Magnetic induction furnace with improved heating efficiency

Abstract

A magnetic induction furnace (1) suitable for heating solid or tubular billets (5) of various lengths and diameters, made of non-ferrous material, for example to be extruded, comprises a fixed body or structure (16) housing an electric motor having an electric stator (23), into which an annular electric rotor (25) is inserted, coupled to a rotor body or tubular support (26) carrying a plurality of permanent magnets (27) arranged to form a hollow magnetic cylinder with a hollow bore (10) suitable for housing the non-rotating billet (5) to be heated. The permanent magnets (27) of the rotor body (26) comprise primary permanent magnets (27A) magnetized radially relative to the annular electric rotor (25) and secondary permanent magnets (27B) magnetized axially, the primary permanent magnets (27A) and secondary permanent magnets (27B) generating a magnetic field flux (X) directed toward the interior of the hollow bore (10) adapted to receive the billet (5) to improve induced heat generation compared to conventional magnetic structures.

Description

[Technical Field]

[0001] The object of the present invention is a magnetic induction furnace as described in the preamble of an independent claim, which is suitable for heating at least one solid or tubular billet of various lengths and diameters and made of a non-ferrous material to be extruded, for example. This preamble is described in Korean Patent Publication No. 2019-0006782. [Background technology]

[0002] Such magnetic induction furnaces utilize the well-known physical principle of placing a ferromagnetic, paramagnetic, or diamagnetic material, i.e., a conductive metal body, in a magnetic field to induce an induced current in the conductive metal body, thereby heating the conductive metal body through the Joule effect.

[0003] This physical principle is utilized to heat a metal billet to make it flexible and malleable, for example, for subsequent extrusion or subsequent heat treatment steps.

[0004] Various solutions utilizing this physical principle are known. For example, WO 2010 / 100082 discloses an apparatus, i.e., a heating furnace, for heating a metal object, i.e., a billet, by electromagnetic induction. The heating furnace includes an electric stator configured to move at least one rotor within a ring-shaped permanent magnet, and the rotor accommodates a metal object, e.g., a cylindrical metal object. The rotor generates an induced current in the metal object, heating the metal object and thereby achieving a desired temperature distribution profile along the longitudinal axis of the metal object. This allows for exceptional heating of the metal object, i.e., the billet, for uniform subsequent extrusion.

[0005] However, in WO 2010 / 100082, each billet or metal object is subjected to a rotatable movement about and along the longitudinal axis of the metal object during heating, in order to obtain a uniform temperature distribution along its longitudinal axis between both ends of the billet. This requires the provision of suitable means for rotating and axially moving the billet, which complicates the manufacture of the heating furnace and increases its manufacturing costs.

[0006] Furthermore, in this billet support structure, vibrations occur due to manufacturing errors in the billet, and it is necessary to provide means for absorbing the vibrations, which makes the support structure more complicated.

[0007] Furthermore, because the billet is moved axially in and out of the furnace, there is a risk that it may fly out of the furnace during movement, the ends of the billet must be continuously heated and then cooled (which is a significant waste of energy), while the center of the billet is constantly exposed to the fluctuating or rotating magnetic field of the furnace, resulting in a higher or elevated temperature compared to the ends of the billet, which adversely affects extrusion and renders the billet unusable for subsequent extrusion.

[0008] Furthermore, the means for movably supporting the billet during its movement is also subject to heat and can become damaged over time.

[0009] Another known solution is described in US Patent Publication No. 2010 / 147833. This prior art document provides an apparatus for heating a billet or workpiece to be treated by magnetic induction. The heating apparatus comprises a first annular magnetic unit that rotates around the billet or workpiece to be treated and is enclosed (axially) in a second annular magnetic unit. The first annular magnetic unit is housed in a thermal insulating member that is coaxial with the first annular magnetic unit, and the first annular magnetic unit uses an iron core surrounded by windings of high temperature superconductor (HTSC) with a transition temperature above 77 K (i.e., about 196 °C).

[0010] This solution necessarily requires cooling the first magnetic unit in close proximity to the workpiece to be heat treated, which is extremely difficult to do both because the first magnetic unit is located within the heating device (and therefore difficult to cool) and because the first magnetic unit is located in close proximity to the item to be heated.

