Investigation of mixed hBN/Al2O3 nanoparticles as additives on grease performance in rolling bearing under limited lubricant supply

Grease plays an important role in reducing friction and wear of rolling bearings and improving their service life and reliability. However, increasing attention is being paid to the environmental pollution caused by discarded grease. In this paper, calcium sulfonate complex grease (CSCG) was prepared by using green raw materials, namely poly-alpha-olefin oil as the base oil and complex calcium sulfonate soap as thickener. In order to improve the lubrication and damping performance of the grease, hexagonal boron nitride (hBN) and nano-Al2O3, which have the potential to replace toxic additives, are mixed into the grease in different mass proportions. The thickener structure of each grease was characterized and analyzed. According to the bearing vibration and life of the two key performance indicators, four-ball tests and bearing vibration tests under limited lubricant supply (LLS) were performed. The results show that CSCG with 0.75 wt% hBN and 0.25 wt% Al2O3 (BN75AL25) has the best tribological and vibration suppression performance. The mean friction coefficient decreased by 11.3%, the wear scar diameter decreased by 6.1%, and the worn surface morphology improved significantly compared with CSCG. The frequency domain analysis showed that high, medium and low frequency vibrations were suppressed by 19%, 11.7% and 16.4%, respectively. In conclusion, BN75AL25 has the potential to become a green high-performance grease under LLS, which is worth further research and exploration.