| 摘要 |
982,030. Mine roof support bars. K. M. GROETSCHEL. June 7, 1961 [June 11, 1960] No. 20505/61. Heading E1E. A cantilever mine roof support bar is provided intermediate its ends with one or more weak regions which may for example take the form of a hollow, tapered or reduced crosssectional portion. The bar, Fig. 1, is provided with a construction a and is apertured at e <SP>1</SP> , e <SP>11</SP> to selectively receive a pivoted extension b of box section. In a modification, Fig. 2, the bar is provided with a hollow section h<SP>1</SP> which is welded to the clamp portion h and carries a set of springs i loosely bolted together at k and extending within a box section extension l. The weakened portion may be replaceably mounted on the clamp portion or incorporate weakening holes, see Figs. 3 and 4 (not shown), respectively. |
