Individual Metal Support

mine reinforcement at the working face that supports the roof of a seam in the work area. The supports are moved as the stope advances by completely or partially dismantling them into bearing and supporting elements (props and roof girders).

Individual props are classified according to purpose as face supports, which are installed and moved by hand, and screw supports, which are moved by hand and with light moving equipment, winches, and hydraulic jacks and are installed by hand or with hydraulic equipment. Face supports are classified according to operating characteristics as types with fixed-level, flat-slope, and steep-slope resistance and according to adjustment mechanism as friction props and hydraulic props. The resistance of a friction prop to lowering of a ceiling is provided by the friction forces in the prop lock. A hydraulic prop consists of a cylindrical housing and a moving part that acts as a plunger. Props of this type can be made with a closed hydraulic system (the working fluid is mineral oil) or with an outside source of working fluid (water-oil emulsions). Face supports are used on seams that slope by as much as 35°. Friction props of several standard sizes are made in lot production in the USSR for seams from 0.5-3.2 m thick, with prop strength of 150-300 kilonewtons (kN), or 15-30 tons-force, and weighing 11-75 kg. Soviet hydraulic props have a maximum resistance of 150-250 kN (15-25 tons-force) and have a maximum height of 790-3,300 mm. They can be expanded from 170 to 800 mm and weigh 16-85 kg. If necessary, the props of face supports can be made of interchangeable supports in order to reduce the specific pressure on the ground. Some types of props are made with a spacing device, whose force should not exceed 800 N (80 kilograms-force).

The most progressive roof girders are stiff hinged or spring types. A hinged roof girder is a welded, stamped, or cast beam of steel or aluminum alloy 600-1,400 mm in length, about 100 mm high, and weighing 13-32 kg. The permissible load on the overhang of a hinged roof girder is 10-30 kN (1-3 tons-force). The improvement of face supports is aimed at the standardization of types and sizes of supports according to the conditions of use, at the development of designs for supports for inclined and steep seams, and at the use of polymeric materials.