Roeckner's Pulp Strainers.—This invention consists in constructing boxes, with one or both ends open, forming the strainers, fixed, or to slide in or out, so as to be readily cleaned. One or more fans are fitted in these boxes, and are put in motion from the outside, so as to cause what is called "suction" through the strainers. One or a number of such boxes are fixed into a vat, the open ends discharging the pulp which has passed through the strainers to the paper-machine, and can be so arranged that all the fans are worked on one shaft. The vat may be divided into compartments, so that the stuff flows from one to the other. Instead of boxes, the strainers may be formed of tubes, in which suitable slits or perforations have been provided. The tubes will be perfectly closed at one end, and the strained pulp, after passing through them, will be delivered to the paper-machine from their open ends, which may fit into a ring, so that when cleaning is required they may be easily lifted out or in. The suction is provided inside these tubes by the fans, which are oscillated by suitable gear from the outside of the vat. The strainers may, instead of being stationary, be attached to the fans and oscillate with them, in which case the open ends would have to be attached to the vat by an indiarubber or cloth ring, or the strainers may oscillate whilst the fans are stationary. Any number of these strainers may be fixed into vats, disposed vertically or otherwise. In the vat A, Fig. 28, which receives the pulp to be strained, are several tubes, p p p, with one end open, having slits in them similar to strainer plates. Inside of these are two, three, or more plates, f f f, Fig. 29, running the full length of the tube fixed to the shafts, s s s, and to the sides of the tubes, which serve as fans, besides giving strength to the tubes. The shafts s s s are carried in bearings at each end, and have each one end projecting through, upon which are keyed levers, h h h, which, being connected to a rod r, worked by an eccentric, e, at the end, gives an oscillating motion to the tubes and fans. Any number of tubes may be in the vat, and may either work separately or divided. With several tubes it is preferable to have them arranged as shown in the drawing by division plate d, so that the accumulated "knots," &c., may flow finally into the end compartment (which will form an auxiliary strainer), and may be mixed with more water, so that the fine pulp still contained in the stuff can flow away through the slits and the knots, &c., be taken out when necessary. The tubes should be placed so far apart that a workman can get his hand between. The closed ends work free in the stuff, while the open ends run through indiarubber sheet or other material, fitted so well to the tube that the fibre can only get through the slits of the tube to flow on to the paper-machine through the channel at side by the sluice v. The arrows indicate the direction of the flow of pulp.
Fig. 30.
Mr. Dunbar says, "the straining power necessary to pass and clean pulp in an efficient manner for 25 tons of finished paper per week is two revolving strainers, consisting of four rows of plates, or 7 feet by 18 inches of straining surface on each of the four sides, the plates being cut No. 2½ Watson's gauge."
After passing through the strainers the pulp should be absolutely free from knots or objectionable particles of any kind, and in a proper condition for conversion into paper.
The Machine Wire and its Accessories.—On leaving the strainers the pulp passes into a vat, in which is a horizontal agitator, which causes the pulp and water to become well mixed, and ready to flow on to the endless wire-cloth of the machine. The wire-cloth is made of exceedingly fine wire, the meshes ranging from 60 threads and upwards to the inch, there being sometimes as many as 1,900 holes per square inch, but the meshes usually employed run from 2,000 to 6,000 per square inch. The ends of the cloth are united by being sewn with very fine wire. The width of the wire-cloth varies considerably, the greatest width being, we believe, that supplied for the large machine at Mr. Edward Lloyd's mill at Sittingbourne, which is 126 inches. The length of the wire-cloth is generally from 35 to 40 feet, the latter being considered preferable. Beneath the wire is placed a shallow box called the "save-all," which receives the water as it flows through the wire cloth from the pulp. In order to effect a further saving of pulp which escapes through the meshes of the wire-cloth, a machine called a "pulp-saver" is used at some mills, through which the backwater, as it leaves the box or save-all referred to, is passed.
The wire-cloth is supported by a series of brass tube rolls, which are so placed as to render the layer of pulp on the wire absolutely uniform, by which a regular thickness of the finished paper is ensured. The wire is attached to a malleable iron frame, having a sole-plate of cast iron, and carries a brass or copper breast-roll, 18 inches in diameter, a guide-roll 7 inches in diameter, and four brass or copper rolls 5 inches in diameter under the wire, with shafts extending through the rolls, and furnished with brass bushes and brackets, and a self-acting guide upon the 7-inch guide-roll. The tube-rolls or "carrying tubes" are carried upon brass bearings. Attached to the sole-plate of the wire framing are three cast-iron stands on each side for supporting the save-all beneath the wire. To regulate the width of the paper there is on the top of the wire a set of brass "deckles," carried on a brass frame passing over the first suction box, of which there are two, and supported on the wire frame by iron studs fixed in the frame. At each end of the deckle-frame is a pulley for carrying the deckle-strap, with three similar pulleys for expanding it. The deckle-frame is furnished with two endless straps of india-rubber, these straps keeping the pulp to the width required for forming ledges at the sides of the web.
Fig. 31.
The Conical Pulp-saver, which is shown in Fig. 31, was invented by the late Mr. George Bertram and Mr. Paisley, and is manufactured by Bertrams, Limited. Its use is to extract fibres from the washing water before going into the river or otherwise. For the water from the drum-washer, washing and beating engines, and for the water from the paper-making machine, save-all, &c., it has proved itself of great utility. It is simple in construction, small in cost, takes up little room, and is easily repaired. When placed to receive the washings from the beaters or paper-machine, the pulp saved, if kept clean, can always be re-used. A is a conical drum which is covered with wire-cloth, and it is made to revolve slowly by suitable gearing. The water enters by the pipe B, which is perforated, as shown, and passes through the meshes of the gauze, while the pulp gradually finds its way to the wider end of the drum, where it escapes into the box C, and can be conveyed again to the beating-engines.