Abstract: To elucidate the effects of base oil structure and composition on the performance of stain-free bearing gear oils, the hydrocarbon compositions and structural differences of three industrial white oils were analyzedusinggas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy. The sensitivity of polyisobutylene (PIB) toward different industrial white oils was investigated, and the high-temperature annealing detergency of the industrial white oils, PIB, and their blended base oils was evaluated. Furthermore, the mechanism by which hydrocarbon composition and component structure affect the performance of base oils and bearing gear oils was analyzed. The results showed that there were significant differences in the hydrocarbon composition and isomerization degree among the three industrial white oils. Changcheng white oil had the highest proportion of naphthenes at 84.6%, predominantly multi-ring naphthenes, with a molecular branching index of 59.32% and the highestisomerization degree. Hengli white oil had the lowest naphthene content at only 36.9%, mostly low-ring naphthenes, with a branching index of 43.29% and the lowest isomerization degree. Kaiwei white oil exhibited intermediate values for both naphthene content and isomerization degree. The hydrocarbon composition and structural characteristics of the industrial white oils exerted a significant impact on oil performance. The viscosity index (VI) and high-temperature annealing detergency of the base oils increase following the order: Changcheng white oil <Kaiwei white oil < Hengli white oil, while the evaporation loss showed the opposite trend. PIB demonstrated the most pronounced thickening effect and viscometric property improvement when blended Changcheng white oil, followed by Kaiwei white oil, with the least effect observed for Hengli white oil. Industrial white oils with higher paraffin content and lower isomerization degree yielded composite base oils and stain-free bearing gear oils with higher VI and superior high-temperature annealing detergency.

Key words: industrial white oil, stain-free gear oil, hydrocarbon composition, viscosity-increasing effect, high-temperature annealing detergency