Touch-down bearings

Abstract

Magnetic bearings have a load capacity which is defined by design and limited in size. If the actual load surpasses this load capacity, or if the magnetic suspension fails to work for any reason, the rotor will not hover freely any more but will touch its mechanical boundaries. In order to avoid damage to the rotor laminations and the AMB stator during such a touch-down the rotor is equipped with touch-down bearings. These are an additional set of passive bearings, and the rotor will only come into touch with them in extraordinary situations. In literature they are also known as retainer bearings, or in a more general way as back-up or auxiliary bearings. For such touch-down bearings, usually simple retainer rings or special ball bearings are used. They should be able to support the rotor for a limited time period until the normal operating mode can be recovered or until the rotor can run down safely. In addition to that, at zero power to the AMB, the rotor rests on the touch-down bearings, which allows the rotor to be rolled over easily, for inspection and maintenance. © 2009 Springer-Verlag Berlin Heidelberg.