EP3939058A2 - Manufacturing sintered permanent magnets with a reduced deformation - Google Patents

Manufacturing sintered permanent magnets with a reduced deformation

Info

Publication number
EP3939058A2
EP3939058A2 EP19733947.6A EP19733947A EP3939058A2 EP 3939058 A2 EP3939058 A2 EP 3939058A2 EP 19733947 A EP19733947 A EP 19733947A EP 3939058 A2 EP3939058 A2 EP 3939058A2
Authority
EP
European Patent Office
Prior art keywords
magnetic
molding chamber
sintered
powder
block
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19733947.6A
Other languages
German (de)
French (fr)
Inventor
Ziad Azar
Adriana Cristina Urda
Hans-joergen Thougaard
Dong Yl
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens Gamesa Renewable Energy AS
Original Assignee
Siemens Gamesa Renewable Energy AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Gamesa Renewable Energy AS filed Critical Siemens Gamesa Renewable Energy AS
Publication of EP3939058A2 publication Critical patent/EP3939058A2/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0205—Magnetic circuits with PM in general
    • H01F7/021—Construction of PM
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
    • H01F41/0266—Moulding; Pressing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/02—Compacting only
    • B22F3/03—Press-moulding apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/0555—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together
    • H01F1/0557—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together sintered
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
    • H01F1/08—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together
    • H01F1/086—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together sintered

Definitions

  • the present invention relates to an apparatus and to a method for manufacturing a sintered permanent magnet. Further, the present invention relates to a sintered magnet being produced with the described method and to an electromechanical trans ducer and a wind turbine comprising at least one of such a sintered magnet.
  • Permanent magnetic materials are used in a plurality of dif ferent fields of application. Probably the technically and economically most important field of applications are elec tromechanical transducers, i.e. electric motors and electric generators.
  • An electric motor being equipped with at least one permanent magnet (PM) converts electric energy into me chanical energy by producing a temporary varying magnetic field by means of windings or coils. This temporary varying magnetic field interacts with the magnetic field of the PM resulting e.g. in a rotational movement of a rotor assembly with respect to a stator assembly of the electric motor.
  • an electric generator con verts mechanical energy into electric energy.
  • An electric generator is a core component of any power plant for generating electric energy. This holds true for power plants which directly capture mechanical energy, e.g. hydroe lectric power installations, tidal power installations, and wind power installations also denominated wind turbines. How ever, this also holds true for power plants which (i) first use chemical energy e.g. from burning fossil fuel or from nu clear energy in order to generate thermal energy and which (ii) second convert the generated thermal energy into mechan ical energy by means of appropriate thermodynamic processes.
  • the efficiency of an electric generator is probably the most important factor for optimizing the production of electric energy.
  • PMs permanent magnets
  • the spatial magnetic field distribution produced by PMs has an impact on the generator efficiency.
  • PM devices or PM ar rangements which have a non-uniform magnetic domain alignment pattern resulting in an intentionally inhomogeneous magnetic field strength or magnetic flux density in particu lar in an air gap between a rotor assembly and a stator as sembly.
  • EP 3 276 642 A1 dis closes a sintered rare earth PM having a focusing magnetic alignment pattern with an integrally formed or single piece PM body.
  • EP 2 762 838 A2 discloses apparatuses and methods for manufacturing PMs, wherein during a sintering process an non-uniform external magnetic field is applied in order to magnetize different regions of a PM in different directions.
  • Magnetic flux focusing offers a large increase in the airgap flux density leading to higher torque/power of electro mechanical transducers such as electric generators for di rect-drive wind turbines.
  • FFPM Flux Focusing Permanent Magnet
  • the PM / FFPM might be deformed. This means that its final shape differs from a desired ideal shape.
  • a sintered PM cannot be pro swiped exactly with a desired final geometry.
  • the PM / FFPM needs to be machined to the desired geometry and/or di mensions.
