An element of an induction heating device suitable for receiving a coolant

Abstract

An element suitable for use as a component of an induction heating device, in particular an element of an oscillating circuit for generating an electromagnetic field for inductively heating a product, or an element arranged in said electromagnetic field and through which a current induced by said electromagnetic field flows, comprising a first metal sheet (3) and a second metal sheet (4), the two metal sheets being made of copper or a copper alloy, the first metal sheet (3) at least partially covering a first large surface of the second metal sheet (4), the two metal sheets forming a boundary (7). Element, characterized in that they are connected by a circumferential continuous weld (6), inside of which the metal sheets (3, 4) are mainly spaced apart to form between them a free space intended to receive a circulating coolant, and in that the mechanical resistance to plastic deformation of the first metal sheet (3) is lower than the mechanical resistance of the second metal sheet (4), to the extent that pressurization of the free space between the two metal sheets (3, 4) can cause plastic deformation of the first metal sheet (3) without causing plastic deformation of the second metal sheet (4).

Description

[Technical field]

[0001] (Specify related technical field) The present invention relates to induction heating devices, and more particularly to elements of an oscillator circuit and elements that are placed in the magnetic field generated by the oscillator circuit and that experience induced currents therein. [Background technology]

[0002] Technical Problem Addressed by the Invention and Background Induction heating devices comprise elements made of a conductive material that allows the current to flow, typically copper sheets, the thickness of which is generally between 0.5 and 5 mm. These metal sheets are used, among others, to form the inductor, the supply plate between the power source and the inductor, the magnetic shield around the inductor, the shorting coils, or the plates at the ends of the inductor or the heat sink. Since the current density is often very high, these elements must be cooled by a fluid to maintain a maximum allowable temperature of about 80 °C. The usual means of cooling these elements involves brazing several copper tubes, typically 16 mm in diameter, to the copper plate. This involves assembling a large number of parts, reducing reliability by the risk of leakage or poor mechanical and thermal contact between the tubes and the metal sheet, and reducing the ability to dissipate heat. Summary of the Invention [Problem to be solved by the invention]

[0003] The present invention provides a solution to these problems by optimizing heat dissipation through a more uniform distribution of coolant, while limiting the number of parts to be assembled. The present invention thus makes it possible to optimize the sizing of the cooling system and limit the presence of hot spots on the elements of the induction heating device. [Means for solving the problem]

[0004] According to a first aspect of the invention, an element is proposed that is suitable for use as a component of an induction heating device, in particular an element of an oscillating circuit for generating an electromagnetic field intended for inductive heating of a product, or an element that is placed in said electromagnetic field and through which a current induced by said electromagnetic field flows, comprising a first metal sheet and a second metal sheet, the two metal sheets being made of copper or a copper alloy, the first metal sheet at least partially covering a first large face of the second metal sheet, the two metal sheets being connected by a circumferential continuous weld that forms a boundary, inside which the metal sheets are mainly spaced apart to form between them a free space intended to receive a circulating coolant, and in which the mechanical resistance to plastic deformation of the first metal sheet is lower than the mechanical resistance of the second metal sheet, to an extent that a pressurization of the free space between the two metal sheets can cause a plastic deformation of the first metal sheet without causing a plastic deformation of the second metal sheet.

[0005] The element according to the invention forms a rigid and robust assembly suitable for receiving a coolant between two metal sheets inside the boundary formed by the circumferential continuous weld, the element is simpler and less costly to manufacture than elements according to the prior art, and there is less risk of coolant leakage for a more distributed and more efficient cooling.

[0006] This element allows the passage of alternating current of any frequency, for example 80 kHz, without overheating due to the rejection of heat generated by the Joule effect, thanks to the coolant flowing between the metal sheets.

[0007] According to one variant of the invention, the element comprises a third metal sheet, the mechanical resistance to plastic deformation of which is lower than that of the second metal sheet, the third metal sheet being arranged on a second large face of the second metal sheet, the third metal sheet and the second metal sheet being connected by a circumferential continuous weld defining a boundary inside which the third metal sheet and the second metal sheet are mainly spaced apart to form a free space between said metal sheets in which a coolant can circulate.

[0008] This configuration makes it possible to increase the cooling capacity of the element, which can for example be doubled.

