Effect of Sulfuric EP Additive at Very Low Concentrations on Cutting Tool Wear and Finished Surface Roughness.

Abstract

In the authors' previous cutting tests, using dibenzyl disulfide (DBDS) with a concentration range of 0.1 to 1.2 wt% as sulfur (usual sulfur concentration level in actual cutting oils with sulfurous EP additive) in base oils, DBDS was found to increase flank boundary wear of cutting tools and to deteriorate finished surfaces, against expectation. This increase of the flank boundary wear seems to be caused by excessive corrosive action due to the excessive DBDS concentrations used. Thus, the behavior of DBDS at lower concentrations was investigated, using DBDS with a sulfur concentration range of 10-5 to 5 × 10-1% in the base oil. As a consequence, it was found that, at much lower sulfur concentrations than usually used for actual cutting oils, DBDS reduced not only the flank boundary wear and side flank wear, but also the finished surface roughness. Optimum sulfur concentrations that minimized the flank wear and the finished surface roughness were observed in the range of 10-5∼10-3%. The existence of an optimum sulfur concentration for flank wear was explained in terms of the formation of an optimum amount of antiwear surface film. The reason for the existence of the optimum concentrations for the finished surface roughness was explained in connection with the front boundary wear, whose groove depth has a dominant influence on the finished surface roughness.