  • This machining leads to a waste of magnetic materi al which, in particular for sintered Rare Earth (RE) , is a big economic disadvantage and particularly for a FFPM because a machining required to get to a desired final shape will cut away an magnetic domain alignment angle at corners of the FFPM.
  • RE sintered Rare Earth
  • an apparatus for manufacturing a sintered permanent mag net comprises (a) a mold having a molding chamber for receiving a powder of a permanent magnet material; (b) at least two magnetic devices (also denominated poles) for generating a magnetic field for magnetizing the powder being accommodated within the molding chamber; and (c) at least one die for compacting the powder being accommodated within the molding chamber, the magnetizing and compacting resulting in a magnetized compacted block of the powder.
  • the molding chamber and/or the die comprises at least one surface which is curved in such a manner that an unwanted deformation of a sintered block, which has been obtained by sintering the magnetized compacted block in a sintering oven, whereby the unwanted deformation is given after a removal of the sintered block from the molding chamber, is compensated at least par tially.
  • the described apparatus is based on the idea that by choosing an appropriate geometric shape of the molding chamber and/or of the die, which both define the shape of the volume with which the sintered block is produced, deformations towards an undesired geometry can be reduced at least partially. This means that the deformations are not eliminated but they
  • the mentioned unwanted deformation ( s ) may physically result from shrinking effects which may occur during or after the sintering process in the sintering oven.
  • the sintering oven is typically external from the described apparatus. However, is may not be excluded that the described apparatus and the sintering oven may be combined into one and the same device.
  • a potential further physical reason for a deformation are in ternal magnetic forces resulting in magnetostriction. It is mentioned that irrespective of the physical reason for defor mation the extent of a deformation can be evaluated by means of test procedures for manufacturing sintered blocks. Based on the evaluated "test deformations" the at least one surface can be geometrically shaped in a proper manner.
  • the described "pre-accounting" of the deformation during man ufacturing by means of an appropriate "pre-shaping" of the molding chamber and/or the die may provide a maximum benefit for a manufacture in particular of a sintered Flux Focusing Permanent Magnet (FFPM) because for such a Permanent Magnet (PM) it is essential that its final geometric shape exactly corresponds to a desired geometric shape.
  • FFPM Flux Focusing Permanent Magnet
  • the de scribed "deformation pre-accounting" principle is also appli cable for a parallel or radial magnetized PM With the de- scribed apparatus a sintered PM can be produced with an exact desired geometric shape even when during manufacturing there are given unwanted deformation and shrinkage effects.
  • the molding cham ber comprises two opposing surfaces which are both curved. This may provide the advantage that expected and unwanted de formations can be compensated to a large extend. This holds true in particular for shrinkage effects which occur when the sintered block cools down after having been removed from the sintering oven.
  • a first surface is a convex surface and the second surface is a concave surface.
  • mag netic devices are designed in such a manner that the magnetic field within the molding chamber is associated with a spread angular distribution of magnetic flux lines.
  • the spread angular distribution of magnetic flux lines may be used in particular for causing, within the sintered block, a spread angular distribution of magnetic domain alignment di rections which may result in a focused magnetization of the sintered block.
  • a magnetic focal point or at least a magnetic fo cal region may be defined outside from the bulk of the sin tered block.
  • the magnetic flux density caused by the respective FFPM is increased as compared to points or regions outside from the focal point respectively the focal region.
  • the appa ratus further comprises a further magnetic device for gener ating a magnetic field acting on the powder being accommodat ed within the molding chamber.
  • a further magnetic device may allow to generate a highly spatially inhomogeneous magnetic field within the molding chamber. This may be in particular of advantage when a sintered magnet block for a FFPM is produced.
  • At least one of the now at least three magnetic de vices comprises at least one electromagnetic coil and a cur rent through the electromagnetic coil can be controlled there is given the opportunity to modify (the in-homogeneity of) the overall magnetic field by an appropriate current adjust ment. This may allow the described apparatus to be used for manufacturing sintered magnetic block with different flux fo cusing characteristics.
