Method and apparatus for the heat treatment of amorphous ribbons

Abstract

In a method for the heat treatment of amorphous ribbons (1), the amorphous ribbon (1) is guided by a guide device (2), wherein at least one laser beam (3) from at least one laser beam source is focused onto at least one surface of the amorphous ribbon (1) so that the amorphous ribbon (1) is heated. Furthermore, a measuring device continuously measures the surface temperature of the ribbon (1) and transmits the measured values ​​to a control device, wherein the control device compares the transmitted measured values ​​with a setpoint and then adjusts at least one operating parameter of the laser beam source and / or the guide device (2) such that the ribbon (1) is heated completely.

Description

[0001] The present invention relates to a method and a device for the heat treatment of amorphous ribbons.

[0002] Soft magnetic materials are used in electrical machines to amplify and direct the magnetic flux. Their ease of remagnetization distinguishes them from hard magnetic materials, also known as permanent magnets. The coercive field strength is the determining factor here. It is the magnetic field strength at which a previously magnetized material becomes demagnetized. The lower this coercive field strength, the lower the remagnetization losses in the low-frequency range. At frequencies above 1 kHz, eddy current losses become dominant. These losses depend, among other things, on the specific electrical resistance of the material and the thickness of the soft magnetic layer.

[0003] To achieve the highest possible power density of the component, the soft magnetic material used should also possess the highest possible saturation polarization. The group of soft magnetic nanocrystalline alloys was discovered towards the end of the 1980s. These alloys are initially produced in the form of thin amorphous ribbons using a rapid solidification process, specifically melt spinning. Heat treatment above the crystallization temperature leads to the formation of grains just a few nanometers in size within an amorphous matrix.

[0004] Due to their unique microstructure, these nanocrystalline soft magnets exhibit extremely low coercive field strengths. However, the saturation polarization is reduced as a result of the non-ferromagnetic alloying elements, which are necessary for glass formation and to inhibit grain growth. In recent years, alloy development has progressed significantly, leading to the discovery of systems with a considerably higher proportion of ferromagnetic elements. These combine low coercive field strength with high magnetic saturation polarization. The absence of alloying elements that inhibit grain growth necessitates a significant reduction in the duration of heat treatment. Heat treatment with a heating rate on the order of several Kelvin per second is not feasible in a conventional furnace.

[0005] To achieve these heating rates, methods are described, for example, in US 11 352 677 B2 and US 0 112 587 A1, in which amorphous ribbons are clamped between preheated copper blocks and heated at a rate of at least 10 K / s. However, due to the batch operation, the throughput is low, making this method more suitable for laboratory applications.

[0006] The present invention is therefore based on the objective of proposing a method and a device for the heat treatment of amorphous ribbons, whereby the process time is reduced and installation space is saved at the same time.

[0007] This problem is solved according to the invention by a method according to main claim 1 and by a device according to dependent claim 9. Advantageous embodiments and further developments are described in the dependent claims.

[0008] A method for the heat treatment of amorphous ribbons involves guiding the ribbon using a guide device. At least one laser beam from at least one laser beam source is focused onto at least one surface of the amorphous ribbon, thus heating the ribbon. A measuring device continuously measures the surface temperature of the ribbon, and the measured values ​​are transmitted to a control device. The control device then compares the transmitted measured values ​​with a target value and subsequently adjusts at least one operating parameter of the laser beam source and / or the guide device such that the ribbon is heated completely.

[0009] The term "fully heated" initially means that the strip has a temperature above its crystallization temperature at every point along its entire thickness. The crystallization temperature depends on the material used. Heating with the laser beam allows for high heating rates (> 10 K / s), thus preventing grain growth. The heat-treated strips therefore exhibit a low coercive field strength. The thin oxide layer applied by the laser treatment also provides electrical insulation for the strips in the final component. Furthermore, this process is particularly energy-efficient because the laser directly heats the strip surfaces, minimizing heat loss to the surrounding environment.

[0010] Due to the very high radiation intensities achievable with lasers, very high heating rates and high tape speeds or feed rates can be achieved. Because lasers can be controlled quickly (down to the microsecond range), the temperature distribution on the tape surface during laser processing can be controlled directly and precisely through the interaction of measuring and control devices. This allows for rapid responses to local effects, such as those that disrupt energy coupling or are caused by varying tape materials, thus increasing process stability.

