GB1246132A - Abrading machines - Google Patents

Abstract

1,246,132. Blasting. ABRASIVE DEVELOPMENTS Ltd. 19 June, 1969 [21 March, 1968], No. 13669/68. Heading B3D. An abrading machine wherein air-borne abrasive is directed at a workpiece includes abrading means provided with air/abrasive input conduits 22 and a suction conduit (21), Fig. 2 (not shown), leading to means for recovering reusable abrasive, an upper hopper 37 for collecting the recovered abrasive, a lower hopper 43 for feeding it to the conduits 22, an intermediate middle hopper 38, and automatic pressure-controlled means for cyclically passing accumulated abrasive from the upper to the middle hopper, and then the middle to the lower. The suction conduit (21) leads to a cyclone 26 via a duct 27, re-usable abrasive being separated by the cyclone to enter the upper hopper 37. A pivotable flap 41 closes an outlet to the middle hopper 38, a similar flap 46 being disposed between the middle and lower hoppers 38, 43, of which the latter is open to atmospheric pressure. On applying operative suction from a fan 34 through a filter 31 and dust extractor 12 the pressure in the upper hopper 37 becomes subatmospheric, and air is drawn from the middle hopper 38 via pipes 75, 64, Fig. 4. When the pressures in the hoppers 37 and 38 have equalized, the flap 41 pivots under the weight of any abrasive above it, which abrasive enters the middle hopper 38, the flap 46 being held closed by atmospheric pressure. As the pressure in the hopper 38 falls, air is exhausted from a space 97 in a diaphragm housing 57 through a pipe 77 at a rate controlled by slots 87 in the seating 86 of a ball valve 82, Fig. 5, the ball valve 82, and a vent 81 being closed by the reduced pressure in the pipe 77. When the pressure in the space 97, and the corresponding pressure in the pipe 64 fall sufficiently, atmospheric pressure in a part 59 of the housing 57 deflects the diaphragm 63 from its seating 70, allowing atmospheric pressure to enter the hopper 38 through the pipe 64, so that the upper flap 41 is closed and the lower flap 46 opened, abrasive from the hopper 38 entering the hopper 43 to reach the conduits 22, Fig. 3 (not shown). Atmospheric pressure in the pipe 64 enters the pipe 77, opening of the vent 81 allowing rapid return of the space 97 to atmospheric pressure so that the diaphragm 63 returns to its seating 70 and the cycle is restarted. In a modification the lower hopper 43 may be maintained at a superatmospheric pressure.