The effects of the slip amplitude and lubricant type on the rate of false brinelling in roller bearings

Master Thesis


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University of Cape Town

False brinelling is a wear phenomenon that occurs in stationary rolling element bearings. Vibrations from adjacent running machinery are transmitted to the stationary bearing via the machinery foundations, and result in relative motion between the rollers and the races. This results in wear scars at the point of contact between the rollers and the race. The wear scars result in premature failure of the bearings. There are a large number of parameters that affect the rate of false brinelling. Most of these parameters are not free to be altered by the user of the bearing. There are two parameters that can be altered, the type of lubricant, and the slip amplitude of the vibration. The slip amplitude can be altered by changing the stiffness of the foundation of the equipment. By varying these two parameters it should be possible to limit the amount of damage to the bearing. In the work reported here, a shaker was used to axially vibrate a flat "outer race" in a lubricant bath, against a cylindrical roller. The relative motion was measured by means of a proximity probe. Two lubricants were tested: SAE 30 oil and LGEP 2/1 grease. Two different wear mechanisms, exhibiting vastly different wear rates, were discovered for the oil tests. At low slip amplitudes, smaller than 25um, the results suggested that elastic deformation of the contacting surfaces was the means of displacement accommodation. At larger slip amplitudes the results suggested relative motion between the two contacting surfaces, which was marked by a bifurcation in the wear rate versus slip amplitude curve. The one branch of the curve, which for ease of explanation is called wear mechanism one, exhibited a low wear rate, which increased in a linear fashion with respect to the slip amplitude. The second branch of the curve, wear mechanism two, approximated a step function, with a very rapid increase in the wear rate with respect to the slip amplitude. This rapid increase is followed by a slow linear increase in the wear rate with respect to the slip amplitude.

Bibliography: pages 79-83.