EP1148762B1 - Induction heating device having transverse flux and variable width inductor - Google Patents

Abstract

An electrical winding (2) elongated across the width of a running metal plate (4) is located above the plate and orientated parallel to it. Magnetic bars (9) associated with the winding may be individually slid along it to adjust the field traversing the metal plate and produce an homogeneous heating effect. Further adjustment may be obtained from placing sheets of conducting material in the air gap and profiling the magnetic bars.

Description

The present invention relates to a heating device with the parade, by electromagnetic induction, magnetic or nonmagnetic strips of low and medium thicknesses (of the order of 0.05 to 50 millimeters). It is more particularly a transverse flux induction heating device.

In known manner, the heating by electromagnetic induction of a metal strip is achieved by means of coils which are arranged to surround the strip to be heated by creating a magnetic field parallel to the outer surface of this strip according to the scrolling direction (longitudinal flow, cf. figure 1a ). This results in a ring distribution of the induced currents which traverse the continuous displacement band at its peripheral surface, which results in a heating of which the transverse temperature homogeneity is generally considered satisfactory.

When it comes to heating thin magnetic strips, the efficiency of this type of longitudinal flow heating is high. However, it falls sharply, + for these materials, as soon as we exceed the temperature of the point Curie (about 750 ° C). This is particularly due to the fact that the relative permeability of the material to be heated decreases rapidly during the heating process to reach the value of 1 at the same temperature. The yield is also limited for non-magnetic materials (stainless steel, aluminum ...), whatever the temperature of the product.

According to another known solution for induction heating of flat metal products, there are two coils on either side of the product to be heated, facing each of the large faces of the latter so as to create a perpendicular magnetic field to the large faces of the product according to the so-called transverse flow technique (cf. figure 1b ).

The main disadvantage of this type of installation lies in the fact that the loop distribution of the currents induced by the magnetic flux through does not generally make it possible to achieve satisfactory temperature homogeneity, especially the ends in the direction of the width of the the band (the banks) are too much or too little heated according to the relative dimensions of the coils and the magnetic circuit used with respect to the bandwidth.

To solve this problem, it has already been proposed to use transverse flux electromagnetic induction heating in which the inductors comprise magnetic circuits. These are intended to guide the magnetic flux generated by the coils to act on the distribution of induced currents.

However, such devices have the disadvantage of not being easily modifiable in order to adapt to the widths of band to be heated. To overcome such a drawback, an electromagnetic induction heating device described in US Pat. No. 4,678,883, for example, is known in which the inductors consist of a plurality of magnetic strips coupled together (by "coupled" means). means mutually reinforcing bars so that the magnetic flux generated by the inductors can pass from one bar to the other bar), arranged parallel to the direction of movement of the strip to be heated and can be individually moved perpendicular to the surface of said strip so as to adapt the flow distribution to the width of the strip, according to the dimensions of the latter.

Even this type of electromagnetic induction heating does not make it possible to correctly control temperature fluctuations at the edges of the strip to be heated. Indeed, the magnetic strips recessed with respect to said band continue to exert an influence, albeit lower, on the magnetic flux distribution and therefore on the temperature and it follows that the temperature distribution curve shows a concentration of induced currents on the banks.

Moreover, it is also known EP-A-0 667 731 which discloses a transverse flux electromagnetic induction heating device in which the length of the coils is varied in order to adapt the flux distribution to the bandwidths. To do this, this document proposes to make these windings by assembling two opposing J-shaped inductors which can freely translate in a direction parallel to the bandwidth. As for the US patent mentioned above, this device does not provide a very satisfactory transverse temperature homogeneity.

EP-A-0 308 182 discloses a transverse induction heating device in which the total width of the magnetic coil-core assemblies can be varied according to the width of the part to be heated. The magnetic circuits constituted by magnetic plates or bars are not independent of the electrical windings which are thus displaced with the magnetic cores, which complicates the installation, in particular for the power supply of the windings to be moved. In addition, the mass to be moved is increased by that of the coils.

US 4,587,392A also relates to an induction heating device in which the electric winding is to be moved with the magnetic strips for a width adjustment.

