Patent GB-878582-A (GB)
Title: Blast cleaning apparatus
Inventor: HILL ERIC JOHN
IPC: B24C3/06
Filed: 1959-07-16
Abstract: 878,582. Abrasive blasting. VACU-BLAST Ltd. June 23, 1960 [July 16, 1959], No. 24437/59. Class 60. Apparatus for the supply, recovery after use, and reclamation of abrasive material for blast cleaning, used in conjunction with a gun or head, spillage or abrasive or debris from the gun or head being prevented by means of a pervious maze seal around the lower edge of the gun so that no abrasive or debris can escape although air is drawn into the gun from outside, the apparatus being characterised in that the several operational functions are carried out inside one single enclosure enabling the apparatus to be made readily portable by virtue of its lightness, compactness and simplicity of shape. A gun or head A is connected to apparatus comprising an abrasive storage hopper B, an abrasive reclaimer C, a preliminary dust extractor unit D, a final dust extractor unit E and a vacuum generator unit F. A supply of compressed air is connected to the inlet 18. Opening of valve 19 allows air to flow (a) via tee 20 and pipe 21 through nozzle 22, exhausting to atmosphere via ejector throat tube 23, the effect of this flow being to induce a recovery air flow at the ejector inlet, and (b) via tee 20 and hose 25 through blast control valve 26 into ejector blast nozzle 27, the effect of this flow being to induce abrasive in the abrasive storage hopper 29 to flow via metering nozzle 30 and supply hose 31 into the ejector blast nozzle 27 where it is directed on to the work surface 32 via inner casing 33. The spent abrasive and debris are drawn away via the gun body 34 and suction recovery hose 35 by means of the recovery air flow which also draws in air through the pervious maze seal 36 preventing the escape of abrasive or debris from the gun. Operating in conjunction with the metering nozzle 30 is a by-pass abrasive control line 37. During blasting, ejector blast nozzle 27 draws air via line 37 from above the level of the abrasive in the hopper 29 this air conveying abrasive falling through the metering nozzle 30 to the gun. When blast control valve 26 is closed the vacuum in the abrasive storage hopper 29 immediately causes the air flow down line 37 to reverse, instantly stopping the flow of abrasive to the gun and also completely evacuating the supply hose 31 of abrasive thus eliminating possible clogging by abrasive in the supply hose 31 when blasting is resumed. The spent abrasive and debris drawn away via the suction recovery hose 35 enter the reclaimer 40 via pipe 41. Abrasive and large debris are centrifugally carried down the wall of the reclaimer 40 on to separator screen 43 which retains the oversize debris but passes the abrasive. Dust and broken down particles of abrasion are carried out of the reclaimer in the inner vortex. Control of the amount of fine abrasive and dust removed from the re-usable abrasion is provided by a vortex arrestor plate 47 forming below it a " quiet zone ". The reclaimer has an outlet tube 48. The air inlet section 50 is centralised by vanes 49 shaped to maintain the rotationed motion of the air, so that the larger particles of dust or broken down abrasion are carried centrifugally round the wall 52. Baffles 53, 54 form a " quiet zone " where the larger particles of dust or broken down abrasive can settle, thus constituting a preliminary dust extractor unit. The air containing fine dust passes upwards where it is drawn into the final dust extractor unit 55 which may be a cloth type filter unit of corrugated cylindrical pattern to give a large surface area, or may be a cylinder of closely pocket filter brushes. The cleaned air is drawn into the air inlet section 50 and exhausts via throat pipe 23 and exhaust nut 58 to atmosphere. In a modification, the vacuum generating unit is an air ejector of the annular type. In a further modification, the vacuum generating unit is mechanical, such as a pump or centrifugal fan, and the compressed air supply is taken directly to the ejector blast nozzle 27. One stage of dust extraction may be omitted.