..KNITTING DEFECTS AND REMEDIES..

Made by:Raisa Gupta (15)

Defected and Defect-free Fabric..

• What is a Fabric Defect? A Fabric Defect is any abnormality in the Fabric that

hinders its acceptability by the consumer.

• What is a Defect-Free Fabric?1. A Fabric that exhibits a consistent performance within

the boundaries of human use & human view.2. A Fabric that exhibits a consistent appearance within

the human sight boundaries.

A Glossary of Fabric Defects..

• Askewed or Bias : condition where where courses are not square with wale lines on knits.

• Barre : occurs in circular knit. Caused by mixing yarn on feed into machine. Fabric will appear to have horizontal streaks.

• Birdseye: Caused by unintentional tucking from malfunctioning needle. Usually two small distorted stitches, side by side

• Bowing : Usually caused by finishing.In knits the course lines lie in an arc across width of goods. Critical on stripes or patterns and not as critical on solid color fabrics.

• Broken Color Pattern :Usually caused by color yarn out of place on frame.

• Crease Streak : Occurs in tubular knits. Results from creased fabric passing through squeeze rollers in the dyeing process.

• Drop Stitches Results from malfunctioning needle or jack. Will appear as holes, or missing stitches.

• End Out : Occurs in Warp knit. Results from knitting machine continuing to run with missing end.

• Hole : caused by broken needle.• Missing Yarn : Occurs in warp knit. Results from wrong

fibre yarn (or wrong size yarn) placed on warp. Fabric could appear as thick end or different colour if fibers have different affinity for dye.

• Mixed Yarn Occurs in Warp knit. Results from wrong fiber yarn ( or wrong size yarn) placed on warp. Fabric could appear as thick end or different color if fibers have different affinity for dye.

• Needle Line: Caused by bent needle forming distorted stitches. Usually vertical line.

• Pin Holes :Holes along selvage caused by pins holding fabric

while it processes through tenter frame.Major if pin holes extend into body of fabric far enough to be visible in the finished product.

• Press-Off : results when all or some of the needles on circular knitting fail to function and fabric either falls off the machine or design is completely disrupted or destroyed. Many knitting needles are broken and have to be replaced when bad press-off occurs. Bad press-offs usually start a new roll of fabric.

• Runner :Usually caused by broken needle. Will appear as vertical line. (most machines have a stopping device to stop machine when a needle breaks).

• Sanforize Pucker :Results from uneven wetting out on sanforize; usually caused by defective spray heads. Fabric will appear wavy or puckering when spread on cutting table. Difficult to detect during inspection on inspection machine with fabric under roller tension.

• Slub (Knit fabric) : Usually caused by a thick or heavy place in yarn, or by ling getting onto yarn feeds

• Straying End : Warp Knit. Caused when an end of yarn breaks and the loose end strays and is knit irregularly into another area.

..Some Knitting Defects..

Measurement of Bias ..Skew or Bias - Measure the skew in three places spaced as widely as possible along the length of the fabric or along a minimum of 1 linear yard.  If possible,                make no measurement closer to the ends of the roll or piece of fabric than 1 yard.  Draw a line perpendicular to the selvage across the fabric from a point C where the marked yarn or course meets one selvage, meeting the other selvage at point B.  Measure the distance between points A and B or D and B, and B and C, as shown in Fig. 2.  Record the three or more skew or bias measurements.  Calculate the maximum skew or bias as a percentage of the fabric width using the equation: "% Skew = Distance AB or DB x 100 / width BC"

Measurement of Bowing.. Bow – A straightedge is

placed across the fabric between the points at which a marked filling yarn or knitting course meets the two selvages or edges. The greatest distance between the straightedge and the marked filling yarn or course is measured parallel to the selvages (Fig. 1 Distance "D").

Different Causes of Fabric Barre..

Raw material, Knitting and Yarn consideration

Machine-Related Factors:• Failure of spinning preparation to eliminate or minimize shortand long-term variation• Failure of opening and cleaning machines to completelyeliminate contaminants and trash particles• 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

What are the factors that could lead to fabric defects?

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 unfavorable fiber characteristics• Weight variation• Twist variation• Excessive Hairiness

What are the factors that could lead to fabric defects?

Some other Fabric Defects..

Small bits of contaminants spun into the yarn

White specs

Synthetic fibre contaminant

Pointers focussing on the Defected area..

Pointers focussing on the Defected area..

Factors Affecting Defects in Plain-Weft Knitted Fabrics due to Knots of Spun Yarns..

