Twisting is simply the process of combining together multiple fibers, threads or yarns in a wrapping around (twisting) motion. Twisting fibers will create a thread (or singles), twisting threads will create a yarn, and twisting yarns will create a cord or cable - and so on.
The twisting process is when one end of a fiber strand is held and the other end is turned back to form a yarn.
For staple fibers, twisting is necessary to turn the fibers into a yarn. Before twisting, the loose fibers are usually coalesced into a fiber strip, and after twisting the outer fibers are squeezed towards the inner layers to create centripetal pressure, which causes the strand to gain friction along the direction of the fiber elongation.
For filament yarn and ply yarn, twisting creates a compact structure that is not easily damaged by lateral external forces, and twisting also creates deformed filaments and fancy threads. The amount and direction of twisting affects not only the feel and appearance of the fabric but also its intrinsic quality.
After twisting, the outer fiber is twisted back in an inclined spiral, the fiber is twisted and deformed and the yarns are held together, changing the collective structural form and mechanical and physical properties of the fibers.
Twisted yarn can be classified into 2 types depending on the direction of the twisted.
- S twisted yarn is the left twisted
- Z twisted yarn is the right twisted
In the other word, the portion of the fiber on the yarns indicates where the yarn is S or Z twist. Regular weaving industry usually used a Z twisted yarn. The direction of the twisted may observe by holding the yarns in a vertical position. If the twisted direction of the slope of the center part of the letter “S”, the yarn has an S twist. If the yarn spiral conforms to the slope of the letter “Z”, the yarn has a ‘Z” twist.
Two sections of the yarn produce an angular displacement of 360°, which becomes a twisting round, commonly referred to as one turn.
Yarns are generally twisted in the Tex system, expressed as the number of twisting rounds per 10cm of yarn length. For combed woolen yarns and chemical filaments, use the metric count system, expressed as the number of twisting rounds per meter. In addition, there is the English count system, expressed as the number of twisting rounds per inch.
The twisted affects the strength, flexibility, elasticity and shrinkage of the yarn. If the twisted increases, the strength of the yarn would be increased, but the twist must not exceed a certain value, otherwise the strength decreases, which is called the critical twist of the yarn. The critical twisted is different for yarns made from different raw materials. In general, as long as the strength requirements are met, the less twist the yarn has, the better, because an increasing in the twisted makes the yarn stiffer to the touch, less elastic and more shrinkage, this is the reason why filament yarns are twisted as little as possible.
Most of fabrics are made by using yarn with an ordinary twisted. This is the amount necessary to hold the fibers close enough together to prevent them from slipping apart. Thus gives strength to the yarn.
The amount of twisted can be measure by the number of twisted per inch.
Low twisted – 0 to 3 twisted per inch
Ordinary twisted – 4 to 7 twisted per inch
High twisted – 8 to 12 twisted per inch