Management of Quality in Knitting Part 2: Specification & Control STARFISH Workshop

Management of Quality in Knitting Identify key control parameters Establish appropriate specifications Identify potential sources of variation Establish reliable monitoring procedures Variations in grey fabric cannot be eliminated during finishing STARFISH Workshop

Key Control Areas For Each Fabric Quality Yarn Quality type, count, twist Average Stitch Length these determine the Reference Dimensions STARFISH Workshop

Yarn Quality Fibre Quality Yarn Type Count & Count Variation Twist & Twist Variation Irregularity & Imperfections Strength & Strength Uniformity Friction STARFISH Workshop

Yarn Specification Yarn properties are inter-dependent Low variation is often more important than high mean values High quality usually means high price Consider the end product STARFISH Workshop

Control of Yarn Quality Difficult for the knitter Depends on reliability of ALL suppliers Good relationships essential Quality checks must be installed STARFISH Workshop

Yarns from Different Spinners Specification = Ne 38 ± 2.5% Measured Yarn Count, Ne 41 40 39 38 37 36 35 Supplier A Supplier B Supplier C Ne 39.0 CV 0.5% Ne 38.0 CV 2.8% Ne 37.6 CV 1.9% Test Number 20 40 60 80 100 120 140 STARFISH Workshop

Effect of Yarn Count Variation Fabric: Interlock 20g 30d 1884n Knit Spec: Ne 1/38, SL 3.4 mm Process: Winch-jet: Mid Tension, White Finish Spec: 14.5 c/cm, 68 cm tub (200 gsm) Variation due to Yarn Count only Weight, gsm 195 to 207 Length Shr.% -4.4 to -5.5 Width Shr.% -4.4 to -6.0 No allowance for variation in SL or Processing STARFISH Workshop

Yarn Count Variation If fabrics finished to the same weight and width Range in Length Shrinkage increases to between -1.6% and -8.5% Variation in Ne between deliveries of ± 3% is not unusual For Ne 38, range is Ne 39.14 to Ne 36.86 Actual range was Ne 39.2 to Ne 36.9 STARFISH Workshop

Monitoring Yarn Quality Obtain test data from ALL suppliers Identify and check EACH delivery for count, twist & friction before knitting NB moisture content COMPARE with agreed Specification Establish PROCEDURES for out of tolerance deliveries STARFISH Workshop

Monitoring Yarn Quality Use charts to monitor suppliers Establish NORMAL variation for each supplier over time Establish appropriate tolerances Establish guide-lines for action Communicate results to suppliers STARFISH Workshop

Monitoring Yarn Count Measured Yarn Count, tex ? Sample Number Specification = 19.3 tex ± 2.5% Measured Yarn Count, tex 20.2 19.8 19.4 19.0 18.6 +2.5% Spec. ? -2.5% Sample Number 10 20 30 40 STARFISH Workshop

Control of Yarn Quality should get more stringent checking until their reliability is proved New Suppliers STARFISH Workshop

Control of Yarn Quality Finally Pay attention to yarn storage e.g. temperature and relative humidity Check for damaged cones or boxes NEVER MIX LOTS STARFISH Workshop

Good Yarn Makes Good Fabric Lowest price is seldom the lowest cost Dependability of supply is valuable Consistency is important Limit the number of suppliers STARFISH Workshop

Knitting Specification For each quality on each knitting machine the key production control parameters are Course Length (SL * Needles) - determines reference dimensions Courses per Roll (revs * feeders) - determines roll length & weight STARFISH Workshop

Control of Course Length Positive (driven) Feed Instrumentation Memminger-Iro: MPF_L Control Procedures Memminger-Iro: MLT-Wesco STARFISH Workshop

Variation Between Feeders Negative (passive) Feed Course Length, inches 125 123 121 119 117 115 113 Mean = 119.2 in CV = 2.0% Feeder Number 1 3 5 7 9 11 13 15 17 19 21 23 25 Source: SITRA STARFISH Workshop

Variation Between Feeders Positive (driven) Feed 125 123 121 Course Length, inches 119 117 115 113 Mean = 116.2 in CV = 0.32% 1 3 5 7 9 11 13 15 17 19 21 23 25 Feeder Number Source: SITRA STARFISH Workshop

Control of Course Length Yarn input tension and take-down tension Can influence knitting efficiency and fabric appearance therefore proper control is important But they do not affect stitch length provided positive feed is used STARFISH Workshop

Effect of Yarn Input Tension Using Negative Feed Course Length, cm 125 120 115 110 105 100 Waxed Unwaxed Input tension, g 4 6 8 10 12 14 16 Source: HATRA STARFISH Workshop

Effect of Take-down Tension Courses /3cm 50 55 60 45 65 Fabric Tightness Factor = 16.4 High TD tension Low TD tension Time in Winch, min 200 400 600 800 Hydro Finished Reference STARFISH Workshop

Effect of Take-down Tension 50 Fabric Tightness Factor = 13.4 45 High TD tension Low TD tension 40 Courses /3cm 35 30 Hydro Finished Reference 200 400 600 800 Time in Winch, min STARFISH Workshop

Control of Course Length Positive Feed alone is not enough Accurate setting of positive feed drives is needed Drive wheel markings not accurate enough Modern systems should be more accurate Memminger-Iro: Drive pulley Memminger-Iro: Modern system STARFISH Workshop

Control of Course Length Positive Feed alone is not enough Accurate setting of positive feed drives drive wheel markings are not accurate enough Regular Maintenance wax and fly contamination Independent Checks using appropriate instrumentation STARFISH Workshop

Course Length Instruments: Examples Direct length per revolution measurement Wesco (Memminger-IRO) Unilength (Meiners-del) Schmidt LMC STARFISH Workshop

