Experimental and numerical investigation of plain bearings under minimal lubrication

• Applicants: Privatdozent Dr.-Ing. Thomas Hagemann; Professor Dr.-Ing. Michael Müller; Professor Dr.-Ing. Hubert Schwarze
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 527815977

Nominally hydrodynamically lubricated plain bearings are used under a wide variety of boundary conditions in machines, for example for energy conversion or in mobility. A reduction of the occurring friction is an overriding goal in order to increase the efficiency and robustness of the bearing. The planned research project deals with the experimental identification and theoretical description of plain journal bearings under minimum quantity lubrication, which occurs away from nominal operation, e.g. during start-up, emergency running or idling processes. Often these operating conditions represent critical and damaging parts of the a priori known operating spectrum of machines. However, due to the lack of understanding of the system and the absence of theoretical descriptions, these operating states, which are important in industrial practice, can only be inadequately assessed. Thus, resource-intensive measures, such as the application of hydrostatic auxiliary units, are often implemented to avoid them, although the necessity of these modifications is unclear. On the other hand, experimental work on different contact lengthscales shows that small amounts of lubricant are sufficient to minimise friction with still a moderate wear rate. For an improved quantitative assessment of the friction and wear behaviour of plain bearings under minimum quantity lubrication conditions, the proposed research project therefore pursues the goal of developing a fundamental theoretical description of this problem on the bearing lengthscale in conjunction with the roughness lengthscale and validating this through experimental investigations. On a special mixed friction plain bearing test rig, friction values and surface changes over time are recorded at different degrees of minimum quantity lubrication and different load-speed combinations. The experimental micro-contact investigation using a pin-on-disc tribometer identifies the variable contact types and intensities that exist as a function of the amount of lubricant present in the gap. The results of these investigations are incorporated into specific models for microcontacts in order to enable predictability of the tribological contact parameters by means of suitable model extensions, including for material rearrangement. The findings of the aforementioned steps represent the input into an extended calculation procedure for the macro level of the sliding bearing contact, whose iterative algorithms have to be optimised for the questions to be investigated. The research results of this project provide significant progress in the field of minimum quantity lubricated contacts and are also transferable to other tribological systems due to the choice of general model descriptions.

• DFG Programme: Research Grants