Manufacturing sintered permanent magnets with reduced deformation

Abstract

A device (460, 560, 660) for manufacturing a sintered permanent magnet (250, 350) is described. The device comprises (a) a mold (470, 570); (b) at least two magnetic devices (461, 464; 561, 564); and (c) at least one mold for compacting a powder contained in a mold cavity; magnetizing and compacting produce a magnetized compacted mass of the powder (495, 595, 695). The mold cavity and / or the mold comprises at least one surface (470a, 470b; 570a, 570b) that is curved in such a way that an undesired deformation of the sintered mass is at least partially compensated, the undesired deformation being obtained by sintering the magnetized compacted mass in a sintering furnace. A method for manufacturing a sintered permanent magnet using such a device, a sintered permanent magnet produced using such a method, and an electromechanical transducer (140) and a wind turbine (100) comprising such a sintered permanent magnet are further described.

Description

Technical Field

[0001] The invention relates to an apparatus and a method for producing a sintered permanent magnet. Furthermore, the invention relates to a sintered magnet produced by means of said method, and to an electromechanical transducer and a wind turbine comprising at least one such sintered magnet. Background Art

[0002] Permanent magnetic materials are used in a number of different application areas. Probably the most important application areas in terms of technology and economy are electromechanical transducers, i.e. electric motors and generators. Electric motors equipped with at least one permanent magnet (PM) convert electrical energy into mechanical energy by generating a temporarily changing magnetic field with the aid of windings or coils. This temporarily changing magnetic field interacts with the magnetic field of the PM, which is generated, for example, in the rotational movement of the rotor assembly of the electric motor relative to the stator assembly. In a physically complementary manner, the generator converts mechanical energy into electrical energy.

[0003] The generator is the core component of any power plant for generating electrical energy. This applies to power plants that directly obtain mechanical energy, for example hydroelectric power plants, tidal power plants and wind power plants also known as wind turbines. However, this also applies to power plants that (i) first use chemical energy, for example from burning fossil fuels or from nuclear energy, in order to generate thermal energy and (ii) convert the generated thermal energy into mechanical energy by means of appropriate thermodynamic processes.

[0004] The efficiency of a generator is probably the most important factor for optimizing the production of electrical energy. For a PM generator, it is essential that the magnetic flux generated by the permanent magnets (PM) is strong. This can be best achieved using sintered rare earth magnets, for example, using an NdFeB material composition. However, the spatial magnetic field distribution generated by the PM also has an impact on the generator efficiency. In the latter case, it is often advantageous when using a PM device or PM arrangement with a non-uniform magnetic domain arrangement pattern, which produces a non-uniform magnetic field strength or flux density, especially in the air gap between the rotor assembly and the stator assembly.

[0005] It is known to configure a non-uniform magnetic domain arrangement pattern in a PM in order to achieve so-called "flux focusing". WO 2012 / 141932A2 discloses a PM magnet arrangement in which differently magnetized PMs are combined so that "magnetic focusing" is achieved. EP3276642 A1 discloses a sintered rare earth PM with a focused magnetic arrangement pattern, which has an integrally formed or single-piece PM body. EP2762838 A2 discloses an apparatus and method for manufacturing a PM, wherein a non-uniform external magnetic field is applied during the sintering process in order to magnetize different regions of the PM in different directions.

[0006] Flux focusing provides a substantial increase in the air gap flux density, which results in higher torque / power for electromechanical transducers, such as generators for direct drive wind turbines. However, during the manufacture of the PM, and in particular during the manufacture of flux focusing permanent magnets (FFPM) and due to the methods of pressing, sintering and magnetizing, the PM / FFPM may deform. This means that its final shape is different from the desired ideal shape. In addition, under normal circumstances, a sintered PM with the desired final geometry cannot be precisely produced. Therefore, the PM / FFPM needs to be processed into the desired geometry and / or size. This processing results in a waste of magnetic material, which is a great economic loss, especially for sintered rare earths (RE), and in particular for FFPM, because the processing required to achieve the desired final shape will cut off the magnetic domain arrangement angles at the corners of the FFPM.

[0007] It may be desirable to provide a method that allows permanent magnets to be manufactured in an efficient manner. Summary of the invention

[0008] The apparatus for manufacturing a sintered permanent magnet, the method for manufacturing a sintered permanent magnet, the sintered permanent magnet, the electromechanical transducer and the wind turbine for generating electric power according to the present invention may meet this need.

