SPI*Thd. strength*1. 7 = estimated Seam Strength

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Seam Engineering In Apparels
When apparel industry is concerned, we first start thinking, how apparels are generated, which engineering is playing an important role into it. Right from the beginning of conceiving an idea for designing arrangement and finished with a brand name. The tiniest unit of a garment is fibre which, further takes shape to yarn and threads.
Threads similarly play a vital role in Apparel Industry in construction and stitching of garment. Now, here we will talk what is seam engineering.
Seam Engineering
It includes seam and stitch construction. The more thread a stitch consumes, the greater is the strength. This is clearly visible when we compare lock stitch and chain stitch. Lock stitch is one in which thread is locked both sides of the fabric and starts with 301 lock stitch. It undergoes more shearing as compared to chain stitch and over edge stitch. As in lockstitch threads are interlocked rather than inter-looped.
Another concept attached to seam strength is SPI (stitch per inch)- this again goes back to the words that more is the thread in the seam, the more is the strength of the seam. This again varies as per the fabrics where, too many stitches might damage the fabric as picking at one place increases, leading to weakening of the yarn. However, it also leads to production loss with increase in the puckering number.
How to estimate seam Strength
Now, for estimating the strength there are certain formulas that are developed for different kinds of fabric strength.
1) 301 lock stitch formula 401 chain stitch formula
SPI* Thd. strength*1. 5* = estimated seam strength
For e. g. 10*4. 01 bs*1. 5 = 601 bs
2) For apparels, normal loop strength
SPI*Thd. strength*1. 7 = estimated Seam Strength
For e. g. 10*4. 01 bs*1. 7 = 681 bs
3) For Woven Fabrics
Stitch Type- 301 lock stitch or 401 chain stitch
Thread strength- Single end breaking strength of the threads measured in Pounds.
Machine Adjustments for stitch tensions
Greater seam strength can be obtained by adjusting the sewingthreads tensions, threads controls and eyelets etc.
More of sewing machine thread tension will lead to reduce of the seam strength along with many sewing problems.
Factors for Seam Strength
Abrasion Resistance: this is an important factor for upholstery, footwear and in carpet manufacturing as well as into apparels. This includes fiber type, fibre size and shape, thread construction and, thread size.
Stitch and seam construction: Present quality measurement standards of apparels ASTN, AATCC for evaluating the toughness of sewing threads. They are conducting comprehensive test using a modified crokometer.
Threads of various types are now available and each one has its own tickets no. and weight through which it is identified. A manufacturer should be more careful while making a choice of thread for a garment.
Revolution in thread manufacturing has ensured the availability of thread quality as per the fabric demands. One who is aware of quality, parameters of threads and, machine type, lubrication of machine and to thread can successfully lead adding quality to apparels and its manufacturing.
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