[0011] Furthermore, the windings of the HTSC need to be powered, i.e. energized, and cooling is difficult to implement given the location of the first magnetic unit within the heating device.

[0012] Furthermore, due to the special nature of using HTSC, the space in which the HTSC is placed (surrounded by insulating members) is in a vacuum state, which makes implementation extremely difficult.

[0013] Generally, this known solution is inefficient due to the need to provide a vacuum to cool and insulate the HTSC windings.

[0014] In addition to the above, in this prior art heating device, the workpiece to be heated is movable relative to the heating device and does not remain entirely within the heating device in any case (the workpiece to be heated must be movable). Therefore, the workpiece to be heated is heated in parts, and the heating process cannot be maintained uniformly. Therefore, when one part of the workpiece to be heated is heated, the temperature of the other part of the workpiece to be heated (the part outside the heating device) decreases.

[0015] This also reduces the efficiency of this prior art solution.

[0016] US Patent Publication No. 2010 / 147834 also discloses the use of windings which may be made of superconductors and which in any case must be powered to generate a magnetic field to heat the workpiece being machined (with the same drawbacks as discussed above with respect to US Patent Publication No. 2010 / 147833).

[0017] Thus, even in this prior art, the energy required to heat the billet is significant, primarily due to the need to cool the superconductor windings and maintain them at constantly cryogenic temperatures to maintain the superconducting effect.

[0018] Furthermore, U.S. Patent Publication No. 2010 / 147834 discloses that the workpiece to be heated, i.e., the billet, rotates, which causes deformation of both ends of the billet supported by the gripping members, which has a negative impact on the subsequent extrusion process. Summary of the Invention [Problem to be solved by the invention]

[0019] It is an object of the present invention to provide an improved magnetic induction furnace for heating solid or tubular metal billets of any desired length, cross section or diameter, made of a non-ferrous material (e.g., aluminum or an aluminum alloy), for example, to be extruded or subjected to subsequent heat treatment, which magnetic induction furnace is more efficient than prior art magnetic induction furnaces.

[0020] In particular, it is an object of the present invention to provide a magnetic induction furnace of the type described above which is capable of providing a magnetic flux having a greater penetration capacity to the billet contained therein than that of similar prior art magnetic induction furnaces.

[0021] Another object of the present invention is to provide a magnetic induction furnace which can uniformly heat a billet to a desired temperature over the entire length and cross section of the billet, thereby minimizing heat dissipation.

[0022] Another object of the present invention is to provide a magnetic induction furnace of the type described above in which the magnetic flux exiting the furnace is reduced relative to similar prior art magnetic induction furnaces. [Means for solving the problem]

[0023] These objects, as well as other objects that will become apparent to a person skilled in the art, are achieved by a magnetic induction furnace as set forth in the independent claims. [Brief explanation of the drawings]

[0024] For a better understanding of the invention, the following figures are attached, given by way of non-limiting example:

[0025] [Figure 1] FIG. 1 shows a perspective view of a heating system for heating a metal billet using multiple furnaces equipped with magnetic induction units according to the present invention, the furnaces being arranged in series with respect to a support of the heating system with respect to a horizontal longitudinal axis. [Figure 2] FIG. 2 shows a perspective view of a magnetic induction furnace according to the present invention. [Figure 3] FIG. 3 shows a cross-sectional view taken along line 3-3 of FIG. [Figure 4] FIG. 4 shows a partially exploded perspective view of the cross-sectional area of ​​FIG. [Figure 5] FIG. 5 shows a further partially exploded perspective view of the cross-sectional area of ​​FIG. [Figure 6] FIG. 6 is an enlarged view showing the details of the portion indicated by A in FIG. [Figure 7] FIG. 7 shows a longitudinal cross section of the structure of the magnetic induction furnace shown in FIG. [Figure 8] FIG. 8 shows a cross-sectional view taken along line 8-8 of FIG. [Figure 9] FIG. 9 shows a perspective view of a portion of the structure shown in FIG. [Figure 10] FIG. 10 is an enlarged view showing the details of the portion indicated by E in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0026] With reference to the accompanying drawings, an example of a furnace according to the present invention is generally designated by the reference numeral 1. Figure 1 shows a heating system 2 comprising three adjacent successive magnetic induction furnaces 1 fixed to one another (see also Figure 10 which shows elongated flat members 90 fixing the magnetic induction furnaces 1) and supported by a fixed structure 3.