[0009] According to a first aspect of the present invention, there is provided an apparatus for manufacturing sintered permanent magnets. The apparatus provided comprises: (a) a mould having a mould cavity for receiving a powder of a permanent magnet material; (b) at least two magnetic devices (also referred to as poles) for generating a magnetic field for magnetizing the powder contained in the mould cavity; and (c) at least one mould piece for compacting the powder contained in the mould cavity, magnetizing and compacting to produce a magnetized compacted block of the powder. The mould cavity and / or the mould piece comprises at least one surface which is curved in such a way that an undesirable deformation of the sintered block is at least partially compensated, the undesirable deformation being obtained by sintering the magnetized compacted block in a sintering furnace, thereby imparting the undesirable deformation after the sintered block is removed from the mould cavity.

[0010] The described apparatus is based on the idea that by choosing appropriate geometries of the mould cavity and / or mould piece (both defining the shape of the volume in which the sintered block is produced), deformations towards undesired geometries can be at least partially reduced. This means that deformations are not eliminated, but they "start" from the undesired geometry and at least approximately lead to the desired geometry of the sintered block. Thus, the potential processing of the sintered block towards the final permanent magnet (PM) can be achieved with minimal waste of (usually expensive) magnetic material.

[0011] The mentioned undesirable deformations can be physically produced by shrinkage effects which may occur during or after the sintering process in the sintering furnace. The sintering furnace is usually external to the device. However, it cannot be excluded that the described device and the sintering furnace can be combined into one and the same device. Potential further physical causes of deformations are internal magnetic forces which lead to magnetostriction. It is mentioned that, whatever the physical cause of the deformation, the extent of the deformation can be assessed with the aid of a test process for producing the sintered blocks. Based on the assessed "test deformation", at least one surface can be geometrically shaped in a suitable manner.

[0012] The described "pre-consideration" of deformations during manufacturing, by means of appropriate "pre-forming" of the mold cavity and / or the mold piece, can provide the greatest benefit for the manufacture, in particular of sintered flux focusing permanent magnets (FFPMs), since for such permanent magnets (PMs), it is essential that their final geometry corresponds exactly to the desired geometry. However, the described "pre-consideration of deformations" principle also applies to parallel or radially magnetized PMs. With the described device, sintered PMs with exactly the desired geometry can be produced even in manufacturing processes that impart undesirable deformation and shrinkage effects.

[0013] According to an embodiment of the invention, the mould cavity comprises two opposite surfaces, both of which are curved. This may provide the advantage that expected and undesired deformations may be compensated to a large extent. This applies in particular to shrinkage effects which occur when the sintered block is cooled after it has been removed from the sintering furnace.

[0014] According to another embodiment of the invention, the first surface is a convex surface and the second surface is a concave surface with respect to the center of the mold cavity. This can provide the advantage that on the one hand the mold cavity and / or the corresponding surface of the mold part can be formed in a simple and reliable manner, and on the other hand preforming can be achieved so as to produce effective deformation compensation.

[0015] According to a further embodiment of the invention, the magnetic arrangement is designed in such a way that the magnetic field within the mould cavity is associated with an extended angular distribution of the magnetic flux lines.

[0016] The extended angular distribution of the magnetic flux lines can be used in particular to produce an extended angular distribution of the magnetic domain alignment directions within the sintered block, which can produce a focused magnetization of the sintered block. Thus, outside of the bulk of the sintered block, a magnetic focus or at least a magnetic focus region can be defined. In this point or in this region, the magnetic flux density caused by the corresponding FFPM is increased compared to points or regions outside the focus and the corresponding focus region.

[0017] By designing the generator in such a way that the focal point and corresponding focusing region are located within the air gap between the stator assembly and the rotor assembly, the electrical power that can be generated by the generator can be significantly increased.

[0018] According to another embodiment of the invention, the apparatus further comprises another magnetic device for generating a magnetic field acting on the powder contained in the mould cavity.

[0019] In addition to the two magnetic means described above, the use of further magnetic means may allow the generation of a highly spatially inhomogeneous magnetic field within the mould cavity. This may be particularly advantageous when producing sintered magnet blocks for FFPM.

[0020] In case now at least one of the at least three magnetic devices comprises at least one electromagnetic coil and the current through the electromagnetic coil can be controlled, the opportunity is given to modify (the inhomogeneity of) the overall magnetic field by appropriate current regulation. This can allow the described apparatus to be used to manufacture sintered magnetic blocks with different flux focusing properties.

[0021] According to another embodiment of the invention, at least one of the two magnetic devices comprises: (a) at least one electromagnetic coil for generating a magnetic field and (b) a magnetic yoke for guiding and / or shaping the magnetic field generated by the electromagnetic coil.

