EP0822733B1 - Induction heating apparatus and installation for continuous thermal treatment using such apparatus - Google Patents

Abstract

A device is claimed for the induction heating of a metal product (1) defiling continuously in a protective atmosphere, comprising an induction system (4) and a sealed enclosure (3) that is thermally and electrically insulated and gas-tight, arranged around the defiling product (1) between the defiling product and the induction system (4). The induction system (4) incorporates at least one induction winding of a conducting material connected to a high frequency current generator (45) and extending around the defiling product (1) in a plane perpendicular to the direction of defilement (F) of the product (1). The sealed enclosure (7) is arranged inside the winding(s) of the induction system (4) and extends in the direction of defilement (F) upstream and downstream of the induction system (4) over a distance sufficient to create a zone traversed by the return induction flux.A thermal treatment installation incorporating this device is also claimed

Description

The present invention relates to a device for induction heating of a moving metal product continuously under protective atmosphere.

It also concerns an installation of continuous heat treatment of a moving product comprising such a device.

This invention is particularly applicable to heat treatment under a protective atmosphere such as than realized in hot coating lines for galvanizing, aluminizing, etc ... and the lines of continuous heat treatment such as continuous annealing for steel sheets or patent lines for a steel wire.

The use of space heaters induction to heat metallic materials scrolling has been known for a long time. We use generally an inductor consisting of one or several turns traversed by high current frequency, which completely surround the product scrolling. This inductor creates a longitudinal flow, that is to say in the direction of travel of the product and thus allows to heat magnetic materials.

We also know a heating device by induction comprising a turn traversed by current, arranged in a plane parallel to the surface of the scrolling product so that the magnetic flux, transverse, is perpendicular to the surface of the product.

However, when the moving product is not coated and treated at a temperature where it risks oxidize, induction heating must be done under protective atmosphere, such as a mixture of nitrogen and of hydrogen, and the enclosure of the heater by induction must be completely airtight so avoid any oxidation of the product.

In known applications of this type of induction heating, as described for example in French patent 2,688,802, a induction heater which is placed directly inside a watertight enclosure the air.

This tightness, produced all around the means of induction, requires to provide passages, also waterproof, for the arrivals and returns of electric current supplying the inductor, and cooling water circuits for cooling means of induction.

These water circuits inside the enclosure waterproof pose a great risk to the quality of the protective atmosphere, since the slightest leak of water will pollute it and risk oxidizing the product.

On the other hand, placing the inductor in waterproof enclosure greatly complicates operations maintenance and requires the provision of openings sufficient and handling means to remove the entire induction device of the enclosure.

In addition, when the induction means are withdrawn, the moving product to be treated must necessarily be cut in the absence of having provided an opening in the means of induction surrounding this moving product.

In addition, when the means of induction are placed inside an oven, it is necessary to have non-conductive support means electricity and resistant to very high temperatures.

Finally, any intervention on the means induction involves shutdown of the entire installation whole, air and gas tightness no longer being assured.

There are also known induction heating, as described in the patent American US 1,749,700 and British Patent GB 2,155 740, in which the means of induction are arranged outside a gas-tight enclosure suitable for maintain a protective atmosphere around the product metallic scrolling.

However, in these achievements, there is no electrically insulating enclosure, extending beyond means of induction.

Conductive parts of the enclosure may thus be the seat of electric current induced by the induction flow returning to the induction means.

The object of the present invention is to remedy the disadvantages mentioned above and to propose a device for induction heating of a moving metal product in a protective atmosphere, guaranteeing at best the air and gas tightness around this product scrolling, allowing easier intervention on means of induction and limiting any overheating of the device.

The present invention relates to a device for induction heating of a moving metal product continuously under a protective atmosphere, including induction means, a sealing enclosure, insulating thermally and electrically and gas tight, arranged around the moving product, between this product and the means of induction, the means of induction comprising at least one turn of conductive material connected to a high frequency current generator and extending around the product moving in a plane perpendicular to the direction of travel of the product, the sealing enclosure being arranged inside the turns of the induction means.

This device is characterized in that the sealing enclosure extends in the direction of scrolling, upstream and downstream of the induction means, enough distance to create an area flow through the return induction flow.

This sealing enclosure creates a zone in which the induction flow returns to induction means without heating any metallic part.

Thus, thanks to the invention, the seal is not more performed around the means of induction but simply between these means of induction and the products scrolling.

It is no longer necessary to plan passages waterproof for power and water supply means of induction.

In addition, intervention on the means induction, especially during disassembly, do not not disturb the protective atmosphere surrounding scrolling products.

Even when the means of induction surround completely scrolling products, we can intervene on these induction means and dismantle them while leaving the scrolling product protected by the enclosure sealing.

According to another aspect of the invention, a continuous heat treatment installation of a moving product, such as steel strip or wire, under protective atmosphere, includes several successive heat treatment.

