Single-cylinder Machines.

FIG. 56.

It resembles the Fourdrinier machine as far as the couch-rolls A and B. The paper is taken off the wire-cloth on to an endless felt running round the upper couch-roll A, and travelling in the direction of the arrows. It is taken from the felt on to the large drying-cylinder C, of about 10 feet diameter, heated with steam. It is carefully turned and polished so as to impart a high gloss to the surface of the paper with which it is in contact. Calender-rolls are sometimes supplied in addition.

The arrangement shown at D is for the purpose of washing the felt. This is necessary to cool and open it out after passing between the cold press-roll E and the hot cylinder. {165}

The paper, after passing over the greater part of the surface of the cylinder, is sufficiently dried, and it is then wound off at F.

FIG. 57.

A machine of a very dif­fer­ent con­struc­tion from the or­di­nary form is shown in Fig. 57. The pulp, after passing through the strainer A, enters the vat B, in the centre of which a large drum or cylinder C revolves. This cylinder is covered with fine wire-cloth, and on it the paper is made. As it revolves, the fibres attach themselves to the wire, and the water passes through the meshes, being assisted by means of a pump. The sheet of paper thus formed is taken on to the endless felt passing round the couch-roll D, and travels along with it to the large drying-cylinder E, heated by steam. It leaves the felt at F, and is then taken on to the cylinder, after travelling round which it is sufficiently dried, and is then wound off as at G. The felt on its return journey passes through the washer H, where it is cleaned and freed from adhering particles by the scraper I. It is squeezed free from excess of {166} water by the rolls K. Paper made on such a machine is weaker than that made in the ordinary way, because it has not been found possible to give a shaking motion to the cylinder, and thus the fibres are only imperfectly felted.

A modification of this machine is used for making millboards, the difference being that it has no drying-cylinder. The felt carrying the paper passes between a pair of press-rolls, which squeeze out the water. The sheet of paper is then allowed to wind round the top press-roll until of the required thickness. When this happens, it is cut off the roll by a knife. The thick sheets so produced are dried either in the open air or in a room heated for the purpose. (See p. [108], Fig. 31.)

{167}

CHAPTER XI. CALENDERING, CUTTING, ETC.

The paper, as it leaves the machine, is for many purposes not sufficiently highly glazed, and it is therefore necessary for it to undergo a further process of calendering. This may be done in various ways.

FIG. 58.

One method, called “web glazing,” is to pass the paper between a number of rolls, alternately of polished iron and very highly compressed paper or cotton. The construction of such a calender will be understood by reference to Figs. 58 (end elevation) and 59 (front elevation). The reel of paper, as taken from the machine, is shown at A (Fig. 58), its course over the rolls being indicated by arrows. After passing over the bottom roll, it is wound off on a wooden or hollow iron cylinder B (Fig. 58), driven by the toothed wheel shown by the dotted line C, on the same shaft as the wheel D, which is driven by E, keyed upon the bottom roll. The whole machinery is driven by the large toothed wheel F (Figs. 58 and 59), which is itself driven by the small wheel G on the main shaft H. The paper rolls are marked P, and the iron rolls I. It will be seen that there are two paper rolls in the middle, for the purpose of, as it were, reversing the paper, and so making both sides alike. Pressure is applied to the rolls by means of the screws K, and by the weight L (Fig. 58) acting on the compound lever M. The brake, which consists of a strap of leather, pressing, by means of the weight and lever N, on the circumference of the wheel O, connected by toothed wheels with the cylinder A on which the paper is wound, is used for the purpose of preventing the paper from leaving {168} the cylinder too rapidly. But for this appliance, the paper would be apt to crease. The paper rolls have an inner core of iron, the paper only extending to a depth of about 5 in. The iron rolls are hollow, and are connected with steam-pipes, by which they can be heated. {169}

FIG. 59.

Another method, known as “friction-glazing,” employed for giving a very high finish to paper, generally on one side only, is to pass it between a large paper roll and a smaller iron one, the latter revolving at a much greater speed than the {170} former. By this means a very smooth surface can be obtained. It is sometimes assisted by rubbing a small quantity of bees’-wax on the small iron roll. The above-mentioned methods apply to the glazing of paper in the web. Paper cut into sheets may also be treated in the same way. Various modifications of these calenders have been devised; they do not, however, involve the application of any special principle. Plate-glazing, a method that is adapted to hand-made and the better qualities of paper, consists in applying heavy pressure to sheets placed between polished plates of copper or zinc. The metallic plates and the sheets of paper are made into bundles, and the whole is passed between two strong rolls, heavy pressure being communicated to them by means of screws or levers and weights applied to the ends of the upper roll.

FIG. 60.

A calender for this purpose is shown in Fig. 60. The bundle of plates and paper is passed along the table a; after {171} passing through the rolls c, it slides along the inclined table d, where it is received by a workman. The pressure on the rolls is regulated by the handle e and the weights b.

By passing paper between rolls on which devices have been cut, the “repped” and other similar papers are produced.

With calender rolls of the ordinary construction, as the pressure is applied at the extreme ends, the roll is liable to assume a slightly curved shape, the effect of which is to produce an uneven surface on the paper, the outer portion of the web being more highly finished than the centre.

FIG. 61.

This defect is obviated to a very large extent by Schurmann’s Patent Anti-Deflection Rolls (Fig. 61). The roll proper consists of an outer shell a, through the centre of which and securely wedged in at b is the centre core c, the ends of which run in journals, and to which pressure is applied in the usual way. The pressure is communicated to the outer shell at the point of contact b, the result being that the parallelism of the surfaces of the rolls is maintained, and in consequence, the paper tends to be equally finished in every direction.