The effects of some factors on the defect in plain-weft knitting due to knots, using a cotton yam and a worsted yarn. The results obtained are as follows:

• The knitting defect due to the knot is almost the knitting hole caused by the end breakage in plain-weft knitting zone. The end breakage occurs near the knot on the take-down side.

• The end breakage rate increases together with the increase of the depth of stitch draw, the input tension, the take-down weight, the machine gauge, the coefficient of yarn friction, the step length of cam, and the machine speed. But the increase of the cam angle decreases the end breakage rate.

Shade Variation and some Defect examples..

Filling streaks and slubs of varying lengths

Weak spots (over bleaching)

Shade variation in knitted fabrics is an issue of concern. It could be during dyeing and finishing. Mixing could be a suspect. The problem can be machine related or material related.

Another Fabric Defect..

Another Fabric Defect..

Knit-in Contaminants..

There can be certain defects which arise during the knit-in process thus are shown here.

Modelling Fabric Defects-The Problem Theory..

DEFECTS SEVERITY Barre Usually major

Askewd or bias Could be major or minor

Birdseye Major

Bowing Major or minor

Broken colour pattern Major

Crease streak Major or Minor

Drop stitches Major

End Out Usually Major

Hole Major

Missing Yarn Major

Mixed Yarn Major

Needle Line Major or Minor

Pin Holes Major

Runner Major

Slub Major or Minor

Straying End Major

Industry Practise..

PURPOSE• To establish a uniform method for determining, quantifying and measuring

the quality of warp knit elastomeric fabrics; and a method for measuring length, width, and other physical properties.

METHOD• Four-Point System - Penalty points are attributed to a piece of fabric

according to the length of its defects measured in inches. The following schedule of penalty points is based on fabrics 60/62 inches in width for defects visible when inspected on face side of fabric only:

• Length of Defects: 3 inches or lessOver 3, but not over 6 inchesOver 6, but not over 9 inchesOver 9 inches

Industry Practise..

Number of Penalty Points • 1• 2• 3• 4• Four penalty points per linear yard are the maximum assessable for fabrics

up to 60/62 inches in width. • For fabrics over 60/62 inches in width, maximum allowable penalty points

are to be increased in proportion as the width exceeds 60 inches. • Regardless of the length of fabric, the quality shall be expressed in the

number of penalty points per 100 yard length. (Example: A 40-yard piece width six penalty points is to be rated as 15 points per 100 yards.)

Industry Practise..

Identification and Rating Defects: Examples of defects in evaluating quality are these: • Knitting defects, including holes other than pinholes• Grease/oil spots• Dye spots• Stains• Slubs-except where they are an inherent part of the yarn• Picks • Bowing and Skewing (bias): bowing and skewing may not exceed 5% of overall

width. Examples: 60" width - 3" tolerance and 72" width - 3.5" tolerance• Any yard containing bowing or skewing in excess of these limits shall be penalized

four points.• Fabrics are to be examined for these defects only on the agreed upon selling face

(which may be the technical face, or technical back).

Facts about Fabric Defects..

• 99% of Fabric-Defects can be diagnosed with minimum or no testing if every involved personnel from the fiber to the fabric sector is willing to honestly tell his/her side of the story. Fabric-defect diagnostic work has become more of detective work because of missing facts.

• Poor Cotton Mixing is a Sure Defect-Causing Factor & Good Mixing alone does not always guarantee a Defect-Free Fabric. Machine-Related Factors cannot be emphasized enough.

• High cost yarn testing equipments available today reveal minimum or no prediction of potential fabric defects. Indeed, there is a significant gap between yarn quality as tested in the yarn raw form and corresponding yarn quality as it exists in the fabric.

• 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.

• Fabric faults or defects are responsible for nearly 85% of the defects found in the garment industry.

Current Usual method of Detection and Optimal measure..

Present Scenario- Inspection is done manually, ie., when a significant

amount of fabric is produced,the fabric roll is removed from circular knitting machine and then sent to an inspection frame.

Optimal Solution-To automatically inspect fabric as it is being produced

and to encourage maintainence personnel to prevent production of defects or to cahnge process parameters automatically and consequently improve fabric quality.

Fabric faults, their Causes and Solutions..Varied defects are mentioned here .Each defect can have innumerable number of reasons behind it’s occurrence and there can be many alternative ways to correct the problem.

Precautions Taken to Minimize Defects..

• Yarn mixing during feed into the machine should be prevented.

