EP0129160B1 - Continuous-induction-heating arrangement for metallic products - Google Patents

Description

The invention relates to a device for heating metal products by induction induction according to the preamble of claim 1. Such a device is known from document FR-A-2495752.

In another device, known from document US-A-3 008 026, the magnetic stack of each transport roller is constituted by thick removable disks which can have various values of their magnetic permeabilities to allow obtaining a suitable distribution of the magnetic flux of heating according to the width of the product to be heated. The transport rollers are arranged in pairs above and below the product to be heated and the magnetic disks are in contact with this product. The inductor coils surround the transport rollers above and below the product to be heated to ensure a symmetrical distribution of the flow. These rollers are in contact with the latter to prevent any vertical displacement of this product, this latter under the action of magnetic forces created by the heating flow.

It is clear to the specialist that this known device is intended exclusively for heating a thin strip at a low temperature, probably always less than 500 ° C., even though this document mentions heat treatment and forming among the possible applications of this device. . The heating power indeed appears low due to the arrangement of the coils and the fact that a high flux would raise the temperature of the magnetic discs above their Curie point, which would make them lose their magnetic permeability. Such a flow would also directly heat the shafts constituting the stiffening elements of these rollers, since such shafts are normally made of a steel having a significant magnetic permeability and would therefore be traversed by this flow. The heating of these trees would make them lose part of their mechanical qualities. The heating of these shafts and of these discs would be all the more important since no thermal insulation is provided between the product to be heated and the transport rollers. Finally, the maintenance of such a device would become expensive due to the presence of coils below a very hot product capable of dropping hot debris such as oxidation flakes.

It follows from the above that this document does not appear to a specialist as being able to give a useful indication in the case where a thick and heavy product must be heated to a high temperature.

On the contrary, the present invention applies to the case where thick metallic products have to be heated or reheated to a high temperature, suitable for example to facilitate their subsequent deformation. It applies more particularly to the case where these products are long steel products, for example flat steel products which are still hot during rolling and which must be reheated to a temperature of the order of 1000 to 1200 ° C. to allow the rolling process to continue under good conditions. The thickness of such a product can for example be between 25 and 250 mm approximately, and the power which must be dissipated to heat it between 10 and 200 W / cm ² approximately and most often between 50 and 200 W / cm ² . This dissipation results from the fact that the product is crossed by the variable magnetic flux created by an inductor, and that this product is electrically conductive. Its temperature prevents it from being ferromagnetic, because it is located above the Curie point, which varies according to the alloys while remaining below 770 ° C. However, it could also sometimes be trays of aluminum or other non-magnetic metals to be maintained at the correct rolling temperature.

More precisely, the heating of such a product can be obtained by a flow passing through the smallest dimension or thickness of the flat product. As for the necessary variation of this flux, it can be obtained by a periodic variation - for example sinusoidal - of an inductive current in fixed coils. It can also be obtained by the longitudinal or transverse displacement of the waves of a sliding field generated by a fixed polyphase inductor. It can also result from the periodic variation of reluctance of a magnetic circuit excited in direct current, or of the mechanical displacement of poles excited in direct current.

In known industrial devices where a roller transport is associated with high temperature and high power induction heating elements, these elements are installed between the rollers so that the latter are located as far as possible from the variable flows and are not not themselves heated, and there are no intermediate slabs between the rollers to support the product to be heated. This is the case, for example, in the device according to document GB-A-1 453 489 or in the device according to document US-A-3 471 673.

These latter known devices have the drawback that the heating power supplied by the inductors is limited by the small space available between or next to the transport rollers for the passage of the variable magnetic flux. If this flow is vertical this power is often particularly small due to the absence of intermediate support slabs, because this absence means that only small intervals between rollers are required if the temperature of the. product to be heated decreases its resistance to bending between rollers.

It has been proposed to increase the heating power of these two known devices by increasing their length according to the direction of transport. But it not only increases their cost, but also that of the buildings that house them. In addition, the heat losses are increased and it is more expensive to reach the temperatures desired for the product with heating r.

