Electrical Resistance Method for Lubrication Condition Monitoring of Oil and Grease Lubricated Point Contacts

In high-end equipment and precise mechanical systems, accurate monitoring of the lubrication status of tribological interfaces is critical to maintaining reliable mechanical performance, extending service life and improving productivity. However, there are still many challenges in the real-time monitoring and evaluation of lubrication status for metallic contacts under real operating conditions. An equivalent contact resistance measurement system was developed in this work to realize the real-time condition monitoring by extraction of the electrical signal in the lubrication area of a metallic ball-disc tribo-pair. By adjusting the resistance of the balance resistor and the applied voltage in the developed circuit, the voltage gained by the lubricated contact could be controlled, and the transition of the lubrication regimes could be captured. At the same time, combined with optical interference technology and synchronous monitoring of the changes in friction, a multi-parameter evaluation system for determining the lubrication status was built. The relation among contact resistance, film thickness and friction was explored at different entrainment velocities. Results showed that the developed contact resistance method could effectively reflect the lubrication regimes of the contact zone, as well as the dynamic evolution of lubrication status. Subsequently, the developed electrical resistance method was applied to the condition monitoring of grease lubricated point contacts. In the process of continuous monitoring of the evolution of the electrical signal over time, the lubrication regime of grease lubrication varied, and the critical point of parched lubrication and the rupture of the lubricating film were effectively captured. The experimental results of both oil and grease preliminarily verified the reliability of the developed electrical resistance method, which could provide a solution for the lubrication condition monitoring of mechanical systems (such as bearings and gears) in engineering by taking essential insulation measures.