| 单词 | prop-free front |
| 释义 | > as lemmasprop-free front prop-free front n. Mining an area in front of a coalface where no props are placed, so as to leave access for a mechanical conveyor, the roof being supported by cantilever bars; the system of supporting a roof in this way. ΘΚΠ society > occupation and work > equipment > mining equipment > [noun] > pit supports > system of prop-free front1956 1956 F. S. Atkinson in D. L. Linton Sheffield xiv. 270 Much pioneer work has been done in the coalfield to the north-east of Sheffield and in Nottinghamshire to develop a new method of mining at the coalface, known as the ‘prop-free front’ system... To maintain intact the roof between the vertical supports and the wall of coal, cantilever bars are used which are supported by the props behind the conveyor. 1964 Times 1 Sept. 5/2 The increased use of power loading and prop-free front faces give greater opportunities for reducing the number of accidents but they have not been realized. 1990 Mining Mag. (Nexis) Nov. 363 Certain operating constraints were removed, such as the ‘prop-free’ front face distance restrictions, that allowed more powerful machinery to be installed, to great effect. < as lemmas |
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