DOWN-HOLE HAMMER DRILL HAVING REVERSE CIRCULATION AND DRILL BIT FOR THE HAMMER DRILL

摘要

A down-the-hole hammer drill having a reverse circulation system which conducts pressurized air downwardly to a lower cutting face (44) of a drill bit (42). The air travels across the cutting face and upwardly through a central exhaust passage (54). The air is conducted to the cutting face through longitudinal (74) and lateral (80) passages in the bit which are kept isolated from the environment surrounding the bit so that no appreciable amount to pressurized air can escape, and so that the passages do not become clogged with dirt. The drill bit comprises upper (42A) and lower (42B) pieces. Upper sections of the longitudinal passages are formed in the upper piece, and lower sections of the longitudinal passages are formed in the lower piece.