Feature Article
By Guillermo MoralesEspejel, Principal Scientist, Research and Technology Development, at SKF
bearing life a reality check
lower operating temperatures. They also have a higher resistance to surface damage from particulate matter and they avoid the possibility of steel-to-steel surface welding. In addition, they have other useful properties such as high electrical resistance and low weight. The range of uses for hybrid bearings has expanded, partly due to the lowering of costs as manufacturing technology has advanced, but they remain a higher-priced option. Engineers considering their use need to know whether the extra cost will be justified by performance benefits.
Hybrid bearings, combining ceramic rolling elements with steel raceways, have proved superior in many applications, but how can you predict their suitability for yours? The answer is a new bearing life model that assesses and compares bearing performance in real-world conditions. Process Industry Informer • October - November 2019
Rating life is a key factor – although not the only consideration – when choosing bearings. Over the last 50 years and more, hybrid units have been shown to outperform and outlive all-steel bearings in many situations. For instance, they have become an obvious choice for use with high-speed machine tool spindles. Ceramic materials are particularly useful under demanding lubrication and contamination conditions. Their lower boundary-lubrication coefficient of friction enables greater efficiency when lubrication is poor, and they tend to exhibit
Conventional bearing life modelling limitations Traditionally, engineers enter information on their application’s expected loads and speeds into an equation which determines the bearing design’s rating life. The dynamic load rating (C) of a bearing principally indicates its performance in relation to sub-surface fatigue. Over millions of loading and unloading cycles, fatigue accumulates and the bearing eventually fails. For hybrid bearings however, this bearing life model’s focus on subsurface fatigue presents problems. Ceramic rolling elements are stiffer than steel ones, so they deform less under load. The result is a concentration of loading over a smaller area, which increases stress and
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