Sizing is defined as a process of addition of starch to warp yarn in order to withstand stresses and strains during weaving.
After winding and warping operations, sizing is done during beam preparation.
Causes of stresses and strains during weaving:
By the following ways the warp yarns are subjected to mechanical stresses.
During weaving, Chaffing or abrasive forces acting on warp sheet due to back rest, lease rods, held wire, reed, shuttle, front rest, drop wires etc.
stretching of warp yarn due to opposite forces acting on let off and take off motion.
Objectives of sizing:
To prepare warp to withstand stresses and strains during weaving operation.
To reduce the chances of breaking or fraying during weaving.
To impart wearability to warp sheet.
To impart strength to warp yarn.
To retain the elongation.
To decrease hairiness
To improve strength.
To increase yarn elasticity and smoothness of yarn.
To remove hairiness by binding the fiber to surface of yarns.
Characteristics of sized yarn:
Higher abrasion resistance
Higher bending rigidity
Lower frictional resistance
Forms of sizing:
It is in decentralized sector and done manually in open truff.
The size pick up cannot be estimated correctly because the method followed is crude.
The method does not follow any technical condition.
Ball warp sizing:
In this method warping is done in rope form by winding the yarn to a spindle device like a ball of twine or cylindrical barrel.
The main aim of ball warping is to prepare a log for rope dyeing machine.
Dyeing of warp yarns in the rope form is carried out in this method.
Then the long chain beaming takes place where the rope form is converted to open width form. Then the sizing is done. And this type of sizing is called as ball warp sizing.
Tape sizing or slasher sizing:
It is in centralized sector.
This method is performed in mill sector and suitable for large scale operations.
It is a very popular method.
To apply the size on warp yarns, there are some operations which has to be performed such as separation of ends, measuring warp length, marking into cut lengths, and winding.
These operations are performed by slasher or tape sizing machine.
Factors governing size add on:
The percentage of size application varies with different yarns as the resistance offered by yarn to stress and strain is not same for all fibers.
Continuous filament yarns have good elastic behavior and strong cohesion due to continuity of their filaments.
In manmade fibers (spun yarn), the degree of twist is inadequate to hold fibers together, so needs sizing.
It is also based on the properties like cross section, linear density, twist and uniformity of fiber and yarn.
Thus, depending upon mechanical and relative properties of fiber and the yarns, it is necessary to prepare size recipe to improve wearability of warp sheet.
For example, 100% cotton requires a maximum of 14% size whereas polyester blends require 4-6% of size.