Patent ID: 6502650
Filing Date: 2003-01-07
Classification: E21B

Abstract:
A down-the-hole percussive hammer for rock drilling, comprising:a generally cylindrical casing; a drill bit disposed at a front end of the casing, the drill bit comprising: a front portion protruding forwardly from the casing and including a forwardly facing cutting surface, and a center longitudinal passage extending forwardly through a rearwardly facing rearwardmost end surface of the drill bit, the passage communicating with the front surface and including a rearwardly facing impact surface spaced forwardly from the rearwardmost end surface; a top sub mounted in a rear portion of the casing; a hollow feed tube mounted to the top sub and extending forwardly therefrom along a longitudinal center axis of the casing and defining a center passage adapted to conduct pressurized air, and a piston mounted in the casing longitudinally behind the drill bit for reciprocation in a longitudinal direction, the piston including an axial through-hole slidably receiving the feed tube, and a front portion sized to enter the center passage of the drill bit during a forward stroke of the piston, the front portion including a front end defining a forwardly facing striking surface for striking the impact surface during each forward stroke of the piston.