Officer-Technical Services, Application Research centre,

(Resil chemicals Pvt Ltd, Bangalore)


Introduction


Cotton sewing thread is the only general-purpose sewing thread made from natural raw material. Before the advent of synthetic sewing threads, cotton was used for most sewing operations. With the introduction of wash and wear fabrics and higher machine speeds, cotton threads were no longer adequate. They provide good sewing performance but have inferior strength and abrasion resistance as compared to synthetic sewing threads. Today cotton-sewing threads are used only for over-dyed cotton apparel.


With development of modern high-speed sewing line operations, the performance of thread in the garment business has become extremely crucial. It is the thread, which defines the garment.


Synthetic Threads:


The most popular sewing threads available today, are mainly of the following types:


Spun polyester: the most widely used apparel thread it can be used on sheer as well as heavyweight apparel.


Core spun polyester: Of two primary types cotton wrapped and polyester wrapped, each has a polyester filament core. The fibre wrapping around gives it its superior all-round performance.


Cotton Wrapped Polyester Core: excellent sewability. Commonly used for all apparel and preferred for denim Polyester Wrapped Polyester Core: excellent sewability and color retention.

Preferred by industrial garment manufacturers and denim apparel.


Continuous Filament


Synthetics: mainly produced from Nylon and polyester- they are the strongest

Threads and are lint free. Mainly used for footwear, mattresses, tents etc.


The Performance Parameters:


Usually 100% spun polyester or even texturized polyester sewing threads are used for industrial garment making. Specialty threads (such as embroidery threads) frequently use cotton; rayon or blended yarn is used.


Taking a basic every-day operation such as an eight stitches per inch straight seam, sewn with a general-purpose lockstitch machine, sewing speeds can be 5500 stitches a minute. The needle moves downward roughly one inch through the fabric, and then back up again the same distance for every stitch it forms whilst the feed mechanism moves the fabric along. Thus the needle on that machine has the potential to move up and down sixteen times, or inches, per inch sewn.


At 5500 stitches per minute, with both an up and down movement every stitch, the needle actually moves 11000 inches per minute - a speed equivalent to approximately 10.5 miles per hour.


The top thread, however, not only goes the distance of the needle but is looped round the bobbin and then pulled taut. If the distances of the thread from the top needle point, down through the fabric and throat plate, round the bobbin and back up again and pulled tight is approximately double that of the needle movement, the thread is traveling at over twenty miles per hour, through a fabric whose individual yarns are normally smaller than the thread and tightly woven or knitted together. When the needle penetrates the fabric being sewn, the yarns have to give way to the needle within a timeframe that can be as low as 0.0003 seconds.


Passing through a thick, tightly woven fabric causes considerable resistance, friction, and heat build-up - all of which affect the needle and the thread. Research work shows, for example, that needle temperature can rise within seconds to 350C (100C above the melting point of polyester).


So it is hardly surprising that needles get broken, bent, points and throat plates damaged, stitches slipped and fabric damaged, puckered and distorted.


Thus the reasons for the uncompromising performance parameters especially in a thread business are easily understandable.