THE FOURDRINIER PAPER-MAKING MACHINE
From the Jordan engine the pulp is passed on into the Fourdrinier machine, which we are now ready to investigate. The principal element of this machine is a traveling belt of copper wire gauze which takes the place of the screen or sieve used in the hand process. To confine the pulp to the belt there are two endless bands of rubber, known as “deckles,” along each edge of the screen, which travel with the screen. To insure proper interlacing of the fibers, as in the hand process, the screen is shaken laterally at the rate of about 300 vibrations per minute.
The fluid pulp enters the machine through a flow box, where a constant hydraulic head is maintained, so as to preserve a uniform discharge to the wire gauze. The milky stream issues through a narrow opening in the flow box, known as a “slicer.” This may be adjusted to alter the width and also the thickness of the stream. No one would suspect from the appearance of the milky fluid that it is filled with fibers, but a microscopic examination of a drop of the thin liquid shows that it is filled with tiny particles floating in the water like logs in a river. It is interesting to watch this stream, as it passes out upon the screen, change magically before one’s eyes, from a milky stream into solid mass of pulp.
FIG. 71.—DIAGRAMMATIC VIEW OF THE FOURDRINIER PAPER-MAKING MACHINE
| A. Flow Box | EE. Pulleys | I. The Final Suction Box for Drying |
| B. Copper Gauze Belt | FF. Drums | J. Couch Roll |
| C. Rollers | G. Suction Boxes | K. Canvas Belt |
| D. Deckles Confining Pulp | H. Dandy Roll |
In Figure 71, which is a diagrammatical view of a portion of a Fourdrinier machine, the flow box is shown at A and the copper gauze belt at B. This belt is supported on a series of rollers, C. The deckles which confine the pulp along the margins of the screen are shown at D. These belts travel with the wire gauze for a certain distance and then pass back over the pulleys, EE, while the wire cloth passes on and around the drums, FF. As soon as the pulp flows out upon the wire gauze, the water it contains begins to drain away through the gauze. But it does not do this fast enough under the mere pull of gravity and it must be helped by means of suction. At GG there are boxes or troughs that fit against the under side of the wire gauze. In them a partial vacuum is maintained by means of suction pumps and a large part of the water remaining in the pulp is sucked out here. A dandy roll is shown at H, which presses lightly upon the moist pulp, squeezing out the moisture in it, and at I there is a final suction box which further dries the web of fibers. It is the dandy roll that puts a patterned surface on the paper. If the face of the dandy roll is of finely woven wire cloth with diagonal mesh, a “wove” paper is produced, while if it is of such surface as to impress parallel lines in the half-formed paper, “laid” paper is produced. Water marks are also produced by placing a suitable raised or depressed pattern on the dandy roll, producing a corresponding thickening or thinning of the pulp. Even after passing the last suction box, the thin web of paper is still very wet and so flimsy that it cannot be handled. Right here comes the most delicate part of the whole process. The web must be picked off the wire cloth and carried across a narrow gap to a felt belt which conducts it through another set of rollers, A felt-covered roll, J, known as a “couch” roll, presses down upon the web and the latter clings to the felt in place of the wire cloth which passes down around the roller F. In starting a web of paper very skillful manipulation is required to transfer the web from the couch roll to the felt belt, but after it has once bridged the gap it has enough tensional strength to pull itself across the gap. The felt belt carries the web through a pair of heavy rollers which press out more of the water. Because the paper passes through the rolls with the felt belt it receives an impression from the felt on the under side. This is now corrected by running the paper through a second pair of rolls in the reverse direction, and on a second felt belt, so that both sides of the paper receive the same impression. From here on the paper passes through a long series of steam-heated drying rolls and emerges eventually as a perfectly dry sheet.
Our largest Fourdrinier machines make a web 200 inches wide and they can be run at a rate of 800 feet per minute, or more than nine miles per hour. The paper is made in lengths eight miles long, which are wound up into rolls to be fed into the huge printing presses of our metropolitan newspaper plants.
The difference between the making of news print and finer papers lies chiefly in the quality of pulp used and the quantity of clay and sizing added. After the finer grades have issued from the drying rolls, they are put through calenders to give them a glazed surface. This consists virtually in ironing the paper between smooth rolls of iron on one side and compressed paper or cotton on the other. Just as in ironing clothes, the paper must be moistened before being ironed and steam is used to supply the necessary moisture. In some cases a high glaze is given to one side only of the paper by means of friction. The paper passes between two rollers of different size. The smaller one travels faster than the larger one and consequently it slips on the paper, giving it a very smooth surface.