If we see a knitted fabric very closely, we see loops or
stitches in it. The horizontal row of loops are called A Course The vertical column of loops are called A Wale According to the definition the A wale and A course of a knitted fabric should lie perpendicular to each other.
But due to some causes wale line doesnt always stand
perpendicular to the course. This phenomenon is called spirality. 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. The angle between wale and a line drawn perpendicular to the course is the measure of spirality.
Spirality is a very common problem in single jersey
fabric and it may exist in grey, washed or finished state. However, it does not appear in interlock and rib fabrics because the wale on the face is counter balanced by a wale on the back. Some of the practical problems arising from the spirality in knitted garments are: mismatched patterns, displacement or shifting of seams and sewing difficulties.
Fiber is twisted during yarn formation and during
knitting this twisted yarn is bended in to loops. The fiber of the yarn has a tendency to untwist and to return to its original state. Again the bended yarn in loops form has a tendency to be straightened. For these reasons the loops are deformed and does not follow the normal line.
The causes of spirality depends on the following: 1. Yarn parameters.
2 . Fabric parameters.3. Machine parameters.
Yarn twist: If we take a piece of yarn and bring its two ends closer the middle part of the yarn will entangle itself. This is called snarling. This snarling is the main cause of spirality. Snarling is caused by yarn twist which makes it lively. Greater the twist amount greater is the spirality. The amount of twist in yarn is measured by T.P.I. (Twist per inch) If T.P.I. increases spirality also increases. (T.P.I. - Spirality )
If we produce single jersey fabric with S twist yarn
then the wale line will be inclined towards left to the normal line. If we produce single jersey fabric with Z twist yarn then the wale line will be inclined towards right to the normal line.
Yarn count: Freedom of yarn movement in the fabric structure contributes significantly to the increase in spirality. If yarn diameter is reduced, its resistance to deformation is lowered. It indicates that, deformation of loop structure is influenced by yarn count. Again we know that T.P.I. = T.M. count, which indicates higher (finer) the yarn count higher the yarn twist. So spirality will be higher.
Fabric stitch length: Higher the stitch or loop length higher the spirality. Stitches with longer length of yarn can move more freely than the smaller one. (Stitch length - Spirality ) Fabric structure: Spirality is more in single jersey fabric due to non-arrest of loops. In double jersey fabric like rib or interlock, the effect of spirality is nullified.
Number of feeders: More the number of feeders - more number of course per revolution of knitting machine. The more number of courses per revolution - course inclination will increase. Due to more course inclination spirality will be more. Gauge: In knitting technology the needle per inch is called gauge. Smaller the gauge, lesser will be the spirality. ( Gauge - Spirality ) The knitting machine produces fabric in a spiral way. So the courses are produced in an inclined path. For this reason the wales are inclined not perpendicular with the courses. This is a inherent problem of a S/J knitting machine
Spirality can be minimized by the following methods: Knitting with coarser yarn with short stitch length will produce less spirality. Using S and Z twist yarn in alternate feeders. Using ply yarn. Compacting, Resin treatment and heat setting.
THANK YOU ALL