Comparison between flat aerostatic gas-bearing pads with orifice and porous feedings at high-vacuum conditions

This paper presents an analytic model for the calculation of circular high-vacuum compatible gas-bearing pads with arbitrary feedings. The algorithms afford the reliable dimensioning of load-bearing properties as well as the required seal structures and the exhaust equipment. Theoretical and experimental investigations on orifice-bearing pads with micro-channel structure and porous bearing pads identify differences of characteristics in a high-vacuum environment compared to ambient conditions. At vacuum conditions, stiffness and gas load of the bearing pads are significantly degraded and the operating point of the orifice-bearing pad is shifted to larger gap heights. Gap height and gas load are identified as essential impact parameters for the gas leakage flow. Thus, the bearing pad design parameters have to be adapted for application in vacuum. Both investigated bearing pad types are comparably suitable for application at vacuum conditions. The gas leakage flow is analysed depending on the number of exhaust stages. With a single-stage exhaust system, high vacuum is already maintained in the test chamber. A second exhaust stage further reduces the gas leakage flow by two orders of magnitude.