1. Sewability of Fabrics
“Sewability of fabric is the characteristic property of a fabric which allows it to be seamed at the full limit of high-speed sewing machinery, without the mechanical degradation of fabric.”
Generally, the strength of woven fabric is considerably reduced by the seaming operation which intern reduces the overall life of a garment. Cutting, scorching, or fusing of yarns in fabric by a sewing needle are the reasons behind the loss in fabric strength as well as poor seam appearance. Fabric sewability is one of the top ten quality problems in garment industry.
|Sewability of Fabrics|
2. Sewability Test
- The proportion of fabric yarns cut by the needle (Needle Cutting/Yarn Severance).
- Loss in fabric strength caused by needle damage.
2.1 Needle Cutting Index/Yarn Severance
Needle cutting or yarn severance in a fabric is unreceptive because due to frayed yarns it may result in reduced seam strength, poor seam appearance or both.
2.1.1 ASTM test method for needle cutting or yarn severance:
Sewn seams are prepared for testing. After seaming operation is over, the sewing threads are removed from the test specimens. The count of the number of yarns in fabric and the count of the number of severed (detached/disengaged/ cut) and fused fabric yarns in the direction nearly perpendicular to the direction of sewing are used to calculate the needle cutting index. Needle cutting index can be determined by following formula.
|Formula: Needle Cutting Index|
One of the reason behind the needle cutting or yarn severance occurs is the stiffness of the yarns in fabric (fabric yarns) and a lack of mobility of the yarns. Instead of moving and/or deforming when the needle penetrates the fabric structure, the yarns remain taut and are ruptured or burned. Some damage may result from:
- Excessive heat generated due to the friction of the sewing needle and the fabric.
- Use of wrong size needle will result in sewing damage.
2.2 Seam Efficiency
There is loss in fabric strength after sewing which is because of damage caused by needle to yarn in fabric during needling.
The measurement of the loss in fabric strength due to needle damage consists of sewing a seam in the fabric, breaking the fabric at the line of stitching, and establishing a ratio between the original and the seamed fabric strength. Seam efficiency can be given by following formula:
|Formula: Seam Efficiency|
“If seam efficiency falls below 80%, the fabric has been excessively damaged by the sewing operation”.