Search results

The heating of flat workpieces of different materials and geometrical characteristics (width, thickness) is often required in the metal industry. The temperature requirements depend on the process to which the workpiece should undergo and the mechanical and chemical characteristics which must be obtained by the heat treatment. For certain applications in which the electrical resistivity of the workpiece material is low or the ratio between the width and thickness of the body is high, the classical longitudinal flux induction heating is efficient only if high frequencies are used. A good alternative is the travelling wave induction heating (TWIH) which has a structure similar to the linear induction machines (LIM).

In this paper an analytical method, based on Fourier's series, which allows to determine the eddy currents distribution in travelling wave induction heaters with cylindrical symmetry is described. The method is particularly suitable for parametric analyses of heating systems with magnetic or non‐magnetic, solid, bimetallic or hollow loads, with inductors (with or without external magnetic yoke) of the transverse flux or travelling wave type. Useful results can be obtained also for the heating of “flat” metal loads, by inductors facing one side of the load.

The paper aims to deal with the induction heating of metal billets rotating in a DC magnetic field.

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.”

The main process parameters have been evaluated for the heating up to 500°C of an Al billet 200 mm diameter.

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.

The paper analyses the induction heating of a infinitely long billet rotating in a uniform DC magnetic field.

Introduces the fourth and final chapter of the ISEF 1999 Proceedings by stating electric and magnetic fields are influenced, in a reciprocal way, by thermal and mechanical fields. Looks at the coupling of fields in a device or a system as a prescribed effect. Points out that there are 12 contributions included ‐ covering magnetic levitation or induction heating, superconducting devices and possible effects to the human body due to electric impressed fields.

Introduces papers from this area of expertise from the ISEF 1999 Proceedings. States the goal herein is one of identifying devices or systems able to provide prescribed performance. Notes that 18 papers from the Symposium are grouped in the area of automated optimal design. Describes the main challenges that condition computational electromagnetism’s future development. Concludes by itemizing the range of applications from small activators to optimization of induction heating systems in this third chapter.

Distribution of alternating current density and internal power sources in the cross‐section of curvilinear hollow work pieces under resistance heating are presented in this paper. The calculation is based on an analytical model. The results of analytical calculations are compared with experimental data. The received expression was investigated in a wide range of geometrical parameters.

The purpose of this paper is to present a calculation optimization method that is able to achieve the best induced power profile (and subsequent temperature distribution) in a disk or billet workpiece processed by induction heating.

A volume integral method, also known as the mutually coupled circuits method, is implemented in MatLab^® environment to solve axial‐symmetrical induction systems. It is completed with an optimization procedure based on Nelder‐Mead simplex algorithm, with the goal of obtaining a specified distribution of the induced power in the load. In this way, it is possible to predict current amplitudes for implementing the so‐called “zone controlled induction heating” (ZCIH) process.

Some examples of calculation results are given, both for disc and billet loads. By the excitation of the inductor coils with a set of currents of appropriate amplitude and phase values, it is possible to achieve an optimized profile of induced power distributions.

This paper validates a method to predict currents and phases in a load‐inductor ZCIH system, confirming the possibility of obtaining specified induced power density distributions, according to the process requirements, e.g. for compensation of the load edge‐effect.

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.

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.

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.