CN111834116A

CN111834116A - Manufacturing sintered permanent magnets with reduced deformation

Info

Publication number: CN111834116A
Application number: CN201910328341.4A
Authority: CN
Inventors: Z.阿扎尔; A.C.乌尔达
Original assignee: Siemens Gamesa Renewable Energy AS
Current assignee: Siemens Gamesa Renewable Energy AS
Priority date: 2019-04-23
Filing date: 2019-04-23
Publication date: 2020-10-27
Also published as: WO2019202172A2; EP3939058A2; WO2019202172A3

Abstract

An apparatus (460, 560, 660) for manufacturing a sintered permanent magnet (250, 350) is described. The apparatus includes (a) a mold (470, 570); (b) at least two magnetic means (461, 464; 561, 564); and (c) at least one die member for compacting the powder contained in the die cavity; the magnetizing and compacting produces a magnetized compacted mass of powder (495, 595, 695). The mould cavity and/or the mould part comprises at least one surface (470 a, 470 b; 570a, 570 b) which is curved in such a way that an undesired deformation of the sintered block, which is obtained by sintering the magnetized compacted block in a sintering furnace, is at least partially compensated. Further described is a method of manufacturing a sintered permanent magnet with such an apparatus, a sintered permanent magnet manufactured with such a method, and an electromechanical transducer (140) and a wind turbine (100) comprising such a sintered permanent magnet.

Description

Manufacturing sintered permanent magnets with reduced deformation

Technical Field

The present invention relates to an apparatus and a method for manufacturing a sintered permanent magnet. Furthermore, the invention relates to a sintered magnet produced with the method, as well as an electromechanical transducer and a wind turbine comprising at least one such sintered magnet.

Background

Permanent magnetic materials are used in a number of different fields of application. Perhaps the most technically and economically important application areas are electromechanical transducers, i.e. motors and generators. An electric motor equipped with at least one Permanent Magnet (PM) converts electrical energy into mechanical energy by generating a temporarily varying magnetic field by means of windings or coils. This temporarily varying magnetic field interacts with the magnetic field of the PM, which is generated, for example, in the rotational movement of the rotor assembly relative to the stator assembly of the electric motor. In a physically complementary manner, the generator converts mechanical energy into electrical energy.

A generator is a core component of any power plant for producing electrical energy. This applies to power plants which directly extract mechanical energy, such as hydroelectric power plants, tidal power plants and wind power plants also known as wind turbines. However, this also applies to the following power plants: the power plant (i) first uses chemical energy, for example from burning fossil fuels or from nuclear energy, in order to generate thermal energy, and (ii) converts the generated thermal energy into mechanical energy by means of a suitable thermodynamic process.

The efficiency of the generator is probably the most important factor for optimizing the production of electrical energy. For PM generators, it is necessary that the magnetic flux generated by the Permanent Magnets (PM) is strong. This can be best achieved with sintered rare earth magnets, for example, using NdFeB material compositions. However, the spatial magnetic field distribution produced by the PM also has an effect on the generator efficiency. In the latter case, it is often advantageous when using PM devices or PM arrangements having non-uniform magnetic domain alignment patterns, which create non-uniform magnetic field strength or flux density, particularly in the air gap between the rotor and stator assemblies.

It is known to arrange a non-uniform magnetic domain arrangement pattern in the PM in order to achieve so-called "flux focusing". WO 2012/141932a2 discloses a PM magnet arrangement in which differently magnetized PMs are combined such that "magnetic focusing" is achieved. EP 3276642 a1 discloses a sintered rare earth PM having a focused magnetic alignment pattern with an integrally formed or one-piece PM body. EP 2762838 a2 discloses an apparatus and a method for manufacturing PMs, wherein an inhomogeneous external magnetic field is applied during the sintering process in order to magnetize different regions of the PM in different directions.

Flux focusing provides a substantial increase in air gap flux density, which results in higher torque/power for electromechanical transducers, such as generators for directly driving wind turbines. However, PM/FFPM may be deformed during the manufacture of PM, and in particular during the manufacture of flux-focusing permanent magnets (FFPM) and due to the methods of pressing, sintering and magnetizing. Which means that its final shape differs from the desired ideal shape. In addition, under normal circumstances, sintered PM having a desired final geometry cannot be produced accurately. Therefore, it is desirable to machine the PM/FFPM into a desired geometry and/or size. This machining results in a waste of magnetic material, which is a significant economic loss, particularly for sintered Rare Earth (RE), and particularly for FFPM, since the machining required to achieve the desired final shape will cut the domain alignment angle at the corners of the FFPM.

