Induction furnace with linear flux concentrator

Details Induction furnace with linear flux concentrator Induction furnace with linear flux concentrator

1994-05-23

1996-11-26

Hoang, Tu

Electric heating

Inductive heating

Specific heating application

219672, 219647, H05B 610

Patent

active

055782337

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an improved induction furnace for heating or re-heating flat products of steel industry, particularly to re-establish a homogeneous temperature, suitable to rolling thin steel slabs.
2. Description of the Prior Art
It is known from the Italian patent application No. 20534 A/89, corresponding to the International publication WO 90/14742, an induction furnace comprising an array of coils, which are separately fed by one or more frequency converters and crossed in succession by the strip being supported and caused to move forward by pairs of rollers between each coil and the subsequent one, wherein flux concentrator devices are provided, mounted in pairs at the ends of each inductor, at least on an upper or lower side, with respect to the plane defined by the strip itself.
Although this solution gives best results, as it allows for the first time to exploit satisfactorily the induction heating in connection with longitudinal flat products, whereas the magnetic flux was previously mainly directed such as to cross transversely the strip in the thickness direction, with poor results but for the thermal treatment of the edges only, however some inconveniences have been experienced, mainly due to the great leakage of magnetic flux which, as it closes at the outside of the strip, crosses the structural metal parts of the apparatus, thus causing an undue heating thereof in spite of the presence of lateral flux concentrators, possibly movable.
Previously, with longer inductors (along the longitudinal size of the product to be heated), as it was possible for thicker products, the possible utilization of concentrators would be useless, since the little improvement in the efficiency and reduction of leakage would not be worth in comparison with the increase of costs. With a short inductor, as necessarily adopted in connection with flat products such as thin slabs, also the presence of lateral flux concentrators according to the above-mentioned previous patent does not solve the problem of flux leakage and leads to relatively low efficiencies, e.g. of 0.6 or less, when considering the ratio between power entering the flat product to be heated, including losses due e.g. to radiation, and supplied active power.
As a matter of fact, the longitudinal size of coils cannot be made too great, since to keep a reduced value of the space between two subsequent coils, above which the thin product could not be fed forward in a suitable way, a reduced diameter of the rollers would result, which is to be avoided in order not to have a too small bending radius, with consequent stumbling of the flat product and problems of heat transmission. An attempt was then made to modify the mechanical parts to overcome the drawbacks caused by the flux leakage. A solution of this type requires providing rollers coated with refractory material, to prevent sparkling and consequent "dotting" on the strip, and/or making not solid rollers, but formed of isolated sectors to hinder the generation of eddy currents, or finally mounting the rollers on separate pillars, such as of concrete. This way a structure would be obtained not only more complex and costly, but also less solid and compact, certainly not so suitable to this type of processing and steel industry environment.


SUMMARY OF THE INVENTION

Surprisingly it has now been found that by the use of a flux concentrator extending along the whole coil, being formed e.g. of two lamination packets having a substantially C-shaped cross section, such as to surround the induction coil at both upper and lower side with respect to the plane defined by the product to be heated, whereby only a passage for the product itself is left free, the flux leakage decreases by at least 90% and the above-mentioned efficiency may rise up to about 0.7 and more. In addition to energy saving, a mechanical structure of merely traditional construction can be obtained, i.e. sound and adapted to the steel manufacturing field, where on the cont

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