Patent GB-920488-A (GB)
Title: Improved centrifugal wheel blasting machine
IPC: B24C9/00
Filed: 1961-10-20
Abstract: 920,488. Blasting. VACU-BLAST Ltd. Oct. 20, 1961 [Nov. 9, 1960], No. 37665/61. Class 60. An abrasive blasting apparatus comprising an enclosing cabinet, a rotatable abrasivethrowing wheel having a plurality of radially extending vanes positioned in said cabinet adjacent a space within the cabinet for accommodating articles to be abraded and a hopperlike collecting means below said space for collecting and storing abrasive from said space for re-use, is characterized in that the vanes of the abrasive-throwing wheel end short of the centre of the wheel to form a cavity within which a reduced air pressure is formed upon rotation of the wheel, fluidization means is provided below the said hopper-like collecting means to fluidize the abrasive as it leaves the latter and conduit means connect the fluidization means and the cavity in the said wheel by means of which fluidized abrasive is fed to the wheel. Abrasive blasting apparatus comprises a centrifugal suction wheel 12 mounted at the upper end of a cabinet 11 and including a circular plate 15 connected to the shaft 13 of an electric motor 14, a motor control unit giving the desired speed, e.g. 10,000 r.p.m. Radial vanes 16 are welded to the plate 15, detachably secured thereto or integral therewith. Along the outer edge of each vane 16 is a flange portion 55 bent up slightly in the direction of rotation of the wheel. The vanes are faced with abrasion resistant material 57, e.g. tungsten carbide, bonded to the vane. Extending into the space between the inner ends of the vanes is a feed tube 18 having a closed end 59 and an outlet orifice 19, the tube being secured in the desired angular position by a setscrew 60 and being connected to a conduit 20 connected to a feeder-fluidizer 21 in the bottom of the cabinet 11. The cabinet 11 is preferably made of sheet metal and may be so constructed that workpieces can be either mechanically conveyed through or hand-held in the blasting stream. As shown, the cabinet has side walls 24, 25, end walls 26, 27, a bottom 28, a top 29 and a sloping top 30 partially of glass to provide viewing of the workpieces. A partition 31 forms a blasting chamber 32. Openings 33, 34 in the walls 24, 25 have attached protective gloves for manual manipulation of the workpieces in the blasting chamber 32. Below the chamber 32 is a collecting hopper 35 formed by downwardly converging side members 36 terminating in an opening 37. A partition 39 is provided between the partition 31 and end wall 27. Connected to and extending between the partition 31 and end wall 27 are parallel bulkheads 40, 41. Between the latter a portion of partition 31 is out out and a sloping section 42 extends from the upper edge of hopper 35 adjacent partition 31 to wall 27. The wheel 12 rotates in a space 43 between bulkheads 40, 41, the space having an open side communicating with the blasting chamber 32. Adjacent the space 43 the parts 31, 39, 40, 41, 42 form a dust-free compartment 44. The motor 14 is mounted on bulkhead 40 by a support comprising a vertical member 45a and a horizontal member 45b together forming a compartment 46 at the end of motor 14 next to bulkhead 40, the compartment 46 being sealed around the motor 14 from the compartment 44 and being open to atmosphere through exhaust ports 52. The motor shaft 13 extends through bulkhead 40. Below the motor 14 is an airpervious dust bag 48 connected to the blasting chamber 32 through an opening 49 in partition 31 partially covered by a baffle 50. Motor 14 has a cooling fan 51, located in compartment 46, which draws filtered air from the compartment 44 through the motor 14 and thence into compartment 46 and to atmosphere through ports 52. Air exhausted from the cabinet is replaced by air drawn into the blasting chamber 32 through vents 53 in top 29. The fluidizer-feeder 21 comprises a chamber 23 having an annular top 61 attached by latches 62 to flanges 38 of the hopper 35. A relatively heavy mesh screen 63 fixed across the hopper opening 37 prevents the passage of larger debris particles into chamber 23 and also provides a pressure drop for air flowing downward from the hopper 35. At the lower end of the chamber is attached a housing 64. A feed tee 68 extends up through the housing 64 into the interior of chamber 23. Surrounding the feed tee 68 and extending across opening 65 in chamber 23 is a porous disc 69, e.g. of reinbonded quartz, held above the bottom of housing 64 by a spring 70 to form a cavity 71 which communicates with atmosphere through inlet 72. The lower end of the feed tee 68 is joined to a conduit 73 attached at one end to feed conduit 20 and connected at the other end to a conduit 74 attached to an outlet 75 near the upper end of chamber 23. A baffle 76 prevents abrasive entering conduit 74 as it falls through screen 63. With the wheel 12 rotating, suction induced at the central space of the wheel draws air through the slot 19 from the feed tube 18, thus drawing air through conduits 20, 74 and screen 63 from hopper 35. The reduced pressure in chamber 23 causes air flow through inlet 72 and porous disc 69 which fluidizes the powdered abrasive material 22. This flows at a uniform rate into the upper end of feed tee 68 and thence down into the stream of air through conduit 73 so that the abrasive is carried through conduit 20 and feed tube 18 to the centrifugal wheel 12.