Drafting
Draw-frame
and Drawing:
Carded
Slivers are fed into the Draw-Frame and are stretched/ Straightened and made in
to a single sliver. Also fibre blending can be done at this stage.
At
drawing stage, material passes not only one m/c but usually 2, arranged 1 after
the other & combined to form a group. Processing in 2 passages is necessary
completely to fulfill the requirements. The 2nd passage is often superfluous
after combing m/c because then it does not normally generate any improvement in
quality.
So
we can say that, A process in short staple spinning in which the sliver are
blended, doubled, leveled and drafted by passing the sliver through a series of
pair of rollers each pair moving faster
than the previous one is called drawing.
The
machine by which drawing is accompanied is called draw frame.
Objects
of drawing:
●
To improve the short medium and long term unevenness of the sliver by doubling.
●
To produce a more uniform sliver.
●
To achieve a fairly through parallelization of the fibre along the sliver axis.
●
To reduce the knot/unit length of card sliver.
●
To mix the fibre intimately.
●
To make the perfect blend of fibre.
●
To remove the dirt, dust from carded sliver.
Necessity
of draw frame:
To
parallelization of fibre and blending → Carded sliver
In
carded sliver, fibre present in hook form, i,e. Trailing hooks and leading
hooks.
To
parallel those hooks, draw frame is used. Majority of fibre hooks in a carded
sliver are trailing form. Whereas leading hooks are comparatively less.
Trailing hooks are also known as major hooks, while leading hooks are known as
minor hooks.
Definitions
of different term of draw frame:
Doubling: The process of combing two or more
sliver rovings or yarns into one is called doubling. This
term is not restricted to the combination of two units only.
Draft: The reduction of weight / yard of
sliver and increase in length is called drafting. Or Attenuation of sliver
without breaking is called draft.
Drafting:
The process of attenuating or increasing length per unit weight of sliver. It
is mainly due to peripheral speed of the roller.
Requirement
of drafting arrangement:
The
drafting arrangement is the heart of draw frame and thus the part which
influence the quality. The requirements placed on the drafting arrangement in
general are correspondingly high.
I. Simple,
uncomplicated construction.
II. Stable
design with smooth running of the rollers.
III. A
mode of operation giving a high quality product even at high running speed.
IV. High
degree of flexibility i,e. suitable for all raw materials.
V. Optimal
control over the movement of fibres during the drafting operations.
VI. High
precision both on operation and adjustment.
VII. Rapid
and simple adjustability of roller spacing and draft levers.
VIII. Ease of
maintenance and cleanings.
IX. Optimal
economic design.
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