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:
