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道之间的润滑接触中显示出电侵蚀和电流流动。这些轴承损坏导致了巨大的经济损失。由于变频器的使用越来越多，电流缺陷轴承的损坏数量将大幅增长。电流在轴承中流动的结果是轴承表面上的弹坑和后来的表面上的凹槽，称为凹槽。在许多情况下，润滑剂也被损坏或至少改变其润滑行为。这些损坏导致轴承的寿命结束，在计算寿命结束之前很长一段时间。过去几年的研究有助于确定不同的损害影响。结果表明，两种损伤机制是重要的。如果轴承在绝缘润滑膜下运行，则可能发生电火花加工效应（EDM），其中润滑膜被电弧冲压。弧在轴承座圈上产生凹坑，这可能导致凹槽。如果没有形成完全隔离的润滑膜，则第二种机制正在工作。在这种情况下，电流流过金属接触区域。在这些混合摩擦条件下，非常靠近电流流动区域的润滑剂被热负荷损坏。润滑剂燃烧，轴承失去其预期寿命。从微观角度看，与赫兹理论计算的标称接触面积相比，真实的接触面积要小得多。这导致在局部接触区域中的大得多的电流流动。到目前为止，还不知道与该接触区域相关的电流有多强。因此，润滑剂的损坏机制尚不清楚。本项目致力于研究混合摩擦条件下的充流滚子轴承。因此，需要通过模拟确定取决于载荷和取决于表面的局部接触面积。通过这种对真实的接触面积的评估，可以确定在滚子接触中的电流密度。局部非常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，主题将涵盖模拟和实验，以了解轴承润滑剂系统的表面特性和热，流体动力学，机械和电气行为的相互依赖性。该项目的目标是开发一个局部细化的模型来分析摩擦电系统，并研究轴承和润滑剂的电流负载接触面积。研究润滑剂的化学相互作用作为电流负载的结果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.