It may be desirable to provide a method that allows the permanent magnet to be manufactured in an efficient manner.

Disclosure of Invention

This need may be met by the subject matter according to the independent claims. Advantageous embodiments of the invention are described by the dependent claims.

According to a first aspect of the present invention, there is provided an apparatus for manufacturing a sintered permanent magnet. The provided apparatus includes: (a) a die having a die cavity for receiving a powder of permanent magnet material; (b) at least two magnetic means (also called poles) for generating a magnetic field for magnetizing the powder contained in the die cavity; and (c) at least one die member for compacting the powder contained in the die cavity, magnetizing and compacting to produce a magnetized compacted mass of powder. The mould cavity and/or the mould part comprise at least one surface which is curved in such a way that an undesired deformation of the sintered cake, which is obtained by sintering the magnetized compacted cake in a sintering furnace, is at least partially compensated, whereby an undesired deformation is imparted after the removal of the sintered cake from the mould cavity.

The described device is based on the following idea: by selecting an appropriate geometry of the mold cavity and/or mold piece (both defining the shape of the volume creating the sintered mass), deformation towards an undesired geometry may be at least partially reduced. This means that the deformations are not eliminated, but they "start" from an undesired geometry and at least approximately give rise to the desired geometry of the agglomerates. Thus, potential machining of the sintered mass towards the final Permanent Magnet (PM) can be achieved with minimal (usually expensive) waste of magnetic material.

The mentioned undesired deformations may be physically caused by shrinkage effects which may occur during or after the sintering process in the sintering furnace. The sintering furnace is usually external to the plant. However, it may not be excluded that the described apparatus and sintering furnace may be combined into one and the same device. A potential further physical cause of deformation is internal magnetic forces that cause magnetostriction. It is to be mentioned that, irrespective of the physical cause of the deformation, the degree of deformation can be evaluated by means of a test procedure for producing the sintered compact. Based on the evaluated "test deformation", at least one surface may be geometrically shaped in a suitable manner.

By means of a suitable "preforming" of the mold cavity and/or the mold parts, the described "pre-consideration" of the deformation during manufacturing can provide the greatest benefit for the manufacture, in particular for sintered flux-focusing permanent magnets (FFPM), since for such Permanent Magnets (PM) it is necessary that their final geometry exactly corresponds to the desired geometry. However, the described "deformation preplanning" principle is also applicable to parallel or radially magnetized PMs. With the apparatus, sintered PM having a precisely desired geometry can be produced even during manufacturing processes that impart undesirable deformation and shrinkage effects.

According to an embodiment of the invention, the mould cavity comprises two opposite surfaces, which are both curved. This may provide the advantage that expected and unwanted deformations may be compensated for to a large extent. This applies in particular to the shrinkage effect which occurs when the agglomerates are cooled after they have been removed from the sintering furnace.

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

According to another embodiment of the invention, the magnetic means are designed in such a way that the magnetic field within the mold cavity is correlated with the spread angle distribution of the flux lines.

The spread angle distribution of the flux lines may be particularly useful for creating a spread angle distribution of the domain alignment direction within the sintered mass, which may result in a focused magnetization of the sintered mass. Thus, outside a large part of the sintered cake, a magnetic focus or at least a magnetic focusing area may be defined. In this point or in this region, the magnetic flux density caused by the respective FFPM is increased as compared to a point or region from the focal point and outside the respective focusing region.

By designing the generator in such a way that the focal point and the corresponding focal zone are located within the air gap between the stator and rotor assemblies, the power that can be generated by the generator can be significantly increased.

According to another embodiment of the invention, the apparatus further comprises further magnetic means for generating a magnetic field acting on the powder contained in the die cavity.

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

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

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 yoke for guiding and/or shaping the magnetic field generated by the electromagnetic coil.

By providing a suitable yoke to support the electromagnetic coil generating the magnetic field, the advantage is provided that the magnetic field and the corresponding magnetic flux (density) can be significantly increased at least in selected regions of the mould cavity. Furthermore, by designing the shape and/or geometry of the yoke in a suitable manner, a spread angle distribution of the flux lines may be generated, which results in a desired focused flux magnetization design.

