EP1407462B1 - Method for producing nanocrystalline magnet cores, and device for carrying out said method - Google Patents

Description

The invention relates to a method for the production of nanocrystalline magnetic cores and to devices for carrying out such a method.

Nanocrystalline soft magnetic iron-base alloys have been known for a long time and have been described, for example, in US Pat EP 0 271 657 B1 described. The magnetically soft iron-based alloys described therein generally have a composition with the formula:

(Fe ₁ -a M _a ) _100-xyz-α Cu _x Si _y B _z M ' _α

in which M is cobalt and / or nickel, M 'is at least one of the elements niobium, tungsten, tantalum, zirconium, hafnium, titanium and molybdenum, the indices a, x, y, z and α are each the condition 0 ≤ a ≤ 0.5; 0.1 ≤ x ≤ 3.0; 0 ≤ y ≤ 30.0; 0≤z≤25.0; 5 ≤ y + z ≤ 30.0 and 0.1 ≤ α ≤ 30.

Furthermore, the soft magnetic iron-base alloy may also have a composition having the general formula

(Fe ₁ -a M _a ) _{100-xyz-α-β-γ} Cu _x Si _y B _z M ' _α M " _β X _γ

where M is cobalt and / or nickel, M 'is at least one of niobium, tungsten, tantalum, zirconium, hafnium, titanium and molybdenum, M "is at least one of vanadium, chromium, manganese, aluminum, a platinum group element , Scandium, yttrium, a rare earth, gold, zinc, tin and / or rhenium and X is at least one of the elements carbon, germanium, phosphorus, gallium, antimony, indium, beryllium and arsenic and where a, x, y, z, α, β and γ respectively satisfy the condition 0 ≦ a ≦ 0.5, 0.1 ≦ x ≦ 3.0, 0 ≦ y ≦ 30.0, 0 ≦ z Satisfies ≦ 25.0, 5 ≦ y + z ≦ 30.0, 0.1 ≦ α ≦ 30.0, β ≦ 10.0 and γ ≦ 10.0.

In both alloy systems, at least 50% of the alloy structure is occupied by fine crystalline particles having an average particle size of 100 nm or less. These magnetically soft nanocrystalline alloys are increasingly being used as magnetic cores in inductors for a wide variety of electrical engineering applications. For example, summation current transformers for AC sensitive and also pulse current sensitive residual current circuit breakers, reactors and transformers for switched power supplies, current-compensated chokes, smoothing chokes or transducers made of band cores, which have been made of strips of nanocrystalline tapes described above, known. This goes, for example, from the EP 0 299 498 B1 out. Furthermore, the use of such annular band cores is also known for filter sets in telecommunications, for example as an interface transmitter for ISDN or DSL applications.

The nanocrystalline alloys in question can, for example, be produced inexpensively by means of the so-called rapid solidification technology (for example by melt-spinning or planar-flow-casting). In this case, an alloy melt is first provided in which subsequently by rapid quenching from the melt state, an initially amorphous alloy is produced. The cooling rates required for the above-mentioned alloying systems amount to about 10 ⁶ K / sec. This is achieved with the aid of the melt spin method, in which the melt is injected through a narrow nozzle onto a rapidly rotating cooling roll and thereby solidified into a thin strip. This method allows the continuous production of thin strips and films in a single operation directly from the melt at a rate of 10 to 50 m / sec., With tape thicknesses of 20 to 50 μ m and bandwidths to about a few cm are possible.

The initially amorphous strip produced by means of this rapid solidification technology is then wound into geometrically widely variable magnetic cores, which can be oval, rectangular or round. The central step in achieving good soft magnetic properties is the "nanocrystallization" of the previously amorphous alloy ribbons. From a soft magnetic point of view, these alloy strips still have poor properties since they have a relatively high magnetostriction | λ _S | of about 25 x 10 ^-6 . When carrying out a heat treatment adapted to the alloy, an ultrafine microstructure is created, ie an alloy structure is formed in which at least 50% of the alloy structure is occupied by cubic body-centered FeSi crystallites. These crystallites are embedded in an amorphous residual phase of metals and metalloids. The solid-state physical background for the formation of the finely crystalline structure and therefore the drastic improvement of the soft magnetic properties, which is therefore the subject of detailed discussion, are described, for example, in US Pat G. Herzer, IEEE Transactions on Magnetics, 25 (1989), pages 3327 et seq , described. Thereafter, good soft magnetic properties such as a high permeability or small hysteresis losses arise by averaging out the crystal anisotropy K _{u of} the randomly oriented nanocrystalline "microstructure".

