Patent GB-1256921-A (GB)
IPC: B24C3/06
Filed: 1969-01-13
Abstract: 1,256,921. Blasting. WHEELABRATOR CORP. 13 Jan., 1969 [6 Feb., 1968], No. 1817/69. Heading B3D. [Also in Division B8] Apparatus for grit &c. blasting of large areas e.g. ships' bottoms, includes a blasting head mounted by travelling frame and gimbal means on a tower for movement in all necessary directions relative to-the surface to be cleaned. The head has resilient sealing means for engaging the surface and grit &c. throwing means within the head. Grit and separate dust collecting means are provided. A machine for cleaning a ship's hull, or the walls of a large capacity storage tank, has a blasting head 10 including a blast chamber 12 within the base of which is a bladed throwing wheel 16 rotated about a vertical axis by a motor 18. At its forward end the chamber has an opening 14, preferably oval or rectangular with its major length perpendicular to the axis of the wheel. Inner and outer resilient seals 22, 24, e.g. of polyurethane, extend continuously about the opening 14 and are secured to a large flanged plate 20, Figs. 4, 5, secured to the open edge of the chamber. The seals are protected from thrown abrasive by a baffle plate 26 secured to the plate 20. Air inlet spaces encircling the upper end portion of the chamber communicate through openings 32 with the space between the seals whereby air flows into the space to cool the seals and to assist in the removal of abrasive from between the seals. Spent abrasive falls down through the space between the seals and through a slot 36, through a slot 38 in the plate 20 at the base of the inner seal 22, or over the plate 26 and shed plates 40. An air inlet 42 is provided immediately below the shed plates 40, 44, 46, 48 for the introduction of air which passes upwardly about the inner ends of the shed plates and through the descending spent abrasive to remove dust and fines and to cool the abrasive. The lower side walls 50 of the chamber converge to define a shoot through which the air washed abrasive falls into a trough 52 having a screw 54, Fig. 5, displacing the abrasive over a screen 56. Particles of paint, rust, scale &c. pass over the screen to a discharge shoot 58; reusable abrasive passes through the screen into a trough 60 whence it is returned to the hopper 62 which feeds the throwing wheel. The abrasive passes from the trough 60 into a continuous length of rigid tubing 63, Figs. 1, 5, encircling the blast assembly, and containing a link chain 64 carrying discs 66, e.g. of polyurethane, to convey the abrasive. The chain is driven by an electric motor 72 and speed reducer 74. Abrasive, e.g. steel shot or grit, passes from the hopper to the throwing wheel through a valve 76, e.g. electromagnetic, which is closed by a sensing means 80, Fig. 5, when the level of abrasive in the hopper is too low. Mounting means for the blast assembly, Figs. 1, 6 (comprising blast chamber, spent abrasive collector, hopper and elevator) includes a tower 90 having columns 92, 94, 96, 98; the tower is normally stationary while the blasting head is in operation, but is capable of being moved intermittently to a new position alongside the work surface by means of a barge, tracked vehicle or otherwise. Vertically movable in the tower 90 is a main frame 100 comprising angle members 102, 104, 106, 108 and having rollers 110 engaging tracks 112 on the columns; vertical movement, e.g. through a range of 30-70 feet, is effected by a chain 116 passing over a motor-driven sprocket 118 and carrying a counterweight 120. The main frame could be supported and moved vertically by means of overhead cables, cranes, telescoping supports or other means instead of the tower. Rollers 140 on the main frame members 106, 108 support an inner frame 130 for transverse movement on the main frame 100, e.g. through a range of 4-10 feet; the inner frame is moved by a piston and cylinder 144, 146 or rack and pinion. A head frame 150, Fig. 6, is mounted on rollers 156, 158 in the inner frame 130 for forward and backward movement effected by a piston and cylinder (160, 162), Fig. 7 (not shown), or rack and pinion. A yoke 170 on each side of the blasting head is centrally pivoted on a pin 172, Fig. 4, rigid with a side wall of the blast chamber and carries castors 174 for rolling engagement with vertically spaced portions of the work surface; an arm (178), Fig. 2 (not shown), pivoted on the yoke operates a four-way valve (180) mounted on the head. The blasting head is pivoted at 196 to a yoke 190, Fig. 8, for movement about a horizontal pitch axis effected by a piston and cylinder (198), (200) controlled by the valve (180), Figs. 2, 3 (not shown). The yoke 190 is pivoted at 195 to the head frame 150 for movement about a vertical yaw axis effected by a piston and cylinder 204, 208. Proximity sensing members 210 are mounted on the blasting head on opposite sides thereof in substantially vertical alignment with the castors 174; the members 210 are connected to valve means controlling the piston and cylinder 204, 208 for angular movement of the head about its yaw axis in response to signals from one or other of the members; the sensing members also control the piston and cylinder (160, 162) for adjustment of the head toward and away from the work surface so as automatically to maintain the desired pressure contact. The sensing members may also control the valve 76, shutting down the flow of abrasive to the throwing wheel responsive to loss of contact between both of the sensing members and the surface. The control achieved by the rollers 174 can be embodied in the sensing members; the rollers and supporting structure would then be omitted, and sensing members would be arranged in vertically spaced relation as well as in laterally spaced relation to detect changes in curvature or angle of the surface while at the same time sensing sealing engagement with the surface. The main frame 100 supports a platform 220 for an operator and a control panel 222. Ducts 82 connect outlets 84, Figs. 4, 5, at the top of the blast chamber with a dust collector which maintains subatmospheric conditions within the blast chamber. The dust collector could be mounted on the main frame for vertical movement with the blasting head; preferably, however, a stationary dust collector 230, Figs. 1, 9, is used. A vertical rigid duct 232 of rectangular, triangular or polygonal section has an open side 234 covered by a fan belt 236 slightly longer and wider than the opening, the length of the latter corresponding to the vertical travel of the main frame. The upper and lower ends of the belt are fixed to the duct. The belt is trained round rollers 252, 256, 254 mounted within a box 240 mounted for vertical movement with the main frame. The box has guide plates 258, 260 for the belt. The duct 82 is connected to an inlet opening 264 in a side wall (250) of the box; an outlet duct in a side wall of the duct 232 is connected to the dust collector.