| 摘要 |
<p>The present invention relates to a down-the-hole hammer comprising an external cylindrical outer wear sleeve (5), a sliding piston (8) mounted for reciprocating movement within the outer wear sleeve to strike a percussion bit (1) of a drill bit assembly located at the forward end of the outer wear sleeve. The drill bit assembly comprises a percussion bit having a head portion formed with an axially extending stub shank (32); axially extending splines (36) on the stub shank slideably engageable with complementary splines (35) formed on a drive chuck (4) whereby rotational drive from the chuck may be transmitted to the stub shank; a bit retaining ring (141) adapted for engagement with a retaining shoulder (37) on the stub shank to retain the stub shank in the drill bit assembly; and engagement means on the chuck adapted for connecting the chuck to a drive means of the fluid-operated percussion drill tool; the bit retaining ring comprises a shoulder (144) for engagement with an upper end of the chuck to hold the retaining ring in place in the assembly. The assembly further comprises a bushing (61) arranged above the chuck. An upper portion of the bushing has an internal diameter (B) dimensioned to provide a sealing fit with the piston nose (20). The bit retaining ring or the lower portion of the bushing has an internal diameter (E) dimensioned to provide a close sliding fit with the outer diameter of the retaining shoulder (37) on the stub shank (32).</p> |
