Effect of Twist on Yarn Strength

Effect of Twist on Yarn Strength:

Short staple yarn:
Twist is imparted into a staple yarn to bind the fibers together and provide coherence to give strength to the yarn. Firstly, with the increment of twist, the lateral force holding the fibers also increases, which allows more fibers to contribute to the yarn strength. But secondly, when twist increases from the optimum level, the angle of fibers made with the axis of the yarn also increases, which makes the fibers contribute less to the yarn strength. The influence of increasing twist on the strength of a staple spun yarn is shown in Figure-1.

Continuous filament yarns:
In the case of filament yarns, a small amount of twist is needed to hold the filament fibers together. Therefore increase in twist will decrease the strength of filament yarn. This is due to the fact that the filaments are stronger than short staple fibers, so less twist is needed to impart strength in the case of filament yarns. Theoretically the maximum strength of a continuous filament yarn is possible when the filaments are oriented parallel to the axis of the yarn. Since the filaments are of variable strength, so the primary function of twist is to provide support to weaker filaments thus resulting in an increase in the yarn strength. The influence of increasing twist on a continuous filament yarn is shown in Figure-2.