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Management of Quality in Knitting Part 1: Fabric Appearance & Knitting Efficiency
STARFISH Workshop
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Fabric Appearance is influenced by Fibre Quality Yarn Type
Count Variation & Evenness Imperfections & Faults Twist Variation Hairiness STARFISH Workshop
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Fibre Properties The two most important are Fibre Fineness
- average linear density Fibre Maturity - relative degree of thickening of the fibre wall STARFISH Workshop
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Micronaire Value is a function of Fineness and Maturity
indicates fibre specific surface area is governed by Fibre Perimeter (surface area) Cell Wall Thickness (amount of cellulose) indicates dyeing performance STARFISH Workshop
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Micronaire & Dyeing Efficiency
C.I. Direct Red 81 : 1% o.w.f. Colour depth K/S 90 80 70 60 50 Nineteen different cottons US cottons African cottons Micronaire Value 2.0 3.0 4.0 5.0 2.5 3.5 4.5 5.5 STARFISH Workshop
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Barré in Weft Knitted Fabrics
due to variation in Micronaire Source: Uster® Technologies AG STARFISH Workshop
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Effect of Micronaire Fibre Micronaire affects Colour Yield
Cost of Dyeing Uniformity of Dyeing NEVER MIX YARN DELIVERIES STARFISH Workshop
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Yarn Count Variation within and between packages, can cause Stripes
Bars Streakiness across the fabric width STARFISH Workshop
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Variation Within Packages
Source: Uster® Technologies AG STARFISH Workshop
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Variation Between Packages
Source: Uster® Technologies AG STARFISH Workshop
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USTER® World Statistics 2007
Count Variation CVcb% : Ne 30 between bobbin variation 50% 25% combed ring ~1.5 ~1.1 carded ring ~1.6 ~1.2 carded rotor ~0.9 ISO 2060 Source: Uster® Technologies AG STARFISH Workshop
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Mass Variation (Yarn Irregularity)
within package variation causes all-over effects moiré effects cloudiness STARFISH Workshop
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Periodic Mass Variation
Source: Uster® Technologies AG STARFISH Workshop
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USTER® World Statistics 2007
Mass Variation CVm% : Ne 30 measured on bobbins 50% 25% combed ring ~12.3 ~11.4 carded ring ~15.2 ~14.3 carded rotor ~14.9 ~13.8 CV% = 1.25 x U% (approx) Source: Uster® Technologies AG STARFISH Workshop
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Yarn Imperfections are defined as Thin places (-50%)
Thick places (+50%) Neps (+200%) can cause Blemishes on fabric surface White specks in dyed fabrics STARFISH Workshop
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Thin Places Source: Uster® Technologies AG STARFISH Workshop
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Thick Places Source: Uster® Technologies AG STARFISH Workshop
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Fibre Nep Source: Uster® Technologies AG STARFISH Workshop
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Seed Coat Nep Source: Uster® Technologies AG STARFISH Workshop
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Biological Nep Undyed white specs caused by
clumps of immature (dead) cotton fibres Low magnification High magnification Source: Uster® Technologies AG STARFISH Workshop
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Neps Source: Uster® Technologies AG STARFISH Workshop
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USTER® World Statistics 2007
Imperfections : Ne 30 (50% level) measured on bobbins Thin Thick Neps carded rotor ~28.5 ~116.2 ~30.4 carded ring ~11.9 ~191 ~232.8 combed ring ~0.9 ~20.3 ~36.7 NB For Rotor Yarns Neps +280% Source: Uster® Technologies AG STARFISH Workshop
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Classimat Defects are classified according to length & diameter
Source: Uster® Technologies AG STARFISH Workshop
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Classimat Defects Exceptionally long thick and thin places cause
Periodic stripes Blemishes Needle damage holes needle lines STARFISH Workshop
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Classimat Defects Classimat defects are removed during
winding & clearing according to a clearing profile A3, B3, C2, D1 profile will remove the most serious faults STARFISH Workshop
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Hairiness and Twist Variation is the problem Surface appearance
Abrasion resistance Colour variation Stitch clarity STARFISH Workshop
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Effect of Difference in Twist
Band of “rogue” yarns with high twist Source: Uster® Technologies AG STARFISH Workshop
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USTER® World Statistics 2007
Hairiness : Ne 30 measured on bobbins combed ring carded ring carded rotor H S 4.6 1.0 5.0 1.2 4.1 1.1 5.8 1.4 4.7 1.3 50% 25% NB measurements on packages may be higher Source: Uster® Technologies AG STARFISH Workshop
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TESTEX Twist Statistics 1997
Twist Variation CV%: Ne 30 measured on bobbins 50% 25% combed ring ~3.3 ~2.9 carded ring ~3.5 ~3.0 carded rotor ~2.8 ~2.3 ASTM D Untwist-Retwist Source: Testex STARFISH Workshop
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Hairiness and Yarn Type
Combed yarns less hairy than carded Rotor yarns less hairy than ring Rotor yarns develop less hairiness during wear and laundering STARFISH Workshop
