Jigger
This
machine is most commonly used for dyeing almost all kinds of cotton fabrics at
full width. The fabric is dyed in this form on the jigger to a larger extent
than in any other form. The jigger is a simple machine which consists of a
V-shape trough fitted with two draw rollers one along each side of the machine.
At the commencement of dyeing, cloth in open width is wound on one of these
rollers called the 'let-off roller from which it is unwound and passed through
the dye-liquor in the trough with the help of guide rollers and an immersion
roller on to the other roller called the take-up roller’ on which it is
wound.The roll of cloth at either. end is stitched with about : 5 m grey cloth
called the 'end piece' so that during the run of the cloth through the liquor from
one draw roller to the other, a part of the end piece remains on the roller hut
the end portions of the cloth to be dyed pass through the liquor (which
otherwise would have remained undyed ). The
passage of cloth from one draw roller to the other through the dye-liquor is
called 'one end' or 'one turn' .The number of 'ends' to be given depends on the
depth of shade absorption capacity of the cloth, type of dyestuff used and the
time required for one 'end' .An even number of ends
is
always given to prevent a portion of cloth getting a darker shade than the
other. Most of the penetration of the dye-liquor or actual dyeing takes place
when the cloth is resting on the roller.. before going through the liquor again
and not when the cloth is running through the liquor. The dye-liquor is heated
by perforated or closed steam coils and the liquor can be drained off through
an outlet. Even when the liquor in the trough is at the boil, the temperature
of the roll of the cloth is usually about 70°c; dyeing are not suitable for jigger
dyeing, unless enclosed jiggers are used for the purpose.
The cloth has to be uniformly wound on the draw roller in such a way that no part of the selvedge comes out of the roll one during winding. If a part of the selvedge comes out of the roll, then while dyeing vat dyes, the portion containing the leuco vat get oxidation by air then when it enters the dye-liquor again, it picks up more dye than the rest of the cloth thus giving a darker ends selvedge. When dyeing naphthol colors, the selvedge shade
The cloth has to be uniformly wound on the draw roller in such a way that no part of the selvedge comes out of the roll one during winding. If a part of the selvedge comes out of the roll, then while dyeing vat dyes, the portion containing the leuco vat get oxidation by air then when it enters the dye-liquor again, it picks up more dye than the rest of the cloth thus giving a darker ends selvedge. When dyeing naphthol colors, the selvedge shade
becomes lighter because the naphthol decomposes duc to the ac of CO2, from
If the jigger is to be stopped during dyeing, the entire s cloth
so wound on one of the draw rollers and the roll is kept rotating that the
liquor does not drain down and make the lower half darker than the upper half of
cloth
The older type of jiggers were made of wooden roller and
wooden troughs; such troughs absorb colour and get stated and their cleaning is
difficult They are used to dye dark shade or for dyeing the same shade again
and again. But they have been practically superseded by modern jiggers which
are made metal or stainless steel and
have smooth surface when can be easily cleaned. They can be heated quickly and
also cooled quickly Both the rollers are power driven and can run at constant
speed; tension can be controlled with ease and varied as required The direction
of motion can be reversed automatically at the end of each tarn by means of a
time switch and can be stopped after the required number of turns. A
differential driving mechanism is used
for changing the speed so that the cloth move at a uniform speed; otherwise the
differential in speed results a tailing effect ie, weakening of the
shade. Expanders are also fitted to keep the fabric free from creases and at
full width So preventing uneven dyeing
In the earlier machines,
the m:l ratio was very high, now the
jiggers are constructed with small trough in winch the ml ratio is 1:5 or I:4 thereby
saving consumption of water, steam and
chemicals (like caustic soda and sodium hydrosulphite when dyeing vat dyes).
For better penetration of liquor in the case of The heavy fabrics like canvas
or drill, heavy rubberized rollers mounted is on a moveable frame are used
to press the draw rollers and squeeze
the liquor. Improved jiggers have recently been developed is which ensure constant tension and constant
speed and ate provided with direct and indirect heating and automatic temperate
of the dye-bath
Disadvantage of Jigger Dyeing
1 It is a batch-wise
or discontinuous process: only a small lot dyeing of say. 100 m can be dyed at
a time.
2 During dyeing. the fabric is pulled from one roller to the
other exerting considerable lengthwise tension (ranging from 5 to 10 % ) which
is injurious - to delicate fabrics like viscose rayon fabrics which have low tensile
strength in wet condition, knitted goods can be damaged. The special pebble
appearance of seer sucker fabrics (obtained by crimp or crepon style of
printing) gets distorted by stretching the fabric lengthwise.
3 If the cloth is not properly batched and the selvedges are
non-coincident, then on dyeing, such selvedges come out lighter or darker than
the body of the cloth
4 In the case of heavy fabrics like canvas or drill, only
surface dyeing of the material takes place particularly with vat dyes because
of the difficulty of penetration of the dye-liquor, in spite of increasing the
time of contact. For such fabrics the pigment padding method has to be used by
padding the fabric with a suspension of a vat dye in the unreduced state and
then developing it with caustic soda and hydrosulphite followed by oxidation.
