THE FOURDRINIER MACHINE consists of the following parts: A. The screens; B, the wire. with dandy roll. deckel straps, and suction boxes: C, the couch rolls; D, the first press; E, the sec ond press; F, the driers: G, the caienders; the reel; and I, the slitter.
A. The Sereens.—From the second stuff chest the pulp. which is now diluted with a large amount of water. flows through sand settlers and regulating gates to the screens. These con sist of brass plates with a large number of longitudinal V-shaped slits cut in them, the opening being very small, only a few thou sandths of an inch. A continuous jarring is given to these plates, which forces the fine pulp through the slits, but the lumps and impurities are retained. In some forms of screen a vacuum pump is used combined with an oscillating mo tion of the screens, which keeps the pulp flow ing back and forth, preventing the clogging of the slits.
wire reeeives a lateral motion. which greatly assists in the felting of the fibres into a strong sheet. The forward motion of the wire tends to arrange the fibres in the same direction, and the side shake is necessary to offset this tendency, giving strength in both directions. Notwith standing. it is easy to tell by tearing which way a sheet of paper was made on the machine. The water drains rapidly away front the pulp, assisted by two or three boxes' under the wire, which are connected with an air pump and exhaust the water much faster than would otherwise be possible. At this point, between the first and second suction boxes, is situated the 'dandy roll,' a light cylinder covered with w ire, which rest: on the upper surface of the moist paper, giving it the impression of whatever design is on it. 'Vi ore' paper has both sides impressed with the fine woven wire; that is, the dandy roll is covered with the same wire a- the paper is formed on. In /aid paper. on the ot her haml, the dandy is covered with parallel wires, with a cross wire at intervals. Water mark; are impressed in the paper by affixing the re wired design on the dandy roll. A false water mark is sometimes made after the paper is partly dried by passing between rolls engraved with a design.
C. Couch Rolls.—At the end of the wire (that is, where it turns down over a roll to return to the starting point) are the 'couch' rolls. covered with felt, through which the Wire passes bearing the web of paper. These rolls press the water out still more, and consolidate the fibre, giving it strength to Cross alone the gap between the wire and the felt of the first press roll. These rolls correspond in function to the pressure ap plied to the 'post' of alternate sheets of damp paper and felts in hand-made paper.
D and E. The J'reRs RolIR.—An endless woolen blanket (the 'felt') supports the tender web of paper through a pair of highly polished brass rolls under considerable pressure. giving the upper side of the sheet a smooth surface, and B. The Thire.—The strained and purified pulp
flows over an apron onto an endless traveling wire cloth. the mesh of which is 611 to 90 threads to an inch. The wire is supported perfectly level on a great many small rollers (the 'table rolls'). under which is a shallow wooden box, the 'save-all,' into which much of the water runs, leaving the pulp on the wire. The water in the 'save-all' contains much pulp and is used over again. The boundary of the flow of pulp on the sides is made by endless rubber bands. called deckel straps, which travel with the wire. These are adjustable so that varying widths of paper may be made. The frame supporting the leaving the impress of the felt on the tinder side. From the first press. 1). the sheet runs under the second pair of rolls. E. and back through them in the rere rse direction. thus smoothing the other side of the sheet and as even-sided results as possible.
F. The Driers.—Tbe paper is now formed and it only remains to dry it. The driers are a series of steam-heated metal cylinders. two to four feet. in diameter, arranged in one, two. or three tiers. The paper is carried nearly round each in turn. and on to the next. being, held to the hot surfaces by an endless blanket. usually of cotton. Sometimes there are smoothing rolls when the paper is partly dried. The size and number of driers determine how fast a paper can be run. With a given machine thin papers can be run (and dried) very fast ; thick ones slowly.
The Culenders.—After being thoroughly dried the web of paper is passed through a 'stack' of smooth chilled iron rolls, which by their own weight, and pressure applied by screws or weights, smooths the paper and produeeks what is called Inaeltine finished' paper, as contrasted with `superealendered' paper. described farther on. `It is now• wound on a reel.
11 and 1. The Reel and Nliticr.—Aftcr being wound on a reel the paper is passed through the slitter, the rough outside edges trimmed, and if necessary the single web slit into any required widths. It is then rewound and is ready for shipment, if intended for printing in the roll or for coating; or for supercalendering, sheeting, and packing.
The Fourdrinier machine makes automatically an endless web of paper from 60 to 160 inches wide at a speed of 10 to 400 feet per minute. The plate shows the reels, calenders, and driers of one of the largest machines in the world, 160 inches wide, belonging to the International Paper Company at Rumford Falls, Maine. It can run at a speed of 300 feet per minute and produces 64.000 pounds of paper in 24 hours.
SurauteAtENDEEs. Much book paper requires a high finish, that is, a very smooth surface, and this is given by passing it between alternate iron and compressed paper rolls under great pressure. These machines are called the super ea lenders. It is then sheeted, counted into reams of 480 or 500 sheets, and packed in cases or bundles.