Technical Committee Lubricants

Development of a Screening Test Method for Lubricating Greases by Coupling Thermo-Oxidative Test Methods with a Mechanical-Dynamic Multi-Station Rolling Bearing Test Rig

The aim of this research project was to determine faster and more resilient statements on the suitability of lubricating greases in rolling bearings at high temperatures by coupling thermo-oxidative and mechanical-dynamic laboratory test methods. Numerous standard ageing tests for greases were carried out and evaluated at OWI for this purpose. One focus was also on the chemiluminescence method, which was the focus of industry interest at the beginning of the project. At KTM, the focus was on the mechanical-dynamic rolling bearing tests in a new universal multi-station rolling bearing test rig. In addition, thermal ageing tests were carried out on various catalyst plates and evaluated using rheological measurements (flow curve and limit).
The project showed the application areas and limits of the individual thermal oxidative laboratory tests as well as the simple tribological model tests. Here, the chemiluminescence method showed limits with regard to the investigation of used fats and the evaluation of different formulations using isothermal measurements. The thermogravimetric analysis made it possible to distinguish the greases used depending on the load and the load time. In addition, the activation energies determined correlated with the change in the condition of the lubricating greases.
The tribological model tests showed only a small agreement with the rolling bearing tests. The combination of various investigations allows a practice-relevant characterization of the greases. The investigations in the rolling bearing and during thermal ageing on catalyst plates showed that with greases based on soap thickeners the thickener degeneration limits the service life and not the actual oil ageing.
The project objective of investigating a potential screening method for lubricating greases by coupling thermo-oxidative processes with mechanical-dynamic tests was achieved even though the originally favoured method of chemiluminescence measurement was not suitable.