an automatic unit for the removal of overburden and for dumping it onto the inner spoil banks of opencut mines. The bridge is used with a multibucket excavator. Conveyor bridges are used in working horizontally layered deposits with soft overburden rock in areas where mean annual temperatures are above freezing.
A conveyor bridge consists of girders resting on two or three supports mounted on rails, or sometimes on crawler tracks. The distance between the supports ranges from 35 to 250 m, and the dumping arm is 40–170 m long. The bridge is set across the pit and moves along the face at 4–6 m/min, taking its rail-and-tie foundation with it. The rock is moved from the excavator to the bridge by connecting conveyors. A conveyor bridge usually has two lines of conveyors 1,000–1,500 mm wide, which move the rock at 7.5–12 m/sec.
The dumping support of a conveyor bridge may rest on the soil of the seam or on a dumping mound specially poured and packed by the bridge itself, depending on the stability of the rock. The spoil bank is 40–50 m high. For loosened rock, a bridge weighing 9,500 tons with a total electric motor capacity of 4,860 kilowatts has a productivity of up to 7,500 m3/hr.
Conveyor bridges are produced in the German Democratic Republic, where plans have been developed (1975) for bridges to strip overburden up to 60 m thick. These units have capacities of up to 23,000 m3/hr, a main girder 270 m long, and a weight of 10,500 tons. With a five-support composite bridge they could strip overburden up to 80 m thick and achieve a productivity of 11,000 m3/hr, with a weight of about 15,000 tons (seeQUARRY TRANSPORT).
REFERENCEAndreev, A. V., and E. E. Sheshko. Transportnye mashiny i kompleksy dlia otkrytoi dobychi poleznykh iskopaemykh. Moscow, 1970.
IU. I. ANISTRATOV