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This paper presents the results of a series of tests made in order to validate the magneto‐thermal module of the new FLUX3D v3.40. The tool was conceived to solve the coupled problems of electromagnetic and thermal phenomena. The solving method of the program considers a thermal‐transient problem during a certain period of time and it solves, at each time step, the thermal and electromagnetic equations (in quasi‐stationary magneto‐harmonic formulation), alternatively. We have modelled the inductive longitudinal welding of steel pipes. The results of 3D simulations are compared with measurements on a laboratory device.

The paper presents the results of computer simulation of the process of induction heating with series transistor inverter. In the simulation of induction heating system the coupled harmonic electromagnetic and transient thermal fields were combined with the simulated real energy source. As a source, the transistor bridge inverter with series resonant circuit was applied. The source parameters (inductor voltage and frequency) depend on the load parameters obtained by numerical calculations of the coupled fields. As the examples, the induction heating before hardening of stationary cylindrical workpiece and of the moving flat workpiece were considered. The simulation results were compared with these obtained in the simulation at constant inductor voltage and frequency.

Effect of unstable “wavy” temperature distribution on the part surface during the process of induction heating of ferromagnetic materials was observed and reported by two Russian scientists in 1940 (Babat and Lozinskii, 1940). They reported that under certain conditions, one can observe periodical or quasi-periodical bright stripes on the part surface when its temperature passes through the Curie point. In time, these stripes expand and merge, forming a normal temperature pattern. They called this phenomenon “polosatiy nagrev” (striation heating). Let us call it the “zebra effect” for simplicity. It can exist for a relatively long time, from several seconds to several tens of seconds. Several explanations of the zebra effect were proposed with not very convincing arguments. The purpose of this study is to improve the understanding of this effect.

Wider spreading of induction technology and use of computer simulation of induction processes create a demand and open new possibilities for study of the zebra effect. This study provides an overview of the available information about the zebra effect and gives new explanation of this phenomenon based on existing experimental data and new results of simulation. Conditions for zebra occurrence and its technological importance or limitations are discussed.

Computer simulation using the Flux 2D program allows to demonstrate the striation (zebra) effect that can appear in the process of heating magnetic materials and reproduce main experimental findings related to this effect. Simulation provides a great opportunity to investigate the zebra phenomenon in virtual reality, providing qualitatively correct results. Results of simulation show that the zebra effect can appear in a relatively narrow range of material properties and operating conditions. The main factor is a big enough gradient of permeability near the Curie point. At present, it is difficult to expect high quantitative accuracy of simulation due to multiple assumptions in simulation algorithms and insufficient or inaccurate information about the material properties near the Curie point.

Several explanations of the zebra effect were proposed with not very convincing arguments. There were concerns that the zebra effect could set significant limits on the use of induction heating for surface hardening due to non-uniform temperature distribution along the part (Babat and Lozinskii, 1940; Babat, 1965; Lozinskii, 1949, 1969). However, it did not happen. There were no complaints from scientists or practitioners regarding any negative effect of the zebra phenomenon. Moreover, the authors of this paper did not find any original publications on this issue for more than half a century. Only few old induction experts confirm that they observed the zebra effect or something similar, whereas a great majority of induction community members never heard about it.

The aim of this paper is to simulate, test and evaluate an induction heating process considering the converter's performance.

In case of continuous induction hardening processes, the load changes abruptly during the transition to Curie temperature, becoming significant considering the converter's behavior. In this paper, an induction heating system is simulated combining the numerical analysis of the electromagnetic‐thermal and electrical problem, focusing mainly on the converter's performance. The simulations are realized by using commercial FEM software and the voltage and the frequency are manually varied according to the converter's control. The system has also been implemented in an experimental setup and the results obtained have been compared with the simulations.

The importance of considering the converter's dynamics was observed during the simulations. The simulation results showed a correspondence with the experimental results, validating the simulation procedure and demonstrating that the converter's behavior has to be considered.

A power converter for a real industrial induction heating process where there is a sudden change in the load parameters is simulated and experimentally tested. The importance of considering the variation of frequency and voltage during the simulation of induction heating systems is demonstrated. Some considerations for induction heating modeling regarding converter's performance are given and the importance of converter's dynamics is introduced. In addition, a simple and flexible method of simulating the converter operation with commercial software is presented.

Temperature dependence of magnetic susceptibility has been approximated by the extension of Curie‐Weiss law to ferromagnetic states. Application of similar relations to other properties and corresponding model parameters of magnetic materials would enable thermal analysis of circuits containing ferromagnetic cores.

