68 International Scientific Colloquium Modelling for Material Processing Riga, June 8-9, 2006 Laboratory Prototype of Double Frequency Longitudinal Electromagnetic Levitator for Levitation Melting M. Bullo, F. Dughiero, M. Forzan, S. Lupi Abstract Longitudinal electromagnetic levitators (LEL) have been proposed and studied for many years. In spite of these studies the configuration with double frequency supply has been taken into consideration only in few papers. Aim of this work is the presentation of some new results obtained at the Laboratory for Electroheat of Padua University by numerical calculations and experiments on a double frequency LEL prototype. Introduction Longitudinal electromagnetic levitators consist of a set of exciting conductors, parallel to the axis of a non-magnetic cylindrical levitating load, carrying large high-frequency currents [1,2,3]. The exciting conductors are constituted by copper tubes appropriately end- connected in order to give rise to a convenient alternating electromagnetic field distribution. The currents induced in the cylindrical load by this field, interacting with it, generate Lorentz forces that support the sample against gravity and at the same time produce its heating due to Joule losses. The two phenomena (levitation and heating) are closely coupled together, but different optimum frequency values exist for each of them corresponding to their maximum intensity [4]. The existence of these distinct optimum values offers the possibility of designing levitation systems with separated heating and levitating coils excited at two different frequencies which optimise the heating and the levitation effects respectively. At the Laboratory for Electroheat of Padua University (LEP) longitudinal electromagnetic levitators have been studied in the last years. A single frequency laboratory prototype has been first analysed and constructed and preliminary studies of a double-frequency LEL have been developed [5,6,7]. This prototype has been now modified in order to be able of supplying different levitation and heating conductors with two frequency values with the aim of verifying by experiments the reliability of the calculation models for LEL design purposes and obtaining general guidelines for the design and optimisation of a new prototype with double-frequency excitation. 1. Laboratory prototype and geometry used for calculations The laboratory prototype available at LEP, already described in [5], corresponds to the basic geometry of the exciting conductors and the experimental set-up shown in figure 1; they are made of water cooled copper tubes 6x6x2 mm cross-section, whose barycenter positions – with reference to an origin placed on the symmetry axis and the upper surface of the lower conductors – are given by the coordinates given in table I.