Patent ID: 9068399
Filing Date: 2015-06-30
Classification: E21B

Abstract:
1. A down-hole hammer drill including: a hammer casing having an interior surface with a plurality of longitudinal grooves formed therein; a top sub at the upper end of said casing, adapted to connect the hammer to a pressurized drill string, the drill string and top sub forming a compressed air supply; a drill bit comprising a bit shank extending from a bit head to an anvil end and a bit head mounted on said bit shank; a plurality of key and keyway pairs arranged in spaced relation circumferentially about the bit shank and the casing bore; a free piston motor powered by said air supply and dividing the casing into an upper working chamber defined between an upper piston hammer face and the top sub and a lower working chamber between a piston hammer face and the anvil end of the drill bit; an air control assembly on which the free piston slides, said assembly including a ported tube extending axially from said air supply to an axial bore in the shank of the bit to guide exhaust air through discharge ports at the cutting face of the bit, the bit reciprocating on the end of the tube; and upper and lower check valves in the air control assembly and openable by supply pressure against a spring bias in response to working fluid supply pressure; wherein the shank is located and retained within the casing by sacrificial drive pins and sacrificial linear retention pins.