Patent GB-427793-A (GB)
Abstract: 427,793. Washing granular materials. TUGWOOD, R. J., 77, Chancery Lane, London.-(Jeffrey Manufacturing Co. ; 1st Avenue, Columbus, Ohio, U.S.A.) July 24, 1933, Nos. 4959/35 and 11146/35. Divided out of 424,834. [Class 82 (ii)] Granular material to be stratified according to specific gravity is maintained as a bed on a screen and subjected to pulsations of liquid, the pulsations being controlled so that in the pulsion period the upward velocity of the liquid varies according to a velocitytime curve in which the initial rate of increase of upward velocity is smaller and the subsequent rate of increase larger than in the corresponding parts of the sine curve having the same maximum amplitude and a period equal to the pulsion period. The smoothly rounded crest of the velocity-time curve is smaller than that of the corresponding sine curve. The upward acceleration of the liquid may be constant but is preferably small at first and then increases rapidly and the initial rate of decrease of upward velocity is preferably greater than in the corresponding sine curve. The pulsion period is preferably followed by a suction period in which the liquid flows downwardly through the screen with an increasing velocity until a maximum downward velocity is reached, after which the downward velocity is reduced for a period during the latter part of which the rate of change of velocity is preferably relatively small. Typical velocity-time curves are represented in Figs. 14-17 (not shown). The effect of the movement of the liquid according to such velocity-time curves is that the bed of material expands quickly until it is just in full mobility and is then closed quickly, full mobility being maintained only for a short period. The pulsations may be produced by means of an imperforate piston forming the effective bottom of the tank in which the screen carrying the material is mounted, the piston being actuated by a cam the shape of which may be obtained by integrating the particular velocity-time curve desired. In the form shown in Fig. 9 the material, e.g. coal, is first washed on an inclined screen F, the heavy materials are discharged by a float-controlled rotary valve 267 into a compartment from which they are removed by a bucket elevator, and the lighter materials pass over a weir 191 on to an inclined perforated plate 270<a> and then on to a second washing screen F<1> where the bone coal is separated and discharged by a rotary valve and clean coal passes out of the apparatus at 130. The screens F and F<1> may be fixed or each screen may be pivoted at one end and mounted on adjustable brackets at the other. The pulsations of water are produced by the reciprocation of diaphragms K mounted below and preferably parallel with the screens F, F<1>, each diaphragm comprising a plate 201 connected to flanges on the compartment walls by a flexible ring 203. As shown in Fig. 9, the diaphragm K is mounted on a rod 208 pivoted at 209a to a lever 210 pivoted at 211 on a support 212 and having an arcuate rack 220 on its underside. The rack is engaged by a pinion 222 mounted on a shaft extending through a yoke 224, the pinion being kept from rotation by a spring-pressed pawl. The pinion shaft is carried by an arm 225, the lower end of which forms a yoke which carries a roller 226 mounted on a pin 227 which passes through the arm 225. A pivoted link 228 connects the pin 227 and the support 212. The roller 226 rides on a cam 239 rotating on a shaft 238 and the stroke of the diaphragm is adjusted by withdrawing the pawl and rotating the pinion 222 to move the rack 220 and the lever 210. To maintain the diaphragm parallel to the screen throughout its motion an arm 248 is pivotally connected at one end to a pin 250 extending through the rod 208 and at the other to a bracket 253. In order partly to counterbalance the load on the diaphragm a plunger is pivoted to the end of the lever 210, the head of the plunger being acted on by a spring 259 in a housing 256. In an alternative method of reciprocating the diaphragm K the plate 201 of the diaphragm is carried by a rod which moves in a sleeve provided with a bushing and lubricating means. The lower end of the sleeve is enlarged to form a cylinder provided with vent openings and to the lower end of the rod is secured a piston pivotally connected by a pin to a pitman the lower end of which is formed as a yoke and can be adjustably connected by a pin to a lever pivotally mounted on a bracket and having a plurality of holes disposed in an arc so that the stroke of the diaphragm may be varied. The lever has a downwardly extending portion forming a bearing for a shaft on the ends of which rollers are secured. The rollers run in cam grooves formed between shoulders and flanges on the inner faces of co-operating members keyed to a driving shaft. The heavy materials pass along the screen into a shoot 266 at the lower end of which is the rotary discharge valve 267. The working of the rotary valve mechanism is shown in Figs. 5, 7 and 9. The valve comprises pockets formed by paddles 272 mounted on a shaft 268 which carries a ratchet wheel 270 the teeth of which are engaged by a pawl 274 pivotally mounted on one end of a bell-crank lever 277 rotatably mounted on the shaft 268. The other end of the bell-crank lever 277 is connected by a rod 279 to a crank pin on the shaft 238 on which the cam 239 is mounted, so that the ratchet wheel 270 and the valve are continuously rotated. To regulate the speed of rotation a shield plate 282 is provided which can be moved round the ratchet wheel to vary the position in which the pawl comes into contact with the ratchet teeth on its downward stroke. The shield plate 282 is carried by a metal sector 284 stiffened by ribs 292 293 extending from hubs 296 rotatably mounted over a sleeve on the shaft 268. A rod 283, the length of which can be adjusted by a turnbuckle, is pivotally connected by means of a bracket 285 to the sector 284 and the upper end of the rod is connected by a lever to a transverse shaft 288, Fig. 9, to which is secured a lever 290 one end of which is provided with an adjustable weight 290<a> and the other end of which is pivotally connected to a float 291 which rests on the heavy material on the screen F. A link 287<a> pivoted to the float and to a bracket 291<a> is provided to keep the float in a vertical position. As the depth of heavy material on the screen increases the float rises, turns the shaft 288 and withdraws the shield plate 282 from the ratchet wheel and increases the effective action of the pawl 274. To prevent the rotation of the valve 267 by the weight of the materials in the pockets, brake mechanism comprising shoes 112, 113 is provided, the shoes being pivotally mounted on levers 112<a>, 113<a>, pivoted on a bracket 116 and pressed against the sides of the ratchet wheel by the action of a spring 117 carried on a bolt 118 pivoted on the lower end of the lever 113<a> and passing through an aperture in the lever 112<a>. The materials discharged by the rotary valve fall to the bottom of a compartment L and are carried up a lateral extension by a bucket elevator. A plate 198 extends across the upper part of the compartment L to prevent surging. The cam shafts 238 of the two compartments are connected by chain and sprocket gearing, one motor being used to drive the two pulsators and discharge valves. The two bucket elevators are also driven by a single motor. Specifications 424,834 and 424,878 are referred to.