Axial Air-Gap Motor for Liquid-Metal-Bearing Test Rig

A test rig for liquid-metal-bearing development required a motor drive. The initial test rig utilized liquid potassium. at temperatures up to 600° F for the working fluid. A conventional two-pole induction motor with standard bearings was first used as a drive motor. It required shaft seals which were separated by an argon barrier; however, leaking seals and potassium, contamination due to seal wear and the motor bearing lubrication presented a large problem. For a liquid-mercury test rig it was decided that the drive motor should be directly coupled to the test bearing shaft. This led to the development of an axial air-gap, unskewed motor. The windings were to be sealed in epoxy-glass laminate, but the rotor was to be exposed to the mercury vapor. Such a motor was built and tested, and proved to be so successful that a second motor was built and adapted to the liquid-potassium-bearing test rig.