Patent GB-683025-A (GB)
Title: Improvements in rock drills
IPC: E21B19/086
Filed: 1949-06-03
Abstract: 683,025. Portable drilling-machines. HOLMAN BROS., Ltd., and COOMBES, F. BROWN-. Sept. 1, 1950 [June 3, 1949], No. 14954/49. Class 83 (iii). [Also in Group XXVIII] A rock-drill, Fig. 1, has a body 10 adapted to be secured to a stand (not shown), and a compressed air motor 12 for driving the pump 13, Fig. 2, of a closed-circuit hydraulic system that supplies liquid under pressure to either side of a piston 35 for moving longitudinally a supporting member 44 for the drill bit (not shown), the member 44 also being rotated by the motor. Compressed air is admitted to the motor by adjusting a lever 26 to align an aperture 25 in a sleeve 24 with an inlet port 23, the supply being regulated automatically by a centrifugal governor 27 on the spindle of the motor operating a slide valve within the sleeve. The member 44 carries a chuck or adaptor (not shown), to support the bit and is driven through gears 21, a shaft 32 and gears 45, 46 in the drill-head 43, the shaft 32 being splined within a tubular layshaft 20 carrying one of the gears 21. The gear 45 is splined on the shaft 32 so that it may be disengaged from the gear 46 by turning a lever 47 connected by a crank 48 and forkedarm 49 to the gear 45. A rod 17 connects the piston 35 to the head 43 and feeds the latter when oil is forced by the swash-plate pump 13, which is driven from the lay-shaft 20 through gears 22, along a pipe 41 and passage 39 into a cylinder comprising an outer tube 34, an inner tube 33 and end-parts 36, 37. A tube 9, attached to the head 43 and slidable within the body 10, reacts the cutting torque of the bit which may be supplied with water through the bore of the tube 33 or, when a chuck is used, a drill-rod may extend through the tube 33 and be provided with a swivel for a water lead. The drill is supported on a stand by a hinge plate 51, Fig. 1, pivoted to either of two lugs 52 and secured by a bolt 53. The pump 13, which forces oil under pressure into a passage 59 in communication with a pressure-control valve 61, a combined cut-out and pressure-control valve 62, and a reversing valve 60 housed in a control block illustrated diagrammatrically in Fig. 3, is provided with an expansible reservoir 14 having an end-plate held in position by a spring 56 and co-operating with a rod 57 for indicating the position thereof and hence the quantity of oil in the reservoir. Oil is fed to the feeding piston 35 through the pipe 41, or a pipe 42, from the reversing valve 60 which also returns oil to the reservoir 14 from the other side of the piston through a passage 64, the setting of this valve being controlled by a knob. An intermediate setting, at which oil returning from the feeding cylinder is throttled through a narrow passage past a spring-pressed ball 60a, is provided for the valve 60 so that when a feed is started in the downward direction, the weight of the drill rods (not shown), will not over-influence the rate of feed. The pressure at which a spring-urged piston 65 in the pressure-control valve 61 rises to exhaust the oil to the reservoir through a passage 67 can be adjusted to a predetermined value by the knob 68. The valve 62 operates in conjunction with a further valve of which the piston 69 is disposed adjacent the tube 9 and enters recesses 70 therein when the tube is at either end of its travel. Between end positions of the tube 9, the piston 69 is disposed as shown with a passage 71 in the control block 15 conveying compressed air from the motor inlet port 23 through the piston 69 and along a passage 73 to the chamber of valve 62 where it forces the valve forward against a ball 75 and compresses a spring 74. When the piston 69 enters a recess 70, the supply of compressed air along the passage 73 is interrupted and the valve returned by the spring 74. The spring-pressed ball 75 then restricts the pressure in the circuit to the feeding piston to a value sufficient to support the weight of the drill rods when drilling upwardly. This condition is also produced if the supply of air is interrupted at the port 23. Also due to the valve 62 being controlled by air pressure, it prevents a high rate of feed when the motor is starting.