EP3363263A1

EP3363263A1 - Induction furnace, extrusion press and method

Info

Publication number: EP3363263A1
Application number: EP16766293.1A
Authority: EP
Inventors: Helmut Soltner; Peter BLÜMLER; Harald GLÜCKLER; Werner Witte
Original assignee: Bueltmann GmbH; Forschungszentrum Juelich GmbH
Current assignee: BUELTMANN GmbH; Forschungszentrum Juelich GmbH
Priority date: 2015-10-13
Filing date: 2016-09-15
Publication date: 2018-08-22
Anticipated expiration: 2036-09-15
Also published as: EP3363263B1; ES2869968T3; DE102015219831A1; WO2017063811A1

Abstract

The invention relates to an induction furnace for heating a workpiece consisting of metal, in particular to temperatures between 400°C and 1100°C, for industrial applications. The invention also relates to an extrusion press comprising an induction furnace and also to a method for heating a workpiece with the induction furnace. The object of the invention is to heat a workpiece with little expenditure of energy. To achieve the object, an induction furnace comprises a plurality of permanent magnets for generating a magnetic field in an interior space. There is a holding device, by which a workpiece can be held in the interior space for heating. There is a drive, preferably with a controllable speed, for producing a relative movement between the holding device and the permanent magnets.

Description

Induction furnace, extrusion plant and process

The invention relates to an induction furnace for heating a metal workpiece, in particular to temperatures between 400 ° C and

1100ºC for industrial applications. The invention further relates to an extrusion press comprising an induction furnace and a method for heating a workpiece in an induction furnace.

In an induction furnace, an eddy current is generated by means of a magnetic field which changes relative to the workpiece made of metal. This heats the workpiece.

With little technical effort, changing magnetic fields can be generated by means of a coil. A coil can be adapted to desired geometric requirements with little technical effort. Coils have a relatively low weight and a relatively small space. Conventional induction furnaces therefore comprise coils for generating alternating magnetic fields.

From DE 39 10 777 A1 discloses a device with a crucible for melting

Substances known. A changing magnetic field is generated by means of a coil. In addition, permanent magnets are used to generate a magnetic DC field, with the u. a. a melt flow should be calmed. With the aid of a linear drive, melted material can be transported into and out of the device.

In order to avoid electrical power losses in such induction furnaces, coils of superconducting material can be used. The then to be operated However, technical effort is very high, so that such induction furnaces have not prevailed in practice.

It is an object of the invention to be able to heat a workpiece, in particular for forming, with a low expenditure of energy.

The object of the invention is achieved by the subject matter of claim 1 and a method having the features of the independent claim. Advantageous embodiments emerge from the dependent claims.

The induction furnace comprises a plurality of permanent magnets for generating a magnetic field in an interior to solve the problem. There is a holding device by which a workpiece can be held in the interior for heating. It is a drive preferably with a controllable speed for generating a relative movement between the holding device and the

Permanent magnets available.

By the permanent magnets, a magnetic field is provided without having to spend electrical energy. Due to the relative movement generated by the drive, it is achieved that the magnetic field in the metallic

Workpiece changes, which should be heated. It is thus generated an eddy current in the metallic workpiece, through which the workpiece is heated. If the speed of the drive can be regulated, the heating process can be controlled by a speed change.

There are a plurality of permanent magnets available to align their magnetization directions differently. The different orientation makes it possible to provide in the interior a particularly strong magnetic field of, for example, 0.5 to 1 T, which makes it possible to a workpiece To heat temperatures above 400 ° C, without having to perform an excessively fast relative movement between the permanent magnet and the workpiece.

The expended for the drive drive energy, usually electrical energy for an electric motor torque applied is almost lossless converted by the resulting eddy currents in the workpiece into heat energy. Overall, it is thus possible to heat a metallic workpiece to a forming temperature with comparatively low energy, which enables shaping such as extrusion.

The material-dependent forming temperatures required for such forming as extrusion usually lie between 400 ° C. and 1100 ° C., which can be achieved with the induction furnace claimed above, above all non-ferrous metals such as aluminum, copper or brass are processed by extrusion, for example to aluminum profiles for Window or to aluminum semi-finished products, too

Aluminum or copper tubes or copper and brass profiles. Typically, "studs" are used as the workpiece, and such studs of aluminum, copper or brass usually have circular cross-sections with diameters of 100 to 400 mm and lengths of between 250 and 1500 mm.These workpieces can be brought to the temperatures required for hot-forming them then, for example, by extrusion.

