12 Woven fabric defects

B. A. Muralidhar

1. INTRODUCTION

Woven fabric / textile clothingis a commonly used material in everyday life, it is manufactured with spun (or) filament yarns made of natural, synthetic (or) blends of both natural and synthetic materials. A woven fabric is manufactured by the interlacement of warp ends and weft picks in a predetermined pattern called “weave”. Woven fabric defects in textile and apparel industry refers to the inhomogeneous areas of the woven fabric surface. A defect means a fault on the fabric surface, as a result of the manufacturing process. Fabric inspection is a quality control process meant at classifying and locating defects. The changing fashion industry has produced larger product diversity and shorter life cycle for production. Since textile fabric constitutes about 50-60% of the total cost in garment manufacturing, garments with fabric defects sell with a massive discount of 45-65%. As such quality control of fabrics before further value addition is essential to ensure the quality of the finished products. Undeniably improved inspection performance leads to better product image.

Currently, fabric inspection process is mainly performed manually. Manual inspection is the means to assure quality, it helps correction of small defects. At present there are more than 70 types of fabric defects defined by textile industry. Fabric defects particularly result from, yarn faults, machine problems, excessive stretching, poor finishing, among others. The reliability of manual inspection is limited by inattentiveness and boredom.

However, automatic fabric inspection is advantageous, nonetheless there are challenges such as wide varieties of fabrics, distinct composition and texture, similarity in the shape between defects and background texture. As such it is not easy to tackle all the challenges by a single method.

Textile manufacturing operations are exceedingly complex, and it is not within the scope of this module to discuss each operation in fabric manufacturing which are potential source of trouble in the finished fabric. However, a number of principle operations to which defects may be traced will be highlighted.

2. GRADING OF FABRICS

During the inspection, fabric defects are identified and the mendable defects are mended. Also at this stage, depending on the frequency and type of defects fabrics are examined and graded into different categories depending on the severity of the defects. Grading systems such as the four point and the ten point systems are generally used to evaluate the fabric quality.

• First quality – fabric pieces containing no objectionable faults.
• Short length – fabric pieces having shorter length compared to the length specified by the buyer.
• Seconds – fabric pieces containing minor flaws which are not objectionable are graded as seconds.
• Rags – fabric cut pieces whose length varies in between 25-90 cm. Chindhies – fabric cut pieces having lengths shorter than 25 cm.

2.1 TYPES OF FABRIC DEFECTS

Fabric defects are broadly classified into

• Avoidable and unavoidable Major and minor
• Mendable and unamendable

It is very difficult to avoid certain defects despite best practices like for example the floats. However, majority of the defects can be avoided if certain precautions are taken. A mended starting mark is considered a minor defect whereas weft cracks are major defects. Further, certain defects such as isolated snarls could be mended.

Broad classification of major and minor defects:

3. Weaving defects:

For centuries, the process of weaving has remained unchanged. However, today’s high speed loom are complex equipment’s with automatic, mechanical and electrical controls which are precision built require careful maintenance and fine adjustments.

3.1 Warp imperfections: following the process of drawing in ends through the healds according to the design pattern. At this stage the error which may occur is “wrong drawing-in” or the ends drawn in at improper sequence which would result in distortion of pattern. The warp ends then pass through reed, essentially a comb having a series of metal wires equally spaced, the space between the wires being specified according to the type of fabric. Principle imperfections may be, chafing due to rough metal edges, grease, rust stains from dirty reeds and variations in space between the warp ends due to week or damaged reeds. Other imperfections which may occur are tight and overstretched ends, slack ends etc.

3.2 Weft imperfections: lack of uniformity in size, twist, unremoved tint, stretched yarn are frequent causes of filling streaks. Mixed filling bobbins are usually responsible for bands of different appearance from shuttle change to shuttle change. Certain weft damages may be inflicted by the weft stop motion. Broken picks may be traced to rough shuttle boxes, sharp feeler motions or burrs/cuts in shuttle eyes, yarn guides. Uneven, loopy or weft kinks are usually due to insufficient tension, waste accumulation behind drop wires, weft having been  caught on to the shuttle. Double picks are generally the result of improper harness action. Improper action of the shuttle feeler can be responsible for pulled-in filling. Eccentric take-up rollers, faulty take-up motion are likely to produce “uneven picking”.