According to the invention, this installation comprises an induction heating section comprising a heating device according to the invention, a transfer tunnel in which the moving product performs a single pass connecting the induction heating to said treatment chambers.

So the induction heater warms up the steel strip or wire in a section of oven in which this strip or wire makes only one pass through the tunnel transfer, so as to have access to the entire perimeter of the air induction heater ambient.

Other features and advantages of the invention will also appear in the description below.

• la figure 1 est une vue schématique illustrant une partie d'une installation de traitement thermique comprenant une section de chauffage par induction suivie d'une chambre de maintien à température intermédiaire;
• la figure 2 est une vue schématique d'un dispositif de chauffage par induction conforme à l'invention;
• la figure 3 est une vue en élévation d'un dispositif de chauffage par induction conforme à l'invention; et
• la figure 3A est une vue agrandie du détail A de la figure 3.

In the appended drawings given by way of nonlimiting examples:

• Figure 1 is a schematic view illustrating a part of a heat treatment installation comprising an induction heating section followed by an intermediate temperature holding chamber;
• Figure 2 is a schematic view of an induction heating device according to the invention;
• Figure 3 is an elevational view of an induction heating device according to the invention; and
• FIG. 3A is an enlarged view of detail A of FIG. 3.

The induction heater will be described below in a processing application continuous thermal of a moving product, such as a strip 1, under a protective atmosphere.

This type of heat treatment can also apply to a moving steel wire.

The protective atmosphere is generally composed of a mixture of nitrogen and hydrogen and allows avoid any oxidation of the product during treatment. In known manner, such an installation can successively include a heating chamber of strip 1 at a temperature of 600 to 900 ° C, a temperature maintenance chamber, a slow cooling, a cooling chamber fast, an induction reheating section, a intermediate temperature holding chamber, and finally a final cooling chamber.

In figure 1, the strip 1 comes out, on the left of the figure, of a rapid cooling chamber, passes through a transfer tunnel 3 and a section of induction heating before being introduced into a intermediate temperature holding chamber 2.

The different heat treatment chambers are surrounded by sealing means allowing keep inside each of these rooms a protective atmosphere of reducing gas composed of nitrogen / hydrogen mixture with low dew point and very low residual oxygen content.

The strip 1 traverses these treatment chambers 2 in one or more vertical paths separated by deflection rollers.

As illustrated in Figure 3, the induction heating according to the invention, includes induction means 4 and a sealing enclosure 7, non-metallic and gas-tight, which is arranged around the moving product 1, between this product 1 and the induction means 4. The sealing enclosure 7 is thermally and electrically insulating, allowing thus surrounding the moving product with a non-conductive enclosure.

In this example, and as illustrated in the figure 2, the induction means 4 comprise at least one turn of conductive material connected to a generator 45 of high frequency current and extending around the moving product 1, in a plane perpendicular to the scroll direction F of this product.

The sealing enclosure is thus arranged at inside the coil of the induction means 4.

The sealing enclosure 7 extends parallel to the direction of travel F, upstream and downstream of induction means 4, over a distance sufficient to create an area crossed by the induction flow of return.

This distance is at least 200 mm, and preferably 300 mm.

The sealing enclosure being non-conductive, it is not the seat of any current induced by the flow return induction.

Of course, in Figure 3 a single inductor consisting of a single turn is shown. Many inductors 4 could however be arranged successively in the direction of travel F, each inductor being separated by a distance of at least 100 mm, a single sealing enclosure 7 protecting the strip 1 over the entire induction heating section.

This induction heating device being intended to be placed upstream or between chambers of treatment of the product moving under an atmosphere protective, the sealing enclosure 7 is connected sealingly to these processing chambers.

These waterproof connections can be made of known manner by flange and joint 8 or by any other known process.

The sealing enclosure 7 is constituted in this example of a flexible sleeve 7 comprising one or several layers 7a of thermally insulating fabric and electrically coated on the outside with a film 7b of gas-tight and temperature-resistant material at least 100 ° C.

In this example, the ambient temperature in the induction heating section never exceeding 400 ° C., the flexible sleeve 7 consists of seven layers 7a of glass fiber fabric covered on the outside with a waterproof film 7b formed by 'a piece of polytetrafluoroethylene. The insulating fabric 7a of the sleeve could also consist of ceramic fibers. The flexible sleeve 7 is thus kept in tension between the fixing flanges 8 at each end and is pressed against the interior walls of the induction means 4 by the pressure prevailing inside the oven. This pressure is of the order of 1 to 2. 10 ² Pa.

If the induction heater needs to be installed in a warmer region of installation, like the heating furnace itself said, the sealing enclosure 7 may further comprise a muffle 11 of refractory material which is not gas-tight, externally lined with the sleeve.

In addition, one can also use as sealing enclosure, a waterproof ceramic sheath.

