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CHAPTER X. PAPER MACHINES; HAND-MADE PAPER.

The pulp as it comes from the beaters is now ready to be made into paper. We will first consider briefly the manufacture of hand-made paper.

It is made on a mould of wire-cloth, with a movable frame of wood, called the “deckle,” fitting on to the outside of the mould and extending slightly above its surface.

The wire-cloth is generally supported by a much coarser wire-cloth, or by pieces of thick wire, and these again by wedge-shaped pieces of wood, the thin end being next to the wire.

To form a sheet of paper the workman dips the mould, with the “deckle” in position, into a vat containing the prepared pulp diluted with water, lifting up just so much as will make a sheet of the necessary thickness. As soon as the 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 of paper. The felting or intertwining is assisted by lateral motion in every direction given to the frame by the workman. The movable deckle is then removed, and the mould, with the sheet of paper, given to another workman, called the “coucher,” who turns it over and presses it against the felt, by this means transferring the sheet from the wire to the felt. In the meantime the “vat-man” is engaged in the formation of another sheet with a second mould.

The Fourdrinier Paper Machine. Plate I.

A number of the sheets thus formed are piled together, alternately with pieces of felt, and when a sufficient number {145} have been obtained, the whole is subjected to strong pressure, to expel the water. The felts are then removed, and the sheets again pressed.

They are then sized, if required, by dipping them into a solution of gelatine: again slightly pressed, and hung up on lines or poles to dry. Such paper is called loft-dried.

When dry the sheets of paper are calendered. (See Chapter XI.)

The making of paper by hand involves considerable dexterity on the part of the workman; on account of the expensive labour necessary, in comparison with paper-machines, it is comparatively little practised in the present day; certain kinds of paper, however, such as bank-notes, various drawing papers, and printing papers intended for the production of very elaborate editions are always made in this way.

Any pattern or name required on the paper is obtained by means of a raised pattern on the wire-cloth mould: consequently, less pulp lodges there, and the paper is proportionally thinner, thus showing the exact counterpart of the pattern. Such devices are known as “water-marks.” (See also p. 156.)

The Paper Machine.

—The paper machine of the present day, with all its ingenious improvements, differs but little in principle from that originally constructed by Fourdrinier. It consists essentially of an endless mould of wire-cloth, on to which the prepared pulp flows, and on which a continuous sheet of paper is formed. The sheet of paper then passes through a series of rollers and over a number of heated cylinders, where it is completely dried.

A modern Fourdrinier paper machine is shown in plan and side elevation in Plates I. and II.

The pulp, after leaving the beaters, passes into a large vessel called the stuff-chest, of which there are one or more to each machine. As soon as the beater is empty, water is run in to thoroughly rinse out the remaining pulp, the washings also going into the stuff-chests. These may be {146} made either of wood or iron, and should be provided with arms fixed on a vertical shaft, made to revolve by suitable gearing. The arms are for the purpose of keeping the pulp thoroughly mixed, and should only work at a moderate speed, otherwise they are liable to cause the fibres to form into small knots or lumps. The pulp is drawn from the stuff-chests by means of the pump A, and is discharged into a regulating-box (not shown). The object of this box is to keep a regular and constant supply of pulp on the machine. It consists of a cylindrical vessel, having two overflow-pipes near the top, and a discharge-pipe near the bottom. The pulp is pumped in through a ball-valve in the bottom, in larger quantity than is actually needed, the excess flowing away back into the stuff-chests, through the two overflow-pipes. By this means, the box is always kept full, and therefore the stream of pulp issuing out of the bottom pipe is always under the same pressure. It flows from this pipe, the quantity being regulated by means of a cock, according to the thickness of paper required, directly on to the sand-tables. These may be of various sizes and shapes, but should be so large that the pulp takes some little time to travel over them. They consist of long shallow troughs, generally of a sinuous form. The bottoms are sometimes covered with woollen felt, or with thin strips of wood placed across the direction of the flow of the pulp, and at a slight angle. These serve to retain any particles, such as sand and dirt, that may have escaped removal in the previous treatment of the pulp, and that are heavy enough to have sunk down during the passage of the pulp along the sand-tables. In some mills, where great care is exercised, the pulp is caused to flow over sand-tables 200 yards in length. As the pulp, when it leaves the stuff-chests, does not contain sufficient water for the purpose of making paper, it is mixed, where it enters the sand-tables, with a quantity of water from the “save-all” (see p. 154), flowing from the box B placed at a higher level.

