GB1296476A - - Google Patents

Abstract

1296476 Percussive drills BAKER OIL TOOLS Inc 23 July 1970 [6 Oct 1969] 35652/70 Heading B4C [Also in Division E1] In down-hole percussion drilling apparatus a drill pipe B supports a housing 11 and a cylinder sleeve 23 which contains a hammer piston 36. During the lowering of the apparatus an anvil 10, supporting a rotatable drill bit D, extends from the housing such that piston 36 is lowered in a sleeve 23 to an inoperable position. When the bit contacts hole bottom F the housing telescopes over the anvil until it contacts anvil shoulder 60. The piston may only then be reciprocated. Compressed air, supplied via pipe B to annular passage 28, passes through ports 44 and piston passage 40 to lift the piston from the anvil. The rising piston closes ports 43 so that air in chamber 46 does not escape via piston passage 37, the air being compressed to prevent the piston striking the cylinder head. Near the top of its stroke the piston simultaneously uncovers ports 43; to exhaust air below the piston into annular passage 29; and ports 44; to pressurize chamber 46 from passage 28 via groove 54 of port 55 and passage 37. The piston, propelled downwards by the pressurized air in chamber 46, simultaneously closes ports 44 and 43. When the piston strikes the anvil the air in chamber 46 is exhausted via passage 37 and ports 43 into passage 29. Exhausted air passes from passage 29 through the bit to cool it and clear cuttings. Air may by-pass the piston, in passages that may be throttled, to flow through the bit.