[0009] If the element is a component of an oscillator circuit, a large current flows through it, the intensity of which depends on the power delivered. The higher the frequency of this current, the more it flows and is concentrated on the surface of the larger opposing faces of the second, thicker metal sheet. This results in more heating of the two larger opposing faces of the metal sheet and less heating in the center of the metal sheet thickness. It is therefore advantageous to have an element that is cooled by the two larger opposing faces of the thicker metal sheet or that has the highest mechanical resistance.

[0010] According to one embodiment of the present invention, the lower mechanical resistance to plastic deformation of the first metal sheet and / or the third metal sheet is brought about by a smaller thickness of the first metal sheet and / or the third metal sheet compared to the second metal sheet.

[0011] If the metallurgical state of the metal sheets is the same, the thickness difference between the first and third metal sheets and the second metal sheet is selected such that only the first and third metal sheets undergo plastic deformation under the influence of the pressure of the fluid injected into the element until the desired shape is achieved, thus preserving the main shape of the element even when the thinner metal sheets deform, since the thicker metal sheets do not deform.

[0012] The penetration depth ε of the current into the metal sheet of the element depends on the current frequency at which the oscillator circuit operates: this depth decreases with increasing frequency according to the following formula, where f is the frequency of the oscillator circuit current, μ is the relative magnetic permeability of the metal sheet and σ is its electrical conductivity:

[0013]

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[0014] The thickness of the metal sheet is selected so that the current flows preferentially through the thicker metal sheet. The thinner the metal sheet, the less current flows and the higher the frequency, since the current flow is a function of its frequency. Below a certain frequency, for a given thickness, no current or only a small amount of current flows through this thinner metal sheet.

[0015] The first and third metal sheets may be of the same or different thickness. Advantageously, the two metal sheets disposed on either side of the second, thicker metal sheet are of the same thickness. Using metal sheets of the same thickness facilitates the welding operation, since the two thinner metal sheets can be welded using the same welding conditions. Furthermore, if the two metal sheets are simultaneously welded to the thicker metal sheet using the same weld, the use of metal sheets of the same thickness means that the same result can be achieved in both metal sheets, which may not be the case if the two metal sheets were of different thicknesses.

[0016] According to another embodiment of the invention, the lower mechanical resistance to plastic deformation of the first metal sheet and / or the third metal sheet is brought about by a different metallurgical state of the first metal sheet and / or the third metal sheet compared to the second metal sheet, the first metal sheet and / or the third metal sheet being, for example, in an annealed state and the second metal sheet being in a cold worked state.

[0017] The difference in metallurgical state between the first and third metal sheets and the second metal sheet is selected such that only the first and third metal sheets undergo plastic deformation under the influence of the pressure of the fluid injected into the element until the desired shape is achieved. In this way, the main shape of the element is maintained even though the less resistant metal sheets deform, since the more resistant metal sheets do not deform. The first and third metal sheets may have the same or different mechanical resistance to plastic deformation.

[0018] According to another embodiment of the invention, the lower mechanical resistance to plastic deformation of the first metal sheet and / or the third metal sheet is brought about by a combination of a smaller thickness of the first metal sheet and / or the third metal sheet compared to the second metal sheet and a different metallurgical state.

[0019] The thickness and metallurgical state of the first and third metal sheets compared to the thickness and metallurgical state of the second metal sheet are selected such that only the first and third metal sheets plastically deform under the influence of the pressure of the fluid injected into the element until the desired shape is achieved. Thus, the main shape of the element is maintained even as the thinner metal sheet deforms, since the thicker metal sheet does not deform. The first and third metal sheets may differ in thickness. For example, the first metal sheet may be thicker than the third metal sheet, but may have a metallurgical state that provides less mechanical resistance to deformation than the mechanical resistance of the third metal sheet.

[0020] Metal sheets having a work-hardened metallurgical state have a higher mechanical resistance than annealed metal sheets. The higher the level of work hardening, the higher the level of resistance. To facilitate plastic deformation of the work-hardened sheet, the sheet is subjected to a recrystallization anneal by heating the sheet to an elevated temperature, e.g., 300-600°C, for a sufficient period of time, e.g., 15 minutes to 6 hours. The level of mechanical resistance of the annealed metal sheet depends on whether the annealing is complete or partial, i.e., the annealing temperature and the time held at that temperature.

[0021] Advantageously, according to the invention, inside the boundary formed by the circumferential continuous weld, the first metal sheet and the second metal sheet and / or the third metal sheet and the second metal sheet are connected by a plurality of continuous and / or discontinuous welds.

