Induction Heating of Thin Strips in Transverse Flux Magnetic Field

Abstract

An idea of transverse flux induction heating has been well known for more than sixty years. Some of its main principles were presented for instance by Russian physicist Volovgin (Muhlbauer, 2008). Many papers on the topic considering mainly theoretical aspects of the task were published in the last sixty years (Baker, 1950), (Jackson, 1972), (Barglik, 1992), (Muhlbauer et al, 1995), (Tudorache & Fireteanu, 1998), (Nacke et al, 2001), (Dughiero et al, 2003). Usage of transverse flux induction heating system have been effective in case of thin strips of the thickness comparable with the depth of electromagnetic field penetration δ . It makes it possible to obtain required parameters of the process like: uniformity of temperature distribution within the workpiece and big total energy efficiency at rather low frequencies of the field current (in many cases also for mains frequency f = 50 or 60 Hz) in comparison with more often used classical induction heaters working with longitudinal magnetic field. The chapter deals with continual transverse flux induction heating of thin non-ferrous metal strips. The three-dimensional model used for the analysis was based on a system of non-linear differential equations for coupled electromagnetic and temperature fields that were solved by numerical methods. Development of the mathematical modelling of transverse flux induction heating as well as the computations by means of professional software and supplementary user codes reach quite a high level. But there is still a problem with the accuracy of calculations that was associated mainly with reliability of existing mathematical and numerical models with respect to the physical reality. The reason consists in various simplifications accepted for shortening the time of calculations and level of knowledge of temperature dependent material properties as well as convection and radiation heat transfer coefficients for the particular task. So the best way for obtaining data necessary for an optimal design and construction of induction heaters seems to be a numerical analysis supported by well planned experiments. Illustrative examples of continual transverse flux induction heating were analyzed. Results of numerical simulation were presented and compared with measurement data taken from laboratory stands. Quite good accordance between calculations and measurements was achieved. An illustrative example demonstrates that one of the ways making possible to obtain an uniform temperature distribution along the width of the workpiece could be a proper selection of suitable frequency of the field current.