Effect of lubricant oxidation on tribological performance of gear contact interfaces in three gorges ship lift: experiments and simulation

Purpose This paper aims to investigate the high-temperature degradation behavior of lubricating oils used in the gearboxes of the Three Gorges ship lift, which operate under harsh environmental conditions. The study seeks to understand the correlation between the evolution of physicochemical properties, oxidation mechanisms and the resulting tribological performance to address excessive gear wear. Design/methodology/approach High-temperature oxidation experiments were conducted to simulate the degradation process. The evolution of physicochemical properties was characterized by monitoring color, acid number and kinematic viscosity. Oxidation products were analyzed using Fourier transform infrared spectroscopy and GC-MS chromatography. Furthermore, ReaxFF reactive molecular dynamics simulations were used to reveal microscopic reaction pathways. Finally, the tribological performance of the degraded oil was evaluated using a friction tester and a 3D profilometer and X-ray photoelectron spectroscopy (XPS) analysis was performed on the worn surface to characterize the compositional changes of the friction film, thereby revealing the friction-induced damage mechanism of the oxidized lubricating oil. Findings The results indicate that thermal oxidation leads to the formation of acidic polar molecules, such as carboxylic acids, aldehydes and esters, resulting in an increasing trend in both acid number and kinematic viscosity. ReaxFF simulations revealed that high-temperature oxidation proceeds through multiple specific reaction pathways. Crucially, the study confirms that the decline in tribological performance is directly related to these physicochemical changes and the accumulation of oxidation products. Originality/value This study uniquely combines macroscopic experimental characterization with microscopic ReaxFF molecular dynamics simulations to provide a comprehensive understanding of lubricant degradation in the specific context of large-scale ship lift gearboxes. The findings offer theoretical support for optimizing oil monitoring indicators and maintenance strategies for critical hydraulic engineering equipment.