Effects of fumed silica weight fraction on rheological properties of magnetorheological polishing fluids

Magnetorheological (MR) polishing fluids with excellent rheological characteristics are efficient in material removal of workpiece. In this study, fumed silica (FS) was used as thixotropic agent in MR polishing fluid with ten different weight fractions to find the proper additive amount for good rheological and sedimentation properties. The rheological behavior of samples at several additive concentrations was determined by examining flow properties using a rotational rheometer connected to an external magneto-cell. Experimental results showed that, by adding FS to MR polishing fluids, apparent viscosity and yield stress exhibited an obvious increase, while the shear-thinning index decreased sharply. Model fitting showed that all the MR polishing fluids exhibited shear-thinning behavior and followed the Herschel-Bulkley model. Further investigations suggested that 0.5-0.6-wt% FS was the most promising additive proportion for proper rheological and sedimentation properties, while a further increase in FS weight fraction greatly increased apparent viscosity and decreased yield stress undesirably.