Electrically-Driven Magnetically-Supported Vacuum-Type Ultracentrifuge

Abstract

A large rotor or centrifuge, an armature, and a small iron rod are anchored coaxially one above the other, in the order named, on a small flexible shaft. The shaft passes through a vacuum‐tight oil gland which seals a vacuum‐tight chamber surrounding the large rotor. A direct current which energizes an electromagnet situated vertically above and coaxial with the iron rod is adjusted so that the pull on the iron rod is slightly greater than necessary to support all of the rotors. The extra lift is balanced by a slight thrust against the upper end of the shaft by an oiled bronze stop in the pole piece of the electromagnet. The adjustments are made to maintain a small air gap between the rotating iron rod and the stationary pole piece. The rotors are driven by a piezoelectrically‐controlled a.c. through the field of a single‐phase induction motor which surrounds the armature. Six‐inch centrifuges have been spun to over 1000 r.p.s. at very constant speed.