Internal friction coefficients have been measured by a direct shear tester for a number of powders having different particle diameters and densities, and for their binary mixtures. The binary powders have been mixed by V-type (V), horizontal cylinder (HC), horizontal ribbon (RH) and vertical ribbon (RV) mixers to assess the effect of internal friction coefficient on the rate of mixing and the final degree of mixing. The performances of the solid mixers have been correlated much better with the internal friction coefficient than with the change in particle diameter or density. While the rate of mixing and the final degree of mixing in the rotary-vessel mixers such as V and HC decrease as the internal friction coefficient increases, those in the stationary-vessel type ones such as RH and RV are hardly influenced by the coefficient.