To increase the heating power without increasing the length of the heating device, it has been proposed to increase the frequency of the variation of the magnetic flux. It is known in fact that the electromotive forces induced within the material to be heated are proportional to this frequency, and that, for an amplitude of variation of the flux unchanged at all points, the power dissipated in this material increases as the square of the frequency. However, in the search for an increased frequency, it is limited by the fact that the variable flux penetrates only over a limited thickness of the material to be heated, and that this thickness decreases when the frequency increases. In addition, and above all, the use of a high frequency creates significant losses in the magnetic circuit of the inductor, and obliges to use an electric current generator with poor efficiency. The price of the energy supplied to the material to be heated therefore increases inconveniently.

Furthermore, the cost of construction of the known devices is increased by the fact that the magnetic circuit must strictly channel the flux in predetermined intervals.

The present invention aims to allow high temperature heating of metal products at the parade with increased power, using a simple device, easy to maintain, without increasing size and consuming no energy electric power only at a moderate frequency, for example at the frequency of the general supply network, that is to say 50 or 60 Hz.

It more particularly aims to allow to economically insert a heating device in a rolling chain.

This object is achieved by the device as defined by claim 1.

With regard to characteristics of a preferred implementation of the invention, reference is made to the subclaims.

It appears that the invention allows the nesting of the transport means and the heating means without the one in any way hindering the implementation of the other, which eliminates the above drawbacks. According to his teaching, recourse is had to rollers and possibly to intermediate slabs, the constitution of which is new, in particular with the use of laminating of magnetic sheets, and can be easily adapted to the particular operating conditions of a mechanical, magnetic and thermal. This makes it possible to apply to the products to be heated induction fluxes having no discontinuity in the direction of transfer of these products. The invention thus allows the greatest possible linear powers and therefore provides great compactness to the heating members. It therefore facilitates economic insertion of heating devices in existing or future rolling installations in which the required heating powers can reach several tens of megawatts.

• - la figure 1 représente une vue schématique de côté avec coupe verticale partielle d'un dispositif selon un premier mode de réalisation de l'invention avec bobinage inducteur monophasé réparti à têtes imbriquées alimenté en courant alternatif.
• - la figure 2 représente un inducteur de la figure 1 vu de dessus.
• - la figure 3 représente un inducteur de la figure 3 vu de côté.
• - la figure 4 représente une vue de face d'un rouleau de transport de la figure 1, pour montrer que ce rouleau est feuilleté transversalement à son axe.
• - la figure 5 représente une vue en coupe axiale d'une extrémité d'un rouleau de transport refroidi par circulation d'un fluide et utilisable à la place du rouleau de la figure 4.
• - la figure 6 représente une vue de côté plus détaillée d'un dallage intermédiaire feuilleté du dispositif de la figure 1.
• - la figure 7 représente le même dallage intermédiaire vu en bout.
• - la figure 8 représente une vue en bout d'un dallage intermédiaire propre à évacuer la calamine et utilisable à la place du dallage des figures 6 et 7.
• - la figure 9 représente schématiquement une vue de dessus, l'inducteur d'un deuxième mode de réalisation avec bobinage inducteur monophasé réparti à têtes concentriques alimenté en courant alternatif.
• - la figure 10 représente en vue frontale l'inducteur d'un troisième mode de réalisation avec bobines polaires alimentées en courant alternatif.
• - la figure 11 représente une vue de dessus de l'inducteur de la figure 10.
• - la figure 12 représente schématiquement en vue de dessus l'inducteur d'un quatrième mode de réalisation avec bobinages inducteurs triphasés alimentés en courants alternatifs déterminant un champ glissant parallèle au sens du transfert.
• - la figure 13 représente schématiquement en vue de côté un cinquième mode de réalisation dans l'inducteur duquel un rotor bipolaire porteur d'un bobinage réparti excité en courant continu génère les variations de flux par sa rotation.
• - la figure 14 représente schématiquement une vue de côté un sixième mode de réalisation dans lequel un rotor bipolaire à pôles saillants excités par bobines polaires génère les variations de flux par sa rotation.
• - la figure 15 représente schématiquement une vue de côté d'un septième mode de réalisation dans lequel un flux de base fixe généré par des bobines alimentées en courant continu est pulsé par la rotation d'un organe présentant une anisotropie magnétique suivant deux axes perpendiculaires.

These advantages and the particularities of the invention will be better understood on reading the description which follows, given on nonlimiting examples and illustrated by the appended figures. In these figures, the laminated metal elements comprise partial hatching directed along the planes of the sheets constituting these elements, and do not comprise hatching when these planes are parallel to that of the sheet.