The yoke, which may also be referred to as a 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 providing mechanical rigidity may also be used.

According to another embodiment of the invention at least one of said magnetic means comprises one electromagnetic coil and another magnetic yoke or one magnetic yoke and another electromagnetic coil.

By designing the respective magnet coils in an asymmetric 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 flux lines can be achieved in an easy and efficient manner. As described above, this non-uniform magnetic field allows FFPM to be manufactured.

According to another embodiment of the invention, one of the two magnetic means is a first magnetic means having a first yoke and the other of the two magnetic means is a second magnetic means having a second yoke. With respect to the mold cavity, the first and second yokes are located at opposite sides. Further, the first yoke has a first outer yoke surface facing the mold cavity, and the second yoke has a second outer yoke surface facing the mold cavity. Further, the first outer yoke surface is concave (with respect to the mold cavity) and the second outer yoke surface is convex.

The described spatial design of the two yokes can provide the following advantages: for manufacturing FFPM, a suitably and well-defined spread angle distribution of magnetic flux lines can be generated in an easy and efficient manner. The curvature of the outer yoke surface may be regular (without any corners and edges ("nubs and bumps") or irregular, depending on the particular application.

At least one of the outer yoke surfaces may have an at least approximately cylindrical shape. This produces a one-dimensional (1D) flux focus, which produces a linearly extending focal region. This magnetic focusing corresponds to optical focusing by means of a cylindrical optical lens. Alternatively, at least one of the outer yoke surfaces may have an at least approximately spherical shape. This causes two-dimensional (2D) flux focusing, which produces at least an approximate focus. This magnetic focusing corresponds to optical focusing by means of a spherical optical lens.

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: higher alignment angles at the side edges of the agglomerates and relative to the alignment direction of the magnetic domains at the side edges of the agglomerates can be achieved.

According to another aspect of the present invention, a method for manufacturing a sintered permanent magnet is provided. The provided method comprises the following steps: (a) filling permanent magnet material powder into a die cavity of a die; (b) generating a magnetic field for magnetizing the powder contained in the die cavity; (c) compacting the powder contained in the mould cavity by means of a mould, magnetizing and compacting to produce a magnetized compacted mass of powder; (d) sintering the magnetized compacted cake in a sintering furnace, thereby producing a sintered cake; and (e) removing the agglomerates from the sintering furnace. The shape of the mould cavity is designed in such a way that an undesired deformation of the sinter cake, which is imparted after removal of the sinter cake from the sintering furnace, is at least partially compensated.

The described method is also based on the idea that undesired deformation effects, which are usually caused by shrinkage during sintering, can be compensated with pre-consideration by means of a suitably shaped mould cavity which differs from the shape of the finally produced sintered block.

Typically, the step of generating a magnetic field to obtain the magnetic alignment and the step of compacting the powder are at least partially accomplished simultaneously.

The described deformation process may occur after removal. However, internal stresses leading to deformation may have occurred prior to removal.

According to an embodiment of the invention, the permanent magnet material comprises a rare earth material, in particular NdFeB. This may provide the following advantages: very strong PMs can be manufactured without the need to generate large amounts of waste (rare earth materials are typically very expensive) for achieving the desired PM geometry.

In this respect, it is mentioned that other components of the permanent magnet material may comprise ferrite and/or SmCo.

According to another aspect of the present invention, there is provided a sintered magnet produced by performing the above-described method.

According to another aspect of the invention, an electromechanical transducer, in particular a generator, is provided. The electromechanical transducer includes (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 a support structure.

The electromechanical transducer provided is based on the idea that it can be built with a rotor assembly comprising suitably shaped sintered PM, which has been efficiently manufactured without substantial material waste.

According to another aspect of the invention, a wind turbine for generating electrical 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).

The wind turbine provided, also called wind energy plant, is based on the following idea: the electromechanical transducer described above allows to realize a wind turbine in a cost-effective manner with respect to the PM material used. This may help to increase the attractiveness of wind turbine technology for regenerative power production compared to other technologies, such as solar power plants.

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, whereas other embodiments have been described with reference to apparatus type claims. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one type of subject-matter also any combination between features relating to different subject-matters, in particular between features of the method type claims and features of the apparatus type claims, is considered to be disclosed with this document.

The above aspects 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.

Drawings

FIG. 1 shows a wind turbine according to an embodiment of the invention.

