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.
Dr. Markus Grebe
Stephan Hiesinger
Christian Müller
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