Friday, November 30, 2018

FABRIC DEFECTS DUE TO YARN FAULTS

VARIOUS TYPES OF FABRIC DEFECTS DUE TO YARN FAULTS

Fabric defect: 

Any abnormal area of the fabric surface which does not appear in the form repeated pattern is termed as fabric defect. The defects appearing on the surface of the woven fabric can be classified into the following main categories:

Fabric defects due to yarn faults:

The fabric defects appearing on the fabric surface due faults present in the yarn used is termed as fabric defects due to yarn faults. The various types of fabric defects appearing due to yarn faults are given below:

Big knots in the fabric:

The knot in the yarn is always a serious issue for the woven fabric. A big knot clearly appears on the fabric. It causes the holes in the fabric too. If a weaver weaves a fabric with single ply yarn, knotless (auto spliced) yarn should we used in the warp as well as in weft to avoid such types of defects. If the double or multi plied yarn is used in the fabric, then this problem cannot be rectified completely. Any breakage during the doubling process generates the knot, this knot appears on the fabric surface. The knot should be of the smallest in size. These knots are removed during fabric mending process. The mender inserts the small piece of same yarn and this yarn overlaps the broken end or pick at both the tails of the broken end or pick. When this fabric goes under tension during processing, this overlapped yarn prevents to generate the holes in the fabric. The weaver should use weavers knot during warp breakage repairing on the loom to minimize this defect.

Thick and thin places in the yarn in the fabric:

A place in the yarn having yarn diameter in excess of +50% of the average yarn diameter and the length 8-12 millimeters is considered as a thick place. A place in a yarn having yarn diameter -50% or more than average diameter and any length is considered as a thin place. If the yarn has these yarn irregularities, these appear on the fabric surface in different forms in warp and weft. If the warp yarn has this kind of fault, then an individual end looks like slub yarn. This uneven look of an individual end draws user attention at that particular place of the fabric. Since this look in an irregular pattern on the fabric surface, therefore it is not acceptable in the fabric.

If these irregularities come in the weft yarn, then matter becomes much serious. This yarn irregularity in the weft yarn appears more prominently on the fabric surface than warp. Weft wise slub look results for some fabric length. A weaver can minimize this defect up to some extent by using two weft feeder in the loom during weaving. The yarn having low imperfection should be used to avoid this defect up to the optimum level. These defects are repaired during mending by eliminating the thick or thin place. These yarn are replaced by mender with same yarn through mending needle. 

Yarn count variation:

Any type of variation in the count of warp yarn results in the form of a thick end or thin end which is visible on the fabric. This kind of uneven appearance of the fabric cause rejection of the fabric. The mending of this type of defect depends upon the length of the defected fabric. If the length is short say 2-3 meters, then mender can change this end with the same count of yarn. If the length is too much, then the fabric gets rejected because the exchange of defective thread with the fresh thread is a much time-consuming process. If mending cost is more than fabric cost, then it is better to reject the defective fabric.

If there is a count variation in the weft yarn, then it results in the form of weft bars, variation in GSM, thick and thin areas across the full fabric width. Individual weft bar can be repaired but GSM variation, thick and thin areas are not repairable. These irregularities are unacceptable in the fabric. Sometimes these thick and thin areas do not become visible in grey fabric. These appear prominently after dyeing of the fabric.

Contaminated yarn:

Sometimes foreign materials like polyester, polyethylene, plastic material or coloured fibres are mixed with yarn during various spinning processes. These defects can be seen on the fabric surface in grey stage too but some types of contamination are not possible to see in grey fabric. When this fabric is dyed, the contaminated material appears clearly on the fabric surface. If the fabric has low contamination, then it can be eliminated in the mending process. If a fabric has high contamination, then it is almost impossible to remove it completely. The fabric can get rejected due to this contamination.  

Immature fibres in the yarn:

If the yarn has many immature fibres in it, then these immature fibres appear in the form of small balls on the fabric surface. These immature fibres have very poor dyeing affinity and do not pick up the colour in dyeing. These immature fibres can be dissolved in the mercerisation process up to the maximum extent. These immature fibres become a much serious issue when yarn dyed fabric is woven. These fibres appear in the form of undyed fibres on the fabric surface. These fibres can be removed by bio polish (enzyme wash) up to some extent. Please note, there is always a chance of change in the shade during this process.

Hairiness of the yarn:

Variation in the yarn hairiness level of the weft yarn causes low and high hairiness areas across the full width of the fabric. If the hairiness level varies in warp yarn it does not reflect prominently on the fabric surface. This type of fabric defect can be rectified up to singeing process. The bio – polish of the fabric also helps to dilute this defect up to some extent.

Yarn strength variation:

The variation in the yarn strength causes poor tensile strength and tearing strength in the warp and weft. This kind of fabric defect is almost unrepairable.

Yarn twist variation:

The yarn twist variation causes variation in yarn diameter. The thick and thin area across the full width may be generated if weft yarn has twist variation. This type of fabric defect does not look clearly in grey fabric. When the fabric is dyed, this defect appears prominently on the fabric surface. This defect is not repairable.

If the warp yarn has twist variation, then it appears as a thick or thin end on the fabric surface. This defect becomes more prominent after processing. If the length of the defect is small, then it can be replaced in the mending process with fresh yarn of the same count. If the length is too much, then the fabric gets rejected.

Dirty yarn:

Any type of dirt present in the yarn is always a serious issue. If warp or weft yarn has any dirt in it, then it gets dissolved during fabric processing. Thus dirt present in the fabric causes pinholes in the fabric after processing. A weaver should always be careful about this defect.

Snarls in the yarn:

The excessive twist in the yarn causes to generate snarls in the yarn during warping or during weft package unwinding. as soon as yarn tension decreases, snarls generate immediately. When these snarls get woven into the fabric, thick places in the fabric created. These defects can be rectified in fabric mending process. Weaver should always be careful about the excessive degree of yarn twist. If the yarn has an excessive degree of yarn twist, then the yarn tension during warping should we enough to prevent snarls formation in the warp. Snarls formation in the warp may create a very serious problem during weaving. It creates false warp breakage stops during weaving. If the snarls form in the weft yarn, these snarls appear as thick places on the fabric surface.  

Slough-off in the yarn:

This is totally yarn package defect. If the nose of the package is very soft, there are always chances of slough-off in the yarn. The yarn in the bunch form gets woven into the fabric. This is repairable fabric defect in mending process.

Missing ply in double yarn:

If the fabric is woven with double plies yarn, there are always chances of ply missing in the warp or weft yarn. It can be repaired in the mending process.

Lot mixed yarn:

A weaver should always be careful about yarn lot. Two yarn lots neither should be mixed in the warp yarn nor in the weft yarn.

If there are yarn lots mixing in the warp in grey fabric, then it will become more prominent and will look different due to variation in colour affinity. If weft yarn has lots mixing problem, then it will result in the form of colour variation areas in the across the full width of the fabric. Normally, it is very difficult to judge lot mixing problem in grey fabric.
Air permeability of the fabric 

Fabric pilling


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