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.
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 more 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.
Evaluation of Spirality:
AATCC Test method 179 -2004:
This test method determines change in skewness in woven and
knitted fabrics or twist in garments when subjected to repeated automatic laundering
procedures commonly used in the home. Washing and drying procedures used for
shrinkage tests and other home laundering tests are specified for this method.
For some fabrics the degree of twist of fabric in garments
is not solely dependent on its behavior in the unsewn state; it also may be
dependent on the manner of garment assembly.
This method is based on the following principle:
Change in skewness in fabric or twist in garment specimens
resulting from procedures typical of home laundering practices is measured
using bench marks applied to the specimens before laundering. Fabrics or
garments that are distorted in their unlaundered state due to faulty finishing
of the fabric or faulty assembly of garments may give deceptive results when
laundered by any procedure. In such cases, it is recommended that specimens not
be used, or if used, the results be considered as indicative of those specimens
only.
One of the common methods of measurement of spirality in
garment is indicated below:
Figure 1: Inverted T marking
