Magnetic induction furnace with improved heating efficiency

Abstract

A magnetic induction furnace (1) suitable for heating, for example, solid or tubular metal blanks (5) to be extruded, made of non-ferrous metal material, having various lengths and diameters, comprising a fixed body or framework (16) in which an electric motor (21) defined by an electric stator (23) is arranged, the invention relates to a heating device (1) comprising an electric stator (2) into which an annular electric rotor (25) connected to a rotor body or tubular support (26) carrying a plurality of permanent magnets (27) arranged to define a hollow magnetic barrel in which a cavity (10) adapted to receive a non-rotating blank (5) to be heated is provided; the permanent magnets (27) of the rotor body (26) comprise main permanent magnets (27A) magnetized in the radial direction and auxiliary permanent magnets (27B) magnetized in the axial direction with respect to the rotor body (25), said magnets (27A, 27B) generating flux lines of the magnetic field (X), said flux lines pointing deeply into the interior of a cavity (10) adapted to receive the blank (5), in order to improve the induction heating of the blank relative to conventional magnetic arrangements.

Description

Technical Field

[0001] An object forming the present invention is a magnetic induction furnace according to the preamble of the independent claim, which is suitable for heating at least one solid or tubular metal billet, for example to be extruded, made of non-ferrous material, of various lengths and diameters. Such a preamble is reported in KR 20190006782. Background Art

[0002] Such magnetic induction furnaces utilize a known physical principle according to which, by introducing a ferromagnetic, paramagnetic, diamagnetic or conductive metal body into a magnetic field, parasitic currents are generated in such a body, which lead to heating of the metal body due to the Joule effect.

[0003] This physical principle is used to heat a metal blank, wherein the aim is to make it more pliable and therefore more ductile for subsequent steps such as a subsequent extrusion operation or a heat treatment process.

[0004] Various solutions using this physical principle are known. For example, WO 2010 / 100082 discloses a device or furnace for heating a metal object or blank by electromagnetic induction, comprising an electric stator adapted to move at least one rotor inside an annular permanent magnet, and wherein the object, for example a cylindrical object, is positioned in the furnace. Such a rotor generates parasitic currents in the metal object to heat it so as to obtain a desired distribution or temperature distribution along its longitudinal axis. This allows a differential heating of the object or blank so that it can be subsequently extruded uniformly.

[0005] However, in WO2010 / 100082, each blank or metal object is subjected to a movement during its heating, which may be a rotation around its axis and / or a longitudinal rotation along this axis. This is to obtain a uniform temperature distribution along the above-mentioned axis between the ends of the blank. This necessarily requires having means suitable for rotating the blank and / or producing such an axial movement of the blank, which complicates the manufacture of the furnace and increases its cost.

[0006] Furthermore, due to the manufacturing tolerances of the blank, vibrations may exist in the support structure of the blank, which dictates the need to produce means suitable for absorbing such vibrations, leading to greater complexity of the structure.

[0007] Furthermore, the axial movement of the billet into and out of the furnace, or in any case its possible extension from the furnace during displacement, requires continuous heating and subsequent cooling of the ends of the billet (with considerable waste of energy), while the temperature of the central part - always immersed in the variable or rotating magnetic field of the furnace - is higher or greater than that of the ends. This has a negative impact on the extrusion operation to which the billet is subsequently subjected, making it unusable for such an operation.

[0008] Additionally, the device that movably supports the blank during movement is also subject to heating, which may damage the device over time.

[0009] Another known solution is described in US 2010 / 147833. This prior art document provides a device for heating a blank or workpiece to be processed by magnetic induction. The device is provided with a first annular magnetic unit which rotates around the blank or workpiece to be processed and is (coaxially) inserted into a second annular magnetic unit. The first magnetic unit is contained in a concentric (thermal) insulating element, because the first magnetic unit uses an iron core around which a winding of a high-temperature superconductor or HTSC is arranged, which has a transition temperature above 77K (i.e. approximately -196°C).