As best illustrated in Figures 2 and 3A, the or the inductors 4 consist of a single turn of rectangular section surrounding the moving product 1 and comprising three metal sheets 42, 43, 44, on which are welded water coils 41 for cooling the induction means 4.

The metal sheets 42, 43, 44 are assembled removably to each other and, possibly to the current generator 45.

In this example, inductor 4 includes five copper sheets: two sheets 43 connected to the generator current 45, two sheets 42 extending face to face and forming the sides of the turn parallel to the strip scrolling 1, and a sheet 44 closing the opposite side of the turns on the current generator 45. These sheets are closely related to each other, to ensure a perfect electrical contact, by fixing means removable 46, such as bolts 46.

This structure of the inductors 4 allows in particular by dismantling the plate attachments, to intervene on the inductors 4 without cutting the strip 1 and break the sealing enclosure 7.

In this example, we use frequencies of current higher than 15 KHz, and preferably higher than 30 KHz.

Preferably, the entire space comprising the induction means 4 and the enclosure 7 is surrounded by a body of protection 9 not waterproof and avoiding any circuit continuous electric around the inductor. In addition, on either side of the induction heating section, stabilizer rollers 10 are capable of inflicting a slight deflection at band 1, so as to reduce, if necessary, the camber of band 1 and position it at the center of the induction means 4.

All of the sheets 42, 43, 44 and serpentines 41 is generally made of copper.

A transfer tunnel 3, in which the product scrolling 1 makes a single pass, connects the induction heater to the chamber rapid cooling (not shown) and in the chamber to maintain intermediate temperature 2.

It is essential indeed that the induction heating is installed in a section of the oven in which the strip performs only one pass so as to have access to its entire circumference in the air ambient.

Of course, many modifications can be made to the example described above without depart from the scope of the invention, as defined by all of the claims.

Claims (12)

1. Device for induction heating of a metal product (1) moving continuously under a protective atmosphere, comprising induction means (4) and a thermally and electrically insulating gas-tight sealing enclosure (7) arranged around the moving product (1), between the said product (1) and the induction means (4), the induction means (4) comprising at least one turn of conductive material which is connected to a radiofrequency current generator (45) and extends around the moving product (1), in a plane perpendicular to a movement direction (F) of the said product (1), the sealing enclosure (7) being arranged inside the turn or turns of the induction means (4), characterized in that the sealing enclosure (7) extends in the movement direction (F), upstream and downstream of the induction means (4), over a sufficient distance to create a region permeated by the induction flux in which the induction flux returns to the induction means without heating the metal part.
2. Heating device according to Claim 1, characterized in that the said distance is at least equal to 200 mm.
3. Heating device according to one of Claims 1 to 2, arranged between or upstream of chambers (2) for processing the product (1) moving under a protective atmosphere, characterized in that the sealing enclosure (7) is connected to the said processing chambers (2) in a leaktight fashion.
4. Heating device according to one of Claims 1 to 3, characterized in that the sealing enclosure (7) consists of a flexible sleeve (7) comprising one or more layers of thermally and electrically insulating fabric (7a), which is externally covered with a film (7b) of gas-tight material withstanding a temperature of at least 100°C.
5. Heating device according to Claim 4, characterized in that the insulating fabric (7a) of the sleeve (7) is a glass-fibre fabric or a ceramic-fibre fabric.
6. Heating device according to one of Claims 4 and 5, characterized in that the said film (7b) is composed of polytetrafluoroethylene.
7. Heating device according to one of Claims 4 to 6, characterized in that the sealing enclosure furthermore comprises a muffle of refractory material externally lined with the sleeve (7).
8. Heating device according to one of Claims 1 to 3, characterized in that the sealing enclosure (7) is a leaktight ceramic sheath.
9. Heating device according to one of Claims 1 to 8, characterized in that the induction means (4) comprise a single turn of rectangular cross section, surrounding the moving product (1) and comprising at least three metal sheets (42, 43, 44) assembled removably with one another and with a current generator (45).
10. Installation for continuous heat treatment of a moving product (1), such as a steel strip or wire, under a protective atmosphere, comprising a plurality of successive heat treatment chambers (2), characterized in that it comprises an induction-heating section comprising a heating device according to one of Claims 1 to 9, and a transfer tunnel, through which the moving product performs a single pass, connecting the induction-heating device to the said processing chambers (2).
11. Heat treatment installation according to Claim 10, characterized in that the entire space comprising the induction means (4) and the sealing enclosure (9) is surrounded by a non-leaktight protective structure (9) preventing any continuous electrical circuit around the induction means (4).
12. Heat treatment installation according to one of Claims 10 and 11, characterized in that stabilizing rolls (10) are arranged on either side of the induction-heating section and are designed to impart a slight deflection to the strip (1), so as to reduce the curvature of the strip (1) and to position the said strip (1) at the centre of the induction means (4).

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