| 摘要 |
<p>758,746. Pit props. BELLMANN, E. Jan. 8, 1954 [Feb. 21, 1953], No. 568/54. Class 20(2). The inner member 2 and outer member 1 of a telescopically extensible pit prop are locked together by clamping wedges 7 in the inner member forced outward against the outer member by a tapered member 6 between which and the wedges are roller bearings 5. The member 6 is operated by a rod 4 and cap 17 moved down by roof pressure. The wedges may engage the outer member 1 directly or the inner member 2 may be slit and pressed against the outer member by the wedges. The pit prop may be of oval or circular cross-section and is shown with two and four wedges or may be polygonal with the number of wedges corresponding to the number of sides of the polygon. The member may be a cone with longitudinal grooves in which are the roller bearings and into which project the clamping wedges. In a further modification a cone having rollers in grooves engages in a slit conical counterbearing. The prop is released by a wedge 14 or a toggle operated by hand or fluid-pressure.</p> |
