Fabric Faults or Defects in Circular Knitting Machine

Defects in Circular Knitting:
Circular knitting machine is widely used through out the knitting industry to produce fabric. It has been designed and manufactured for mass production of knitted fabrics. The special properties of knitted fabrics, especially fine fabrics made by the circular knitting process. Among them huge positive this knitting machine also has some problems and limitations. Many faults and defects occurred during knitting. These faults and defects are given below.

Fabric Faults or Defects in Circular Knitting Machine
  1. Barre
  2. Holes in fabric
  3. Lower GSM
  4. Spirality
  5. Tight loops
  6. Slack loop
  7. Slack loop
  8. Snagging in ladies suits
  9. Bird’s eye
  10. Dropped stitch
  11. Needle line
  12. Bowing
  13. Streak or stop mark
  14. Skewing
  15. Slub
  16. Press off
  17. Run
  18. Scrimps
  19. Boardy
  20. Ladder
  21. Tucking
  22. Float
  23. Missing plush loop
  24. Stain
  25. Thin yarn
  26. Thick yarn
A short description of the defects are given below:  
 
1. Barre – Barre is an unintentional repetitive visual pattern of continuous bars and stripes usually parallel to the filling of woven fabric or to the courses of circular knitted fabric. Mixing of yarns of different lots or counts, fibre micronaire variation, fibre colour variation, yarn linear density variation, yarn twist variation, yarn hairiness variation, knitting tension variation, improper mixing of cotton from different origin, improper mixing of cotton from different varieties and improper mixing of cotton grown in different seasons, difference in tension between the feed packages, yarns/filaments of different elongation properties fed without proper control of tensions, improper stitching cam setting, uneven take down pull, over stretching of fabrics and exposing of cones to sunlight of a long time are the main causes of barre attributed to knitting operation. Barre can be caused by physical, optical or dye differences in the yarns, geometric differences in the fabric structure or by any combination of these differences. It is basically a visual phenomenon and any property of yarn which makes it ‘look’ different from the adjacent yarn in a fabric would result in this defect. All barre is the consequence of subtle differences in yarn reflectance between individual yarns in the knit structure. Any mechanism that can change the reflectance of a yarn in a knit structure is a potential barre source A barre streak can be one course or end wide or it can be several - a “shadow band”. It is not the inadequacy of the raw material property which results in barre; it is the inconsistency or the variability of the particular property which results in Barre.
Baree in fabric
Baree in fabric
2. Holes in fabric – A hole or a press off is the result of a broken yarn at a specific needle feed so that knitting cannot occur. Fluff accumulation on the knitting creel if fall on the needle zone, or the knots and slubs if present in the yarn are the main reasons for holes in the fabric. Yarn imperfections in which one or several yarns are sufficiently damaged to create an opening also contribute to this problem. A good and clean working area is very essential. The blowing or suction fans can be provided to prevent fluff accumulation on the cones, yarn and the knitting area.
Hole in fabric
Hole in fabric
3. Lower GSM – Count of the yarn finer than the required, a lower loop length, and lesser course and wales are the main reasons for lower GSM of knitted fabric.

4. Spirality – A higher twist in the grey yarns, improper steaming or conditioning of yarn, take-up roller set in a slanted position are the main reasons for Spirality.

5. Loop to loop variation – Variation in loop parameters at micro level such as loop-to-loop variation in dimension, geometrical shape of loop and localized variation in loop density can be reduced by improvement of knit structure by better understanding of mechanics of loop formation, fluidity of knit structures and their influence on quality of knit fabrics. The quality of hosiery yarn viz. the uniformity and twist factor for the staple length of fibres used has to be considered with due weightage to these aspects. The machine parameters such as gauge, needle type, cam type, yarn feeding system, number of feeders, take down system, cloth rolling or spreading are to be monitored and controlled.

6. Tight loops – This may take the form of a shadow (several courses involved) or a discreet line (one course involved). It will normally show up as a dark or dense line or shadow

7. Slack loop – Slack loop shows up as a sheer or light line

8. Snagging in ladies suits – A snag is a desirable surface loop of varying size on woven or knitted fabrics often caused by catching on sharp points or objects. To prevent this ensure adequate twist in the yarn, firm fabric construction, proper handling of materials, and smooth surface at all fabric moving and storing areas.

9. Bird’s eye – In knitting, an unintentional tuck stitch is called as a Bird’s Eye. The tension variation and hairiness are the main reasons for this.

10. Dropped stitch – Defect in knitted fabric; recurrent openings in one or more wales of a length of knitted fabric because the stitches did not knit.
Dropped stitch
11. Needle line – Lengthwise streak in knitted goods caused by improper alignment of a needle or its incorrect spacing cause the Needle Lines. This is caused by needle movement due to a tight fit in its slot or a defective sinker.

12. Bowing – A line or a design may curve across the fabric. This bowing is the distortion caused by faulty take-up mechanism on the knitting machine.

13. Streak or stop mark – A straight horizontal streak or stop mark in the knitted fabric is due to the difference in tension in the yarns caused by the machine being stopped and then restarted.

14. Skewing – Skewing effect is seen as a line or design running at a slight angle across the cloth.

15. Slub – Unexpected sudden thickness in the yarn

16. Press-off – Condition in knitting when a yarn breaks or fails to knit

17. Run – In reference to knit goods, a series of dropped stitches is called as a Run, as a run in hosiery.

18. Scrimps – A wrinkle caused by excessive strain, tension, or pressure on a fabric.

19. Boardy – The knitted fabric becomes boardy (a stiff or harsh hand) when the stitches have been knit very tightly.

20. Cockled or puckered – Uneven stitches or yarn sizer result in cockling or puckering.

21. Ladder – A ladder indicates a row of dropped stitches in the wale.

22. Tucking – This is the result of an unintentional tucking in the knitted fabric. This is also called the bird’s eye defect.

23. Float – This is caused by a miss stitch which is the result of failure of one or more needles to have been raised to catch the yarn.

24. Missing plush loop – Malfunctioning of loop

25. Stains – Stains are mainly due to improper house keeping, oil leakages in the machines, improper handling, uncleaned containers of materials and lack of awareness among the employees and the management.

26. Thin yarn – Variations in count, singles in yarns, sliver or rove, partial lapping in speed frame drafting rollers, are normal reasons for a thin place in the yarn.

27. Thick yarn – Variations in counts, doubles in sliver and rove, lashing in, low pressure on drafting rollers are normal causes for thick yarn.

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