In some mills, instead of being pumped into the {147} regulating-box, the pulp flows into a small vessel below the stuff-chest, and is lifted on to the sand-tables by means of buckets fastened on the circumference of a wheel.

The pulp, after leaving the sand-tables, passes on to the strainers. These consist of strong brass or bronze plates, having a large number of very fine V-shaped slits cut in them, the narrowest end being on the outside.

Strainers.

—The strainers are for the purpose of removing from the pulp all lumps formed by the intertwining of the fibres, and all pieces of unboiled fibre, which, if allowed to pass on, would show in the paper as inequalities in the surface, or as dark specks. The slits are made narrow at the top, and gradually increasing in width, so as to prevent them from getting choked up. These slits allow only the individual fibres to pass through, and their width varies according to the quality of the paper. They are from 2 to 3 in. long, and they vary in width from ·007 to ·05 in. They are put at distances of about 1⁄4 in. apart. Several plates, each containing about 500 slits, are bolted together, and form a strainer. The whole strainer receives a violent shaking motion, to assist the passage of the fibres through the slits. In the machine represented, two of these strainers are shown at C. The shaking motion is produced by the ratchet-wheel or cams a acting on the hammer b. An improved form, called the “revolving strainer,” has of late years been introduced. The pulp generally passes first through one of these, and then through the ordinary or “flat” strainers, as they are called. A revolving strainer is shown at D. It consists of a rectangular box, the sides of which are formed of plates perforated with slits. Inside this box, a slight vacuum is formed by means of an indiarubber bellows worked by a crank on the shaft d. The vacuum is intended to serve the purpose of the shake in the ordinary form. The box revolves slowly inside a vat containing the pulp, and the strained pulp flows into the box D1, and thence on to the flat strainers.
FIG. 45.

Various patents have been taken out from time to time for {148} flat strainers worked by means of a vacuum underneath the plates caused by the motion of discs of indiarubber or thin metal. Fig. 45 shows in plan a set of strainers, as manufactured by Messrs. G. & W. Bertram, similar to those in Plate II., but illustrated somewhat more in detail.

The pulp first passes through the flat strainer B, and from thence to the two revolving strainers A. From these it flows along the shoots placed at the side on to the paper-machine at E.

FIG. 46.

Fig. 46 gives a view of a patent flat vacuum strainer made by the same firm, which may also be used for cleaning straw or esparto previous to its passage over a presse-pâte. The pulp flows on to the strainer at a, and passes away by {149} the cast-iron pipes f. The valve g is for running off waste pulp. The plates are placed at a slope of about 1 in. in their length; those nearest the supply of pulp are provided with coarser slits, as the impetus carries the knots forward. The vacuum pumps are worked by the rods d from the shaft e. By means of the tubes c water can be directed on to the plates, whereby the coarser particles of fibre are carried forward, and the slits are kept clean. The plates can be removed in a few minutes.

Figs. 47 and 48 show in side and end elevation, Messrs. Masson, Scott, & Bertram’s patent self-cleaning strainer. The novelty consists in an arrangement by means of which the upper surface of the plates are continually freed from those portions of the pulp which cannot pass through the slits.

The scrapers d are made of vulcanised indiarubber, and are continually carried forward by an endless chain; the knots, &c., collect in a heap at the end of a strainer. The {150} pulp flows on at a, and passes away through the pipe b. The pumps are driven from the shaft e.

FIG. 47. FIG. 48.