  • At least one of the two magnetic devices comprises (a) at least one electromagnetic coil for producing the magnetic field and (b) a magnetic yoke for guiding and/or for shaping the magnetic field being produced by the electromagnetic coil.
  • Supporting the electromagnetic coil in producing the magnetic field by providing a proper magnetic yoke may provide the ad vantage that the magnetic field respectively the magnetic flux (density) at least within selected regions of the mold ing chamber can be increased significantly. Further, by de signing the shape and/or the geometry of the magnetic yoke in a proper manner a spread angular distribution of magnetic flux lines can be produced which yields a desired focused flux magnetization design.
  • the magnetic yoke which may also be denominated a pole piece, may be made from a ferromagnetic material, in particu lar from iron or cobalt iron for higher saturation.
  • the mold may be made from a non-magnetic and in particular from a non-ferromagnetic material.
  • a (current ly) preferred material is stainless steel.
  • oth er mold materials may be used provided that are mechanical stiff .
  • At least one of the magnetic devices comprises one electromagnetic coil and a further magnetic yoke or one magnetic yoke and a further electromagnetic coil.
  • one of the two magnetic devices is a first magnetic device having a first magnetic yoke and the other one of the two magnetic de vices is a second magnetic device having a second magnetic yoke.
  • the first magnetic yoke and the second magnetic yoke are located at opposing sides.
  • the first magnetic yoke has a first outer yoke surface facing the molding chamber and the second mag netic yoke has a second outer yoke surface facing the molding chamber.
  • the first outer yoke surface is concave and the second outer yoke surface is con vex .
  • the described spatial design of the two magnetic yokes may provide the advantage that for manufacturing FFPMs a proper and well defined spread angular distribution of magnetic flux lines can be generated in an easy and effective manner. De pending on the specific application the bending of the outer yoke surfaces may be regular (without any corners and edges ("lumps and bumps") or irregular.
  • At least one of the outer yoke surfaces may have an at least approximately cylindrical shape. This causes a one dimension al (ID) magnetic flux focusing which results in a linearly extended focal region. Such a magnetic focusing corresponds to an optical focusing by means of a cylindrical optical lens.
  • at least one of the outer yoke surfaces may have an at least approximately spherical shape. This causes a two dimensional (2D) magnetic flux focusing which results at least approximately focal point.
  • Such a magnetic focusing corresponds to an optical focusing by means of a spherical optical lens.
  • the first outer yoke surface has (at least within a portion of the first outer yoke surface) a first radius and (b) the sec ond outer yoke surface has (at least within a portion of the second outer yoke surface) a second radius being different from the first radius.
  • a method for manufacturing a sintered permanent magnet comprises (a) filling a powder of perma nent magnet material into a molding chamber of a mold; (b) generating a magnetic field for magnetizing the power being accommodated within the molding chamber; (c) compacting the powder being accommodated within the molding chamber by means of a die, the magnetizing and compacting resulting in a mag netized compacted block of the powder; (d) sintering the mag netized compacted block in a sintering oven resulting in a sintered block; and (e) removing the sintered block from the sintering oven.
  • the shape of the molding chamber is designed in such a manner that an unwanted deformation of the sintered block, which unwanted deformation is given after removing the sintered block from the sintering oven, is compensated at least partially.
  • the described method is based on the idea that unwanted deformation effects, which typically result from a shrinkage during sintering, can be compensated with pre-accounting by means of a properly shaped molding chamber being different to the shape of the finally manufactured sintered block.
  • the step of generating a magnetic field in order to obtain a magnetic alignment and the step of compacting the powder are accomplished at least partially at the same time.
  • the described procedure of deforming can occur after remov ing. However, internal stress resulting in the deformation can occur already before removing.
  • the permanent magnet material comprises a rare earth material, in particu lar NdFeB. This may provide the advantage that very strong PMs can be manufactured without the need to produce a lot of wastage (of the typically very expensive rare earth material) for achieving a desired PM geometry.
  • compositions of the permanent magnet material may include ferrite and/or SmCo .
