Patent GB-695764-A (GB)
Title: Plate blasting machine
IPC: B24C3/22
Filed: 1951-08-29
Abstract: 695,764. Abrasive-blast machines. PANGBORN CORPORATION. Aug. 29, 1951 [Oct. 9, 1950], No. 20369/51. Class 60. [Also in Group II] An abrasive-blast machine for operating .on plates 100 comprises a drum 16 rotatable about its longitudinal axis to rotate the workpiece which is clamped against its external cylindrical surface, and a device 30 for projecting abrasive, the device 30 being traversed along the length of the drum to operate on the whole surface of the workpiece. One or more lithographic plates 100 may be secured to the drum 16, which may have an outer surface of stainless steel, by clamps 52, Fig. 2b, adjusted circumferentially of the drum to engage the ends of the plates. The clamps 52 may comprise a bar 54 along which one or more spring-pressed plungers 73, engaging the plates 100, can be adjusted, a dog 58 fixed to one end of the bar to engage beneath one edge of the drum, and a catch 68 at the other end of the bar adjustable about a pivot 69a by a screw 68 to engage beneath the other edge of the drum. In a modification, Fig. 2d, the ends of the clamp bars 79 are secured to the drum by toggle linkages each formed by a C- member 80 having a pin 83 to engage a circumferential groove 85 in the drum and a hand-lever 81 pivoted to the bar 79 and C-member such that when it is disposed as illustrated the toggle action clamps the bar to the drum. Dove-tailed slideways 69, Fig. 2f, are formed in the bars to receive carriers 72 for the plungers 73 which are provided with work-engaging pads 77 of rubber or the like. Springs 74 act between pins 75 carried by the plungers 73 and the carriers 72. The drum is supported in a housing 10 carried by legs 12 and rotated by an electric motor 53, Fig. 2, driving through a reduction gear 55, a chain 57 and a clutch 49 operated by a handle 47. Nozzles 30, Fig. 1, trained on the drum, are supplied with a propelling fluid such as steam, water, or a mixture of steam and compressed air, which sucks a mixture 46 of a liquid and an abrading material such as water and grit or sand along flexible tubes 38 from a container 44 and projects it against the workpiece. If water is used to deliver the abrasive, the mixture collecting in the container 44 is withdrawn to separate the abrasive from the water; the abrasive may be kept outside the housing 10 for delivery direct to the nozzles. The propelling fluid is supplied to the nozzles through a hose 34 connected to a manifold 36 which distributes through pipes 32. The mixture in the container 44 is agitated by a centrifugal pump 45 that draws the mixture 46 out of the container through a pipe 43 and returns it to the bottom of the container through a pipe 41. Overflow conduits 39, 59 are provided to limit the level of liquid in the container 44 and remove the very fine particles of abrasive, operation of the upper conduit 59 indicating that the lower one 39 is congested. The container may be drained through pipes 61, 62 into a container 63 and the pump 45 isolated by a valve 64. A. carriage 27 supports the nozzles 30 and has rollers 28, 29 to engage ways 31, 33. The carriage 27 is traversed by an electric motor 22 driving through a reduction gear box 24 to rotate a screw 20 in engagement with a nut 26 on the carriage. The carriage 27 may be traversed slowly in relation to the speed of rotation of the drum in order that one movement along the length of the workpiece is sufficient. Alternatively, it may be traversed along the workpiece more than once, a manuallyoperated or automatic device being provided for reversing the direction of traverse. For this purpose, the motor 22 may be reversible, or the screw 20 may have two threads thereon of opposite hand (not shown) engaged singly by a rockable claw which changes direction at the end of each traverse to be returned by the thread of opposite hand, the threads being continuations of each other at their ends. As a further alternative, the nozzles may be traversed by a reciprocating belt. Instead of rotating the drum continuously, it may be rotated in small steps between which the nozzles are traversed the length of the drum. The housing 10 has an open front 48 to facilitate loading operations, and a suction device is provided to suck air in through the openings in the casing and so prevent the escape of abrasive particles. This device comprises four filter chambers 89 projecting through the top of the housing 10 and connected by pipes 88 to two manifolds 90 leading to a fan 91. Coarse screens 94, 95 and fine screens 93 are provided beneath air filters, such as cylindrical fabric tubes 92, in the chambers 89. The manifolds 90 may be sealed alternately by dampers 97 operated by a pneumatic cylinder 98 controlled by solenoid-actuated valves (not shown) so that the inoperative filters may be cleaned by a spray of water from pipes 96 also controlled by the solenoids which are time-controlled by a switch that may be connected to the motor 22 or that driving the fan 91. The machine may be controlled by a solenoid valve (not shown) in the compressed air hose 34, the valve being connected, electrically or mechanically, to the nozzle-traversing motor 22 and the motor for the fan 91 so that these motors are energized when the abrasive-blast operation is started. Operation of the drum rotating motor may also be linked with the nozzle traverse. A spray 21 is provided for removing abrasive particles from the workpiece before it reaches the unloading opening 48, and a baffle 37, disposed adjacent the drum and extending beneath the surface of the mixture of fluid and abrasive in the container 44, restricts the flow of abrasive particles in the direction of the opening. A grating 50 may support the workpiece while it is being secured to the drum, and the back surface 25 of the housing may extend inside the adjacent lower surface to prevent drips from entering the traversing mechanism. In a modification, Fig. 3, five drums 211, 212, 213, 214, 215, similar to the drum 16, are mounted in compartments 201, 202-205 between the end plates 119, 139 of a wheel 113 that can be indexed by a crank and ratchet mechanism, Fig. 5, to carry the drums in turn past the nozzles 130 which may be similar to the nozzles 30 and traversed by lead screws 120 driven by electric motors 122. A ratchet arm 255 carrying a spring-pressed pawl 257 is mounted pivotally on a shaft 115 supporting the wheel 113 and connected by a link 253 to a crank 247 that is rotated by an electric motor 245. A disc 259, having peripheral notches 261 engaged by spring-pressed catches, is fixed to the shaft 115 and can be rotated to index the wheel 113 in a clockwise direction by engagement between a notch 261 and the pawl 257; catches 263 hold the wheel between indexing. Motors, mounted on the outside of a housing 110 for the wheel 113 in positions adjacent the locations illustrated of the drums 212, 213, 215, rotate these drums through friction discs 123, Fig. 4, which engage inner rims 121 on the drums. Filters and circulating devices, similar to those illustrated in Figs. 1 and 2, are provided for the abrasive-blast zones. The machine may be used with both zones in operation simultaneously on different workpieces, which may be loaded through an opening 148, Fig. 3, and unloaded by a different operator through the opening 149, or singly with one zone held in reserve. Particles of different hardness or of different size and hardness may be used in the different zones. A washing spray may be interposed between the zones or before the unloading opening 149. A further spray 141 is located in the top of the housing 110 to clean the drum rotating in the top position and so prepare it for the next loaded operation. The bottom walls 143, Fig. 4, of the compartments of the wheel 113 are inclined with respect to the shaft 115 and provided with outlets 145 through which liquid in the top compartment may be drained into a trough 147. Ribs 165, Fig. 3, on the housing 110 co-operate with sealing strips 164 on radial walls 117 of the compartments to isolate them from each other. Further sealing strips may be provided on the sides of the walls to co-operate with ribs on the housing 110. The abrasive nozzles may be traversed as described in connection with Fig. 1, and both machines may have an observation panel 11, Fig. 1, providing access to the nozzles and cleaned by a spray 17. U.S.A. Specifications 2,369,576, 2,495,269 and 2,590,819 are referred to.