| 摘要 |
Roller bit drills out a variable section to compensate for varying hardness of the rock strata encountered. A pair of rollers used each has discs axially in tandem relative the roller axis and each is allocated a second set of rollers whose own discs work in the gap left between the discs on the basic pair of roller tools. This second set can be retracted clear of the tunnel or heading face. If during driving, rock of differing hardness is met with, and the section driven has to be changed accordingly, then in the case of rollers having two discs the second disc in relation to the hole axis is removed, thus increasing the drilled width or section. |