After leaving the EP 0 271 657 B1 or the prior art known from EP 0 299 498 B1, the amorphous strips are first wound on special winding machines with as little stress as possible to form ring band cores. For this purpose, the amorphous tape is first wound into a round core ring core and - if necessary - brought by means of suitable shaping tools in a shape deviating from the round shape. However, by using suitable winding bodies, it is also possible to achieve forms that deviate from the round shape directly when winding the amorphous ribbons into toroidal cores.

Thereafter, according to the prior art, the stress-free wound toroidal cores in so-called retort furnaces subjected to a crystallization heat treatment, which serves to achieve the nanocrystalline microstructure. Here, the toroidal cores are stacked and retracted in such an oven. It has been found that a major disadvantage of this method is that weak magnetic stray fields such. B. the magnetic earth field, a position dependence of the magnet values in the magnetic core stack is induced. While high permeability values with an intrinsically caused high remanence ratio of more than 60% are present at the stack edges, for example, the magnet values in the middle of the stack are characterized by more or less pronounced flat hysteresis loops with low permeability and remanence values.

This is for example in the FIG. 1 shown. FIG. 1a shows the scattering of the permeability at a frequency of 50 heart as a function of the current core number within an annealing stack. The FIG. 1b shows the dependence of the remanence ratio B _r / B _m as a function of the current core number within an annealing stack. Like that FIGS. 1a and 1b can be seen, the distribution curve for the magnet values of a Glühfertigungsloses wide and steady. The distribution curve drops monotonically to high values. The exact specific course depends on the alloy, the magnetic core geometry and of course the stack height.

In the nanocrystalline alloy systems in question, the setting of the nanocrystalline microstructure is typically carried out at temperatures of T _a = 450 ° C to 620 ° C, the necessary hold times can be between a few minutes and about 12 hours. In particular, goes from the US 5,911,840 show that in nanocrystalline magnetic cores with a round bra loop a maximum permeability of μ _max = 760,000 is reached when a stationary temperature plateau is used for a period of 0.1 to 10 hours below the temperature required for the crystallization of 250 ° C to 480 ° C for the relaxation of the magnetic core. This increases the duration of the heat treatment and thus reduces the economic efficiency.

The present invention is based on the discovery that in the FIGS. 1a and 1b shown magnetostatically induced parabolic formations in the stack annealing of toroidal cores in retort furnaces are magnetostatic nature and are due to the location dependence of the demagnetization factor of a cylinder. Furthermore, it has been found that the exothermic heat of the crystallization process, which increases with the core weight, can only be dissipated incompletely to the surroundings of the glow stack and can therefore lead to a marked deterioration of the permeability values. It is noted that nanocrystallization is, of course, an exothermic physical process. This phenomenon has already been in the JP 03 146 615 A2 described. The consequence of this insufficient dissipation of the heat of crystallization is a local overheating of the toroidal cores within the stack, which can lead to lower permeabilities and higher remanences. Thus, the permeabilities and remanence of nuclei in the center of the anneal stack are lower than the permeabilities and remanences of toroidal cores at the outer ends of the anneal stack. So far, one has this problem, as far as it has ever recognized, umschifft that one, for example, just as in the US 5,911,840 , In the beginning of the nano-crystallization, that is heated from about 450 ° C, in an uneconomical way very slowly. Typical heating rates were between 0.1 and 0.2 K / min, which alone could be the passage through the range up to the temperature of 490 ° C up to 7 hours. This procedure was very uneconomical.

The US 5,914,088 discloses a device for heat treating amorphous metallic cores in the pass.