[0022] By providing a suitable yoke to support the electromagnetic coils generating the magnetic field, the advantage can be provided that the magnetic field and the corresponding magnetic flux (density) at least in a selected area of ​​the mold cavity can be significantly increased. In addition, by designing the shape and / or geometry of the yoke in a suitable manner, an extended angular distribution of the magnetic flux lines can be generated, which results in a desired focused flux magnetization design.

[0023] The yoke, which may also be referred to as the pole piece, may be made of a ferromagnetic material, in particular iron or cobalt iron for higher saturation. In contrast, the mold may be made of a non-magnetic material, and in particular a non-ferromagnetic material. The (currently) preferred material is stainless steel. However, other mold materials that provide mechanical rigidity may also be used.

[0024] According to another embodiment of the invention, at least one of the magnetic means comprises an electromagnetic coil and a further magnetic yoke or a magnetic yoke and a further electromagnetic coil.

[0025] By designing the respective magnetic coils in an asymmetrical manner with respect to the number of coils and the number of yokes, the generation of a magnetic field associated with an extended angular distribution of the magnetic flux lines can be achieved in an easy and effective manner. As described above, such an inhomogeneous magnetic field allows the manufacture of FFPMs.

[0026] According to another embodiment of the present invention, one of the two magnetic devices is a first magnetic device having a first magnetic yoke, and the other of the two magnetic devices is a second magnetic device having a second magnetic yoke. With respect to the mold cavity, the first magnetic yoke and the second magnetic yoke are located at opposite sides. In addition, the first magnetic yoke has a first outer yoke surface facing the mold cavity, and the second magnetic yoke has a second outer yoke surface facing the mold cavity. In addition, (with respect to the mold cavity) the first outer yoke surface is concave and the second outer yoke surface is convex.

[0027] The described spatial design of the two yokes may provide the following advantages: For manufacturing FFPMs, an extended angular distribution of appropriate and well-defined magnetic flux lines can be produced in an easy and efficient manner. Depending on the specific application, the curvature of the outer yoke surface may be regular (without any corners and edges ("blocks and bumps") or irregular.

[0028] At least one of the outer yoke surfaces may have a shape that is at least approximately cylindrical. This results in a one-dimensional (1D) magnetic flux focusing, which results in a linearly extending focal region. Such magnetic focusing corresponds to optical focusing with the aid of a cylindrical optical lens. Alternatively, at least one of the outer yoke surfaces may have a shape that is at least approximately spherical. This results in a two-dimensional (2D) magnetic flux focusing, which results in an at least approximately focal point. Such magnetic focusing corresponds to optical focusing with the aid of a spherical optical lens.

[0029] According to another embodiment of the invention, (a) the first outer yoke surface has (at least in a portion of the first outer yoke surface) a first radius, and (b) the second outer yoke surface has (at least in a portion of the second outer yoke surface) a second radius different from the first radius. This may provide the advantage that a higher alignment angle of the magnetic domain alignment direction at and relative to the side edge of the sintered block may be achieved.

[0030] According to another aspect of the present invention, a method for manufacturing a sintered permanent magnet is provided. The provided method comprises: (a) filling a permanent magnet material powder into a mold cavity of a mold; (b) generating a magnetic field for magnetizing the powder contained in the mold cavity; (c) compacting the powder contained in the mold cavity by means of a mold member, magnetizing and compacting to produce a magnetized compacted block of the powder; (d) sintering the magnetized compacted block in a sintering furnace to produce a sintered block; and (e) removing the sintered block from the sintering furnace. The shape of the mold cavity is designed in such a way that an undesirable deformation of the sintered block, which is given after the sintered block is removed from the sintering furnace, is at least partially compensated.

[0031] The method described is also based on the idea that undesirable deformation effects usually caused by shrinkage during sintering can be compensated by means of forethought by means of a suitably shaped mold cavity which differs from the shape of the sintered block finally produced.

[0032] Typically, the step of generating a magnetic field in order to obtain a magnetic alignment and the step of compacting the powder are at least partially performed simultaneously.

[0033] The deformation process described may occur after removal. However, internal stresses causing deformation may have occurred before removal.

[0034] According to an embodiment of the invention, the permanent magnet material comprises a rare earth material, in particular NdFeB. This may provide the advantage that very strong PMs may be manufactured without generating a lot of waste (rare earth materials are generally very expensive) for achieving the desired PM geometry.

