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

While a piece of copper on a ceramic substrate was inductively melted by a 9 to 18 kHz AC magnetic field with an 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 base was 30 mm, the volume more than 20 cm³. Replacing the ceramic sub-strate with a non-wetted glassy carbon crucible causes instability of the semi-levitated copper droplet. In the absence of the DC field severe chaotic instabilities of the liq- uid metal shape occurred, causing splashes and uncontrolled contact with the crucible walls. When an axial DC magnetic field with induction 0.35T was superimposed, the liquid metal droplet exhibited a harmonic azimuthal wave deformation of the free sur-face. Higher frequencies lead to smaller characteristic wavelength. The transverse DC magnetic field direction suppressed the travelling wave deformations of the droplet shape. The stabilizing effect of the DC magnetic field during induction melting has been shown for axial and transverse directions of the DC magnetic field. These results experimen-tally demonstrate the possibilities to improve the stability of levitated metal volumes by a superimposed DC magnetic field.