| 摘要 |
The appts. comprises a cylindrical body in a tubular casing and driven by a boring rod, a filter in the casing adjacent the body and a boring tool outside the casing and after the filter. The body has a polygonal cross-section with axially extending edges contacting the casing inner surface to define clearance spaces. - The filter and casing form a slide bearing and centring unit for the tool. The body edges are pref. arcuate, and the body has axial grooves for passage of particles extending to the spaces, and may also have annular grooves. The filter may have at least one peripheral groove and a surface remote from the tool which is united with the body. |