• - Figure 1 shows a schematic side view with partial vertical section of a device according to a first embodiment of the invention with single-phase inductive winding distributed with nested heads supplied with alternating current.
• - Figure 2 shows an inductor of Figure 1 seen from above.
• - Figure 3 shows an inductor of Figure 3 seen from the side.
• - Figure 4 shows a front view of a transport roller of Figure 1, to show that this roller is laminated transversely to its axis.
• FIG. 5 represents a view in axial section of one end of a transport roller cooled by circulation of a fluid and usable in place of the roller of FIG. 4.
• - Figure 6 shows a more detailed side view of a laminated intermediate paving of the device of Figure 1.
• - Figure 7 shows the same intermediate paving seen at the end.
• FIG. 8 represents an end view of an intermediate paving suitable for removing the scale and usable in place of the paving in FIGS. 6 and 7.
• - Figure 9 shows schematically a top view, the inductor of a second embodiment with single-phase inductor winding distributed with concentric heads supplied with alternating current.
• - Figure 10 shows in front view the inductor of a third embodiment with polar coils supplied with alternating current.
• FIG. 11 represents a top view of the inductor of FIG. 10.
• - Figure 12 shows schematically a top view of the inductor of a fourth embodiment with three-phase inductor windings supplied with alternating currents determining a sliding field parallel to the direction of transfer.
• - Figure 13 shows schematically in side view a fifth embodiment in the inductor of which a bipolar rotor carrying a distributed winding excited in direct current generates the flux variations by its rotation.
• - Figure 14 schematically shows a side view of a sixth embodiment in which a bipolar rotor with salient poles excited by polar coils generates the flux variations by its rotation.
• - Figure 15 shows schematically a side view of a seventh embodiment in which a fixed basic flux generated by coils supplied with direct current is pulsed by the rotation of a member having a magnetic anisotropy along two perpendicular axes.

A first preferred embodiment of the invention is illustrated in FIG. 1. The product to be heated 1 is conveyed by rollers 2 and moves over intermediate slabs 3. Laminated magnetic circuits 4 form a longitudinal succession. They carry, housed in notches, inductor windings 5 generating the heating flows. These are stationary pulsed, that is to say fixed in space and variable in time at any point of the product. As shown in the top view of FIG. 2 and the end view of FIG. 3, relating to these same inductors and specifying the direction of the lamination, their winding is of the single-phase type distributed with nested heads and is supplied by terminals A and B in alternating current at industrial frequency (50 or 60 Hz). The inductors are protected from the thermal radiation of the heated product by a screen E, made of ceramic fiber about 5 cm thick for example. In this arrangement, the rollers 2 and the intermediate slabs 3 are designed to have a high magnetic permeability while being the seat of losses by eddy currents and limited magnetic hysteresis and while retaining the mechanical aptitudes necessary for transporting the products to be heated.

According to FIG. 4 and by way of nonlimiting example, the rollers are produced by stacking on a rigid shaft 21, between two clamping flanges 22 and 23, of a series of separators made of refractory non-magnetic steel 24 and of laminated magnetic blocks 25. These blocks each consist of a stack of circular flat sheets. The insulation between sheets is obtained by oxidation of their surface. The stack of these blocks and these separators is clamped between the flanges 22 and 23 with tension of the shaft 21, which makes this stack participate in the overall rigidity of the roller.

Each separator 24 has a circular support edge 24A coaxial with the roller and located radially beyond these blocks to maintain a radiated interval of thermal insulation 24B between these blocks and the product to be heated supported by this support edge.

The design of the rollers can be adapted to each operating case. For example, for less severe thermal conditions determined by cooler products or circulating at a low rate, the separators 24 can be made of more ordinary steels, or even be eliminated, and the magnetic circuits isolated by varnishing. On the contrary, for severe thermal conditions, risking lowering the elastic limit of the constituent parts, or risking bringing the magnetic circuits to a temperature higher than the Curie point for which they would lose their magnetic permeability, it may be necessary to cool the rollers. This cooling can be obtained by watering booms. As shown in FIG. 5, it is also possible to isolate the magnetic blocks 25 by insulating cylindrical rings 26 made up of molten silica and surrounding these blocks, and to ensure cooling by a circulation of a refrigerant fluid - air, water or the like - in channels 27 parallel to the axis. According to this figure, shutters 28 are necessary at the ends of radial channels 27a obtained by drilling and supplying the channels 27 from axial channels 27b.

