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A Text-book of Paper-making

Chapter 84: Chapter XI.
By C. F. Cross
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About This Book

This work provides a comprehensive examination of the principles and processes involved in paper-making, emphasizing the scientific understanding necessary for effective practice. It covers the chemical properties of cellulose, the physical structure of fibers, and the analysis of plant substances, detailing methods for isolating cellulose from various raw materials. The text discusses specialized treatments for different fibers, bleaching, and the mechanical processes involved in paper production. Additionally, it addresses the testing and quality control of paper, along with considerations for site selection and water purification in paper mills. The authors aim to enhance the reader's grasp of the scientific foundations essential for modern paper-making.

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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.

Cutting.

—Except for special purposes, such, for example, as for use in a continuous printing machine, paper is usually sent from the mill in the form of sheets. The form of cutter, called a revolving cutter, generally used, is shown in Fig. 62. The paper from the webs A is drawn forward by the rolls B; it is then ripped into widths of a convenient size by means of two circular knives, the upper one of which is shown at C. It again passes between a pair of rollers, after leaving which it meets a knife D fastened to the revolving drum E, and pressing against a fixed knife not shown. The cut sheets {172} then fall upon the endless travelling felt F. The action of the knives will be understood by reference to Fig. 63. The edges of the two knives are shown at A and B. The knife B has a slot, in which the bolt D slides, and it is kept in position by means of a spring. This spring causes the knife to slide back slightly as it comes against the fixed knife A. The position of the paper is shown by the dotted line C. The knife B is set on the drum not quite horizontally, so that one end meets the stationary knife a little before the other, thus acting in every respect like a pair of scissors. Fig. 64 shows a pair of ripping-knives. The upper one A is kept in position against the lower one B by means of the spring C. The cutting surfaces are slightly hollowed out, so as to have a sharper edge. The paper is shown by the dotted line D. By altering the relative speed of the drum E {173} and the rolls B, by means of the expanding pulley G, sheets of any desired size can be cut. The cutting-knives are sometimes placed inclined to the drawing-in rolls B, so that the sheet, instead of being cut into a rectangle, is cut into a rhomboid. Such paper is used chiefly for the manufacture of envelopes, this shape occasioning a smaller loss when the envelopes are cut out.
FIG. 62.