[0035] In this regard, other components mentioned as permanent magnet materials may include ferrite and / or SmCo.

[0036] According to another aspect of the present invention, there is provided a sintered magnet manufactured by performing the above method.

[0037] According to another aspect of the present invention, an electromechanical transducer, in particular a generator, is provided. The electromechanical transducer comprises (a) a stator assembly and (b) a rotor assembly. The rotor assembly comprises a support structure and at least one sintered magnet as described above. The sintered magnet is mounted to the support structure.

[0038] The provided electromechanical transducer is based on the idea that it can be built with a rotor component comprising appropriately shaped sintered PMs which have been efficiently manufactured without significant material waste.

[0039] According to another aspect of the present invention, a wind turbine for generating electric power is provided. The provided wind turbine comprises: (a) a tower, (b) a wind rotor arranged at a top portion of the tower and comprising at least one blade, and (c) an electromechanical transducer as described above. The electromechanical transducer is mechanically coupled to the wind rotor (110).

[0040] The proposed wind turbine, also referred to as a wind energy device, is based on the idea that the above-described electromechanical transducer allows a cost-effective implementation of the wind turbine with respect to the PM material used. This can contribute to increasing the attractiveness of wind turbine technology for renewable electricity production compared to other technologies such as solar power plants.

[0041] It is noted that embodiments of the present invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to method type claims, while other embodiments have been described with reference to device type claims. However, a person skilled in the art will gather from the above and following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter, any combination between features relating to different subject matters, in particular any combination between features of method type claims and features of device type claims, is considered to be disclosed with this document.

[0042] The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment.The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A wind turbine according to an embodiment of the invention is shown.

[0044] Figure 2 The schematic diagram shows Figure 1 Generators of wind turbines.

[0045] Figure 3 A flux focusing permanent magnet (FFPM) made according to an embodiment of the present invention is shown.

[0046] Figure 4 An apparatus for manufacturing sintered permanent magnets is shown, the apparatus comprising: (i) a mold having two opposing curved surfaces, and (ii) two magnetic devices for (non-uniformly) magnetizing a sintered magnet block located in the mold.

[0047] Figure 5 An apparatus for manufacturing sintered permanent magnets is shown, the apparatus comprising (i) a mold and a mold piece, each having a curved surface, and (ii) three magnetic devices for (inhomogeneously) magnetizing a sintered magnet block located in the mold.

[0048] Figure 6 A device for producing a sintered permanent magnet having two yokes, each having an outer yoke surface with a different radius of curvature, is shown.

[0049] Figure 7 The geometry of the mold, the sintered magnet block and the final PM in a known manufacturing process for sintered permanent magnets is shown.

[0050] Figure 8 The geometries of a mold, a sintered magnet block and a final PM in a manufacturing process for a sintered permanent magnet according to an embodiment of the present invention are shown. DETAILED DESCRIPTION

[0051] The illustrations in the drawings are schematic. It is noted that in different drawings, similar or identical elements or features are provided with the same reference numerals or with reference numerals which differ from the corresponding reference numerals only within the first digit. In order to avoid unnecessary repetition, elements or features which have already been explained with respect to the previously described embodiments are not explained again at a later point in the present description.

[0052] Figure 1 A wind turbine 100 according to an embodiment of the invention is shown. The wind turbine 100 comprises a tower 120, which is mounted on a foundation not shown. On top of the tower 120 a nacelle 122 is arranged. Between the tower 120 and the nacelle 122 a yaw angle adjustment device 121 is provided, which enables the nacelle 122 to be rotated about a vertical axis not shown, which is aligned with the longitudinal extension of the tower 120. By controlling the yaw angle adjustment device 121 in a suitable manner, it can be ensured that during normal operation of the wind turbine 100 the nacelle 122 is always properly aligned with the current wind direction.

[0053] Wind turbine 100 further includes a wind rotor 110 having three blades 114. Figure 1 In the perspective view of FIG. 1 , only two blades 114 are visible. The rotor 110 is rotatable about an axis of rotation 110 a. The blades 114 mounted on the hub 112 extend radially relative to the axis of rotation 110 a.

[0054] A blade angle adjustment device 116 is provided between the hub 112 and the blades 114, respectively, to adjust the blade pitch angle of each blade 114 by rotating the corresponding blade 114 around an axis not shown, which is substantially aligned parallel to the longitudinal extension of the corresponding blade 114. By controlling the blade angle adjustment device 116, the blade pitch angle of the corresponding blade 114 can be adjusted so that at least when the wind is not too strong, the maximum wind force can be obtained from the available mechanical power of the wind-driven wind rotor 110.