[0027] It goes without saying that the heating system 2 may include one magnetic induction furnace 1, or may include a plurality of magnetic induction furnaces, three or more.

[0028] The magnetic induction furnace 1 is arranged along a longitudinal axis W (see FIG. 2) that is horizontal or parallel to a surface or support P on which the heating system 2 is placed, although the invention is not limited to this embodiment.

[0029] In a variant of the heating system 2, one or more magnetic induction furnaces 1 may be arranged along a longitudinal axis W that is perpendicular or orthogonal to the plane P. The magnetic induction furnaces may be arranged one above the other or adjacent to each other. It should be understood that the present invention also encompasses at least one magnetic induction furnace arranged along the vertical axis W.

[0030] FIG. 10 is enlarged compared to FIG. 1 and shows only a plurality of magnetic induction furnaces 1.

[0031] Each magnetic induction furnace 1 is adapted to heat, by magnetic induction, a workpiece 5 (such as an aluminum alloy billet, for example and without limitation) having a cylindrical body 6 (solid, hollow, tubular, or any cross-section). As is known, the workpiece or billet 5 is positioned in a hollow bore 10, which is part of the magnetic induction furnace, via known components 8 (not described in detail) of a heating system 2. At the hollow bore 10, there are provided means for generating, by magnetic induction, a radially rotating magnetic field of varying intensity around the billet, so as to generate an induced current in the billet, which heats the billet to a desired temperature, for example, about 500°C (if an aluminum alloy is to be extruded) or above (for other non-ferrous materials, such as alloys known as copper, bronze, brass, silver, magnesium, titanium, or cupronickel).

[0032] The radial magnetic field generated in the magnetic induction furnace according to the invention, unlike the longitudinal magnetic field typically generated in prior art magnetic induction furnaces, provides a more homogeneous and better heating of the billet than that achieved by recent prior art solutions. In particular, the heating of the billet occurs such that the outer temperature (surface temperature) of the billet 5 differs only slightly from the inner temperature (core temperature) of the billet.

[0033] The bore 10 of each magnetic induction furnace 1 is adapted to accommodate the billet 5 such that, during heating, the billet 5 is prevented from undergoing rotational movement about its longitudinal axis, even when magnetic induction generates a magnetic field within the magnetic induction furnace bore 10 that heats the billet. Thus, with respect to rotation about its longitudinal axis, the billet is held in an absolutely fixed, stationary position (with respect to a horizontal or vertical axis) within the bore 10 of each magnetic induction furnace during heating, supported by known members 13 for holding axially moving members.

[0034] More specifically, the magnetic induction furnace 1 comprises a main body or tubular cylindrical tubular part 16 which is integrally connected to the fixed structure 3 of the heating system 2. The tubular cylindrical tubular part 16 is closed on two opposite faces 1A, 1B of the magnetic induction furnace 1 by an outer annular flange 17 which has a plurality of openings 18 for dissipating the heat generated in the magnetic induction furnace. The tubular cylindrical tubular part is provided with a ring 20 for the movement of the tubular cylindrical tubular part.

[0035] The outer cylindrical tubular body 16 comprises two inner annular cavities 19 (connected to heat dissipation openings 18) separated by a high efficiency electric motor, e.g. a synchronous electric motor (up to 97% efficiency), powered by an inverter (not shown in the accompanying drawings) of the heating system 2.

[0036] In particular, the synchronous electric motor comprises an electric stator 23 integrally coupled to the tubular cylindrical body 16 .

[0037] Whether the motor is a permanent magnet synchronous motor or a synchronous reluctance permanent magnet motor, an annular electric rotor 25 provided with permanent magnets rotates about a longitudinal axis W within the electric stator. A rotor body, i.e., a cylindrical or tubular rotor support 26, is integrally connected to the permanent magnets and supports a plurality of permanent magnets 27 defining a hollow bore 10 in which a billet 5 is received during heating, supported by the load support member 13 of the heating system 2. The electric rotor 25 is mounted on a portion of the rotor body, i.e., rotor support 26, that is a portion of the outer surface facing the annular cavity 19.