[0010] This solution requires cooling of the first magnetic unit close to the piece to be heated, and this operation is very difficult because such a unit is inside the heating device (and therefore difficult to achieve) and because it is close to the element to be heated.

[0011] Additionally, however, the HTSC windings must be supplied with power or energized, and this operation is difficult to perform in view of the location of the first magnetic unit inside the device.

[0012] Furthermore, in particular due to the use of HTSCs, the cavity in which they are arranged (defined by insulating elements) is subjected to a vacuum, and this has very high implementation difficulties.

[0013] Generally, known solutions are inefficient in view of the need to cool the HTSC windings and to create a vacuum for their insulation.

[0014] In addition to the above, it should be observed that in the devices of the prior art the workpiece to be heated is movable relative to the device and that in any case the workpiece is not completely contained in the device (and that the workpiece should therefore be movable): the heating of the aforementioned workpiece is therefore carried out in sections, but it is not possible to obtain and withstand maintenance operations uniformly, considering that while one part of such a workpiece is being heated, another part (outside the device) is being cooled.

[0015] This also reduces the efficiency of existing technical solutions.

[0016] US2010 / 147834 also discloses the use of a winding which may be a superconductor (with the same disadvantages described above in relation to US2010 / 147833) and which in any case should be supplied with power to generate a magnetic field for heating the blank to be processed.

[0017] Therefore, in this case too, there is a significant energy consumption for heating the blank, mainly due to the need to cool the superconductor windings and to keep them at a very low temperature at all times in order to maintain the superconductor effect.

[0018] Furthermore, US 2010 / 147834 discloses that the workpiece or blank to be heated rotates, and this may also cause deformation of the end of the blank supported by the clamping member, and this may have a negative impact on the subsequent extrusion operation. Summary of the invention

[0019] An object of the present invention is to provide a magnetic induction furnace for heating solid or tubular metal billets, such as those to be subjected to extrusion or subsequent heat treatment, of any length, cross-section or diameter, made of non-ferrous material, such as for example aluminium and aluminium alloys, which is improved with respect to the furnaces of the prior art and has an improved efficiency with respect to the furnaces of the prior art.

[0020] In particular, an object of the present invention is to provide a furnace of the above-mentioned type which allows a magnetic flux acting on the blanks arranged therein to have a greater penetration capacity than that found in similar prior art furnaces.

[0021] Another object is to provide a furnace in which the blank can be heated uniformly over its entire length and cross section at the desired temperature, thereby reducing heat dissipation to a minimum.

[0022] Yet another object is to provide a furnace of the above mentioned type in which the magnetic flux that can escape towards the outside thereof is smaller than in similar prior art furnaces.

[0023] These and other objects which will be more apparent to a person skilled in the art are achieved by a furnace according to the main claim. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] For a better understanding of the invention, the following drawings are attached by way of non-limiting examples only, in which:

[0025] Figure 1shows a perspective view of a system for heating a metal blank using a furnace according to the invention having magnetic segments arranged in series relative to a support of the system and having a horizontal longitudinal axis;

[0026] Figure 2 A perspective view of a magnetic induction furnace according to the present invention is shown;

[0027] Figure 3 Shown according to Figure 2 A cross-sectional view of line 3-3;

[0028] Figure 4 Shows Figure 2 A partially exploded perspective view of a section of

[0029] Figure 5 Shows Figure 2 A perspective view of a further exploded part of the

[0030] Figure 6 Shows Figure 3 an enlarged view of the detail indicated by A in FIG.

[0031] Figure 7 Shows Figure 2 A longitudinal cross-sectional view of a component of a furnace;

[0032] Figure 8 Shown according to Figure 7 A cross-sectional view taken along line 8-8;

[0033] Fig. 9 Shows Figure 7 a perspective view of a portion of a component of; and

[0034] Fig.10 Shows Figure 1 Magnified view of the detail indicated by E. DETAILED DESCRIPTION

[0035] With reference to the aforementioned figures, a furnace according to the present invention is indicated generally at 1 . Figure 1 A system 2 is shown comprising three magnetic induction furnaces 1 arranged adjacently and in succession relative to one another, fixed to one another (see also Fig.10 , which shows an elongated flat body 90 ) constraining the furnace 1 and supported by a fixed structure 3 .