3.3Miscellaneous damages:

Temple marks: Temple are used to hold the fabric to its proper width while weaving, temple leave a permanent impression on some fabrics. Roller type temples due to eccentric rolls may cause distortion in some constructions which would be difficult to correct.

Shuttle and box marks: may be due to improper shedding, to picking which causes rebound of shuttle, to damaged shuttle, or due to inadequate plush covering on the race board. Box marks are from the chafing of weft yarn as it sloughs off the bobbin and is trapped under the shuttle.

Sand-roll cuts: the covering of the take up roll may damage the fibres of woven fabric.

Creases: hard creases may be introduced into the fabric by careless take-up, such as inspection and re-rolling. In certain cases creases are impossible to remove in wet processing, and show up as streaks.

Selvedge’s: are extremely troublesome, and causes a lot of problems such as tight selvedge, loose selvedge, torn selvedge, uneven selvedge etc.

Damage to woven fabrics: Very few imperfections are introduced after the cloth has been woven. Dangers such as staining, cutting or tearing, insect or mildew damage and simple mechanical damages as nail holes while packing is to be blamed.

3.4Common fabric defects and their causes

Bar:appears as a band of yarns running crossways across the full width of the fabric from selvedge to selvedge primarily due to difference in appearance from its adjoining ends.

A pick bar is due to different pick spacing from its adjacent surface.

A starting mark, starts abruptly and shades away gradually to normal fabric this is also due to the change in the pick spacing.

A weft bar caused by the variation in the tension of the weft, causes the pick to shine may be caused by large knots, rough spots in the cop.

A weft bar is chiefly due to the variance in weft yarn count, twist, material, colour, lustre etc. from the adjoining weft yarns.

The bar defect is primarily caused due to restarting of loom after, prolonged stoppage, pick finding or un-weaving or pull back.

Box Mark:these are due to staining or scrubbing of the weft yarn while it is in or near the shuttle boxes. It shows up as a crosswise line in the body of the fabric owing to stained or damaged weft yarn rubbing or rebounding from the dirty box.This defect is predominantly caused due to shuttle riding over the weft yarn, lubricant, oil or grease from the shuttle tongue, oil splashes from loose crank, spindle or buffers, dirty picking sticks etc.

Broken Pattern:It is the discontinuity of design or weave pattern. This defect is mainly caused due to wrong drawing in of the warp threads, incorrect lifting of the warp ends or due to the insertion of the wrong pick in the wrong shed.

Broken Pick or weft breaks:this defect occurs when a portion of the weft yarn is missing from the width of the fabric. Some of the key reasons for the high number of broken picks could be summed up as, Improper build of pirn, high weft tension, knots, shuttle tongue not in line, fragmented nylon loops, poor winding, rough shuttle eyes, rough shuttles may cut the weft yarn leading to broken pick faults.

Weft cracks: it is a narrow opening of variable length or width between two adjacent yarns running parallel to the weft direction in the body of the fabric. The defect would appear in the fabric as a stripe with lower pick density than normal. This defect is caused due to the erratic operation of the sley, a loose reed, worn out crank, crank arm, crank shaft bearing, loose belt etc.

Cut weft: this defect is chiefly caused by the use of weak weft yarns with a strong warp, which shows up as a pin hole in the finished fabric. Sharp reed and tight selvedge may also be responsible for this defect.

Defective selvedge: selvedge’s are extremely troublesome and are prone to many defects such as curled, cut, pulled-in, rugged, slack, tight, uneven selvedge etc.

Curled, rolled or turned over selvedge are principally caused due to incorrect balance between the body and the selvedge, differential shrinkage between the body and the selvedge, weft tension etc.

Cut, torn or burst selvedge are caused due to the selvedge sticking to damaged temple roller or to the emery roller.

Pulled in selvedge are principally caused due to isolated tight picks.

Rugged selvedge is a wavy selvedge showing indentations or corrugations at the fabric edges, this defect occurs due to tension variation of selvedge ends.

Slack selvedge is a selvedge which is slacker than the body fabric this may lead to cut, torn or burst selvedge during subsequent processing. This defect is caused due to incorrect balance of cloth structure between the body and selvedge.

Tight selvedge, a selvedge tighter than the body fabric may also cause tear, cut or burst selvedge during subsequent processing, principle cause being imbalance of structure between the body and selvedge.

Uneven selvedge, variation in width along the length of the fabric. Chiefly caused due to weft tension variation.

