GB1474501A - Bore hole air hammer - Google Patents

Abstract

1474501 Pneumatic hammer piston drill BAKERDRILL Inc 16 Jan 1975 [11 Feb 1974] 1854/75 Heading B4C [Also in Division E1] A down-the-hole pneumatic percussion drill includes a housing 10, an anvil 18 connected to a drill bit 21, a reciprocating hammer piston 20 having short upper and lower end sealing portions 37, 40, the piston 20 being relieved along its entire length between the end parts 37, 40 to be free from contact with the inner wall of the housing 10, the relieved length of the piston being greater than the combined length of the end parts 37, 40, and flexible inlet and exhaust tubes 78, 54 extending into central passages in the piston 20, the tubes 78, 54 being capable of being flexed laterally by the piston 20. This arrangement minimizes binding of the piston 20 should the housing distort under stress. The drill operates as follows: when the hammer piston 20 is at the bottom of its working stroke (Figs. 2a, 2b) air flows from the inlet tube 78 through ports 91 and passages 84, 85, 86, 95 to below the piston 20 to move it upwardly, air from above the piston 20 being exhausted through passages 44, 32, 36a, 51, exhaust tube 58 and ducts 55, 56. When the piston 20 is at the top of its stroke (Figs. 4a, 4b) air flows from the ports 91 in the inlet tube 78 through passage 82 to above the piston 20 to move it downwardly, air from below the piston 20 being exhausted through passages 34a, 36a, 51, 53, 55 and 56, the operating cycle then being repeated. When the bit 21 is lifted off the hole bottom E the air flows past the piston and through a by-pass passage 64, 68 in the bit so that the drill does not operate. A choke member 150 having an orifice 151 is located between the inlet and exhaust passages 79, 53 in the piston 20 to allow excess air to flow into the exhaust passages 55, 56. When no excess volume of air is available the choke member 180 would be replaced by a blank member, i.e. one having no orifice.