Influence of Kinematic Viscosity of Base Oil on Magnetorheological Grease

In order to explore the effect of kinematic viscosity of base oil on the rheological properties of magnetorheological(MR)grease,MR grease samples containing 70%(mass fraction)carbonyl iron powder and carrier liquid separately with kinematic viscosity of 10mm^(2)/s,100mm^(2)/s,350mm^(2)/s and 500mm^(2)/s were prepared.The influence of kinematic viscosity of carrier liquid on the settlement performance of MR grease was analyzed.The rheological properties of MR grease were tested and analyzed under steady-state shear and oscillatory shear modes.The results show that the kinematic viscosity of base oil has a significant effect on the settling stability of MR grease.The zero-field viscosity of MR grease increases with the increase of the kinematic viscosity of the base oil,and the sedimentation performance is better.The colloid stability of MR grease is poor after the kinematic viscosity of base oil is lower than a threshold,and static oil bleed will occur immediately.In addition,the shear stress of MR grease increases with the increase of magnetic induction.When the shear rate is less than 10 s−1,the shear stress increases rapidly with the increase of shear rate.When the shear rate further increases,the shear stress tends to a stable value.The reason is that the thickener fibers in MR grease are subjected to the shear stress between laminar flows,the entanglement occurs,which makes MR grease exhibit shear thinning,and its rheological properties conform to the Herschel-Bulkley constitutive model.In the process of preparation,some carbonyl iron powder will be embedded into the thickener fiber,which shows different magnetic saturation phenomena due to shear thinning under steady-state shear and oscillatory shear.