[0055] from Figure 1 As can be seen in FIG. 1 , a gearbox 124 is arranged inside the nacelle 122. The gearbox 124 serves to convert the number of revolutions of the rotor 110 into a higher number of revolutions of a shaft 125, which is coupled to an electromechanical transducer 130 in a known manner. The electromechanical transducer is a generator 130.

[0056] At this point it is noted that the gearbox 124 is optional and the generator 140 may also be coupled directly to the rotor 110 via the shaft 125 without changing the number of revolutions. In this case, the wind turbine is a so-called direct drive (DD) wind turbine.

[0057] Furthermore, a brake 126 is provided in order to stop the operation of the wind turbine 100 or in order to reduce the rotational speed of the rotor 110, for example in an emergency situation.

[0058] The wind turbine 100 further comprises a control system 143 for operating the wind turbine 100 in an efficient manner. Besides controlling eg the yaw angle adjustment device 121, the depicted control system 153 is also used for adjusting the blade pitch angles of the rotor blades 114 in an optimized manner.

[0059] According to the basic principles of electrical engineering, the generator 130 includes a stator assembly 135 and a rotor assembly 140. In the embodiment described here, the generator 130 is implemented in a so-called "inner rotor-outer rotor" configuration, in which the rotor assembly 140 surrounds the stator assembly 135. This means that the non-illustrated permanent magnets and corresponding magnet assemblies of the rotor assembly 140 travel around an arrangement of multiple non-illustrated coils of the inner stator assembly 135, which coils produce an induced current generated by picking up the time-varying magnetic flux from the traveling permanent magnets.

[0060] According to the embodiments described herein, each permanent magnet (PM) assembly includes at least three sintered permanent magnet arrangements made of a Nd—Fe—B material composition.

[0061] Figure 2 A schematic diagram of a generator 130 is shown in cross-section. The generator 130 includes a stator assembly 135. The stator assembly 135 includes a stator support structure 237 including a stack of multiple laminations and a plurality of stator windings 239 housed within the stator support structure 237. The windings 239 are interconnected in a known manner by means of electrical connections not shown.

[0062] The rotor assembly 140 of the generator 130 is separated from the stator assembly 135 by an air gap ag, and the rotor assembly 140 includes a rotor support structure 242 that provides a mechanical base for mounting a plurality of sintered permanent magnets 250. Figure 2 , the rotation axis of the rotor assembly 140 is indicated by reference numeral 230a.

[0063] In the exemplary embodiment described here, three sintered permanent magnets are arranged adjacent to each other at each angular position of the rotor assembly 140. Figure 2In the figure, for ease of explanation, only three sintered permanent magnets 250 assigned to one angular position are shown. In practice, a plurality of sintered permanent magnets 250 are mounted to the rotor support structure 242 according to the size of the generator 130. The sintered permanent magnets 250 are preferably arranged in a matrix-like structure around a curved surface area of ​​the support structure 242 having a substantially cylindrical geometry around the generator shaft 240a.

[0064] As from Figure 2 As can be seen in FIG. 2 , the sintered permanent magnets 250 are not mounted directly to the rotor support structure 242. Instead, a back plate 244 made of a ferromagnetic material, such as iron, is provided. The back plate 244 is provided in order to ensure proper magnetic flux guidance. This significantly reduces the strength of the magnetic stray fields in an advantageous manner.

[0065] Figure 3 A flux focusing permanent magnet (FFPM) 350 made in accordance with an embodiment of the present invention is shown.

[0066] The FFPM 350 is magnetized in a manner that imparts an extended angular distribution of magnetic domain alignment directions 352. According to the embodiments described herein, each magnetic domain alignment direction 352 follows a straight magnetization line. The straight lines are angled or tilted relative to each other in a fan-shaped manner. Specifically, the extended angular distribution of the straight magnetization lines produces a focus 354 in an area above the main surface 350a of the FFPM 350, and the focus 354 is characterized by a local maximum of the magnetic field and corresponding magnetic flux density generated by the FFPM 350.

[0067] According to the exemplary embodiment described herein, the depicted magnetic domain arrangement pattern is symmetrical with respect to a symmetry axis 354a. In this document, the symmetry axis 354a is also referred to as the magnetic axis. The magnetic axis 354a is the normal axis of the major surface 350a, which runs through the focal point 354.

