Investigating the lubrication mechanism and stiffness of oil-based ferrofluids in spur gear drives

Due to both liquid properties and ferromagnetic material characteristics, ferrofluids are developed as the favored component solvents. The art of investigating the lubrication mechanism of ferrofluids in spur gear drives is significant for improving the anti-wear of gear pairs and prolonging the service life. This paper proposes a mathematical model of oil-based ferrofluids lubrication and derives a system of governing equations. The tribology performances of oil-based ferrofluids are investigated in comparison with their counterparts of pure base oil. Furthermore, the effects of ferromagnetic particle size and bulk concentration on the tribological property and film stiffness of oil-based ferrofluids are studied. Finally, the influence of magnetic field intensity is analyzed and discussed. Results show that oil-based ferrofluids induce greater increases in film thickness and film normal stiffness in comparison with their counterparts of pure base oil; the decrease in ferromagnetic particle size causes considerable increases in film thickness and remarkable decreases in friction coefficient; the increase in bulk concentration induces a significant increase in film thickness and a remarkable decrease in friction coefficient, meanwhile the normal stiffness of ferrofluids film maintains stable; the increase in magnetic field intensity causes small increases in film thickness and small reductions in friction coefficient. Therefore, ferrofluids with ferromagnetic particles of small size and large bulk concentration are beneficial to lubrication and anti-wear of magnetized spur gear drives.