[0011] Furthermore, the use of laser optics allows for the control of an intensity profile in the laser focus via dynamic beam shaping and one-dimensional scanner technology.

[0012] The laser optics allow for optimal intensity distribution within the laser focus, resulting in a uniform temperature distribution across the surface of the strips. The diameter of the laser focus typically ranges from 1 mm to 20 mm. Various optics can be employed, such as a rectangular focus with a homogeneous intensity distribution, a rectangular or linear focus with an adapted intensity distribution to account for locally varying heat dissipation conditions (e.g., heat buildup effects at the strip edges), or the dynamic beam shaping described above using one-dimensional or two-dimensional scanning technology. The intensity profile can be dynamically adjusted by modifying the local scan speed or laser power.

[0013] When using scanner technology for laser beam shaping, the local scan speeds and / or laser power can be precisely adjusted by the controller during each scan cycle based on temperature information. This ensures that the temperature required for material transformation is generated at any time and at any point on the strip surface, without requiring operator intervention. The process control can generally compensate for the following disruptive factors: fluctuations in the strip feed rate, variations in the absorption properties of the surfaces for laser radiation due to different roughness or metallographic structures, heat build-up effects from edge effects or variations in local strip thickness, and changes in the surface profile due to short-term distortion effects during the laser treatment.

[0014] In this scanner technology, a collimated (approximately parallel) laser beam or a focused laser beam with a focal length of at least several hundred millimeters and a circular, rectangular, or linear laser spot (projected onto the tape surface) can be guided over one or more oscillating mirrors and moved at high frequencies, with scan frequencies from 100 Hz to several kHz, relative to the tape feed rate, by means of harmonic or arbitrary scanning motion of the oscillating mirrors. By appropriately adjusting the scanning motion, in particular the scan amplitudes and local scan speeds, a region of the tape surface can be heated to the processing temperature quasi-simultaneously, and the local heat input can be selectively controlled depending on location and time.

[0015] Furthermore, the strip can be actively cooled and / or shredded after heat treatment.

[0016] Active cooling of the strip ensures that it retains the desired structure with the described advantageous properties. Furthermore, it is possible to produce so-called "flakes" by shredding the strip, which can then be pressed into magnetic cores.

[0017] Furthermore, the surface temperature of the strip during heat treatment can be in the range of 400–1000 °C, preferably in the range of 400–600 °C. The feed rate of the strip, which is set by the guide device, can also be in the range of 0.1–100 m / min, preferably in the range of 1–50 m / min. With these process parameters, the method can ensure optimal throughput rates and consistent microstructures of the strips. When selecting the temperature ranges, it is particularly important that the temperature is above the crystallization temperature of the amorphous strip used.

[0018] Furthermore, the amorphous ribbon can have a thickness in the range of 10–40 µm, particularly in the range of 20–30 µm, and is made of an iron-based alloy, which in turn contains 10–15 at.% (atomic percent) boron. This ensures complete heating of the ribbon. These ribbons are also particularly suitable for use in magnetic cores, allowing them to be used directly if necessary.

[0019] Furthermore, the iron in the iron-based alloy can be partially replaced by up to 2 at.% Cu, up to 30 at.% Ni, up to 60 at.% Co, up to 10 at.% P, up to 10 at.% Si, or up to 5 at.% of the transition metals Nb, Hf, Zr, Sn, Ta, or Mo. This further increases the potential range of applications for the heat-treated strips.

[0020] A device for the heat treatment of amorphous ribbons comprises a guide device configured to guide the amorphous ribbon and at least one laser beam source configured to focus the laser beam onto at least one surface of the amorphous ribbon, thus heating the ribbon. Furthermore, a measuring device is provided, configured to continuously measure the surface temperature of the ribbon and transmit the measured values ​​to a control device. The control device is additionally configured to compare the transmitted measured values ​​with a target value and to regulate at least one operating parameter of the laser beam source and / or the guide device such that the ribbon is heated completely.

[0021] The device is therefore very compact, as the processing length for heating the strip is in the range of centimeters or a few tens of centimeters. This allows for considerable space savings.

[0022] Furthermore, a multi-functional unit can be provided, designed to tension the amorphous strip during heat treatment and / or to cool and / or crush it after heat treatment. Combining the cooling and crushing functions allows for further space savings, as fewer components are required.

[0023] Typically, the multi-functional unit is designed as a pair of rollers. Furthermore, as soon as the amorphous strip reaches the multi-functional roller, the strip may already have oxides on its surface.

