The pulp slurry is pumped, at 2-3% concentration of pulp, from a stuff chest to a smaller stuff box at a higher level, is diluted to -75%–I% with re-used or "white" water, whence it flows on to a sand trap, which is a serpentine channel to settle any heavy particles present, and then through a strainer, to stop any larger particles. From the strainer the pulp passes to the "breast box" which is the same width as the wire of the machine.
Then it passes on to the endless wire, moving forwards, on which it is spread evenly by a spreader or slice, and thus a continuous wet sheet or "web," the width of the wire, is gradually formed : the pulp is prevented from flowing off the two edges of the wire, before the water has had time to run away through the wire, by an endless "deckel" strap, each side, made of vulcanized rubber, which moves at the same speed as the wire and in close contact with its corresponding surface. Thence the web passes to the dry end, i.e., to a series of press rolls which remove water and consolidate the web, then to a number of steam heated cylinders to dry it into paper and to a further number of rollers to calender it. The steam heated drying cylinders are usually divided into two or more sets or stacks separated by "nip rolls" or smoothers, the object of which is to flatten and smooth the surface of the paper, while it is yet not quite dry.
The deckel straps serve to guide the paper from the moment the pulped half stuff is spread on to the wire as it issues from the "breast box" and until the web is sufficiently dry to retain its edges : the distance between the two deckel straps can be increased or diminished at will, to determine the width of paper produced. The water that drains through the wire drops into a flat copper or wooden tray along the lines of contact between the wire and a series of tube rolls, which serve to keep the wire in position: this "white" water contains fragments of pulp, and is made to flow into a tank from which it is pumped and the fragments of pulp re-used. At the far end of the wire, the wet web is passed
over two or more "suction boxes" for the further removal of water, between them is the "dandy roll," a light skeleton cylinder made of wire cloth to give the water mark and wove or laid markings to the paper. The frame of the machine, from the breast roll support at one end of the wire to the first suction box at the other end, is hung on a pair of strong hinges, and is capable of a slight horizontal to and fro motion, imparted to it by a horizontal connecting rod which is keyed to an adjustable eccentric, in appropriate manner : and thus a "shake" is imparted to the forming web, as is done by hand for the hand made paper.
From the second suction box the damp web of pulp passes between "couch rolls," named by analogy with the couching in the hand made paper process : their purpose is to squeeze out more water and to impart sufficient consistency, thereby, to enable the web to leave the wires. These couch rolls are covered with felt, and the upper one is provided with levers and weights to enable the pressure on the web to be adjusted. Modern machines do not use a top couch, but use a lower couch provided with suction to remove the water. The web is now fully formed into a wet paper, and usually passes through two sets of press rolls to the dry end of the machine. The more gently and more gradually it is dried the better is the final result : rapid drying is not so economic since it is apt to make contraction uneven and excessive, and the paper brittle : the heating surface is therefore made as large as possible, and for this reason and because machines are now driven at high speeds, a large number of drying cylinders is used. All these cylinders, except the first two or three where the greatest amount of evaporation occurs, are encased by continuous, travelling felts, and they are so stacked that each surface of the paper alternates in being in contact with a heating surface. The drying cylinders are generally distributed in two or more sets or stacks with intervening nip rolls to flatten and smooth the paper while it is still moist and responsive. After the drying comes the calendering and there are usually two or more sets or stacks of calendering rolls, according to the grade of surface required. These calenders consist of vertical stacks of chilled iron rolls, generally five in a stack, which revolve on one another and some of which are bored for heating by steam : pressure is applied to them at will, by adjusting levers at the top of each stack. Finally the paper passes to cooling rolls, where the paper can be cooled by water spray if necessary and is then wound on to a reel.