Influence of Properties of Base Oil for Cutting Oil on Action of Sulfurous EP Additive during Turning. 2nd Report. Influence of Molecular Weight Distribution of Base Oil.

Abstract

In the previous paper, the authors investigated the influence of the viscosity grade of base oil for cutting oil on the action of an active sulfurous EP additive during cutting, by performing a series of cutting tests on a lathe using mineral base oils with narrow-range molecular weight distribution and dibenzyl disulfide (DBDS) at a common concentration (as sulfur) used in actual cutting oils. It was revealed in the paper that at such a concentration, DBDS increased flank boundary wear of cutting tools and degraded surface finishes, while slightly improving side flank wear of the tools. However, it has been proven in earlier studies by one of the authors that even if the viscosity grades of mineral base oils of the same hydrocarbon type are equal, i. e., their mean molecular weights are equal, base oils with wide-range molecular weight distribution are superior to those with narrow-range distribution in optimizing cutting performance, due to the former's predominance in the cooling ability and spreadability (penetrating capability). Therefore, also for oils containing an EP additive, the difference in the molecular weight distribution of base oil should affect the action of EP additive. Thus, cutting test investigations were performed using wide-range oils containing DBDS at a common concentration, and the results were compared with those for the narrow-range oils containing DBDS which were reported in the previous paper, for clarifying the influence of the molecular weight distribution of base oil for cutting oil on the action of a sulfurous EP additive during turning.