[0022] The presence of a circumferential continuous weld results in a uniform open free space between the two metal sheets, which does not allow the flow of the coolant to be directed between the two metal sheets and limits turbulence, resulting in less than optimal heat dissipation. According to the invention, the addition of multiple continuous or discontinuous welds inside the boundary formed by the circumferential continuous weld has the effect of forming channels through which the coolant can flow, thus allowing the coolant to be directed and distributed over the entire surface of the element while creating hydraulic turbulence to increase the exchange coefficient and remove more heat. Thus, multiple continuous or discontinuous welds improve the efficiency and distribution of cooling inside the boundary formed by the circumferential continuous weld. These welds are advantageously discontinuous so that there is no high resistance surface of the metal sheet that does not have access to the coolant inside the boundary formed by the circumferential continuous weld, or to limit the surface that does not have access to this coolant.

[0023] The multiple continuous or discontinuous welds inside the circumferential continuous weld also help to limit the deformation of the less resistant metal sheet, thereby giving the deformed metal sheet more rigidity and better mechanical strength to the element, thus making it more mechanically resistant to deformation in the event of a mechanical shock.

[0024] Advantageously, the three metal sheets are connected by the same circumferential continuous weld and by the same continuous and / or discontinuous welds inside the boundary formed by the circumferential continuous weld.

[0025] A continuous weld is produced, for example, by two rotating rollers on the outer surface of a thin metal sheet, arranged opposite each other on either side of the element and supplied with an electric current. The electric current flowing between the rollers melts the metal sheets and welds them together. Each discontinuous weld is, for example, a spot weld, obtained, for example, by two rollers as described above or by two electrodes. Welds can also be produced, for example, by laser welding or blending. Welds can also be produced by joining. It should be noted that in the case of joining, the term "weld" as used herein is not entirely appropriate.

[0026] Connecting the three metal sheets with a single weld limits the number of welds required to produce the element, thus reducing manufacturing time and cost. It also means that the element is symmetric along a plane that passes through the middle of the central metal sheet, and therefore cooling is symmetric on its two large faces.

[0027] Advantageously, the elements have a flat or curved shape or a shape combining one or more flat portions or one or more curved portions.

[0028] The invention can be easily implemented for a wide variety of element shapes, thus making it possible to adapt as required, for example, to the function and position of the element within the induction heating apparatus or to the geometry of the workpiece to be inductively heated.

[0029] According to a second aspect of the invention, an inductor for heating a product by induction is proposed, the inductor comprising a wall arranged facing the product to be heated and connected to a supply plate connected to an alternating current source, the wall and / or the supply plate of the inductor comprising an element according to the first aspect of the invention.

[0030] The inductor may be formed of a single element or an assembly of elements according to the invention. An assembly of elements may be advantageous for inductors of large size or complex shape. The elements may all be identical or they may differ to best suit the characteristics of the inductor.

[0031] The two feed plates of an inductor are often identical, each advantageously being formed in a single element according to the invention.

[0032] If the wall of the inductor comprises an element according to the invention having only two metal sheets, the first metal sheet being thinner and the second metal sheet being thicker, the element forming all or part of the wall arranged facing the product to be heated has its second, thicker metal sheet facing the inside of the inductor.

[0033] By taking the path of least resistance, the current circulating in the inductor will preferentially flow through the thickest metal sheet of the element. The latter is therefore said to generate most of the electromagnetic field for inductively heating the product. By placing the thinner metal sheets of the element on the outer surface of the inductor, the magnetic field generated by the thicker metal sheets is not hindered from being directed towards the product to be heated.

[0034] According to a third aspect of the present invention, there is proposed an induction heating apparatus comprising an inductor according to the second aspect of the present invention and a magnetic shield around the inductor, the magnetic shield including an element according to the first aspect of the present invention.

[0035] The magnetic shield around the inductor prevents the magnetic field from heating metal parts in the vicinity of the inductor, in particular the framework supporting the heating appliance. According to the invention, if the magnetic shield element is made up of metal sheets of different thicknesses, the thickest metal sheet of the element is placed facing the source of the magnetic field, i.e. towards the product to be heated, in order to promote the circulation of the magnetic field in the thickest metal sheet.

