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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ROPE SHOVELS The HydraCrowd system, shown here, uses a massive, tube-enclosed hydraulic cylinder to reduce stress on a shovel's frontend components, replacing maintenance-heavy cable arrangements. • Altitude package (standard, high, extreme), • Weather package (extreme; hot +50°C; and cold -20°C or -40°C), • Dipper size and type (standard vs. LatchFree, liner package and GET), • Filtration system, • Air compressor (make), • Cable couplers (make), • Support document language, • Field assembly support, and • Training. Some of these decisions could involve features that are relatively new to the market, or may still be in the late stages of Cat's product testing and introduction program, such as the Power Demand Management System, HydraCrowd crowd system, Cat Air Filtration System and LatchFree dipper. These features were, for the most part, originally conceived by Bucyrus, then carried through and further refined by Cat after the acquisition. The power management system, HydraCrowd and LatchFree dipper are currently designated as "limited release" features that are still being evaluated under real-world operating conditions. With its Power Demand Management System, Cat offers off-the-grid technology that enables mining companies to power a Cat 7495 or 7495 HF electric rope shovel on just 4 MW of generator power, compared with conventional setups that use multiple generators with a total of 8 MW or more capacity to achieve rapid response when peak power 40 E&MJ; • JANUARY 2014 is required. In addition to the increase in maintenance and fuel costs associated with a multi-unit generator setup, generator-powered electric rope shovels require additional systems to dissipate regenerated energy because they can't feed electricity back into the power grid. Caterpillar's off-grid power system, however, affords mining operations the opportunity to use electric rope shovels at the onset of production in a greenfield mine, or to quickly move into a new area at an existing mine in which a stable power supply isn't readily available. And, using ultra-capacitor technology, the offgrid system stores regenerative energy created during swing deceleration and bucket lowering, then uses that power during periods of high demand to reduce the generator load cycle. The system's peak-shaving technology also provides power management benefits to mining operations that are operating on an electrical grid. This technology configuration reduces peak power requirements on the power distribution system, allowing rope shovel customers the opportunity to reduce costs with smaller substations. The lower peak power requirements also allow smaller-gauge trail cables, or longer trail cable runs, which can also reduce costs and minimize downtime. Both the 7495 shovel and Cat's yetto-be-released 6120B H FS hydraulic shovel will use the ultra-capacitor technology that is at the core of the power management system. The HydraCrowd design was developed to reduce stress on a rope shovel's front-end components: With any shovel, as the dipper crowds the bank, the handle recoils slightly. On Cat shovels, this force is absorbed in the ropes (rope crowd) or with hydraulic fluid (HydraCrowd), reducing stress on the handle. On a rack-and-pinion system, the force is absorbed where the rack and pinions mesh, often leading to broken teeth and increased handle cracking. With HydraCrowd, hydraulic components inside the tubular dipper handle replace a conventional, maintenance-intensive wire rope and gear mechanism, using instead a massive hydraulic cylinder to eliminate the need for crowd/retract rope maintenance and replacement. Offering a two-year major maintenance interval, Cat said HydraCrowd improves safety and cuts downtime by reducing the number of maintenance events needed. The LatchFree dipper door-locking mechanism is designed to eliminate the conventional latch assembly, replacing it with a steel link mounted to the dipper back, away from material flow. Cat also is working on a line of ground-engaging tools (GET) specifically for its shovels, but these are not yet market-ready. However, another new shovel-specific feature that is now commercially available is Cat's Dynamic Hoist Brake, offered for the 7495 and 7495HF shov- Cat's new Dynamic Hoist Brake is designed to stop the dipper from dropping during an uncontrolled event such as a power drop or an emergency stop. www.e-mj.com