The holding device is preferably realized by a clamping device. A workpiece to be heated is clamped in a preferred embodiment between two clamping cylinders of the holding device and so preferably by alone

Traction or friction held. This embodiment makes it possible to arrange the holding device including its clamping cylinder outside the interior or at least largely outside the interior and thus outside of the existing strong magnetic field. There is thus an undesirable heating of the holding device by eddy currents occurring in the holding device as a result of

Relative movements avoided or at least kept low. In one embodiment, the permanent magnets are thermally shielded from the interior. The permanent magnets preferably have a relatively small distance to the workpiece to be heated in order to heat sufficiently high energy with little energy. In order not to endanger the magnetization of the permanent magnets by the heated workpiece, the thermal shield is provided, which thermally separates a workpiece located in the induction furnace from the permanent magnets.

The thermal shield comprises in particular a polished, adjacent to the interior surface. In a particularly simple technical way so the permanent magnets can be protected against heat suitable. At least the polished surface helps to protect the permanent magnets sufficiently from heat. The polished surface is basically made of metal, such as aluminum with a polished surface or a stainless steel with a polished surface that the

Interior is facing.

Preferably, the thermal shield against end faces of the permanent magnets is apparent, so further improves the permanent magnets to protect against overheating, without having to cool active technically consuming.

The induction furnace preferably comprises no active, for example electrical energy consuming cooling, so as to keep the technical complexity and space small. If necessary, it can nevertheless be provided to provide, for example, active cooling.

In one embodiment, the thermal shield comprises as thermal shielding or thermal shielding a plurality of walls, which are preferably spatially separated from one another by spacers. Each wall may consist of a metal sheet which faces the interior Side is preferably polished. As a shield, one or more hollow cylinders may be provided which separate the permanent magnets from the interior. Because of spacers, a gap then remains between two hollow cylinders. Between two hollow cylinders then remains with a gas - so for example with air - filled gap. Permanent magnets can thus be further improved from the heat generated in the interior due to the heating of the material. It succeeds to heat existing workpieces to temperatures of 400 ° C and more, without having to cool permanent magnets technically consuming active.

In one embodiment of the invention, a device is provided which is rotated around the interior during operation and thereby generates a gas or air flow through the induction furnace. In particular, the device comprises deflection means, which by means of a rotary movement are able to deflect air so as to be able to deflect a gas or air flow is generated through the induction furnace. As a result, permanent magnets can be suitably protected against overheating.

In one embodiment, wall regions of the shield are structured in such a way that an air or gas transport along the shield is thereby supported, in order thus

Dissipate heat. In particular, webs, fins or gutters are provided which extend from an inlet opening into the induction furnace to an exit opening out of the induction furnace or at least are directed so as to promote the desired air or gas flow through the induction furnace. The webs, fins or grooves run in particular relative to the axis of rotation of the

Permanent magnets oblique and thus anti-parallel to the axis of rotation, so as to promote the desired gas or air transport in a particular degree.

The thermal shield can preferably be moved by a drive, in particular together with the permanent magnets. Preferably, only one drive is provided in order to minimize the technical complexity. As a result, an exchange of gas or air along the shield and / or inside the shield is promoted and so the thermal shield further improved without having to use active cooling for permanent magnets.

In one embodiment, a drive is provided which drives a wing assembly so that thereby an air flow is generated adjacent to the interior and preferably along the interior and / or through the induction furnace. Permanent magnets are thus further improved protected against excessive heating, without having to actively cool for it. The wing assembly is preferably moved together with the permanent magnets by only one drive to minimize the number of required drives and thus the technical complexity. Wings in the sense of the present invention comprise attachments on end faces of the induction furnace which, in the case of relative movements, cause an air flow into and / or out of the induction furnace.

The respective drive is in particular an electric drive, which basically comprises an electric motor. The speed of the motor is preferably adjustable. There is then basically a control available, with the speed of the motor can be adjusted and therefore also changed. Preferably, exactly one drive is present in order to keep the technical complexity and the installation space low.

The magnetization direction of a permanent magnet extends from the south pole to the north pole of the permanent magnet. Such magnetization directions of

Permanent magnets are preferably oriented differently in order to provide a particularly strong magnetic field in the interior. The orientation of a magnetization direction of a permanent magnet is tilted in particular relative to the orientation of the magnetization direction of an annularly adjacent permanent magnet. This tilting direction is maintained along a ring shape, so that the magnetization direction of the permanent magnet to Permanent magnet is tilted in one direction, so as to be able to provide a particularly strong magnetic field in the interior.