[0038] Within the hollow bore 10, preferably facing the permanent magnets 27 and between them, is a cylindrical tubular body 29 made at least partially of ceramic material that, when the billet 5 is housed within the magnetic induction furnace 1, functions as a shield for heat radiated by the billet 5 when exposed to magnetic flux generated by permanent magnets 27 carried by a rotor body or rotor support 26 rotating about its longitudinal axis W. The cylindrical tubular body or heat shield 29 provides a barrier to heat coming from the billet 5 and protects and insulates the permanent magnets 27 from the billet's thermal radiation. The cylindrical tubular body 29 also serves the purpose of protecting the permanent magnets from impact or foreign objects that may enter the hollow bore 10.

[0039] When such cylindrical tubular bodies or heat shields 29 need to be replaced due to damage or soiling or due to loss of heat insulating properties over time through use, they can be replaced by sliding them out of the hollow bore 10. Such cylindrical tubular bodies or heat shields 29 may be made entirely of ceramic or refractory material, or may be metal supports coated with ceramic or refractory material on the interior (the surface facing the hollow bore 10) or on both sides of the cylindrical surface (interior and exterior surfaces).

[0040] A plurality of ribs or fins 30 are provided on the surface of the rotor body, i.e., the rotor support 26, for the purpose of cooling the rotor support 26 from the outside by the airflow entering through the heat dissipation openings 18. These ribs or fins 30 are housed in the two inner annular cavities 19 mentioned above.

[0041] To cool the rotor support 26 (and therefore the permanent magnets and the entire magnetic induction furnace), the cylindrical tubular portion 16 (see FIGS. 1 and 10) is provided with airflow directed against the sides of the cylindrical tubular portion. To prevent the air from impacting the hollow bore 10, a number of fans or mechanical ventilation elements 100 are provided. The airflow provided by the fans 100 is shown in FIG. 10 by the dashed line at 95.

[0042] To cool the magnetic induction furnace 1, means are provided between the electric stator 23 and the cylindrical tubular portion 16 for circulating a fluid (e.g., water or glycol) intended to cool both the cylindrical tubular portion 16 and the electric stator 23, i.e., the electric motor 21 of the magnetic induction furnace 1; this "cooling" fluid circulates through a plurality of grooves 110 via ducts 31A, 31B opening on the outside of the cylindrical tubular portion 16. The cooling fluid circulates through the grooves 110, which are provided only at the electric stator between the electric stator and the cylindrical tubular portion 16, entering through the first duct 31A, passing over the entire outer surface of the electric stator 23 and exiting through the other duct 31B. For example, the grooves may be arranged in a spiral around the electric stator to effect circulation.

[0043] To increase and transfer air flow between the annular electric rotor and the electric stator, the electric rotor also includes a plurality of air fins 33. In particular, the air fins 33 are secured to support members 34 (e.g., arcuate members) that fit into the rotor support 26 and are secured to the rotor support in a known manner. It will be apparent that the air fins 33 may be otherwise secured to the rotor support 26 or may be directly attached.

[0044] Furthermore, the outer annular flange 17 has an annular body or flat annular strip 37 mounted on the annular electric rotor 25, the annular strip being arranged laterally on both sides (at the end faces 1A and 1B of the magnetic induction furnace 1) of the permanent magnets 27 in order to prevent or limit the leakage of the magnetic field lines from the opposite end faces 1A and 1B of the magnetic induction furnace 1. This leakage occurs due to the particular shape of the rotor support 26, or rather due to the particular arrangement of the permanent magnets 27 which generate a magnetic flux in the hollow bore 10 that penetrates as much as possible into the hollow bore and reaches as far as possible into the cylindrical body 6 of the billet 5 contained therein. Furthermore, the annular strip 37 carries heat by conduction towards the outside of the magnetic induction furnace 1, in particular to the finned annular body 37A on the outside of the magnetic induction furnace and adjacent to the outer annular flange 18, where the heat is removed by the air flow 95 generated by the fan or ventilation element 100 in contact with the finned annular body 37A. This allows the temperature of the permanent magnets 27 to be kept at a relatively low level, ensuring efficiency in terms of magnetic field generation.