• Needle and jack should be checked for defects.• Yarn placement should be in the frame.• Always check the fabric is not creased during passage

through breaking and squeeze roller ends.• Follow bundling and shadesorting procedures

cautiously.• Make sure the waste fluff nad lint does not mix up

with the garment.• Keep checking from time to time that the machine is

working properly and the speed is as per requirements

Recent Advancement in dealing with Fabric Defects..

• A novel approach is developed to identify fabric defects through the integration of image processing techniques and Neural Nets.

• In industrial setting, knitted fabric defects can be eliminated or reduced by means of on-line monitoring system and automatic defect detection devices.

• Morphological analysis: A system has been developed to measure knitted fabric parameters using image analysis techniques. This technique can be used to evaluate courses per unit length, wales per unit length,fabric cover and weight per unit area.

• Development of an Intelligent Fabric classification System: The overall approach encompassed six steps: knitting fabric

samples, image capturing using a CCD camera, image processing, binary image preparation as a preprocessor for Neural Nets,image feature extraction and finally Neural Nets classification.

Hardware Components used in the Inspection Structure..

Flowchart of Defect Segmentation..

On-line Fabric Defect Detection..

Circular Knitting Machine

Fabric Defect Detection Scanning

for Circular Knitting..

• These designed defect scanners are known to be extremely accurate, self-cleaning and with high resolutions through their unique mounting hardware systems.

• Through a system of choker and expander assemblies, a vertical air gap is created, allowing RunStop scanning for maximum fabric-scanner interfacing.

• These hardware systems are easily adaptable to differing brands of knitting machines and to varying production abilities of those machines

• .Various sizes of the infrared scanner facing are also easily adaptable to a variety of machines, while infrared light is employed to eliminate ambient light interference. Wire guarding of the scanner mount ensures protection against press-offs. Robust scanner designs ensure durability in the harsh conditions of the mill environment.

• Fabric defect detection is the basic work of the System. With defect scanning, circular knitting has been revolutionized, and has increased textile profits globally.

Defects and Mending at RANA POLYCOT..Some of the most common defects,mending strategies and

requirements in that industry:• Incase a panel is curved from it’s path rather than being

a straight line,a latch needle is used to mend the side of the panel and bring it in line with the initial garment line.

• Fastening at the edges of the panels done by the SHIMA SEIKI machine should follow a straight line,in case it does not it needs to be mended.It is all done manually by the latch needle.

• In case the machine stops workin properly during construction and ruins the fabric,the panels are rejected but in case of an urgency and with extra cash flow,it is mended.

• While makin the rib and conjoining with the top,at times,the hook leaves the yarn and a hollow is created.

My Industrial Visit Experience..Defects found at RANA POLYCOT,MOHALI and the causes :• While using the needle,the latch failed to cast off it’s

loop,takin one yarn after the other and putting extreme pressure thus creating a defect.

• Torque of the comb at the sides got less thus the cloth jumps from it’s place leading to a minor defect in the rib structure.

• Machine speed increases at times,so does the take down and so the stitch becomes tight and the cloth rips.

• A defect comes into picture when a double thread works all through the stitching but suddenly it starts with single.

• A fault may also occur because of the needle,when the latch does not cast off properly and thus can’t be mended.Needle shape gets distorted.

• High speed of the machine, more take down and transfer speed,more roller speed,the inability of the needle to make a proper loop can create defects.

Defects and Mending at RANA POLYCOT..• At times the fastening line left at the edges gets a reduction

from the boundary eg. From line 5 to 3 and thus needs mending.

• At times the edge lock leaves the edge and the fabric starts disentangling.This requires immediate hand-mending.

• During cable construction,there is a case where 3 up,3 down technique is followed but suddenly the machine leaves the area,mending comes to the rescue here.

• Sometimes,the stripe width of the striper varies all the way.This needs serious mending.It is also a knitting fault.

• In some cases,the thread edges left at the corners get pulled which distorts the entire garment.It needs to be pressed and stretched and brought back to shape.Hurrieda nd harsh action can ruin the cloth.

• At times fastening spacing goes berserk,if rectified,it follows a loose-tight sequence.Gives the garment a shabby look.

Bibliography..• RANA POLYCOT industry report• www.matrixcontrols.com• www.fibre2fashion.com• http://158.132.122.156/itc/macau/defects/tsld003.htm• www.saarczone.com• www.apparelsearch.com• www.highbeam.com• www.encyclopedia.com• www.resil.com• www.ntcresearch.org• www.iso.org• www.trg.sagepub.com• www.indiantextilejournal.com• www.sitra.org• www.taispk.com

..THANK YOU..