Advanced Energy Saving Induction Heating Technologies in the Steel
Industry and its Modeling
V. Demidovitch*, B.Nikitin*, V.Ivanov*, V.Chervinsky*, A.Titov*,
I. Barankova**, F.Tchmilenko***
*VNIITVCH, 1 Shuvalovsky park, St.Petersburg, 194362, Russia
**Magnitogorsk Technical University, 38 Lenin av., Magnitogorsk, 455000, Russia
***St.Petersburg Electrotechnical University, 5 Prof. Popov str., St.Petersburg, 197362, Russia
Abstract—Different energy saving applications of induction heating galvannealing lines can be delivered in various sets including
are presented in this report. The advanced 3D software was developed those for:
for induction heating of steel products with arbitrary cross section. This Low-temperature strip heating from the ambient
software is intended for electrical and thermal computation both
stationary, and non-stationary processes of stage and continuous temperature to 150–300 °С.
working regime an induction heater with magnetic and non-magnetic Strip heating before entering a radiation tube furnace to
loading with any of cross section shape. The combination of the most 700–750 °С.
effective numerical methods for modeling induction heating process was Strip reheating in the line (~100–300°С) between gas
used in this software: Final Differences Method (FDM), Final Elements
Method (FEM), Boundary Element Method (BEM), and Integral fired furnaces and radiation gas (or electric) furnaces. In
Equation Method (IEM). addition to increasing the line capacity, induction heaters
reduce the rejection rate during changeover from one strip
I. INTRODUCTION size to another and improve transient thermal processes.
Russian steel industry has strong demand to deliver to Strip reheating from ~460°С to 600–650°С after leaving
metallurgical works complete sets of automated equipment Zn+Al melt bath in the galvannealing process. In this
and processes for induction heating of slabs, blooms, case, steel sheets have better anticorrosion properties,
cylindrical billets for lines of rolling and sizing mills, improved weldability, paintability and dust-resistance.
induction heaters of steel strip for heat treatment, drying, Strip edge heating to ~100°С.
coating, hot deep galvanizing and galvannealing lines. Numerical models of above induction heating applications
Induction equipment for induction heating of slabs, in steel and non-ferrous industry are developed.
blooms, bars and tubes in lines of rolling and sizing mills is
II. 3D MODEL OF ELECTROMAGNETIC AND THERMAL PROCESSING
used in various sets including those for: OF SLABS BEFORE HOT ROLLING
Metal heating from ambient temperature to rolling
temperature (1150–1250 °С). Accurate and effective 3D model for computation of
Metal heating after leaving a gas furnace (900–1150°С) electromagnetic and temperature fields during thermal
to rolling temperature (1150–1250°С). It is the most cost- processing of slabs before hot rolling is presented in this
efficient approach that decreases the cost of heating per
report. Typical design of induction heaters and gas-fired
ton of metal while significantly reducing scale generation
furnaces is used in the model for evaluation of heating
processes. Influence of the cooling and soaking zones on the
Metal reheating in the line between rolling mill stands
temperature distribution in the slab could also be simulated in
including hot-rolled coils to compensate for the
this model. Usually the aim of the heating is achievement of
temperature loss or to reheat from room temperature.
Metal reheating and metal temperature equalizing (100– the given temperature with the certain allowable non-
200°С) downstream of the continuous casting plant uniformity in the volume of the product. For the complete
before rolling. description of the temperature field in a heated up body it is
Reheating of semi-finished rolled strip edges upstream of necessary to know as temperature distribution in the cross
finishing stands (to 100°С). section, as along the length of the billet. Usually continuous
Temperature equalizing over the length of the product in-line induction heaters are used for heating of metal with
before it enters finishing stands. high production rate. The power of these installations can
Induction equipment for steel strip heating in heat reach 10-15 MW and accurate prediction of the
treatment, drying, coating, hot deep galvanizing and electromagnetic and temperature field’s distributions in the
billets is very important at the design stage of installation as
well for the control of the induction heaters.
