Weaving:
Weaving is the intersection of two sets of straight yarns, warp and weft, which cross and interlace at right angles to each other. The lengthwise yarns are known as warp yarns and width wise yarns are known as weft or filling yarns and the fabric produced is known as woven fabric. The machine used for weaving fabric is a loom. It is a complex work. A number of faults occur in fabric during weaving process. Main faults in weaving are given below.
Faults/Defects/Problems in Weaving:
Major problems/faults/defects of weaving are pointed out below:
- Warp streaks
- Reediness
- Weft bar
- Weft crack
- Thick and thin places
- Weft loops
- Box marks
- High incidence of warp breaks
- Weft breaks
- Shuttle traps
- Shuttle flying
- Smashes
- Bad selvedge
- Broken picks
- Bullet
- Half pick
- Broken end
- Coarse end
- Coarse pick
- Slough off
- Thick end and thick picks
- Double end
- End out
- Fine end
- Jerk-in
- Knot
- Loom bar
- Loom barre
- Misdraw (Color)
- Mispick
- Reed mark
- Reed streak
- Set mark
- Shade bar
- Stop mark
- Tight end
- Pilling
- Float
- Pin marks
- Contamination of fluff
Causes and Remedies of Weaving Defects:
Warp streaks: Warp streaks are narrow, barre and dense stripes running along the warp direction. Main reasons are the variation in density of adjacent group of warp ends due to non-uniform dent spacing, wrong drawing-in, or count variations. Also, the variations in lustre, reflectance of dye pick-up of adjacent groups arising out of differences in raw materials, blend composition or yarn constructions contribute for streaks.
Reediness: These are very fine cracks or lines between groups of warp threads, caused due to excessive warp tension, late shedding, use of coarse reed with more number of ends per dent, bent reed wires, improper spacing of reed wires, wrong drawing, and insufficient troughing of shed, i.e. tension difference between top and bottom shed lines during beat up.
Weft bar: It is a band running weft-wise across the full width of the cloth. The normal reasons are the periodic medium to long term irregularity in the weft yarn, count difference in weft, excessive tension in the weft feed package, especially in filaments, variability in pick density and difference in twist, colour or shade of adjacent group of picks, difference in blend composition or in the cottons used.
Weft crack: It is a thin place or missing weft across the body of the fabric. The main causes are improper setting of anti crack motion, loose fitting of reed, loose or worn out crank, worn out crank arm,worn out crank shaft bearings, loose belt, worn out duck bills and beaters, weft fork not functioning properly, faulty take up, brake motion not acting instantaneously, shuttle striking on the weft fork due to weak picking, swing rail worn out, weaver not adjusting the fell of cloth properly at the time of starting a loom, and gripper not holding the weft firmly.
Thick and thin places: These are similar to weft bar, but unlike weft bars, it repeats at intervals. They are mainly due to irregular let-off, incorrect setting of holding and releasing pawls on the ratchet wheel of take-up motion, gears of take-up motion not meshing properly, and gear wheel teeth worn out or broken.
Weft loops: Loops project from the surface of cloth either on one or both sides of a cloth because of a small portion of weft getting caught by the warp threads. The main reasons are late shedding, low warp tension and use of bad temples.
Box marks: Box marks are due to something bruising or staining the weft while it is in or near the box. Main causes are dirty boxes, shuttle riding over the weft, oil from shuttle tongue, dirty shuttles, weft flying about too freely, oil splashes from loose cranks, oily spindles and buffers and dirty picking stick for under pick.
High incidence of warp breaks: Excessive warp tension, blunt or loose shuttle tip, rough shuttles, too small or too big shed formation, bottom shed line beating down on slay race, jerky movement of healds, too early or too late shedding, race board badly worn out, healds catching each other, sharp or rigid reed wires, warp size accumulation on reed, pirns projecting above or below shuttle, improper sizing, improper humidity in the loom shed, a weaker warp yarn, a higher speed of loom, more number of ends per inch for the count being used, less air space in reed are the main causes for excessive warp breaks.
Weft breaks: High weft tension, improper build of pirn, knots at the nose or chase of pirns, back stitches in cones fed as weft in shuttle less looms, rough and damaged surface of pirns, shuttle tongue not in level, rough places inside the shuttle, damaged nylon loops, sloughing off or loosely built weft package, shuttle eye chipped or broken, weft trapped in the box, selvedge ends cutting the weft, weft fork too far through the grate, rough box fronts or shuttle guides, improper alignment of cone in weft feeder, lower twist in weft resulting in weft opening out in air-jet looms, grippers missing the picks, improper knotting of tail ends, and rough handling of cones are the main reasons for higher weft breaks.
Shuttle traps: Entangled warp ends due to fluff falling on the warp, broken warp end entangled to adjacent end, knot with a long tail resulting in entanglement, snarls in yarn getting entangled, too muchhairiness in yarns, weak picking, faulty shuttle checking, gear wheels slipping due to broken teeth, loose stop rod finger, and uneven joint of flat belt are the normal reasons for shuttle trap.
Shuttle flying: Fibrous yarns, knots with long tail ends, slack warp, uneven race board, small sheds, bottom line too high, worn pickers, swells giving twist to the shuttle as it leaves the box, early picking,late shedding, unbalanced shuttle, box spindle not set properly, box front not set properly and missing shuttle guard are the main reasons for shuttle flying.