Fig. 2 shows a generator of the wind turbine of fig. 1 in a schematic view.

FIG. 3 illustrates a Flux Focusing Permanent Magnet (FFPM) made according to an embodiment of the present invention.

Fig. 4 shows an apparatus for manufacturing a sintered permanent magnet, 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 within the mold.

Fig. 5 shows an apparatus for manufacturing a sintered permanent magnet, which includes (i) a mold and a mold piece, each having one curved surface, and (ii) three magnetic devices for (non-uniformly) magnetizing a sintered magnet block located within the mold.

Fig. 6 shows an apparatus for manufacturing a sintered permanent magnet having two yokes each having an outer yoke surface with a different radius of curvature.

Fig. 7 shows the geometry of the mold, the sintered magnet block and the final PM in a known manufacturing process for sintered permanent magnets.

Fig. 8 shows the geometry of the mold, the sintered magnet block and the final PM in a manufacturing process for sintered permanent magnets according to an embodiment of the invention.

Detailed Description

The illustration in the drawings is schematically. It is noted that in different figures, similar or identical elements or features are provided with the same reference signs or with reference signs, which differ from the corresponding reference signs only within a first digit. In order to avoid unnecessary repetition, elements or features that have been elucidated with respect to the previously described embodiments are not again elucidated at a later position in the description.

FIG. 1 shows a wind turbine 100 according to an embodiment of the invention. The wind turbine 100 comprises a tower 120, the tower 120 being 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 adjusting device 121 is arranged, which yaw angle adjusting device 121 is capable of rotating the nacelle 122 about a not shown vertical axis aligned with the longitudinal extension of the tower 120. By controlling the yaw angle adjustment arrangement 121 in a suitable manner, it may be ensured that during normal operation of the wind turbine 100 the nacelle 122 is always properly aligned with the current wind direction.

Wind turbine 100 further includes a wind rotor 110 having three blades 114. In the perspective view of fig. 1, only two blades 114 are visible. The rotor 110 is rotatable about a rotation axis 110 a. Blades 114 mounted on hub 112 extend radially with respect to rotational axis 110 a.

Between the hub 112 and the blades 114, blade angle adjustment means 116 are provided, respectively, for adjusting the blade pitch angle of each blade 114 by rotating the respective blade 114 about an axis, not shown, which is aligned substantially parallel to the longitudinal extension of the respective blade 114. By controlling the blade angle adjustment devices 116, the blade pitch angle of the respective blades 114 may be adjusted such that the maximum wind power may be extracted from the available mechanical power of the wind driven wind rotor 110, at least when the wind is not too strong.

As can be seen in FIG. 1, a gear box 124 is disposed within nacelle 122. The gearbox 124 serves to convert the number of revolutions of the rotor 110 into a higher number of revolutions of the shaft 125, the shaft 125 being coupled to an electromechanical transducer 130 in a known manner. The electromechanical transducer is a generator 130.

At this point, it is noted that the gearbox 124 is optional and that 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.

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 case of an emergency.

The wind turbine 100 further comprises a control system 143 for operating the wind turbine 100 in an efficient manner. In addition to controlling, for example, the yaw angle adjusting device 121, the depicted control system 153 serves to adjust the blade pitch angle of the rotor blades 114 in an optimized manner.

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 herein, the generator 130 is implemented in a so-called "inner rotor-outer rotor" configuration, wherein a rotor assembly 140 surrounds the stator assembly 135. This means that the not shown permanent magnets of the rotor assembly 140 and the corresponding magnet assembly travel around an arrangement of a plurality of not shown coils of the inner stator assembly 135 which generate induced currents resulting from picking up time varying magnetic flux from the traveling permanent magnets.

According to embodiments described herein, each Permanent Magnet (PM) assembly includes at least three sintered permanent magnet arrangements made of a Nd-Fe-B material composition.

Fig. 2 shows a schematic view of the generator 130 in a sectional view. The generator 130 includes a stator assembly 135. The stator assembly 135 includes a stator support structure 237, the stator support structure 237 including a stack of a plurality of 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.

The rotor assembly 140 of the generator 130 is separated from the stator assembly 135 by an air gap ag, the rotor assembly 140 including a rotor support structure 242, the rotor support structure 242 providing a mechanical base for mounting the plurality of sintered permanent magnets 250. In fig. 2, the axis of rotation of the rotor assembly 140 is indicated by reference numeral 230 a.

