Method of Determining the Temperature Characteristics of the Thermal and Electrical Properties of Conductive Materials on a Stand for Induction Heating

Abstract

In induction heating processes, knowledge of the charge material parameters, i.e., thermal conductivity and volumetric heat capacity, as well as resistivity and magnetic permeability, is important both at the stage of preparatory process simulations and during their implementation. The paper presents a measurement method for estimating the thermal diffusivity, volumetric heat capacity, and resistivity of the charge material as a function of temperature on a single measuring setup, using a generator for induction heating as the source of signals. The method is based on the study (for forced temperature levels) of the temperature responses of cylindrical samples of the test materials and the voltage induced in the designed measuring coil after short- or long-term step excitation impulses. The presented approach enabled the dedicated computer-controlled system to obtain the initial values of the searched parameters with an accuracy of several percent. The procedure constitutes an introductory step in the simultaneous determination of a set of searched characteristics, and, by performing measurements, significantly narrows the range of variability in the decision variables of the optimization process.

An Inductive Method for Comprehensive Estimation of Temperature-Dependent Electrical and Thermal Properties of Conductive Ferromagnetic Materials

“…A set of basic measurements will be carried out on a test stand containing an IHS induction heating system (inductor-charge), which constitutes the equivalent R IHS resistance and L IHS inductance for the generator powering it. After the analyses [11], the use of a cylindrical inductor-charge system was adopted, in which the tested material sample constituting the charge has the shape of a cylindrical disc, as shown in Figure 2a. A view of the actual IHS is shown in Figure 2b.…”

“…The basic analysis of the possibility of using IHS from Figure 2 to estimate the temperature characteristics of the sought thermal and electrical properties of conductive materials, including ferromagnetic ones, was based on simulation calculations based on the FEM finite element method. [11], the use of a cylindrical inductor-charge system was adopted, in which the tested material sample constituting the charge has the shape of a cylindrical disc, as shown in Figure 2a. A view of the actual IHS is shown in Figure 2b.…”

“…By analysing conductive non-magnetic materials [11], it was found that in the system in Figure 2a, it is possible to use the modified Flash method [12][13][14][15][16][17] to estimate the thermal diffusivity of a cylindrical sample of the tested material. The application of the Flash method in the considered inductor-charge system consisted of implementing, using the system from Figure 2c, excitation in the form of short 20 or 10 millisecond pulses of the inductor current with a frequency of f = 40 kHz and RSM values of I = 1100 and 1550A, respectively.…”

“…On the other hand, growing technological requirements increasingly lead to the need for precise, reliable information about the properties of the processed material, which leads to the need to verify them in situ. The importance of the problem raised is confirmed by numerous publications [2][3][4][5][6][7][8][9][10][11], in which the issue of the possibly simplest and quickest way to determine material properties is considered, preferably several at once using one measurement station. The cited literature examples mainly concern attempts to determine thermal properties, that is, thermal diffusivity and volumetric heat capacity.…”

“…This allows for a very significant reduction in the range of variability of these parameters, the exact value of which can then be determined in the procedure of solving the inverse heat conduction problem (for example, in [8,9]), where a comprehensive multi-factor analysis is performed. A full development of this approach using the induction method as a source of excitation was presented for conductive, non-magnetic materials in [11]. Due to the significant influence of magnetic permeability on the effect of inducing eddy currents in the tested material, the method presented there cannot be directly transferred to ferromagnetic materials.…”