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The rolling contact fatigue testing of low oxygen, high quality, rolling bearing steels is a major challenge to steel makers, bearing producers and end users. Material specimen based rolling contact fatigue tests were used for a number of years, mainly as acceptance tests. Often in this type of test, the applied contact stress exceeds the stress normally found in rolling bearing applications and also exceeds the limit stress for rapid cyclic micro-plastic groove formation in the rolling contact. For these reasons the established methods have limited ability to discriminate material quality effects in modern high cleanliness rolling bearing materials. Furthermore, the results of tests based on a material specimen are difficult to translate into life calculation factors for the bearings. In this paper a novel test method is presented and used to determine the effect of steel internal cleanliness on the performance of rolling bearings. To achieve this result considerable care is required in the preparation of the test elements, the selection of the specific test conditions and in the analysis of the results. This work also led to an ability to determine the dependence of steel quality on the steel making processes. Material cleanliness is characterized using the statistics of extreme values of the micro-inclusion size population allowing the steel cleanliness quality rating to be related directly to the fatigue performance of rolling bearings through the introduction of a material cleanliness factor ?. The expected bearing life performance for materials with different inclusion size ratings can thus be calculated. Results correlate well with measurements demonstrating that the quality rating of the material can now be reliably included in standard bearing life calculations.
Rolling bearings are rated for their capabilities to withstand rolling contact fatigue. All other means of bearing failure are considered preventable through proper attention to bearing manufacture, mounting, lubrication, and minimization of contaminant ingress. The standard methods for calculation of rolling bearing capacities and fatigue lives are based on the 1947 and 1952 publications of Lundberg and Palmgren. They defined separate material factors for ball bearings and roller bearings fabricated from 52100 steel, through-hardened to at least 58 Rockwell C; the fatigue life predictions, were strongly influenced by these capacity-multiplying factors. The standard was in use for less than five years, when it became apparent bearings fabricated from ever-cleaner materials; for example vacuum degassed and vacuum melted steels, were out-performing standard life predictions. Moreover, tapered and cylindrical roller bearings routinely fabricated from carburizing steels such as SAE 4118, 4320, 8620, etc. were not directly covered by the standards. This deficiency is accommodated by the use of material-life factors applied to the Lundberg-Palmgren life equations. The Society of Tribologists and Lubrication Engineers (STLE) recommends the use of separate material-life factors to cover basic steel metallurgy, heat treatment, and metal shaping. It has been demonstrated that, together with other life factors for lubrication effectiveness and contamination, this cascading of life factors is insufficiently accurate to predict life because in most cases, these effects on bearing endurance are interdependent.
The definitive book on the science of grease lubrication for roller and needle bearings in industrial and vehicle engineering. Grease Lubrication in Rolling Bearings provides an overview of the existing knowledge on the various aspects of grease lubrication (including lubrication systems) and the state of the art models that exist today. The book reviews the physical and chemical aspects of grease lubrication, primarily directed towards lubrication of rolling bearings. The first part of the book covers grease composition, properties and rheology, including thermal and dynamics properties. Later chapters cover the dynamics of greased bearings, including grease life, bearing life, reliability and testing. The final chapter covers lubrications systems – the systems that deliver grease to the components requiring lubrication. Grease Lubrication in Rolling Bearings: Describes the underlying physical and chemical properties of grease. Discusses the effect of load, speed, temperature, bearing geometry, bearing materials and grease type on bearing wear. Covers both bearing and grease performance, including thermo-mechanical ageing and testing methodologies. It is intended for researchers and engineers in the petro-chemical and bearing industry, industries related to this (e.g. wind turbine industry, automotive industry) and for application engineers. It will also be of interest for teaching in post-graduate courses.
Rolling-contact fatigue tests were performed on SAE 52100 207-size deep-groove ball bearing determine the relation between bearing fatigue life and actual bearing component hardness differences and the effect of actual component hardness differences on bearing fatigue life scatter. The 207-size bearings with inner and outer races from the same heat of SAE 52100 material and with nominal Rockwell C hardnesses of 63 were assembled with SAE 52100 balls from the same heat of material tempered to nominal Rockwell C hardnesses of 60, 63, 65, and 66. Test conditions included an inner race speed of 2750 rpm, a radial load of 1320 pounds, which produced maximum Hertz stresses of 352 000 and 336 000 psi at the inner and the outer races, respectively, and a highly purified naphthenic mineral oil as the lubricant. Subsequent to testing, the bearings were disassembled, and all component hardnesses were measured. The bearings were regrouped according to their actual values of AH for Rockwell C hardness increments of 0. 5 and 1. 0, where AH is the difference between the actual hardness of the rolling elements in the bearing and the actual hardness of the inner race. The fatigue life and scatter results were compared with component hardness combinations and data previously obtained from the five-ball fatigue tester. The following results were obtained
The influence of material factors, such as types of steels, steelmaking process, cleanliness, fiber orientation, forging ratio, subzero treatment upon rolling contact fatigue life, was investigated for rolling bearing steels produced recently. Rolling contact fatigue life of recent steels which have high cleanliness has increased remarkably, and the influence of fiber orientation or subzero treatment upon rolling contact fatigue life is negligible, contrary to previous steels. Rolling contact fatigue life levels of each type of steels tested under three different test conditions were described. Depending on test conditions, their rolling contact fatigue strengths relative to others differed significantly in some cases.