The ever increasing demand of knitted apparels has attracted attention in global niche market. In comparison to woven garment, around 50% of the clothing needs are met by the knitted goods. It is well known that weft knitted fabrics tend to undergo certain dimensional change that causes distortion in which there is a tendency of the knitted loops to bend over, causing the wales to be at diagonal instead of perpendicular to the courses (Figure 1).

Figure 1: Angular relationship of course and wales in a knitted structure

In other words, spirality occurs in knitted fabric because of asymmetric loops which turns in the wales and course of a fabric into an angular relationship other than 90 degree. This is a very common problem in single jersey knits and it may exist in grey, washed or finished state and has an obvious influence on both the aesthetic and functional performance of knitwear. However, it does not appear in interlock and rib knits because the wale on the face is counter balanced by a wale on the back.

Course spirality is a very common inherent problem in plain knitted fabrics. Some of the practical problems arising out of the loop spirality in knitted garments are: displacement or shifting of seams, mismatched patterns and sewing difficulties. These problems are often corrected by finishing steps such as setting / treatment with resins, heat and steam, so that wale lines are perpendicular to the course lines. Such setting is often not stable, and after repeated washing cycles, skewing of the wales normally re-occurs.

Causes of generation:

The residual torque in the component yarn caused due to bending and twisting is the most important phenomenon contributing to spirality. The residual torque is shown by its twist liveliness. Hence the greater the twist liveliness, the greater is the spirality. Twist liveliness of yarn is affected by the twist factor or twist multiple. Besides the torque, spirality is also governed by fibre parameters, cross-section, yarn formation system, yarn geometry, knit structure and fabric finishing. Machine parameters do contribute to spirality. For instance, with multi-feeder circular knitting machines, course inclination will be more, thus exhibit spirality.