GB958759A - Improvements in or relating to abrasive blasting apparatus - Google Patents

Abstract

958,759. Abrasive blasting. VACU-BLAST Ltd. Nov. 2, 1962, No. 41501/62. Heading B3D. A device for fluidizing and metering a flow of finely-divided abrasive particles contained in an air stream comprises a source of air under pressure, a pressure vessel adapted to contain a supply of abrasive particles, a housing secured below the pressure vessel, a porous partition having a large number of air passages therethrough separating the housing from the pressure vessel positioned to provide a space in the housing below the partition, a first conduit leading from the source of air under pressure to the housing below the partition, a second conduit leading from the source of air under pressure and adapted to be connected to a blast nozzle, an abrasive feed tube at the bottom of the pressure vessel extending through the porous partition and the housing and having an orifice at its upper end open to the interior of the pressure vessel, the tube also being connected at its outer end to the second conduit, and pressure-reducing means in the second conduit for reducing the air pressure in the latter and thereby controlling the metering of abrasive particles through said feed tube, whereby when the device is started up a flow of air is provided upwards through the feed tube directly into the pressure vessel to rapidly fluidize the abrasive particles therein and subsequently, when pressure equilibrium is reached within the pressure vessel, the abrasive particles are continuously fluidized by the flow of air through the first conduit and porous partition and a flow of abrasive-laden air is retained by way of the feed tube and into the air stream of said second conduit. A steel pressure pot 11 is loaded with abrasive material 12 of size from 100 mesh to 5000 mesh depending on the work to be done. Attached to the bottom of the pressure pot is a feeder fluidizer 13 including a housing 14 with a feed tee 15 extending vertically through it and terminating at a restricted orifice 16 in the lower portion of the pressure pot. The lower end of the tee 15 is connected into a straight tube section 18 attached to the bottom of the housing 14. One end 19 of the tube section 18 is connected by a conduit 20 to a blasting gun or nozzle 21, and the other end 22 is connected to a conduit 23. A compressor 24 supplies air, e.g. at 100 p.s.i., through an outlet conduit 25, the compressor being turned on or off to start or stop the blasting operation. A conduit 26 extending directly from the conduit 25 supplies air to the housing 14 at full pressure. The conduit 25 is connected to a spring check valve 27 having a constant pressure drop orifice so that at the outlet of the valve 27, which connects to the conduit 23, the air is at a reduced pressure, e.g. 95 p.s.i. The housing 14 has a circular centre cavity 28 surrounded by a shoulder 29 supporting a circular porous stone partition 30, e.g. a resinbonded quartz filter, of substantially uniform thickness through which the feed tee 15 extends. The blast gun 21 is operated within a blasting cabinet 35 from which spent abrasive and debris are conveyed through a conduit 36 to a cyclone separator 34. The separator, which has an air inlet 40, is fixed to the top of a collecting hopper 33 attached to the upper end of the pressure pot 11. A screen 37 within the hopper 33 filters out any large pieces of debris passing through the separator. The hopper 33 and pressure pot 11 are separated by a plate 48 having an orifice 49 controlled by a valve 50. The valve 50 is opened by gravity or by a spring and is closed by admitting air to a bellows 53 through a conduit 47. A conduit 38 is connected from the pressure pot 11 through a valve 39 to the separator inlet 40. The valve 39 has a diaphragm 42 forming one wall of a chamber 43, the diaphragm being responsive to pressure through a conduit 46 to shut off the flow of air through the conduit 38. When blasting ceases, valve 39 opens releasing the pressure in the pot 11 so that the valve 50 can open. Specification 834,878 is referred to.