Magnetic Flux Controllers in Induction Heating and Melting
MAGNETIC FLUX CONTROLLERS are materials other than the copper coil that are used in induction systems to alter the flow of the magnetic field. Magnetic flux controllers used in power supplying components are not considered in this article. Magnetic flux controllers have been in existence since the development of the induction technique. Michael Faraday used two coils of wire wrapped around an iron core in his experiments that led to Faraday’s law of electromagnetic induction, which states that the electromotive force (emf) induced in a circuit is directly proportional to the time rate of change of the magnetic flux through the circuit. After the development of the induction principle, magnetic flux controllers, in the formof stacks of laminated steel, found widespread use in the development of transformers for more efficient transmission of energy (Ref 1, 2). Magnetic cores gained widespread use in the transformer industry because they increased the amount of magnetic flux produced with the same alternating current. The higher the magnetic flux, the higher the emf, which results in an increase in energy transfer efficiency from the primary winding to the secondary winding. Similar to transformers, magnetic cores were used on early furnaces for induction melting (Ref 1, 2). The benefits of magnetic flux controllers vary depending on the application. For induction heating, magnetic flux controllers can provide favorable and unfavorable paths for magnetic flux to flow, resulting in increased heating in desired areas and reduced the heating in undesirable areas, respectively. Magnetic flux controllers are not used in every induction heating application, but their use has increased (Ref 3, 4).
Magnetic core loss behavior at high fields in magnetic materials
Many induction heating coils use soft magnetic composite materials (SMCs) to improve induction system performance. In demanding induction heating applications, the core loss in the soft magnetic composite material is one of the critical factors in predicting the reliability of the induction coil using computer modelling. In this paper we have used calorimetry method for experimentally determining core losses in SMCs up to ≈1 T magnetic flux densities at a frequency near 150 kHz. This paper contains a discussion on the limitations of current methods for calculating core losses. To address these limitations, a new method for calculating core losses is presented. Using the new method, the results of the core loss measurement did not fit well with traditional core loss models over the full range of magnetic flux densities. A discussion on the different models and a hypothesis for the source of the variation from the models is presented. INTRODUCTION SMCs are used on many different types of induction heating coils. One of the important factors in the design and optimization of a reliable induction heating coil is the accurate calculation of power losses in the soft magnetic composite materials. In order to properly model induction coils with SMCs, it is critical to understand the magnetic core loss behavior over the entire operating range of induction heating conditions. The source of heat generation or the magnetic core loss in SMCs can be divided into two main categories: Hysteresis losses (h) and eddy current losses. The eddy current losses can be further divided into individual particle eddy current losses (ipe), local eddy current losses (local) and global eddy current losses (global). The total power loss is the sum of these losses [1]. Ptotal = Ph + Pipe + Plocal + Pglobal (1) For proper characterization of a magnetic material, it is desirable to make a measurement of the non-geometry dependent components of core loss (hysteresis and individual particle eddy currents). Computer modeling software is appropriate for calculation of local eddy currents and global eddy currents in the core used on an induction heating coil. For many decades, empirical equations have been used to statistically fit the experimental data to provide estimates of core losses in the materials. In 1892, Steinmetz [2] proposed an equation to fit power loss with magnetic field, given by
Garnitures mécaniques d'étanchéité
Keywords: etancheite ; mecanique Reference Record created on 2005-11-18, modified on 2016-08-08