[0024] The described procedure can typically be carried out with the described device, i.e., the device can perform the described procedure.

[0025] Exemplary embodiments of the invention are shown in the drawings and are described below with reference to the Fig. 1 and Fig. 2 described. Recurring features are provided with identical reference symbols.

[0026] They show: Fig. 1 a schematic drawing of a device for the heat treatment of amorphous ribbons with a cooling unit and a comminution unit and Fig. 2 a schematic drawing of a device for the heat treatment of amorphous ribbons with a multi-functional unit.

[0027] In Fig. Figure 1 shows a variant of a device for the heat treatment of amorphous strips 1, in which an amorphous strip 1 is guided through a guide device 2. The feed rate is determined by the guide device 2, which in this embodiment is formed by two rotatably mounted rollers. Furthermore, it can be provided that the strip 1 is unwound from the guide device 2 by a winding device (not shown), for example, a roller.

[0028] Subsequently, the strip 1 is heated by two laser beams 3, each focused on opposite surfaces of the strip 1. This means that in this variant, the strip 1 is heated on both sides. Alternatively, it is also possible to heat the strip 1 on only one side with at least one laser beam 3 focused on only one surface of the strip 1. Furthermore, in both the two-sided and the one-sided variant, a multitude of laser beams 3 focused on the surface of the strip 1 can be used.

[0029] The focusing of the laser beams 3 is ensured here by two separate laser optics 4. The following optics can be used: • Rectangular focus with homogeneous intensity distribution, • Rectangular or linear focus with adapted intensity distribution to account for locally varying heat dissipation conditions (e.g., heat build-up effects at the band edges) • Dynamic beam shaping using 1D or 2D scanner technology

[0030] In particular, dynamic beam shaping, in combination with one-dimensional or two-dimensional scanning technology, makes it possible to dynamically adjust the intensity profile by modifying the local scan speed or the local laser power. Here, the temperature distribution on the surface of strip 1 is continuously and spatially resolved measured by a measuring device. For example, the temperature distribution can be measured non-contact using thermal imaging cameras or pyrometers. By transmitting these measured values ​​to a control device and continuously comparing them with a target value, at least one operating parameter of the laser beam source and / or the guide device 2 can be adjusted by the control device. Operating parameters that can be adjusted during each scan cycle include, for example, the feed rate of strip 1 and / or the guide device 2.or the local scanning speed of the laser beam 3 or the local laser power. This ensures that the temperature required for the material transformation is generated at any time and at any point on the strip surface, without requiring intervention by a system operator.

[0031] Furthermore, in this embodiment, after the heat treatment of the strip 1, a cooling unit 6 actively cools the strip 1, which is then subsequently reduced in size by a comminution unit 7. The cooling unit 6 can, for example, be designed as a nozzle that actively cools the strip 1 with compressed air, nitrogen, or another protective gas. Generally, laser processing can be carried out under a protective gas atmosphere to prevent oxidation effects on the processed surfaces. Since oxidation significantly affects laser absorption, suppressing oxidation in this way can considerably improve process stability. In this embodiment, the comminution unit 7 is designed as a shredder, allowing the strip 1 to be reduced to flakes quickly and easily.

[0032] Fig. 2 reveals, in contrast to Fig. 1. A multi-functional unit 5, designed to both cool and shred the strip 1. In this embodiment, the multi-functional unit 5 consists of two rotatably mounted and cooled rollers. This makes it possible to further reduce the installation space of the device and simultaneously to selectively build up mechanical stresses in the strip 1, thus reducing distortion effects during heat treatment. The introduction of mechanical stresses into the strip 1 can also be achieved in Fig. 1. This can be achieved by using a pre-tensioning device. The pre-tensioning device can, for example, consist of an additional pair of rollers.

[0033] In summary, the laser heat treatment of strip 1 can be performed continuously by the unwinding device, i.e., during the unwinding process of the amorphous strip 1. Heating is carried out using at least one laser system on one side, or multiple laser systems on one or even both sides. The laser system comprises at least one laser beam source that emits at least one laser beam 3. The laser system can also include laser optics 4. Processing both sides of the strip 1 offers advantages in terms of a symmetrical temperature distribution, allowing the optimal processing temperature to be set on both sides of the strip 1. This also makes the heating of the strip 1 more effective and simultaneously minimizes the temperature gradient along the thickness of the strip 1. Thus, in addition to enabling significantly higher feed rates during heat treatment, a reduction in the distortion of the strip 1 is also possible.

