Page:EB1911 - Volume 20.djvu/788

Rh of the two sets of bars can be increased or reduced. The pulp flows into the top of the beater at the smaller end of the cone through a box provided with an arrangement for regulating the flow and passes out through an opening in the casing at the other end. The roll or plug revolves at from 350 to 400 revolutions per minute, and requires a power to drive it of from 25 to 40 h.p.,

. 9.—Jordan Beater.

according to the work to be done, and one engine is capable of passing as much as 1000 lb weight of dry pulp per hour. The Kingsland beater consists of a circular box or casing, on both inside faces of which are fixed a number of knives or bars of steel or bronze; inside the case is a revolving disk of metal fitted on both sides with corresponding and similar bars. The contact between the revolving and stationary bars can be regulated, as in the Jordan engine, to give the required amount of beating action on the pulp. The refiner is essentially a finishing process as an adjunct to the beating process proper. The advantages to be derived from its use are a considerable saving in the time occupied in beating and the production of a more uniform and evenly divided pulp, particularly where a mixture of different fibres is used. By the use of the refiner the time occupied in the beater can be reduced by nearly one-half, the half-beaten pulp passing through the refiner from the beater on its way to the paper-machine. It is not, however, generally employed for the best kinds of paper.

During the operation of beating various materials and chemicals are added to the pulp for the purposes of sizing, loading, colouring, &c. Papers for writing and most of those for printing purposes must be rendered non-absorbent of ink or other liquid applied to them. To effect this some form of animal or vegetable size or glue must be applied to the paper, either as a coating on the finished web or sheet, or mixed with the pulp in the beating engine. The former, called "tub-sizing" will be described later; the latter which is known as "engine-sizing" consists in filling up the interstices of the fibres with a chemical precipitate of finely-divided resin, which, when dried and heated on the cylinders of the paper machine, possesses the property of being with difficulty wetted with water. Except in the very best qualities of paper, it is usual to add to the pulp a certain quantity of cheap loading material, such as china-clay or kaolin, or pearl-hardening, a chemically precipitated form of sulphate of lime. The addition of such loading material to a moderate extent, say 10 to 15%, is not entirely in the nature of an adulterant, as it serves to close up the pores of the paper, and for ordinary writing, printing and lithographic papers renders the material softer, enabling it to take a much better and more even surface or glaze. But if added in excess it is detrimental to the strength and hardness of the sheet. Most materials, however well bleached, have a more or less yellowish tinge; to produce the desired white shade in the paper certain quantities of red and blue in the form of pigments or dyes must be added to the pulp. The blues usually employed are ultramarine, smalts and the aniline blues, while the red dyes are generally preparations of either cochineal or the aniline dyes. Other colours are required in the manufacture of papers of different tints, and with one or two exceptions they must be mixed with the pulp in the beater.

There are two distinct processes of producing the finished paper from the pulp, known respectively as "hand-made"

Paper Machine.

and "machine-made." The expense of manufacture of hand-made paper and the consequent high price render it too costly for ordinary use; the entire process on the machine occupies a few minutes, while in the ordinary state of the weather it could not be done by hand in less than a week.

A brief description of the hand-made process will suffice and it will at the same time facilitate the right comprehension of the machine process. Only the finest qualities of rags are used for hand-made paper; and the preparation of the half-stuff is the same as that already described under treatment of rags. The pulp after being prepared in the beating engine is run into

. 10.

large chests from which the vat is supplied; before reaching this it is strained as on the paper-machine (see below). The sheet of paper is made on a mould of fine wire-cloth with a removable frame of wood to keep the pulp from running off, extending slightly above the surface of the mould, called the "deckel."

To form the sheet, the paper-maker dips the mould into a vat (see fig. 10) containing the prepared pulp, lifting up just so much as will make a sheet of the required thickness; as soon as the

. 11.—Mould and Deckel for hand-made paper.

mould is removed from the vat, the water begins to drain through the wire-cloth and to leave the fibres on the surface in the form of a coherent sheet, the felting or intertwining being assisted by a lateral motion or "shake" given to the mould by the workman; the movable deckel is then taken off, and the mould is given to another workman, called the "coucher," who turns it over and presses it against a felt, by this means transferring or " couching " the sheet from the wire to the felt. A number of the sheets thus formed are piled one above another alternately with pieces of felt, and the whole is subjected to strong pressure to expel the water; the felts are then removed and the sheets are again pressed and dried, when they are ready for sizing. Any pattern or name required in the sheet is obtained by making the wire-cloth mould in such a way that it is slightly raised in those parts where the pattern is needed (fig. 11); consequently less pulp lodges there and the paper is proportionately thinner, thus showing the exact counterpart of the pattern on the mould; such are known as " watermarks." The expense of manufacturing paper in this way is very much greater than by machinery; but the gain in strength, partly owing to the time allowed to the fibres to knit together, and partly to the free expansion and contraction permitted them in drying, still maintains a steady demand for this class of paper.

The paper-machine (fig. 12) consists essentially of an endless mould of fine wire-cloth on which the pulp flows and on which a continuous sheet of paper is formed; the sheet then passes through a series of press rolls and over a number of steam-heated cylinders until it is dry. From the beating engines, the pulp is emptied