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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GRINDING TECHNOLOGY 32 E&MJ; • JULY 2017 www.e-mj.com Over many years of use, shell-supported ball mills similar to those pictured above have proven their efficiency and reliabili- ty, and a large number of mining projects would not have been viable without them. A large and increasing number of refer- ences show that shell-supported ball mills work efficiently and reliably under the most stringent operating conditions. Their design advantages have earned them wide acceptance in the minerals industry, where they are used to grind copper, gold, and silver ores and other hard-rock materials. Shell-supported mills comprise a steel cylinder, which is attached to the end walls. The mill cylinder is supported on two integral slide rings. Each bearing as- sembly consists of four to six white met- al-coated sliding shoes, allowing the cyl- inder to rotate. Adjustment of the sliding shoes de- veloped by thyssenkrupp is carried out by hydraulic cylinders, whose working pres- sure (maximum: 180 bar) is equalized ac- cording to the master-slave principle (one master cylinder each controls one or two slave cylinders). In this way, the load acts uniformly and radially, thus ensuring that the bearing is almost completely mainte- nance-free. On each bearing side, several thousand liters of high-viscosity mineral oil ensure that the cylinder rotates at low friction on an even oil film. As an example of their size and per- formance capabilities, consider the Cer- ro Verde mine in Peru, one of the larg- est copper operations in the world. Final grinding of the pre-ground ore from 12 Polycom high-pressure grinding rolls is handled by 10 large ball mills made by thyssenkrupp Industrial Solutions, the engineering and construction arm of the thyssenkrupp group and a leading manu- facturer of grinding mills of this type. Cerro Verde is currently capable of grinding up to 360,000 metric tons per day (mt/d) of copper ore, a major increase from its former capacity of 120,000 mt/d just a few years ago. The boost in throughput came from the installation of the world's largest shell-supported ball mills, which were successfully commissioned there in 2015. The tripling of the mine's grinding capacity was enabled by a second-phase upgrade that included six shell-supported ball mills, with world-record dimensions of Shell-supported Ball Mills: Grinding Technology on a Large Scale A major ball mill manufacturer presents a persuasive case for choosing this proven — and improved — design over other types Figure 2—There are two well-established ball mill design types. Figure 3—Shell-supported ball mill design. Figure 1—Six shell-supported ball mills — the world's largest to date — were installed at the Cerro Verde copper mine in 2015 as part of an expansion upgrade, enabling the mine to triple its existing grinding capacity.