GB842046A - Improvements in abrasive blasting machines - Google Patents

Abstract

842,046. Abrasive blasting. ASHWORTH, N. 1. Nov. 14, 1957 [Nov. 27, 1956], No. 36185/56. Class 60. In an abrasive blasting machine comprising a hopper with a conical bottom for abrasive particles mixed with water to moisten them, a delivery opening in the conical bottom, means for forcing the particles through the opening by compressed air in the hopper and an ejector which receives the particles and through which air under pressure flows and picks up the particles for discharging them on the surface being treated, a metering plate is detachably fitted to the bottom of the hopper, the plate having a discharge aperture which is approached by a conical passage connecting the edge of the discharge aperture and the edge of the opening in the conical bottom of the hopper. An open upper compartment 11 communicates through an opening controlled by a valve 14 with an intermediate compartment 15 which communicates through an opening controlled by a valve, 17 with a lower compartment 1a. The valves 14 17 are operated by chains 19 wrapped around shafts having handles 20a, and are shaped so that when closed they are held closed by air pressure below them. The lower compartment 1a has a conical bottom to which is fitted one of a set of interchangeable plates 3 having metering apertures of different sizes. The aperture in the plate is connected by a conduit 4 containing a valve 6 with an ejector chamber 5, the inlet of this chamber is connected to a compressed air supply A and the outlet is connected by a flexible pipe 8 to a spray gun or discharge nozzle. The size of the discharge orifice in the gun is related to the size of the aperture in the plate 3. The supply of compressed air from source A is controlled by a main valve 20; valves 21, 22, 23 control the admission of compressed air to the ejector, the lower compartment 1a and the intermediate compartment 15 ; air can escape from the latter under the control of valve 24. A valve 31 controls the admission to the intermediate chamber 15 of water from a mains supply, and a valve 32 controls the admission to the intermediate chamber 15 of rust-inhibiting solution, from a tank B to which compressed air can be admitted under the control of valve 25. A measured quantity of abrasive, e.g. sand, is placed in the upper compartment 11, the valve 14 being closed. Valve 17 is closed, valve 23 closed and valve 24 opened ; valve 14 is then opened and the abrasive passes into the intermediate compartment 15. Water in the required quantity is then admitted to the intermediate compartment 15, to wet the abrasive, valve 14 is closed, valve 24 is closed and valve 23 opened to pressurize compartment 15 and hold valve 14 closed. Valve 17 is then opened and the abrasive passes into the lower compartment 1a. Valve 17 is then closed. Valve 22 being open, compartment 1a is pressurized and valve 17 is held closed. The abrasive passes to the ejector and enters the air stream, valve 21 being open.