EP0340057B1 - Protecting device for induction poles and inductor provided with this device - Google Patents

Abstract

The device for protecting the poles of an electromagnetic inductor comprises a heat exchanger formed by one or more co-planar metal tubes (6) designed to allow the circulation of a cooling fluid therein and of such an arrangement that there is at most one electrical junction between any two tubes or tube elements. The exchanger is fastened to a rigid electrically insulating support plate (5) coated with refractory concrete (10) and covers the entire polar surface as far as the cowls (3). The exchanger can be shaped in the form of a series of alternating hairpins or in the form of a spiral with one or more branches. The device serves especially for protecting the poles of inductors used for the induction heating of metal products.

Description

The present invention relates to a device for protecting the poles of inductors, in particular used for heating or reheating metallic products by induction.

It is known to use for this purpose electromagnetic inductors with traversing field. Such inductors are described in particular in document FR 2583249. In general, they comprise a C- shaped magnetic yoke, the ends of the C forming the two poles of the inductor, carrying the induction coils, being placed on either side of the product to be heated.

To maintain good performance, the poles must be as close as possible to the product. This causes the poles and the induction coils they carry to be subjected to the strong thermal radiation of the hot product. In addition, under industrial operating conditions, for example during reheating of the edges of slabs or rolled products, the inductors and especially their poles are subjected to chemical and mechanical attack, for example heavy watering, deposit of scale, risk of shock with the heated product.

There is a known device for protecting the poles consisting of a porous refractory plate placed on the face of the pole opposite the product, this refractory being cooled by internal circulation of air. These devices constitute good thermal protection, but nevertheless have the drawback of oxidizing and clogging easily, and of being attacked by the scale coming from the heated product. This results in the need to replace this porous refractory quite frequently, which requires stopping the installation, resulting in operating costs which are added to the high cost of said refractory.

The object of the present invention is to ensure the protection of the inductor poles subjected to thermal, mechanical and chemical stresses, in a reliable and durable manner, without causing loss of heating efficiency.

Another aim is to solve the various problems mentioned above.

With these objectives in view, the present invention has for object a device for protecting, in particular thermal, the poles of an electromagnetic inductor.

According to the invention, this device comprises a heat exchanger formed by one or more non-magnetic metal tubes substantially coplanar arranged to allow the circulation of a cooling fluid and in an arrangement such that there is at most a single electrical junction between any two tubes or tube elements, so as to limit the electrical loops between tubes or portions of adjacent or non-adjacent tubes.

It is specified that the term electrical junction here relates to direct contact or low resistance connections, to the exclusion of high resistance connections existing in materials which are not perfect insulators.

According to a particular arrangement of the invention, the exchanger is shaped according to a succession of alternately inverted hairpins.

According to another arrangement, the exchanger is shaped in a spiral to one branch or more.

According to another particular arrangement, the exchanger is supported and fixed on a rigid electrically insulating plate, and coated with refractory concrete, the assembly forming a composite panel of small thickness, of dimensions sufficient to cover the pole face of each pole.

The device according to the invention in fact makes it possible to reconcile two functions of divergent incidence: on the one hand, the thermal protection of the pole by forced cooling by means of a metal tube exchanger, on the other hand, the conservation of a good heating efficiency of the inductor.

Indeed, a set of metal tubes interposed between pole and product, generally forms a screen which opposes the passage of the magnetic flux and in which can be generated high intensity electric currents which have the effect of opposing the passage of the flow and heat up the circuit where they are created.

The arrangement of the tubes according to the invention makes it possible to avoid these effects and to ensure maximum "transparency" of the intense magnetic field created by the inductor.

The subject of the invention is also an inductor provided with the pole protection device as described above, which will then advantageously be dimensioned and placed opposite each of the pole faces whose shape it matches so as to cover them as well. as the induction coils and the insulators and cowlings, so as to achieve good sealing of the entire pole and its circuits.

Other characteristics and advantages will appear on reading the description which will be given by way of example, of a device according to the invention.

• la figure 1 est une vue simplifiée d'un pôle d'inducteur pourvu de son dispositif de protection et montrant celui-ci en coupe ;
• la figure 2 est un schéma du circuit de l'échangeur dans sa configuration en "épingle" ;
• les figures 3 et 4 sont deux schémas du circuit de l'échangeur dans la configuration en spirale.
• la figure 5 est une vue de détail partielle d'une variante utilisant des blocs réfractaires au lieu d'un enrobage de béton monobloc.

Reference is made to the appended drawings in which:

• Figure 1 is a simplified view of an inductor pole provided with its protection device and showing the latter in section;
• Figure 2 is a diagram of the exchanger circuit in its "pin"configuration;
• Figures 3 and 4 are two diagrams of the exchanger circuit in the spiral configuration.
• Figure 5 is a partial detail view of a variant using refractory blocks instead of a one-piece concrete coating.

