The bleached pulp is now ready for the final treatment. If it were attempted to make paper from the pulp in the state in which it leaves the “potchers” or “steeping” chests, it would be found to be wanting in evenness of texture and uniformity of surface. This result can only be secured by an elaborate process of comminution or disintegration. This is in effect the result produced by the action of the “beaters.”

They resemble in general appearance the breaking engines previously described; the roll, however, carries more knives, and it is usually let down much nearer to the bed-plate. In the case of fibrous substances, whose ultimate fibres are relatively short (see table, p. 39), it is only necessary to split up the filaments into their constituent fibres: esparto, straw, and wood are of this class. In the case of straw, the disintegration is for the most part ac­com­plished in the boiling and bleaching processes, and therefore but little work devolves upon the beater. Esparto and wood require a certain amount of beating, but this should be regulated to the drawing asunder of the individual fibres, any cutting of the fibres being carefully avoided. This is ac­com­plished by adjusting the distance of the roll from the bed-plate, so that by the friction of the fibres upon themselves, when passing over the plate, a kind of rubbing or “brushing” is produced. If a carefully-made paper of esparto or wood be examined by the microscope, it will be found that the majority of the fibres preserve the pointed or slightly rounded ends {118} characteristic of bast cells. On the other hand, it is obvious that cotton, whose ultimate fibres have a length of 20 to 40 mm., and flax (25–30 mm.), with other similar fibres, will require to be broken up into short fragments in order to develop to the fullest the felting property of the pulp. Not only are the fibres reduced to the most favourable dimensions, but in cotton and linen a further contributory advantage accrues; for on account of the internal structure of the ultimate fibres they tend to split up at the point of rupture into a number of fibrillÆ, which, in the case of cotton, take the form of a network; and in case of linen, are seen as a bundle of distinct fibres parallel to and continuous with the fibre. This gives to ends of the fragments a ragged contour, which has considerable influence on the felting power of the pulp, and therefore on the strength of the paper into which it is made.

With these fibres, therefore, the “cutting” as distinguished from the “breaking” action should be avoided as much as possible, otherwise the effect described above will not be produced, and the fibres will show instead a clean cut. The appearance shown by cotton and linen pulp, when thoroughly “beaten” and ready to be made into paper, is given in the frontispiece, which is taken from the author’s micro-photographs.

The “half-stuff” is furnished to the “beater,” or “beating” engine as it is sometimes called, previously partially filled with water. The furnishing is done in successive portions, the first being allowed to mix thoroughly with the water before another lot is added. This is continued until the mass is so thick that it will only just turn round in the beater under the action of the “roll.” Owing to the construction of the beater it frequently happens that a portion of the pulp lodges in the corners, from which the beaterman removes it by means of a wooden paddle, which also serves to push forward the pulp to the roll in case the motion is inclined to be sluggish. The proportion of water to pulp should not be too high, otherwise the beating is not so effective; at the same time, {119} if the mass is allowed to get too thick, imperfect circulation results.

The operation of “beating” occupies a considerable time, and consumes a large amount of power. Cotton and linen rags naturally take longer—in some cases as much as ten hours is given to the operation.

Esparto, on the other hand, can be sufficiently disintegrated in from two to four hours.

Wood pulp requires very gentle beating; it is therefore necessary to prolong the time to about six hours.

These differences in the duration and method of beating should be borne in mind when pulps of different natures are mixed together in the same beater, as is frequently the case. It is better, with very dissimilar fibres, to “beat” each separately, and only to mix them in the stuff-chests. This, however, is open to the objection that the pulps may be insufficiently mixed.

The length of fibre to which pulps should be reduced depends to some extent upon the kind of paper to which it is to be applied. The authors have examined a number of papers by well-known makers, and find the dimensions in millimetres of various pulps to be as follows:—

Wood and straw pulp, when imported in the form of dry sheets, may, before being beaten, be conveniently disintegrated and thoroughly mixed with water by means of the edge-runner described under “Broke Paper,” p. 104, Fig. 28.

In making the finer kinds of paper, the roller bars or knives, instead of being made of steel are made of bronze, thus any contamination with oxide of iron is avoided. This is especially liable to take place in case of steel knives when the beater has been allowed to stand for some time. {120}

The inside of the heater itself is often lined with lead, a material which is not liable to oxidize, and which can very readily be cleaned.

