Patent GB-179562-A (GB)
Title: Improvements in and relating to grizzlies or screens for grading materials
IPC: B07B1/14
Filed: 1922-05-08
Abstract: 179,562. Ross, W. May 6, 1921, [Convention date]. Endless moving sieves; rotary sieves. - A screen of the type described in Specification 123,201 and comprising two sets of horizontal bars moving in closed paths of different lengths, the paths of these bars coinciding in the screening-zone, in which the bars are separated by spaces of predetermined size, and diverging as the bars pass out of the screening-zone thus automatically increasing the distance between them, is arranged so that (a) the release and discharge of material which may become lodged between the bars in the screening-zone is ensured (b) wear and elongation of the chain-belts which carry one set of the screen bars may be taken up (c) oversize material is prevented from falling through the bars at the end of the screening- zone. (d) oversize material of a slabby character which may pass through the bars in the screening-zone is prevented from becoming trapped at the rear inner end of the screen (e) oversize and elongated material is prevented from passing through the screening-zone. (f) the automatic release of material wedged under the lower edges of the top skirt plates is effected. As shown in Figs. 1 to 4, one set of bars, called the main bars 5, is carried by two sprockets-wheels 3 mounted on a shaft 2, the other set of bars, called the displaceable bars 6, is carried by two chain-belts 4. The two sets of bars have the same pitch, but the chain-belts carry one bar more than the sprocket-wheels, and the chainbelts hang from the sprocket-wheels on the upper displaceable bars 6, which engage recesses 7 between the main bars 5. The upper surface formed by the two sets of bars constitutes the screening-zone, to which the material is fed as by a shoot S. The chain belts drop away from the sprocket-wheels at the lower side, allowing the fine material that has passed through the screening-zone to fall out freely. The chainbelt is constructed of links connected bv pins 9, alternate joints being provided with bearings 8 for the ends of the displaceable bars. The centres of the pins 9 are substantially on the same radial lines as the centres of the main bars 5 but, are eccentric thereto as shown in Fig, 3, so that as the chain belts swing away from the sprocketwheels, the bars 6 move relatively to the adjacent rear main bars in curved paths divergent to circles described from the centres of the adjacent rear main bars. Elongation of the chainbelts due to wear in the pivot joints can be adjusted so as to secure exact register of the displacelable bars 6 with the recesses 7 by means of set-screws 11 secured to flanges 10 on the sprocket-wheels and provided with rounded tips which bear against the inner edges of intermediate links of the chain. In a modification, Fig. 5, two pairs of chain-belts 20, 21 each carrying one set of bars are used and are mounted on pairs of sprocket-wheels 16, 17, 18, 19. The bars 22, 23 are carried by lugs 24 attached to alternate links of the chains, the upper run of the chains forming the screening-zone. The rear sprocketwheels 18 for the bars 23 are placed to the left of the rear wheels 17 for the bars 22, thus maintaining spaces of maximum size between the bars at the bottom so as to prevent oversize material from being trapped at the left-hand end of the lower sections of chain. As the chains pass over the sprocket-wheels 16, the space between the bars increases and to prevent oversize material falling through with the fines, a drum 25 provided with longitudinal ribs 26, is fitted, which catches such material and discharges it on to the tail board. In a further modification, two pairs of sprocket-wheels of unequal size on shafts one vertically above the other, are substituted for the wheels 17. 18 shown in Fig. 5. To ensure the automatic release of material lodged under the lower edges of the top skirt plates 34, Fig. 7, these lower edges diverge as shown toward the discharge end of the screen. To prevent oversize or slabby material from passing through the screen, pins 27, Fig. 4, are secured to the bars, the bars being prevented from rotating in the bearings so that the pins lie in the plane of the screening-zone.