Textile value Chain

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Process Control of Sizing

Sizing of Warp Yarn


The sizing of yarn absolutely essential to render it wearable; without sizing the end breakage rate of warp, particularly in the case of single yarns, is so high that weaving becomes impossible. The objective of sizing, however, sizing cannot be looked upon as a process that improves the basic quality of yarn. The fact is that by endowing the yarn with abrasion resistance, proper sizing bring out the full potential of a yarn to weave.

 

A properly sized yarn should have adequate improvement in abrasion resistance, indirectly indicated by the increase in tensile strength, minimum loss of extensibility and required amount of moisture. For satisfactory weaving the quality of the beam also important; the beam should be firm and it should not have excessive missing ends, crossed ends, taped ends (sticky ends) etc., so that it unwind smoothly in the loom shed. 
 

We also want that in the sized yarn there should be

 

§  Some increase in tensile strength in the yarn

§  Minimum loss of extensibility in yarn ( about 4.4-4.6% elongation at break is required for cotton)

§  Required moisture content ( 8-10% of cotton)

§  Good quality of sized beam (neither too soft nor too firm + free from yarn defects)

§  Good productivity and efficiency

§  Reduced Cost

 

Some Important Parameters for the Process Control of Sizing

 

Process Control in Sizing


The process control program in sizing should, therefore, comprise of the following aspects
1. Selecting the correct size recipe and size pick -up level.
2. Ensuring correct ratio of size paste.
3. Control of the followings 

§  size pick up

§  stretch

§  moisture content

§  quality of beam

§  machine speed

§  machine efficiency

§  a method to calculate the expected level of productivity

 

©Effects of Sizing on Yarn Properties 


The following properties of yarn are affected by sizing

§  Yarn elasticity decreases.

§  Yarn strength increases.

§  Hairiness of yarn increases.

§  Flexibility of yarn decreases.

§  Smoothness of yarn increases.

§  Irregularity of yarn decreases.

§  Yarn diameter increases.

§  Yarn weight increases.

 

©Factor on which Sizing Recipe depends on: 

§  Composition of yarn

§  Yarn count

§  Total no. of ends

§  Weight of yarn

 

©Factors Influencing Size Pick up% 


Viscosity of size paste in size box

 

Any variation in the concentration or temperature alters the viscosity of the paste which in turn affects both the level of size pick up and extent of penetration. Initially as the viscosity increases, the size pick-up also increases. But as the viscosity increases beyond a point, the size pick up is reduced. 

Squeezing pressure and condition of squeezing nip

 

The squeezing pressure determines the extent of penetration of the size paste between the fibers of the yarn and also of the removal of excess size paste and hence the level of the size pick up. 

Speed of the sizing machine

 

Other sizingconditions remaining unchanged, the size pick up increases with increasing sizing speed and vice versa. This is because the time available to squeeze the surplus size from the yarn is less at high speeds. 

Depth of immersion roller in size paste

 

The depth of immersion roller in the paste determines the duration for which the yarn remains immersed in the paste. This duration in turn influences both the level of size pick up and the extent of size penetration.
 

Level of size paste in the size box

 

Variation in the level of size paste is an important source of size pick-up variations both within and between beams. 

Density of ends

 

When the density of ends is high, difficulties are encountered in obtaining adequate and uniform size penetration. Therefore size pick up may vary at these fabrics. 

Yarn tension

 

In case of higher tension during sizing the set of warp yarns encounter a stretch of comparatively higher tension and thus the set of yarn increases in length. If this increase is too high then the elongation property of the yarn will be decreased. So the yarn will face comparatively higher breakage in subsequent processes. On the other hand lower yarn tension leads to uneven sizing. So the yarn tension must be optimal. 

Yarn twist

 

In case of high twisted yarn penetration time should be increased in order to obtain the optimal pick up %. 

Dia. of the yarns

 

Yarn with greater dia consumes higher size paste. Therefore, the higher the dia of yarn, the higher the pickup will be added.

 

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