  • ferrite and/or SmCo ferrite and/or SmCo .
  • an electromechanical transducer in particular an elec tric generator.
  • the electromechanical transducer comprises (a) a stator assembly and (b) a rotor assembly.
  • the rotor as sembly comprises a support structure and at least one sin tered magnet as described above.
  • the sintered magnet is mounted to the support structure.
  • the provided electromechanical transducer is based on the idea that it can be built up with a rotor assembly comprising a properly shaped sintered PM, which has been effectively manufactured without a lot of material wastage.
  • a wind turbine for generating electrical power.
  • the provided wind turbine comprises (a) a tower, (b) a wind ro tor, which is arranged at a top portion of the tower and which comprises at least one blade, and (c) an electro mechanical transducer as described above.
  • the electro mechanical transducer is mechanically coupled with the wind rotor (110) .
  • the provided wind turbine also denominated a wind energy in stallation, is based on the idea that the above described electromechanical transducer allows to realize the wind tur bine, with regard to PM material being used, in a cost saving manner. This may contribute for improving the attractiveness of wind turbine technology for regenerative power production compared to other technologies such as solar plants.
  • Figure 1 shows a wind turbine in accordance with an embodi ment of the present invention.
  • Figure 2 shows in a schematic representation the generator of the wind turbine of Figure 1.
  • Figure 3 shows a Flux Focusing Permanent Magnet (FFPM) proucked in accordance with an embodiment of the inven tion.
  • FFPM Flux Focusing Permanent Magnet
  • Figure 4 shows an apparatus for manufacturing a sintered per manent magnet, the apparatus comprising (i) a mold having two opposing curved surfaces and (ii) two magnetic devices for ( inhomogeneously) magnetizing a sintered magnet block being within the mold.
  • Figure 5 shows an apparatus for manufacturing a sintered per manent magnet, the apparatus comprising (i) a mold and a die each having one curved surface and (ii) three magnetic devices for (inhomogeneously) magnet izing a sintered magnet block being within the mold.
  • Figure 6 shows an apparatus for manufacturing a sintered per manent magnet with two magnetic yokes each having an outer yoke surface with a different curvature radi us .
  • Figure 7 illustrates the geometries of a mold, a sintered magnet block and the final PM in a known manufactur ing process for a sintered permanent magnet.
  • Figure 8 illustrates the geometries of a mold, a sintered magnet block and the final PM a manufacturing pro cess for a sintered permanent magnet in accordance with an embodiment of the invention.
  • FIG. 1 shows a wind turbine 100 according to an embodiment of the invention.
  • the wind turbine 100 comprises a tower 120 which is mounted on a non-depicted fundament.
  • a nacelle 122 On top of the tower 120 there is arranged a nacelle 122.
  • a yaw angle adjustment device 121 which is capable of rotating the na celle 122 around a non-depicted vertical axis being aligned with the longitudinal extension of the tower 120.
  • the wind turbine 100 further comprises a wind rotor 110 hav ing three blades 114. In the perspective of Figure 1 only two blades 114 are visible.
  • the rotor 110 is rotatable around a rotational axis 110a.
  • the blades 114 which are mounted at a hub 112, extend radially with respect to the rotational axis 110a.
  • a blade angle adjustment device 116 in order to ad just the blade pitch angle of each blade 114 by rotating the respective blade 114 around a non-depicted axis being aligned substantially parallel with the longitudinal extension of the respective blade 114.
  • the blade angle adjust ment device 116 By controlling the blade angle adjust ment device 116 the blade pitch angle of the respective blade 114 can be adjusted in such a manner that at least when the wind is not too strong a maximum wind power can be retrieved from the available mechanical power of the wind driving the wind rotor 110.
  • a gear box 124 is used to convert the number of revolutions of the rotor 110 into a higher num ber of revolutions of a shaft 125, which is coupled in a known manner to an electromechanical transducer 130.
  • the electromechanical transducer is a generator 130.
