Study on Different Types of Knitting Faults, Causes and Remedies of Knit Fabrics

In this assignment some knitting faults their possible causes and remedies are discussed.

1. SOUTHEASTUNIVERSITY
Department of Textile Engineering

Course Code:- TEX-4013
Course Title:-FMT-III
Assignment Topic:- Study on Different Types of Knitting Faults, Causes and
Remedies of Knit Fabrics

Submitted To:- Syeda Sanjida Wasim,
Lecturer, Department of Textile Engineering,
Southeast University


Submitted by:-
Md. Ariful Islam
ID:- 2013200400058

Date of Submission:-11-12-2016

2. 1. Introduction:
Knitting is one of the important industrial sectors of Bangladesh. The maximum share our export oriented
RMG is originated from knit fabrics Export means quality; we must ensure 100% quality of our export
oriented RMG products. [1] Due to increasing demand for quality knitted fabrics, high quality
requirements are today greater since customer has become more aware of “non-quality “ problems, in
order to avoid fabric rejection , knitting mills have to produce fabrics of high quality, constantly [2, 3].
Detection of faults during production of knitted fabric with circular knitting machine is crucial for
improved quality and productivity any variation to the knitted process needs to be investigated and
corrected. The high quality standard can be guaranteed incorporating appropriate quality assurance.
Industrial analysis indicate that quality can be improved, and defect cost minimized, by monitoring the
circular knitting process. [3]
[4], Detection of faults during production of knitted fabric with circular knitting machine (CKM) is
crucial for improved quality and productivity. Any variation to the knitting process needs to be
investigated and corrected. The high quality standard can be guaranteed by incorporating appropriate
quality assurance. Industrial analysis indicate that product quality can be improved, and defect cost
minimized, by monitoring of the circular knitting process (Jearranai and Tiluk), 1999.
Many researchers have applied computer vision to improve inspection method of human vision in textile
products, in most of them, the image of knitted garments had been considered to specify the faults
features. Others work aimed to classify defects in knitted fabrics by using image analysis and neutral
network algorithm or fuzzy logic. All these methods are not completely reliable because image analysis of
knitted fabrics involves difficulties due to the loop structures and yarn hairiness, compare to woven
fabrics consisting of neat warp and weft yarns. Knitted fabric faults can also be detected by inspecting
yarn input tension and loop but only few types of faults are concerned by these methods.
Human inspection by using knitted fabric inspection machines remains today the most used way to
classify faults after knitting and after finishing [5]. Generally, faults are classified by type and by
frequency in the inspected knitted roll. The inspection assessment permits to appreciate fabric quality.
The judgments of fabric quality depend on faults tolerance levels fixed by each knitter and could be in
some cases subjective because it is often based only on the number of faults and not on fault size and
gravity [6].
[7]. A new inspection method was proposed in order to classify faults and help knitter to appreciate more
objectively fabric quality.

3. Factors that lead to fabric defects:


A. Material-Related Factors
 Fiber contaminants
 Excessive neps and seedcoat fragments
 Excessive short fiber content
 Excessive trash content
 High variability between and within-mix
 Clusters of unfavourable fiber characteristics
 Weight variation
 Twist variation
 Excessive Hairiness



B. Machine-Related Factors:
 Failure of spinning preparation to eliminate short and long-term variation
 Failure of the mixing machinery to provide a homogenous blend
 Excessive machine stops particularly during spinning
 Excessive ends piecing during spinning preparation
 Poor maintenance and housekeeping
 Knitting-related defects
 Dyeing and Finishing-related defects

4. Different Types of Fabrics Defects:
1. Drop stitches (holes)
2. Barriness
3. Pin hole
4. Star Mark etc.
5. Patta
6. Snarls
7. Snagging
8. Contaminations
9. Fly
10. Streakiness
11. Imperfections
12. Broken needles
13. Needle lines
14. Sinker lines
15. Lycra out
16. Spirality
17. Bowing
18. Oil Lines
19. Surface Hairiness & Piling
20. Lycra and cotton mixed

