Influence of Properties of Base Oil for Cutting Oil on Action of Sulfurous EP Additive during Turning. 1st Report. Influence of Viscosity Grade of Base Oil.

Abstract

In the authors' previous cutting experiments on a lathe, using cutting oils containing an active sulfurous EP additive, dibenzyl disulfide (DBDS) at various concentrations, it was revealed that in a common concentration range (as sulfur) used in actual cutting oils containing sulfurous EP additive, DBDS unexpectedly increased flank boundary wear of cutting tools and degraded surface finish, but that in much lower concentration range, DBDS showed optimum concentrations at which flank boundary wear decreased and surface finish was improved. In these experiments, however, mineral base oils with limited viscosity grades were used, and so the influence of the difference in the viscosity grade of the base oil on the action of DBDS were not examined. In general, there exist interactions between an additive and a base oil, so that the difference in the viscosity grade of the base oil should affect the action of the additive. Therefore, in order to establish criteria for selecting or designing a base oil for EP cutting oil, it is necessary to determine optimum viscosity grade conditions in which tool wear and/or surface finish are minimized. From this viewpoint, the influence of the viscosity grade of base oil for cutting oil on the action of a sulfurous EP additive was investigated in a common concentration range of DBDS, using several mineral base oils with a variety of viscosity grades.