[0036] The shorting coil or plate guides the magnetic field as close as possible to the inductor. Like a magnetic shield, it prevents the magnetic field from extending over a large volume and heating up metal parts in the vicinity of the inductor. Usually there are two shorting coils or plates, one at each end of the inductor in a first direction. When the shorting coil or plate is placed in the magnetic field generated by the inductor, a current is induced in the coil or plate that needs to be cooled. According to the prior art, the shorting coil or plate is formed by a copper metal sheet to which a copper tube through which a coolant flows is welded.

[0037] An induction heating device according to the invention may comprise an inductor with at least one short-circuited coil or plate, which may comprise an element according to the first aspect of the invention. For the same reasons as the inductor, it is therefore advantageous to form the short-circuited coil or plate with an element according to the invention.

[0038] The induction heating device according to the invention may comprise a heat sink. Literally, the function of a heat sink is to evacuate heat. A heat sink is therefore a part that needs to be cooled. There are several models that are chosen depending on where they are positioned, for example a magnetic cylinder head. According to the prior art, a heat sink comprises a copper part designed to take heat away from the device to be cooled, to which copper tubes are soldered, through which a coolant circulates. For the same reasons as for the inductor, it is advantageous to form the heat sink with an element according to the invention. The induction heating device according to the invention may therefore comprise a heat sink, which includes an element according to the invention.

[0039] According to a fourth aspect of the invention, a process is proposed for manufacturing an element according to the first aspect of the invention, in which the free space formed between the first and / or third metal sheet and the second metal sheet is obtained by plastic deformation of the first and / or third metal sheet caused by injecting a pressurized fluid between the two metal sheets inside the boundary formed by the circumferential continuous weld.

[0040] Injecting a pressurized fluid between two metal sheets causes the metal sheet to deform, since the metal sheet has a lower mechanical resistance to plastic deformation, for example because it is thinner, or due to its metallurgical state.

[0041] Injecting a pressurized fluid has the advantage of distributing the pressure exerted by the fluid inside the boundary formed by the circumferential continuous weld. The distribution of the welds inside the boundary formed by the circumferential continuous weld therefore makes it easy to make the coolant distribution channels formed by the deformation of the metal sheet the same size over the entire surface. It is also possible to simply modify the dimensions of the distribution channels on the surface of the element, for example to enhance cooling in that particular zone, by having continuous or discontinuous welds of different distribution in this zone.

[0042] It should be noted that without a continuous or discontinuous weld inside the boundary formed by the circumferential continuous weld, the deformation of the thinner metal sheet obtained by the pressurized fluid would have the effect of moving the two metal sheets further apart in the middle of the boundary formed by the circumferential continuous weld. The thickness of the element would increase, which may be detrimental to constructions where compactness is required. In addition, the stiffness and mechanical resistance to plastic deformation of the element in the case of mechanical impact would be lower.

[0043] Depending on its thickness, the initial metallurgical state of the first or third metal sheets may not be suitable for the metal sheets to be deformed by the desired pressure level of the fluid injected to achieve the deformation. Annealing of the first and / or third metal sheets according to the invention is performed on at least a portion of the metal sheets that is located or intended to be located inside the boundary formed by the circumferential continuous weld that is plastically deformed by injection of the pressurized fluid.

[0044] This annealing reduces the mechanical resistance of the metal sheet to a level that allows it to deform. The annealing may be performed on the entire metal sheet before it is welded to a second metal sheet.

[0045] Alternatively, annealing can be performed only on the part to be plastically deformed. This local annealing can be performed before the metal sheet is welded to a second metal sheet or after the circumferential continuous weld has been created.

[0046] According to one embodiment of the present invention, annealing is performed after the circumferential continuous weld is produced, and the metal sheet is heated to the annealing temperature by the means used to produce the circumferential continuous weld and / or the continuous or discontinuous weld inside the boundary formed by the circumferential continuous weld, or by any other means.