[0036] Obviously, the system 2 may also be provided with only one furnace 1 or a plurality of induction furnaces, and the plurality of induction furnaces may also be more than three.

[0037] Without limiting the invention, such a furnace 1 is arranged with a longitudinal axis W (see Figure 2), the longitudinal axis W is horizontal or parallel to the plane or support P on which the system 2 is located.

[0038] In different embodiments of the system 2, one or more furnaces 1 may be arranged with a longitudinal axis W that is vertical or perpendicular to the plane P. Such furnaces may be arranged superimposed on each other or adjacent to each other. Such a solution of at least one furnace having a vertical axis W is also considered to be included in the invention.

[0039] Fig.10 Only the relative Figure 1 Enlarged magnetic induction stove1.

[0040] Each furnace 1 is suitable for heating by magnetic induction a body 5 (aluminium alloy billet as a non-limiting example) having a cylindrical body 6 (solid or hollow or tubular and of any cross section). Such body or billet 5 is suitable for being positioned in a known manner, by means of a general component 8 of a system 2 (which will not be further described below), in a portion or chamber 10 of such a furnace, where the following means are provided: means suitable for generating by magnetic induction a radially rotating magnetic field and having variable intensity around the billet, so as to generate in the billet a parasitic current that heats it to a desired temperature, for example about 500° C. (in the case of aluminium alloys to be extruded) or higher (in the exemplary case of other non-ferrous materials such as copper, bronze, brass, silver, magnesium, titanium or the alloy known as white copper, etc.).

[0041] The radial magnetic field generated by the furnace according to the invention is opposite to the longitudinal magnetic field usually generated in the induction furnaces of the prior art, making it possible to heat the blank more uniformly and better than the heating that can be obtained using the current prior art solutions; in particular, the radial magnetic field generated by the furnace according to the invention makes it possible to heat the blank 5 so that the outer temperature of the blank 5 (surface temperature) is very slightly different from its inner temperature (core temperature).

[0042] The cavity 10 of each furnace 1 is suitable for housing the blank 5 during its heating, without the blank 5 having to undergo any rotational movement about its longitudinal axis when the magnetic field for heating the blank is generated by induction in such cavity 10. The blank 5 is therefore in an absolutely fixed and stationary position (about a horizontal or vertical axis) in such cavity 10 during its heating, with respect to the rotation about its longitudinal axis, supported by known means carrying an axially movable element 13 which locks the blank 5 in rotation.

[0043] More specifically, the furnace 1 comprises a body or tubular drum and a tubular member 16 integrally joined to the fixed structure 3 of the system 2. On two opposite sides 1A, 1B of the furnace 1, the tubular drum and the tubular member 16 are closed by annular external flanges 17 having openings 18 for dispersing the heat generated in the furnace. On the frame there are rings 20 for its movement.

[0044] The tubular outer frame 16 includes two inner annular chambers 19 (arranged to communicate with the opening 18), which are separated by a high efficiency (up to 97%) electric motor such as a synchronous electric motor 21, which is powered by an inverter (not shown) of the system 2.

[0045] In particular, the synchronous electric motor comprises an electric stator 23 integrally connected to the tubular frame 16 .

[0046] In such a stator, there is an annular electric rotor 25 suitable for rotation about a longitudinal axis W, provided with permanent magnets in the case of a synchronous or reluctance electric motor, to which is integrally connected a cylindrical or tubular rotor body or support 26 supporting a plurality of permanent magnets 27 delimiting a cavity 10 into which the blank 5 is suitable for being introduced for heating thereof, the cavity 10 being supported by the load-bearing members 13 of the system 2. The electric rotor 25 is arranged on a portion of the rotor body or support 26, a portion of the outer surface of which faces the cavity 19 mentioned above.

