| 摘要 |
A rock drilling apparatus includes a drill string terminating in a drill chuck (32) and a drill bit (16) detachably fitted into the drill chuck, the drill bit having a shank (18) received in the drill chuck, the drill chuck (32) and the drill bit shank (18) having complementary splines and grooves allowing rotation or movement of the drill chuck to be transmitted to the drill bit whilst allowing limited longitudinal movement of the drill chuck relative to the drill bit. The drill bit has a drill head (22) at its lower end which is of greater diameter than said shank, said head having a part (26) above that lower end and below the splined region. The part (26) and the surrounding part (38) of the chuck provides respective parts of a bayonet connection arrangement which is substantially unstressed in normal operation of the drill, the arrangement being such that, in normal operation, the weight of the drill string and the weight of the drill bit during lifting of the drill string are supported by complementary formations on the drill shank and the chuck, whereas the bayonet connection arrangement prevents complete detachment of the drill bit head from the chuck in the event of a fracture of the bit above the drill head.
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