Abstract
Observation on the logarithmic decay of the levitation forces is important not only to evaluate the bearing performance, but also to clarify the influence of the flux creep on the force relaxation in YBCO superconductors. The study on magnetic bearings is pursued on the superconductors from the view of industrial-scale application. The levitation force and the magnetic flux density in the bearing gap are measured on two disc-type superconductors as a function of time at 77K. The measured results clearly show strong dependence of the loading hysteresis on levitational force relaxation. On applying the increased load on virgin state of the superconducting bearing, the gap length logarithmically decays and the absolute value is relatively large. Almost no change, however, is observed in the levitation forces when the load changes backward slightly from the last load value. Long term stability of the superconducting bearing will much more be improved if such an operational condition is adopted in practical use.
