A gas cushion for highest purity and lowest maintenance: Gas bearings not only increase the lifetime but also enable complete oil-free operation. With Celeroton gas bearings this is also achievable at the highest possible speeds for various gases.
Gas bearings have appeared throughout the history of drive systems in several places. They had a first commercial success in the application of foil bearings in aviation and aerospace in the 1950s and 60s. Common synonyms for gas bearings are the terms “fluid bearings” or often simplified “air bearings”. This means that the bearing of, say, a rotor-stator-system is formed from a thin gas cushion between the rotor and the stator case. To establish the required lifting power, an overpressure is built in the gas cushion, which increases with deflection. The gas exerts force against the deflection of the rotor and keeps it in the centre of the stator case, and therefore ensures a contactless bearing of the rotor from the stator. The main required technical characteristic of the gas cushion is having the correct stiffness and damping in order for the gas cushion to absorb disruptions such as unbalance and vibration. The following figures show profile examples of a gas bearing and a ball bearing rotor.
Basically, there is a difference in how the pressure can be built-up by the gas cushion. On the one hand there is the so called externally pressurized gas bearing and on the other hand there is the self-acting gas bearing.
The pros and cons of gas bearing technology compared to ball bearings can be summarised as follows:
An extended comparison of different bearings technologies can be found here.
The behaviour of a gas bearing is strongly dependent on the viscosity of the gas in the bearing clearance. The viscosity again is dependent on temperature of the gas and the gas itself. The gas bearing is designed to run stably over the expected range of these parameters and throughout the entire speed range and with a range of manufacturing tolerances (e.g. the lowest gas bearing clearance can be critical at high temperature and maximum speed or the largest bearing clearance at minimum temperature at medium speeds). Furthermore, the gas bearing is designed to withstand the required maximum shock and vibration levels throughout the entire speed range (where low speeds are usually more critical than high speeds).
The specific challenges in designing a high-speed turbo compressor with gas bearings:
The design challenges increase significantly with increasing the rotational speed. The following considerations are needed:
An air bearing as in the Celeroton turbo compressor CT-2X-series for the supply of air to fuel cells, is designed according to the expected viscosity, temperature, and pressure range during operation, but only for air. For a gas other than air, e.g. noble or inert gases, which has a different viscosity, the gas bearing behaviour is different, and therefore the compressor that designed for air is usually not directly applicable. However, the gas bearing can be adapted to the new gas properties and operating specifications. For the Celeroton turbo compressor CT-NG-2000, which is operated with different inert and rare gases, there are gas bearing designs already available for several gas types.
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