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:—
| Fibre. | Maximum. | Minimum. | Mean. |
|---|---|---|---|
| Cotton | 1·32 | 0·23 | 0·75 |
| Linen | 1·20 | 0·20 | 0·76 |
| Esparto | 1·40 | 0·40 | 1·00 |
| Straw | 1·50 | 0·50 | 0·88 |
| Wood | 2·60 | 1·00 | 2·00 |
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}