NORMAL-MODE AND LUMPED MASS ASSESSMENT OF ACOUSTIC DEGASSING OF LIQUID METALS IN AN INDUCTIVELY HEATED CYLINDRICAL FURNACE

摘要

In a number of aerospace materials processing applications, including float zone refining of electronic materials, forming of metallic glasses and induction melting of light alloys, time-dependent electromagnetic forces associated with the processing are found to influence surface shape, nucleation of precipitates, evolution of crystal nucleation sites, segregation of alloy components, grain refinement and degassing. For this last action, which finds its prime occurrence in specially designed induction furnaces, the scale up from test stand to prototype is especially sensitive to a detuning that can occur when a common set point is sought for optimizing the concomitant electrical and mechanical performance of the system. This paper outlines a continuum based model that can be used to identify a favorable set of operating conditions so that an effective and efficient, electromagnetically-induced vibrational degassing operation can proceed within the furnace. The optimization metric utilizes a coupled magnetoacoustic system of governing equations, which is subsequently solved to obtain the dynamic response of a molten metallic to an eddy current-type excitation. The solutions display both a transient and steady state response, as well as eigenmode and eigenfrequency characteristics which capture both the spectral signatures of the furnace as well as the optimum operating conditions for degassing. The solutions are obtained with the aid of higher transcendental functions of Bessel type, generated within a MATLAB environment. A set of operating conditions is identified which would promote optimal degassing for light alloys in commercial size induction furnaces. The magnetic field model embedded in the solution is sufficiently general to allow for use in analyzing a DC field biasing method which has recently shown promise for use in grain refinement and metallic glass forming applications for which the characteristics of the vibrational field can be utilized to effectively diminish crystal nucleation.