Messrs. C. H. & F. L. Roeckner’s patent strainer (No. 7932, 1885) consists of a series of cylindrical tubes, open at one end and perforated with slits. They are placed in a vat into which the pulp flows. Inside the cylinders are placed two, three, or more plates, fixed to the shafts on which the cylinders are supported, and extending to the circumference. These plates form a kind of fan, which, together with the cylinders, are caused to oscillate by means of a rod and cranks. This oscillating motion serves to draw the fibres through the slits, and at the same time to keep the outsides of the cylinders clean. The cylinders are easily removable.
After a time, the slits in the plates get too large, owing to the plate having been worn away by the constant friction of the fibres, and as they are very expensive, various attempts have been made to invent plans for partially closing them again. Hammering will effect this, but is liable to break the plates. Annandale of Beltonford has introduced a method of closing the plates, by means of heavy pressure acting on small steel rollers moving on each side of the slit, in which is placed a small sheet of metal the exact thickness of the width desired. {151}
Another method of closing the plates consists in filling them up by means of electrically deposited copper or other metal. They can then be recut in the usual way.
In the case of revolving strainers, all that cannot pass through the slits falls to the bottom of the vat, in connection with which it is customary to have an auxiliary strainer, or “patent knotter,” as it is called, shown at E. All fibre that passes through this one, which is of the ordinary flat kind with shaking motion, goes into a box near E′, called the “low box” for “save-all” water (see p. [154]).
The pulp, after passing through the strainers, should be perfectly free from knots and impurities, and in a fit condition for making paper. In the machine shown, it passes from the last strainer directly on to the wire, its flow being regulated by a movable gate e. In some cases, however, it first flows into a small vat, in the centre of which revolves a rod carrying paddles, with the object of keeping the pulp well stirred up. It is carried right on to the wire by means of the apron, a piece of canvas, oil-cloth, or sheet rubber, one end of which is fastened to the breast-board e′, the other end resting on, and covering the wire to the extent of about 15 in. The edges of the apron are rolled up to prevent the pulp from overflowing. After leaving the apron, it passes under a gate, or “slicer,” as it is sometimes called, made of two pieces of brass, overlapping each other in the centre, and bolted together. It is made thus to enable it to be lengthened or shortened according to the width of the paper; its height from the wire-cloth can be altered by means of screws, and should be equal at all points, in order to ensure a uniformly thick sheet of paper. The ends of the two pieces forming the slicer are fastened to the frame f or “deckle,” as it is called, and this again is carried by two or more rods stretching right across the wire, and fastened by small upright supports on both sides to the frame g. The deckle-frame also carries the grooved pulleys h, along which the deckle-straps i, endless square bands of indiarubber, move. {152}
FIG. 49.
The object of the deckle-straps is to regulate the width of the paper; they form, together with the wire-cloth, a kind of mould into which the pulp flows, thus corresponding to the mould used in hand-made paper-making. The width of the paper can be altered by shifting the position of the frame f, and also the deckle-straps, which are carried on it as described, the pulleys h being so arranged that they slide along the rods on which they revolve. In order to alter the width of the paper it is necessary to stop the flow of pulp on to the wire, and it not only consumes a considerable amount of time, but generally necessitates a partial cleaning up of the machine. Various attempts have, therefore, been made to devise an arrangement whereby the change can be effected while the paper is being made. Several {153} contrivances have lately been introduced, all similar to the one shown in Figs. 49 and 50.
In it the frame f carrying the deckle-strap is made to slide along the rods e by means of the small wheel b, and by a similar arrangement on the opposite side and geared with it. The movable apron l, Fig. 49, is wound round the spindle g, and is kept taut by the cords m connected with the springs n. As the deckles approach each other, the excess of apron is wound up, when they are separated it unwinds again. The flow of pulp is regulated by two slices a a, which are kept in position by the screws h. The whole arrangement is securely bolted to the frame of the machine; c (Fig. 50) represents the breast-roll, and corresponds to F, Plates I. and II.
