Patent GB-744466-A (GB)
Title: Improvements in or relating to grit blasting apparatus
Inventor: HAMILTON HOPTON FOWNES
IPC: B24C3/06
Filed: 1952-05-15
Abstract: 744,466. Abrasive blasting. VACU-BLAST, Ltd. May 6, 1953 [May 15, 1952], No. 12328/52. Class 60 Grit blasting apparatus of the kind having an open sided box-like hood surrounding a nozzle from which abrasive material is projected in a stream of air towards the open side and within which hood the spent abras:ve material and the debris is collected, is characterized in that during the blasting process the hood makes a substantially air-tight seal around the open side of the hood with the surface being treated, the nozzle being adjustable to direct the stream to cover .the surface within the open side of the hood and the hood (or a frame to which the hood is movably attached) is selfadhesive to the surface to such a degree as to be supported therefrom unaided against the force of gravity. A nozzle 1 is attached to the end of a rigid pipe 2 to which a connection is made by means of a flexible pipe. The pipe 2 is supported for angular and horizontal movement in a gimbal mounting 4 supported towards the apex of a hood 5 of truncated pyramidal form; a gas tight seal is provided between the hood and the pipe 2 by a corrugated flexible sleeving 3 which allows the nozzle to be directed anywhere over the area being treated. The open end has sealing means comprising a brush ring 6 and a soft rubber ring 7. The brush is pervious to air but impervious to'grit and is provided so that the hood may be moved about over the work between the areas being treated without spillage of the grit. The brush ring is movable inwardly against the action of springs 8 to allow the rubber ring 7 to contact the work surface and form an effective seal so that, while the treatment is being carried out sufficient difference of pressure is maintained between the inside and the outside of the hood to hold the apparatus in contact with the work to such a degree as to be wholly supported therefrom against the force of grayity. Castors 9 are mounted for movement towards the hood against the action of a spring 10 so that when the pressure is relieved the apparatus may be moved about upon the castors. When being moved from one position to another the pressure difference may not be sufficient to support the apparatus from the work but adequate flow of air is maintained to recover the grit. The seal may be maintained with the brush either by means of a straight rubber web 11 or by a bellows which may be constructed to act also as a spring in place of the springs 8. The castors mav be fitted with a micro-switch to interrupt the flow of grit when the load on the castors' springs is released. Recovery of spent abrasive material and collection of debris takes place at connectors 12, 13, mainly through 12 when the apparatus is used on a vertical surface and mainly through 13 when the apparatus is used on the underside of a horizontal surface. To ensure a balanced flow of air and to prevent blockages of grit in the recovery line, a restrictor plate 14 is provided in one of the arms of the Y- junction 15, the connections being interchanged when changing from a vertical to a horizontal surface. The base 16 of the junction 15 is connected to a dust collector via a grit recovery apparatus. A short bent pipe 17 may be provided into which the nozzle 1 .may be directed and held by a spring clip 17a if it is required to remove the hood from the work without interrupting the flow of grit. which is returned directly to the recovery apparatus. In oder to maintain a. pressure in the hood well below atmospheric pressure so as to make the hood adhere to the work to such a degree as to be supported therefrom against the fo-ce of gravity, a substantially greater volume of air is withdrawn from the recovery line 18 than is passed to the supply line 2. Some of the difference in volume is made up by any small quantity of air inadvertently entering around the mouth of the hood while the remainder enters by way of a spring loaded relief valve 19 adjusted to maintain the pressure wtihin the hood at the desired sub-atmospheric pressure. When it is required to move the hood over the surface, air is allowed to enter the hood bv a pressure breaking valve 20, controlled bv a flexible cable 21 and hand lever 22 attached to a handle 23. The hood has infection windows 24 and infection lamps 26. Tn ensure economical treatment of the surface, a guide frame 27 supported within the hood has a series of parallel bars 28 attached onlv at one end, by which the nozzle is urged to follow a sinuous path. thus ensuring that the band of surface treated on one stroke registers correctly with the band on the previous stroke. The frame 'is curved to keep the nozzle at a uniform distance from the surface. T:o assist in the positioning of the hood at the commencement of the treatment of each area, and to prevent overlapping or leaving a gap, markers may be provided, e.g. arrows 29 which define the area covered by the nozzle and by means of which the position of the hood may be set up from chalk or other marks on the work surface or e.g. by the use of marking suckers fixed to the work surface. Alternatively markers may be provided within the hood. or a retractible frame 30 may be provided with the aid of which the hood may be registered in relation to an area just completed. In a modification, Fig. 3. for use when the surface being treated is of ferromagnetic material. electromagnets 32 attached to the hood 5 support the whole of the weight of the apparatus or share the task with the suction supporting means. Permanent magnets mav be provided in pairs and arranged so that their fields may be opposed when it is required to remove the apparatus from the work surface. In another modification, Fig. 4, suckers 34 attached to the hood 5 are connected to a source of sub-atmospheric pressure. and may support the whole weight or only part. For use with curved surfaces, the mouth of the hood is shaped as shown in Fig. 5; magnetic or sucker attaching means may be mounted on the hood bv universal joints so as to adapt themselves to the curved surface. In a further modification, Fig. 6 the hood 5 is slidably mounted on a framework having magnetic or suction supporting means 34. The mouth of the hood may have various shapes other than square and may be rigid or of flexible material.