Theoretische und experimentelle Untersuchungen an ebenen aerostatischen Gaslagerelementen unter Hochvakuumbedingungen (English shop)

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The thesis presents results of theoretical and experimental fundamental investigations on planar rotationally symmetric gas bearing elements that can be used directly in a high-vacuum environment. The aim of the work is to contribute to the development of gas guides suitable for high vacuum. The investigations focus on orifice bearing elements with micro distribution channels and porous bearing elements. Sealing systems integrated into the bearing elements almost completely remove the continuously inflowing gas required to form the load-carrying lubricating film. Due to the evacuation of the gas, a transition from continuum flow to molecular flow takes place in the load-carrying gas film. For dimensioning the bearing elements, a simple numerical model is developed which, by taking this transition into account, enables the design of the bearing elements for any ambient pressure. Extensive calculation tools are also provided for the design of the sealing system. It is shown to what extent the characteristics of both types of bearing element are changed by the sealing system and the vacuum environment compared with operation under normal atmosphere. In a comparison, good load-carrying properties and very low leakage rates <0.3 µlN/min are demonstrated for both types of bearing element in high vacuum at 10-7 mbar. The theoretical results are confirmed very well by the experimental investigations. For both types of bearing element, possibilities for optimising the static properties are analysed which arise from a modification of the restrictor parameters or from the use of special gases. It is shown experimentally that the bearing elements, which operate stably at normal atmosphere, tend towards self-excited vibrations in vacuum once a stability limit is exceeded. The occurrence of the stability limit is explained theoretically and the influence of various factors on the stability limit is analysed. Likewise, the outgassing rate produced on various materials, which occurs during a translational relative motion between the bearing element and the counterpart used, is determined in experimental investigations. The work succeeds in successfully demonstrating the possibility of using gas bearing elements directly in a high-vacuum environment. Design guidelines are derived from the investigation results which lead to good load-carrying properties, low leakage and outgassing rates and stable operating behaviour of the bearing elements.