According to FIGS. 6 and 7 and by way of nonlimiting example, the intermediate slabs are produced by stacking non-magnetic refractory steel separators 31 and laminated magnetic blocks 32, the whole assembled and stiffened by the mechanically welded elements 33, 34 and 35.

Changes in shape, size or material can of course be adopted to maintain or improve the mechanical strength and the magnetic permeability of the rollers and of the intermediate slabs depending on the thermal conditions. In particular, the cooling systems described above for the rollers are directly adaptable to these pavements.

Returning to FIG. 1, the series of rollers and intermediate slabs constitutes an almost continuous magnetic circuit. The air gaps separating the rollers and slabs can indeed have a thickness of the order of a centimeter, which does not significantly increase the reluctance of the total magnetic circuit, while practically avoiding any risk of blockage of the rollers by disturbing elements such as pieces of scale. The purpose of this arrangement is that the main air gap (of the order of one or more decimeters) encountered by the flow of the inductor is that which is formed by the vertical thickness of the product, the air above it. ci and the thermal protection of the inductor. It allows an easy channeling of the flows intended for heating and avoids, during the design of the inductors, having to be concerned with the presence of the rollers and slabs and their positions. In Figure 1 the pitch of the inductors is greater than that of the rollers, but it could obviously be less than or equal to it.

FIG. 1 represents an embodiment of inductors in modules of a pitch, or a pole, without this being a necessity but rather a convenience. It is always possible to make multipole modules or all inductors in one block. According to this figure the magnetic circuit 4 has a longitudinal succession of polar teeth 4X extending vertically, ending downward facing the product to be heated, and connected by their vertices, the inductor coils 5 inducing in these teeth a flux vertical variable magnetic.

FIG. 8 shows, in a top view of the pavements, a graded embodiment of sheets 36 in the magnetic blocks of the pavements to provide between these blocks and the separators 31, a space through which the scale which forms on the heated product can evacuate or be evacuated by an external means. Other arrangements can of course allow this evacuation of scale.

In this first embodiment, the product to be heated is for example constituted by a steel plate emerging from rolling mill rolls. This dish is for example 40 mm thick, 1.6 m wide, and travels at a speed of 1 m / s. It reaches a temperature of 925 ° C and must be reheated to 1050 ° C, which requires dissipating within it a short distance a power of about 25 MW.

The rollers are liquid cooled. They have a diameter of 400 mm, and their pitch of longitudinal succession is 950 mm

The inductor comprises 10 elements which each induce a power of 2.5 MW, at 50 Hz. They each extend over a length of 1.25 m.

The sheets of all the magnetic elements have a thickness of 0.5 mm and are isolated by oxidation according to the usual methods. The inductor leaves a free gap of 150 mm above the product to be heated. The bending of this product between rollers is not shown. It is limited to 20 mm by intermediate paving.

The heated product goes to other rolling mill rolls to be brought to a thickness of 10 mm.

According to a second embodiment of the invention, it is possible to use, as shown in top view of FIG. 9, a succession of single-phase inductors with concentric coils 5A supplied with alternating current. These inductors are integrated with their magnetic circuits 4A in place of the inductors of FIG. 1.

According to a third embodiment, it is possible to use, as shown in the end view of FIG. 10 and the top view of FIG. 11, pole coils 5B on cores supplied with alternating current. These coils are integrated with their magnetic circuits 4B in place of the corresponding elements of FIG. 1.

According to a fourth embodiment, the magnetic inductor circuit 4C can carry a polyphase winding 5C, for example three-phase as shown partially in FIG. 12. This winding creates a sliding field whose direction of movement A or B depends on the succession phases, this direction agreeing or being opposite with that C of the transport of the product to be heated. This magnetic circuit and its winding are integrated in place of the corresponding elements of FIG. 1. The winding can be performed with concentric heads instead of nested heads as shown in FIG. 12.

According to a fifth embodiment, and as shown in FIG. 13, the excitation coils 5D are carried by a magnetic cylinder 6 not necessarily laminated driven in rotation, the rest of the magnetic circuit of the inductor being shown in 4D.

According to a sixth embodiment and as shown in Figure 14, the excitation coils 5E are carried by poles 7 not necessarily laminated driven in rotation, the rest of the magnetic circuit of the inductor being shown in 4E.

