| 摘要 |
PROBLEM TO BE SOLVED: To provide an expansion-contraction bit, which can correspond to the kinds of a drill rod or the like by a simple mechanism by which the installation and maintenance of a bit are facilitated and which does not dropout, in which only a wearing section can be exchanged, which is economical and in which the defective rotation of the bit and the closing of a fluid injection path for washing are prevented. SOLUTION: The expansion-contraction bit has a bit body in which a plurality of bits are rotatably mounted axially symmetrically, a bit adapter, to which the bit body is connected rotatably by screws, and a locking member being arranged in a baggy space formed between the bit body and the bit adapter under the state, in which the member is held by the bit body and the bit adapter, and locking the bits by engaging with the bits. The expansion-contraction bit is constituted in such a manner that the fluid injection paths are secured to each of the bits and the bit body while check valves are set up into each fluid injection path, and the check valves are opened and closed at pilot pressure with fluid injection.
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