Tribological Properties of Cutting Fluid Sterilized by Atmospheric-Pressure Plasma Treatment

Abstract

Plasma jet sterilization of cutting fluid was performed under atmospheric pressure, and the tribological properties of the resulting fluid were investigated. The mechanisms of atmospheric-pressure plasma jet sterilization were also clarified. The number of bacterial colonies in the sterilized fluid was reduced by more than 90% compared with the untreated fluid. After exposure to ultraviolet light, no comparable reduction was observed. We concluded that the sterilization observed in the study was caused by the reaction of excited N2, N, and Ar. The IR spectra of the plasma-treated cutting fluid were the same as those of the untreated fluid. However, the transmittance of the C=O peak decreased in proportion to the discharge voltage. The treated cutting fluids maintained a low friction coefficient 2.4 times longer than the untreated fluid. The sliding angle and adhesive energy of the untreated cutting fluid were considerably lower than those of the unused cutting fluid. Furthermore, the sliding angle and adhesive energy of the plasma-treated cutting fluid were higher than those of the untreated cutting fluid. Therefore, we consider that the lower friction coefficient of plasma-treated cutting fluid as compared to that of the untreated cutting fluid is related to this result. The study demonstrated that the life of a cutting fluid can be prolonged by this novel plasma treatment, with an associated improvement in tribological properties.

Keywords

• plasma sterilizing
• cutting fluids
• plasma jet
• tribological properties