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.
Evaluation of Powder Processed Turbine Engine Ball Bearings.
Abstract : Rolling element fatigue life testers, as well as full-scale bearing testers, were used to develop a highly rolling contact fatigue resistant powder processed material (P/M) for use in aircraft turbine engine bearings. Ball and rod elemental tests were conducted, for screening purposes, on three P/M alloys; M-50, T-15 and CRB-7. The best results were realized with the P/M CRB-7 material, a 14 percent chrome corrosion resistant alloy, which demonstrated a B10 life almost twice that of the baseline, conventionally processed VIM-VAR M-50. Twenty full-scale 140 mm ball bearings were subsequently fabricated from P/M CRB-7 alloy. The B10 life realized with these bearings was equivalent to that expected from these same bearings had they been made from conventional VIM-VAR M-50 material. This good result was achieved in spite of an inner ring land wear problem which was alleviated by plating the lands with hard nickel. (Author)
Dimensional Errors of Fixtures, Locating and Measurement Datum Features in the Stream of Variation Modeling in Machining
Machining processes are usually multi-station processes involving a large number of operations and several locating datum changes. Machining errors are thus introduced, transformed and accumulated as the workpiece is being machined. This paper introduces procedures for expressing the influence of errors in fixtures, locating datum features and measurement datum features on dimensional errors in machining. These procedures are essential in the derivation of the Stream of Variation model of dimensional machining errors using the CAD/CAPP parameters of the machining process. The linear state space form of the Stream of Variation model allows for advanced control theory achievements to be employed in formal solutions to problems in multi-station machining. Modeling procedures presented in this paper were experimentally verified in machining of an automotive cylinder head.