[0047] If a welding means is suitable, for example used for laser welding, it may be advantageous to apply the heat required for annealing by the welding means directly to the surface sheet of the metal to be deformed. The welding means may also make it possible to heat the surface of the metal sheet in order to further reduce the mechanical resistance of the already annealed or partially annealed metal sheet and to facilitate its deformation. [Brief description of the drawings]

[0048] Further features and advantages of the present invention will become apparent from the following detailed description, which may be read in conjunction with the accompanying drawings. [Figure 1] FIG. 2 is a schematic front view of an element according to a first embodiment of the present invention; [Diagram 2] FIG. 4 is a schematic front view of an element according to a second embodiment of the present invention. [Diagram 3] FIG. 11 is a schematic front view of an element according to a third embodiment of the present invention. [Figure 4] FIG. 11 is a schematic front view of an element according to a fourth embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic cross-sectional side view of the element shown in FIG. [Figure 6] 1 is a schematic cross-sectional side view of an element according to one embodiment of the present invention; [Figure 7] 1 is a schematic cross-sectional view of an example of an apparatus for induction heating of flat products according to an embodiment of the present invention; [Figure 8] 1 is a schematic cross-sectional view of an example of an apparatus for induction heating of a cylindrical product according to an embodiment of the present invention; [Figure 9] FIG. 2 is a front view of an inductor for heating a flat product with a shorted coil according to one embodiment of the present invention; [Figure 10] FIG. 2 is a front view of an inductor for heating a flat product including a shorting plate according to one embodiment of the present invention; [Figure 11] FIG. 2 is a front view of a heat sink according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] With reference to the diagram in [Fig. 1], one can see a schematic front view of an element according to a first embodiment of the invention. The element is made of metal sheets 3, 4, stacked so that only one metal sheet can be seen in this view. The metal sheets are connected by a continuous weld around their periphery in order to maximize the surface area inside the boundary 7 formed by the continuous weld 6. Inside this boundary, the discontinuous welds 8 connecting the two metal sheets 3, 4 are present in a regular mesh. The discontinuous welds in this case are spot welds. Two ducts, one 17 for the supply and the other 18 for the discharge, allow the coolant to flow between the two metal sheets. These ducts can be located on the same metal sheet as shown in [Fig. 1] or they can be arranged on different metal sheets.

[0050] 2, there can be seen a schematic front view of an element according to a second embodiment of the invention. This element differs from the first example in that it has a discontinuous linear weld 80.

[0051] Referring to the diagram in FIG. 3, a schematic front view of an element according to a third embodiment of the invention can be seen, incorporating discontinuous linear welds 80 and discontinuous spot welds 8 .

[0052] With reference to the diagram in [Figure 4], one can see a schematic front view of an element according to a fourth embodiment of the invention, where, inside the circumferential continuous weld 6, discontinuous spot welds 8 and a continuous weld 800 are combined. The continuous weld 800 can have the function of providing, for example, mechanical reinforcement at the location of the element where it is produced. According to another illustrative example, the continuous weld can be used to prevent the presence of coolant inside the surface that defines the boundary.

[0053] The nature and location of the continuous and / or discontinuous welds arranged inside the boundary 7 formed by the circumferential continuous weld influences the flow of coolant and the mechanical resistance of the element. Depending on the function of the element and its location in the inductor or heating device, it is possible to select the nature and location of the continuous and / or discontinuous welds inside the boundary formed by the circumferential continuous weld.

[0054] With reference to the diagram in [Fig. 5], one can see a schematic side cross-sectional view of the element in [Fig. 1], along the section AA passing through the discontinuous weld shown in [Fig. 1]. A first thinner metal sheet 3 is arranged on the large face 5 side of a thicker metal sheet 4. Between the welds, the metal sheet 3 is moved away from this face 5 to create a free space 9 between the two metal sheets by injecting a fluid between them, the pressure of which is chosen in particular according to its mechanical resistance to deformation as well as the desired deformation level of the thinner metal sheet.

[0055] With reference to the diagram in [Figure 6], one can see a schematic cross-sectional side view of an element similar to [Figure 5], but according to an embodiment of the invention, the element comprises two thinner metal sheets 3, 30, 1, one on each side 5, 50 of the thicker metal sheet 4. In this example, the two thinner metal sheets have the same thickness. However, the two thinner metal sheets may be different, for example one side having a greater thickness if a greater mechanical resistance is desired on one side of the element or if the metal sheets on said side have a lower mechanical resistance than the other side of the thicker metal sheet 4.

[0056] In the example shown in FIG. 6, the continuous welds 6, 60 and the discontinuous welds 8, 80 are positioned opposite each other. This allows, for example, three metal sheets to be joined by a single weld. The continuous and / or discontinuous welds can also be staggered between two large faces of a thicker metal sheet. For example, the welds can be staggered so that the thickest metal sheet is always in contact with the coolant over its height and width against at least one of its faces.

