Contactless ultrasonic treatment of melts using EM induction

Ultrasound Treatment (UT) is commonly used in light alloys during solidification to refine microstructure, or disperse immersed particles. A sonotrode probe introduced into the melt generates sound waves that are strong enough to produce cavitation of dissolved gases. The same method cannot be used in high temperature melts, or for highly reactive alloys, due to probe erosion and melt contamination. An alternative, contactless method of generating sound waves is proposed and investigated theoretically in this paper, using electromagnetic (EM) induction. In addition to strong vibration, the EM induction currents generate strong stirring in the melt that aids distribution of the UT effect to large volumes of material. In a typical application, the same induction coil surrounding the crucible used to melt the alloy may be adopted for UT with suitable frequency tuning. Alternatively - or in addition - a top coil may be used. For industrial use, instead of multiple sonotrodes as has been the practice in scaling up, modelling shows that one simply has to alter the coil geometry and current to suit. To reach sinusoidal pressure fluctuations suitable for cavitation it may be necessary to tune the induction coil frequency for resonance, given the crucible dimensions.