Sergio Lupi

Experimental and Numerical Analysis of DC Induction Heating of Aluminum Billets

We have analyzed the characteristics of dc-induction heating of aluminium billets both numerically and experimentally and developed a numerical model for the calculation of the power and temperature distributions inside the billet during the heating. We validated the model by comparison with the experimental results from a laboratory-scale prototype using permanent magnets. We studied the heating process of a real scale system by means of the model, taking into account the weakening of the mechanical properties during the heating. We provide an example of design of an industrial scale dc induction heater.

Electromagnetic and thermal analysis of the induction heating of aluminum billets rotating in DC magnetic field

Purpose – The paper aims to deal with the induction heating of metal billets rotating in a DC magnetic field.Design/methodology/approach – The induced power distributions are analysed and the main heating parameters are estimated with reference to an infinitely long Al billet 200 mm diameter. The paper refers to the activity developed in the frame of a National Italian Project carried out by research groups of the Universities of Bologna, Padua and Roma “La Sapienza.”Findings – The main process parameters have been evaluated for the heating up to 500°C of an Al billet 200 mm diameter.Practical implications – This innovative technology appears to be very promising for improving the efficiency of the through heating of high‐conductivity metals (e.g. copper, aluminum) before hot working, by using superconducting magnets.Originality/value – The paper analyses the induction heating of a infinitely long billet rotating in a uniform DC magnetic field.

Comparison of edge-effects of transverse flux and travelling wave induction heating inductors

In this paper a comparison of the edge-effects in the induction heating of thin aluminium strips by transverse flux (TF) and travelling wave (TW) inductors at power frequencies is presented. The main attention is focused on the choice of the optimal position of the inductor relative to the strip for both systems in order to minimise the unevenness of power density distribution, both in the workpiece cross section and along the strip movement direction. The calculations of the electromagnetic field quantities have been made by 3D finite element models.

Optimal shape design of devices and systems for induction‐heating: methodologies and applications

The paper reports recent experiences of the authors in the automated optimal design of devices and systems for induction heating. The results presented have been obtained in the frame of a long‐lasting cooperation between Laboratory of Electroheat, University of Padova and Electromagnetic Devices CAD Laboratory, University of Pavia. In particular, two case studies are discussed; in both cases, the shape design of the inductor is carried out in a systematic way, by minimizing user‐defined objective functions depending on design variables and subject to bounds and constraints. When the design problem is characterized by many objectives which are in mutual conflict, the non‐dominated set of solutions is identified.

Numerical and experimental analysis of an electro-thermal coupled problem for transverse flux induction heating equipment

This paper describes a quasi 3D-FEM electromagnetic and thermal computation of transverse flux inductors used in the metal industry for the continuous heating of metal strips. The coupled steady-state eddy current and thermal problem is solved for the prediction of the temperature distribution in the workpiece, a fundamental step towards the optimum design of the inductors. The computation has been used for the design of a heater for the continuous heat treatment of golden or silver metal strips. The suitability of the method presented here for the optimum design of transverse flux inductors has been confirmed by measurements on a laboratory prototype with thin silver strips workpieces.

Multi–objective optimisation of induction heating processes: methods of the problem solution and examples based on benchmark model

The main goal of the researches is the development of new approaches, algorithms and numerical techniques for multi–objective optimisation of design of industrial induction heating installations. A multi–objective optimisation problem is mathematically formulated in terms of the typical optimisation criteria, e.g., maximum heating accuracy and minimum energy consumption. Various mathematical methods and algorithms for multi–objective optimisation, such as Non–dominated Sorting Genetic Algorithm (NSGA–II) and optimal control alternance method, have been implemented and integrated in a user–friendly automated optimal design package. Several optimisation procedures have been tested and investigated for a problem–oriented mathematical model in a number of comparative case studies. A general comparison of the design solutions based on NSGA–II and alternance method leads to their good agreement in all investigated cases. The methodology developed is planned to be applied to more complex real–life problems of the optimal design and control of different induction heating systems.

3D solution of electromagnetic and thermal coupled field problems in the continuous transverse flux heating of metal strips

In the design of induction heating systems, the prediction of thermal transients is very important. While for classical longitudinal flux configurations, thermal transients are predictable by classical theory formulae, on the contrary the thermal profiles in transverse flux heating have to be evaluated by experimental results on prototypes or by the use of numerical packages. In this paper, a method based on the use of 3D FEM packages for the electromagnetic and thermal design of transverse flux induction heating systems is presented. The method was used for the design of a heating system for the heat treatment of gold metal strips.

A new high efficiency technology for the induction heating of non magnetic billets

Purpose – Low electrical resistivity metal billets can be heated by the currents induced by the rotation of the billet itself inside a transverse DC magnetic field produced by a superconductive coil. The main drawback of this approach is related to cost of installation that requires an adequate refrigerating system. The purpose of this paper is to propose a more convenient solution, which allows the same high efficiency to be achieved at lower cost. In this solution, the billet is kept still and a series of permanent magnets, positioned in the inner part of a ferromagnetic frame, is rotated.Design/methodology/approach – Some results of the new induction system are shown. These results are obtained applying for the electromagnetic solution both an FE commercial code and an analytical method. The analytical code is developed because several parameters of the system need to be optimized.Findings – The performance of the solution presented is comparable with those of the system with superconductive coils. The...

Optimal design of an inductor for transverse flux heating using a combined evolutionary‐simplex method

Transverse flux induction heating (TFH) is a process advantageously applied for the heat treatment of thin non‐ferrous metal strips. In comparison with the better known longitudinal flux heating the design of TFH inductors is more complex. In fact both the prediction of power density distribution in the strip and the calculation of the thermal transient during the heating process require a solution of 3D electromagnetic and thermal problems. Moreover the requirements for a good inductor design are in conflict with each other. In the paper a code for the solution of 3D electromagnetic and thermal problems suitable for the design of TFH systems is presented. The analytical‐numerical approach (analytical for the electromagnetic problem, numerical for the thermal one) is suitable for coupling with optimisation algorithms. Both evolutionary strategy and simplex methods and their combination have been used in order to obtain an optimal design for a particular application of TFH.

TFH - transverse flux induction heating of non-ferrous and precious metal strips: Results of a EU research project

In the years 1999 and 2000 the Universities of Hannover and Padua and four industrial partners from Italy and Germany have developed a common research project on TFH financed by the EU (Project JOE3‐CT98‐7023). In this paper, the main results obtained are shortly described.