Patent GB-834219-A (GB)
Title: Improvements in or relating to portable blast cleaning machines
IPC: B24C3/06
Filed: 1956-06-26
Abstract: 834,219. Abrasive blasting. HASTRUP, H., and HASTRUP, R. C. June 26, 1956 [July 13, 1955], No. 19692/56. Class 60. A portable abrasive blast cleaning machine, for removing paint, rust or other coatings from surfaces comprises an abrasive container 49, a blast head 10 having an inner channel for the passage of abrasive toward a surface to be cleaned and an outer channel 23 for the passage of spent abrasive and debris from the surface, a surface contactor boot 25 on the blast head 10 adapted to contact the surface, a blast nozzle 12 to discharge a blast stream against the surface, a separator chamber 48 wherein spent abrasive is separated from debris and dust, an exhaust nozzle 64 adapted to create suction in the outer channel 23 of the blast head 10, and passages to provide, when the contactor boot 25 is in contact with the surface and the machine is connected with a single source of compressed air, a short, endless and always open recirculatory path for abrasive material from the abrasive container 49 to the blast head 10 are against the surface thence to the separator chamber 48 and back to the container 49 ; the blast head 10 and separator chamber 48 are connected by a swivel joint permitting rotation of the blast head with respect to the separator chamber there being separate passageways through the swivel joint for the passage of compressed air to the blast nozzle, abrasive material to the inner channel of the blast head and spent abrasive and debris from the outer channel of the blast head to the separator chamber. The housing 10<SP>1</SP> of the blast head 10 has an inner shoulder 11 on which is seated a blast nozzle 12 held in place by spring 13 and screw plug 14. An eductor sleeve 16 has its upper end seated against an inner shoulder 17 in the housing 10<SP>1</SP> and its lower end seated in the inner rubber coating 18 of a hollow blast cone 19 held in the housing 10<SP>1</SP> by thumb screw 20. The blast-cone 19 has an outer rubber coating 201 provided with a shoulder 21 which seats against the lower end of a sleeve part 22 of the housing 101. The sleeve part 22 together with the blast cone 19 form with the outer wall of housing 10<SP>1</SP> an annular passageway or outer channel 23 in blast head 10 ; the passageway through eductor sleeve 16 and blast cone 19 forms the inner channel in blast head 10. The inner suface of the housing 10<SP>1</SP> has a rubber coating. A cylindrical rubber member 25 secured to the lower end of housing 10<SP>1</SP> by a groove and lip thereon adapted to snap over a mating shoulder 26 on the housing is formed into a boot having at its lower end a mouth-piece 27<SP>1</SP> adapted to contact the surface to be blasted; it is preferably reinforced by sleeve 27 of aluminium or other material. A blast air tube 28 has one end mounted by threaded, press or other fit in a bore 29 in the housing 10<SP>1</SP>, this bore communicating with the space 151 above the blast nozzle 12. The outer end of tube 28 is fitted with rubber bushing 291 and is threaded to receive a nut 30 within which is inserted barbed hose insert 32 having an outer circumferential shoulder 33. An 0-ring 34 provides a sea]. A retaining washer 35 fitted around hose insert 32 is retained by the crimped over end of nut 30. A compressed air hose 36 is held on insert 32 by a ferrule 37. The blast head housing 10<SP>1</SP> has an inner cylindrical portion 38 providing a passageway 39 about its air tube 28,'the passageway being in open communication with the space surrounding the lower end of blast nozzle 12 leading into the mouth of eductor sleeve 16. The blast head housing 10<SP>1</SP> is also formed with an outer casing 401 providing a space 41 in communcation with the outer channel 23 in blast head 10. Separator housing 42, enclosing separator chamber 48, is formed with a casing 421 rotatably connected with the part 401 of the blast head and sealed with 0-ring 44. A cylindrical-portion 43 of the casing 42<SP>1</SP> is connected to the portion 39 of the blast head by a sleeve 40 ; the space outside the portion 43 communicates with the separator chamber 48. The casings 40<SP>1</SP>, 42<SP>1</SP> are held together by a shoulder on the bushing 29<SP>1</SP>. A side port 45 in the portion 43 communicates through adaptor 46 with a hose 47 so that the space 39 is connected to the abrasive container 49. The latter fits against that part of the separator housing 42 forming the main body of the separator chamber 48. Between the separator chamber and the abrasive container is a screen 51 above which is a circular baffle plate 52. The abrasive container 49 has a small bleed hole 58 and an outlet spout 59 to which the hose 47 is connected. The upper part of the separator housing 42 contains a passageway 63 provided with a suction nozzle 64 facing a suction tube 66 to the end of which a dust bag is fitted. Compressed air is supplied to the machine through a nipple 98 and is controlled by spring closed valves 75, 78. When valve 75 is opened, air flows through elbow 60 to the suction nozzle 64 and when valve 78 is opened air flows through pipe 99, hose 36 and tube 28 to the nozzle 12, this causing abrasive to be drawn through hose 47 and space 39 to the eductor tube 16. The valves are opened by a hand lever 93, the construction being such that valve 75 opens before valve 78 does, so that suction exists in the boot 25 before blasting starts ; valve 78 closes before valve 75, so that suction exists after blasting stops, U.S.A. Specification 2,723,498 is referred to.