US 4,258,241A relates to a slit induction heating device in which elongated parts, such as shafts, arranged parallel to each other are introduced and moved in a direction orthogonal to the large dimension of the parts. Axially spaced areas of the parts are heated passing between conductors parallel to the direction of movement of the parts. The electrical conductors can be moved in a direction parallel to the large dimension of the parts and orthogonal to the direction of advance of these parts to change the position of the heated areas of the rooms. Again, the electrical conductors are moved.

Given the disadvantages of the solutions of the prior art recalled above, the present invention proposes to provide an original solution by providing a transverse flux electromagnetic induction heating device whose magnetic circuit, made by a plurality of independent magnetic strips, adapted to the width of the strip to be heated. This device thus makes it possible to improve the thermal homogeneity in the direction of the width of the strip to be heated.

For this purpose, the invention provides a device for heating by electromagnetic induction of a metal strip moving in a determined direction comprising at least one electric coil arranged facing at least one of the large faces of said strip in order to heat the latter. by induction with a cransverse magnetic flux, each winding being associated with at least one magnetic circuit, each circuit being divided into a plurality of magnetic strips not coupled together and arranged parallel to the running direction of the strip, said device being characterized in that said magnetic circuit, consisting of said plurality of strips, independent of each other, adapts to the width of the strip to be heated by spacing or bringing said strips closer to each other, so as to continuously adapt the distribution of said magnetic flux to the characteristic dimensions of said strip.

Thus, thanks to the present invention, whatever the width of the band to be heated, the volume and therefore the weight of the magnetic circuit remains invariable.

According to an advantageous characteristic of the invention, the electromagnetic induction heating device also includes screens of good electrical conductivity material placed in the air gap on both sides of the strip and at the edges of the latter, so as to optimize the homogeneity of the transverse temperature.

According to another advantageous characteristic of the invention, the surface of the magnetic circuit facing one of the large faces of the strip to be heated is given a suitable "polar" profile (for example bisinusoidal) by cutting the magnetic sheets. constituting this circuit so as to obtain a better distribution of the magnetic flux, and more particularly at the edges of said strip. By "polar" profile is meant a surface of the magnetic circuit which is curved in the three directions of space.

• les figures 1a et 1b illustrent des dispositifs de chauffage par induction électromagnétique connus de l'art antérieur, respectivement à flux longitudinal et flux transverse ;
• les figures 2a et 2b sont des vues partielles, en perspective du dispositif de chauffage par induction selon l'invention dans deux positions ;
• les figures 3a et 3b sont des vues partielles, en perspective du dispositif de la figure 1 muni d'écrans en matériaux de bonne conductibilité électrique couplés à des plots magnétiques ;
• la figure 4 est une vue schématique et partielle d'un exemple de profil polaire (surface du circuit magnétique en regard de la bande à chauffer) ;
• la figure 5 est une vue schématique et partielle d'une installation classique de recuit brillant d'acier inoxydable.

Other features and advantages of the present invention will become apparent from the description given below, with reference to the accompanying drawings which illustrate exemplary embodiments and application devoid of any limiting character. On the drawings:

• the figures 1a and 1b illustrate electromagnetic induction heating devices known from the prior art, respectively longitudinal flow and transverse flow;
• the Figures 2a and 2b are partial views, in perspective of the induction heating device according to the invention in two positions;
• the Figures 3a and 3b are partial views, in perspective of the device of the figure 1 equipped with screens made of materials of good electrical conductivity coupled with magnetic studs;
• the figure 4 is a schematic and partial view of an example of polar profile (surface of the magnetic circuit facing the strip to be heated);
• the figure 5 is a schematic and partial view of a classic stainless steel bright annealing installation.

If we refer to the drawings, and more particularly to Figures 2a and 2b it can be seen that the transverse flow electromagnetic induction heating device according to the present invention comprises in particular two magnetic armatures respectively 1 and 1 'provided with at least one electric winding 2 and arranged face-to-face on either side a band 4 to heat. The latter may for example be guided in the gap defined between the magnetic circuits using rollers (not shown) and thus be transferred into the heating zone. Its displacement is generally continuous during the heating process according to the invention.

