Patent ID: 6125952
Filing Date: 2000-10-03
Classification: E21B

Abstract:
An air-actuated down-the-hole hammer for rock drilling, comprising:a generally cylindrical casing defining an axis;a drill sub mounted to a rear end of the casing;a drill chuck mounted to a front end of the casing;a drill bit mounted in the drill chuck and including a front cutting face and a rear anvil portion, the anvil portion including a rearwardly facing anvil surface, the drill bit including a first central passage extending through the anvil surface;a piston mounted in the casing behind the drill bit and including a forwardly facing impact surface and a second central passage extending through the impact surface and aligned with the first central passage, the piston mounted for axial reciprocation toward and away from the drill bit whereby the impact surface impacts the anvil surface during a forward stroke of the piston;a foot valve extending partially in the first central passage and partially in the second central passage when the impact surface impacts the anvil surface for transferring pressurized air from the second central passage to the first central passage;the anvil surface being inclined whereby a radially inner portion thereof is situated farther rearwardly than a radially outer portion thereof, for opposing the creation of liquid streams tending to strike the foot valve when the impact surface impacts the anvil surface.