Quality Control in Knitting Technology PDF

Knitting Technology  Aspect of Knitting Science ►A scientific approach to study knitted fabric especially with knitted garment size variation. ►Three Basic Laws were established on knitted fabric behavior Loop length is the fundamental unit of weft knitting structure; Aspect of Kni...

Knitting Technology  Aspect of Knitting Science ►A scientific approach to study knitted fabric especially with knitted garment size variation. ►Three Basic Laws were established on knitted fabric behavior Loop length is the fundamental unit of weft knitting structure; Aspect of Knitting Science Loop shape determines the dimensions of the fabric and this shape depends upon yarn used, treatment and fabric received; The relationship between loop shape and loop length may be expressed in the form of simple equations  Fabric Quality ►First, what is fabric quality ? The general trade interpretation is that two fabrics are of same quality when their weights per unit area are the same; their course per inch and wales spacing are similar; their handles are identical; and their elastic properties are the same.  Fabric Quality ►For two fabrics to conform to these four requirements, and be of identical quality; when the fabrics are knitted from yarns of similar count and quality; the constructional details of the fabrics are identical  Fabric Quality ►So the only factors affecting two fabric’s identical quality are : take down tensions on the machine; length of yarn knitted into a stitch  Cause Effect Very Uneven Yarn Cloudy Fabric Yarn with very low strength Holes or Cracks and/or too many thin places Yarn with Long period Fabric with stripes unevenness Bad dyeing or blending Horizontal stripes Too large or weak knots or Yarn end separation or break bad splicing during knitting Too much yarn hairiness Diffused stitch appearance and fluff build up  Loop Length ►Loop length is the basic element (cell) in the knitted fabric and is defined as the amount of yarn used to form one unit loop. ► Loop length = course length / number of loops  Loop Length ► Loop length will affect the following parameters : Stitch length; Tightness factor; Fabric weight; Fabric width; Panel length; Dimensional stability  Loop Length ►Experiment shows that the fabric thickness, weight, tightness factor and stitch density are INVERSELY PROPORTIONAL to the loop length.  On-machine Control ► Yarn Speed Meter Control Yarn speed meter is used to check the yarn consumption speed on the knitting feeders. The results are good for circular knitting machine with positive feed. Yarn speed is affected by loop length, structure and machine speed.  On-machine Control ► Yarn tension meter control Tension meter can be used to check the yarn winding tension, unwinding tension and knitting tension. The usual tension (medium to fine gauge) on circular machine is 2-5 gm.  On-machine Control Knitting Tension Effect on loop length High Smaller loop length Fluctuation Variation on loop length Very low Drop stitches Low and even tension Good quality fabric  On-machine Control ► Yarn Length Meter The yarn length meter can be fixed on machine to record yarn consumption for a number of courses or machine revolutions. The results can be used to calculate the loop length between machine of the same gauge.  Positive Feed Control ►The function of positive feeders for circular knitting machine is to regulate the yarn knitting tension to desired value (low and even tension) and results in better fabric can be produced. ►The positive feeders are almost standard equipment for high speed non-jacquard machines.  Positive Feed Control ►Types of positive feeding device for non-jacquard machines Trip-tape positive feeder Multi-coil positive feeder  Trip-tape Positive Feeder ►It is the simple measured yarn speed feeding system.  Trip-tape Positive Feeder ►The yarn speed is controlled by speed tape pulley which in turn, controlled by machine gearbox.  Trip-tape Positive Feeder ►Two to three speed tapes are equipped which machine can have two to three yarn feeding speeds for the fabric. ►When machine is properly adjusted, the yarn speed is equal to tape speed, and the tape speed can control the suitable yarn tension and results in regular loop length Multi-coil Positive Feeder  Multi-coil Positive Feeder ►Due to the slippage between the tape and the yarn, the efficiency of trip-tape positive feeder method is not 100%. ► That is the Yarn Speed IS NOT EQUAL To Tape speed. ► The multi-coil method is used to achieve this target. Multi-coil Positive Feeder  Multi-coil Positive Feeder ►The yarn instead of directly driven by the tape, is first to the pin wheel for 10 coils before feeding to the needles. ►The principle is the yarn coils on the wheel can neutralise the yarn tension variation from cone and avoid any yarn slippage. Positive Feed Control Positive Feed Control  Yarn Tension Control ► Yarn unwinding method The yarn tension is different from the first layer to the bottom layer. ► Package size The size of the package (cone diameter and cone height) will affect the winding tension.  Yarn Tension Control ► Package density Unusual high package density will give higher friction to yarn between coils, results in higher unwinding tension. ► Yarn fault Yarn faults mean sudden increase of yarn diameter with results in change of yarn tension in knitting process.  Yarn Tension Control ► Spring wire on tensioner This will affect on V-bed machine when the cam carriage changing the direction on RHS to LHS and vice versa.