Magnetic Shielding of Levitation Melting Devices.

Magnetic shielding of levitation melting induction heating devices does not only reduce the stray field of the device; it has also an influence on the position of the workpiece. The aim is to investigate the change in magnetic field, and the change in steady-state position of the workpiece caused by adding copper or soft magnetic shields to the device. The calculation of the force on the workpiece and the magnetic field around the induction heater is done by either a 2-D or 3-D finite element model, or by a circuit model combined with analytical expressions for the magnetic field and the force. By adding an axisymmetric copper shield surrounding the inductor (shielding by induced currents), the levitated workpiece moves downward, for the same excitation current. By adding a nonaxisymmetric wall of soft magnetic ferrite tiles at one side of the induction heater (shielding by flux-shunting), the workpiece moves upward, and it shifts away from the axial symmetry axis. [ABSTRACT FROM AUTHOR]