The behaviour of greases in elastohydrodynamic contacts

Abstract

The ability of grease to generate elastohydrodynamic (EHD) films has been studied and interpreted in terms of the response of grease structure to contact conditions. For most liquid lubricants, EHD film thickness depends upon the rheological properties of the fluid in the contact inlet. This mechanism is reasonably well understood for fluids that are Newtonian in behaviour. However, greases have complex bulk structures, the scale of which is larger than the dimensions of a contact inlet. The EHD performance of grease must therefore depend upon the response of grease structure to the high-shear inlet conditions. In this study, EHD film thickness has been measured for a range of greases using optical interferometry. In parallel work, grease structural changes have been monitored directly in the inlet of EHD contacts using reflection-absorption infrared spectroscopy. By using these two approaches in combination, changes in composition and loss of bulk grease structure have been observed and correlated with the ability of greases to form films under EHD conditions.

Film Thickness and Friction Relationship in Grease Lubricated Rough Contacts

“…It was also found that the higher the base oil viscosity and/or thickener content, the higher is the film thickness [4]. Moreover, other studies suggest that under fully flooded conditions, the grease generates a thicker film than its base oil [1,2,5,6].…”

“…Moreover, other studies suggest that under fully flooded conditions, the grease generates a thicker film than its base oil [1,2,5,6]. The difference was attributed to the base oil viscosity but also the thickener type and its content [4], although the opposite relationship is generally observed in starved conditions. Furthermore, Cann et al [7] has used ball-on-disc interferometry measurements to show that the grease's film thickness was actually composed of static film (a residual layer adsorbed on the surfaces, mainly composed by sheared thickener material) and a dynamic film resultant from the elasto-hydrodynamic effect.…”

Effects of nano thickener deposited film on the behaviour of starvation and replenishment of lubricating greases

“…The effect of grease property on its lubrication performance was also studied. Cann et al [2,9] reported that high thickener concentration and base oil viscosity might cause more severe starvation. Huang et al [10] found that thickener type and the polarity of base oil also play very important roles in central film thickness generation and lubricant reservoir formation during operation.…”

“…Thickeners have been observed to pass through contact [15]. Cann et al [9] assumed that thickener debris is squeezed out of the contact and then deposited in the rolling track. The properties of deposited film and its influence on lubrication remain unclear, and these properties may change with different grease types.…”

Microbubble Phenomenon in the Grease Lubricating Film Induced by Micro-Oscillation

“…The primary role of the grease lubricant is to form and maintain a lubricating film between two moving surfaces. A significant body of experimental and theoretical work has so far been conducted on understanding the underlying mechanisms and exploring the relevant applications of grease lubrication [1][2][3][4]. The results of such studies have led to many different views on grease lubricant [5][6][7][8][9][10][11][12][13][14].…”