Paper and Its Uses/Chapter 4
CHAPTER IV
PAPERMAKING BY MACHINE
The Fourdrinier machine bears the same relation to the hand mould that the rotary press does to the hand press. Instead of making paper sheet by sheet, it makes it in a continuous web, on an endless band of woven wire. The machine in a much simpler form was invented by a Frenchman, Nicholas Robert, the first machine being made in 1799, and so rapidly did the machine find favour that in fifty years over 150 papermaking machines were at work.
Papermaking by hand involves the processes of transferring a certain and regular quantity of pulp from the vat to the mould, shaking the mould to felt the fibres and to remove the water, couching the paper and drying the waterleaf. Machine-made paper follows the same processes exactly, everything being done by the one machine, including sizing. Viewing the papermaking machine, it appears to be a collection of machines carrying out the separate functions in proper sequence. The different parts of the machine can be controlled and driven at different speeds for special reasons. Thus a definite and regular quantity of pulp is taken, shaken, the water removed, the soft paper couched, pressed, dried, and a finish given to the surface of the paper, all in the compass of the one machine.
The pulp as left at the end of Chapter II. was merely beaten fibre, and if an unsized paper 
Fig. 5.—Diagram showing elevation of Papermaking Machine. Shown in Sections.
Total length of machine 144 feet.
(Built by Bertrams Limited, Sciennes, Edinburgh.)
Paper can be made without filling or loading; in fact all-rag papers seldom contain mineral matter, and many excellent papers are made from other fibres without loading. The purposes of loading are to fill the spaces between the fibres, to give opacity to papers, such as those made of sulphite wood pulp, which would otherwise be very transparent, and to enable the paper to take a higher finish than would be possible in a paper without loading: a smoother and more absorbent, even if a little weaker, sheet, resulting. In a blotting paper mineral matter is an adulteration; in writing papers 5 per cent, is sufficient for improvement of surface; in printings 10 to 16 per cent, is as much as is permissible. In an imitation art paper as much as 25 per cent, may be added, and yet a serviceable paper result; but of course the tenderness of imitation art paper will be present.
China clay is the usual material used for filling or loading. It is mixed with water, and strained before filling into the beating engine, and the colour is added, either to produce a coloured paper, or to correct the tendency to greyness in the finished paper. In the latter case, a little blue and perhaps a little red is added, while in the former case the colour may be added, or formed in situ by the mixture of different chemicals in the beating engine. Dry colours, whether pigment as ultramarine or aniline colours, are mixed with water (dry patches being difficult to deal with in the pulp), and then added to the pulp in the engine; when the colours are thoroughly mixed, alum is put in. Alum serves to mordant or fix the colour, and also serves to precipitate the resin size which is next added.
There are various prepared sizes on the market to take the place of the size prepared by the papermaker from resin and a solution of soda. The resin is melted and added to the soda solution, and boiled until the solution is complete. The size solution is added to the pulp in the beating engine, and thus we get a clue to the meaning of E.S., or engine-sized paper.
The pulp now consists of innumerable fibres, to which and in which are fixed small particles of china clay, colouring matter, and resin. In many writing papers a small amount of starch paste is added, and that also adheres to the tiny fibres. The engine is emptied by gravity into the stuff-chest, where the revolving arms keep the fibres in the mixture from precipitation. Then there is a short journey to the machine, during which the pulp undergoes great tribulation, first being diluted with a large quantity of water, then passing over sand traps which intercept grit, metallic fragments, and such matter that is heavier than the pulp and so tends to sink, and then through strainers, which retain foreign matter, unbeaten particles, and knots of fibre. The flow of pulp is governed by a system of valves, which can be quickly manipulated to alter the substance of the resulting paper.
