INTRODUCTION: Bearing efficiency and expected service lifetime are the main parameters attempted to be improved when designing lubricated roller bearings. Both of them can be studied through the analysis of the roller-end / flange contact. This contact is crucial as several physical and mechanical phenomena take place, namely, a complex kinematics (induced by a spin and a skew angle); high power dissipation; severe operating conditions in the form of high pressures and temperatures, which have a direct impact on the lubricant properties (density and viscosity); as well as a limiting amount of lubricant flowing through the contact.
Starvation is an important factor to take into consideration, as contacts rarely operate under fully-flooded conditions, since the lubricant feed of the contact is set by the amount of lubricant ejected from the previous element. The influence of starvation has been extensively studied for different contact configurations1,2 and operating conditions3,4,5. However, the research of starvation in conjunction with the spin motion, as is the present case, is very limited. In this sense, the work of Dormois6 investigated friction in large-sized elastohydrodynamic (EHD) contacts with spin motion and concluded that the spin motion had a clear influence on the thermal dissipation, the contact symmetry and the lubricant loss of the contacting surfaces. This work was later completed by those of Doki-Thonon7, who focused on the study of the thermal effects in this kind of contacts, and Wheeler8, who researched the performance of non-elliptical point contacts (torus-on-plane) under various operating conditions and subjected to a spin motion.
The present study introduces some preliminary numerical results and conclusions on the influence of starvation in large-size spinning contacts. A finite element model has been developed to recreate the phenomena occurring in the roller-end / flange contact.
METHODS: A finite element model has been developed to solve the spinning three-dimensional isothermal EHD circular contact problem. The model takes into account two computational domains separated by a free (unknown) boundary: a pressurized domain, in which the lubricant completely fills the gap between the two contacting solids, and a starved domain surrounding it, in which the gap is partially filled. The location of the free boundary is established by the pressure distribution on the contact as well as the rheology of the lubricant, whose density is described by the Jackobsson-Floberg-Olsson (JFO) pressure-density law. This mass flow-conserving model is chosen to better represent the changing nature of the lubricant in the different regions of the model. In order to fully describe the physics of the spinning contact, the generalized Reynolds equation has been adopted, which allows the lubricant rheology to vary across the film thickness.
The elastic deformation, defined in accordance with the equivalent body theory, is computed at the same time as the lubricant pressure and film thickness.
RESULTS: Numerical film thickness measurements under spin motion can be extracted from the computational model. An example is given in Fig.1a by illustrating the lubricant film thickness, the lubricant density and the pressure distribution at the centerline of the contact, for an entrainment velocity of the 10m/s and a load of 10N, and in Fig.1b by depicting the lubricant film thickness across the contact region, for the same operating conditions.