GB689340A - Improved screening and winnowing apparatus - Google Patents

Abstract

689.340. Middlings purifiers. ZUNDAPPWERKE GES. Dec. 21, 1950 [Aug 7, 1950], No. 31107/50. Class 117 In a screening apparatus comprising a shaker screen 2 and means of passing an air current through the screen, a feedsensitive means 14 controls a motor device 30 which actuates valve means 26 to adjust the air current through the screen in accordance with the loading of the screen with the material to be screened. As shown, the screen 2 comprises four sections 5, 6, 7 and 8 surmounted by separate suction chambers 9, 10, 11 and 12 respectively, the ceilings 17 of each of which have an air outlet 18, 19, 20 or 21 leading into a suction passage 34. Material is fed to one end of the screen 2 via a feed pipe 13 which contains a spring-loaded float 14 which is depressed according to the rate of feed. Depression of the float 14 lifts, by means of a lever 33, a control member 32 of a servomotor 30 which in turn causes a depression of the working piston 29 of the servomotor. The piston 29 is connected, by a link 27, and a bell-crank lever 26a, 26b, to a common actuating rod 26 of four valve devices 22, 23, 24, 25 which operate to increase or reduce the air outlets 18-21 of the suction chambers 9-12, so that depression or lifting of the piston 29 on depression or lifting of the float 14 causes rod 26 to increase or reduce respectively the air outlet openings. To maintain a constant suction in the passage 34 on variation of the air inlet openings 18-21 a spring-biased air inlet valve 36 is provided in the wall of passage 34 and is adjusted to operate, by means of linkages and levers 37a, 37b, 37c, 37d connected to the bell-crank lever 26a, 26b, on movement of the servomotor piston 29 to open or close on closing or opening respectively of the air inlets 18-21. A feed indicator pointer 33b is connected to the float lever 33 and a further pointer 26c operated on movement of the rod 26 is arranged to give visual and audible alarm signals on excessive overloading or underloading of the screen. The various indicators may transmit to a central control.