Concept: By twisting the fiber structure of the wire, the relative angular displacement between the cross sections of the wire is produced, and the structure of the wire is changed by the inclination of the straight fibers and the axis. Twisting can make the thread have certain physical and mechanical properties such as strength, elasticity, elongation, luster, and feel. It is expressed by the number of twists per unit length, usually the number of twists per inch (T.P.I) or the number of twists per meter (T.P.M) .
Twist: Rotate 360 ​​degrees around the axis as a twist.
Twist direction (S direction or Z direction): When the sliver is vertical, the inclination direction of the helix formed by rotating around the axis. The inclined direction of the S twist direction is the same as the middle part of the letter S, that is, the right-hand direction or the clockwise direction. The inclined direction of the Z twist direction is the same as the middle of the letter Z, that is, the left-handed direction or the counterclockwise direction.
The relationship between twist and strength: The twist of the thread is proportional to the strength, but after a certain twist, the strength decreases. If the twist is too large, the twist angle will increase, the luster of the thread will be poor and the hand feeling will be poor; if the twist is too small, hairiness will occur and the hand will be loose. This is because the twist increases, the frictional resistance between fibers increases, and the strength of the thread increases. However, as the twist increases, the axial component force of the sliver becomes smaller, and the internal and external fiber stress is unevenly distributed, resulting in inconsistent fiber breakage.
In short, the breaking performance, strength and twist of the thread are closely related. The twist and twist direction are determined according to the needs of the finished product and post-processing, generally the Z twist direction.
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