The Contactless Electromagnetic Sonotrode

Ultrasonic pressure waves generated using a tuned electromagnetic induction coil promote cavitation in alloy melts as an alternative to the immersed sonotrode technique. The method targets the same benefits offered by traditional UST (degassing, microstructure refinement, dispersion of particles), but without some of its drawbacks. The method is contactless, meaning it can be applied equally to high temperature/reactive melts, avoiding contamination due to probe erosion, and consequently, it is maintenance free. Due to induction stirring, larger volumes of melt can be treated (a major limitation of the traditional method), as the liquid is forced to pass repeatedly through zones of cavitation activity. The coil configuration used will depend on application. In the installation shown, a top conical coil immersed in aluminium melt (contactless due to EM repulsion) was used. Simulations of sound, flow and EM fields are given, compared with experiments and indicating strong stirring, evidence of cavitation through emitted sound signals and, most importantly, grain refinement.