In one embodiment, the permanent magnets located opposite one another in an annular form have the same direction of magnetization so as to provide a particularly strong magnetic field in the interior.

In one embodiment, the tilt angle by which the direction of magnetization of two permanent magnets arranged along a ring shape is tilted is at least 10 °, preferably at least 20 °, particularly preferably at least 30 ° and / or not more than 60 °, particularly preferably not more than 50 °. The magnetization direction of the one permanent magnet then encloses an angle of at least 10 °, preferably at least 20 °, particularly preferably at least 30 ° and / or not more than 60 °, particularly preferably not more than 50 ° with the magnetization direction of the permanent magnet adjacent to the annular shape , Such tilt angles have been found to be suitable to provide a suitable strong magnetic field in the interior, which allows heating to forming temperatures even with relatively slow relative movements.

Preferably, the drive can rotate the permanent magnets around the interior. It is thus avoided to have to turn a highly heated workpiece, which is technically not easy due to the heat and the limited space It is also possible to rotate the workpiece in addition relatively slowly in the opposite direction. In addition, it is also possible to rotate only the workpiece so as to heat the workpiece to forming temperature.

In one embodiment, an annular, preferably multi-layered arrangement of the permanent magnets around the interior is provided in order to provide a strong magnetic field in the interior can. The permanent magnets are preferably arranged one above the other, next to each other and / or behind one another, in the interior to provide a strong magnetic field. The permanent magnets are particularly preferably arranged in multiple layers, wherein the layers are arranged offset from one another in order to provide a strong magnetic field in the interior, without having to provide an excessively large space for the permanent magnets. Preferably, there remains a gap between a ring mold formed from permanent magnets and an adjacent or underneath adjacent ring mold formed from permanent magnets. This distance makes it possible to hold the permanent magnets by a permanent magnet holder suitable or to fix. This distance is particularly filled with structural material, which also provides for the capture of centrifugal forces during rotation.

The permanent magnets are rotatably held in a configuration by such a permanent magnet holder relative to each other and in particular by positive engagement. If the permanent magnets are to be moved, then it is sufficient to move the permanent magnet holder and thus also the entirety of the permanent magnets. The technical complexity can be kept so low.

In one embodiment, a magnetic shield and / or a thermal shield are attached to the permanent magnet mount on the outside

The permanent magnet holder is preferably made of aluminum, titanium and / or stainless steel, ie of a metal which is not magnetizable or only weakly magnetizable. In particular, no ferromagnetic material is used for the holder. This contributes to the fact that a strong magnetic field can be provided in the interior.

If the permanent magnets are arranged in multiple layers, external permanent magnets preferably have a larger diameter than internal permanent magnets in order to provide a particularly strong magnetic field in the interior provide. External permanent magnets have a greater distance from the interior than internal permanent magnets. The diameter of the magnets increases in particular continuously from the inside to the outside. It succeeds so further improved to provide a strong magnetic field in the interior.

In one embodiment, the permanent magnets have a non-rotationally symmetrical cross section. The cross section is in particular polygonal and / or comprises a chamfer. This allows a technically simple way a rotationally fixed storage, which ensures the desired orientation of magnetic fields. In addition, the magnetization direction of the respective permanent magnet can be displayed, for example, by a bevel in order to facilitate a correct arrangement in the construction of the induction furnace. For example, in one embodiment, a chamfer is always present at the north pole of each permanent magnet so as to indicate the north pole.

In one embodiment, a permanent magnet holder is provided with inserts for permanent magnets, which specify a mounting direction and installation position. It is then only possible in exactly one way to bring a permanent magnet with non-rotationally symmetrical cross section in a slot. Installation errors are thus avoided particularly reliably. [For example, this

Embodiment, the permanent magnets include a chamfer or other alignment means, by which it is ensured that only one installation direction is possible.

In one embodiment, in addition to the already mentioned permanent magnets, there are further magnets, specifically adjacent to areas of the holding device for the workpiece. The further magnets reduce the magnetic field generated by the permanent magnets in the region of the holding device or components thereof. The werteren magnets are preferably arranged annularly around the area in which the magnetic field is to be reduced. It will be an undesirable heating of the Holding device avoided. The further magnets are arranged in particular adjacent to front sides of said permanent magnets.

