GB611261A - Improvements in or relating to telescopic pit props - Google Patents

Abstract

611,261. Pit props. HELLEGERS. A. C. April 25, 1946, No. 12532. [Class 20(ii)] Relates to telescopic pit props and consists in clamping the upper member 1 between the wedge 4 and a pressure plate 6. Fig. 1, or between the wedge 4 and another wedge 15, Fig. 4, with friction insets 8 on their working surfaces, held in a clamping band 3 rigidly connected to the top of the lower member 2 and arranged so that the wedge 4. whose angle is smaller than the angle of friction, is drawn with the member 1 as it slides under the roof pressure into the member 2 to an extent limited by the contact of the nose N With the clamping band 3. The back surface of the wedge 4 and its bearing surface in the clamping band 3 are smooth, and it rests on a spring 9 supported bv the lower member 2. A member T having a cam C and a lever 7 is carried by trunnions t in slots B in the parallel arms of the clamping band 3. In Fig. 1 a transverse horizontal wedge 5 is interoosed between the pressure plate 6 and the member T. In Fig. 4 a pressure plate 16 is interposed between the wedge 15 and the member T. and the wedge 15 may have another friction inset 18. The wedge 5, or the, wedge 15, is first placed loosely in the clamp, the wedge 4 then being held up by the spring 9 and the member T being in the position for the cam C to exert horizontal pressure, i.e. with the leyer 7 downwards. By the alternate use of wedges 19 inserted through slots S in the lower member 2 and engaged either beneath the member 1 or under the upper margin of a slot s therein, and hammered in, the upper member is adjusted hard against the roof. The wedge 5, or the wedge 15, is then driven in tightly and the wedges 19 withdrawn. When the roof pressure increases the member 1 slides into the member 2 and takes with it the wedge 4, so increasing the clamping pressure which, if the working surfaces of the member 1 are parallel, reaches its maximum when the nose N meets the clamping band 3. The wedge 15 is not drawn down with the wedge 4, since its angle is greater than the angle of friction. The working surface of the member 1 may be at a slight angle, small enough for the clamping pressure, though increasing on further sinking of the member 1. to remain below the limit of destruction of the prop by splitting. To release the prop the member T is rotated through 90 degrees. by a cable connected to the lever 7 or by hammering lateral projections 17 thereon. In the arrangement of Fig. 1 the prop may also be released bv hammering the thin end of the wedge 5, and in this case a bar mav replace the member T. The pressure plate 6 may be symmetrical, so that the wedge 5 can be inserted from either side. The friction insets may consist of base members of soft iron in which aluminium or aluminium alloy is inset.