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Knitting Efficiency Can be affected by Strength Uniformity
Irregularity Imperfections Faults Fibre Fly Friction Twist Liveliness STARFISH Workshop
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Strength Uniformity Average strength is usually good enough
Variation is the key weak places cause the problems Elongation must be adequate at least 5% extension at break STARFISH Workshop
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USTER® World Statistics 20077
Yarn Strength : Ne 30 (50% level) measured on bobbins cN/tex CV% El% carded rotor ~12.1 ~8.7 ~5.8 carded ring ~17.8 ~8.0 ~5.95 combed ring ~17.2 ~7.3 ~5.1 Source: Uster® Technologies AG STARFISH Workshop
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Yarn Uniformity Slubs and Knots cause Needle damage Fabric holes
Yarn breaks Yarn should be properly cleared Spliced yarn better than knotted STARFISH Workshop
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Can reduce knitting efficiency
Fibre Fly Can reduce knitting efficiency by up to 25% Control is Important STARFISH Workshop
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Amount of Fibre Fly Depends on Fibre quality Yarn structure
Twist multiple Yarn finishing Moisture content Yarn friction and, especially, the speed of knitting STARFISH Workshop
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Fibre Fly: Effect of Yarn Construction
Carded ring, 23 mm Fibre Fly g / Kg yarn 2.2 1.8 1.4 1.0 0.6 0.2 Combed ring, 25 mm Combed ring, 28 mm Carded OE rotor Twist Multiple 2.8 3.2 3.6 4.0 4.4 4.8 5.2 Source: ITV Denkendorf STARFISH Workshop
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for efficient knitting
Yarn Friction Large tensions can be generated because of friction Low Friction is essential for efficient knitting Coefficient of friction against steel must be below 0.2 Knitting yarns must be waxed STARFISH Workshop
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Friction and Yarn Tension
q T2 T1 T2 = T1 . e mq knitting zone STARFISH Workshop
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Wax Application & Coefficient of Friction
Combed cotton ring yarns Coefficient of Friction 0.4 0.3 0.2 0.1 Wax add-on % 0.2 0.4 0.6 0.8 Source: Savio STARFISH Workshop
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Yarn Waxing Optimum level Uniform application Wax quality Yarn storage
Easy removal STARFISH Workshop
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High Yarn Twist Liveliness Causes
Snarling Fabric Faults Yarn Breaks Good yarn control required STARFISH Workshop
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Minimising Knitting Faults
Yarn Quality Machine Set Up Fibre Fly Machinery Maintenance Good Housekeeping STARFISH Workshop
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Yarn Quality Yarns properly waxed Damaged cones Yarn storage
temperature & moisture content Yarn identification no mixing of yarn lots STARFISH Workshop
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Yarn Input Tension Should be monitored using
appropriate instrumentation Excessive tensions can cause Schmidt ZEF stitch distortions fly generation yarn breaks STARFISH Workshop
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Yarn Input Tension Excessive tensions can be caused by
badly adjusted or sticking stitch cams damaged yarn packages creeling faulty waxing faulty feeding units STARFISH Workshop
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Fibre Fly is generated at Yarn package Yarn guide elements
Yarn furnishing installation Knitting point 25% of all knitting faults can be attributed to fibre fly STARFISH Workshop
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Control of Fibre Fly Enclosed creels to humidify and filter air
Feeder tubes Yarn speed Regular cleaning STARFISH Workshop
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Control of Fibre Fly Enclosed creel with lint filters and tube feeds
Source: Memminger-IRO STARFISH Workshop
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Effect of Yarn Speed on Fibre Fly
Carded 30 Ne Fibre fly g /Kg yarn 2.8 2.4 2.0 1.6 1.2 24g, 30", 10 rpm 24g, 30", 50 rpm Yarn speed m/min 50 150 250 350 450 Source : ITV Denkendorf STARFISH Workshop
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Knitting Faults Holes Stains Missed stitches Needle lines Sinker lines
STARFISH Workshop
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Control of Knitting Faults
Yarn detectors Memminger-Iro: UFW STARFISH Workshop
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Control of Knitting Faults
Yarn detectors Knot & Slub catchers Memminger-Iro: MPF_L STARFISH Workshop
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Control of Knitting Faults
Yarn detectors Knot & Slub catchers Needle detectors Memminger-Iro: Needle detector Latch openers STARFISH Workshop
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Control of Knitting Faults
Yarn detectors Knot & Slub catchers Needle detectors Latch openers Fabric fault detectors Memminger-Iro: LMW-3 Record and analyse faults, identify sources e.g. yarn supply or machinery maintenance STARFISH Workshop
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Preventive Maintenance
Regular cleaning of machines Clean working areas Efficient lubrication systems Regular flushing of needle bed Checks for wear and rough places Service positive feed units STARFISH Workshop
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Preventive Maintenance
needles and sinkers using high quality spares Regular proactive replacement of Ad hoc replacement inevitably means variations in quality and efficiency STARFISH Workshop
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STARFISH Workshop
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