In the exemplary embodiment described herein, three sintered permanent magnets arranged adjacent to each other are arranged at each angular position of the rotor assembly 140. It is noted that in fig. 2, for the sake of convenience 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, depending on the size of the generator 130. The sintered permanent magnets 250 are preferably arranged in a matrix-like configuration around the curved surface area of the support structure 242, which has a substantially cylindrical geometry around the generator shaft 240 a.

As can be seen from 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. A back plate 244 is provided to ensure proper flux guidance. This significantly reduces the strength of the magnetic stray field in an advantageous manner.

Fig. 3 illustrates a Flux Focusing Permanent Magnet (FFPM) 350 made in accordance with an embodiment of the present invention.

The FFPM 350 is magnetized so as to give a spread angle distribution in the magnetic domain alignment direction 352. According to the embodiment described herein, each magnetic domain alignment direction 352 follows a straight magnetization line. The lines are angled or inclined relative to each other in a fan-like manner. Specifically, the spread angle distribution of the straight magnetization lines produces a focal point 354 in a region above the major surface 350a of the FFPM 350, the focal point 354 characterized by a magnetic field produced by the FFPM 350 and a corresponding local maximum in magnetic flux density.

According to the exemplary embodiments described herein, the depicted magnetic domain alignment pattern is symmetric with respect to the axis of symmetry 354 a. In this document, the axis of symmetry 354a is also referred to as the magnetic axis. Magnetic axis 354a is the normal axis to major surface 350a, which travels through focal point 354.

Fig. 4 shows an apparatus 460 for manufacturing a block in the form of a pressed magnet powder that can be sintered in a furnace and become a sintered permanent magnet. Specifically, the apparatus 460 is used to magnetize and compact the magnetic material powder 495. The subsequent sintering of the resulting magnetized compacted mass is carried out in a sintering furnace, not shown. Apparatus 460 includes a mold 470, and a mold cavity 472 is formed within mold 470. The mold cavity 472 may be closed by a mold, not shown, for compacting the powder 495 of magnetic material, which powder 495 of magnetic material must be filled into the mold cavity 472 according to a general process for manufacturing a sintered magnet. The not depicted module performs a movement in a direction perpendicular to the plane of the drawing.

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

According to the exemplary embodiments described herein, the first yoke 463 assigned to the north pole and the second yoke 466 assigned to the south pole have different geometries. Specifically, the radii of curvature of the outer surfaces of the two

yokes

463 and 466 are different from each other. This has the following effect: an uneven magnetic field and corresponding magnetic flux will be provided within the mold cavity 472, which results in an uneven magnetization of the powder 495. As shown in fig. 3, such non-uniform magnetization may produce a spread angle distribution of the magnetic domain alignment direction 352.

As can be seen in fig. 4, according to the embodiments described herein, mold cavity 472 comprises a different geometry than a rectangular parallelepiped. Thus, the cross-section of the mold cavity 432 depicted in FIG. 4 is not rectangular. Specifically, according to the embodiments described herein, the lower first surface 470a of the mold 470 is curved in a convex manner (with respect to a center point of the mold cavity 472). In addition, the opposing upper second surface 470b of the mold 470 is concavely curved (again relative to a center point of the mold cavity 472).

At first sight, such shaping of the mold cavity 472 will produce a geometry of the produced sintered compact that deviates from the generally desired rectangular parallelepiped shape of the Permanent Magnet (PM). However, when considering (when looking again) undesirable deformation that occurs periodically during the upcoming sintering process and/or during the subsequent cooling period of the sintered magnet block, the geometry of the mold cavity 472 may anticipate such deformation. Thus, a mold cavity 472 with appropriately shaped

curved surfaces

470a, 470b may result in a cuboid sintered PM body that is at least approximately perfectly shaped. Thus, when the sintered PM mass is finalized or further processed towards a PM sheet having a rectangular parallelepiped shape, less PM material will have to be removed from the sintered PM mass. This makes the manufacture of a single permanent magnet very efficient, especially from an economic point of view, since less material has to be machined away and although the material can be reused, it usually represents wasted material.

It is noted that the pre-consideration of the described deformation can be realized not only with a PM that should be in the shape of a rectangular parallelepiped. By appropriately shaping the inner surface of the mold cavity 472, a magnetized compacted mass can be made that has at least approximately the desired shape and corresponding geometry after the deformation process is completed. Thus, in some applications, the mold cavity may be defined not only by two but also by three or more curved surfaces.

