Abstract: A guide rail 4 is used for movably mounting a coal hewing machine on a chain scraper conveyor 3. The hewing machine has a guide shoe 26 guided by the guide rail 4 and a chain wheel. The conveyor 3 has a conveyor channel 2 and, on the filling side, a mounting plate 1 for the guide rail 4. The guide rail 4 defines a chain passage 19 for a chain 20. The guide rail 4 also defines, in its roof side, an engagement groove 17 for the chain wheel and, in its floor side, openings 18 for the discharge of material. The chain 20 comprises long horizontal members 22 and short vertical members 21. The guide rail 4 is of box-shaped configuration and substantially rectangular cross-section. All four sides of the guide rail 4 are engaged by the guide shoe 26. On the filling side, the guide rail 4 has an upper portion in the form of an overhead bar 13 which is screwed to the lower portion 12. The vertical members 21 of the chain 20 project into the engagement groove 17.

Abstract: In a roof-shield support system employed in mines, at least two levelling rams each acting between a shield frame unit and an associated gap-seal plate, the latter being arranged so as to be slidable relative to the associated shield frame unit. Each levelling ram comprises a cylinder, piston and piston rod, is arranged so that the piston rod has a longitudinal bore which is open at the piston end of the piston rod, and an elongated rod which is sealed relative to the piston rod being disposed within said bore. The bore is in use in communication with a hydraulic fluid system of the ram and after levelling has occurred by actuation of the ram the pressurized hydraulic fluid admitted into the bore applies a force to the associated gap-seal plate so as to ensure its continuing tight engagement with the adjacent shield frame unit.