5. Knitting Faults, Causes and Remedies:
1. Drop Stitches:
Drop Stitches are randomly appearing small or big holes of the, same or different size, which appear as
defects, in the Knitted fabrics.
Causes:
 High Yarn Tension
 Yarn Overfeed or Underfeed
 High Fabric Take Down Tension
 Obstructions in the yarn passage, due to the clogging of eyelets, yarn guides & tension discs, with
wax & fluff etc.
 Defects like; Slubs, Naps, Knots etc.
 Incorrect gap between the Dial & Cylinder rings.


Fig: Drop Stitch

Remedies:
 Ensure uniform yarn tension on all the feeders, with a Tension Meter.
 Rate of yarn feed should be strictly regulated, as per the required Stitch Length.
 The fabric tube should be just like a fully inflated balloon, not too tight or too slack.
 Eyelets & the Yarn Guides, should not have, any fibers, fluff & wax etc. stuck in them.
 The yarn being used, should have no imperfections, like; Slubs, Neps & big knots etc
 The gap between the Cylinder & the Dial should, be correctly adjusted, as per the knitted loop siz

6. 2. Barriness
Horizontal stripes or streaks of uniform or uneven width, visible in the fabric.
Causes:
 High Yarn Tension
 Count Variation
 Mixing of the yarn lots
 Package hardness variation


Fig: Barriness

Remedies:
 Ensure uniform Yarn Tension on all the feeders.
 The average Count variation in the lot, should not be more than ± 0.3
 Ensure that the yarn being used for Knitting is of the same Lot / Merge no.
 Ensure that the hardness of, all the yarn packages, is uniform, using a hardness tester.

7. 3. Pin Hole:
Cause:
 Improper tension
 Same drive for both knit & tuck stitch
 Curved needles latch


Fig: Pin Hole


Remedies:
 Different drive have to maintained
 Good quality needle should use

8. 4. Star Mark:
Causes:
 Yarn tension variation during production.
 Buckling of the needle latch.
 Low G.S.M fabric production

Fig: Star Mark
Remedies:
 Maintain same Yarn tension during production.
 Use good conditioned needles.


5. Patta
Causes:
 Yarn count variation
 Yarn tension variation

Fig: Patta
Remedies:
 Proper yarn count & tension should be maintained.

9. 6. Snarls:
Snarls appear on the fabric surface, in the form of big loops of yarn getting twisted, due to the high twist
in the yarn (Unbalanced twist yarn).
Causes:
 High, twist in the, yarn.
 Hosiery yarns are soft twisted. High, twist in the yarn, is the cause of snarling.
 (Snarls cause, fabric defects & needle breakages)


Fig: Snarls

Remedies:
 Ensure using Hosiery Yarns, of the recommended T.P.M. only.
 (Hold a few inches of the yarn in both the hands, in the form of a ‘U’.
 The yarn has a balanced twist, if it doesn’t tend to rotate or turn, in the form of a snarl.
 (Such yarn can be used for Hosiery applications.)

10. 7. Contaminations
Causes:
 Presence of dead fibers & other foreign materials, such as; dyed fibers, husk & synthetic fibers
etc.
 Dead Fibers appear in the fabric, as a result of the, presence of excessive immature Cotton fibers,
in the Cotton fiber crop.
 Dead fibers do not pick up color during Dyeing.
 Presence of the foreign materials, in the, staple fiber mixing
 (Kitty, Husk, Broken Seeds, dyed fibers & fibers like Poly Propylene, Polyester, Viscose etc)
 Dyed & other types of fibers flying from the adjacent Knitting machines cling, to the yarn being
used for knitting & get, embedded in the Grey Fabric.



