Patent GB-1419294-A (GB)
Title: Abrasive surface treatment of workpieces
IPC: B24C7/00
Filed: 1973-04-13
Abstract: 1419294 Blasting DEVELOPMENT & RESEARCH ENTERPRISES (DERBY) Ltd 19 March 1974 [13 April 1973] 17957/73 Heading B3D A method of treating a workpiece comprises directing a stream of liquid containing abrasive particles on to the surface of the workpiece, and varying the proportion of abrasive particles in the stream in a controlled manner without interruption of feed of the particles. The apparatus for carrying out the method comprises means 22 for pumping a stream of liquid through a nozzle 3, a reservoir 2 for abrasive particles having an outlet 57 through which the particles are discharged into the stream of liquid, a conveyer 52 associated with the outlet for feeding the particles along a feed path 53 from the reservoir towards the nozzle, the conveyer having at least one element 58 for displacing the particles along the path and being power driven, and means for recovering the liquid and particles after they have been projected on to the workpiece. In use, the workpiece is treated in a blast box 4, Fig. 1, water and abrasive particles being fed from respective reservoirs 1, 2 to the nozzle 3. The box may be a room in which the operator works or a chamber and have a lining of polymeric material. An outlet 5 from the box is connected by a pump 6 to a first separator 7 which returns a slurry containing a major part of the particles to the reservoir 2 and passes a stream consisting mainly of water to a tank 8. A pump 9 connected to an outlet of tank 8 pumps its contents to a second separator 10 which separates any remaining abrasive particles for return to the reservoir 2, the remaining liquid which may contain fine particles being pumped to a tank 11. A pump 12 passes the contents of tank 11 to a third separator 13 which discharges any remaining particles into a waste trolley 14 having a fine mesh screen through which water passes into a waste tank 15 having a pump 21 which returns the water to the blast box 4. The water from separator 13 passes through a pipe 16 and fine filter 17 to the reservoir 1. Valves 18, 19, 49 associated with level controls are connected between the reservoir 1 and tanks 8, 11 and the blast box 4 to ensure that the pumps 6, 9, 12 do not run dry. Water from reservoir 1 is fed to the nozzle 3 by a high pressure pump 22 having a header tank 23 connected by a valve 24 to the reservoir 1. The supply from the pump 22 is connected by a valve 26 to a flexible conduit 43 and a mixing chamber 27 of the nozzle or to a return line 28 and a line 29 leading to the blast box 4. The reservoir 2 for the abrasive particles has a frusto-conical outlet 57, Fig. 2, connected to one end of the tubular duct 58 of a screw conveyer 52 having a drive 31 of variable speed. The other end of the duct has a tapered connection with the flexible conduit 53, which connection can be closed by an hydraulicallyoperated valve 33. The conduit 53 is connected to one end of the mixing chamber, the other end of which is connected to the nozzle 3. The abrasive passes through a spool 39 in the chamber, and water from the flexible conduit 43 is connected by a groove 41 to inclined bores 44 which form jets acting on the abrasive passing through the nozzle to direct the abrasive against the workpiece surface 48. A housing 45 which becomes filled with high pressure liquid prevents bouncing of the particles after impinging at 46 and cause abrasion at a further position 48. Jets 37 connected by a line 38 to the output of separator 7 wash abrasive from the face of valve 33 to assist operation of the valve. The flow of abrasive to the nozzle is controlled by the speed of conveyer 52 and may be varied during treatment of a single workpiece, e.g. the speed of conveyer 52 may be progressively reduced from a rate sufficient to remove scale from a workpiece to zero so as to effect polishing of a workpiece. In another embodiment, two separators are provided for removing large and small particles, respectively, and each reservoir has a respective screw conveyer and associated reservoir connected to the mixing chamber whereby first the large particles and then the smaller particles are used to treat the workpiece, the rates of feed of the particles being varied inversely. The water may contain a wetting agent, such as sodium metasilicate and isopropyl alcohol, a deflocculating agent, such as sodium pyrophosphate, sodium tripolyphosphate and sodium hexameter phosphate, and an anti-foaming agent, such as ligin sulphonic acid and ethylene oxide condensation products.