Fig. 5 shows an apparatus 560 for manufacturing a magnet block from magnet powder prepared for sintering in a furnace according to another embodiment of the present invention.

According to the embodiment shown in FIG. 5, the non-rectangular parallelepiped 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. A mold member, not shown, is used to compact the magnetic material powder 595 filled in the mold cavity 572. The movement of the modules is in a direction perpendicular to the plane of the drawing.

Apparatus 560 differs from apparatus 460 shown in FIG. 4 in that the spatially non-uniform magnetic field/flux within mold cavity 572 is generated not only with two magnetic devices, but also with three magnetic devices. In particular, the device 560 comprises two

magnetic means

561 and 567, which generate a magnetic north pole from the angle of the powder 595 to be magnetized. Furthermore, the device 560 comprises a magnetic means 564 which generates a magnetic south pole from the angle of the powder 595 to be magnetized. Each of the

magnetic devices

561, 564, and 567 includes one electromagnetic coil (see

reference numerals

562, 565, and 568) and one yoke (see

reference numerals

563, 566, and 569).

Fig. 6 shows an apparatus 660 for manufacturing a sintered permanent magnet from a magnetic material powder 695, according to another embodiment of the invention. In this embodiment, two magnetic devices with differently shaped yokes are used to generate a spatially non-uniform magnetic field/flux within mold cavity 672. In particular, the first magnetic means producing a magnetic north pole comprises a first yoke 663 and the second magnetic means producing a magnetic south pole comprises a second yoke 666. 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 or flux lines are indicated with reference numeral 630.

Although not necessary to generate a suitable spatially inhomogeneous magnetic field/flux, in the embodiment described herein the second (concave) radius R2 is larger than the first (convex) radius R1. By appropriate selection of the two radii R1 and R2, the focus strength and corresponding focal length of the resulting FFPM can be adjusted.

Fig. 7 and 8 show the geometry of the mold, sintered magnet block and final PM installed in the generator for different sintered PM manufacturing processes. Fig. 7 shows these geometries for a known manufacturing process, while fig. 8 shows these geometries for a manufacturing process according to an embodiment of the invention.

Fig. 7a and 8a show the final PM part 250 to be produced as a reference. According to the exemplary embodiment described herein, the final PM piece 250 has a rectangular parallelepiped shape. As mentioned above, the desired final shape may also deviate from a pure cuboid. For example, the desired shape may have rounded corners or edges.

Fig. 7b and 8b show the geometry of the die cavities 772, 872, which are used for the compaction and magnetization process of the magnetic powder material. Mold cavity 772 has a rectangular parallelepiped shape, while mold cavity 872 is non-rectangular in shape because it includes two curved opposing surfaces.

Fig. 7c and 8c show the geometric relationship between the resulting sintered PM blocks that have undergone deformation (a) after they have been removed from the respective mold cavities 772, 872, (b) after they have been sintered in a sintering furnace, and (c) after they have been removed from the sintering furnace. The sintered PM block 775, which is produced with the aid of a (known) cuboid mold cavity 770 and a known sintering furnace and has already undergone deformation effects, differs greatly from the cuboid shape. In contrast, a sintered PM block 875 produced with the aid of a non-cuboid but curved mold cavity 870 and also subjected to a deformation effect has the shape of a cuboid or at least a shape which deviates only to a small extent from the desired cuboid shape.

Fig. 7d and 8d show the (volume) difference between (i) the final PM piece 250 and (ii) the made sintered PM bodies 775, 875. As can be seen, the waste of PM material to produce the final PM piece 250 from the bent sintered PM block 775 is significantly greater than the waste of PM material to produce the final PM piece 250 from the at least approximately rectangular parallelepiped sintered PM block 875. Since the large amount of PM material waste increases the manufacturing costs of the PM magnet piece, pre-considering deformation by means of proper bending of the mold cavity is an effective measure to make the production of sintered PM pieces (economically) more efficient.

