2013 Volume 58 Issue 2 Pages 109-119
The high-pressure viscosity expression for base oils by HATA et al. was applied to binary system mixtures. The characteristic parameters necessary for the calculation of the high-pressure viscosity are atmospheric pressure-viscosity coefficient (αot), effective cohesion energy density (CEDeff), effective molecular weight (MWeff) and characteristic reference temperature (θp). We can obtain αot and CEDeff from the bulk properties which are viscosity, density and molecular weight of base oil under the atmospheric pressure. Mixing rule for these characteristic parameters, named αot-mix, CEDeff-mix, and θp-mix, was analyzed using eight kinds of binary system mixture consisting of thirteen kinds of base oil. As a result, the mixing rule of these characteristic parameters was fundamentally expressed to the same form as the formula of the number-average molecular weight. However, as for αot-mix of two kinds of mixture, in mixtures of mineral oils of the same hydrocarbon group and mixtures of synthetic naphthene and polyalphaolefin, the weight-average rule and a modified number-average rule were more preferable respectively.