[0045] The finned annular body and annular strip 37 also have a plurality of through holes 35 and 35A formed therein, respectively.

[0046] The through-hole 35 may be provided with a flow diverter.

[0047] The permanent magnets 27 on the rotor support 26 may be divided into two groups, alternating with one another in terms of permanent magnet arrangement: a first group of permanent magnets (the "primary permanent magnets" generally designated 27A in FIGS. 7, 8, and 9) magnetized in a radial arrangement along the rotor support 26 (i.e., in relation to the north and south poles, i.e., in relation to the north and south polar axes), or along an axis K (see FIG. 9) that leads to north and south poles that are arranged according to the radius of the cylindrical or tubular rotor body or transverse flat section of the rotor support 26 (as shown in FIG. 8); and a second group of permanent magnets (the "auxiliary permanent magnets" generally designated 27B in FIGS. 8 and 9) magnetized in an axial arrangement along the electric rotor. The main permanent magnets 27A have their north and south poles overlapping radially (along the axis K), while the auxiliary permanent magnets 27B have their north and south poles arranged adjacent to each other in a coronal configuration along the longitudinal axis of the rotor body or tubular rotor support 26, and the multiple permanent magnets (each having a north and south pole) are separated by planes perpendicular to the longitudinal axis W (see Figure 8).

[0048] In other words, for the auxiliary permanent magnet 27B, the "axial alignment" of the auxiliary permanent magnet means that the auxiliary permanent magnet is magnetized in a circumferential direction around the hollow bore 10 of the magnetic induction furnace, i.e., the north and south poles, or polar axes, of the auxiliary permanent magnet are aligned in a circumferential direction around the hollow bore 10 of the magnetic induction furnace. In other words, the north and south poles are aligned along the periphery of the hollow bore (thus, the polar axes are perpendicular to the radius of the circumference around the hollow bore). The auxiliary permanent magnet is separated by the main permanent magnet 27A, and the inner end (i.e., first end 38) of the main permanent magnet faces inward of the hollow bore 10 and is preferably flush with the curved (or plate-like) surface so as to be continuous with the auxiliary permanent magnet 27B (which is in a curved or plate-like shape), and the first end 70 of the auxiliary permanent magnet, corresponding to the first end 38 of the main permanent magnet, is aligned in a circumferential direction around the hollow bore 10. In this manner, the primary permanent magnet 27A and the auxiliary permanent magnet 27B define or at least partially define a hollow hole 10 (which is cylindrical).

[0049] It is clear that the shape of the permanent magnet described above is not essential, as long as the permanent magnet is a parallelepiped.

[0050] The main permanent magnets 27A constitute the poles of the rotor support 26, and the number of permanent magnets constituting the main permanent magnets is two or more.

[0051] The first group of magnets, the main permanent magnets 27A, have an "arc" or circular cross section (see FIGS. 8 and 9). These main permanent magnets 27A may be configured as a single magnet or as multiple magnetic elements arranged adjacent to each other. For example, FIGS. 8 and 9 show the main permanent magnets as two magnetic "arc" elements arranged adjacent to each other in a pair along the hollow bore 10. This simplifies assembly and improves the efficiency of the radial field lines of the magnetic field generated by the main permanent magnets 27A.

[0052] It is clear that each of the arc-shaped members does not have to have a curved surface, but each of the arc-shaped members may have a polygonal cross section such as a trapezoid, a square, a rectangle, etc. However, such shapes are also considered to be "arcuate" in this specification.

