GB1299522A - Screening apparatus for granular materials - Google Patents

Abstract

1299522 Sifting apparatus D R MULLEN 23 Feb 1970 [24 Feb 1969] 8620/70 Heading B2H An apparatus for screening granular material comprises a main frame 2 Figs. 4 and 5, defining a screening chamber 13, Fig. 3, flexible metal straps 4, Fig. 2, for connecting the frame 2 to a support 3 to enable vibration of the frame relative to the support, and a number of, sieves 15, Fig. 4 mounted within the screening chamber 13 in vertically spaced relationship and held against movement relative to the frame, each sieve having a mesh surface 16 for receiving granular material thereon and being arranged to laterally discharge material that has not passed through the mesh surface whereby, in use, granular material is deposited from a supply source on to the uppermost sieve and vibration of the frame causes at least some of the material to pass downwardly through each sieve in turn. The straps 4 which are vertically adjustable are secured to the support 3 by vibration-damping rubber blocks 5. The apparatus includes two main frames 2 which are vibrated by way of connecting rods 11 and eccentrics 9, Fig. 3, mounted on a common motor-driven shaft 7. Each frame 2 contains two screening chambers 13 separated' vertically by an air chamber 14, Figs. 2 and 3. Each sieve 15 slopes downwardly and is removably mounted in a sieve compartment, an access door 18 being provided at the front end of each compartment for removal and replacement of the respective sieve. A cowling plate 19 hingedly mounted at 22 is located above each sieve 15 and is provided with longitudinal slots 23, the edges of each of which are bounded by upstanding lips 24 defining between them channels 25. In each sieve compartment chutes 26, 27 are provided at the lower end of the sieve 15 and the cowling plate 19 and extend side by side between the side walls 28 and 29 of the screening chamber 13, Fig. 6, sloping downwardly in opposite directions. A transfer chute 35 is mounted beneath each sieve 15 and serves to transfer material from the. lower end of an upper sieve to the upper end of a lower sieve via a transfer duct 38 which may be provided with an air-flow restricting control flap valve. Each sieve 15 is cleaned by two elongated brushes 41 projecting in opposite directions from a bar 39 which is slidably and rockably mounted on a guide track 42. Inlet and outlet draught apertures 46, 44 are located in the side walls 28, 29 respectively below and above the respective sieve 15 and cowling plate 19 in each sieve compartment. An opening 47 is provided in the top wall of the air chamber 14 for removal of air and fine material. In operation, material is introduced into each screening chamber 13 through an inlet 48 and is distributed substantially evenly across the entire width of the upper end portion of the uppermost sieve 15 by means of an adjustable control gate 49. An upward draught is induced in each chamber 13 by means of a fan connected to the opening 47 of the air chamber 14. In each sieve compartment, as the respective frame 2 is vibrated, coarse material 55 passes down the sieve 15 to the associated discharge chute 26 and thence, as the case may be, to a down-pipe 31 and an outlet 32, or to an outlet 70 or to a downpipe 71 or 72. Intermediate material 54 passes through the sieve 15 to the transfer chute 35 of the respective compartment and thence on to the next sieve 15. Fine material 56 is lifted from the screen 15 by the induced draught and subsequently passes through the slots 23 in the respective cowling plate 19. On issuing from the slots the air expands thereby causing some of the fine particles entrained in it to drop on to the upper surface of the cowling plate to be directed downwardly by the channels 25 towards the associated discharge chute 27 and thence through the air chamber 14 to an outlet below the chamber. Fine particles which are not deposited on the cowling plate 19 or within the chamber 14 are withdrawn through the air chamber outlet 47 to which a precipitator may be connected. During the operation, the screen 15 is kept cleaned by the brush assembly 39, 41 being moved up and down the track 42 due to the vibrations. In a modification, the apparatus may include two main frames each of which houses a single screening chamber. A single air chamber may be located to one side of the apparatus in communication with both chambers. Knocker or ball cleaners may be used instead of brushes to clean the screen. In a further modification, Figs. 16 and 17, a grain cleaning apparatus is provided with discharge ducts 126 to collect and direct material discharged from the lower end of each sieve 115 to waste. The angle of slope of each screen in the longitudinal direction of the driving shaft 107 is adjustable. Aspiration of the material is effected at the inlet 148 and discharge 136 of each screening chamber 113 via an expansion chamber 114 which is operatively connected through an outlet 147 to an exhaust fan.