Latent heat of steam 540 Cal /g
Heating 100 g of cotton from 20 to 100 °C takes 100 * 0.3 * 80 / 540 = 4.4g steam
If the cotton contains 7% moisture, then a further 1g of steam is condensed
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27. Steam Condensation: Examples
Fabric starting condition 20
Temp °C
After steaming
Moisture % 50 7 2
12.4
4.5
Optimum moisture content for compacting is 10 to 15 %
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28. Steam will NOT condense on a hot, dry fabric
Rule Five
Steam will NOT condense on a hot, dry fabric
Fabric must be cool and have uniform moisture content before the calender or compactor
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29. Limitations of Compacting
Can change surface appearance
polishing
apparent colour depth
surface irregularities
Does not develop proper consolidation
easily pulled out
Problems are most apparent at high levels of compaction
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30. Rule Six
COMPACTORS should be used to give only small amounts of compressive shrinking
Their primary function is to deliver a precisely controlled density of courses
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31. Resin Finishing (Crosslinking)
Cell - OH X – R – X HO - Cell
Cell - O – R – O - Cell
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32. Effect of Resin Finish On Reference Dimensions
Usually significantly longer
Usually slightly wider
Usually lighter
- lower shrinkage at target weight - slightly lower spirality
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33. Resin Finishing: Advantages
Lower shrinkage at the same weight
Slightly lower spirality
Better appearance retention
Better easy care performance
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34. Resin Finishing: Problems
Change in Reference Dimensions
Effect on colour and handle
Free formaldehyde emission
Strength and abrasion resistance
Stitching damage and dusting
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35. Effect of Resin on Bursting Strength
20g Interlock
600
550
500
450
Burst Strength
400
350
300
250 1 2 3 4 5
Resin Concentration % owf
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36. Rule Seven Resin Finishing needs considerable expertise
It should be avoided if at all possible
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37. On-line Measurements Moisture content at dryers
Weight at stenters / compactors
Course density at stenters / compactors
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38. Moisture meters must be very carefully calibrated
Moisture Content
For optimum drying cost and to ensure cool fabric for compacting
control moisture at 8 – 10%
To develop maximum shrinkage and consolidation in relax dryers
control moisture at 2 – 4%
Moisture meters must be very carefully calibrated
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39. Fabric Weight
Monitoring weight for on-line process control is useful only if …
… moisture content and course density and width are also monitored …
… and included in the control software.
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40. Course Density
On-line monitoring of course density with feedback control for the overfeed …
… is the only way to guarantee delivery of the target fabric length
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41. On-line Control of Course Density
Automation Partners
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42. On-line Control of Course Density
Mahlo
Strandberg
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43. Rule Eight Variations in fabric weight and shrinkage due to …
variations in grey yarn count
differences in process weight loss
almost all other random effects
… are minimized by delivering the fabric with constant width and course density
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44. STARFISH Workshop