| 摘要 |
PROBLEM TO BE SOLVED: To provide an excavation tool capable of smooth excavation at a low cost. SOLUTION: The excavation tool comprises both a cylindrical casing top 1 joined to a tip of a cylindrical casing pipe 2 and a cylindrical ring bit 3 coaxially attached to a tip of the casing top 1 rotation-freely around the axial line O of the casing top 1 and engaged with an inner bit 5 inserted in the casing pipe 2 at the tip side in the direction of the axial line O around the axial line O. A plurality of protrusions 8 circling around the axial line O are formed at the outer circumferential surface of the ring bit 3 at intervals in the direction of the axial line O. By the formation of a plurality of ring-like grooves 9 in the direction of the axial line O which house the protrusions 8 at the inner circumferential surface of the casing top 1 at the same intervals as those of the plurality of protrusions 8, the ring bit 3 is engaged with the casing top 1 rotation-freely around the axial line O and with its tip side and rear end side in the direction of the axial line O. COPYRIGHT: (C)2011,JPO&INPIT |
