Model for determination of thermal loads of the lubricant due to the mechanical and electrical loading in roller bearings

• Applicants: Professor Dr.-Ing. Andreas Binder; Professor Dr.-Ing. Bernd Sauer
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 407468812

Damaged roller bearings from industrial use show electric erosion and current flow in the lubricated contacts between roller and races. These bearing damages lead to enormous economic losses. Due to the increasing use of converters the number of damages of current-defected bearings will grow strongly. The results of current flow in the bearings are craters on the bearing surfaces and later grooves, called fluting, on the surfaces. In many cases also the lubricant is damaged or at least changes its lubrication behavior. These damages lead to the life-time end of the bearing, long time before the end of calculated life-time. Research from the last years contributed to the identification of the different damage effects. It was found, that two kinds of damage mechanism are of importance. If the bearing is running under an isolating lubricant film, it is possible that the electric discharge machining effect (EDM) can occur, where the lubrication film is punched by an electric arc. The arc produces craters on the bearing races, which may lead to fluting. The second mechanism is working, if no fully isolating lubricant film has built up. In this case, the current flows by the metal contact areas. Under these mixed friction conditions the lubricant very close to the areas, where the current is flowing, is damaged by the thermal load. The lubricant is burnt, and the bearing loses its projected life-time. With a microscopic view the real contact areas are much smaller, compared with the nominal contact area, calculated by the Hertz´ian theory. This leads to a much bigger electrical current flow in the local contact region. Until now, it is not known how strong the current flow related to this contact area is. Due to that, the damage mechanism of the lubricant is not known in detail. The project is devoted to the research of the current-charged roller bearings under mixed friction conditions. Therefore it is required to determine by simulation the load-depending and surface-depending local contact areas. Due to this evaluation of the real contact area the density of current flow in the roller contact can be determined. The locally very high current density and the high temperature act on the nearby lubricant. In the working program of the project the topics will cover both simulation and experiments to understand the interdependency of surface properties and the thermal, hydrodynamic, mechanical and electrical behavior of the bearing-lubricant system. The goal of the project is the development of a locally refined model to analyze the tribo-electric system and to investigate the current-loaded contact areas of the bearing and of the lubricant. The research of the chemical interaction of the lubricant as a consequence of current loads is not in the focus of the research project.

• DFG Programme: Research Grants