A description is given of the design and operation of high-power magnetic drives developed to enable shaft seals and glands to be dispensed within deepculture vessels, in tissue homogenizers, and in mixing and filling processes where sterility is essential. The drives operate at speeds of 300 to 2000 rpm in volumes of 300 1. to 10 ml with clearances up to 16 mm between the pole faces of the magnets.
Two types of drive are described, one in which the driving and driven magnets form an integral unit on the lid of a vessel: such vessels are used for transporting material. To initiate stirring, it is only necessary to connect a motor directly, or through a cable-drive, to the magnetic-drive assembly. In the other type of unit the driving magnet is attached permanently to the driving motor. Locating pins on the base of the motor and corresponding sockets on the lid of the vessel ensure that when the motor is in position, the driving and driven magnets are located correctly in relation to one another.
The design of these drives is based on the use of multipole, ceramic magnets.
The advantages of their use in such units, compared with metal magnets, are discussed. Earlier magnetic drives are also discussed and explanations offered for the difficulties formerly met in scaling up.