Wednesday, 10 June 2009

How to determine Seam Strength

Seam strength is the strength of seam assembly in a garment. It is a function of the strength of the thread used for the seam, type of seam assembly in a garment and type of fabric used, among other factors.

Failure of seam assembly can occur either by breaking of sewing thread, tearing of the fabric at the seam, excessive yarn slippage adjacent to the stitches or a combination of the above mentioned conditions.

How to determine seam strength in laboratory

In a lab CRE type tensile testing machines such as INSTRON is used. Before testing the samples are prepared.The method is called Grab Test

If the specimens are from manufactured items such as garment then five speicmens are cut having a length of 270 mm on either side of the stitch line and a width of 100 mm parallel to the stitch line.

If the specimens are prepared from fabric then seam strength is measured in warp, weft and bias directions. In such cases swatches are cut in these three directions.

Also two such swatches from two different rolls are joined by the seam assembly- for which we want to test the strength- to measure the parameters.

Before testing the material is conditioned to standard temperature.

The specimen is mounted on the tensile tester. It is operated until the sewn seam or fabric ruptures. The observation is made whether the rupture is caused by Fabric yarn rupture, sewing thread rupture, sewn seam yarn slippage or a combination of two or more of the foregoing. This will give the seam strength.

Repeat this Grab Test for the fabric specimens from which seam failure test is carried out. The result will give the base fabric strength.

Seam strength ( for each direction) will be calculated by the formula:

Seam strength ( gms/cm)= ( Individual specimen seam breaking force in gms)/ Width of specimen in Jaws i.e. 2.5 cm.

Base fabric breaking strength of the individual specimens are calculated by the formula:

Base fabric strength (gms/cm)= (Base Fabric breaking force in gms of individual test specimen)/ Width of specimen in jaws i.e. 2.5 cm

Seam Efficiency= Seam Strength ( Seamed Fabric Strength) x 100)/ Base Fabric Strength

If this seam efficiency ratio falls below 80%, the fabric has been excessively damaged by the sewing operation.

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