The DE 35 42 257 A1 discloses a continuous furnace for annealing ferromagnetic layers, comprising a magnet for generating a magnetic field and a heating coil for generating a temperature gradient. This continuous furnace is used to magnetize ferromagnetic layers and to reduce anisotropic field strength.

The US 2,960,744 discloses a tunnel kiln for producing ferrites of ceramic materials, wherein the tunnel kiln may be divided into different zones having different temperatures and different atmospheres.

It is therefore an object of the present invention to provide a novel process for the production of toroidal cores in which the problem of parabolic scattering and other, in particular exothermic, deteriorations of magnetic characteristics mentioned at the outset can be avoided, and which works particularly economically.

According to the invention this object is achieved by a method for the production of toroidal cores of the type mentioned, in which the finished wound amorphous toroidal cores are heat treated unstacked in the flow to nanocrystalline toroidal cores.

By separating the toroidal cores an identical magnetostatic condition for each ring core ring is brought about. The consequence of this magnetostatic crystallization condition, which is identical for each individual annular band core, results in the elimination of the magnetostatic crystallization condition FIGS. 1a and 1b shown "parabolic effect" and thus a limitation of the scattering on alloy-specific, geometric and / or thermal causes. The heat treatment of the unstacked amorphous toroidal cores is performed on heat sinks, which have a high heat capacity and a high thermal conductivity, which also already from the JP 03 146 615 A2 is known. In particular, a metal or a metallic alloy may be considered as the material for the heat sinks. In particular, the metals copper, silver and thermally conductive steel have proved to be particularly suitable.

However, it is also possible to perform the heat treatment on a ceramic heat sink. Furthermore, an embodiment of the present invention is conceivable in which the heat to be treated amorphous toroidal cores are introduced into a mold bed of ceramic powder or metal powder, preferably copper powder.

As ceramic materials, both for a solid ceramic plate or for a ceramic powder bed, in particular magnesium oxide, aluminum oxide and aluminum nitride have been found to be particularly suitable.

The heat treatment for crystallization is carried out in a temperature range of about 450 ° C to about 620 ° C, wherein the heat treatment passes through a temperature window of 450 ° C to 500 ° C and thereby with a heating rate of 0.1 K / min to approx 20 cycles per minute.

The invention is preferably carried out with an oven, the oven having a furnace housing having at least one annealing zone and a heating source, means for charging the annealing zone with unstacked amorphous magnetic cores, means for conveying the unstacked amorphous magnetic cores through the annealing zone and means for removal the unstacked heat-treated nanocrystalline magnetic cores from the annealing zone.

Preferably, the annealing zone of such a furnace is subjected to a protective gas.

In a first embodiment of the present invention, in this case, the furnace housing in the form of a tower furnace, in which the annealing zone extends vertically. The means for conveying the unstacked amorphous magnetic cores through the vertically extending annealing zone are preferably a vertically extending conveyor belt.

The vertically extending conveyor belt in this case has perpendicular to the conveyor belt stationary supports made of a material with high heat capacity, ie either from the metals described above or the ceramics described above, which have a high heat capacity and high thermal conductivity exhibit. The toroidal cores rest on the supports.

The vertically extending annealing zone is preferably divided into several separate heating zones, which are provided with separate heating controls.

In an alternative embodiment of the furnace according to the invention, this has the shape of a tower furnace, in which the annealing zone extends horizontally. Here, the horizontally extending annealing zone is again divided into several separate heating zones, which are provided with separate heating controls. As a means for conveying the unstacked amorphous toroidal cores through the horizontally extending annealing zone, at least one, but preferably a plurality, of support plates rotating about the turret axis is provided.

The support plates in turn consist entirely or partially of a material with high heat capacity and high thermal conductivity, on which rest the magnetic cores. In this case, in particular metallic plates come into consideration, which consist of the metals mentioned above, d. H. So copper, silver or thermally conductive steel exist.

In a third alternative embodiment of the furnace according to the invention, this has a furnace housing which has the shape of a horizontal continuous furnace, in which the annealing zone in turn extends horizontally. This embodiment is particularly preferred because such a furnace is relatively easy to manufacture.

