Bowing and Skewness in the Fabric

Bow: When weft yarns are even at two edges but arched across the middle is known as Bow. Bowing is a condition in the woven fabric where filling yarns are displaced from a line perpendicular to the selvages and lie in an arc across the width of the fabric. Bowing appears as rows of courses or yarn-dyed stripes forming a bow-shaped curvature along the fabric width. 

Skew: Skewing is a similar condition in which filling yarns are angularly displaced from a line perpendicular to the edge or side of the fabric. It is a condition resulting when filling yarns or knitted courses are angularly displaced from a line perpendicular to the edge or side of the fabric due to uneven distribution of tension. 

Bowing and skewing affects striped or patterned fabric quality more than for solid color fabrics, as the greater contrast in patterns makes the distortion more prominent.

Effect Of Bowing and Skewing

If this defect is not resolved, it may cause cutting and sewing problems. This may also create serious problems during production. Although the garment may look perfect after the final pressing and packaging, the defect can appear after home laundering. The garment may have visible spirality, Twist or torque. 

Measuring Bow

The bow is defined as the greatest distance, measured parallel to the selvages, between a filling or course yarn, stripe, or dominant line and a straight line perpendicular to the selvages. A bow may have different forms:

Single Bow%= Dip of the Bow (Maximum deviation from the perpendicular line) × 100 ½ Width of the fabric.

Double Bow%= Dip of the Bow (Maximum deviation from the perpendicular line) ×100 ¼ Width of the fabric

1. Lay at least three yards of fabric, without tension, on a horizontal surface.

2. Place a straight edge across the fabric perpendicular to the selvages at a point where a filling or course yarn, stripe, or dominant line begins at the selvage.

3. Measure the greatest distance between the perpendicular line and the yarn, stripe, or dominant line at any point across the width of the fabric.

4. Repeat this procedure at least three places along the length of the fabric and report the average maximum bow along with the location of the occurrence.

Measuring Skew:

Skew: Distortion in the construction of the fabric i.e. in the yarn that constitutes the fabric. The pattern on one side of the fabric is ahead of the pattern on the opposite side. Skew(bias) is defined as the distance measure parallel to and along a selvage between the point at which a filling or course yarn, stripe, or dominant line meets the other selvage.

Skew%= Dip of the Skew (Maximum deviation from the perpendicular line) × 100 Width of the fabric

1. Lay the fabric, without tension, on a horizontal surface at least three yards long.

2. Place a straight edge across the fabric perpendicular to the selvages at a point where a filling or course yarn, stripe, or dominant line begins at the selvage.

3. Measure the distance parallel to and along a selvage between the point at which the yarn, stripe, or dominant line meets this selvage and the perpendicular line to the selvage form the point at which the same yarn, stripe, or dominant line meets the opposite selvage.

4. Repeat this procedure at least three places along the length of the fabric and report the average maximum bias.

Residual Bowing

This defect occurs during weaving or dyeing. Normally, the bowing effect generates during the dyeing process. Generally, the grey fabric has 1” to 1.5” bowing at both the selvage of the fabric. This is known as residual bowing.

Excessing bowing  in grey fabric: 

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.

When the warping of the beam is done on the sectional warping machine, then the warper needs to be careful about the selection of required cone height or warping drum traverse speed according to warp beam parameters.

Warp tension is also a very important factor. 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. 

If the warping is being done on the direct warping machine, the warping creel tension plays a very important role to avoid the bowing effect.

 If warper places equal dead weight washers on each warp end throughout the warping creel, then a tension difference results between front warp end and rare warp end. The tension of rare warp ends is decreased slightly. This decreased tension causes bowing in the grey fabric at both the selvage sides.

Solution:-

If warper observes this kind of situation, then he should adjust the creel tension 

• Divide the creel into three sections,(front section, middle section, and rare section) 
• Adjust the creel tension in such a way that front section ends should have the lowest tension, the middle section ends should have more tension than front ends.
• The rare section ends should have the highest tension. This tension arrangement avoids the chances of bowing in the grey fabric.
• If there is no bowing in the fabric but bowing appears after finishing. This may happen due to the wrong practice during processing
• Since we know that a dyeing lot is completed by joining together many pieces of grey fabric by stitching, The tailor should look carefully at the direction of residual bowing and join the pcs accordingly.