Southwest Research Institute (SwRI), a San Antonio-based nonprofit and applied research and development organization, has designed and built a 60000rpm gas bearing test rig to test the rotordynamic stability of gas bearings.

The test rig consists of two coaxial shafts capable of rotating at different speeds. The outer shaft, driven by an electric motor, rotates inside the foil air bearing and is responsible for generating the hydrodynamic pressure that supports the rotating shaft.

The inner shaft excites the vibration in the shaft system by using end discs where unbalance can be added and adjusted easily. Its speed is controlled by an eddy current brake system.

The bearing undergoing evaluation is supported by a cantilever bearing housing that prevents pitching of the bearing and allows the bearing to transmit forces to load cells mounted in the horizontal and vertical planes.

Two accelerometers mounted on the bearing housing measure the inertial forces of the bearing in the horizontal and vertical planes, and proximity probes measure the relative displacement. A patent is being pursued on the concept.

According to the research institute, gas bearings have many advantages over traditional oil-lubricated or rolling-element bearings. The gas bearings typically have a longer life span, can accommodate high shaft speeds and can operate over a range of temperatures. And because there are no lubricants, there is no process contamination.