[0047] In the cavity 10, there is preferably a cylindrical tubular body 29, at least partially made of ceramic material, facing the permanent magnets 27 and between the permanent magnets 27 and the blank 5 when the blank is introduced into the furnace 1, suitable for acting as a barrier to the heat radiated by the blank 5 when subjected to the magnetic flux generated by the permanent magnets 27 carried by the rotor body or support 26 rotating about the axis W. The cylindrical body or thermal barrier 29 allows the formation of a barrier to the heat coming from the blank 5, protecting and isolating the permanent magnets 27 from the thermal radiation of the blank, such a body 29 also having the other purpose of protecting the magnets from any impact or foreign body that may penetrate into the cavity 10.

[0048] Such a body or thermal barrier 29 can be replaced and, when it needs to be replaced because it is damaged, dirty or because it has lost its insulating properties over time and due to use, it can be slid off or removed from the cavity 10. The body of such a barrier can be made entirely of ceramic or refractory material, or it can include a metal support covering the inside (i.e. towards the cavity 10) or on two opposite cylindrical surfaces (inner and outer) made of ceramic or refractory material.

[0049] On the surface of the rotor body or support 26 there are ribs or fins 30 which also have the purpose of cooling such body 26 from the outside by the air flow coming from the openings 18. Such ribs or fins 30 are housed in the two cavities 19 mentioned further above.

[0050] In order to cool the body 26 (and therefore the magnets and the furnace as a whole), a fan or mechanical ventilation device 100 is provided on the tubular frame 16 (see Figure 1 and Fig.10 ), a fan or mechanical ventilation device 100 directs air blades to the lateral surface of such a frame, taking care not to allow such air to impact the cavity 10. The airflow or blades generated by the fan 100 are Fig.10 It is shown with a dotted line and indicated by 95.

[0051] In order to cool the furnace 1, there is a circulating fluid (for example water or glycol) between the stator 23 and the frame 16, suitable for cooling the tubular frame 16 of the furnace and the stator 23 or the electric motor 21, said "refrigerant" fluid circulates in the furnace 1 through pipes 31A, 31B leading to the outside of the frame 16. Such fluid circulates only in the grooves 110 present when the stator is between said stator and the tubular frame 16, entering from a first pipe 31A and leaving from another pipe 31B after flowing over the entire outer surface of the stator 23. For example, the grooves are arranged in a spiral form around the stator to obtain such a circulation.

[0052] In order to increase and move the air flow present between the rotor and the stator, a plurality of air fins 33 are also associated with the rotor. In particular, such air fins 33 are fixed to a support element 34 (for example an annular portion) which is fitted to the rotor body 26 and fixed to the rotor body 26 in any known manner. Obviously, the air fins 33 can be associated with the rotor body 26 in another way, or they can be obtained directly on the rotor body 26.

[0053] Furthermore, at the outer flange 17, there is an annular body or annular flat strip 37 associated with the rotor 25, arranged laterally opposite (towards the sides 1A and 1B of the furnace 1) with respect to the plurality of permanent magnets 27, so as to avoid and reduce the projection of magnetic field lines from the opposite sides 1A and 1B of the furnace 1. Such projection is due to the particular configuration of the rotor body 26, or more precisely to the particular arrangement of the permanent magnets 27, which are adapted to generate in the cavities 10 a magnetic flux which enters as much as possible into said cavities, so as to penetrate deeply into the body 6 of the blank 5 present in such cavities. Moreover, such strip 37 carries the heat by conduction towards the outside of the furnace 1 and in particular on the finned annular body 37A situated outside the furnace and close to the flange 17, so that the heat can be removed from the air blades 95 generated by the fan 100 and in contact with such finned body 37A. This allows the temperature of the permanent magnets 27 to be kept at a relatively low level, so as to ensure effectiveness in generating the magnetic field.

