| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a double-pipe drilling unit excellent in constructibility and capable of minimizing the number of drilling blades installed in a ring bit for being left in ground after excavation. Ž<P>SOLUTION: In this double-pipe drilling unit 1, an inner bit 100 includes a rotation imparting portion 120 which is equipped with a rotation imparting surface 123 and a rotation imparting portion locking surface 126, and a strike imparting portion 140 which is equipped with a strike imparting surface 142. An outer bit 200 is provided with a driven portion 220 which is equipped with a surface 224 to be rotated, a surface 228 to be locked, and a surface 226 to be struck. When the inner bit 100 axially moves inside the outer bit 200 and the rotation imparting portion 120 rotates after passing between driven portions 220, the rotation imparting surface 123 abuts on the surface 224. Additionally, in front-direction movement, the striking surface 142 abuts on the surface 226. On the contrary, in rear-face-direction movement, the rotation imparting portion locking surface 126 is locked to the surface 228. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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