In this case, as a means for conveying the unstacked amorphous toroidal cores through the horizontally extending annealing zone, a conveyor belt is provided, wherein the conveyor belt is in turn provided with pads consisting of a material with high heat capacity and high thermal conductivity, on which rest the toroidal cores. Come here again the metallic and / or ceramic materials discussed at the outset.

Typically, again, the horizontally extending annealing zone is divided into several separate heating zones, which are provided with separate heating controls.

In a further development of the present invention, the transverse magnetic field treatment required for the generation of flat hysteresis loops can also be generated directly and simultaneously in the pass. For this purpose, at least a portion of the enclosed by the furnace housing flow channel between the two pole pieces of a magnetic yoke, so that the continuous magnetic cores are acted upon in the axial direction with a homogeneous magnetic field, thereby forming in them a uniaxial anisotropy transverse to the direction of the wound tape. The field strength of the yoke must be so high that the magnetic cores are at least partially saturated during the heat treatment in the axial direction.

The hysteresis loops become all the flatter and more linear, the greater the proportion of the length of the furnace channel over which the yoke is laid.

In all three alternative embodiments of the furnace according to the invention, the separate heating zones have a first heating zone, a crystallization zone, a second heating zone and a maturing zone.

Figur 2

den Einfluß des Ringbandkerngewichts auf die Permeabilität (50 Hz) von ohne Wärmesenke durchlaufgeglühten Ringbandkernen,

Figur 3

den Einfluß von verschieden dicken Wärmesenken auf das exothermische Kristallisationsverhalten von durchlaufgeglühten Ringbandkernen,

Figur 4

den Einfluß von verschiedenen Dicken von Wärmesenken auf die Maximalpermeabilität von durchlaufgeglühten Ringbandkernen unterschiedlicher Geometrie und unterschiedlicher Ringbandkernmasse,

Figur 5

den Einfluß des Ringbandkerngewichts auf die Permeabilität (50 Hz) nach einer Durchlaufglühung auf einer 10 mm dicken Kupfer-Wärmesenke,

Figur 6

die Stirnflächen von zwei Vergleichsringbandkernen nach einer Durchlaufglühung ohne Wärmesenke und mit Wärmesenke,

Figur.7

schematisch im Querschnitt einen erfindungsgemäßen Turmofen mit vertikal laufendem Förderband,

Figur 8

einen erfindungsgemäßen mehrstöckigen Karusellofen,

Figur 9

einen erfindungsgemäßen Durchlaufofen mit horizontal verlaufendem Förderband und

Figur 10

eine Querfelderzeugung mittels eines Jochs über dem Ofenkanal.

The invention is illustrated below with reference to the drawing, for example. Showing:

FIG. 2

the influence of the toroidal core weight on the permeability (50 Hz) of toroidal cores annealed without heat sink,

FIG. 3

the influence of different thicknesses of heat sinks on the exothermic crystallization behavior of continuous annealed toroidal cores,

FIG. 4

the influence of different thicknesses of heat sinks on the maximum permeability of continuously annealed ring band cores of different geometry and different ring band core mass,

FIG. 5

the influence of the toroidal core weight on the permeability (50 Hz) after a continuous annealing on a 10 mm thick copper heat sink,

FIG. 6

the end faces of two comparative ring cores after a continuous annealing without heat sink and heat sink,

Figur.7

schematically in cross-section a tower furnace according to the invention with vertically running conveyor belt,

FIG. 8

a multi-storey carousel furnace according to the invention,

FIG. 9

a continuous furnace according to the invention with horizontal conveyor belt and

FIG. 10

a transverse field generation by means of a yoke above the furnace channel.

In particular, for the production of so-called round hysteresis loops annealing processes are needed, which allows the formation and maturation of an ultrafine nanocrystalline structure under as field-free and thermally exact conditions. As mentioned above, according to the prior art, the annealing is usually carried out in so-called retort furnaces, in which the magnetic cores are retracted stacked.

The key disadvantage of this method is that weak by stray fields such. B. the magnetic field of the earth or similar stray fields, a position dependence of the magnetic characteristics in the magnetic core stack is induced. This can be called an antenna effect. While there are indeed round hysteresis loops with a high permeability and an intrinsically caused high remanence ratio of more than 60% at the stack edges, more or less pronounced flat hysteresis loops with lower permeabilities and remanence ratios are present in the stack center. This was initially in the FIGS. 1a and 1b shown.

