Facilitating Hydrodynamic Lubrication of Zero-entrainment-velocity Contacts in Retainerless Ball Bearings Based on Boundary Slip
DescriptionCan the basic design of rolling element bearings be simplified by removing the retainer?If it does, the largest possible number of balls can be installed between the inner and outer raceways. Thus, bearings become more rigid, space saving, and able to support much heavier radial loads. Such retainerless bearings are available in the market (termed as full-complement bearings). However, two adjacent running elements sliding against the other in opposite directions would lead to serious problems of friction and wear because of their kinematic conditions of zero-entrainment-velocity (ZEV). Theoretically, no hydrodynamic lubricating film can be generated without entrainment speed. Thus, full-complement bearings can only be lubricated by boundary films and utilized in applications requiring high load capacity and limited to fairly low speeds.Approximately 10 years ago, my research group initiated a study on boundary slip at the liquid/solid interface in elastohydrodynamic lubrication (EHL). Our studies and similar investigations by others confirmed that by using an oleophobic surface as one of the bounding surfaces in an EHL contact, the overall friction can be reduced by the sliding of the lubricant on the oleophobic surface (boundary slip). We have recently applied the same concept to a ZEV EHL contact. It is amazing thatfull EHL films are successfully generated at ZEV conditions with a conjunction of oleophobic and oleophilic surfaces. To our knowledge, this is the first experimental evidence ever reported. As such, a novel design of full-complement bearings alternately incorporating slip and non-slip rolling elements is devised.The idea of using boundary slip to facilitate hydrodynamic lubrication for ZEV contacts is verified. Even though we know it functions, how and how good it functions need to be further explored. Thus, this project is proposed to completely understand the lubrication mechanism.What do we plan to do? Theoretically, a complete (thermal-EHL) numerical analysis of ZEV lubricated contacts, taking into account the boundary slip, will be performed. Experimentally, we will (i) search and evaluate various commercially available oleophobic coatings, (ii) conduct ZEV tests with various operating conditions to obtain the effects of speed, load and viscosity on film thickness, and (iii) appraise the use of nano-/micro-porous surfaces to prolong the service life of an oleophobic coating.The most original aspect of this proposed project is the attempt to facilitate oil entrainment at ZEV conditions (making impossible possible).When the project is completed, we can obtain a full theoretical understanding of the coupling effects of boundary slip and thermal on ZEV lubrication. The knowledge and insight acquired in the project contribute certainly to a new design of full-complement rolling element bearings and a novel idea to generate hydrodynamic lubricating effect for ZEV contacts.?
|Effective start/end date||1/09/17 → …|