[0053] The (outer) end (face) (or second end) 39 of the primary permanent magnet is spaced from the corresponding outer end (second end 40) of the auxiliary permanent magnet 27B. Each of the second ends of the primary permanent magnet terminates at and rests on the rotor body or rotor support 26. Meanwhile, the second ends 40 of the auxiliary permanent magnets are spaced from the rotor body or rotor support 26, forming a gap 41. A complementary member 42, made of a thermally conductive and non-magnetic material (e.g., aluminum), is housed in the gap and fills the entire gap. Each complementary member 42 is formed with a longitudinal groove 43 (parallel to the rotor body or rotor support 26 and the longitudinal axis W of the magnetic induction furnace 1) that functions as a groove with a smooth or finned inner surface to further cool the plurality of permanent magnets 27. The ends of the groove open at the opposing faces 1A and 1B of the magnetic induction furnace, at the openings 35 in the finned annular member 37A. As mentioned above, when billet 5 is in magnetic induction furnace 1, heat generated within the billet and heating permanent magnets 27 is removed by outer annular flange 17 and finned annulus 37A from the air generated by fan 100 and adjacent to the outer annular flange and finned annulus. Deflectors at openings 35 improve the throughflow of air and into grooves 43.

[0054] The hollow hole 10 may be formed by arranging a plurality of permanent magnets in a single layer in the circumferential direction to form the hollow hole. Also, as shown in the accompanying drawings, a plurality of layers of permanent magnets 27 (e.g., three layers in Figures 3, 4, 5, and 7) are arranged annularly (so that three adjacent layers form the hollow hole 10) in the rotor body, i.e., rotor support 26, adjacent to each other and maintaining a predetermined magnetic direction relative to each other. This facilitates assembly of the "magnetic induction section" (composed of a plurality of permanent magnets) of the magnetic induction furnace 1. To further facilitate assembly, annular separators 47 are provided between the plurality of permanent magnets and one or more adjacent permanent magnets, positioned in a plane perpendicular to the axis W of the rotor body, i.e., rotor support.

[0055] Furthermore, being magnetically offset (i.e., alternating magnetic polarity of the permanent magnets in each group as shown in FIG. 8) provides continuity of magnetic polarity of the hollow bore 10 along the longitudinal axis of the magnetic induction furnace, with the multiple groups of permanent magnets all functioning as if they were a single magnet (along the longitudinal axis of the magnetic induction furnace).

[0056] Compared to known solutions that utilize magnetic flux generated by a rotating permanent magnet to heat the billet, the unique arrangement of the polarities of the permanent magnets (see FIG. 8) allows the magnetic flux to be formed in the hollow bore 10 so as to penetrate deep into the billet placed in the magnetic induction furnace. In fact, as shown diagrammatically in FIG. 8, the magnetic flux of the main permanent magnet 27A (indicated by the flow line X in FIG. 8) can penetrate all the way to the inside of the cylindrical body 6 of the billet 5 placed in the magnetic induction furnace.

[0057] If the poles of the auxiliary permanent magnets 27B are the same as those of the adjacent main permanent magnets 27A, and the poles of the main permanent magnets are magnetized 90° apart from the poles of the auxiliary permanent magnets, an "expansion" and increase in the magnetic field lines of the magnetic field generated by the main permanent magnets 27A towards the interior of the billet 5 is obtained (see FIG. 8). The magnetic field (magnetic flux X) generated by the main permanent magnets 27A penetrates deep into the central bore 10 and reaches the interior of the billet 5, i.e., deep inside the cylindrical body 6 of the billet 5, heating the billet to its interior more strongly than prior art solutions. Moreover, a reduction (a large reduction) occurs in the magnetic field penetrating into the rotor body, i.e., the tubular rotor support 26.

[0058] Another advantage of the solution according to the invention is that the rotor body or tubular rotor support 26 can be thinner than in a solution in which all magnets are arranged like the main permanent magnets 27A. The magnetic flux generated by the main permanent magnets is influenced by the auxiliary permanent magnets 27B, which displace the magnetic field more towards the interior of the hollow bore 10 than the magnetic flux that crosses the rotor body or tubular rotor support 26 (see dotted lines in FIG. 8). This increases the ratio of the magnetic flux generated towards the interior of the magnetic induction furnace 1 to the magnetic flux that is directed towards the outside of the magnetic induction furnace but does not leak out (i.e. towards the rotor body or tubular rotor support 26 of the permanent magnets 27) from about 70% to 75% to about 30% to 25% (generating more than twice the magnetic flux towards the interior of the rotor body or tubular rotor support than the magnetic flux that does not leak out of the rotor body or tubular rotor support 26). Furthermore, it should be noted that the magnetic flux generated by the permanent magnets 27 towards the outside of the magnetic induction furnace remains within the rotor body, i.e. the tubular rotor support 26 (see line F in Figure 8), and does not interfere with the magnetic flux in the electric rotor 25 of the electric motor 1, which itself remains magnetically fluxed.

