Sizing

What is sizing?
 
The sizing of yarn absolutely essential to render it weavable; 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. The objective of sizing is to impart those property which it does not possess but which are essential to good weaving-the resistant to abrasion. This objective is achieved by applying on the yarn a uniform and smooth protective film of suitable sizing material. This improves the abrasion resistance and incidentally, also the tensile strength of the yarn. 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.



Function of sizing:

1.      To lay in the protruding fibres in the body of the yarn and to cover weak places by encapsulating the yarn by a protective coating of the size film. The thickness of the size film coating should be optimized. Too thick a coating will be susceptible to easy size shed-off on the loom.

2.      To increase the strength of the spun warp yarn without affecting its extensibility. This is achieved by allowing the penetration of the size into the yarn. The size in the yarn matrix will tend to bind all the fibres together, as shown in. The increase in strength due to sizing is normally expected to be about 10 to 15% with respect to the strength of the upsized yarn.

3.     To make a weaver’s beam with the exact number of warp thread density for weaving.

 

 

 

(a) Too much penetration, no surface coating;

(b) Too much penetration, more size added to provide surface coating;

(c) Too little penetration, no anchoring of yarn structure;

(d) Optimal distribution.

Figure-1illustrates various possible conditions that may occur in practice depending upon the properties of the size employed. This emphasizes the importance of an optimal balance between the penetration of the size into the yarn and providing a protective coating around the yarn, as shown in Fig-d. The flow properties of the size liquid and the application temperature have important effects on the distribution of the size within the yarn structure. More size at the periphery of the yarn will tend to shed off on the loom under the applied forces because the size is not well anchored on the fibres. Too much penetration, as shown in Fig-, may leave too little size around the yarn surface to protect it against the abrasive action. To rectify such a condition, a higher size add-on is required to provide the required protective surface coating.

Before sizing & after sizing Yarn: