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Specially developed machines for fatigue testing of rolling bearing steels frequently operate at stresses higher than the elastic limit, have contact conditions that differ widely from those in practice, or require special expensive test pieces. An alternative view is that standard bearings should be tested under conditions more closely simulating practice but at a stress level high enough to produce an acceptable test duration.
To this end, a rig containing four size 6208 bearings was developed and has been in use for many years. This paper describes the rig, which has recently been approved by the appropriate committee of the British Institute of Petroleum as a proposed test method for lubricating fluids and their effect on fatigue life. Normally, 32 bearings are tested to minimize the effects of scatter inherent in fatigue life testing, and since the rig is relatively in-expensive several may be run concurrently. When the sudden death technique is used, a test may be completed in less than 4 weeks.
The results from the rigs presented show the life improvement associated with vacuum-degassed steels manufactured by a basic electric arc process and the effects of oil film thickness on these lives. Other work exposes the severe life reduction caused by some fire-resistant fluids, and results from modified rigs at elevated temperatures are reported. The technique of sudden death testing is discussed, and results are presented which tend to confirm its validity.
rolling bearings, bearing test rig, sudden death tests, oil film thickness, fire-resistant fluids, fatigue life, bearing steels
Principal applications engineer, RHP Industrial Bearings Ltd., Newark-on-Trent, Nottinghamshire