Seam strength

Published on: 16.10.2017
Did you know that the appropriate seam strength can be determined for each seam application? 
It is well known that the thread makes the seam and so using the correct type of thread in the correct manner to create the seam determines its strength. One of the deciding factors in the strength of the seam is the number of stitches to the cm. The seam strength is directly influenced by two parameters: The longitudinal and transverse strength of the thread. A distinction is made in transverse strength between loop strength and knot strength. Only the loop strength is of relevance to the strength of the seam.

Below is a list of some loop strengths: 
Polyester endless high-strength = 60 – 65 %
Polyester 6.6 endless high-strength = 70 – 80 %
Polyester 6.6 textured = 90 – 95 %
Carbon = 4 – 6 %

It is helpful to know this if, for instance, the machinist wishes to change to a thinner and less tear-resistant sewing thread while retaining the same seam strength. If a finer fabric in a new collection is being worked on, the closing seam can be just as strong if the stitch count is raised slightly. Raising the stitch count from 3 to 4.5 stitches/cm, for example, results in only a slight increase in thread consumption of about 10%, whereas the seam strength increases by about 50%. The outcome of this is that no compromises have to be made in the optimum construction of a garment. Use the thread thickness that seems appropriate to the fabric and stitch a seam that is just as strong.

It should be noted that a higher stitch count does not necessarily mean that thread consumption is greater. For double chain stitch, for instance, a higher stitch count makes a difference only to needle thread consumption and barely any difference to looper thread consumption. This increase in needle thread consumption depends, of course, on the thickness of the material being stitched but the gain in strength remains in the seam. Increased loss of strength is an indication that the sewing machine is unsuitable or has been wrongly adjusted. It may also be when sewing technical textiles, that the material is so hard that the sewing thread becomes damaged by heat, resulting in a loss of strength.

Seams unlimited – with A&E Gütermann threads.