Double ends: in this defect two or more warp ends accidentally become woven as one. The defect is characterised by a thick bar. This defect mostly occurs due to faulty drawing-in of warp ends.

Floats Stitches: this defect shows up in a fabric where ends and picks escape interlacement, mainly caused due to un-mended broken ends, long tails of the knots, unsatisfactory working of the stop motions.

Fuzzy: Presence of an abraded filament yarn would cause a fibrous appearance on the fabric surface.

Gout: in this defect lint or other foreign maters such as leather, wood, plastic, hardened fluff etc. accidentally get woven in to the fabric. This defeat could be prevented by proper maintenance and housekeeping practices.

Hang Pick: a pick producing a triangular shaped hole in the fabric, caused by knots which are not tied properly and prevent the weft from being beaten up firmly to the fell of the cloth.

Harness Skip or Warp Skip: in this the warp ends continuously appearing without any interlacements with the weft pick on the fabric surface. Mainly caused due to broken heald wire, improper shed timing, broken dobby peg etc.

Lashing in: this defect is caused by an extra yarn being dragged into the cloth along with the regular weft yarn. These defects are more common in a drop box – power loom and in auto looms. There could be many reasons for the defect which include lively weft, rough pickers, broken leather buffer, rough shuttle, inadequate working of the shuttle eye cutter on an auto loom etc.

Loose Warp Ends: the loose warp ends are a common defect caused by loose ends forming a distinctive warp line in the woven fabric, often these loose ends cause a smash by entangling with other warp yarn.

Hanging Threads: loose threads hanging on the face of the fabric, chiefly due to ends not removed by the weaver after piecing up of broken ends.

Missing ends:this is one of the most commonly occurring fabric defects. It accounts for about 40-50% of the total defects. This defect is categorised by missing ends with a gap of one or more warp ends in the cloth at its intended place. Their main causes are broken ends not mended immediately, missing ends, poor quality yarn, loom fault, improper working of the warp stop motion, carelessness of the weaver etc.

Reed Marks (or) reediness:these are fine lines in between a group of warp threads. A reedy fabric would show spacing between warp ends grouped together across the width of the fabric, chiefly caused due to late shedding. This defect can be overcome by toughing of the back rest so that the top shed ends are slacker than the lower ends during the process of beating up.

Shuttle Marks: are width wise abrasion of ends by the shuttle. Improper shedding, too early or too late shedding may cause shuttle marks.

Slough-off: this defect is primarily caused due to loosely wound pirn. During weaving the weft yarn slips off the loosely wound pirn and gets entangled in the warp. The removal of the slough off from the fabric will cause a hole to be formed.

Stains: one of the grave problems in the textile industry, occurs chiefly in the weaving shed. Stains could be from lubricants, oil, rust, grease, sweat, box marks, dirt etc. Poor material handling, cleaning and oiling practices are the chief cause for the stains

Tear Drop: this type of defect occurs as a short curved pick, generally caused due to insufficient warp tension, oversized warp or incorrect heald timing.

Temple Mark: holes, surface disturbances along the selvedge may leave a permanent impression on some fabrics. Eccentric roller temples may cause distortion in some constructions which would be difficult to correct.

Wrong Denting: Warp ends wrongly drawn through the reed.

Wrong Drawing: Warp ends not drawn through the healds-shaft as per the design requirements.

4. Weaving defects:

The quality of fabric in a weaving shed is influenced by entire sequence of operations from weaving preparatory to weaving. Periodic and systematic preventive inspection of loom mechanisms and accessories should be carried out to ensure defect free fabric. Training the workers and making them quality conscious is a preventive method of avoiding weaving defects.

5. Conclusions:

In this module on woven fabric defects, the viewers are briefed about fabric grading and few common fabric defects and their causes. The foregoing, by no means is a complete description of all defects which may be introduced into a woven fabrics. However, this module presents a general idea of some of the more frequent conditions which may result in weaving faults.

References

1. Talukdar M. K., Sriramulu P. K., Ajgaonkar D. B. “Weaving”, Mahajan PublishersPrivate Limited 1998.
2. Gordeev P., Volkov P., Blinov I. Svyatenko M. “Cotton Weaving” Mir Publishers Moscow 1987.

Web links

http://shodhganga.inflibnet.ac.in/bitstream/10603/40774/17/17_appendix.pdf