2024 年 64 巻 Extra-edition 号 p. ex175-ex180
Heat treating oils are composed of base oil and additives, with the heat treating oils composed mainly of the base oil. Therefore, the properties of the base oil significantly affect the quality of the heat treating oil. Base oil is classified into mineral oil and synthetic oil, and mineral oil is generally used for heat treating oil. Mineral oils are classified according to the degree of refining. In recent years, due to improved refining technology, highly refined base oils, known as Group III base oils, have been produced and distributed in the market. The demand for high quality base oils has caused a decrease in the production of Group I base oils, which are lower in degree of refining, due to the closing of older refineries and the impact of newer processes. These backgrounds require the use of Group III base oils for heat treatment oils. Heat treating oils are used at high temperatures, in contrast to general petroleum products. The oxidation stability test specified for heat -treated oil was compared with the oxidation stability test for general lubricating oil. The results for Group III base oils showed oxidation progress under heat-treated oil conditions, unlike the results for general lubricating oils. Therefore, it is difficult to compose a heat treating oil using only Group III base oil. In this paper, in order to improve the oxidation stability of heat treating oils, a study was conducted to determine the most suitable composition by adding a Group I base oil to a Group III base oil. The addition of Group I base oil to Group III base oil gave good results. The sulfide in the Group I base oil was found to be a factor.
