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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