[0068] Figure 4 An apparatus 460 is shown for manufacturing a block in the form of a pressed magnet powder, which can be sintered in a furnace and become a sintered permanent magnet. Specifically, the apparatus 460 is used to magnetize and compact a magnetic material powder 495. The subsequent sintering of the resulting magnetized compacted block is carried out in a sintering furnace not shown. The apparatus 460 includes a mold 470, in which a mold cavity 472 is formed. The mold cavity 472 can be closed by a mold member not shown, which is used to compact the powder 495 of the magnetic material, which must be filled into the mold cavity 472 according to the usual process for manufacturing sintered magnets. The mold member not depicted performs movement in a direction perpendicular to the plane of the drawing.

[0069] The apparatus 460 further comprises means for generating a magnetic field which is applied to the compacted powder 495 during the sintering process. These magnetic field generating means comprise a first magnetic device 461 and a second magnetic device 464. Figure 4 In the embodiment shown in , the first magnetic device 461 generates a magnetic north pole N, and the second magnetic device 464 generates a magnetic south pole S. According to known equipment, the first magnetic device includes (i) a first electromagnetic coil 462 for generating a magnetic field, and (ii) a first yoke 463 for guiding and / or for shaping the magnetic field (line) present in the mold cavity 472. Correspondingly, the second magnetic device 464 includes (i) a second electromagnetic coil 465 and (ii) a second yoke 466.

[0070] According to the exemplary embodiment described here, the first magnetic yoke 463 assigned to the north pole and the second magnetic yoke 466 assigned to the south pole have different geometries. Specifically, the curvature radii of the outer surfaces of the two magnetic yokes 463, 466 are different from each other. This has the following effect: an inhomogeneous magnetic field and a corresponding magnetic flux will be provided in the mold cavity 472, which leads to an inhomogeneous magnetization of the powder 495. Figure 3 As shown in , this non-uniform magnetization can produce an extended angular distribution of magnetic domain alignment directions 352.

[0071] As from Figure 4 As can be seen in FIG. 4 , according to the embodiments described herein, the mold cavity 472 comprises a geometry different from a rectangular parallelepiped. Thus, Figure 4 The cross-section of the mold cavity 432 depicted in FIG. 4 is not rectangular. Specifically, according to the embodiment described herein, the lower first surface 470a of the mold 470 is curved in a convex manner (about the center point of the mold cavity 472). In addition, the opposite upper second surface 470b of the mold 470 is curved in a concave manner (again with respect to the center point of the mold cavity 472).

[0072] At first glance, this shaping of the die cavity 472 will produce a geometry of the sintered block produced that deviates from the generally desired cuboid shape of a permanent magnet (PM). However, when considering (on second glance) the undesirable deformations that occur periodically during the upcoming sintering process and / or during the subsequent cooling period of the sintered magnet block, the geometry of the die cavity 472 can take into account such deformations. Therefore, a die cavity 472 having appropriately shaped curved surfaces 470a, 470b can result in a cuboid sintered PM body that is at least approximately perfectly shaped. Therefore, when the sintered PM block is finalized or further processed toward a PM sheet having a cuboid shape, less PM material will have to be removed from the sintered PM block. This makes the manufacture of a single permanent magnet very efficient, particularly from an economic point of view, because less material must be processed away and although the material can be reused, it usually represents wasted material.

[0073] It should be noted that the deformation considerations described can be achieved not only with PMs that should be cuboid in shape. By appropriately shaping the inner surface of the mold cavity 472, a magnetized compact can be made that has at least an approximate desired shape and a corresponding geometry after the deformation process is completed. Thus, in some applications, the mold cavity can be defined not only by two but by three or more curved surfaces.

[0074] Figure 5 An apparatus 560 for manufacturing magnet blocks from magnet powder ready for sintering in a furnace is shown according to another embodiment of the present invention.

[0075] according to Figure 5 In the embodiment shown in FIG. 5 , the non-cuboid mold cavity 572 is formed by two curved surfaces, a first curved surface 570a of the mold 570 and a second curved surface 570b of the mold 570. The mold member not shown is used to compact the magnetic material powder 595 filled into the mold cavity 572. The movement of the mold member is along a direction perpendicular to the plane of the drawing.

[0076] Device 560 and Figure 4 The difference of the device 460 shown in FIG. 5 is that the spatially inhomogeneous magnetic field / magnetic flux within the mold cavity 572 is generated not only by two magnetic devices, but by three magnetic devices. Specifically, the device 560 includes two magnetic devices 561 and 567, which generate a magnetic north pole from the perspective of the powder 595 to be magnetized. In addition, the device 560 includes a magnetic device 564, which generates a magnetic south pole from the perspective of the powder 595 to be magnetized. Each of the magnetic devices 561, 564 and 567 includes an electromagnetic coil (see reference numerals 562, 565 and 568) and a magnetic yoke (see reference numerals 563, 566 and 569).

