Design of a foil-coiled inductor for the heating of steel wires

The main advantage of induction heating over other electroheating methods resides in its speed and efficiency of heating. In some cases, however, practical constraints can make high efficiencies hard to obtain by using classical solenoid inductors. Therefore, the design of a foil-coiled inductor as a possible alternative for classical coils is presented. This inductor consists of a wide thin copper sheet that is coiled around an insulating central tube. When studying classical induction coils, it is sufficient to consider only one turn. This leads to relatively small finite element models. A similar approach is not possible in the case of the foil-coiled inductor. To avoid very large models, the foil-coiled inductor has been studied by using two small and complementary models. One of these represents the end part of the inductor; the other one represents the middle section. Both non-linear time-harmonic electromagnetic calculations and coupled thermal electromagnetic calculations have been performed on these models. The results of these calculations allowed a prototype coil to be constructed and measurements were carried out on an experimental set-up. The match between calculations and measurements was satisfactory.