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Drying






Following on the washing comes the final operation of the dyeing
process, that of drying the dyed and washed goods. Now textile fabrics
of all kinds after they have passed through dye-baths, washing
machines, etc., contain a large amount of water, often exceeding in
amount that of the fabric itself, and to take the goods direct from
the preceding operations to the drying plant means that a considerable
amount of fuel must be expended to drive off this large amount of
water. It is therefore very desirable that the goods be freed from as
much of this water as possible before they are sent into any drying
chambers, and this may be done in three ways, by wringing, squeezing
and hydro-extracting. The first two methods have already been
described (pp. 198, 199) and need not again be alluded to, the last
needs some account.


Hydro-extractors are a most efficient means for extracting water
out of textile fabrics. They are made in a variety of forms by several
makers. Essentially they consist of a cylindrical vessel with
perforated sides, so constructed that it can be revolved at a high
speed. This vessel is enclosed in an outer cage. The goods are placed
in the basket, as it is termed, and then this is caused to revolve; at
the high speed at which it revolves centrifugal action comes into play
and the water contained in the goods finds its way to the outside of
the basket through the perforations and so away from the goods.
Hydro-extractors are made in a variety of sizes and forms, in some the
driving gear is above, in others below the basket, in some the driving
is done by belt gearing, in others a steam engine is directly
connected with the basket. Figures 29 and 30 show two forms which are
much in use in the textile industry. They are very efficient and
extract water from textile goods more completely than any other means,
as will be obvious from a study of the table below.

The relative efficiency of the three systems of extracting the
moisture out of textile fabrics has been investigated by Grothe, who
gives in his Appretur der Gewebe, published in 1882, the following
table showing the percentage amount of water removed in fifteen
minutes:--

Yarns. Wool. Silk. Cotton. Linen. (p. 208)
Wringing 44.5 45.4 45.3 50.3
Squeezing 60.0 71.4 60.0 73.6
Hydro-extracting 83.5 77 81.2 82.8

Pieces.
Wringing 33.4 44.5 44.5 54.6
Squeezing 64.0 69.7 72.2 83.0
Hydro-extracting 77.8 75.5 82.3 86.0

In the practical working of hydro-extractors it is of the utmost
importance that the goods be carefully and regularly laid in the
basket, not too much in one part and too little in another. Any
unevenness in this respect at the speed at which they are driven
leaves such a strain on the bearings as to seriously endanger the
safety of the machine.

After being wrung, squeezed or hydro-extracted the goods are ready to
be dried. In the case of yarns this may be done in rooms heated by
steam pipes placed on the floor, the hanks being hung on rods
suspended from racks arranged for the purpose.

Where large quantities of yarn have to be dried it is most economical
to employ a yarn or drying machine, and one form of such is shown in
figure 31. The appearance of the machine is that of one long room from
the outside, internally it is divided into compartments, each of which
is heated up by suitably arranged steam pipes, but the degree of
heating in each compartment varies, at the entrance end it is (p. 209)
high, at the exit end low. The yarn is fed in at one end, being
hung on rods, and by suitable gearing it is carried directly through
the various chambers or sections, and in its passage the heat to which
it is subject drives off the water it contains. The yarn requires no
attention from the time it passes in wet at the one end of the (p. 210)
machine and comes out dry at the other end. The amount of labour
required is slight, only that represented by filling the sticks with
wet yarn and emptying the dried yarn. The machine works regularly and
well.

The drying is accomplished by circulating heated air through the
yarns, this heating being effected by steam coils; fresh air
continually enters the chambers while water-saturated air is as
continually being taken out at the top of the chamber. One of the
great secrets in all drying operations is to have a constant current
of fresh hot air playing on the goods to be dried, this absorbs the
moisture they contain, and the water-charged air thus produced must be
taken away as quickly as possible.

#Piece Goods.#--The most convenient manner of drying piece goods is to
employ the steam cylinder drying machine such as is shown in figure
32. This consists of a number of hollow tin or copper cylinders which
can be heated by steam passing in through the axles of the cylinders,
which are made hollow on purpose. The cloth to be dried passes round
these cylinders, which revolve while the cloth passes. They work very
effectually.





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