Accordingly, the distribution curve for the magnetic characteristics of a production lot is wide, continuous and decreases monotonically to high values. As mentioned above, the exact course depends on the respectively used soft magnetic alloy, the magnetic core geometry and the stack height.

In addition to the magnetostatically caused parabolic formation, the batch annealing in retort furnaces has the further disadvantage that with increasing magnetic core weight, the exothermic heat of the crystallization process can only be released incompletely to the environment. The result is overheating of the stacked magnetic cores, which can lead to lower permeabilities and to high coercivities. To circumvent these problems must be in the field of onset of crystallization, d. H. So from about 450 ° C to be heated very slowly, which is uneconomical. Typical heating rates are there at 0.1 to 0.2 K / min, which alone the passage through the range up to 490 ° C can be up to 7 hours.

The only economically viable large-scale alternative to batch annealing in the retort furnace is in a glow in accordance with the present invention in the run. By separating the magnetic cores by the continuous process identical magnetostatic conditions are created for each individual magnetic core. The consequence is the elimination of the above-described parabolic effects, which are the dispersions on alloy-specific, nuclear-technological and thermal causes.

While the first two factors are well controllable, the fast heating rate typical of continuous annealing can result in exothermic heat generation, even with isolated magnetic cores, which is consistent with the FIG. 2 causing an increase in core weight increasing damage to the magnetic properties. The FIG. 2 shows the influence of the magnetic core weight on the magnet values ( μ ₁₀ ≈ μ _max ) when the magnetic cores are heat-treated directly without a heat sink.

Since a delayed heating would lead to an uneconomical multiplication of the length of the passage, this problem can be solved by the introduction of heat-absorbing underlays (heat sinks) of highly thermally conductive metals or by metallic or ceramic powder beds. Copper plates have proven to be particularly suitable since they have a high specific heat capacity and a very good thermal conductivity. As a result, the exothermic heat of crystallization can be removed from the front side of the magnetic cores. In addition, such heat sinks reduce the heating rate, which further limits the exothermic over temperature. This is done by the FIG. 3 illustrated. The FIG. 3 shows the influence of different thicknesses of copper heat sinks on the exothermic behavior in toroidal cores having dimensions of approximately 21 x 11.5 x 25 mm.

Since the rate of temperature compensation depends on the temperature difference between the magnetic core and the heat sink, its thermal capacity across the thickness of the mass and height of the magnetic core is adjusted.

The FIG. 4 shows the influence of the thickness of the heat sinks on the maximum permeability of toroidal cores of different geometries or magnetic core masses. While after the FIG. 4 With magnetic cores with a low core weight and / or a small magnetic core height, a 4 mm thick copper heat sink already leads to good magnetic characteristics, heavier or higher magnetic cores require thicker heat sinks with a higher heat capacity. It has proved to be an empirical rule of thumb that the plate thickness should be d ≥ 0.4 x the core height h.

Like from the FIG. 5 As a result, excellent magnetic characteristics ( μ _max (50 Hz)>500,000; μ ₁ > 100,000) can be achieved over a wide weight range, taking this rule into account.

The lowering of the magnetic properties in continuous annealing without heat sinks is usually associated with lamellar distortions and buckling of the band layers, resulting from the FIG. 6 evident. The FIG. 6 shows the faces of two ring cores of dimensions 50 x 40 x 25 mm ³ after a continuous annealing without heat sink (left core) and on a 10 mm thick copper heat sink (right core). In the case of the right core, virtually no further faults occurred on the front side. In the case of the left magnetic core, on the other hand, the maximum permeability is μ _max = 127,000, whereas it was approximately 620,000 for the right magnetic core.

It has been shown that only when more than about 85% of the end faces of a core are free of warpage, good magnetic characteristics can be achieved.

The FIG. 7 schematically shows a first embodiment of the present invention, a so-called tower furnace. The tower furnace in this case has a furnace housing in which the annealing zone is vertical. The unstacked amorphous magnetic cores be promoted by a vertically extending annealing zone by a vertically extending conveyor belt.

