CHAPTER VI. SPECIAL TREATMENT OF VARIOUS FIBRES; BOILERS, BOILING PROCESSES, ETC.
We have already, in Chapter V., discussed in a general way the principles upon which the treatment of the various fibres should be based; we now proceed to consider each fibre in detail, giving at the same time such information as is necessary regarding the preliminary treatment of the various fibres and describing the forms of apparatus in which these operations are conducted. We shall consider the fibres in the order of their simplicity of treatment.
Rags
(Linen and Cotton).—The treatment necessary for rags differs largely with the quality and, of course, with the kind of paper for which they are intended. These different qualities are known in the trade by different names and marks, such for example as the following:—New linen pieces, new cotton pieces, superfines, dark fines, grey linen, sailcloth, seconds, thirds, &c., &c.The two former consist of the cuttings produced in the manufacture of various garments, &c.; not having been worn, they are usually free from dirt, and are, in fact, if bleached, nearly pure cellulose, containing only the starch and other sizing material which has been added in the process of finishing the goods. They may, of course, contain considerable quantities of china clay or other loading material. In purchasing rags, therefore, regard should be had to the probable presence of these bodies. Such rags require only a very slight treatment; in fact, for certain classes of paper they might be used without any preparation. If, as is sometimes the case, the rags are unbleached, a rather more severe boiling is necessary. {80}
The greater part of the rags used in paper-making, however, consist of the residual portions of garments, household linen, &c., which vary in quality from clean, almost unused portions, to the very foulest sorts; the latter require a very drastic treatment. The first thing to be done with the rags is to “sort” and cut them into convenient pieces. This is usually done by women, who stand at tables furnished with broad knives firmly fixed into them, with the backs towards the worker, and inclined at a slight angle. Near to the women are placed a number of boxes, corresponding with the number of qualities of rags, lined at the bottom with coarse wire gauze, into which the different sorts are put. The distinctions made are purely arbitrary, but as a general rule the rags are sorted with special reference to their colour and the material of which they are composed. The coloured rags may be allowed to accumulate, and then made into a coloured paper. During the process of cutting, all hard substances, {81} such as buttons, pieces of iron, &c., are carefully removed. The rags are cut into pieces of from two to five inches square. In some mills machines are used for cutting.
Fig. 16 shows the construction of a machine that may be used either for rags or rope. The material is passed into the machine along the table A, where it passes between the stationary knife C and the knives B, fixed in the revolving drum D. The cut rags fall into a receptacle placed underneath the drum.
Notwithstanding the extra expense of cutting by hand, it is nevertheless preferred by many, especially for the finer grades of paper. One reason for this is to be found in the fact that more perfect sorting and removal of impurities can be effected. It is moreover said that less waste of fibre occurs in the subsequent operations.
The next process which the rags undergo is that of removing all loose extraneous matter. This may be done in a machine such as is shown in Fig. 17. The rags are fed continuously by the endless travelling platform A into the willow. This consists of two wrought-iron drums, B B, furnished with wrought-iron teeth C, which when the drums revolve pass rapidly near to the stationary teeth fixed into the cast-iron framework of the willow. The sides are covered in with cast-iron doors, and the top is covered over {82} with sheet iron. Underneath the drums is a grating for the escape of dust.
The rags, having been thoroughly beaten by the teeth of the drums, pass into the duster D, consisting of a kind of hollow cylinder E, made of strong iron bars securely fastened to the circular ends F, the bars being covered with wire cloth or perforated zinc. It is made to revolve almost horizontally, a slight dip being given to it in order that the rags may be carried forward to the lower end. The bars or skeleton of the cylinder are furnished with a number of teeth securely bolted on. The whole is enclosed in a strong wooden box in which it revolves, and which serves to collect the dust passing through the wire cloth. The cylinder E is driven by the gearing G. This combined willow and duster may be used for dusting and cleaning not only rags, but almost any other kind of fibre. The willow and duster sometimes form two separate machines.
The cleaned and dusted rags are now ready to be boiled, although it is the practice in some mills to give them a preliminary washing with water.
The boiling may be conducted either in spherical or cylindrical boilers, or in the ordinary vomiting boilers described under Esparto. (See p. 92.) In Fig. 18 is shown, part in section and part in elevation, a spherical rag-boiler, as manufactured by Messrs. G. & W. Bertram.
This boiler, of from 8 to 9 feet diameter, is supported by means of the hollow journals A on the standards B, and is made to revolve by means of the gearing C.
Steam enters by the pipe D, which is fitted with a safety-valve E, and vacuum valve F. The steam on entering the boiler is distributed by means of the “baffle-plate” G. Lye enters by the pipe H. The boiler is fitted with two doors I, wherewith to fill and empty; the waste lye is run off by the cock J. L is a small blow-through cock. The false bottom K prevents the rags from choking up the cock and also serves to drain off the waste liquor.