GB682384A - Improvements in or relating to pit props - Google Patents

Abstract

682,384. Mine props. WETZELS, H. J. Feb. 2, 1949 [Feb. 3, 1948], No. 2918/49. Class 20(ii) In a pit prop comprising an upper inner member sliding in a lower outer member, and a locking device including a wedging element adapted to be frictionally carried down with the inner prop member to increase the locking force, the number of frictionally engaged pairs of surfaces tending to cause such movement of the wedging element is greater than the number of frictionally engaged pairs of surfaces opposing the movement: The wedging element may be a plain wedge, a cam or eccentric, or a tumbler. In Fig 1 the wedge 5 is carried down by friction between'the wedge and one part 12 of a two-part upper prop-member and by a plate 6, coupled to the wedge by arms 8, subject to frictional forces from both parts 2, 12 of the upper member. The locking device also includes a transverse or setting wedge 4. A modification, Figs. 4-6 (not shown), is also described in which the prop parts and wedge are of channel section and the plate 6 is replaced by a hollow member shaped to fit in the channels of the two upper prop parts. In Fig. 7 the wedge 5 is dispensed with, the part 26 between the parts 32, 32<SP>1</SP> of the upper prop member being itself a wedge. Fig. 8 is simliar to Fig. 1 with the wedge 5 replaced by a shoe 34 and tumbler 35. In all embodiments stops, (7, Fig. 1; 27, Fig. 7; 37, Fig. 8), are provided which come up against a fixed part of the prop after a predetermined movement of the' wedging element to limit the force created by the element. The prop can then support, without further movement of the upper prop member, an increasing load up to that sufficient to force down the upper member against the frictional forces created by the wedging element and/or by the member between the two parts of the upper prop member, and by the contacting surfaces of the upper prop member and the locking device. After this yield point a further increase in load can be obtained by making the upper prop member slightly tapered. The wedge and/or the member coupled thereto in the embodiments of Figs. 1 and 4 may be of aluminium to obtain increased friction. The Specification as open to inspection under Sect. 91, also describes a prop, Fig. 1 (Cancelled), in which a wedge 5, carried down with the single part upper prop member 2 as the prop yields, is coupled to the member 2 by a strap 6. The strap 6 assists the frictional force carrying the wedge downwards and is eventually uncoupled from the member 2 by striking the top edge 3a of the locking device 3. The part 2 is tapered slightly. This subjectmatter does not appear in the Specification as accepted.