[0077] Figure 6 660 is shown for manufacturing a sintered permanent magnet from a magnetic material powder 695 according to another embodiment of the present invention. In this embodiment, two magnetic devices with magnetic yokes of different shapes are used to generate a spatially non-uniform magnetic field / magnetic flux in a mold cavity 672. Specifically, the first magnetic device that generates a magnetic north pole includes a first magnetic yoke 663, and the second magnetic device that generates a magnetic south pole includes a second magnetic yoke 666. As shown in FIG. Figure 6 As can be seen in FIG. 6 , the first yoke 663 has an outer (convex) curved yoke surface 663a having a first radius R1 and the second yoke 666 has an outer (concave) curved yoke surface 666a having a second radius R2. The corresponding magnetic field lines or flux lines are indicated by reference numeral 630.

[0078] Although it is not necessary to generate a suitable spatially inhomogeneous magnetic field / flux, in the embodiment described here, the second (concave) radius R2 is larger than the first (convex) radius R1. By appropriately selecting the two radii R1 and R2, the focusing strength and corresponding focal length of the generated FFPM can be adjusted.

[0079] Figure 7 and 8 The geometries of the mold, the sintered magnet block and the final PM installed in the generator are shown for different sintered PM manufacturing processes. Figure 7 These geometries are shown for known manufacturing processes, and Figure 8 These geometries are shown for a manufacturing process according to an embodiment of the present invention.

[0080] Figure 7 8a and 8a show the final PM part 250 to be produced as a reference. According to the exemplary embodiment described here, the final PM part 250 has a rectangular parallelepiped shape. As mentioned above, the desired final shape can also deviate from a pure rectangular parallelepiped. For example, the desired shape can have rounded corners or edges.

[0081] Figure 7 8b and 8c show the geometry of the mold cavities 772 and 872 used in the compaction and magnetization process of the magnetic powder material. The mold cavity 772 has a rectangular parallelepiped shape, while the shape of the mold cavity 872 is non-rectangular because it includes two curved opposing surfaces.

[0082] Figure 7 c and 8c show the geometrical dimensional relationship between the manufactured sintered PM blocks, which have undergone deformation after (a) being removed from the corresponding mold cavities 772, 872, (b) having undergone deformation after being sintered in a sintering furnace, and (c) having undergone deformation after being taken out of the sintering furnace. The sintered PM block 775 produced with the aid of a (known) rectangular mold cavity 770 and a known sintering furnace and having undergone deformation effects is very different from the rectangular shape. In contrast, the sintered PM block 875 produced with the aid of a non-rectangular but curved mold cavity 870 and also subjected to deformation effects has a rectangular shape or at least a shape that deviates only to a small extent from the desired rectangular shape.

[0083] Figure 7d and 8d show the (volume) difference between (i) the final PM part 250 and (ii) the manufactured sintered PM body 775, 875. It can be seen that the PM material waste for producing the final PM part 250 from the curved sintered PM block 775 is significantly greater than the PM material waste for producing the final PM part 250 from the PM block 875 sintered at least approximately rectangular. Since a large amount of PM material waste increases the manufacturing cost of the PM magnet part, anticipating deformation by means of appropriate bending and forming of the mold cavity is an effective measure to make the production of sintered PM parts (economically) more efficient.

[0084] It should be noted that the term "comprising" does not exclude other elements or steps, and the use of the article "a" or "an" does not exclude a plurality. Elements described in connection with different embodiments may also be combined. It should also be noted that the reference numerals in the claims should not be interpreted as limiting the scope of the claims.