The magnetization direction of another magnet runs from the south pole to the north pole of the other magnet. Such magnetization directions of the others

Magnets are preferably oriented differently so as to reduce the overall resulting magnetic field in the region of components of the holding device. The orientation of a magnetization direction of a further magnet is tilted in particular relative to the orientation of the magnetization direction of an annularly adjacent further magnet. This tilting direction is along a

Maintain ring shape, so that the magnetization direction is tilted from more magnet to further magnet in one direction, so as to be able to keep the resulting magnetic field in the area which is surrounded by the other magnets low.

In one embodiment, the further magnets located within a ring shape have the same direction of magnetization so as to provide a particularly well-reduced magnetic field in said inner region.

In one embodiment, the tilt angle by which the magnetization direction is tilted by two further magnets arranged along a ring shape is at least 10 ", preferably at least 20 °, particularly preferably at least 30 ° and / or not more than 60 °, particularly preferably not more The magnetization direction of the one further magnet then closes an angle of at least 10 ", preferably at least 20 °, particularly preferably at least 30 ° and / or not more than 60 °, particularly preferably with the magnetization direction of the further magnet adjacent to the ring shape not more than 50 °. Such tilt angles have proven to be suitable in order to provide a suitably reduced magnetic field in said inner area in order to protect internal components of the holding device from being heated. Preferably, a drive, preferably the already mentioned a drive, rotate the further magnets around said inner area. It is thus possible to generate eddy currents in electrically conductive components of the holding device, which are directed counter to the eddy currents induced by the permanent magnets. An undesirable heating of components of the holding device is thus further improved avoided.

The other magnets are rotatably held in a configuration by a magnetic holder relative to each other and in particular by positive engagement. The magnet holder is in particular part of said permanent magnet holder.

If the other magnets are to be moved, then it is sufficient to move the magnet holder and thus also the entirety of the other magnets. The technical complexity can be kept so low.

In one embodiment, the further magnets have a non-rotationally symmetrical cross section. The cross-section is in particular polygonal and / or comprises a chamfer, groove or other alignment means. This allows a technically simple way a rotationally fixed storage, which ensures the desired orientation of magnetic fields. In addition, for example, by a chamfer, groove or the other alignment means, the magnetization direction of the respective further magnet can be displayed to facilitate a correct arrangement in the construction of the induction furnace. For example, in one embodiment, a chamfer is always present at the north pole at each other magnet to indicate the north pole.

In one embodiment, a magnetic holder is provided with slots for other magnets that specify a mounting direction and installation position. It is then only possible in exactly one way to bring each other magnet with non-rotationally symmetrical cross section in a slot. Installation errors are thus avoided particularly reliably. For example, this

Embodiment, the other magnets include a chamfer or another Alignment means by which it is ensured that only one installation direction is possible.

The said further magnets are preferably also permanent magnets.

Alternatively or additionally, in one embodiment, in addition to the further magnets which reduce the magnetic field in the region of the holding device, there is a magnetic shield for the holding device. This magnetic shield for the holding device is arranged in particular end side adjacent to the permanent magnets and in particular adjacent to the inner circumference of the permanent magnets. This magnetic shield for the holding device is preferably hollow cylindrical, disc-shaped or funnel-shaped, with the funnel shape opening outwards as seen from the interior. A funnel shape is preferred because it is particularly suitably shielded and a compact design is still possible. This magnetic shield is made of ferromagnetic material, for example. In the case of a hollow cylinder, the diameter of the funnel base adjoining the permanent magnets is preferably less than or equal to the diameter of the inner circumference of the annularly arranged permanent magnets.

In the case of other magnetic shielding such as a hollow cylindrical shield, the diameter of the portion of the shield adjacent to the permanent magnets is preferably less than or equal to the diameter of the inner circumference of the annularly disposed permanent magnets. This helps to protect the holding device suitably against heating.

In one embodiment, the holding device comprises one or more ceramic cutting discs, by which a heat conduction from the workpiece to the holding device is inhibited. In addition, the holding device consists entirely or predominantly of metal. The metal is then chosen to be this particular is temperature-resistant The forming temperature of the metal for the holding device is preferably more than 800 ° C, more preferably more than 1000 ° C, most preferably more than 1100 ° C.

