The design of lubricant recirculating hydrodynamic spiral groove bearings using grease lubricants

Molyneaux, Alexander Kenworthy (1983) The design of lubricant recirculating hydrodynamic spiral groove bearings using grease lubricants. University of Southampton, Doctoral Thesis.

Abstract

This report presents new theoretical and experimental work on the behaviour of the recirculating spiral groove bearing using a grease lubricant. This bearing has a unique recirculation system which enables (for the first time) grease to be used as a hydrodynamic lubricant in a hemispherical spiral groove bearing. Since its invention in the early 1970's considerable interest has been shown in the use of this bearing in low noise applications. The objective of this work was to produce a theoretical model of the behaviour of this bearing, substantiated by experimental data, to enable the formulation of accurate design methods. A theory has been developed which describes the flow of those non-Newtonian fluids (such as greases) which exhibit a variation of viscosity with shear rate. This theory, based on the method of Equivalent Newtonian Viscosity, has been incorporated into an existing finite cell numerical analysis of fluid and heat flow within spiral groove bearings. To enable results to be produced for the recirculating bearing, an analysis of the heat flow away from the bearing clearance has also been performed. Experiments were conducted using a modified cone-and-plate viscometer, and a purpose built capillary viscometer, to measure grease viscosity at shear rates up to 104x-1 and temperatures up to 55°C. The Sisko power law model has been used to approximate the measured grease variation of viscosity with shear rate. Theoretical results have been produced using this Sisko power law model which shows the effect on spiral groove bearing performance of using a grease lubricant. For comparison with results from this theory experiments have been performed on a large thrust spiral groove bearing that was force fed with a grease lubricant. A novel pressure sensor was designed to enable the pressures to be measured over individual grooves in this bearing. The experimental results from this bearing agreed well with the theoretical predictions. To study the grease recirculation system, flow visualisation experiments have been performed on recirculating hemispherical spiral groove bearings. Experiments have also been performed on a new rig to measure the performance of these recirculating grease bearings. Comparison of these results with the theoretical predictions has revealed a discrepancy for certain geometries. After examination of various hypotheses it is suggested that cavitation is the most probable cause. Results are also presented which show how reliable these recirculating grease bearings have been in low noise toroidal fans.

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