GB1445502A - Bore hole hammer drill - Google Patents

Abstract

1445502 Percussive drills BAKERDRILL Inc 3 May 1974 [10 Aug 1973] 19507/74 Heading B4C [Also in Division E1] A downhole percussion drill includes a hammer piston 20 engageable with an anvil section 18 of a bit C drivingly connected to the housing 14 by arcuate keys 28 located in windows 29 in a drive head 15 threaded into the housing. The piston slidably receives an exhaust tube 54 and a supply and valve tube 78, these tubes being of Delrin (Registered Trade Mark) and being secured in the anvil and in a top sub 11 by snap-fitting flanges 57, 80. With the bit in contact with the bottom of the borehole, as the piston impacts against the anvil at 100, air delivered into the tube 78 via check valve 70 can pass out of ports 91 and flow down around the tube to passages 95 opening at the underside of the piston, and since air in the space above the piston is free to pass to the bit via the passages 44 around the piston, ports 51 and exhaust tube 54 the piston is driven upwards and its upper external land 37 eventually enters bore 30 to shut off the exhaust path from the space above the piston. The upward movement of the piston also causes its lower internal land 85 to engage land 93 on tube 78 to shut off the supply of air to the space below the piston, and the upper internal land 82 of the piston clears the land 98 of tube 78 so that air from the tube can pass to the space above the piston, the lower external land 40 of the piston eventually clearing shoulder 33 of the housing so that the piston is driven downwards to impact against the anvil, the cycle then repeating. When the drill string is picked up, the bit drops until shoulders 110 on the anvil abut the keys 28, and in this position of the bit the slots accommodating the keys provide a by-pass path across sealing section 66 of the drive head 15, the piston simultaneously dropping so that its land 40 clears shoulder 35 in the housing while its land 82 engages land 93 of tube 78, whereby air is routed to the space above the piston but is exhausted therefrom via the passages around the piston and the anvil as well as via the passages 53-56 in the anvil, thus providing a desired high volume flushing flow. With the bit and the piston in their extreme lower positions, the land 85 of the piston engages land 88a of tube 78 to cut off the supply of air to passages 95 to provide additional assurance against reciprocation of the piston while the bit is clear of the bottom of the hole.