[0057] With reference to the diagram in [Figure 7], one can see a schematic cross-sectional view of an example of an apparatus for induction heating of a flat product 2, here a metal strip. This example comprises an inductor 10 connected to an alternating current source 13 by means of two feed plates 12, and a magnetic shield 14 around the inductor. The inductor, the feed plates and the magnetic shield are mainly formed of elements according to the invention, which in their variant comprise a single thinner metal sheet.

[0058] According to one variant, only the inductor and / or only the supply plate and / or only the magnetic shield, or only two of the three devices may be formed with elements according to the invention.

[0059] The elements forming the inductor have thinner metal sheets arranged outward from the center of the inductor, where the product to be heated is located. The thickest metal sheets are therefore arranged where the current tends to flow. The magnetic field generated by the inductor is therefore mainly generated by the thickest metal sheet, since the current preferentially flows through the thickest metal sheet. This arrangement makes the heating of the product more efficient. Similarly, the elements forming the magnetic shield have thinner metal sheets arranged outward from the heating device to enhance the effect of the magnetic shield. This is because the current generated by the magnetic field flows inside the shield and therefore over the thickest metal sheet. This is also the case for short-circuited coils or plates.

[0060] With reference to the diagram in [Figure 8] one can see a schematic cross-sectional view of an example of an induction heating device according to the invention for a cylindrical product 2. The inductor 10 can advantageously be formed only by a single cylindrical element according to the invention.

[0061] 9, there can be seen a front view of an inductor 10 having two shorted coils 15 for heating a flat product according to one embodiment of the present invention. In this example, the large face of the inductor is formed by two elements according to the present invention, and the large face of the shorted coil is formed by a single element.

[0062] Referring to the diagram in FIG. 10, there can be seen a front view of an inductor 10 similar to the inductor of FIG. 9, but with two shorting plates 150 in place of the shorting coil according to one embodiment of the present invention.

[0063] Thus, the inductor resembles a padded mattress, with the bulges between the welds resembling the bulges of the mattress between the stitches of the mattress.

[0064] Referring to the diagram in FIG. 11, there can be seen a front view of an example of a heat sink 16 formed from a single element, in accordance with the present invention.

[0065] 1- Elements according to the invention 2-Induction heated products 3- The first thinner metal sheet 30-Third thinner metal sheet 4- A second thicker metal sheet 5—the first large surface of the second metal sheet 4 50—Second large surface of second metal sheet 4 6-Continuous welds 60-Continuous Welds 7-Continuous weld boundary 70-Continuous weld boundary 8-Discontinuous welds 80-Discontinuous Welds 800—Continuous weld formed by the circumferential continuous welds 6, 60 and disposed inside the boundary 7 9 - Free space between the first and second metal sheets 90—Free space between the second and third metal sheets 10-Inductor 11-Inductor wall facing product 2 12- Supply plate of inductor 10 13- Alternating current source 14-Magnetic Shielding 15-Short circuit coil 150-Short circuit plate 16-Heat sink 17-Coolant inlet 18-Coolant outlet 100-Heating device

Claims

1. An element suitable for use as a component of an induction heating device for inductively heating a product (2), in particular an element of an oscillator circuit for generating an electromagnetic field, or an element arranged in said electromagnetic field and through which a current induced by said electromagnetic field flows, comprising a first metal sheet (3) and a second metal sheet (4), said two metal sheets being made of copper or a copper alloy, said first metal sheet (3) at least partially covering a first large surface (5) of said second metal sheet (4), said two metal sheets (3, 4) having an outer surface forming a boundary (6). Element connected by a circumferential continuous weld (7), inside which the metal sheets are mainly spaced apart to form a free space (9) between them intended to receive a circulating coolant, and characterized in that the mechanical resistance to plastic deformation of the first metal sheet (3) is lower than that of the second metal sheet (4), to the extent that pressurization of the free space (9) between the two metal sheets (3, 4) can cause plastic deformation of the first metal sheet (3) without causing plastic deformation of the second metal sheet (4).

2. 2. The element according to claim 1, characterized in that the element comprises a third metal sheet (30) having a lower mechanical resistance to plastic deformation than the second metal sheet (4), the third metal sheet being arranged on a second large face (50) of the second metal sheet, the third metal sheet and the second metal sheet being connected by a circumferential continuous weld (60) defining a boundary (70) inside which the third metal sheet (30) and the second metal sheet (4) are mainly spaced apart to form a free space (90) between the metal sheets in which a coolant can circulate.

