How to Determine Seam Strength in Garment Industries

How to Determine Seam Strength in Garment Industries

Joyankar Mojumder
Inspector (FCAI)
Modern Testing Services (BD) Ltd.
280, East Narshinghpur, Ashulia, Savar, Dhaka.
Email: mozumderjoy@yahoo.com

What is seam strength?
The main factors of the seam strength are seam type, the stitch type, stitch density, fabric strength, thread strength, and the tension of thread which is applied in the seam. In this article, I will discuss how to determine seam strength of garment.

A lapped seam is the strongest of all seams because the fabric is lapped upon itself and the sewing threads contribution is mainly to hold the lapped plies in place.

The lockstitch is the most common stitch type in garments industries, but it is easily damaged. Chain stitch and over edge stitch types are higher seam strength and greater extensibility than a lockstitch.

The number of stitches over a given length of seam that is called “stitch density” which is direct influence on seam strength. Up to a point higher stitch ratings create stronger seams.

The seam should be engineered to deliver a balance between the stitching and the strength of the material being sewn. In most cases it is better for the stitching to fail prior to the material failing because the stitching can be repaired.

Thread tension is critical for the seam strength and seam elongation. If the thread is too tight in the seam it’s natural elongation is withdrawn allowing the thread to fail prematurely. This is particularly true when garments are subjected to after-make laundry processes.

Seam engineering:
Garments are made up using a range of different stitch and seam types. The engineering of the seam is more than just a matter of looking up the specification on a chart. There are many factors to be considered if high quality, durable seams are to be produced. The most important characteristic of any seam is seam strength.

How to determine seam strength:
The simple method of determining seam strength based on two parameters.

For lockstitch: 
Approximate seam strength can be determined as the number of stitches per inch multiplied by the single thread strength multiplied by 1.5

Seam strength = SPI x STS x 1.5

Here, stitch per inch (SPI) = 8

Single thread strength (STS) = 1100 grams

So, seam strength = 8 x 1100 x 1.5

= 13200 grams or 13.2 kg

For chain stitch: 
The approximate seam strength can be derived from the stitches per inch multiplied by the single thread strength multiplied by 1.7

Here, stitch per inch (SPI) = 11

Single thread strength (STS) = 1100 grams

So, seam strength = 11 x 1100 x 1.7

= 20570 grams or 20.57 kg