PERCUSSIVE DOWN-THE-HOLE ROCK DRILLING HAMMER, AND A PISTON USED THEREIN

摘要

A down-the-hole percussive hammer comprises a casing (11), a drill bit (13) mounted at a lower end of the casing, a hollow feed tube (15) fixed within t he casing and extending along a center axis (CL) thereof, and a piston (16) mounted for axial reciprocation within the casing for transmitting impacts t o the drill bit. The piston has a stepped configuration in that a lower portio n (16B) thereof is of smaller outer diameter than an upper portion (16A) thereof. The upper portion (16A) forms a downwardly facing surface (22) at t he junction between the upper and lower portions. Air-conducting passages are formed in the upper portion of the piston and are supplied with pressurized air from the hollow feed tube. One (18) of those passages intersects the downwardly facing surface of the upper portion of the piston. The present invention also relates to the piston (16) per se.