Course Length Instruments: Examples Indirect and integral systems SDL yarn length & speed meter Decotex (Memminger-Iro) Intus (Mayer & Cie) Knit Master (Barco) STARFISH Workshop

Course Length Instruments Check Results by measuring stitch length of yarns taken from fabric Calibrate Instruments on a regular basis Establish Accuracy and Variability using Control Charts STARFISH Workshop

Course Length Instruments: Variation 28g Single Jersey Stitch Length, mm 2.64 2.60 2.56 2.52 2.48 2.44 2.40 2.36 +1.5% Lab -1.5% Instrument 1 Instrument 2 Feeder Number 1 3 5 7 9 11 13 15 STARFISH Workshop

Course Length & Needles Number of needles can vary between different makes and models Stitch Length depends on Course Length SL = Course Length / Needles Needles must also be specified when Course Length is the Control Parameter Fabric Width depends on No. of Needles Width = Needles / Wales STARFISH Workshop

Variation in Cylinder Needles SJ 30" Diam, 20 Gg Needles % Diff Theoretical 1884 Falmac "B" Series 1848 -1.9 Monarch VXC-73S 1860 -1.3 Pai Lung FS3A/T 1872 -0.6 Vanguard 1SJ4 1920 +1.9 STARFISH Workshop

Course Length & Stitch Length Use Course Length to set-up and control production on individual machines CL may be different, depends on needles Use Stitch Length to specify quality and compare production across all machines Stitch Length should be the same on all STARFISH Workshop

Monitoring Stitch Length Target = 2.82 mm Stitch Length, mm 2.70 2.75 2.80 2.85 2.90 2.95 Mean = 2.832 : SD = 0.042 Sample Number 10 20 30 40 50 60 70 80 STARFISH Workshop

Stitch Length Variation Fabric: 1 x 1 Rib 14g 20d 876n Knit spec: Ne 1/30, SL 2.82 mm Process: Winch-jet: Mid tension, Medium Finish spec: 17.6 c/cm, 41 cm tub, 200 gsm Variation due to Stitch Length only Weight, gsm 194 to 206 Length Shr% -0.8 to -8.1 Width Shr% -5.1 to -9.6 No allowance for variation in Ne or Processing STARFISH Workshop

Control of Course Length Prevention better than Cure Check average CL before production and record the results establish variation between feeders establish variation between machines determine minimum number of feeders to be checked STARFISH Workshop

Control of Course Length Making Measurements Regular checks throughout production to ensure the quality is maintained Record results so that average values and the variation can be monitored Calculate Standard Deviation of means for each machine, quality & yarn lot STARFISH Workshop

Control of Course Length Frequency of Checking Initially may need to be intensive until true variation established Reduction only with clear proof Increase frequency after maintenance, new parts, new yarn lot Effective monitoring will quickly detect deterioration or drift STARFISH Workshop

Control of Course Length Tolerances and Control Limits Must be Realistic and Achievable Optimum levels take time to establish Normal Tolerance is ± 2 SD 95 in 100 within Normal Tolerance Action Tolerance is ± 3 SD 1 in 300 outside Action Tolerance STARFISH Workshop

Monitoring Stitch Length Target = 2.82 mm : SD = 0.042 2.95 + 3 SD + 2 SD 2.90 2.85 Stitch Length, mm 2.80 2.75 - 2 SD 2.70 - 3 SD 10 20 30 40 50 60 70 80 Sample Number STARFISH Workshop

Control of Course Length Practical Control Tolerances (± 3 SD) reflect current capabilities closer tolerances do not improve control If Practical Tolerances are too high first identify and reduce variation then calculate new tolerances STARFISH Workshop

Monitoring Stitch Length Target = 2.82 mm : SD = 0.042 2.95 + 3 SD + 2 SD 2.90 2.85 Stitch Length, mm 2.80 2.75 - 2 SD 2.70 - 3 SD Machine Diameter 16 18 17 19 20 22 STARFISH Workshop

Stitch Length Sorted by Machine Diam SL mm CV% SD 16 2.850 0.25 0.007 17 2.806 0.76 0.021 ? 18 2.884 0.45 0.013 19 2.785 0.35 0.010 20 2.873 0.39 0.011 22 2.785 0.31 0.009 all data 2.832 1.49 0.042 STARFISH Workshop

Control of Course Length Maintain a Consistent Standard Check on-line instrumentation regularly internal lab measurements of SL external calibration monitor using Control Charts QC independent from production STARFISH Workshop

Control of Roll Weight and Length Consistent roll Weight planning, monitoring & control storage & handling easy composition of dyelots Consistent roll Length improves lay planning reduces cutting waste reduces costs Both can be accurately controlled based on Yarn Count & Course Length STARFISH Workshop

Roll Weight and Yarn Tex Count Roll Weight (kg) = tex * CL(cm) * feeders * revs * 10 -8 therefore tex = CL(cm) * feeders * revs roll weight (kg) * 10 8 590.54 Ne tex = 590.54 tex Ne = STARFISH Workshop

Roll Length Roll Length = Total Courses / Course Density Total Courses = Feeders * No. of Revs Knitting Control Parameter = Revs Use finished Course Density to calculate total courses to knit Don't forget construction effects e.g. Two-thread fleece STARFISH Workshop

Quality Checks on Grey Fabric Grey (machine state) dimensions are Unstable Unreliable They are influenced by Take-down tensions Stretcher board settings which do not affect Reference Dimensions STARFISH Workshop

Quality Checks on Grey Fabric Grey area weight is NOT a reliable check of fabric quality Roll Weight can be useful, but only if Course length is accurately controlled Exact no of courses is known STARFISH Workshop

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