Claims

1. An apparatus (460, 560, 660) for manufacturing a sintered permanent magnet (250, 350), the apparatus (460, 560, 660) comprising: A mold (470, 570) having a mold cavity (472, 572, 672) for receiving permanent magnet material powder (495, 595, 695); at least two magnetic devices (461, 464; 561, 564) for generating a magnetic field for magnetizing a permanent magnet material powder (495, 595, 695) contained in the mold cavity (472, 572, 672); and at least one mold for compacting the permanent magnet material powder (495, 595, 695) contained in the mold cavity (472, 572, 672), The magnetization and compaction produce a magnetized compacted mass of the permanent magnet material powder (495, 595, 695); wherein, The mold cavity (472, 572, 672) and / or the mold element comprises at least one surface (470a, 470b; 570a, 570b) which is curved in such a way that an undesired deformation of the sintered block (885) is at least partially compensated, the undesired deformation being obtained by sintering the magnetized compacted block in a sintering furnace, thereby imparting the undesired deformation after the sintered block (885) is removed from the sintering furnace, The magnetic device (461, 464) is designed in such a way that the magnetic field (630) in the mold cavity is associated with the spread angular distribution of the magnetic flux lines. Wherein, at least one of the two magnetic devices (461, 464; 561, 564) includes an electromagnetic coil (462, 465; 562, 565) for generating the magnetic field (630), and a magnetic yoke (463, 466; 563, 566) for guiding and / or for shaping the magnetic field generated by the electromagnetic coil (462, 465; 562, 565), in, One of the two magnetic devices (461, 464; 561, 564) is a first magnetic device (461, 561) having a first magnetic yoke (463, 563, 663), and the other of the two magnetic devices (461, 464; 561, 564) is a second magnetic device (464, 564) having a second magnetic yoke (466, 566, 666), With respect to the mold cavity (472, 572, 672), the first yoke (463, 563, 663) and the second yoke (466, 566, 666) are located at opposite sides, The first magnetic yoke (463, 563, 663) has a first outer yoke surface (663a) facing the mold cavity (672), The second magnetic yoke (466, 566, 666) has a second outer yoke surface (666a) facing the mold cavity (466, 566, 666), The first outer yoke surface (663a) has a first radius (R1), and the second outer yoke surface (666a) has a second radius (R2) different from the first radius (R1).

2. The device (460, 560, 660) according to claim 1, wherein The mold cavity (472, 572, 672) includes opposing first and second surfaces, both of which are curved.

3. The device (460, 560, 660) according to claim 2, wherein: With respect to the center of the mold cavity (472, 572, 672), the first surface is a convex surface (470a, 570a), and the second surface is a concave surface (470b, 570b).

4. The device (560) according to any one of claims 1 to 3, further comprising: Another magnetic device (567) is used to generate a magnetic field (630) acting on the permanent magnet material powder (595) contained in the mold cavity.

5. The apparatus (460, 560, 660) of claim 1, wherein: The first outer yoke surface (663a) is concave and the second outer yoke surface (666a) is convex.

6. A method for manufacturing a sintered permanent magnet (250, 350) by means of the apparatus according to any one of claims 1 to 5, the method comprising: Filling permanent magnet material powder (495, 595, 695) into the mold cavity (472, 572, 672) of the mold (470, 570); generating a magnetic field (630) via at least two magnetic devices (461, 464; 561, 564) for magnetizing a permanent magnet material powder (495, 595, 695) contained in the mold cavity (472, 572, 672); Compacting the permanent magnet material powder (495, 595, 695) contained in the mold cavity (472, 572, 672) by means of a mold, the magnetization and compaction producing a magnetized compacted block of the permanent magnet material powder (495, 595, 695); sintering the magnetized compacted mass in a sintering furnace to produce a sintered mass (885); and Taking out the sintered block from the sintering furnace (885); wherein the shape of the mold cavity (472, 572, 672) is designed in such a way that an undesired deformation of the sintered block (885) is at least partially compensated, the undesired deformation being imparted after the sintered block (885) is removed from the sintering furnace, and The magnetic device (461, 464) is designed in such a way that the magnetic field (630) in the mold cavity is associated with the expansion angle distribution of the magnetic flux lines.

7. The method according to claim 6, wherein: The permanent magnet material powder (495, 595, 695) includes rare earth material.

8. The method according to claim 6, wherein: The permanent magnet material powder (495, 595, 695) includes NdFeB.

9. A sintered permanent magnet (250, 350) manufactured by performing the method of any one of claims 6 to 8.

10. An electromechanical transducer (130), comprising: a stator assembly (135), and A rotor assembly (140) comprising A support structure (242) and The at least one sintered permanent magnet (250, 350) of claim 9, wherein the sintered permanent magnet (250, 350) is mounted to the support structure (242).

11. The electromechanical transducer (130) according to claim 10, wherein: The electromechanical transducer (130) is a generator.

12. A wind turbine (100) for generating electrical power, the wind turbine (100) comprising: Tower (120), a wind rotor (110) arranged at a top portion of the tower (120) and comprising at least one blade (114), and The electromechanical transducer (130) according to claim 10 or 11, wherein the electromechanical transducer (130) is mechanically coupled to the wind rotor (110).

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