[0034] The process control described above can generally compensate for the following disruptive factors: • Fluctuations in the feed motion of belt 1 • Fluctuations in the absorption properties of surfaces for laser radiation due to different roughness or metallographic structures • Heat build-up effects due to edge effects or fluctuations in local strip thicknesses • Changes in the surface profile due to short-term distortion effects during the laser procedure

[0035] Gas cooling using compressed air, nitrogen, or another protective gas can also be employed to achieve rapid cooling of strip 1 after the laser process. Performing laser processing under a protective gas atmosphere can generally offer advantages by preventing oxidation effects on the processed surfaces. Since oxidation significantly affects laser absorption, suppressing it in this way can considerably improve process stability.

[0036] Depending on the alloy of the strip material and the treatment parameters, significant embrittlement of the material and changes in the cross-sectional geometry due to thermal distortion occur. As an alternative to coiling the strip (roll-to-roll process), further processing of strip 1 (e.g., cutting, shredding, etc.) immediately after the laser process and after sufficient cooling is considered advantageous in this case. Alternatively, the cooling and comminution steps can also be combined using a cooled, contoured multi-function unit 5. This allows for a further reduction in the installation space of the device. The targeted application of mechanical stress in strip 1 using the roller systems, such as the multi-function unit 5, can potentially be used to reduce or even prevent distortion effects during the laser process.

[0037] The advantages thus arise from the fact that bands 1 with high saturation polarization and low coercive field strength can be produced, which is not possible with other soft magnetic material groups. This allows for the production of smaller and, due to the elimination of Nb, also more cost-effective components with significantly higher energy efficiency. Another advantage is that the initial permeability is inversely proportional to the coercive field strength and therefore exhibits the desired high values. The thin oxide layer applied by laser treatment provides electrical insulation between the bands 1 or the flakes. Therefore, eddy currents are effectively suppressed when the bands 1 are stacked, making the thin bands 1 ideal for use at high frequencies. Since the oxide layer is only a few nanometers thick, a high stacking factor can also be achieved. This is particularly advantageous for high power density.

[0038] The invention offers technological advantages, particularly with regard to energy efficiency, since the laser directly heats the strip surfaces and minimizes heat loss to the environment. Furthermore, the very high radiation intensities achievable with lasers allow for very high heating and strip speeds. The temperature distribution on the strip surface during laser treatment can also be controlled directly and precisely. This enables a very quick and flexible response to local effects, such as those that disrupt energy coupling or varying strip materials. Additionally, the production system or line can be designed compactly, as the processing length for heating and, if necessary, cooling the strip is in the range of centimeters or a few tens of centimeters. Moreover, the process can be applied to all high-B alloys.The produced nanocrystalline ribbons 1 can be used to manufacture a wide variety of magnetic cores in electromagnetic components (electric motors, transformers of different frequency ranges as well as components at high frequencies in the form of ring cores or powder cores).

[0039] In principle, two main areas of application emerge. Firstly, the nanocrystalline strips 1, heat-treated using a laser beam 3, can be stacked or wound onto reels. This is particularly suitable for electrical machines such as electric motors or transformers in the medium- or high-frequency range. A transformer is an electrical device capable of transforming alternating current from one voltage level to another, thus converting the input voltage into a higher or lower output voltage. It typically consists of two tightly wound coils arranged around a common magnetic core. This core can be either block-shaped or ring-shaped. Requirements for the soft magnetic material include high magnetic saturation to allow for the smallest possible transformer design, very high permeability, and low hysteresis losses to achieve high efficiency.Since the nanocrystalline strip 1, with thicknesses of approximately 20 µm, is significantly thinner than conventional electrical steel sheets (>200 µm), the eddy current losses, which depend quadratically on the thickness, are significantly reduced at frequencies above 1 kHz, resulting in a significant increase in efficiency.

[0040] Furthermore, the heat-treated strips 1 can be used in powder cores after a grinding and pressing step. Powder cores with high saturation and low losses are currently used, among other things, as power factor correction filters (PFC chokes) or DC / DC converters. A power factor correction filter is an electrical circuit used in AC circuits to improve the power factor. The power factor is the ratio between the actual active power used and the apparent power of an electrical system. A poor power factor occurs when there is a phase shift between voltage and current. This can cause the electrical system to operate inefficiently, as it consumes more apparent power than actual active power used. A power factor correction filter works by reducing the phase shift between voltage and current.This is achieved by using capacitors and soft magnets equipped with coils, which are placed in the circuit in such a way as to reduce the phase angle of the current compared to the voltage.

