| 摘要 |
An otherwise conventional mine roof expansion anchor of the bail-type is provided with a tubular retainer member encircling the shell leaves and having an external cross-dimension significantly (e.g., at least 0.10'') greater than the diameter of the drill hole in which the anchor is to be installed. Thus, as the anchor, supported on the end of a roof bolt, is advanced into the drill hole in the usual manner, the tubular element is pushed off the anchor by contact with the surface surrounding the drill hole, thereby eliminating the previously required manual removal of the retainer. The tubular retainer has the same cross-sectional configuration in all planes perpendicular to its central axis throughout its full length, preferably being formed as a plastic extrusion. |
