Effect of a superimposed DC magnetic field on an AC induction semi-levitated molten copper droplet

While a piece of pure Copper on a ceramic substrate was inductively melted by 9 to 18 kHz AC magnetic field with axial magnetic DC field superimposed, the liquid metal stably semi-levitated in the expected “conical” free surface shape. The diameter of the liquid metal at the basis was 30 mm, the volume – more than 20 cm3. Replacing the ceramic substrate with a Glassy Carbon, which was not wetted by the molten Copper, caused instability of the semi-levitated Copper droplet. In the absence of the DC field severe chaotic instabilities of the liquid metal shape occurred, causing splashes and uncontrolled contact with crucible walls. When axial DC magnetic field with induction 0.35 T was superimposed the liquid metal droplet exhibited harmonic azimuthal wave deformation of the free surface. Higher frequencies lead to smaller characteristic wavelength. Transverse DC magnetic field direction suppressed the travelling wave deformations of the droplet shape. Stabilizing effect of the DC magnetic field during induction melting has been shown for axial, transverse and 45 degree direction magnetic field. These results experimentally demonstrate the possibilities to improve the stability of levitated metal volumes by superimposed DC magnetic field.