The wet end of the machine consists of an endless band of woven wire, some 40 to 80 meshes to the inch, from 48 to 205 inches wide, and a total length of 40 feet or more. The length of wire in use at one time as a paper mould is less than half its total length. This woven wire corresponds to the mould of the vatman in hand-making. Deckle straps, the substitutes for the vatman's deckle, are thick endless rubber bands, square in section, which rest on the wire cloth, and, following the travel of the wire, return over pulleys, serving the same purpose as the deckle, namely, to confine the pulp to the wire surface. The wire cloth is supported by a number of rollers—tube rolls—which keep the wire from oscillating, and assist the passage of the water through the wire. The end of the wire nearest the stuff-chest is kept shaking backwards and forwards to cause the
Fig. 6.—Front View from Strainers of 94-inch Papermaking Machine.
(Built by Bertrams Limited, Sciennes, Edinburgh.)
fibres to felt before the water has passed through the wire. The pulp passes from the strainers under a slice, which distributes the pulp evenly, over a rubber apron, on to the machine wire, and near the end of the wire will be seen a cylinder of wire above, and square boxes below the wire.
The cylinder is the dandy roll, which closes the surface of the paper with slight pressure, and if a water-mark is required the soft pulp is impressed with the design upon the surface of the roll. If the paper is to be "laid" the cylinder will be covered with laid wires, with tying wires at regular intervals, but a wove paper has a woven dandy roll which leaves no mark beyond any watermark that may be on its surface. A dandy roll on which the tying wires run the length of the roll instead of round the circumference is known as a spiral laid dandy roll.
The boxes beneath the wire are suction boxes, open mouth of pumps which suck the remaining water from the paper. The wet end is well named, as for every ton of paper nearly 20,000 gallons of water are used for the dilution of the pulp, so that it may flow evenly and regularly. This water passes through the wire, most of it falling into the save-all and is used again for diluting the pulp.
Passing under the dandy roll and over the last suction box, the wire carries the web of paper through the couch rolls, where the paper is couched or pressed by a felt-covered roll for the same reason as hand-made papers are couched: to consolidate the paper. The wire returns to perform its operations continuously, and the limp paper is carried forward to the press rolls, where it is further pressed by polished rollers, first one side, then the other, to remove the wire and felt marks. Then the paper goes forward to the drying cylinders—massive rolls heated by interior steam; but the heat is so regulated that it is gradually increased, and the speed at which the web of paper travels is arranged so that no undue tension is placed upon the paper, or thinning might result, or the web be broken, and delay caused. The drying section of the 
Fig. 7.—End of Wove Dandy Roll.
Fig. 8.—End of Laid Dandy Roll.
Fig. 9.—End of Spiral Laid Dandy Roll.
At the end of the machine are stacks of rolls through which the paper is led if it is to receive what is known as "machine finish." If, however, the paper is to be super-calendered, it is led past one or more of the stacks of rolls, and as it is reeled off a fine spray of water is projected upon the paper. There are various means of producing a misty cloud, but the object is the same in every case, to restore some of the moisture which has been driven off, and to prepare the paper to receive the finish at the super-calenders. If the paper were finished bone dry it would not be possible to impart the required surface by super-calendering, and, too, the paper would at the first opportunity absorb moisture from the atmosphere, and various troubles would arise. The paper, now reeled, is ready for the finishing department, to which the next chapter is devoted.
Papermaking on the Yankee or single cylinder machine is conducted in the same manner as on the ordinary or Fourdrinier machine as far as the wet end is concerned, but the series of drying cylinders is replaced by a single cylinder of large diameter, as much as 10 feet in some instances: the paper passing round this heated cylinder is dried, and glazed on one side, hence the term M.G., or machine-glazed paper.
Mill numbers survive from the time when all mills were registered, and when paper was a dutiable article. The duty was repealed in 1861, but the mill numbers remain, and are additional to watermarks in distinguishing between papers of the various makers.
Watermarks have been used from very early times to serve as marks of distinction. The watermark used by John Tate of Stevenage in 1494 was an 
Fig. 10.—Single Cylinder or Yankee Papermaking Machine.