Fig: Contamination


Remedies:
 Use rich fiber mixing for the yarns, to be used for Knitting, in order to have less dead fibers,
appearing in the fabric.
 Rigid control measures in the Blow Room, to prevent the mixing of foreign matters in the Cotton
mixing.
 Segregate the Spinning & Knitting Machines, with Plastic Curtains or Mosquito Nets, to prevent
the fibers flying from the neighboring machines, from getting embedded in the yarn / fabric.

11. 8. Fly:
Cause:
 In knitting section too much lint is flying to and fro that are creat from due to low twist as well as
yarn friction. This lint may adhare or attaches to the fabric
 Surface tightly during knit fabric production.


Fig: Fly


Remedies:
 Blowing air for cleaning and different parts after certime time
 By cleaning the floor continuously by useing ducting system
 Cleaning too much lint in the floor
 Over all ensure that lint does not attach to the fabric.

12. 9. Broken Needles/ Laddering :
Defects caused by the broken needles show prominently as vertical lines parallel to the Wales. There are
no loops formed in the Wale which has a broken needle.

Causes:
 High Yarn Tension
 Bad Setting of the Yarn Feeders
 Old & Worn out Needle set
 Cylinder Grooves are too tight restricting needle movement
 Breakage of hook or butt in needle.



Fig: Broken Needles


Remedies:
 Ensure uniform & the right Yarn tension on all the feeders.
 Keep the recommended gap between the Yarn Feeders & the Needles.
 Periodically change the complete set of needles.
 Remove fly or blockage from groove.
 Replace defective needle.

13. 10. Needle Lines:
Causes:
 Bent Latches, Needle Hooks & Needle stems
 Tight Needles in the grooves
 Wrong Needle selection (Wrong sequence of needles, put in the Cylinder or Dial)

Fig: Needle Line


Remedies:
 Inspect the grey fabric on the knitting machine for any Needle lines.
 Replace all the defective needles having, bent latches, hooks or stems.
 Remove the fibers accumulated in, the Needle tricks (grooves).
 Replace any bent Needles, running tight in the tricks.
 Check the Needle filling sequence in the Cylinder / Dial grooves (tricks).

14. 11. Sinker Lines:
Causes:
 Bent or Worn out Sinkers
 inkers being tight in, the Sinker Ring grooves


Fig: Sinker Line


Remedies:
 Replace, all the worn out or bent sinkers, causing Sinker lines in the fabric.
 Sinker lines are very fine & feeble vertical lines, appearing in the fabric.
 Remove the fibers, clogging the Sinker tricks (Grooves)

15. 13. Broken Ends:
Broken ends appear as equidistant prominent horizontal lines along the width of the fabric tube when a
yarn breaks or is exhausted.
Causes:
 High Yarn Tension
 Yarn exhausted on the Cones.


Fig: Broken End


Remedies:
 Ensure correct yarn tension on all the feeders.
 Ensure that the Yarn detectors on all the feeders are working properly.
 Depute a skilled & alert machine operator on the knitting machine.

16. 14. Fabric Press Off:
Fabric press off appears as a big or small hole in the fabric caused due to the interruption of the loop
forming process as a result of the yarn breakage or closed needle hooks.

Causes:
 End breakage on feeders with all needles knitting.
 Yarn feeder remaining in lifted up position due to which the yarn doesn’t get fed in the hooks of
the needles.


Fig: Press Off


Remedies:
 Needle detectors, should be set precisely to detect the closed needles & prevent the fabric tube
from completely pressing off.
 Proper yarn tension should be maintained on all the feeders.

17. 15. Lycra out & tension variation of Lycra:
Causes:
 Breakage of Lycra yarn & uneven tension of Lycra.


Fig: Lycra out


Remedies:
 To maintain uniform tension.

