Thursday, 6 November 2008
Common Fabric Defects-1
Common Fabric Defects
1. Weft Streaks
These are faint or sometimes prominant lines along the lenght of the fabric. Use of good quality reeds will largly reduce streaks due to uneven end spacing. Streaks can also be avoided through careful housekeeping and ensuring that different batches of yarns do not get mixed up.
This defect is characterised by a general grouping of warp ends drawn through individual dents of the reed with a fine crack showing up in between such groups. This is caused by
- insufficient tension difference between the shed lnes during beat up.
- excessive warp tension
- late shedding
3. Irregular reppiness
It is characterised by the prominance of alternate picks over small areas on one face of the fabric. The following precautions can help to minimise the occurrence of reppiness.
a. Worn out tappets and tradle bowls should be replaced
b The back rest should be raised by about 4 cm with respect to the fell line.
c. The emery rolles should be in good condition.
d. An increase in warp tension within workable limits helps to reduce this defects.
4. Small weft loops ( phurkies)
A phurki is a weft loom protruding from the cloth surface. Generally, the length of the yarn in the loop is not sufficient to permit snarling. These loops may protrude from both faces of the fabric. Early shedding, incresing warp tension within workable limits, use of good temples and adequate size pick of about 12% or higher - these measures can be used to prevent the occurrence of phurkies.
5. Curled and folded selvedges
This defect is characterised by the appearance of curls and folds in the fabric selvedges. The following points merit attention:
a. Denting order- the number of ends per reed dent in the selvedge should be 50 to 100% more than that in the body.
b. Warp Tension- An increase in warp tension results in a tighter selvedge.
c. Selvedge construction- The selvedge yarns should be preferably two ply and should be drawn one end per heald eye.
6.Missing Interlacement of weft at selvedges
In this defect, a group of extreme warp ends in the selvedges do not interlace with the weft over a fabric length of 1 to 4 cm. The main cause of this defect is excessive tension in the weft yarn.
7. Weft snarls
A weft snarl in a fabric is caused by a short length of three fold weft yarn of which two folds are intertwisted.
The incidence of such snarls can be reduced by ensuring the process setting of twist and by minimising the possibility of severe rubbing of yarn between the shuttle and the box front plate.
8. Weft Bar
A weft bar is dark or light band across the width of the fabric which shows up prominantly particularly in dyed fabrics.
Medium to long term periodic irregularity in yarn will produce regular weft bars in the fabric.
The remedial measures can be:
a. Better process control such as:
i. uniformity of count on groups of ring frames spinning the same count.
ii. Prevention of periodic irregularity in the yarn.
iii. Control of winding and pirning tension.
iv. Proper maintenance of let off and take up motion
v. Control over blend proportion.
vi. Better housekeeping to prevent mixing up of yarn from frames.
9. Broken Picks
In plain woven fabrics, this defect materialises by the presence of two picks in the same shed for a part of the width of the fabric.
The main cause of weft breaks are rough surfaces of shuttle, shuttle box, rough or incorrect placement of shuttle eye, loose fitting of pirn in the shuttle, incorrect alignment of pirn with shuttle eye and low yarn strength.
Lashing in is the term used to describe bits of extra weft yarn found tucked into the selvedge of the fabric.
Remedial measures are:
a. Proper maintenance of accessories and loom parts.
b. Adjusting the pattern of changes of the boxes.
c. The use on drop-box looms of a suitable brush fixed at the end of the temple rod.
11. Missing End (Chira)
A defect where one or more warp ends are missing in the fabric is called a chira. This is the most frequently occurring defect in Indian fabrics and constitutes 40-50% of the total defects. Most chiras are caused by broken that are not mended immediately.
It can be prevented by minimising missing ends in the beam and efficient maninteance of the warp stop motion.
Effective supervision to ensure that a broken end is not left unmended for long can also minimise the occurrence of chira.