| 摘要 |
PROBLEM TO BE SOLVED: To provide a double tube excavation system capable of using an ordinary bit without using a widening bit or a lost bit (throwaway bit) even in excavation of an excavation rod of a double tube and applying double tube excavation of a down-the-hole hammer capable of imparting a rotary force and a thrust to the external tube (casing), and further smoothly discharging slime. SOLUTION: In an excavation rod having a double-walled structure composed of an internal pipe connected to a drive and to which a rotary force and a thrust, a striking force and a thrust, or a rotary force, a striking force, and a thrust are transmitted, and an external pipe in which the internal pipe is inserted, in a free state, the external pipe is attachably/detachably engaged with the internal pipe in the vicinity of the upper end of the external pipe. The rotary force and the thrust, the striking force and the thrust, or the striking force and the thrust or the rotary force, the striking force, and the thrust transmitted to the internal pipe are transmitted to the external pipe through the engagement part with the internal pipe, in this excavation rod of the double-walled structure. COPYRIGHT: (C)2004,JPO
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