Engineering & Mining Journal

APR 2016

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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SKIP-WAY TRAM 34 E&MJ; • APRIL 2016 www.e-mj.com the frst support mast of the frst unload- ing station up to the separate drive sta- tion at the side. Inside the drive station (Figure 6) the travel rope passes over a double-grooved traction sheave with countersheave and is driven by friction through a wrap angle of 2 x 180°. The travel rope drive unit is a conventional wrap drive of the type used in rope or cable cranes. Its main compo- nents are a variable-frequency induction motor with spur gear unit and service brake, and a double-grooved traction sheave with emergency brake. The entire drive station sits on a concrete foundation close to the ground, easily accessible for inspection and maintenance. The switch- gear and controls for the Skip Way System are located in the machine house. From the drive station, the travel rope passes over a defector sheave in the sec- ond mast station to the downward travel- ing counter skip. Both ends of the travel ropes, like the track ropes, are anchored in the ground or the mine slope at the rear of the unloading stations. If the truck un- loading station at the pit foor is moved, the necessary additional rope length can be drawn from this rope storage point. A typical travel cycle for this steep conveying system with a 1,000 mt/h handling capacity, a vertical lift of 410 m and a roughly 45° slope is shown in Figure 7. Thirty seconds are allowed for skip loading at the bottom of the mine, 10 s for skip acceleration and roughly 87 s for the actual travel distance of 530 m. Forty seconds are planned for simulta- neous skip deceleration and positioning in the loading and unloading stations. With a calculated cycle time of 321 s, the system would still have a time reserve per cycle of 27 s. This spare time is available as additional skip waiting time for truck positioning in the dumping station. As an example, Figure 8 shows the torque curve of the drive motor for a skip's upward trip, taking into account deadweight compensation by the sec- ond, empty skip traveling downward at the same time. The motor's rated torque is reached or exceeded very briefy when the laden skip is positioned slowly in the top station. Due to the different angles of the track ropes in the stopping stations, torque equalization by the dead loads of the skips is no longer fully possible. The skips' bottoms are protected against wear and impact deformation by clamped-on railway rails. The honey- comb-shaped skip sidewalls are lined with replaceable wear plates, so the ro- bust basic structure of the skip can be maintained over many years of operation through replacement of worn plates and rails. Impacts from individual boulders measuring up to 1 m diagonally and weighing up to roughly 1 mt are absorbed by the steel structure without perma- nent deformation. In addition, the initial impact of a boulder on the baseplate is cushioned by a bed of fnes between the wear rails, supported by the spring-load- Figure 6—Travel rope drive station with double-grooved traction sheave and defector sheave for rope return to the traction sheave. Figure 7—Skip working sequence for one of two skips (1,000 mt/h). Figure 8—Typical motor torque curve during skip upward travel.

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