  • the gear box 124 is op tional and that the generator 140 may also be directly cou pled to the rotor 110 by the shaft 125 without changing the numbers of revolutions.
  • the wind turbine is a so caller Direct Drive (DD) wind turbine.
  • a brake 126 is provided in order to stop the opera tion of the wind turbine 100 or in order to reduce the rota tional speed of the rotor 110 for instance in case of emer gency .
  • the wind turbine 100 further comprises a control system 143 for operating the wind turbine 100 in a highly efficient man ner. Apart from controlling for instance the yaw angle ad justment device 121 the depicted control system 153 is also used for adjusting the blade pitch angle of the rotor blades 114 in an optimized manner.
  • the generator 130 comprises a stator assembly 135 and a rotor assembly 140.
  • the generator 130 is realized in a so called “inner stator - outer rotor” configuration, wherein the rotor assembly 140 surrounds the stator assembly 135.
  • each permanent magnet (PM) assembly comprises at least three sintered perma nent magnet devices which are made from a Nd-Fe-B material composition .
  • FIG. 2 shows in a cross sectional view a schematic repre sentation of the generator 130.
  • the generator 130 comprises a stator assembly 135.
  • the stator assembly 135 comprises a sta tor support structure 237 comprising a stack of a plurality of lamination sheets and a plurality of stator windings 239 being accommodated within the stator support structure 237.
  • the windings 239 are interconnected in a known manner by means of non-depicted electrical connections.
  • a rotor assembly 140 of the generator 130 which is separated from the stator assembly 135 by an air gap ag, comprises a rotor support structure 242 providing the mechanical base for mounting a plurality of sintered permanent magnets 250.
  • the rotational axis of the rotor assembly 140 is de nominated with reference numeral 230a.
  • each angular position of the rotor assembly 140 there are arranged three sintered permanent magnets arranged next to each other. It is mentioned that in Figure 2 only three sintered permanent mag nets 250 being assigned to one angular position are depicted for the sake of ease of illustration. In reality, depending on the dimension of the generator 130, a plurality of sintered permanent magnets 250 are mounted to the rotor support structure 242.
  • the sintered permanent magnets 250 are prefer ably arranged in a matrix like structure around a curved sur face area of the support structure 242 having a basically cy lindrical geometry around the generator axis 240a.
  • the sintered permanent magnets 250 are not mounted directly to the rotor support structure 242. Instead, there is provided a back plate 244 made from a ferromagnetic material, e.g. iron.
  • the back plate 244 is pro vided in order to ensure a proper guidance of magnetic flux. This significantly reduces in a beneficial manner the inten sity of magnetic stray fields.
  • FIG. 3 shows a Flux Focusing Permanent Magnet (FFPM) 350 produced in accordance with an embodiment of the invention.
  • the FFPM 350 is magnetized in such a manner that there is given a spread angular distribution of magnetic domain align ment directions 352.
  • each magnetic domain alignment direction 352 follows a straight magnetization line.
  • the straight lines are angled or inclined with respect to each other in a fan like manner.
  • the spread angular distribution of the straight magnetization lines produces, in the region above a main sur face 350a of the FFPM 350, a focal point 354 being character- ized by a local maximum of the magnetic field respectively the magnetic flux density produced by the FFPM 350.
  • the de picted magnetic domain alignment pattern is symmetric with respect to a symmetry axis 354a.
  • the sym metry axis 354a is also denominated magnetic axis.
  • the mag netic axis 354a is a normal axis to the main surface 350a, which runs through the focal point 354.
  • Figure 4 shows an apparatus 460 for manufacturing a block in the form of pressed magnet powder that can be sintered in an oven and become a sintered permanent magnet.
  • the apparatus 460 is used for magnetizing and compacting a powder of magnetic material 495.
  • a subsequent sintering of a resulting magnetized compacted block is carried out in a non- depicted sintering oven.
  • the apparatus 460 comprises a mold 470 within which a molding chamber 472 is formed.
