Efficient melt mixing due to the combined action of a rotating and a travelling magnetic field

Various types of AC magnetic fields are already used as stirrers in liquid metal processing. We distinguish between rotating, travelling and pulsating magnetic fields depending on the coil arrangement and the number of phases of the coil currents. Considering the melt motion driven by each of these AC fields in a cylindrical cavity, the basic flow structures are well-known. As a common feature, they typically consist of a rather rigid flow configuration providing only a limited mixing of the melt. Instead a three-dimensional mixing is often needed in metallurgical applications, for instance, in order to dissolve alloying agents or to submerge lighter parts into the melt.

We report on model experiments for the electromagnetic stirring of liquid metals in a cylindrical cavity using a rotating and a travelling magnetic field. The eutectic melt InGaSn in a cylindrical cavity of aspect ratio 1.5 has been used. Velocity measurements are performed using both the ultrasonic Doppler velocimetry (UDV) as well as local potential probes. UDV delivers profiles of the vertical velocity component. In the case of the rotating magnetic field this component represents only a weak secondary flow compared to the primary azimuthal rotation. In case of a separate action of the two field types, the expected flow fields have been found. An efficient mixing can be obtained by a combination of the two field types. Velocity measurements will be presented demonstrating this behaviour.