Metso Minerals, which manufactured what is now the world's largest roller mill, for a copper mine in Arizona, has revealed that its huge bearings were designed and manufactured by Schaeffler.
The company delivered four giant-sized, double-row spherical roller bearings, with a bore diameter of 1,250mm, outside diameter of 1,950mm and width of 710mm.
Total weight of each bearing is approximately 7.85 tonnes, with each roller weighing in at 50kg.
The mill, which covers a floor area of 60m2, is designed to crush mined copper ore. The ore falls onto two counter-rotating steel rollers, and directed towards a milling gap between the two steel rollers, where it is crushed at milling forces of up to 27,000kN.
Speed of the roller mill is 20rpm, with hydraulic cylinders keeping the grinding rollers in position and provide the required pressure. Output is 10,000 tonnes per hour of crushed copper ore.
Hence the requirement for extremely large and heavy rollers, which weigh 160 tonnes each and have a diameter of three metres.
Schaeffler says its double row spherical roller bearings are extremely durable, with solid brass cages guided on the inner ring and an optimised internal design. They also have a very high load carrying capacity (basic dynamic load rating is 37,500kN) and the bore is tapered with a ratio of 1:30.
The size of the spherical roller bearings created special challenges for Schaeffler's production plant in Wuppertal, Germany. For example, to assemble and position the 50kg rollers into the bearings, a special lifting device had to be designed and built.
The rollers were manufactured at Schaeffler's plant in Eltmann, Germany.
