Bearings: Technology and needs
A brief status report on bearing technology and present and near-term future problems that warrant research support is presented. For rolling element bearings a material with improved fracture toughness, life data in the low Lambda region, a comprehensive failure theory verified by life data and incorporated into dynamic analyses, and an improved corrosion resistant alloy are perceived as important needs. For hydrodynamic bearings better definition of cavitation boundaries and pressure distributions for squeeze film dampers, and geometry optimization for minimum power loss in turbulent film bearings are needed. For gas film bearings, foil bearing geometries that form more nearly optimum film shapes for maximum load capacity, and more effective surface protective coatings for high temperature operation are needed.
Lubricant Films in Rolling Contact of Rough Surfaces
An experimental and mathematical study of elastohydrodynamic film formation is described for a rolling four-ball configuration utilizing steel bearing balls. Wear rates are determined in the microgram range, using a radiotracer tagged ball. Existence and interruptions of elastohydrodynamic films are observed by measurement of electrical conductivity through the Hertzian contact. Surface microgeometry of the rolling tracks on the balls is statistically analyzed by processing electrical analogs of surface profiles through on-line computing equipment. Defining electrical contacts as asperity approaches through a separating film, the average duration and frequency of such approaches is computed from surface microgeometry statistics. A comparison of computed and observed values of contact conductivity parameters shows good order of magnitude agreement and yields estimates of average film thickness as a function of speed and load which agree, satisfactorily with the order of film thickness predicted by elastohy...
Metallic Contact and Friction between Sliding Surfaces
A new device has been developed and used to study metallic contact and friction between sliding, lubricated surfaces. The system consists basically of a fixed metal ball loaded against a rotating cylinder. The extent of metallic contact is determined by measuring both the instantaneous and average electrical resistance between the two surfaces. Friction between the ball and cylinder is recorded simultaneously with contact. In general, the electrical resistance was found to oscillate rapidly between an extremely low value and infinity, suggesting that metallic contact is discontinuous. The average resistance of an oil film is therefore a time-average, that is, a measure of the per cent of the time that metallic contact occurs. The results indicate that metallic contact is much more prevalent than would have been expected from other published studies in which electrical resistance or discharge methods were employed. Using this apparatus, the entire region from hydrodynamic (no metallic contact) to pure “bou...