It is 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. Also elements described in association with different embodiments may be combined. It is also noted that reference signs in the claims shall not be construed 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 a powder (495, 595, 695) of a permanent magnet material;

at least two magnetic means (461, 464; 561, 564) for generating a magnetic field for magnetizing a powder (495, 595, 695) contained in the mold cavity (472, 572, 672); and

at least one mold for compacting the powder (495, 595, 695) contained in the mold cavity (472, 572, 672),

said magnetizing and compacting producing a magnetized compacted mass of said powder (495, 595, 695); wherein the content of the first and second substances,

the mold cavity (472, 572, 672) and/or the mold part comprise at least one surface (470 a, 470 b; 570a, 570 b) which is curved in such a way that an undesired deformation of the sinter cake (885) is at least partially compensated, which undesired deformation is obtained by sintering the magnetized compacted cake in a sintering furnace, whereby the undesired deformation is imparted after the sinter cake (885) is removed from the sintering furnace.

2. The apparatus (460, 560, 660) of the preceding claim,

the mold cavity (472, 572, 672) includes two opposing faces (470 a, 470 b; 570a, 570 b), both of which are curved.

3. The apparatus (460, 560, 660) of the preceding claim,

with respect to the center of the mold cavity (472, 572, 672), the first surface is a convex surface (470 a, 570 a) and the second surface is a concave surface (470 b, 570 b).

4. The apparatus (460, 560, 660) of any one of the preceding claims,

the magnetic means (461, 464) are designed in such a way that the magnetic field (630) within the die cavity is associated with an extended angular distribution of flux lines.

5. The apparatus (560) according to any of the preceding claims, further comprising:

a further magnetic device (567) for generating a magnetic field (630) acting on the powder (595) contained within the mould cavity.

6. The apparatus (460, 560, 660) of any one of the preceding claims, wherein at least one of the two magnetic devices (461, 464; 561, 564) comprises

An electromagnetic coil (462, 465; 562, 565) for generating the magnetic field (630), and

a yoke (463, 466; 563, 566) for guiding and/or for shaping a magnetic field generated by the electromagnetic coil (462, 465; 562, 565).

7. The apparatus of the preceding claim, wherein,

at least one of the magnetic means comprises one electromagnetic coil and another magnetic yoke or one magnetic yoke and another electromagnetic coil.

8. The apparatus (460, 560, 660) according to either of the two preceding claims,

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 yoke (463, 563, 663) has a first outer yoke surface (663 a) facing the mold cavity (672),

the second yoke (466, 566, 666) has a second outer yoke surface (666 a) facing the mold cavity (466, 566, 666), and

the first outer yoke surface (663 a) is concave, and the second outer yoke surface (666 a) is convex.

9. The apparatus (460, 560, 660) of the preceding claim,

the first outer yoke surface (663 a) has a first radius (R1), and the second outer yoke surface (666 a) has a second radius (R2) different from the first radius (R1).

10. A method for manufacturing a sintered permanent magnet (250, 350), the method comprising:

filling permanent magnet material powder (495, 595, 695) into a mold cavity (472, 572, 672) of a mold (470, 570);

generating a magnetic field (630) for magnetizing a powder (495, 595, 695) contained within the mold cavity (472, 572, 672);

compacting the powder (495, 595, 695) contained within the mold cavity (472, 572, 672) by means of a mold, the magnetizing and compacting producing a magnetized compacted mass of the powder (495, 595, 695);

sintering the magnetized compacted mass in a sintering furnace, thereby producing a sintered mass (885); and

removing the agglomerates (885) from the sintering furnace;

wherein the shape of the mold cavity (472, 572, 672) is designed in such a way that an undesired deformation of the sinter cake (885) is at least partially compensated, which undesired deformation is imparted after the sinter cake (885) is removed from the sintering furnace.

11. The method according to the preceding claim, wherein,

the permanent magnet material (495, 595, 695) comprises a rare earth material, in particular NdFeB.

12. A sintered magnet (250, 350) manufactured by performing the method recited in the preceding claim.

13. An electromechanical transducer (140), in particular a generator (130), the electromechanical transducer (130) comprising:

a stator assembly (135), and

a rotor assembly (140) comprising

A support structure (242) and

the at least one sintered magnet (250, 350) according to the preceding claim, wherein said sintered magnet (250, 350) is mounted to said support structure (242).

14. A wind turbine (100) for generating electrical power, the wind turbine (100) comprising:

a tower (120) having a plurality of towers,

a wind rotor (110) arranged at a top portion of the tower (120) and comprising at least one blade (114), an

The electromechanical transducer (130) according to the preceding claim, wherein the electromechanical transducer (130) is mechanically coupled with the wind rotor (110).