3. Element according to claim 1, characterized in that the lower mechanical resistance to plastic deformation of the first metal sheet (3) and / or the third metal sheet (30) when said element is further dependent on claim 2 is brought about by the first metal sheet and / or the third metal sheet being thinner compared to the second metal sheet (4).

4. Element according to claim 1, characterized in that the lower mechanical resistance to plastic deformation of the first metal sheet (3) and / or the third metal sheet (30), if the element is further dependent on claim 2, is caused by a different metallurgical state of the first metal sheet and / or the third metal sheet compared to the second metal sheet (4), the first metal sheet and / or the third metal sheet being, for example, in an annealed state and the second metal sheet being in a work-hardened state.

5. Element according to claim 1, characterized in that the lower mechanical resistance to plastic deformation of the first metal sheet (3) and / or the third metal sheet (30) when said element is further dependent on claim 2 is brought about by the first metal sheet and / or the third metal sheet being thinner compared to the second metal sheet (4) and by their different metallurgical state.

6. 3. An element according to claim 1 or 2, characterized in that inside the boundary (7) formed by the circumferential continuous weld (6, 60), the first metal sheet (3) and the second metal sheet (4) and / or, if this claim is dependent on claim 2, the third metal sheet (30) and the second metal sheet (4) are connected by a plurality of continuous and / or discontinuous welds (8, 80, 800).

7. Element according to claim 6, in combination with claim 2, characterized in that the three metal sheets (3, 30, 4) are connected by the same circumferential continuous weld (6, 60) and the same continuous and / or discontinuous welds (8, 80, 800) inside the boundary (7) formed by the circumferential continuous weld (6, 60).

8. Element according to claim 2, characterized in that the two metal sheets (3, 30) arranged on either side of the second, thicker metal sheet (4) are of the same thickness.

9. Element according to claim 1, characterized in that it has a flat or curved shape or a shape combining one or more flat parts or one or more curved parts.

10. 1. An inductor (10) for inductively heating a product (2), characterized in that the inductor comprises a wall (11) arranged opposite the product to be heated, connected to a supply plate (12) connected to a source of alternating current (13), the wall and / or the supply plate of the inductor comprising an element as defined in claim 1.

11. 11. An inductor according to claim 10, comprising an element according to claim 1 having only two metal sheets, the first metal sheet (3) being thinner than the second metal sheet (4), the element forming all or part of the wall (11) arranged opposite the product (2) to be heated, the second, thicker metal sheet (4) being arranged towards the inside of the inductor where the product to be heated is arranged.

12. 12. An induction heating device (100) comprising an inductor according to claim 10 or 11 and a magnetic shield (14) around the inductor, characterized in that the magnetic shield comprises an element according to claim 1.

13. 13. Induction heating device (100) according to claim 12, characterized in that the inductor comprises a short-circuited coil (15) or plate (150), the short-circuited coil or plate comprising an element according to claim 1.

14. 13. An induction heating device (100) according to claim 12, comprising a heat sink (16), said heat sink comprising an element according to claim 1.

15. 10. A process for manufacturing an element according to claim 1, characterized in that the free space (9, 90) formed between the first metal sheet (3) and / or the third metal sheet (30) when the element further depends on claim 2, and the second metal sheet (4) is obtained by plastic deformation of the first and / or third metal sheet caused by injecting a pressurized fluid between the two metal sheets inside the boundary formed by the circumferential continuous weld (6, 60).

16. 16. A process according to claim 15, characterized in that the annealing of the first metal sheet (3) and / or the third metal sheet (30) if said element further depends on claim 2 is carried out on at least a part of said sheet that is located or intended to be located inside the boundary formed by the circumferential continuous weld (6, 60) that is plastically deformed by the injection of pressurized fluid.

17. 17. The process according to claim 16, characterized in that the annealing is carried out after the circumferential continuous weld (6, 60) has been produced, and the metal sheet is heated to an annealing temperature by the means used to produce the circumferential continuous weld (6, 60) and / or a continuous or discontinuous (8, 80) weld (800) inside the boundary formed by the circumferential continuous weld (6, 60) or by other heating means.

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