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February 2018

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
Sewability of Fabrics

2. Sewability Test

Sewability of a fabric (The degree of its resistance to needle damage) can be assessed by determining:
  1. The proportion of fabric yarns cut by the needle (Needle Cutting/Yarn Severance).
  2. 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
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
Formula: Seam Efficiency
“If seam efficiency falls below 80%, the fabric has been excessively damaged by the sewing operation”.

1.What is Snagging in Fabric?

In this article points like what is snagging in fabric and Fabric snagging test methods are covered. An article covering points like factors affecting fabric snagging, how to prevent fabric snagging, snagging resistance fabric/ anti-snagging fabric will be published soon.
“Snagging is defined as a defect caused by the pulling or plucking of yarns from a fabric surface.”
The snagging of a specific fabric in actual wear varies with the individual wearer and general condition of use. Knits used in a more rugged outerwear application, such as men's slacks, result in very high and unacceptable levels of snagging.



2. Fabric Snagging Test Methods

ASTM has following fabric snagging test methods for testing snag resistance of fabric.
  1. Mace Test
  2. Bean Bag Test



2.1 Mace Test

2.1.1 Test Method

In mace test, fabric specimens are placed on a cylindrical drum in tubular form. A mace (spiked ball) is allowed to bounce randomly against each rotating specimen. Snags could occur to a fabric due to the bouncing action of mace i.e. spiked ball over fabric specimen. The degree of fabric snagging is then evaluated by comparison of the tested specimens with visual standards that may be either fabric or photographs of fabrics. 
Mace Fabric Snagging Test
Mace Fabric Snagging Test

2.1.2 Mace Snag Tester

Assessment/Grading: 

The observed resistance to snagging is reported on a scale ranging from No. 5 (no snagging) to No. 1 (severe snagging).

Suitability of Test:

This method is suitable for a range of woven and knitted fabrics made from textured or untextured yarns containing staple or continuous filaments.



2.2 Bean Bag Test

2.2.1 Test Method

In bean bag test, fabric specimens are cut into dimensions of approximately 9 x18 cm. This is folded in half and sewn into a pouch as shown in fig.2. A "bean bag" weighing approximately 1 lb is placed in the pouch. After placing the bean bag into the pouch of test specimen, the top/open part of that pouch is sewn and closed. This closed pouch is placed in the cylinder, which has eight baffle bars with a series of tenter pins protruding from them at an angle. After placing the pouch in cylinder the machine is started because of which the test specimen is subjected to a random tumble action. The tenter pins act to snag the specimen as the cylinder rotates. The tenter pins carry it (pouch) to the top of the chamber, where it pulls away and drops to the bottom. The specimen is subjected to 100 revolutions of the cylinder. 

Bean Bag Snag Tester
Bean Bag Snag Tester
The specimen is then removed and the degree of snagging is evaluated by two methods:

  1. Comparison of the tested specimen with visual rating standards that may be either snagged fabrics or photographs of snagged fabrics.
  2. Counting the number of snags. 

The resistance to snagging can be reported in the first case on a numerical scale ranging from No.5 (no or insignificant snagging) to No.1 (severe snagging), and simply as number of snags in the second case.
The bean bag method to have the following advantages over other snagging tests in use:
  1. Snagging is multidirectional in end use and the bean bag method simulates this very effectively.
  2. This test is more realistic. The test fabric is mounted in a relaxed state nad tension occurs only as the weighted bean bag pulls the test specimen away from the tenter pins where it was impaled.
  3. Test data obtained from this test method is less variable.
  4. Due to multidirectional testing and low variation, half the number of test specimens were required.

Ashish Hulle

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