Advantageously, there is a magnetic shield, which magnetically shield the permanent magnets to the outside. Magnetic shielding avoids magnetic fields outside the induction furnace. Advantageously, such a heating of electrically conductive objects outside the induction furnace is avoided, which could otherwise take place during movement of the permanent magnets. Also metal parts are then not or rarely unplanned magnetically attracted by the induction furnace or otherwise affected. The magnetic shield is made of, for example, a material of high magnetic permeability. Ferromagnetic materials are suitable for magnetic shielding. For example, the magnetic shield is a μ-metal or tempered steel layer

The interior is preferably elongated. The interior space thus has a relatively large length compared to its diameter. In such an interior, a suitably strong magnetic field can be provided because a small distance between the permanent magnet and the elongated central axis of the interior is possible.

The interior is in particular 25 cm to 150 cm long and / or has a diameter of 10 cm to 50 cm. In such a dimensioned interior, a suitable strong magnetic field can be provided by means of permanent magnets, so as to be able to heat a workpiece to temperatures of more than 400 ° C, without having to perform excessively fast relative movements. In particular, then satisfy low frequencies with which a workpiece must be rotated relative to the permanent magnet. Regular frequencies of 10-20 Hz are sufficient. The holding device for a workpiece is in particular such that it is capable of holding two ends of an elongated workpiece located in the interior, and in principle by positive locking and / or frictional connection or frictional engagement. The holding device can then be arranged outside the interior. The holding device may in this embodiment wholly or at least predominantly consist of metal, without having to worry about excessive heating of the holder device. The holding device is in particular such that it is able to clamp a workpiece. A workpiece is then held by the holding device frictionally or frictionally. In one embodiment of the invention, there is a gas supply device which is arranged so that an inert gas, in particular N ₂ , Ar or C0 ₂ , between an in-furnace workpiece and adjoining walls of the furnace can be passed during heating. It is then the interior of the induction furnace in which a workpiece is to be heated, flooded with inert gas. Oxidation processes on the surface of the workpiece during a longer

Warming or heating occur and can reduce the quality of the workpiece, are thus advantageously avoided.

In a technically simple embodiment, the induction furnace comprises a container which can be flooded with an inert gas. The container is arranged and arranged so that the flooding of the container and the interior of the induction furnace is flooded with the inert gas so as to avoid adverse oxidation processes. The induction furnace may, for example, be enveloped by an outer shell. If the interior of the HüHe flooded, so then also provided for heating a workpiece interior of the induction furnace with

Inert gas flooded. The container is in a technically particularly simple embodiment trough-shaped, so open at the top. It is then a gas such as C0 _{2 is used} as an inert gas, which is heavier than air

In order to avoid oxidation processes and concomitant loss of quality, the induction furnace in one embodiment comprises a device with which a vacuum can be generated in the interior of the induction furnace. The interior of the Induction furnace in which a workpiece can be heated, therefore, can be sealed gas-tight, so for example by a closable outer shell. In addition, gas can be sucked out of the interior by a pump so as to produce the desired negative pressure or a desired vacuum. In one embodiment, the oven includes plates, and generally annular

Plates on end faces arranged to inhibit escape of inert gas introduced into the furnace during heating for avoiding oxidation processes. It can be further improved adverse oxidation processes and a concomitant deterioration in quality can be avoided.

The invention further relates to an extrusion press with a claimed induction furnace. The induction furnace is arranged so that it can heat a workpiece before extrusion, in particular to a forming temperature, which is usually between 400 ° C and 1100 ° C. Is this

Workpiece has been heated to forming temperature, the heated and then deformable with relatively little effort workpiece is transported to another station of the extrusion press and pressed by this additional station in the intended manner to a strand. The other station includes a stamp, with which the workpiece brought to forming temperature is pressed through a die. U. a. rods, wires or pipes can be produced by extrusion.

The invention also relates to a method for heating a metal workpiece in a claimed induction furnace by rotating the workpiece relative to the permanent magnets of the induction furnace until the workpiece has been heated to a temperature above 400 ° C which makes it possible to deform the workpiece by extrusion.

Preferably, during the heating, an inert gas is conducted past one or more surfaces of the workpiece, thereby oxidizing processes the one or more workpiece surfaces obstructed or avoided.

Quality losses can be avoided in this way.

The invention enables a high productivity with a simultaneous significant reduction of the directly attributable energy consumption compared to conventional induction furnaces known from the prior art.

The invention can also be used for the hardening of steels by inductive heating.

Show it:

Figure 1: section through an induction furnace with zweilagkj and annularly arranged permanent magnet;

Figure 2: four-day ring arrangement of permanent magnets for a

Induction furnace;

Figure 3: induction furnace with holding device;

Figure 4: wing assembly for induction furnace;

FIG. 5: heat shield with structuring;

Figure 6: annularly arranged permanent magnets with other magnets for

Reduction of the magnetic field generated by the permanent magnets in the region of the holding device;

Figure 7: funnel-shaped magnetic shield for holding device;

FIG. 8: Induction furnace with inlet for inert gas.

