The bowing effect cannot be defined in few words. This is a very common fabric defect. This defect occurs during weaving or dyeing. Normally, bowing effect generates during the dyeing process. Since we know that end and pick intersect to each other in the woven fabric at a right angle, then the intersecting angle of warp and weft should be identical at every chosen or desired place on the fabric surface. We also know that every grey fabric has 1” to 1.5” bowing at both the selvedge of the fabric. This is known as residual bowing.
This amount of bowing can not be avoided during weaving because the fabric near both the selvedge comes out later than main body fabric. It results in the form of bowing at both the selvedge. It can be rectified easily and completely during processing.
This problem mainly occurs due to faults in weaver’s beam. This kind of situation can reflect in the beams to be manufactured on the sectional warping machine as well as the direct warping machine.
If we mark at one complete pick across the full fabric width and marks at another one complete pick after one-meter interval across the full width of the fabric and now we measure the fabric length at both the selvedge. There will be a difference at both places. Actually, this difference is bowing due to improper setting of cone height.
We know, the nominal count and actual count of warp yarn always differ to each other. This difference makes the difference between actual warp yarn diameter and calculated diameter by machine software. The amount of twist (turns per inch) also affects the actual yarn diameter, this factor is also not taken into consideration by machine software.
The warp tension is also a very important factor in this case. In normal practice, warper does not change the warping creel tension for every warp count, he changes tension only when the warp count increases or decrease highly from previous warp count. This practice is also responsible for bowing effect occurring in the grey fabric. All above-stated reasons cause the bowing effect in the fabric. Apart from warp beam parameters configured in the machine software, machine manufacturer provides another solution to avoid the bowing effect. A special wrap reel is provided with the warping machine. The suggested number of ends are wound on the wrap reel, the number of wrappings is counted. This number of wrappings are fed into the software manually. This process neutralises all causes which can generate bowing in the fabric. If the warper follows this process precisely, the beam diameters at both flanges result equal to each other. Thus the possibility of bowing is avoided.
If warper observes this kind of situation, then he should adjust the creel tension by following below method:
If there is no bowing in the fabric but bowing appears after finishing. This may happen due to the wrong practice adopted during processing. The main possible causes generating bowing effect during processing are given below:
He should always stitch all the pieces in one direction. He should also confirm that the piece cutting is proper at both the ends of the fabric piece.
Pinholes in the fabric
Wrong end, wrong drawing and wrong denting in the fabric
Broken pick in the fabric
Warp floats in the fabric
Fabric defects due to yarn faults