When a beater has been running for some time the knives of the roll and the bed-plate become worn and so far reduced that they must be taken out and re-cut. The bed-plate is removed, firmly fixed in the bed of a planing machine, and the edges trimmed by means of a chisel, so as to cut the knives at the proper angle.

The roll and bed-plate are shown in section in Fig. 32. Fig. 33 is a plan of a bed-plate, and Fig. 34 illustrates the manner in which the knives are fixed.

It will be seen that the knives in the bed-plate are placed so that they do not lie parallel with those of the roll. This arrangement imitates to some extent the action of a pair of scissors. Occasionally the knives are slightly bent, so as to form a very obtuse angle. Bed-plates so fitted are called {121} “knee-plates.” They are largely used in America, but not much in this country.

To obviate the necessity of removing the roll, a small machine has been devised whereby the knives can be cut in situ. This machine, which can be firmly fixed between the mid-feather and the side of the beater, consists of a small steam-engine which actuates a movable cutter, which is made to pass to and fro horizontally along the edge of each knife in succession. The engine is supplied with steam by a piece of strong flexible rubber tubing.

The ordinary form of beater contains only one roll, though some have been constructed containing two or even four rolls. In America, beaters of a totally different construction are much in vogue. The most important of these are the Jordan and Kingsland beaters, so called from the names of the inventors. The former consists essentially of a roll in the shape of a truncated cone, fitted with knives in the usual way, revolving in an iron box of corresponding shape, furnished with knives placed in the direction of its length, but at slightly different angles. The half-stuff enters the beater at the narrow end through a box provided with an {122} arrangement for regulating the flow, and is discharged by two or more openings in the cover at the wider end.

The Kingsland engine consists of a circular chamber, the sides of which are covered with knives, and between which a circular plate, also furnished with knives, revolves. The pulp enters through a pipe in the centre of one of the sides of the chamber, and flows out through an opening in the opposite side.

Another form of beater is that invented by S. L. Gould. The only essential difference between it and the Kingsland beater is that, instead of having a plate which revolves vertically against two stationary ones, the plate, which is placed horizontally, is furnished with knives on one side only, and revolves upon but one fixed plate, much in the same way as a pair of millstones.

The half-stuff supplied to these forms of beater is generally disintegrated to a greater extent in the breaker than is the case with those of the ordinary construction, as it is necessary to make it flow easily through them, and this could not be done if the fibres were kept long. A single passage of the pulp through the beater is sufficient to beat it up ready for making into paper. The chief advantages claimed for them is that they are more economical, both of time and power; also that the pulp is more regularly beaten.

Certain new forms of beaters have lately been introduced in this country, and are rapidly gaining in favour, chiefly on account of the saving of driving power, and the space occupied, compared with the amount of “stuff” they are capable of beating. Fig. 35 shows the construction of Forbes’ patent engine, as manufactured by Messrs. G. & W. Bertram, of Edinburgh. This beater is divided into three channels. The rolls, one of which is shown uncovered, are placed in the outer channels, while in the centre one the mixing and circulating wheel a is placed, the peculiar construction of which enables it to throw the pulp alternately into the two outer channels, from whence, after passing under the rolls again, it enters the central channel at the other end of the beater. {123}

In Umpherston’s patent engine great economy of space is effected by causing the pulp to travel over and under the backfall (a, Fig. 36). Another advantage is that the stuff circulates freely with less water than in the ordinary forms, thus increasing its output. It is also claimed that the pulp is beaten with less power, and as it is less liable to lodge in corners it is more evenly beaten.

The construction of the engine will be readily understood by reference to Fig. 36. The direction which the stuff takes is indicated by the arrows.

Cooke and Hibbert’s beater, as manufactured by Messrs. Masson, Scott and Bertram, resembles, to a certain extent, Gould’s engine, previously described; it differs from it, however, in that the discs are placed vertically, instead of horizontally. Moreover, the general construction of the beater more nearly resembles those in ordinary use. Fig. 37, which shows it in plan and in section at the line D E, illustrates its construction.