[0054] The finned annular body and the strip 37 also have through holes 35 and 35A, respectively.

[0055] A flow director may be provided at such an opening 35 .

[0056] The permanent magnets 27 of the rotor body 26 can be divided into two groups alternating relative to each other according to their arrangement: the first group of permanent magnets (or Figure 7 , Figure 8 and Fig. 9 The first set of permanent magnets are magnetized in a radial arrangement along the rotor body or support 26 (i.e., they have a relative position of polar axes or poles N and S), or they are arranged on an axis K (see FIG. 1 ) to the north and south poles (N and S). Fig. 9 ) are arranged on the radius of the transverse flat section of the tubular cylindrical body or support 26 (such as Figure 8 As shown); a second set of permanent magnets (or Figure 8 and Fig. 9 The second set of permanent magnets, which are "auxiliary permanent magnets" denoted by 27B in the figure, on the contrary, comprises magnets magnetized in an axial arrangement along the rotor. The main permanent magnets 27A have magnetic poles N and S superimposed radially (along the axis K), while the auxiliary permanent magnets 27B have magnetic poles N and S arranged adjacent to each other on each annular crown along the longitudinal axis of the rotor body or tubular support 26, wherein such a plurality of permanent magnets (each provided with their magnetic poles N and S) are formed by a plane orthogonal to the longitudinal axis W (such as Figure 8 ) separated by .

[0057] In other words, in the case of the auxiliary permanent magnets 27B, the fact that they have an "axial arrangement" indicates that they are magnetized or that they have magnetic poles N and S or polar axes arranged circumferentially around the cavity 10 of the furnace. In other words, the magnetic poles N and S are arranged along a circumference around the cavity (so the polar axes are orthogonal to the radius of the circumference). The auxiliary permanent magnets 27B are spaced apart by the main permanent magnets 27A, which have an inner end portion (or first end 38) facing the inside of the cavity 10 and are preferably shaped like a curved surface (or tile-shaped) so as to be continuous with the auxiliary permanent magnets 27B (curved or tile-shaped) having a corresponding first inner end 70, which is arranged circumferentially around the cavity 10. In this way, the main permanent magnets 27A and the auxiliary permanent magnets 27B define or at least delimit the cavity (cylindrical) 10.

[0058] Obviously, the aforementioned shape of the permanent magnet is not mandatory, since the permanent magnet may also be of parallelepiped shape.

[0059] The main permanent magnets 27A define magnetic poles of the rotor body 26 , and they may be equal to or more than two.

[0060] It should be observed that the main permanent magnets 27A of the first set of magnets have a "segmented" or circular cross section (see Figure 8 and Fig. 9 ). Such a main permanent magnet 27A can be made as a single piece or as a plurality of magnetic elements arranged adjacent to each other: for example, Figure 8 and Fig. 9 It shows a main magnet obtained by two magnetic "segments" arranged in pairs adjacent to each other along the cavity 10. This makes it possible to facilitate the assembly of the main permanent magnet and to improve the efficiency of the radial lines of force of the magnetic field generated by such a main magnet 27A.

[0061] Obviously, each segment may also not have a curved surface, but it may have a polygonal cross section such as a trapezoid, square or rectangle. However, in this case, it will also be indicated as a "segment" in this document.

[0062] The (outer) end (surface) (or second end) 39 of the main permanent magnet is spaced apart from the corresponding outer end (second end 40) of the auxiliary permanent magnet 27B. Each second end 39 of the main permanent magnet terminates in the rotor body or support 26 and rests on the rotor body or support 26; on the contrary, the second end 40 of the second permanent magnet is spaced apart from the rotor body 26, and such second end forms a cavity 41, into which a compensator element 42 is inserted, which is made of a thermally conductive material, made of a non-magnetic material (such as aluminum), and which completely fills the cavity. Each compensator element 42 has a longitudinal groove 43 for further cooling the plurality of permanent magnets 27, arranged parallel to the longitudinal axis W of the rotor body or support 26 and the longitudinal axis W of the furnace 1, as a groove with a smooth inner surface or a finned inner surface, said groove opening at its terminal ends at the opposite sides 1A and 1B of the furnace and at the opening 35 of the finned body 37A. As mentioned, the flange 17 and the finned body 37A allow the heat generated in the blank 5 when it is inside the furnace 1 and heating the magnets 27 to be removed from the air generated by the fan 100 and in contact with such flange and finned body. Any deflector present at the opening 35 can improve the throughflow of air and its entry into the grooves 43.

