| 摘要 |
<p>A mechanized prop is proposed as part of a system for extracting coal with a plough or conveyor-plough cutting head. The prop comprises inter alia devices for advancing a base (4) and extending the brackets (10) on sections of the prop. Each device includes a hydraulic jack (6 or 11) with a rod, a main piston rigidly mounted on the rod, and an auxiliary floating piston which can slide between the main piston and a controllable stop on the rod. In the hydraulic jack (6) for advancing the base by measured amounts, a further cavity (22) between the main and floating pistons (19 and 20 respectively) communicates directly with a hydraulic line (27) for advancing the base. One of the two main cavities, i.e. either the rod cavity (41) or the piston cavity (40) communicates via at least one controlled non-return valve (39) with a hydraulic line (28) for forcing the floating pistons against the main pistons; the other main cavity (either the piston cavity or rod cavity, as appropriate) communicates with the hydraulic distributor (33) via at least one controlled non-return valve (38). The proposed prop makes it possible to advance the cutting head by measured amounts towards the work face and to extend the prop brackets in synchrony with that advance, thereby ensuring that coal is cut to a constant depth and the degree of support needed for the roof does not change.</p> |
