The Building of a Book / A Series of Practical Articles Written by Experts in the Various Departments of Book Making and Distributing

by Unknown

Wood fibres for book papers are usually treated in the same general way as rags. First, the logs are peeled and are cut into suitable lengths to be thrown into a wood chopper and cut up in very small pieces. If the wood is treated by sulphurous acid or bi-sulphite of lime fumes, it is called the "sulphite process"; if by caustic soda, the "soda process." This wood is cooked in large upright kettles called "digesters." In one case the sulphite fumes are allowed to permeate through the wood under a high pressure, and in the other the caustic soda is put in "straight," and the wood is cooked under a high pressure of steam. This is done to dissolve out all the gum and resins, in order to leave the pure cellulose matter. After the cooking is done, the stock has to be bleached in very much the same way as the rags and washed thoroughly before it is ready for the "beaters."

For "beating," the stock is thrown into a large revolving tub. Rag and wood fibre may be mixed in different proportions, according to the grade of the paper wanted. The stock is then washed a little to be sure that it is clean and white. Water at first is mixed in with the fibre until it is so diluted that it will flow freely; then it is beaten for several hours by means of an iron wheel covered with iron or steel knives about one-quarter of an inch thick, which revolves over an iron bed-plate with similar knives. During this beating process, clay is mixed with the stock, mainly to give the paper a well-filled and better appearance, and not, as most people think, to add weight, although this is sometimes an object. Sizing material is also added, which helps to keep the fibres together and hold the ink in printing. If it is desired to give the paper a white shade, a small amount of aniline blue or pink is mixed in; otherwise it is called "natural" or "unblued."

The beating part of the process of paper making is the most important. The stock has to be beaten up so that all the fibres are separated and broken into just the right lengths according to the weight and strength of the paper to be made. The harder the roll is set down on the bed plate, the shorter the fibre will be and vice versa, but if the roll is not put down hard, the stock has to be beaten so much longer.

"Machining" may be divided into five processes:—

First. When the stock leaves the beater it is run into a large "stuff" chest, and is continually being stirred so that it will not be lumpy. By this time the pulp is about as clean as possible and is ready for the paper machines. The first thing to be done on the machine is to dilute the stock with pure water to the consistency of buttermilk, according to the thickness of the paper required. Then this liquid stock runs through what are called "sand settlers," which are supposed to collect what dirt, iron, etc., remain.

Second. From the sand settlers the stock runs on to a screen, through which it is drawn by means of suction. This process prevents fibres which are lumpy and too long from getting on to the machine, and allows only those of a certain size and length to go forward to be made into paper. An endless and very fine wire cloth, which is continually moving at the same rate of speed as the rest of the paper machine, takes the stock after it has been screened. This is the first step toward making the material into actual paper. Thick rubber straps on each side of the wire determine the width of the paper. This wire shakes a little in order to weave the fibres together while in a state of suspension. At this period the stock looks like thick cream, but soon changes its appearance to the form of a sheet more or less solid on coming to the end of the wire, where there is what is called a "dandy,"—a roll covered with similar wire cloth pressing lightly on the paper as it runs along the wire. Designs in relief on the surface of this roll produce the well-known marks called "water marks." Just beyond the "dandy," underneath the wire, is a suction box which draws enough of the water out so that the paper can go through the "couch" roll at the end of the wire without being crumbled.

Cross-section of a Paper Machine.

Third. The couch roll is a small hard roll covered with a thick felt called a "jacket," and is used on the paper machine to prevent the paper from being crushed, for it presses out much of the water and flattens the paper so that it will pass from the wire to the felts without breaking and through the press rolls without crushing. From this couch roll the paper leaves the wire and is carried along on an endless woollen felt to the press rolls, which are made of hard rubber, steel, or brass. These rolls press the fibres together well, squeezing out more of the water and flattening the sheet.