[0063] The cavity 10 may be defined by only one plurality of magnets 27 arranged only on one circumference defining the cavity. Alternatively, as shown in the figure, various plurality of permanent magnets 27 (e.g., Figure 3 , Figure 4 , Figure 5 as well as Figure 7 The plurality of permanent magnets 27 are arranged in an annular manner in the rotor body or tubular support 26 (defining three circumferences arranged adjacent to each other and delimiting the cavity 10). This allows facilitating the assembly of the "magnetic part" (defined by the plurality of permanent magnets) of the furnace 1. To further facilitate such assembly, an annular separator 47 is arranged between each magnet of the plurality of magnets 27 and the adjacent magnet / magnets, located on a plane orthogonal to the axis W of the rotor.

[0064] In addition, due to the magnetic phasing of the cavity 10 (i.e., Figure 8 All of the various multiple permanent magnets behave as if they were a single piece (along such a longitudinal axis) with alternation of magnetic polarity of each of the multiple magnets shown, wherein magnetic phasing produces continuity of magnetic poles along the longitudinal axis of the furnace.

[0065] Due to the specific arrangement of the magnet polarities (see Figure 8), a magnetic flux is obtained in the cavity 10 which penetrates deeper into the blank arranged in the furnace than the prior art solutions using the magnetic flux generated by rotating permanent magnets to heat the blank. Figure 8 As schematically shown in FIG. 1 , the magnetic field of the main permanent magnet 27A (shown by Figure 8 The flow line X in FIG. 4 is defined as being able to penetrate into an inner portion of the body 6 of the blank 5 arranged in the furnace.

[0066] Since the poles of the auxiliary magnets 27B are adjacent to the same poles of the main permanent magnets 27A and since the main poles are polarized at 90° relative to the auxiliary poles, an “extension” and amplification of the lines of force of the magnetic field generated by the main permanent magnets 27A towards the interior of the blank 5 is obtained (see Figure 8 ). The magnetic field (streamlines X) generated by the main permanent magnets 27A penetrates deeply into the cavity 10, into the interior and into the blank 5 or body 6, so as to heat the blank even further therein with respect to the prior art solutions. At the same time, a (significant) reduction of the magnetic field penetrating into the rotor body or tubular support 26 is obtained.

[0067] Another advantage of this solution is the fact that the rotor body or the tubular support 26 can have a smaller thickness compared to a similar solution with only magnets all arranged like the main permanent magnets 27A, since the influence caused by the auxiliary permanent magnets 27B on the magnetic field generated by the main permanent magnets displaces such magnetic field towards the inside of the cavity 10 to a greater extent than the influence of the magnetic field on the body or the tubular support 26 (see Figure 8 This allows to obtain a ratio between the magnetic flux generated towards the inside of the furnace 1 and the magnetic flux closed towards the outside (i.e. towards the support 26 of the magnet 27) of about 30% to 25% to 70% to 75% (i.e. the magnetic flux generated towards the inside is equal to more than twice the magnetic flux closed in the tubular support 26). It should also be observed that the magnetic flux generated towards the outside of the furnace by the magnet 27 is closed in the tubular support 26 (see Figure 8 Flow lines F in it), and it does not disturb the magnetic flux existing in the electric rotor 25 of the electric motor 1, the magnetic field in which is closed.

[0068] This also allows reducing the thickness of such a rotor body or tubular support 26 and therefore reducing its diameter, mass, inertia and cost.

