Intrinsic Apparent Viscosity and Rheological Properties of Magnetorheological Grease with Dilution Oils

In this study, the principal rheological properties of the magnetorheological grease (MRG) is experimentally investigated with various types and percentages of dilution oils. The stability in terms of oil separation and rheological properties of the natural plant-based dilution oil; castor oil was compared with petroleum-based; kerosene and hydraulic oils. Several samples of MRGs with different types and ratios of dilution oils were prepared by mixing spherical carbonyl iron (CI) particles and grease using mechanical stirrer. The rheological test was performed under rotational mode of shear rheometer by changing the magnetic fields from 0 to 0.7 T at room temperature condition. The results showed that the apparent viscosity of the dilution oils of kerosene has the lowest apparent viscosity followed by castor and hydraulic oils. It has been observed that by addition of dilution oils more than 10 wt% has reduced the stability of the samples. It is also noted that the increment of dilution oils percentages in MRGs have insignificant effect towards linear viscoelastic (LVE) region. This fact indicated that the improvement of the rheological properties was dependent on the initial viscosity as well as optimum percentage of the dilution oils utilized in the MRG suspension without visibility of the oil separation. In addition, the comparison of the MRG performance in terms of yield stress between different types and percentages of dilution oils was evaluated and discussed in detail.