[0059] In this way, the thickness of the rotor body or tubular rotor support, and therefore the diameter, weight, inertia and manufacturing costs of the rotor body or tubular rotor support 26, can be reduced.

[0060] Apart from this, the provision of the annular strip 37, in combination with the surface ribs 30 and the air fins 33, allows optimal cooling of the rotor support as it rotates about the axis W during heating of the billet 5 during rotation of the rotor support. It should also be noted that the annular strip 37 provides an optimal axial barrier (towards the opposing end faces 1A and 1B of the magnetic induction furnace 1) against the rotating magnetic field generated by the permanent magnets 27 when using a magnetic induction furnace. The rotation of the magnetic field is provided by an electric motor, e.g., a synchronous motor, comprising an electric stator 23 and an annular electric rotor 25. The invention thus offers advantages both in terms of heating of the billet 5, and in particular in terms of the quality of heating (thermal equilibration, i.e., temperature uniformity across the cross section of the billet), in terms of the time required to achieve optimal heating of the billet (reducing the time required for known solutions and increasing the production rate per hour), and in terms of safety for workers and goods in the vicinity of the magnetic induction furnace 1 in the heating system 2.

[0061] Alternatively, the electric motor 21 may be a synchronous motor of any known type, for example one with a squirrel-cage rotor, or a reluctance motor.

[0062] Based on the above description, it is clear that a person skilled in the art can find an equivalent solution to the matter described in this specification to obtain a magnetic induction furnace used for heating metal billets, which is encompassed by the characteristic features set forth in the appended claims.

Claims

1. A magnetic induction furnace (1) intended to heat a solid or tubular billet (5) made of a non-ferrous material to be extruded, The magnetic induction furnace (1) comprises a fixed body or tubular cylindrical tubular section (16) having a fixed electric stator (23) and an annular rotor (25) rotatable about a longitudinal axis (W) within the electric stator (23) and the fixed body (16), the annular rotor (25) being integrally connected to a rotor body or tubular support (26) supporting a plurality of permanent magnets (27), the permanent magnets being arranged to define a hollow bore (10) of the magnetic induction furnace having a longitudinal axis coincident with the rotational axis (W) of the annular rotor, the tubular cylindrical tubular section being adapted to accommodate at least one billet (5) to be heated by magnetic induction by rotation of the annular rotor and the rotor support connected thereto; Any rotation of the billet (5) about its longitudinal axis is prevented once it is received in the hollow bore (10), and the billet (5) remains in this state during the entire heat treatment; The plurality of permanent magnets (27) of the rotor support (26) include primary permanent magnets (27A) magnetized radially within the rotor support (26) and auxiliary permanent magnets (27B) magnetized axially around the central hole (10) of the annular rotor; In a magnetic induction furnace, the main and auxiliary permanent magnets (27A, 27B) are alternately arranged around a hollow hole (10) of the magnetic induction furnace in the rotor support (26), The main permanent magnet (27A) is magnetized in a direction at an angle of 90° to the magnetization direction of the auxiliary permanent magnet (27B), The same poles of the main permanent magnet (27A) and the auxiliary permanent magnet (27B) are arranged side by side facing toward the hollow hole (10) of the magnetic induction furnace; The main permanent magnet (27A) is formed as an arc-shaped member or an arc-shaped member centered on the hollow hole of the magnetic induction furnace, The permanent magnet faces the hollow hole (10) of the magnetic induction furnace and is continuous with the corresponding first inner end (70) of the auxiliary permanent magnet (27B); a second outer end (39) of the primary permanent magnet (27A) rests on the rotor support (26) and a corresponding outer end (40) of the auxiliary permanent magnet (27B) is spaced from the rotor support (26); A magnetic induction furnace characterized in that an air gap (41) is provided between the rotor support (26) and the outer end (40) of the auxiliary permanent magnet (27B).

2. 2. A magnetic induction furnace according to claim 1, wherein each of said main permanent magnets (27A) alternately consists of a single member or a plurality of joined magnets.