  • the molding chamber 472 can be closed by a non-depicted die, which is used for compacting the powder of magnetic material 495, which in accordance with usual procedures for manufacturing sintered magnets has to be filled into the molding chamber 472.
  • the non-depicted die performs a movement along a direc tion being perpendicular to the plane of drawing.
  • the apparatus 460 further comprises means for producing a magnetic field which is applied to the compacted powder 495 during the sintering process.
  • These magnetic field production means include a first magnetic device 461 and the second mag netic device 464.
  • the first magnetic device 461 produces a magnetic North pole N and the second magnetic device 464 produces a magnetic South pole S.
  • the first mag netic device comprises (i) a first electromagnetic coil 462 for generating a magnetic field and (ii) a first magnetic yoke 463 for guiding and/or for shaping the magnetic field (lines) being present within the molding chamber 472.
  • the second magnetic device 464 comprises (i) a second electromagnetic coil 465 and (ii) a second magnetic yoke 466.
  • the first magnetic yoke 463 being assigned to the North pole and the second magnetic yoke 466 being assigned to the South pole have a different geometry. Specifically, the bending radii of the outer surfaces of the two magnetic yokes 463, 466 is dif ferent from each other. This has the effect that within the molding chamber 472 there will be provided an inhomogeneous magnetic field respectively magnetic flux which results in an inhomogeneous magnetization of the powder 495. This inhomoge neous magnetization may result in a spread angular distribu tion of magnetic domain alignment directions 352 as shown in Figure 3.
  • the molding chamber 472 comprises a geometry which is different from a cuboid.
  • the cross section of the molding chamber 432 depicted in Figure 4 is not a rectan gle.
  • a lower first surface 470a of the mold 470 is curved in a convex manner (with regard to a central point the molding chamber 472) .
  • an opposing upper second surface 470b of the mold 470 is curved in a concave manner (again with re spect to a central point the molding chamber 472) .
  • Such a shaping of the molding chamber 472 will, at a first glance, result in a geometry of the produced sintered block which geometry deviates from a typically desired cuboid shape of a permanent magnet (PM) .
  • PM permanent magnet
  • the geometry of the molding chamber 472 can pre-account such de formations.
  • a molding chamber 472 with properly shaped curved surfaces 470a, 470b can lead to at least approximately perfectly shaped cuboid sintered PM bodies.
  • the described pre-accounting of defor mations can be realized not only with PM which are supposed to be of cuboid shape.
  • magnetized compacted blocks can be produced which have, after completing a defor mation procedure, at least approximately a desired shape re spectively geometry.
  • the molding chamber may be defined not only by two but by three or more curved surfaces.
  • Figure 5 shows an apparatus 560 for manufacturing a magnet block from magnet powder ready for sintering in an oven in accordance with a further embodiment of the invention.
  • non cuboid molding chamber 572 is formed by two curved surfaces, a first curved surface 570a of a mold 570 and a second curved surface 570b of the mold 570.
  • a non-depicted die is used for compacting powder of magnetic material 595 filled into the molding chamber 572. The movement of the die is along a di rection perpendicular to the plane of drawing.
  • the apparatus 560 differs from the apparatus 460 shown in Figure 4 in that a spatially inhomogeneous magnetic field / flux within the molding chamber 572 is not only produced with two but with three magnetic devices.
  • the appa ratus 560 comprises two magnetic devices 561 and 567 which both produce, from the perspective of the powder 595 to be magnetized, a magnetic North pole.
  • the apparatus 560 comprises one magnetic device 564 which produces, from the perspective of the powder 595 to be magnetized, a magnetic South pole.
  • Each one of the magnetic devices 561, 564 and 567 comprises one electromagnetic coil (see reference numerals 562, 565, and 568) and one magnetic yoke (see reference nu merals 563, 566, and 569) .
  • Figure 6 shows in accordance with a further embodiment of the invention an apparatus 660 for manufacturing a sintered per manent magnet from a powder of magnetic material 695.