In order to provide an acceptable computation accuracy electromagnetic and temperature fields during computations
for design induction heaters, contemporary software for that provides great accuracy
analyzing induction heating should take into consideration a • Most important features of the induction heating
few features of the process. installations are taken into account, including
Most important is interrelation of electromagnetic and characteristics of power sources and possibility to
heat transfer phenomena. Induction heating is a complex change power, voltage, current and frequency during the
combination of electromagnetic, heat transfer and process as well as possibility to simulate stages of
metallurgical phenomena. Heat transfer and electromagnetic holding billets in the inductor and its transport.
are tightly interrelated because some physical properties of • It is easy to implement procedures of optimal design and
heated materials depend strongly on both magnetic field optimal control of the induction heating installations.
intensity and temperature. One of the major difficulties in the • Special database of materials and refractory that used in
electromagnetic field and heat transfer computation is the the induction heating installations is developed.
nonlinearity of material properties. This exists because the
thermal conductivity, specific heat, and electrical III. MODELING AND COMPARATIVE ANALYSIS OF THE DIFFERENT
conductivity of metals are functions of the temperature, while INDUCTION EDGE HEATERS OF THE PLATE PRODUCTS
magnetic permeability is a function of both magnetic field
intensity and temperature. Inappropriate handling of a 2D and 3D models were developed for analysis different
nonlinear feature of material properties by taking into types of induction heaters of the plate products including slot
consideration their average values can lead to essential design inductors, C-shape inductors and original new types of
errors. inductors. Comparison on the base of different criteria such
It is necessary designing of complex technological line, as electrical efficiency, flexibility, power distribution across
which can consist of several in-line inductors, connected in the width of the plate, weight, cost, and reliability is
serial and/or parallel. presented in the report.
The contemporary design of induction heating equipment
should take into account not only steady state but also the
transient processes as well. The transient processes in
induction heating include start-up and shut-down states, Application of induction heating in the metallurgy
holding or thermostationary processes when it is necessary to industry always results in improvement of product quality,
hold the billet in the inductor. In many applications, the flexibility and automation of continuous lines. It provides an
transient process has a great influence on the overall opportunity to boost the output while considerably reducing
parameters of the induction system. the floor space, facilitates and improves maintenance of
The software UNIVERSAL 3D has been specifically furnaces (as compared to gas furnaces). Service life of rolling
developed for induction heating applications and allows the mill rolls is extended; scale-caused losses do not exceed 0.1-
user to obtain all of the required output design parameters, 0.5% (as compared to at least 2% in gas furnaces); the
including temperature profiles, power factor (or "Q"-factor), absence of combustion products and other pollutants
coil impedance, etc. The designer of induction heating improves the environment. Developed numerical models of
equipment can very quickly obtain such important coil design different induction heating applications in the steel and non-
parameters as required coil power, voltage, current and ferrous industry are necessary tools for designing and
optimal frequency. The program is based on using different implementation of induction heating technology.
numerical methods (such as Finite Difference Method
(FDM), Finite Element Method (FEM), Boundary Element V. REFERENCES
Method (BEM), Integral Equation Method (IEM) and their
combination) for joint computation of electromagnetic and  V. Demidovitch “Modeling of Induction Heating Processes in Steel
temperature fields in 3D areas. A unique numerical Industry”, Proceedings of International Congress Electromagnetic
Processing of Materials, Paris, vol. 2, pp. 443-448, May 1997.
calculation technique has been developed and used to provide  V. Demidovitch, “Special Software IndHeat for Modeling Induction
fast and reliable computation. Heating Processes”, Proceedings of 3rd International Workshop on
The complex of the programs has been designed in the ELECTRIC AND MAGNETIC FIELDS EMF`96, Liege, Belgium, pp.
St.Petersburg’s Electrotechnical University. [1-5], which are 273-278, May 1996.
 V. Nemkov and V. Demidovitch, Theory and Computation of Induction
widely used by leading worldwide companies, which design Heating Devices, Leningrad: Energoatomizdat, 1988, (in Russian).
and produce induction equipment.  V. Demidovitch, F.Tchmilenko, N.Smirnov N., V.Skvortsov. Advanced
Cross-section of the slab could be rectangular or with software for computation and design of induction billet heaters, IHS-
rounding corners. Experimental verification of the model and 98, Padua, Italy, 1998, pp.346-352
 V.Demidovitch, V.Skvortsov, F.Tchmilenko, A.Malyshev Advanced
some results of using this model for analysis of industrial software for simulation of the inductors for heating metal products with
processes are discussed in the paper. arbitrary cross-sections, , IHS-01, Padua, Italy, 2001, pp. 487-493.
The advantages of using this software in comparison with
some commercial packages:
• Software is designed specially for induction heating
applications and it realizes essential coupling of