Rheological Analysis on Hardening of Magnetorheological Grease with Kerosene

Magnetorheological grease (MRG) with dilution oils may suffer from reduced storage stability caused by oil separation. This phenomenon potentially causes a performance reduction of the material due to possible accelerated degradation of the grease medium. The long-term rheological behavior of MRG with kerosene (MRGK) was investigated in this study. MRGK was prepared with 10 wt% kerosene as the dilution oil, together with a sample of MRG without any kerosene as the control. A modular compact rheometer (MCR) was used to obtain rheological data from the MRG samples in an oscillatory strain sweep mode under the influence of magnetic fields, which ranged from 0A to 3A. After one year, the measurement was repeated to observe any changes to the rheology of MRG samples. Results showed a significant hardening of the sample diluted with kerosene, which mainly showed a drastic increase in off-state storage modulus at low strain. This was shown by the off-state storage modulus of MRGK, which after one year showed an increase of 15% in the initial storage modulus, and an increase of 2438% in the storage modulus at 10% strain. The MRG sample showed an increase of 50% and 47%, respectively. The on-state storage modulus did not appear to experience such a drastic change after one year. The study concluded that while dilution oil may be a promising candidate to reduce the initial viscosity of MRG, the resulting performance difference may compromise the long-term performance, and may even cause accelerated degradation when in use.