| 摘要 |
This invention relates to a down-the-hole hammer drill assembly, and has particular application to a reverse-circulation (RC) down-hole face sampling hammer drill assembly. More particularly, the hammer comprises a bit (20) having an elongate shank (22) and a head (23), and a bit retention element (60) disposed around the shank (22) of the bit and comprising one or more channels (62) for the passage of fluid along the bit. |
