Chemical Processing - August 2007 - (Page 27) Don’t head off in the wrong direction when replacing motors By Daniel R. Snyder, SKF For electric motors, there’s no universal “one-size-Fits-all” solution for anti-friction bearings. every bearing type incorporates specific performance characteristics and so suits particular operating conditions. a mismatch between bearings and motor application can lead to significant problems. consider, for example: • using motors larger than 125 hp, faster than 1,200 rpm and having deep-groove ball bearings optimized for direct-connect duty with belts may lead to mechanical overload and premature failure. • Putting a motor designed for heavy belting on a coupled load may not give enough radial loading for the bearing’s rolling elements to roll. they will skate or skid on the race, causing high temperatures and potentially rapid and complete lubrication failure. • underloading a roller bearing, even with a belted load, may result in premature failure from the same skidding phenomenon. • installing a motor with bearings selected for horizontal mounting in a vertical application adds an unplanned axial bearing loading and may cause loss of grease in the bearings. • not addressing stray currents passing across bearings (often encountered in large variable-speed electric motors) may prompt electrical erosion damage leading to premature bearing failure. While there’s always the possibility that a replacement motor may perform differently from the original or, even worse, fail, selecting the bearings inside a motor consistent with application and conditions greatly improves the chances for success. www.chemicalprocessing.com august 2007 • 27 http://www.chemicalprocessing.com
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