In the two cases of FIGS. 13 and 14 the coils are supplied with direct current. This avoids the reactive energy call existing in the previous modes. In these two cases the variation of the heating flows with an appropriate frequency is obtained by rotation in a cylindrical space formed in the magnetic circuit 4D or 4E with a very small air gap with respect to the parts 6 or 7. In these two the moving parts 6 or 7 are shown bipolar, but may include several pairs of poles.

According to a seventh embodiment and in accordance with FIG. 15, the pole coils 5F are supplied with direct current. The variation in flux is obtained by a cyclic variation in the reluctance of the entire magnetic circuit. This variation is caused by rotation. a magnetic piece 8, laminated in the same direction as the rest of the circuit, and whose shape causes a significant variation in the air gap in which it moves and which is formed in the magnetic circuit 4F.

The shape shown in FIG. 15 and the location chosen for the magnetic piece 8 could of course be modified.

The rollers, intermediate slabs and support for the roller bearings, can be produced in different shapes or materials without departing from the scope of the invention.

Claims (6)

1. An induction heating device for moving metallic products, intended to heat thick products up to elevated temperatures while consuming electric energy at a moderate frequency, and comprising, to this effect :

- transport rollers (2) for supporting and moving the product to be heated (1) in a longitudinal and substantially horizontal direction (DL), wherein the rollers follow each other along said longitudinal direction and rotate about axes (2X) disposed parallelly to a transversal direction which is substantially horizontal and perpendicular to the longitudinal direction, while being borne by end bearings,

- intermediary supporting plates (3) for limiting the possible bending of the product between the rollers,

- inductor coils (5) fed with electric current for producing a periodically variable magnetic flux,

- and a looped magnetic circuit constituted of elements of high magnetic permeability disposed above (4) and below (2, 3) the product to be heated, for channelling the flux by forming flux loops which twice traverse the product to be heated, in the downward and upward direction, and which close longitudinally above and below the product, the magnetic circuit comprising said intermediate plates, characterized in that

- the transport rollers (2) are of the composed type and comprise each a laminated magnetic stack (25) constituting a supplementary portion of said magnetic circuit, on the one side, and a stiffening element (21) for ensuring the rigidity of the roller, on the other side, the magnetic stack taking at least half of the roller's volume and being made of magnetic metaf sheets stacked along the axis of the roller, these sheets being electrically resistive and insulated against each other and having thicknesses not substantially greater than 0,6 mm, so that the flux traversing this stack may not heat it up to above its Curie point even if it heats the product to be heated (1) to above 800 °C. the stiffening element being adapted to resist at least the stress forces and extends within the magnetic stack along said transversal direction over the entire length of the roller, so that the roller resists the bending forces created by the weight of the product to be heated, said stiffening element (21) being constituted of a non-magnetic metal, so that the magnetic flux traversing the roller is channelled by the magnetic stack on either side of the stiffening element and is not able to heat the latter up to a temperature susceptible of deteriorating its mechanical qualities,

- each transport roller (2) further comprising separators (24) spread out over the length of a roller, constituted by a refractory non-magnetic material and provided with a supporting circular bearing edge (24A) coaxial to the roller and extending radially beyond the magnetic stack for keeping a thermally isolating radial interval (24B) between this stack and the product to be heated which is supported by said bearing edge,

- a thermal isolation gap being provided between the upper surface of the product to be heated and a magnetic inductor circuit (4), which constitutes the part of said looped magnetic circuit disposed above the product and which is solely equipped with the inductor coils (5).

2. A device according to claim 1, in which the stiffening element is a rigid shaft (21).

3. A device according to claim 1, in which the stiffening element (21) is subjected to a constant effort by abutting against said magnetic stack (25) via clamping flanges (22, 23), so that a prestressing of the stack is ensured for assisting in the stiffening of the roller (2).

4. A device according to claim 1, characterized in that the stationary intermediate supporting plates (3) comprise laminated ferromagnetic blocks (32) realised by stacking of magnetic metal sheets in the transversal direction and perpendicular to it, so as to limit the heating of the plates under the influence of said magnetic flux.

5. A device according to claim 4, characterized in that the intermediate plates (3) comprise refractory non-magnetic separators (31) distributed along said transversal axis and extending beyond the ferromagnetic blocks (32) in order to keep the product to be heated (1) at distance, thereby isolating the same thermally from these blocks.

6. A device according to claim 1, characterized in that each transport roller (2) is equipped with cooling means (27A, 27B).

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