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

工业使用中损坏的滚子轴承在滚子和滚圈之间的润滑接触处表现出电蚀和电流流动。这些承受力破坏导致了巨大的经济损失。由于变流器的使用越来越多，电流缺陷轴承的损坏数量将大幅增加。电流在轴承中流动的结果是在轴承表面形成凹坑，然后在表面形成凹槽，称为凹槽。在许多情况下，润滑剂也被损坏，或者至少改变了它的润滑行为。这些损坏导致轴承的寿命结束，比计算寿命结束的时间要早很长。过去几年的研究有助于确定不同的损害影响。研究发现，这两种损伤机制是重要的。如果轴承在隔离润滑膜下运行，则可能会发生电火花加工效应(EDM)，即润滑膜被电弧冲压。弧形会在轴承套圈上产生凹坑，这可能会导致凹槽。如果还没有形成完全隔离的润滑膜，那么第二种机制就起作用了。在这种情况下，电流通过金属接触区域流动。在这些混合摩擦条件下，非常靠近电流流动区域的润滑剂会被热负荷损坏。润滑剂被烧毁，轴承失去了预期的寿命。从微观角度看，与赫兹理论计算的名义接触面积相比，实际接触面积要小得多。这导致在局部接触区域中有更大的电流流动。到目前为止，还不知道与这一接触区域相关的水流有多强。因此，润滑剂的损坏机理尚不清楚。本项目致力于混合摩擦条件下荷电滚子轴承的研究。因此，需要通过仿真来确定载荷相关和表面相关的局部接触区域。由于这种对实际接触面积的评估，可以确定滚子接触中的电流密度。局部极高的电流密度和高温作用于附近的润滑剂。在该项目的工作计划中，主题将包括模拟和实验，以了解轴承-润滑剂系统的表面特性和热、流体动力、机械和电气行为之间的相互依赖关系。该项目的目标是开发一种局部改进的模型来分析摩擦-电气系统，并调查轴承和润滑剂的电流负载接触区域。作为电流负载结果的润滑剂的化学相互作用的研究并不是研究项目的重点。

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.