[0041] The nanocrystalline powder cores are ideally suited for use as storage inductors in DC / DC converters. These are electrical circuits used to convert one DC voltage to another DC voltage at a different voltage level. They are used, among other things, to boost the generated voltage in photovoltaic systems to grid voltage or in electric vehicles to reduce the battery's high voltage to the 12V vehicle electrical system. The DC / DC converter begins with the input stage, where the input DC voltage is fed in. This input DC voltage can be higher or lower than the desired output voltage. The converter contains a switch that turns on and off rapidly. The switching frequency can be very high, often in the range of several tens of kilohertz to several megahertz. The core component is the storage inductor in the form of a coil with a soft magnetic core.This inductor stores energy in its magnetic field when the switch is closed and releases this energy when the switch is opened. In buck mode, the voltage is reduced. When the switch is on, current flows through the storage inductor, and the output voltage is smoothed by the inductor, the switch, and a capacitor. In boost mode, however, higher voltages are achieved. To do this, the switch is turned off, the magnetic field of the inductor collapses, and the energy is released to the output side. Consequently, the output voltage is increased. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 11 352 677 B2

[0005] US 0 112 587 A1

[0005]

Claims

[1] Method for the heat treatment of amorphous ribbons (1) wherein the amorphous band (1) is guided by means of a guide device (2), wherein at least one laser beam (3) from at least one laser beam source is focused onto at least one surface of the amorphous band (1) so that the amorphous band (1) is heated, and a measuring device continuously measures the surface temperature of the strip (1) and transmits the measured values ​​to a control device, wherein The control device compares the transmitted measured values ​​with a target value and then adjusts at least one operating parameter of the laser beam source and / or the guide device (2) so that the belt (1) is completely heated. [2] Method for the heat treatment of amorphous ribbons (1) according to claim 1, characterized by, that by using a laser optic (4) the control of an intensity profile in the laser focus is implemented via dynamic beam shaping and one-dimensional scanner technology. [3] Method for the heat treatment of amorphous ribbons (1) according to any one of the preceding claims, characterized by , that the strip (1) is actively cooled and / or crushed after heat treatment. [4] Method for the heat treatment of amorphous ribbons (1) according to any one of the preceding claims, characterized by , that the surface temperature of the strip (1) during the heat treatment is in a range of 400 - 1000 °C, preferably in a range of 400 - 600 °C. [5] Method for the heat treatment of amorphous ribbons (1) according to any one of the preceding claims, characterized by , that the feed speed of the belt (1), which is set by the guide device (2), is in a range of 0.1 - 100 m / min, preferably in a range of 1 - 50 m / min. [6] Method for the heat treatment of amorphous ribbons (1) according to any one of the preceding claims, characterized by , that the amorphous band (1) has a thickness in the range of 10 - 40 µm, in particular in the range of 20 - 30 µm. [7] Method for the heat treatment of amorphous ribbons (1) according to any one of the preceding claims, characterized by , that the amorphous band (1) is formed from an Fe-based alloy containing 10 - 15 at.% boron. [8] Method for the heat treatment of amorphous ribbons (1) according to claim 7, characterized by , that the Fe of the Fe-based alloy is partially substituted by up to 2 at.% Cu or up to 30 at.% Ni or up to 60 at.% Co or up to 10 at.% P or up to 10 at.% Si or up to 5 at.% of the transition metals Nb, Hf, Zr, Sn, Ta or Mo. [9] Device for heat treatment of amorphous ribbons comprising: a guide device (2) which is configured to guide the amorphous strip (1), at least one laser beam source configured to focus at least one laser beam (3) onto at least one surface of the amorphous ribbon (1) so that the ribbon (1) is heated, a measuring device configured to continuously measure the surface temperature of the strip (1) and to transmit the measured values ​​to a control device, and the control device which is designed to compare the transmitted measured values ​​with a target value and to control at least one operating parameter of the laser beam source and / or the guide device (2) in such a way that the belt (1) is completely heated through. [10] Device for the heat treatment of amorphous ribbons (1) according to claim 9, characterized by , that a multi-functional unit (5) is provided which is configured to tension the amorphous strip (1) during heat treatment and / or to cool and / or crush it after heat treatment.

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