3. 2. A magnetic induction furnace according to claim 1, characterized in that the gap (41) between the auxiliary permanent magnet (27B) and the rotor support (26) accommodates a thermally conductive complementary member (42).

4. 4. A magnetic induction furnace according to claim 3, characterized in that each of the complementary elements (42) comprises a longitudinal groove (43), and all longitudinal grooves of the complementary elements (42) of the rotor support (26) open outwards of the rotor support (26) at the opposite faces (1A, 1B) of the magnetic induction furnace (1) at the locations of through-holes (35) provided in the outer finned annular body (37A) of the magnetic induction furnace.

5. 5. The magnetic induction furnace according to claim 4, wherein the inner surface of each of the longitudinal grooves (43) is formed with fins.

6. 2. The magnetic induction furnace according to claim 1, characterized in that the permanent magnets (27) cooperate with strips (37) provided on the opposing faces (1A, 1B) of the magnetic induction furnace, the strips (37) moving axially towards the finned annular bodies (37A) provided on the opposing faces (1A, 1B) to confine the axial flow generated by the auxiliary permanent magnets (27B) and dissipate the heat dissipated by the entire permanent magnets (27) to the outside of the magnetic induction furnace (1) by conduction.

7. 7. A magnetic induction furnace according to claim 4 or 6, characterized in that the strip (37) comprises a plurality of through holes (35A) aligned and coincident with the longitudinal grooves (43) of the complementary member and the through holes (35) of the outer finned annular body (37A).

8. 10. The magnetic induction furnace according to claim 1 or 7, characterized in that it comprises a plurality of fins (100) attached to the outer surface of the fixed body (16) of the magnetic induction furnace to generate an air flow in contact with the outer finned annular body (37A) but not in contact with the hollow bore (10) of the magnetic induction furnace, the air penetrating into the through holes (35, 35A) of the outer finned annular body (37A) of the strip (37) and the longitudinal grooves (43) of the complementary member (42).

9. 9. A magnetic induction furnace according to claim 8, characterized in that the outer finned annular body (37A) is provided at its through-holes (35) with flow diverters for directing the air towards the longitudinal grooves (43).

10. 2. The magnetic induction furnace according to claim 1, wherein first ends (38, 70) of the main and auxiliary permanent magnets (27A, 27B) forming the hollow bore (10) in the magnetic induction furnace are provided with tubular cylinders (29) made at least in part of a ceramic material to act as a heat shield for heat dissipated by the billet (5) when the billet (5) is exposed to magnetic flux generated by permanent magnets (27) of a rotor support (26) rotating about the longitudinal axis (W), the tubular cylinders (29) being removable and replaceable.

11. 2. A magnetic induction furnace according to claim 1, characterized in that the electric rotor (25) is integrally connected to the periphery of the rotor support (26), the rotor support (26) having on its outer surface a plurality of ribs (30) for cooling a cavity (19) between the fixed body (16) of the magnetic induction furnace, the electric stator (23) and the electric rotor (25).

12. 12. The magnetic induction furnace according to claim 11, characterized in that the rotor support (26) has a plurality of fins (33) on its outer surface, which are provided in a cavity (19) between the fixed body (16) of the magnetic induction furnace, the electric stator (23) and the electric rotor (25), and the fins increase the air flow existing in the cavity (19) and move towards openings (18) provided in a plurality of flanges (17) attached to the sides of the fixed body (16) of the magnetic induction furnace.

13. 2. The magnetic induction furnace according to claim 1, wherein the hollow bore (10) of the magnetic induction furnace (1) is constituted by a plurality of permanent magnets (27), each of which constitutes a part of the hollow bore (10), the plurality of permanent magnets (27) being longitudinally adjacent and magnetically offset relative to one another within the magnetic induction furnace (1), and between two consecutive longitudinal permanent magnets of the plurality of permanent magnets (27) a corresponding annular spacer (47) is provided in a plane perpendicular to the longitudinal axis (W) of the electric rotor (25).

14. 2. A magnetic induction furnace according to claim 1, characterized in that a coolant is circulated around the electric stator (23) of the electric motor (21) within the fixed body (16) of the magnetic induction furnace.

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