Seam is the joint between the two parts of a garment. For the perfect fitting and look of the garment seam appearance and its strength has to be proper. Many factors like appropriate sewing, needle size and its type, fabrics used and its weight, stitches done on the garment, seam construction and tension level of thread influences the strength of seam.
Seam strength testing is basically an examination of the amount of pressure required to tear or break the seam of the garment. Measurement of seam strength is a part of quality control procedure which is essential for garments. The fabrics are tested for it in the machine that checks the point at which the seam breakage occurs. There are many problems associated with the seam strength if there is any fault during making of seam, for instance- the seam and fabric splits at same point of time and sometimes the seam is safe but the fabric tears off :-
Various criteria associated with appropriate seam implementation:
Stitch and seam construction
The best available option of stitch to ensure strong seams is Locked stitch as in this stitch there is interlocking of the threads which increases the seam strength. There are various types of seam constructions, the list is as follows:-
a) Decorative Seam As the name suggests this seam is done for decorating the garment. This is done on one or more than one layer of fabric through many rows of stitches sewn on them.
b) Super Imposed Seam Superimposing the seam is the simplest and widely used type of seam construction. The border of one piece is kept on another piece of fabric, then sewn together.
c) Applied Seam When some outside material other than the fabric itself like lace, patch, etc are sewn on the seam or edge of the garment, it is known as applied seam.
d) Bound Seam This seam is also used for decorative purpose. Here the edges are attached by means of tapes or through self binding.
e) Single Ply Construction Seam This seam is constructed from single layer or piece of fabric. Generally used for manufacturing belts and belts loops.
f) Edge Neatening Here the edges of the fabric are trimmed, hemmed and folded through stitches.
g) Lapped Seam This is the strongest type of seam usually used for denims. Here the seam is done on the fabrics overlapped.
There are many factors associated with sewing needle which are important from the viewpoint for better seam strength and appearance. The diameter of the needle, the shape of its tip and size of the eye hole of the needle affects the seam construction of the garment. The size of the eye hole of the needle should be in accordance with the thickness of the thread. If the needle hole is smaller and does not provide effortless passing of the thread then there is the possibility of wearing out of the thread during use of the garment. And if the needle hole is larger and the thread is finer than the level required, mis-stitch might result due to low quality of loop formation and thread control. Thus proper ratio of size and type of sewing needle and thread is required. Also to avoid harm to the fabric due to excessive heating of needles while stitching special needles have been developed like- titanium nitride coated needle.
Fabric type and weight
Seam strength and its performance also depends upon the various characteristics of fabrics used. The material of the fabric, the type of fabric weave, thread count, the pattern positioning, type of yarn and seam direction.
Thread type, construction, size and finish
The type of the thread used, its construction, size and finishing influences the seam strength of the garment. There are many types of threads like cotton thread, polyester thread, silk threads, etc. It is a known thing that polyester thread is more durable than cotton thread. However the type of thread used depends upon the fabrics being used, for eg.- for silk fabrics silk thread is used.
There are different types of thread construction like multifilament, core, spun, textured, etc. Continuous filament core threads provide better seam strength compared to other construction of threads. Different thread sizes are available in market but finest thread are preferred more as longer length of finer threads can be wind around the lockstitch machine and they do not acquire much space in the seam. This avoids seam puckering.