In Figure 1 is shown a pole of a C- type inductor with articulated yoke, as described in document FR 2583249 to which reference may be made for more details on the general construction of the inductor. It is simply recalled here that in this type of inductor, intended in particular for reheating the edges of blanks of generally flat metal products, a second pole, similar to that shown in FIG. 1, is arranged opposite the latter, the two poles forming the ends of a "C" shaped magnetic yoke which connects them. The intense magnetic field created by the inductor has the effect of heating the product which passes between the two facing poles. The induced powers are of the order of several hundred KW, which, brought to the surface of the cylinder head, corresponds to powers which can exceed 5 MW / m².

The pole of Figure 1 includes an induction coil 2 surrounding the end of the magnetic yoke 1. A protective cover 3 surrounds the entire polar end (yoke and coil), a heat shield can be interposed between coil 2 and cover 3.

The composite plate 4 forming the protection device according to the invention is formed of a support plate 5 of rigid non-metallic material, electrically insulating, such as a material based on glass fiber, for example in "sillirite 64120" , a few millimeters thick.

An exchanger in stainless steel tube 6 coated with epoxy resin is fixed on the support plate 5. This exchanger has a configuration in successive "hairpins" alternating as shown in FIG. 2. The attachment of the exchanger 6 on the support plate 5 is ensured by screws 7 placed in the hollow of each of the "pins" of the circuit, as indicated diagrammatically in FIG. 2. This arrangement is essentially intended to avoid electrical looping between two adjacent pins which would occur if conductive parts were in simultaneous contact with two pins, successive or not, at a location other than that indicated.

The nut 8 of the screw 7 is placed in a counterbore made in the support plate 5, so as not to protrude from the surface of the latter. A sheet 9 of insulating material is glued under the plate 5, concealing the nuts 8 and thus guaranteeing electrical isolation between the fixing screws 7.

The tubes 6 of the exchanger are coated in a refractory concrete 10,
(for example the concrete based on silicon carbide marketed under the name of "morgan montex CIM 02"). This concrete completely covers the tubes 6 and its low electrical conductivity makes it possible to limit any looping currents between neighboring pins.

Advantageously, but not necessarily, this concrete is covered on one side with a plate of vitro-ceramic material 11, or any other similar material, which has great resistance to heat and especially to thermal shock, combined with good mechanical resistance. . It is also possible to use, instead of this plate, a ceramic textile fabric, or an insulating coating (type coating) based on alumina or silica.

The composite plate 4 is fixed to the pole of the inductor by bolting, either directly on the cylinder head, or on additional supports arranged between coil and cowling.

Whatever the fixing means, these are electrically isolated from the tubes 6 of the exchanger.

The thickness of the plate 4 is approximately 15 mm and its dimensions and shape are determined so as to cover the entire pole, up to the casing 3, a joint cover 12 being placed around the plate 4 to prevent water infiltration or the ingress of dust or other solid bodies inside the enclosure 3.

FIG. 2 schematically represents a preferred arrangement of the tubes of the exchanger. This is here carried out in three independent circuits, which allows for example to adapt the intensity of cooling according to the areas covered by adjusting the flow rate of the cooling fluid, usually water. This arrangement in "pins" makes it possible to cover the surface of the pole as well as possible, since it is easy to adapt the number and the length of the pins according to the shape of the surface to be covered.

Alternatively, the exchanger can have a spiral configuration as shown in Figures 3 and 4.

Figure 4 schematically shows a double inverted spiral arrangement with a single tube; the coolant supply and return are indicated by the arrows A and R.

The arrangement in Figure 3 shows four spirals powered by a central power supply. In this case, the supply is made by a pipe in the axis of the pole, through the cylinder head 1.

A central supply can also be produced in the case of the arrangements in FIGS. 2 and 4, and has the advantage of participating in the cooling of the magnetic yoke.

An essential characteristic of these exchangers is that two tubes or tube elements join at most at one point, so as to avoid any electrical looping in the exchanger.

The tubes are preferably made of non-magnetic stainless steel and for simplicity, of circular section. It is possible, in particular to reduce the thickness of the composite protection plate 4, to use tubes of flattened section, or even possibly of practically rectangular section.

Tubes of reduced thickness will be chosen, always with the aim of reducing any electrical currents generated by the magnetic field, by increasing the electrical resistance of said tubes. The tubes which can moreover, instead of being coated with epoxy resin, as indicated above, be coated with an insulating film or coated with another insulating resin (polyester for example).