[0069] Besides this, the presence of the strips 37, together with the presence of the surface ribs 30 and the fins 33, allows optimal cooling of the rotor during its rotation about the axis W when heating the blank 5. Furthermore, it should be observed that such strips 37 produce an optimal axial barrier (i.e. towards the sides 1A and 1B of the furnace 1) to the rotating magnetic field generated by the permanent magnets 27 when the furnace is in use, the rotation being obtained by an electric motor, for example a synchronous electric motor, comprising the stator 23 and the rotor 25. Thus, the invention obtains advantages both in terms of heating the blank 5 and in particular in terms of the quality of such heating (thermalization or temperature uniformity in each cross section of such a blank), in terms of the time required to obtain an optimal heating of the blank (which is reduced with respect to the time of the prior art solutions, thus resulting in a higher hourly production rate) and in terms of the safety of people and goods in the vicinity of the furnace 1 in the system 2. All these advantages arise from the fact that all the emitted magnetic fields remain confined in the furnace.

[0070] In alternative embodiments, the electric motor 21 may be of any known asynchronous type, for example, it may be provided with a squirrel-cage rotor or it may be of the reluctance type.

[0071] Clearly, from the above description, a person skilled in the art can find solutions equivalent to those described in this document for obtaining a magnetic induction furnace for heating metal blanks according to the characteristics defined in the attached claims.

Claims

1. A magnetic induction furnace (1) suitable for heating solid or tubular metal billets (5) to be extruded and made of non-ferrous metal material, the furnace (1) comprising a fixed body or a cylindrical and tubular frame (16), the fixed body or the cylindrical and tubular frame (16) comprising an electric motor (21), the electric motor (21) having a fixed electric stator (23) and an annular rotor (25), the annular rotor (25) being rotatably movable in the stator (23) and the fixed body (16) about its longitudinal axis (W), the annular rotor (25) being integrally connected to a rotor body or a tubular support (26) supporting a plurality of permanent magnets (27), the plurality of permanent magnets (27) being arranged to define a cavity (10) of the furnace (1), the cavity (10) having a longitudinal axis coinciding with the axis of rotation (W) of the rotor and being suitable for accommodating at least one blank (5) to be heated by magnetic induction, wherein, by rotating the annular rotor and the connected rotor body (26), when the blank is inserted into the aforementioned cavity (10), the rotation of the blank (5) about its longitudinal axis is completely prevented, the blank (5) remaining in this state during the entire heating operation, the plurality of permanent magnets (27) of the rotor body (26) comprising main permanent magnets (27A) magnetized radially in the rotor body (26) and auxiliary permanent magnets (27B) magnetized axially around the cavity (10) of the rotor, the main permanent magnets (27A) and the auxiliary permanent magnets (27B) alternating in the rotor body (26) around the cavity (10) of the furnace, characterized in that The main permanent magnet (27A) is polarized at 90° relative to the polarization of the auxiliary permanent magnet (27B), the same magnetic poles of the main permanent magnet (27A) and the auxiliary permanent magnet (27B) facing the cavity (10) of the furnace are arranged adjacent to each other, the main permanent magnet (27A) surrounds the cavity (10) of the furnace to form a segment part or has a circular cross-section, the permanent magnet has a first inner end portion (38) facing the cavity (10) of the furnace, and the first inner The end portion (38) is continuous with the corresponding first inner end portion (70) of the auxiliary permanent magnet (27B), the second outer end portion (39) of the main permanent magnet (27A) is placed on the rotor body (26), the corresponding outer end portion (40) of the auxiliary permanent magnet (27B) is away from the rotor body (26), and a cavity (41) exists between the rotor body (26) and the outer end portion (40) of the auxiliary permanent magnet (27B).

2. The magnetic induction furnace according to claim 1, characterized in that: Each main permanent magnet (27A) is alternatively made of a single piece or comprises a plurality of coupled magnets.

3. The magnetic induction furnace according to claim 1, characterized in that: The cavity (41) between the auxiliary permanent magnet (27B) and the rotor body (26) contains a compensator element (42) made of a thermally conductive material.