FIG. 1 shows a section through an induction furnace 1 with a plurality of permanent magnets 2, 3 for generating a magnetic field in an interior 4.

The permanent magnets 2, 3 are arranged in two layers and annularly around the interior 4 around. In the interior 4, a cylindrical, consisting of metal workpiece 5 is arranged, which is held at its ends by a holding device.

There are outer permanent magnets 2 and inner permanent magnets 3. The outer permanent magnets 2 have a greater distance from the inner space 4 than the inner permanent magnets 3. The outer permanent magnets 2 have a larger diameter than the inner permanent magnets 3. The outer permanent magnets 2 form a first ring shape. The inner permanent magnets 3 form a second ring shape. There are therefore two annular layers formed by permanent magnets 2 and 3, respectively. The permanent magnets 2 of the first annular layer are not offset from the permanent magnets 3 of the second annular layer. At least one gap remains between the two annular layers, as a rule. Permanent magnets within a ring shape are packed as tightly as possible and therefore have the smallest possible distance between them so that they at least almost touch each other.

A thermal shield consists of two acting as a shield hollow cylinders 6, which are spatially separated from each other by spacers, not shown, that one with air-filled gap between the two hollow cylinders 6 remains. The inner sides, ie the interior 4 facing sides, the hollow cylinder 6 are polished to reflect heat radiation particularly well.

The permanent magnets 2, 3 are magnetically shielded by a high-cylindrical magnetic shield 7 to the outside. The hollow cylindrical magnetic shield 7 can also contribute to the absorption of forces during rotation and therefore be shrunk. The magnetization clearing of each permanent magnet 2, 3 is indicated by arrows 8, 9, 10. The magnetization direction 8 of a first permanent magnet 2 shown in the figure 1 above vertically from bottom to top and from the south pole to the north pole of the associated permanent magnet 2. The adjacent adjacent adjacent permanent magnet 2 has a magnetization direction 9, which is to the right by 45 ° in Comparison with the direction of magnetization 8 is tilted or rotated. The magnetization direction 8 thus encloses a 45 ° angle with the magnetization direction 9. The permanent magnet 2, which is arranged to the right of the permanent magnet 2 with the magnetization direction 9, has a magnetization direction 10 which extends horizontally from left to right. This has thus been further tilted or rotated by 45 * in comparison to the magnetization direction 9. This rotation of the magnetization direction continues from one permanent magnet 2, 3 to the next adjacent permanent magnet 2, 3 along the ring shape, until the direction of magnetization 8, which extends from bottom to top, is reached again. This further permanent magnet 2 with the magnetization direction 8 shown below in FIG. 1 lies opposite the aforementioned permanent magnet 2 with the magnetization direction 8. After passing through a semicircle along the associated ring shape so again the same direction of magnetization is achieved

In the same way, the magnetization directions in the inner permanent magnets 3 change. A permanent magnet 3 of the inner ring shape, as shown in FIG. 1, has the same magnetization direction as an adjacently arranged permanent magnet 2 of the outer ring form.

The permanent magnets 2, 3 are 8-angular in section and are located in Einschoben with 8-cornered cross-section of an existing Permanentmagnethaiterung 11. The thus caused positive connection, the permanent magnets 2, 3 in the Permanentmagnethaiterung 11 rotatably held. The permanent magnet holder 11 can be rotated by an electric or pneumatic drive, not shown, together with the thermal shield 6 around the workpiece 5 around, so as to heat the existing metal workpiece 5 to forming temperature. By rotating the permanent magnet holder 11 at a frequency of about 15 Hz, an air flow through the interior 4 and through the gap between the two Hohlzylindem 6 is generated due to a wing assembly, not shown in the figure 1 whereby heat is removed. By this removal of heat, the permanent magnets 2, 3 are protected from excessive heating.