  • a spatially inhomogeneous magnetic field / flux within a molding chamber 672 is produced with two magnetic devices having differently shaped magnetic yokes.
  • a first magnetic device producing a magnetic North pole comprises a first magnetic yoke 663 and a second magnetic de vice producing a magnetic South pole comprises a second mag netic yoke 666.
  • the first magnetic yoke 663 has an outer (convex) curved yoke surface 663a having a first radius R1 and the second magnetic yoke 666 has an outer (concave) curved yoke surface 666a having a second radius R2.
  • the corresponding magnetic field lines or magnetic flux lines are denominated with reference numeral 630.
  • the second (concave) radius R2 is bigger than the first (convex) radius R1.
  • Figures 7 and 8 illustrate for different sintered PM manufac turing processes the geometries of a mold, a sintered magnet block and the final PM which is installed in an electric gen- erator.
  • Figure 7 shows these geometries for a known manufac- turing process whereas
  • Figure 8 shows these geometries for manufacturing process in accordance with an embodiment of the invention .
  • Figures 7a and 8a show, as a reference, the final PM piece 250 which is to be produced.
  • the final PM piece 250 has a cuboid shape.
  • the desired final shape can also deviate from a pure cuboid.
  • the desired shape can have rounded corners or edges.
  • Figures 7b and 8b show the geometry of a molding chamber 772, 872 which is used for the compacting and magnetizing process of magnetic powder material.
  • the molding chamber 772 has a cuboid shape whereas the shape of the molding chamber 872 is non-cuboid because it comprises two curved opposing surfaces.
  • Figures 7c and 8c show the geometric size relation between a produced sintered PM block which has undergone a deformation after it (a) has been removed from the respective molding chamber 772, 872, (b) has been sintered in a sintering oven, and (c) has been removed from the sintering oven.
  • the sin tered PM block 775 which has been produced by means of the (known) cuboid molding chamber 770 and a known sintering oven and which has undergone deformation effects, strongly differs from a cuboid shape.
  • the sintered PM block 875 which has been produced by means of the non-cuboid but curved molding chamber 870 and which has also undergone deformation effects has a shape of a cuboid or at least a shape which deviates only with a small extend from the de sired cuboid shape.
  • Figures 7d and 8d show the (volume) difference between (i) the final PM piece 250 and (ii) the produced sintered PM bod ies 775, 875. It can be seen that the PM material wastage for producing the final PM piece 250 from the curved sintered PM block 775 is significantly larger than the PM material wast- age for producing the final PM piece 250 from the at least approximately cuboid sintered PM block 875. Since a lot of PM material wastage increases the manufacturing costs for PM magnet pieces the pre-accounting of deformations by means of an appropriate curved shaping of the molding chamber is an effective measure for making the production of sintered PM pieces (economically) more effective.

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Abstract

It is described an apparatus (460, 560, 660) for manufacturing a sintered permanent magnet (250, 350). The apparatus comprises (a) a mold (470, 570) having a molding chamber (472, 572, 672) for receiving a powder of a permanent magnet material (495, 595, 695); (b) at least two magnetic devices (461, 464; 561, 564) for generating a magnetic field for magnetizing the powder being accommodated within the molding chamber; and (c) at least one die for compacting the powder being accommodated within the molding chamber; the magnetizing and compacting resulting in a magnetized compacted block of the powder (495, 595, 695). The molding chamber and/or the die comprises at least one surface (470a, 470b; 570a, 570b) which is curved in such a manner that an unwanted deformation of a sintered block, which has been obtained by sintering the magnetized compacted block in a sintering oven, whereby the unwanted deformation is given after a removal of the sintered block from the sintering oven, is compensated at least partially. Further described is a method for producing a sintered permanent magnet with such an apparatus, a sintered permanent magnet which has been produced with such a method, and an electromechanical transducer (140) and a wind turbine (100) comprising such a sintered permanent magnet.