The vertically extending conveyor belt has perpendicular to the conveyor belt surface standing heat sinks made of a material with high heat capacity, preferably copper on. The toroidal cores lie with their faces on the pads. The vertically extending annealing zone is divided into several separate heaters, which are provided with separate heating controls.

In the FIG. 8 another embodiment of the present invention is illustrated. Again, the shape of the furnace is that of a tower furnace, in which the annealing zone, however, is horizontal. Here, the horizontally extending annealing zone is again divided into several separate heating zones, which are provided with separate heating controls. As a means for transporting the unstacked amorphous toroidal cores through the horizontally extending annealing zone is again one, but preferably a plurality of rotating around the tower kiln axis bearing plates provided, which serve as heat sinks.

The support plates in turn are wholly or partly made of a material with high heat capacity and high thermal conductivity, on which rest the magnetic cores with their faces.

The FIG. 9 Finally, FIG. 3 shows a third particularly preferred alternative embodiment of the present invention, in which the furnace housing has the shape of a horizontal continuous furnace. The annealing zone again runs horizontally. This embodiment is particularly preferred because, unlike the two ovens mentioned above, such an oven can be manufactured with less effort.

The annular band cores are conveyed through the horizontally extending annealing zone via a conveyor belt, wherein the conveyor belt is preferably again provided with pads that serve as heat sinks. Again, copper plates are particularly preferred here. In an alternative embodiment of the transport plates are taken as heat sinks, which slide on rollers through the oven housing.

Like from the FIG. 9 shows, the horizontally extending annealing zone is again divided into several separate heating zones, which are provided with separate heating controls.

In a specific embodiment of the in FIG. 9 shown continuous furnace, the required for generating a flat hysteresis loop magnetic cross-field treatment can be carried out directly in the run. The device required for this is in the FIG. 10 shown. For this purpose, at least a part of the passage channel of the furnace between the pole pieces of a yoke is guided so that the continuous magnetic cores are acted upon in the axial direction with a homogeneous magnetic field, thereby forming in them a uniaxial anisotropy transverse to the direction of the wound strip. The field strength of the yoke must be so high that the magnetic cores are at least partially saturated during the heat treatment in the axial direction.

The hysteresis loops become all the flatter and more linear, the greater the proportion of the length of the furnace channel over which the yoke is laid.

• Bei einer Feldstärke von 0,3 T, die zwischen den Polschuhen des Joches, das entlang der gesamten Heizstrecke wirksam war, wurden Magnetkerne mit den Abmessungen 21mm x 11,5mm x 25 mm mit der Zusammensetzung Fe_balCu_1,0Si_15,62B_6,85Nb_2,98 erzeugt, die Permeabilitätswerte von ca.µ = 23.000 (f= 50 Hz) aufwiesen. Das Remanenzverhältnis wurde infolge der axialen Feldeinwirkung auf 5,6% reduziert.

This measure resulted in the following results:

• With a field strength of 0.3 T, which was effective between the pole shoes of the yoke, which was effective along the entire heating section, were magnetic cores with the dimensions 21mm x 11.5mm x 25 mm with the composition Fe _bal Cu _1.0 Si _15.62 B _6.85 Nb _2.98 produced, the permeability values of about μ = 23,000 (f = 50 Hz) had. The remanence ratio was reduced to 5.6% due to the axial field effect.

With only half the heating distance, the uniaxial anisotropy remained weaker and the hysteresis loop became less flat.

In tempering without a magnetic yoke, the remanence ratio was around or above 50% in comparison and the permeability course as a function of the field strength corresponded to that of round hysteresis loops.

With the method and the devices according to the invention, a large-scale production path can be tread by first crystallizing all the resulting magnetic cores in the passage. Depending on whether the required hysteresis should be round, flat or rectangular, these magnetic cores are then either immediately end-processed, d. H. taken in housing, remixed in a longitudinal magnetic field on a rectangular Hystereschleife or in a magnetic transverse field on a flat hysteresis loop and only then finished.

In contrast to the conventional methods, the cores can be produced much faster and in a much more economical manner.

