| 摘要 |
PROBLEM TO BE SOLVED: To prevent an interference with a hood by a simple structure by providing an outermost movable bit in the front of a cutter face in a manner that allows it to rotate forward and projecting it outward in an standing state and withdrawing it into the cutter face in a rotating state. SOLUTION: The excavation mechanism 20 is furnished with multiple cutting bits 23 in the front face of multiple cylindrical spokes 21 fixed in a radial state and moving bits 25 at the head. The moving bits 25 are supported by a supporting member 29 having an L cross section, that is mounted on an expansion jack 39 through a rod 33 and a blanket 35. When natural ground is to be excavated, the expansion jack 39 is put in a shrunk state and the moving bits 25 are put into in a standing state. When the cutting bits 23 are to be replaced, the expansion jack 39 is extended and the movable bits 25 are rotated forward. And then when a slide ring 3 is moved forward, they are stored inside the slide ring 3 without interfering with the movable bits 25. |
