GB1262170A - Hydraulically actuated percussive tools - Google Patents

Abstract

1,262,170. Percussive drills. WESTINGHOUSE AIR BRAKE CO. 13 Aug., 1969 [13 Aug., 1968], No. 40469/69. Heading B4C. [Also in Division, B3] A percussive drill comprises a piston 38 for impacting upon and driving a striker piston 32 having an enlarged portion 134, a drill bit 28 and a valve 44 controlling the flow of hydraulic fluid to the piston 38 causing a succession of driving strokes, the enlarged portion 134 throttling the hydraulic fluid through a port 130 on the pistons 32's return stroke. This throttling reduces cavitation in a chamber 128. The chamber 124 containing the portion 134 is in the operating fluid circuit so that cushioning heat is removed. Pressurized hydraulic fluid i.e. oil passes from an inlet 76 into an accumulator formed in a chamber 68, then through a port 80 and past a transversely movable spool valve 44 to act on the piston 38. The valve 44 is moved by pins 54, 56, pressure being constantly maintained in a conduit 60 to act on the pin 56 which is of lesser area than the pin 54. With the piston 38 in the position shown in Fig. 2, equal pressures act in conduits 58, 60 hence causing the valve to be positioned as shown due to the difference in the areas of the pins 54, 56. The hydraulic fluid acting on the piston 38, causes it to accelerate, consequently driving the piston 32 and the drill bit 28. The pistons 32, 38 may be returned by a spring (not shown) or by hydraulic pressure applied via a line 106 to an annular chamber 116, so that this pressure may act on a shoulder 120. However, when the piston 38 is in the striking position (Fig. 3, not shown), conduit 58 is connected to exhaust, hence raising (as shown) the valve 44 and allowing oil to be discharged via ports 126/128 into a cavity 124. The oil in this chamber 124 cushions the forward stroke of the piston when trapped between bevelled edges 138, 140 and cushions the return stroke by being throttled by a bevelled edge 136 through the port 130. Excess oil is exhausted from the cavity 124 through a discharge port 144 and some oil may pass through ports 146, 148 for lubrication purposes. The pistons may be returned by a further piston (156) Fig. 7, (not shown) attached to the end of the drill bit 36 and engaging with a passage (154) in the piston 32, the passage (154) being supplied with pressure oil via conduits (158) (170) to return the piston. The drill bit may be rotated by a fluid motor 102 acting through gears 96, 98, 100 and a meshing sleeve 88 splined to a chuck 26.