As a variant, and depending on the desired application of this heating device, it is possible to have at least one magnetic armature 1 provided with at least one electric coil 2 facing only one of the large faces of the band 4 to be heated.

According to the known technique known as the transverse flux, the magnetic flux generated by the electric windings 2 crosses the heating strip 4 and induces in it a current flowing in the plane of said strip and which closes in a loop at the banks . To do this, the winding or coils 2 are powered using a medium frequency alternating current (for example, of the order of 50 to 20000 Hz approximately).

To ensure the guidance of the magnetic flux generated by the coils 2 in particular at the edges of said strip, there is a magnetic circuit 6 over all or part of the length of said coils. This circuit consists of a plurality of magnetic strips 8 arranged parallel to the direction of travel of the strip 4 to be heated.

According to the invention, the strips 8 constituting the magnetic circuit 6 are not coupled together and are arranged parallel to one another. These strips are therefore independent of each other and they are also independent of the electric windings. In addition, they can slide by means 10 at the level of the electric windings 2 so as to deviate or come closer to each other, the electric windings remaining fixed. Thus, the spacing between two adjacent strips can be enlarged or shrunk, continuously, under the action of said means 10. As a result, the magnetic flux distribution can be adapted to the dimensions of the strip 4, and in particular to its width (cf. figure 2b ).

This essential characteristic of the present invention makes it possible not only to obtain an induction heating device adaptable to different widths of the strip to be heated, but above all the thermal homogeneity obtained in the width direction of said strip remains optimal regardless of the width of it.

In fact, the spatial positioning of the magnetic strips associated with a suitable polar profile makes it possible to act on the circulation of the induced currents and thus to control the transverse temperature distribution.

The means 10 making it possible to slide, continuously, the magnetic strips 8 at the level of the electric windings 2, but without moving the latter, are constituted in particular by at least two rails 11 and 11 'parallel disposed on each side of the surface of the strip 4 and perpendicular to the direction of movement thereof. These rails support a plurality of reinforcements 12, each of these armatures being fixed to at least one bar 8. Preferably, the support of the reinforcements of two adjacent bars is alternated on the two rails 11 and 11 'so as to reduce the congestion when the width of the magnetic circuit 6 is minimal (where the spacing between the bars is minimal). The armatures slide on the rails using rollers 13 or the like independently of each other, which enables a very precise, optimal and continuous adjustment of the width of the magnetic circuit and therefore of the flux distribution. Thus, it is possible for example to make a width of the magnetic circuit varying from 800 to 1500 millimeters.

According to an advantageous characteristic of the invention, the spacing between two adjacent magnetic strips 8 can be adjusted manually or automatically in order to obtain the desired magnetic distribution.

According to another advantageous characteristic of the invention (cf. Figures 3a and 3b ), in order to optimize the homogeneity of the transverse temperature of the strip to be heated, screens 14 are placed in the gap on either side of said strip and at the edges thereof. Such screens are made of a material having good electrical conductivity, for example of the copper, aluminum or silver type. Their function is to adjust the magnetic flux at the edges of the strip in order to control the temperature of the banks of said strip.

In addition, these screens are also fixed on frames 15 supported by rails by means of rollers or the like so as to be able to be driven by a translation movement along the width of the band used. Alternatively, one can also fix these screens directly on the end magnetic strips that are opposite the banks of the strip to be heated.

According to yet another advantageous characteristic of the invention, it is also possible to have magnetic pads 16 on the plates 15 supporting the screens 14 so as to refine the distribution of the magnetic flux over the width of the strip, in particular such pads make it possible to fill possible temperature heterogeneities. These magnetic pads 16 may be coupled to screens 15 of good electrical conductivity and / or magnetic strips 8 or be arranged without screens.

According to yet another advantageous characteristic of the invention (cf. figure 4 ), the surface of the magnetic circuit 6 of each armature (1, 1 ') which is opposite one of the large faces of the strip 4 is given a "polar" profile, adapted to obtain a controlled distribution of the magnetic flux generated by the electric windings 2, in particular at the edges of said strip.

