GB718638A - Improvements relating to grit blasting - Google Patents

Abstract

718,638. Abrasive blasting. SCHORI METALLISING PROCESS, Ltd. July 16, 1953, [April 24, 1952.] No. 10366/52. Class 60. [Also in Group XXVII] A method of grit blasting comprises entraining abrasive material in the exhaust gases of a reciprocating piston engine and then discharging through a blast nozzle. A single cylinder air-cooled reciprocating piston internal combustion engine 1 working on. the Otto cycle is supplied with petrol through a carburetter 2 and inlet valve 3. The cylinder head of the engine I has two exhaust valves 4, 5 operating independently of each other. A pipe 6 connects exhaust valve 4 to a receiver 7 for exhaust gases, the pipe and receiver being lagged with heat-insulating material. The exhaust valve 4 is arranged to open at a predetermined position in the working stroke of the engine 1 to allow hot, high pressure exhaust gases to pass into the receiver 7. The valve is arranged to close just before the end of the stroke, where-upon the second exhaust valve 5 opens to allow the engine cylinder to be connected to a atmosphere during the exhaust stroke of the engine. The energy required to carry out the exhaust, suction and compression strokes, and to overcome mechanical and frictional losses is imparted to a flywheel 8 of the engine 1 during the initial part of its working stroke before exhaust valve 4 opens. The gas receiver 7 has a pressure relief valve 9 so that the engine 1 can continue to operate when a blast device 10, connected to the receiver 7 through a lagged pipe 11 containing a control valve 14, is not in use. The gas receiver 7 has a cock 12 for draining off any condensate which accumulates while the plant is being heated up. The engine 1 and receiver 7 are mounted on a wheeled carriage 13. The blast device 10 may be constructed as described in Specification 644,280, [Group XXIX]. Abrasive material is fed from a hopper 15 into a supply vessel 16 of the blast device 10 and discharges through a control valve into a mixing device 18. The pipe 11 is connected with the mixing device 18 so that the abrasive material is entrained in the exhaust gases and conveyed through a flexible hose 19 to a blast nozzle. Four- or six-cylinder engines may be used, giving larger output and less fluctuation in gas pressure; the cylinders may be arranged in line or radially, and cooling effected by a fan or water. The receiver 7 can be omitted and the engine mounted adjacent the blast device 10. With a multi-cylinder engine, one cylinder works on the normal cycle and the engine is provided with a heavier flywheel than usual, so that sufficient energy is available for the exhaust, suction and compression strokes in the other cylinders and to overcome mechanical losses. Each cylinder has only one exhaust valve, but the valve timing is such that the exhaust valves remain open during the full working and exhaust strokes; the exhaust takes place against back pressure from the blast device, the energy for this being supplied from the working cylinder and flywheel. The engines may be supercharged; engines working on the diesel cycle may be employed. When sand blasting ship's hulls, bridges, &c. in the open, damp sand can be used, since the exhaust gases will dry it; the exhaust gases can be used to dry the surface prior to blasting.