18. 16. Spirality:
Spirality appears in the form of a twisted garment, after washing. The seams on both the sides of the
garment displace, from their position & appear on the front & back of the garment.
Causes:
 Spirality is caused, by the Twisting Torque as a result, of the high yarn T.P.M.
 Hosiery yarns are soft twisted, whereas the Warp yarns are hard twisted
 Uneven Fabric Take down tension, on the Knitting machine.
 Unequal rate of Fabric feed on the Stenter, Calender& Compactor machines.


Fig: Spirality

Remedies:
 Use the Hosiery yarns of the recommended TPM level for Knitting
 (Hosiery yarns are soft twisted, in comparison to the Warp yarns)
 Fabric pull or the Take Down tension, on both sides of the grey fabric tube, on the knitting
machine, should be equal.
 Ensure uniform rate of feed of the dyed fabric, on both the edges, while feeding the fabric to the
Calendar, Compactor or Stenter machines.

19. 17. Bowing:
Bowing appears as, rows of courses or yarn dyed stripes, forming a bow shape, along the fabric width
Causes:
 Uneven distribution of tensions, across the fabric width while, dyeing or finishing the fabric.
Remedies
 Bowing can be corrected, by reprocessing the fabric feeding it from the opposite end.
 A special machine (MAHLO) is also available for, correcting the bowing in the knitted fabrics


18. Oil Lines:
Causes:
 Fibers & fluff accumulated in the needle tricks, which remain soaked with oil.
 Excessive oiling of the, needle beds.

Fig: Oil Lines
Remedies:
 Fibers, accumulated in the needle tricks, cause the oil to seep into the Fabric.
 Some lubricating oils are not washable & cannot be removed during Scouring.
 Oil lines appear in the fabric, in the lengthwise direction, even after dyeing.
 Remove all the Needles & the Sinkers of the machine, periodically.
 Clean the grooves of the Cylinder & Dial of the machine thoroughly, with petrol.
 Blow the grooves of the Cylinder, Dial & Sinker ring, with dry air after cleaning.

20. 19. Surface Hairiness & Piling:
Causes
 Abrasion due to the contact with rough surfaces
 Excessive surface hairiness caused, due to the abrasive tumbling action
 (Fabric friction in the Tumble Dryer)
 Rough Dyeing process & abrasive machine surfaces (Soft Flow Machine tubes, Tumble Dryer
drum etc.)
 Reprocessing of the fabric is, also a major cause of piling.

Remedies:
 Avoid using the Tumble Dryer.
 (Control shrinkage by maximum fabric relaxation & over feed in the processing)
 Regularly inspect the fabric contact points on all the machines, for any rough & sharp surfaces.
 (Rectify, if found rough)
 Avoid repeated reprocessing of the fabrics.
 Use anti pilling chemical treatments for the fabrics, prone to pilling.





20. Lycra and cotton mixed:
Causes:
 Lycra yarn twisted with cotton yarn.
Remedies:
 Correct the lycra path.
 Clear the yarn guide.

21. Facts about Fabric Defect:
 99% of Fabric Defects can be diagnosed with minimum or no testing if everyinvolved personal
from the fiber to fabric sector is willing to honestly tell his/her side of the story. Fabric-defect
diagnostic work has become more of detective work beacuse of missing facts.

 There is a great loss of fabric as well as money due to fabric defects so care should be taken to
minimize them as much as can be done.







Precaution Taken to Minimize Defects:

 Yarn mixing during feed into m/c should be prevented.
 Needle and jack should be checked for defects
 yarn placement should be correct in the frame
 Always check the fabrics are not creased during passage through breaking and squeezze rollers
ends.
 Follow bundling and shade sorting procedure continuously
 Make sure waste fluff had lint does not mix up with garment.










Conclusion:
Industrial analysis indicates that product quality can be improved and cost can be minimized by
monitoring of the knitting process. Some faults can be easily avoided by respecting some fundamental
pre-requisites on the knitting m/c such as the use of positive yarn feeders and the respect of rigorous m/c
maintenance and cleaning schedule.