The interior 4 is about 100 cm long and has a diameter of about 30 cm. The induction furnace 1 includes a controller, not shown, which controls the rotation of the permanent magnet holder 11 and the rotational speed

FIG. 2 shows a polygonal ring arrangement formed from four layers

Permanent magnets for an induction furnace around an interior 4 around. The permanent magnets 12 of the outer annular layer are offset from the permanent magnets 13 of an annular layer adjacent thereto. The diameters of the permanent magnets 12 located in the outer layer are larger than the diameters of the permanent magnets 13 located in the annular layer adjacent thereto. Permanent magnets 14, which are likewise arranged annularly and which adjoin the inner side of the annular shape with the permanent magnets 13, are in turn arranged offset relative to the permanent magnets 13. In addition, the diameter of the permanent magnets 14 is further reduced. The same applies to permanent magnets 15 of the innermost annular layer. These permanent magnets 15 of the innermost annular layer are arranged offset relative to the permanent magnets 14 of the adjoining layer. In addition, the permanent magnets 15 of the innermost layer have the smallest diameter. Between the individual annular layers in each case a distance remains. Permanent magnets of a layer touch each other. 3 shows an induction furnace 1 with an outer magnetic shield 7. A holding device for a workpiece 5 comprises two clamping cylinders 16, by means of which the workpiece 5 can be clamped as shown in FIG. The workpiece 5 is then held by frictional connection or frictional engagement. The clamping cylinders 16 are mounted on carriages 17, which can be moved along a rail 18. In this way, the workpiece 5 can be moved into the induction furnace 1 and after heating to forming temperature out. Indicated by an arrow 19 there is a Zuführvomchtung that can perform the workpieces further workpieces.

The clamping cylinders 16 comprise ceramic intermediate layers in order to reduce heat conduction from the workpiece into the clamping cylinders. The rotational speed of the drive not shown for rotating the induction furnace 1 can be controlled so as to be able to control the heating of a workpiece 5.

FIG. 4 shows an example of a vane assembly for the induction furnace. The shields 6 have a distance and rotate during operation as indicated by arrow 21. On the shields 6 shown in plan wings 20 are mounted, which are so inclined that due to the rotational movement 21 inflowing air is deflected by the wings 20 and that in the gap between the hollow cylinder 6 inside.

In this way, the column is generated through an air flow, which is able to remove heat. FIG. 4 further clarifies that the shield preferably protrudes with respect to the permanent magnets 12, 13, 14, 15 in order to protect the permanent magnets 12, 13, 14, 15 particularly well against overheating. FIG. 4 further shows that more than two hollow cylinders 6 are preferably present, for example the six hollow cylinders 6 shown in FIG. 4, in order to further improve the protection of the permanent magnets 12, 13, 14, 15 from overheating.

FIG. 5 shows a preferred embodiment of a thermal shield with a structuring 22 on the surface of a hollow cylinder 6 with a polished surface

Inner side 23. Relative to the axis of rotation 24 of the hollow cylinder 6 extend the Structuring 6 obliquely such that thereby a gas or air transport is conveyed parallel to the axis of rotation 24 when the hollow cylinder 6 is rotated during operation. In the case of FIG. 5, the structurings 22 are in the form of webs. But it can also be alternatively or additionally provided grooves which extend obliquely relative to the axis of rotation 24, so as to promote a heat dissipating gas or air transport.

FIG. 6 shows annularly arranged permanent magnets 12, 13, 14, 15, 25, 26, which generate an eddy current in the case of a relative movement in the workpiece so as to heat the workpiece. Overall, in the case of FIG. 6, there are six ring layers. Further magnets 27 are provided adjacent to the end faces of said permanent magnets 12, 13, 14, 15, 25, 26 for reducing the magnetic field generated by the permanent magnets in the region of the holding device. The magnetization directions of the further magnets 27 are thus suitably aligned opposite to the magnetization directions of the said permanent magnets 12, 13, 14, 15, 25, 26, so that thereby the magnetic field is reduced at the end faces. In this area with reduced magnetic field strength then electrically conductive components of the holding device are arranged, such as clamping cylinder 16. The other magnets 27 are preferably also permanent magnets. These are preferably arranged adjacent to an inner layer, for example, adjacent to the innermost layer or as shown in the case of Figure 6 to a penultimate from the outside situation 25, which abuts the innermost layer 26, so as to be particularly suitable Front sides to reduce the magnetic field.

FIG. 7 shows an embodiment with funnel-shaped magnetic shields 28 which respectively circulate a region provided for the holding device. These magnetic shields 28 for the holding device are arranged frontally adjacent to the permanent magnets 12, 13, 14, 15. Each funnel 28 adjoins the inner circumference of the innermost annular layer formed of the permanent magnets 15. Opening from this inner circumference opens the funnel shape seen from the interior, as shown in Figure 7. This magnetic shield 28 is made of ferromagnetic material.

