Weft knitted fabrics tend to undergo a 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 counterbalanced 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 a 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 a change in skewness in woven and knitted fabrics or twists 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 benchmarks 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 are considered as indicative of those specimens only.
One of the common methods of measurement of spirality in garments is indicated below:
One leg of a right angle marking device is placed along Line YZ so that the second leg is on a perpendicular downward from point “B”. A benchmark is drawn along the perpendicular on line YZ. The intersection of the benchmark and line YZ corresponds with point A’ as depicted in Figure 1. The length of lines AA’ and AB is measured and recorded with a suitable tape or ruler to the nearest millimeter or tenth of an inch or smaller increment. Point A can be shifted to left or right depending on the direction of spirality.
Calculation:
Percent change in spirality can be represented as follows:
X = 100 x (AA’/AB),
where, X = % change in spirality
The practical way of measurement:
Determination of spirality in percentage:
- Align the shoulder of the top (Figure 2) or the waist of the bottom (Figure 3) and lay it flat without tension on the table.
- Gently remove large wrinkles and creases. Begin smoothing at point E working down the garment body.
- Using marking pen, one spirality mark should be placed at uppermost of the garment folded edge (point E) and the other spirality mark should be placed at the lower most point of the same folded edge (Point F).
- Measure and record the distance from point F to point G and measure and record the distance from point H and point G.
- Then, wash and dry the specimen according to care label as per the recommended procedure.
- Condition the specimen after washing.
- Align again the shoulder of the top or the waist of the bottom and lay it flat without tension on the table.
- Gently remove large wrinkles and creases. Begin smoothing at point E working down the garment body.
- Measure and record the distance from point E to point G.
- Measure and record the distance from point F to point G.
- Calculate spirality of garments before and after washing using the following formula – % Spirality = (FG/EG) x 100
As per the experience of world-renowned retailers around the globe, seam twisting/shape distortion/spirality greater than 6% in tops and shorts and 4% in skirts, pants, dresses, and sleepwear detracts from the appearance of the garment.
Determination of angle of wale spirality
- For specimens tested in the original state conditioning is not essential, for processed specimens a minimum of 4 hours in the standard atmosphere is required.
- Determine accurately the path of the course line; this can be achieved by either placing the base of the protractor or a rule along the course line or drawing a line parallel to the course with a fine tip pen.
- Determine accurately the path of the wale line that intersects with the drawn course line, draw along this wale line.
- Place the protractor along a course line ensuring wale intersects with the bottom of the 90° line on the protractor (Figure 4).
- The angle between the 90° line and wale line is measured and the direction of spirality (+ right, – left) is recorded.
- Repeat the process nine more times so that ten results are recorded and the mean is determined.
Notes:
- If any difficulty occurs in finding the accurate course line by eye, unravel a few courses to determine the exact line before measurement is taken.
- This method can be used on knitted constructions other than single jersey, where spirality is a problem.
- Relaxation in a conditioned atmosphere 65%±2%rh & 20±2°C is preferable but where a conditioned atmosphere is not available greater variation in result may occur.
As per the experts and different world-renowned buyers, the angle of spirality lesser than 10 degrees is acceptable as a performance requirement and it is expected that within that threshold limit knit loops will not pose any serious problem.
Remarks :
In an ideal situation, the wales on the knitted fabric are to be perpendicular to the course in the lattice structure. But this is far from being reality due to the fact that the wales are not always perpendicular to the course and skew to the right or left forming a certain angle of spirality. Due to the open and unstable structure, looped yarn with its inherent residual torque has the freedom of movement during the relaxation treatment which relieves the residual torque, thereby uncurls itself inside fabric and transformed to spirality as an after effect. This downgrades the appearance of the merchandise and may not be acceptable to the buyers.
