Patent GB-1247339-A (GB)
Title: Wet blasting apparatus
Inventor: FIELD ANTHONY GERALD
IPC: B24C7/00
Filed: 1967-10-24
Abstract: 1,247,339. Conveying solids in liquids. ABRASIVE DEVELOPMENTS Ltd. Oct.15, 1968 [Oct.24, 1967], No.48171/67. Heading F1R. [Also in Division B3] Wet blasting apparatus comprises a tank for liquid and settled out solid particles, the particles passing through a hole in the bottom into a passage, one end of which connects to the tank above the level of the particles but below that of the liquid and the other connects to a pump. Liquid passing through the passage picks up the particles to form a slurry which is discharged by the pump to a blast nozzle, the excess slurry being by-passed back to the tank. Wet blasting apparatus comprises a cabinet 10 spanned by a grid 11 on which may be mounted a workpiece 12 and below which is a sump 13 having walls 14, 15 converging towards an outlet aperture 17. The latter leads into a pipe 19. One end 20 of the pipe passes through the wall 15 and has a restricted opening 21; the end 20 is covered by a baffle 22 in the form of two inclined plates forming a roof open at 23 to allow liquid to flow into the end 20. The other end 24 of the pipe 19 is connected to the inlet of a pump 25, the outlet being connected to a pipe 26 having an air vent 27, a lead-off 28 to a blast gun 29, and a portion 30 entering the sump; a baffle 31 is positioned opposite the end of the portion 30. The pump 25 may be as in Specification 840,671, the seal between the impeller shaft and the casing being formed by the liquid being pumped, this liquid being returned along a pipe 32 to the sump. A by-pass 33 extends from the pipe 26 to the sump, its outlet having a restriction 34. A plug 35 for the outlet aperture 17 is operated through a rod 36 by a pneumatic cylinder 37. The blast gun 29 is supplied with compressed air through a line 38. Operation. The sump 13 contains a slurry of solid abrasive particles and a liquid, normally water, with or without chemical additives such as rust-inhibiting and wetting agents. The solid particles settle to the bottom with a supernatant layer of liquid. The end 20 of the pipe 19 opens into the sump above the upper level 41 of the particles but below the surface 43 of the supernatant layer. When the pump 25 is started, the plug 35 being clear of the aperture 17, liquid flows along the passage 18 and particles fall through the aperture 17 into the liquid and are carried to the pump inlet. Slurry is delivered by the pump into the pipe 26. Some of the slurry is taken off by pipe 28 to the gun 29 and projected by compressed air against the workpiece, slurry draining from the workpiece back into the sump 13. Excess slurry is returned through the portion 30 to the sump 13, the portion opening below the liquid level 43 and being opposite to the baffle 31 so that the slurry is not aerated. Air vent 27 allows the descent of slurry through the portion 30. A comparatively low-pressure pump is preferably used, e.g. less than 3 p.s.i., the by-pass 33 serving to return some of the slurry to the sump, thus preventing the possibility that an overwhelming head could develop in the pipe 26 due to a transient increase of slurry concentration in the pipe, and cause reverse flow through the pump or the setting up thereof. Preferably the outlet aperture 17 is closed immediately prior to shut down of the apparatus. When the pump is switched on, the cylinder 37 is operated after a delay so that the plug 35 is not removed until flow is established. Sufficient speed of flow in the passage 18 to carry particles to the end 24 is ensured by the restriction 21. A high-pressure pump may alternatively be used, the by-pass 33 being omitted. The plug 35 may be operated manually.