The majority of binders used in paint manufacture are either highly‐viscous or solid materials in their own right. The identification of their chemical constituents has been reported by Haken (71) using infrared spectroscopy at liquid nitrogen temperature. However, the procedure proved to be very expensive since a great deal of breakage of the equipment occurred owing to the need to keep cooling and then reheating to room temperature. A better procedure was considered to be fragmentation of the initial polymer samples to give volatile fractions better suited to GC examination, which was just as accurate as the spectroscopic approach and far simpler and cheaper to carry out.

It is not normally possible to heat a static steel work‐piece past the Curie temperature without incurring reduced inverter utilisation. Since the inverter cost increases with rated power, reduced utilisation implies an increase in investment costs for a given performance. The paper shows that third‐order resonant work‐head circuits can intrinsically allow better utilisation of the inverter for variable‐load heating operations. A further refinement is then shown to allow control of the load impedance, thereby allowing the utilisation to approach 100 percent over the heating cycles.

The inorganic high‐luminosity electroluminescent (EL) panel used in this study is a distributed‐type EL panel, which can be produced using a printing technique. We obtained a panel with a high luminosity of 7940 cd/m2 at 6 kHz. In addition, we believed that the panel temperature and luminosity of this panel were closely related. Therefore, we considered the relationship between the temperature change in the dielectric layer and the luminosity since this relationship is responsible for the supply of electric charge to the phosphor layer. A change in the amount of electric charge by heating in a high‐voltage domain originates at the Curie point of BaTiO3 ferroelectric particles. This indicates that the influence of BaTiO3 was strong.

This study aims to investigate the feasibility of saturated AC heating of magnetic metals. In AC heating of magnetic steel below the Curie temperature, because of the high magnetic permeability, the penetration depth is in the order of 1-6 mm at 50 Hz. Surface heating is then obtained, in practice, if large slabs are processed. The necessity to provide the required surface-to-core temperature uniformity (about 25°C) at the end of the heating process, avoiding excessive thermal stresses which can lead to cracks, thus implies a long heating time.

The penetration depth can be increased if the material is brought to saturation by applying an external DC magnetic field, and a faster in-depth heating can be obtained. The DC saturating field can be produced with no losses over large volumes by means of superconducting (SC) coils.

The feasibility of in-depth induction heating of a 200 × 1,000 × 5,000 mm magnetic steel slab with an applied 2 T DC saturating field is numerically investigated. The results show that the use of a DC saturating field leads to shorter processes which fulfil the heating objectives.

A DC saturating field cannot be produced by means of copper coils because of the large amount of material and the unaffordable power required. However, this field can effectively be produced by means of SC magnets based on state-of-the-art materials.

Superconductivity may be the enabling technology for fast and efficient induction heating of magnetic steel slabs if the increase in productivity can balance the additional costs due to the SC magnet.

The purpose of this paper is to investigate the effect of Mg²⁺substitution on the magnetic and electrical properties of Li_0.35−x Mg_2x Zn_0.3 Fe_2.35−xO₄ thick films synthesized with polyvinyl alcohol (PVA) matrix.

The nanoferrites Li_0.35−x Mg_2x Zn_0.3 Fe_2.35−xO₄ (x=0, 0.07, 0.14, 0.21, 0.28 and 0.35) were synthesized by chemical technique using aqueous solution of PVA (the matrix) and thick films were fabricated by screen printing technique. The DC magnetic hysteresis measurements, AC magnetic susceptibility and DC electrical resistivity were measured as a function of temperature.

The lattice parameter of thick film Li_0.35−x Mg_2x Zn_0.3 Fe_2.35−xO₄ (x=0, 0.07, 0.14, 0.21, 0.28 and 0.35) increases with the substitution of Mg²⁺ions for Li¹⁺and Fe³⁺. The surface morphology of the thick films showed the grain size increasing with Mg²⁺substitution till x=0.21 and then decreasing for the higher concentrations of magnesium. The magnetic moment n_B (μ_B) computed from the M_s obtained by extrapolation of the magnetization curve showed a gradual decrease with the composition till x=0.21, beyond which a sudden decrease was observed. The resistivity of the films at room temperature had variation with composition x, similar to that of magnetic moment. The activation energies ΔE_F and ΔE_P were found to vary with composition x of the ferrite system.

The paper reports, for the first time, the magnetic and electrical properties of fritless Li_0.35−xMg_2xZn_0.3Fe_2.35−xO₄ thick films using PVA polymer matrix. Up to x=0.21 (Mg²⁺), grain size increases and Curie temperature decreases beyond which reverse effect takes place.