Smashes: Daggers not working, frog spring ineffective, bad shuttle, improper boxing of shuttle, worn out picker, worn out transfer hammer, damaged pirn and entanglements are main causes of smashes.
Bad selvedge: Improper shuttle wire tension, bent shuttle jaw, shuttle crack, more tension on selvedge yarns, late shedding resulting in rubbing of shuttle to the selvedge and improper selection of selvedge weave for the fabric being woven are the main reasons for bad selvedge.
Broken picks: A filling yarn that is broken in the weaving of a fabric appears as a defect. Improper functioning of weft stop motion results in broken picks undetected and going in to the fabric.
Bullet: Bullets are low twisted double yarn seen weft wise in fabrics. Those are generally zero twisted parallel yarns. Practical causes of faults are improper functioning of bunch motion, incorrect yarn path through spindle, loose tensioners, capsule and spring working, insufficient yarn as bunch and knot is not applied after removing bunch yarn
Half pick: In case of rapier looms, if the second rapier does not collect the weft, it shall stop in between, and we get half pick.
Broken end: A defect in fabric caused by a warp yarn that was broken during weaving or finishing.
Coarse end: Warp yarn that has a diameter too large, too irregular or that contains too much foreign material to make an even, smooth fabric.
Coarse pick: Filling yarn that is too large and imperfect to appear to advantage in the final cloth.
Slough off: Weft yarn has slipped from the pirn. Proper monitoring of strength and chase in pirn winding can solve this problem.
Thick end and thick picks: Higher diameter in yarn for a short distance can be due to improper piecing at spinning preparatory or drop in pressure on the drafting rollers for a short time. This also can happen due to not removing of spinners double, not piecing the end properly by removing the lapped materials, accumulation of fluff in condensers, cradles and in the necks of the top rollers.
Double end: Two ends that weave as one. This happens because of migration of a broken end to the adjacent reed space along with the neighboring end.
End out: A warp yarn that was broken or missing during weaving.
Fine end: A defect in silk warp yarn consisting of thin places that occur when some of the filaments that should be in the warp yarn are absent, generally caused by improper reeling. Warp end of abnormally small diameter, i.e. long thin places of class I1 and I2 also is referred as fine end.
Jerk-in: An extra piece of filling yarn jerked by the shuttle into the fabric along with a regular pick of filling.
Knot: Knot is defined as a knob or lump formed by interlacing portions of one or more flexible strands or a quantity of yarn, or thread, which varies with the fibre; it consists of a set of coils. Control in pirn winding, the winding to binding coils ratio can solve this problem.
Loom bar: A change in shade across the width of a fabric, resulting from a build up of tension in the shuttle before a filling change.
Loom barre: Repetitive selvedge-to-selvedge unevenness in woven fabric usually attributed to a mechanical defect in the let-off or the take-up motion.
Misdraw (Colour): In woven fabrics the drawing of coloured yarns through the loom harness contrary to the colour pattern and/or design weave is termed as misdraw. In case of warp knits misdraw is the drawing of coloured yarns through the guide bars contrary to the pattern design.
Mispick: A defect in woven fabric caused by a missing or out-of sequence yarn.
Reed mark: A crack between groups of warp ends, either continuous or at intervals, which can happen due to damaged reed or improper spacing of dents.
Reed streak: A warp wise defect attributable to a bad reed like uneven reed space, bent reed wire, slant wire, damaged reed wire etc.
Set mark: Defect in woven fabric resulting from prolonged loom stoppage. Because of the humid weather and the fine dust present in the atmosphere, the cloth exposed shall get slightly different color and also some relaxation takes place. A combined effect gives a line in weft direction.
Shade bar: A distinct shade change of short duration across the width of the fabric. This is normally due to a mix up of weft with different property.
Stop mark: Narrow band of different weave density, across the width of a woven fabric, caused by improper warp tension adjustment after a loom stop. A well trained weaver can reduce this type of defects.
Tight end: Warp yarn in a woven fabric that was under excessive tension during weaving or shrank more than the normal amount.
Pilling: Fibre filaments that break in yarn due to friction leaving small clumps of loose fibres on the surface
Float: Slack warp and Faulty Pattern Card are the main reasons for a float in a woven fabric.
Pin marks: Poorly adjusted temple pins or damaged pins can lead to pin marks.
Contamination of fluff: Different fibres or foreign materials get mixed during spinning, winding or in weaving preparation stage, causing visual objection in fabric. The causes are improper cleanliness, not properly cleaning the machines after each doff and lot changes, improper suction of drafting zones of gill boxes and roving, improper cleaning of scrapper and scrapper plate after every lot change of doff, not using of curtains for partition of machines running on different colours, overhead cleaners of ply winding and ring frames blowing dust on running spindles or drums, material not covered to avoid fly and fluff accumulation, use of compressed air for cleaning machines while in working or while adjacent machine is working and use of common return air ducts and running different coloured fibres in the shed.
References:
- Training and development of technical staff in the textile industry by B. Purushothama
- https://en.wikipedia.org
- https://www.scribd.com
- https://textilelearner.blogspot.com/2012/04/fabric-faults-causes-of-woven-fabrics.html
