This study explores how grease distribution and morphology within bearing raceways affect performance, using five fluorescent greases prepared with polyalphaolefin (PAO) base oils of increasing viscosities. Results show that higher viscosity promotes the formation of ample reserves in the grease reservoir, leading to greater oil storage capacity and stronger replenishment capability. However, higher viscosity inhibited the full release of base oil and increased oil churning losses, doubling friction torque and accelerating raceway wear. Compared to the grease with the lowest viscosity, the grease with the highest viscosity exhibited a 14.1% reduction in root mean square vibration and an 87.4% drop in slide/roll ratio, with grease finger height and volume increasing by 133.2% and 98.5%, respectively. Molecular dynamics simulations revealed that the grease with the highest viscosity, which has a base oil with longer molecular chains, exhibited a 30.2% increase in adsorption energy with the Fe layer and a 74.23% decrease in diffusion coefficient compared to the grease with the lowest viscosity. These findings suggest that while higher viscosity improves vibration behavior and oil replenishment, it compromises lubricant film spread ability and increases viscous resistance.
Wu et al. (Mon,) studied this question.