The role of the protection device being essentially to form a heat shield protecting the pole and its accessories from the radiation of the heated product, we will try to bring the tubes as close as possible to each other. In addition, and more particularly in the case of the device comprising the plate of glass-ceramic material 11, the use of a concrete having a fairly good thermal conductivity allows a diffusion in its mass of the heat received by its surface and therefore allows to obtain cooling of the said ceramic hob, which can thus be maintained at a temperature close to 700 ° C. for example, while the reheated product is at more than 1000 ° C.

We can also, insofar as the mechanical characteristics of the concrete used allow it not to use a support plate.

In another variant, in particular in the case of the "pin" exchanger, instead of drowning the tubes 6 in the refractory concrete 10, it may be replaced by a plurality of blocks 13 made of insulating material with similar characteristics ( refractory concrete, ceramic, quartz, etc.) so as to reconstitute the entire concrete coating 10.

These blocks have a width equal to the distance between two neighboring tubes 6 and they have on their two longitudinal sides concavities 14 matching the section of the tubes so that they can be inserted between them to reconstitute the concrete coating overall 10 Preferably, several of these adjacent blocks will be placed in the same space between tubes. This arrangement in separate blocks allows differential expansions between different areas of the device without the risk of cracking existing in the case of monobloc concrete 10. In order to cover the curved areas of the pins, the first block 13 ′ of each row has an extension 15 of its flat upper part.

The invention is not limited to the device and to its variants described above only by way of example. In particular in the context of the arrangement of the tubes in "hairpins", provision may be made to have, in the same area, two or more tubes having this configuration, but arranged in parallel, each pin of a tube being nested in a pin formed by the other tube, and this in turn, all the pins of course remaining coplanar.

This arrangement makes it possible to reduce the pressure losses in the tubes, in particular because the hairpin curvature of the tube located, at the point of curvature, towards the outside, is less than the curvature of the tube located at this point towards the interior.

It can also be provided to have an additional tube surrounding all of the tubes arranged in a hairpin, this in order to homogenize the cooling in the area near the ends of the pins, and / or to avoid overheating of the angles forming the joint cover 12.

The invention also applies to inductors of different configuration, in particular in the shape of a "U".

Claims (14)

1. Device for protecting an electromagnetic inductor, which comprises a heat exchanger formed by one or more non-magnetic metal tubes (6) arranged in the same plane or substantially in the same plane to constitute a screen between the electromagnetic inductor and a hot metal product heated thereby, said tube(s) being adapted to allow the circulation of a cooling fluid therein from an inlet end to a outlet end of the exchanger, characterised in that the tube(s) is or are so disposed that there is at most only one electrical junction between any two tubes or tube elements (6).
2. Device as claimed in claim 1 characterised in that the exchanger (6′) is in the form of a series of alternately reversed "hairpins".
3. Device as claimed in claim 1 characterised in that the exchanger (6˝, 6′′′) is in the form of a spiral with one or more branches.
4. Device as claimed in claim 1 characterised in that the exchanger (6′, 6˝, 6′′′) is coated completely in refractory concrete (10).
5. Device as claimed in claim 1 characterised in that blocks (13) of electrically insulating refractory material are inserted between two adjacent tubes (6), the longitudinal sides of these blocks being shaped so as to match the shape of the tubes and to cover substantially the entire exchanger.
6. Device as claimed in claim 1 characterised in that the exchanger (6′, 6˝, 6′′′) is fastened to a rigid electrically insulating support plate (5) and is coated with refractory concrete (10), the assembly as a whole forming a thin composite panel (4) of sufficient size to cover the polar face of the pole.
7. Device as claimed in any one of claims 4 to 6 characterised in that the longitudinal sides of it has a plate made of glass-ceramic or similar material (11) covering one face of the refractory concrete (10) of the panel (4).
8. Device as claimed in any one of claims 4 to 6 characterised in that the tubes (6) are made of non-magnetic stainless steel.
9. Device as claimed in claim 6 characterised in that the means for fastening the tubes (6) to the support plate (5) are insulated electrically from one another.
10. Device as claimed in claim 1 characterised in that the exchanger (6′′′) has a central supply of cooling fluid facing one pole of the inductor.
11. Electromagnetic inductor for the induction heating of metal products by a transmitting magnetic field, of the type comprising a C-shaped or U-shaped yoke (1), characterised in that each pole of the inductor is equipped with a device as claimed in any one of claims 1 to 10 opposite the polar face, the form of which it matches.
12. The inductor as claimed in claim 11 characterised in that the protective device (4) covers the entire surface of the pole sealingly.
13. The inductor as claimed in claim 11 characterised in that means for fastening the protective device to the pole of the inductor are provided and are electrically insulated from the exchanger tubes (6).
14. The inductor as claimed in claim 11 characterised in that it has an axial passage reserved in the end of the yoke for feeding cooling fluid to the exchanger.

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