FIG. 8 shows by way of example an inlet 29 in an end wall, through which an inert gas can be introduced into the furnace during heating. Opposite there are one or more end walls 30, which at least impede leakage of the inert gas out of the furnace interior. Quality losses due to oxidation processes can thus be avoided.

Claims

claims

1. induction furnace (1) having a plurality of permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) for generating a magnetic field in an interior space (4), a holding device (16, 17) through which a Workpiece (5) in the interior (4) can be held for heating, and a drive for generating a suitable for heating a workpiece relative movement between the holding means (16, 17) and the permanent magnets (2, 3, 12, 13, 14, 15, 25, 26).

Second

Induction furnace according to claim 1, characterized in that the relative movement is a rotational movement between the holding means (16, 17) and the permanent magnets (2, 3, 12, 13, 14, 15, 25, 26).

3. Induction furnace according to claim 1 or 2, characterized by a thermal shield (6, 20), the permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) of the inner space (4) thermally shield, wherein the thermal shielding (6, 20) comprises, in particular, a polished surface (23) adjacent to the interior space (4) and / or a structured surface for gas transport.

4. induction furnace according to the preceding claim, characterized in that the structured surface one or more webs (22) and / or grooves include, which are anti-parallel to a rotation axis (24) around which the permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) are rotated.

5. Induction furnace according to one of the preceding claims, characterized in that magnetization directions (8, Θ, 10) of

Permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) are different, and preferably such that they follow along a ring shape of a tilting movement.

6. Induction furnace according to one of the preceding claims, characterized by an annular and / or multilayer arrangement of the permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) to the interior (4) around.

7. induction furnace according to one of the preceding claims, characterized in that the permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) by a permanent magnet holder (11) within the permanent magnet holder (11) are held against rotation and in particular by positive locking.

8th.

Induction furnace according to the preceding claim, characterized in that the permanent magnet holder (11) consists of aluminum, titanium and / or stainless steel.

9. Induction furnace according to one of the preceding claims, characterized in that external permanent magnets (2) have a larger diameter than internal permanent magnets (3).

10th

Induction furnace according to one of the preceding claims, characterized in that the permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) have a non-rotationally symmetrical cross section and the cross section is in particular polygonal and / or comprises a chamfer which preferably to indicate the magnetization direction of the permanent magnets.

11th

Induction furnace according to one of the preceding claims, characterized by further magnets adjacent to the holding device (16, 17) for a workpiece (5) which generates the by the permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) Reduce the magnetic field in the area of the holding device (16, 17). 12th

Induction furnace according to the preceding claim, characterized in that the further magnets (27) in a permanent magnet holder (11) are held against rotation and preferably by positive engagement and / or the other magnets (27) comprise an alignment means and / or the other magnets (27 ) have different magnetization directions and / or the further magnets (27) in particular annular on end faces of permanent magnets (2, 3,

12, 13, 14, 15, 25, 26) are arranged.

13th

Induction furnace according to one of the preceding claims, characterized by a magnetic shield (7) which magnetically shields the permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) to the outside.

14. Induction furnace according to one of the preceding claims, characterized in that the interior space (4) is elongated and the

Holding means (16, 17) is capable of holding two ends of an elongated workpiece (5), wherein the holding device can be arranged completely or predominantly outside the interior space (4).

15. Induction oven according to one of the preceding claims, characterized in that the interior space (4) is 25 cm to 150 cm long and / or has a diameter of 10 cm to 50 cm, preferably up to 40 cm

16. Induction furnace according to one of the preceding claims, characterized in that a preferably funnel-shaped magnetic shield (28) are provided for one or more areas, in the holding device (16, 17) is arranged

17. Induction furnace according to the preceding claim, characterized in that the magnetic shield (28) adjacent to the inner circumference of annularly arranged permanent magnets (2, 3, 12, 13, 14, 15, 25, 26) is arranged

18. An extrusion press with an induction furnace according to any one of the preceding claims, wherein the induction furnace is arranged to heat a workpiece (5) prior to extrusion, in particular to 400 ^e C to 1100 ^e C.

A method of heating a metal workpiece (5) in an induction furnace (1) having the features of any one of the preceding claims, in which the workpiece (5) is movable relative to the permanent magnets (2, 3, 12, 13, 14 , 15, 25, 26) is rotated until the workpiece (5) has been heated to a temperature of 400 ° C and more

A method according to the preceding claim, wherein during heating, the interior (4) of the induction furnace in which the workpiece (5) is heated is flooded with inert gas or flooded.