According to yet another advantageous characteristic of the invention, a short-circuit winding (not shown) is added on either side of the heating device, perpendicularly to the bars of the magnetic circuit and embracing the band in displacement in order to reduce the magnetic fields of leakage at the ends of the inductor.

An example of an advantageous application of the electromagnetic induction heating device according to the invention will now be described.

The figure 5 is a schematic and partial view of a bright annealing installation, for example stainless steel. Such annealing line is disposed on a single vertical strand whose total height must not exceed 50 meters. The strip 18 to be heated which is guided by rollers 19, passes through this height, first a heating zone 20 and then a cooling zone 21. In a manner known for a non-magnetic steel strip, the latter between in the heating zone at room temperature (approximately 20 ° C), must come out at a temperature of 1150 ° C and then be cooled to reach a temperature of 100 ° C at the end of the line.

There are known gas heating devices or electrical resistance whose height on such a line is about 30 meters, which leaves little room for cooling the band. Consequently, such devices operate with a speed of movement of the strip to be heated typically of the order of 60 meters per minute.

The electromagnetic induction heating device according to the invention applied to such an installation has the advantage of being able to reduce the overall height of the heating zone to about 10 meters, which provides much more room for cooling and Thus, it is possible to reach a line speed of 120 meters per minute for stainless steel having a thickness of approximately 0.5 millimeters.

The present invention as described above thus offers multiple advantages. It allows from an electromagnetic induction heating device using variable width magnetic circuits to create a high intensity magnetic flux for medium frequencies. This magnetic flux density makes it possible to achieve a power density transmitted to the strip to be heated, which is greater than that of the known heating means. Thanks to the characteristics of the invention, there is no magnetic material in inter-bar spaces, unlike systems according to the prior art. In addition, the electrical efficiency of this device is greater than that of known technologies. In addition, such a device makes it possible to obtain a satisfactory thermal homogeneity in the direction of the width of the strip.

Claims (6)

1. Heating device by electromagnetic induction of a metal plate (4) running in predefined direction, which comprises at least one electrical winding (2) arranged opposite at least one of the large faces of the said plate in order to heat the latter by transverse magnetic flux induction, each winding being connected to at least one magnetic circuit (6), which comprises a plurality of magnetic bars (8) arranged parallel to the running direction of the plate, said device being characterised in that:

   - the magnetic bars (8) are not connected together, are independent of one another and are independent of the electrical windings (2);

   - the bars (8) are mounted so that they are able to slide by way of means (10) at the level of the electrical windings (2) so as to move away from one another or approach one another, the electrical windings (2) remaining fixed, which makes it possible to continually adjust the distribution of magnetic flux to the width of the plate.
2. Heating device according to claim 1, characterised in that it comprises screens (14) with good electrical conductivity arranged in the air gap defined by said magnetic circuits, on either side of the plate and at the edges of said plate so as to adjust the magnetic flux to the ends of said plate in the direction of its width.
3. Heating device according to one of claims 1 or 2, characterised in that it comprises magnetic contacts (16) arranged in the air gap defined by the said magnetic circuits on either side of the plate and at the edges of the said plate so as to optimise the distribution of magnetic flux.
4. Heating device according to any one of the preceding claims, characterised in that the means (10) comprise at least one rail (11, 11') on each side of the plate (4) and perpendicular to the running direction of the latter, said rail supporting by means of rollers (13) or the like a plurality of armatures (12), each of said armatures being fixed to at least one magnetic bar (8) so as to allow the armatures (12) supporting the said bars to be moved away from one another or closer towards one another by sliding on said rails (11,11').
5. Heating device according to any one of the preceding claims, characterised in that the surface of the magnetic circuit (6) of each armature (1,1'), which faces one of the large surfaces of the said plate has a "polar" profile adjusted to obtain a controlled distribution of the magnetic flux.
6. Heating device according to any one of the preceding claims, characterised in that it comprises at least one short-circuit coil arranged on either side of said armature (1,1'), so as to clasp the plate (4) to reduce the magnetic field losses at the ends of the inductor.

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