Rheology of Lubricants in Real Bearing Contacts

Experimental traction-slip and lubricant film-thickness data have been determined for selected lubricants to provide information for use in conjunction with the design of lubricated machine elements. The traction-slip experiments were performed using a rolling-disk rheometer which closely simulates those conditions existent in real lubricated contacts; the film-thickness data were obtained using an X-ray technique. The range of experimental conditions included two rolling speeds (5000 and 10,000 rpm), several contact pressures [(690 – 2400 MN/m²) (100 to 350 ksi)], and three temperatures [(338, 366 and 423 K) (150, 200, and 300 F)]. The slip conditions imposed on the lubricants ranged as high as 6 m/s (1200 fpm) which is equivalent to a shear rate of approximately 0.5 × 10⁸ sec⁻¹. Interpretative analyses have been developed to infer basic lubricant properties from the experimental data. These analyses include time delay parameters and “dynamic” pressure-viscosity parameters. The analytical treatment of the data provides: (1) a generalization of the experimental data to apply over a wider range of conditions than those actually covered, and (2) a basis for comparing lubricants and obtaining a more fundamental understanding of lubricant behavior.