Bearings Are Made for Motors and Generators

The latest Insocoat coated bearings and Hybrid bearings from SKF have been launched to extend significantly the operating life of bearings used in motors and generators. In particular, the new Insocoat and Hybrid bearings have been developed to combat the effects of electrical currents on both the bearing surfaces and lubricants, which can otherwise cause premature wear and potential failure leading to equipment downtime and increased cost of maintenance. Although the effects of electrical currents on bearing life have been recognised for many years, the growing use of high capacity variable speed drives and frequency convertors, together with increasingly powerful motors and generators, is leading to a reassessment of the potential problems. In particular, the risk of flashovers caused by charges induced in both shafts and bearings can dull the surface of ball bearings and cause cratering in metal surfaces and fluting in raceways. Although it is possible to combat the effects of electrically generated currents by insulating either equipment housings or each rotating shaft, both these solutions are relatively expensive and require additional components, leading to increased maintenance costs. By comparison, replacing standard bearings with SKF's latest Insocoat or Hybrid bearings, makes it possible to eliminate the need for additional insulation yet still provide an excellent degree of protection to each bearing. Insocoat bearings feature a specially developed surface coating, just 50um in thickness, which acts as an electrical insulator to provide protection against electrically induced flashovers of up to 500V; thicker coatings are also available to withstand discharges of up to 1000V. Just as importantly, the coating has minimal impact on overall operating temperatures, is unaffected by extremes of temperature or humidity and can be used with all common lubricants, while the bearings offer identical performance to conventional devices and can be fitted using normal techniques. The latest Insocoat bearings are available in a range of sizes for shaft diameters of 55 to 150mm. They can be supplied with brass or steel cages, and used in applications with dynamic loads of up to 276kN and shaft speeds of up to 6700rev/min, depending on the lubricants used. SKF Hybrid bearings incorporate silicon nitride rolling elements to provide excellent insulation properties, making them ideal for isolating housings from shafts in AC and DC motors, as well as generators. SKF Hybrid bearings have been developed for high speed applications, offering low weight and friction to reduce inertia and operating temperatures, and extend bearing service life.