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 N 2 , 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.

Quality improvement of deteriorated cutting fluid treated by atmospheric-pressure plasma jet and in-liquid plasma

“…The UV light generated by the plasma may therefore play an additional role in sterilization. As a result of examining the influence of UV sterilization, we found that UV rays do not affect sterilization under the experimental conditions used in the present work (Miyamoto et al, 2018). We concluded that the sterilization observed in the study was caused by the reaction of excited N 2 , NO, OH, and Ar.…”

“…The friction coefficient of the cutting fluids was investigated using a rotating tribometer. The measurement results of the friction coefficient are shown in the previous report (Miyamoto et al, 2018). The sample material was SKH51 (JIS G 4403) tool steel with a diameter of 30 mm and thickness of 10 mm.…”

“…Moreover, we suggested that the molecular structure of the fluids was not affected by plasma jet treatment (Miyamoto et al, 2018). In our previous study, the number of bacterial colonies in fluid sterilized using atmospheric-pressure plasma was reduced by more than 90% compared with the number in an untreated fluid (Miyamoto et al, 2018). From this report, however, it is unclear whether the remaining bacteria and surface Junji MIYAMOTO*, Ryo TSUBOI*, Masashi YOSHIDA** and Koichiro NAMBU*** characteristics such as tribological characteristics of the cutting fluid sterilized by atmospheric-pressure plasma change over time.…”

“…The widespread use of oil additives has led to the emergence of resistant bacteria, and the additives change the characteristics of the cutting fluid. Therefore, we proposed a sterilization technique using plasma treatment under atmospheric pressure (Miyamoto et al, 2018). Moreover, we suggested that the molecular structure of the fluids was not affected by plasma jet treatment (Miyamoto et al, 2018).…”

“…Therefore, we proposed a sterilization technique using plasma treatment under atmospheric pressure (Miyamoto et al, 2018). Moreover, we suggested that the molecular structure of the fluids was not affected by plasma jet treatment (Miyamoto et al, 2018). In our previous study, the number of bacterial colonies in fluid sterilized using atmospheric-pressure plasma was reduced by more than 90% compared with the number in an untreated fluid (Miyamoto et al, 2018).…”