Why is the acid value of the industrial gear oil in use high?

The equipment maintenance personnel of a cement plant consulted by telephone: "In our stacker-reclaimer drive gearbox, an accidental inspection found that the oil was dark in color and had a pungent odor, so we replaced the industrial Gear Oil for a month. Later, in the process of the company's unified oil analysis and testing, it was found that the acid value of the oil in this tank increased compared with the new oil, and the color became darker, what is the reason?".

The expert gave the following analysis: First, it is necessary to clarify whether the purchased industrial gear oil is a qualified product of a regular manufacturer, and secondly, whether the product of the appropriate quality level and viscosity level is selected for this gearbox. After confirming that there are no problems with the above two basic tasks, I further understood the oil replacement procedure, and the problem gradually became clear: for the gear box of the stacker and reclaimer, the workload is large and the working environment is exposed. The increase in acid value is usually caused by the oxidation of the oil, and the darkening of the color is also a manifestation of the oxidation of the oil. If during the oil replacement process, the severely oxidized oil remaining in the original oil tank, as well as the wear metals and peroxides in the remaining old oil, will quickly consume the antioxidants newly added to the oil, and at the same time The gear box works under heavy load, which may produce wear metal, and at the same time means high temperature work, which will accelerate the oxidation of oil.