4. The magnetic induction furnace according to claim 3, characterized in that: Each compensator element (42) has a longitudinal groove (43), the longitudinal grooves of all compensator elements (42) of the rotor body (26) opening outside the rotor body (26) at through holes (35) provided in the outer annular finned body (37A) of the furnace on opposite sides (1A, 1B) of the induction furnace (1).

5. The magnetic induction furnace according to claim 4, characterized in that: Each longitudinal groove (43) is internally finned.

6. The magnetic induction furnace according to claim 1, characterized in that: The permanent magnet (27) cooperates with a strip assembly (37) arranged on the side of the permanent magnet (27) at the opposite side (1A, 1B) of the furnace, the strip (37) closing the axial flow generated by the auxiliary permanent magnet (27B) and axially transferring the heat emitted by the permanent magnet (27) as a whole towards the finned annular body (37A) present on the opposite side (1A, 1B) by conduction, for dissipating the heat to the outside of the furnace (1).

7. The magnetic induction furnace according to claims 4 and 6, characterized in that The strip (37) has an opening (35A) which is perfectly aligned with the longitudinal groove (43) of the compensator element and with the through hole (35) of the outer annular finned body (37A).

8. The magnetic induction furnace according to claims 1 and 7, characterized in that The furnace comprises a fan (100) externally associated with the fixed body (16) of the furnace, the fan (100) being suitable for generating air flow blades in contact with the finned body (37A) but not in contact with the cavity (10) of the furnace, the air penetrating into the openings (35) of the outer annular finned body (37A), into the openings (35A) of the strips (37) and into the longitudinal grooves (43) of the compensator element (42).

9. The magnetic induction furnace according to claim 8, characterized in that: At the opening (35) of the outer annular finned body (37A) there is a flow director adapted to direct the air into the longitudinal groove (43).

10. The magnetic induction furnace according to claim 1, characterized in that: At the first end portions (38, 70) of the main permanent magnets (27A) and the auxiliary permanent magnets (27B) defining the inner cavity (10) of the furnace, there is a tubular cylindrical body (29) at least partially made of ceramic material, the tubular cylindrical body (29) being suitable for acting as a barrier to the following heat: the heat is emitted by the blank (5) when the blank is subjected to the magnetic flux generated by the permanent magnets (27) of the rotor body (26) rotating around the longitudinal axis (W), and the tubular cylindrical body (29) is removable and replaceable.

11. The magnetic induction furnace according to claim 1, characterized in that: The electric rotor (25) is integrally connected to the circumferential portion of the rotor body (26), and the rotor body (26) has ribs (30) on the outside, and the ribs (30) are used to cool the cavity (19) existing between the ribs (30), the fixed body (16) of the furnace, the electric stator (23) and the electric rotor (25).

12. The magnetic induction furnace according to claim 11, characterized in that The rotor body (26) has externally a plurality of fins (33) located in the cavity (19) between the plurality of fins (33) and the fixed body (16) of the furnace, the stator (23) and the electric rotor (25), the fins being suitable for increasing the airflow present in the cavity (19) and moving it towards an opening (18) provided in a flange (17) arranged laterally on the fixed body (16) of the furnace.

13. The magnetic induction furnace according to claim 1, characterized in that: The cavity (10) of the furnace (1) is defined by a plurality of permanent magnets (27), each of which defines a portion of the cavity (10), the plurality of permanent magnets (27) being arranged longitudinally adjacent to each other in the furnace (1) and magnetically phased relative to each other, and there being a respective annular spacer (47) between two longitudinally consecutive ones of the plurality of permanent magnets (27), the annular spacer being arranged on a plane orthogonal to the longitudinal axis (W) of the rotor (25).

14. The magnetic induction furnace according to claim 1, characterized in that A circulating refrigerant is arranged in the fixed body (16) of the furnace, surrounding the stator (23) of the electric motor (21).

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