Claims (22)

1. Method for producing magnet cores consisting of a magnetically soft iron-based alloy, wherein at least 50% of the alloy structure are represented by finely crystalline particles with an average particle size of 100 nm or less, the method comprising the following steps: a) the provision of an alloy melt; b) the production of an amorphous alloy strip from the alloy melt using rapid solidification technology; c) the winding of the amorphous strip to produce amorphous magnet cores; d) the continuous heat treatment of the unstacked amorphous magnet cores to produce nanocrystalline magnet cores, characterised in that the heat treatment of the unstacked amorphous magnet cores is performed on heat sinks having a high thermal capacity and a high thermal conductivity.
2. Method according to claim 1, characterised in that a metal, a metallic alloy or a metal powder is provided as a material for the heat sinks.
3. Method according to claim 2, characterised in that copper, silver or a thermally conductive steel is provided as a metal or metal powder.
4. Method according to claim 1, characterised in that a ceramic material is provided as a material for the heat sinks.
5. Method according to claim 1, characterised in that a ceramic powder is provided as a material for the heat sinks.
6. Method according to claim 4 or 5, characterised in that magnesium oxide, aluminium oxide or aluminium nitride is provided as a ceramic material or ceramic powder.
7. Method according to any of claims 1 to 6, characterised in that the heat treatment is performed in a temperature range of approximately 450°C to 620°C.
8. Method according to claim 7, characterised in that a temperature window of 450°C to 500°C is passed through in the heat treatment.
9. Method according to claim 8, characterised in that the temperature window is passed through at a heating rate of 0.1 K/min to approximately 20 K/min.
10. Furnace for carrying out the method according to any of claims 1 to 9, comprising: A) a furnace housing having at least one annealing zone and a heat source; B) means for feeding the annealing zone with unstacked amorphous magnet cores; C) means for conveying the unstacked amorphous magnet cores through the annealing zone; and D) means for removing the unstacked heat-treated nanocrystalline magnet cores from the annealing zone, characterised in that the means for conveying the magnet cores comprise heat sinks having a high thermal capacity and a high thermal conductivity for the heat treatment of the unstacked amorphous magnet cores.
11. Furnace according to claim 10, characterised in that there are further provided: E) means for admitting an inert gas to the annealing zone.
12. Furnace according to claim 10 or 11, characterised in that the furnace housing has the form of a tower furnace in which the annealing zone extends vertically.
13. Furnace according to claim 12, characterised in that a vertically running conveyor belt is provided as means for conveying the unstacked amorphous magnet cores through the vertically oriented annealing zone.
14. Furnace according to claim 13, characterised in that the vertically running conveyor belt is provided with supports, which extend perpendicularly to the conveyor belt surface and are made of a material having a high thermal capacity and a high thermal conductivity, and on which the magnet cores lie.
15. Furnace according to claim 14, characterised in that supports mounted on rollers are provided as means for conveying the unstacked amorphous magnet cores through the vertically oriented annealing zone.
16. Furnace according to claim 15, characterised in that the supports on which the magnet cores lie are made of a material having a high thermal capacity and a high thermal conductivity.
17. Furnace according to any of claims 12 to 16, characterised in that the vertically oriented annealing zone is divided into several separate heating zones provided with separate heating controls.
18. Furnace according to claim 10 or 11, characterised in that the furnace housing has the shape of a horizontal continuous furnace in which the annealing zone extends horizontally.
19. Furnace according to claim 23, characterised in that a conveyor belt is provided as means for conveying the unstacked amorphous magnet cores through the horizontally oriented annealing zone.
20. Furnace according to claim 24, characterised in that the conveyor belt is provided with supports on which the magnet cores lie, which are made of a material having a high thermal capacity and a high thermal conductivity.
21. Furnace according to claim 13 or 17, characterised in that the separate heating zones comprise a first heating-up zone, a crystallisation zone, a second heating-up zone and an ageing zone.
22. Furnace according to any of claims 10 to 21, characterised in that, for adjusting the uniaxial anisotropy, the pole shoes of a magnetic yoke are at least partially placed above the continuous passage encompassed by the furnace housing.

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