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.
The effect of cleanliness on the attainable bearing life in aerospace applications
Surface-initiated fatigue and wear caused by contamination is one of the major causes for bearing failures in aerospace applications. This paper outlines a method to precisely define cleanliness with the help of the cleanliness factor s and the contamination factor V. Particle sizes and filtration ratios are defined and allocated to certain V factors. These factors can then be entered into a proposed bearing life calculation method to quantity the effect of system cleanliness/contamination on the attainable bearing life. A procedure to improve system cleanliness is described (pre-cleaning concept) so that contamination related damage can be eliminated.
Wall-to-bed heat transfer in circulating fluidized beds
Heat Transfer from the wall of a circulating fluidized bed to the fast bed suspension has been investigated for several materials. The range of investigation includes dense and dilute phase fast fluidization and pneumatic transport. The overall heat transfer coefficient was found to be a function mainly of cross-sectional average suspension density. Effects of superficial velocity and solids mass flux were obscured by their interrelationship to the suspension density. Two models from the literature are evaluated using present and published data.