Description

DESCRIPTION
Manufacturing sintered permanent magnets with a reduced de formation
Field of invention
The present invention relates to an apparatus and to a method for manufacturing a sintered permanent magnet. Further, the present invention relates to a sintered magnet being produced with the described method and to an electromechanical trans ducer and a wind turbine comprising at least one of such a sintered magnet.
Art Background
Permanent magnetic materials are used in a plurality of dif ferent fields of application. Probably the technically and economically most important field of applications are elec tromechanical transducers, i.e. electric motors and electric generators. An electric motor being equipped with at least one permanent magnet (PM) converts electric energy into me chanical energy by producing a temporary varying magnetic field by means of windings or coils. This temporary varying magnetic field interacts with the magnetic field of the PM resulting e.g. in a rotational movement of a rotor assembly with respect to a stator assembly of the electric motor. In a physically complementary manner, an electric generator con verts mechanical energy into electric energy.
An electric generator is a core component of any power plant for generating electric energy. This holds true for power plants which directly capture mechanical energy, e.g. hydroe lectric power installations, tidal power installations, and wind power installations also denominated wind turbines. How ever, this also holds true for power plants which (i) first use chemical energy e.g. from burning fossil fuel or from nu clear energy in order to generate thermal energy and which (ii) second convert the generated thermal energy into mechan ical energy by means of appropriate thermodynamic processes.
The efficiency of an electric generator is probably the most important factor for optimizing the production of electric energy. For a PM electric generator it is essential that the magnetic flux produced by the permanent magnets (PMs) is strong. This can probably best be achieved with sintered rare earth magnets, e.g. using a NdFeB material composition. How ever, also the spatial magnetic field distribution produced by PMs has an impact on the generator efficiency. In the lat ter case it is often of advantage when PM devices or PM ar rangements are used which have a non-uniform magnetic domain alignment pattern resulting in an intentionally inhomogeneous magnetic field strength or magnetic flux density in particu lar in an air gap between a rotor assembly and a stator as sembly.
It is known to configure a non-uniform magnetic domain align ment pattern in PM in order to achieve a so called "magnetic flux focusing". WO 2012/141932 A2 discloses PM magnet ar rangements where differently magnetized PMs are combined such that a "magnetic focusing" is achieved. EP 3 276 642 A1 dis closes a sintered rare earth PM having a focusing magnetic alignment pattern with an integrally formed or single piece PM body. EP 2 762 838 A2 discloses apparatuses and methods for manufacturing PMs, wherein during a sintering process an non-uniform external magnetic field is applied in order to magnetize different regions of a PM in different directions.
Magnetic flux focusing offers a large increase in the airgap flux density leading to higher torque/power of electro mechanical transducers such as electric generators for di rect-drive wind turbines. However, during manufacturing of a PM and in particular of a Flux Focusing Permanent Magnet (FFPM) and due to the method of pressing, sintering and mag- netization, the PM / FFPM might be deformed. This means that its final shape differs from a desired ideal shape. In addi tion, under normal circumstances a sintered PM cannot be pro duced exactly with a desired final geometry. Hence, the PM / FFPM needs to be machined to the desired geometry and/or di mensions. This machining leads to a waste of magnetic materi al which, in particular for sintered Rare Earth (RE) , is a big economic disadvantage and particularly for a FFPM because a machining required to get to a desired final shape will cut away an magnetic domain alignment angle at corners of the FFPM.
There may be a need for providing a method which allows to manufacture permanent magnets in an efficient manner.
Summary of the Invention
This need may be met by the subject matter according to the independent claims. Advantageous embodiments of the present invention are described by the dependent claims.
According to a first aspect of the invention there is provid ed an apparatus for manufacturing a sintered permanent mag net. The provided apparatus comprises (a) a mold having a molding chamber for receiving a powder of a permanent magnet material; (b) at least two magnetic devices (also denominated poles) for generating a magnetic field for magnetizing the powder being accommodated within the molding chamber; and (c) at least one die for compacting the powder being accommodated within the molding chamber, the magnetizing and compacting resulting in a magnetized compacted block of the powder. The molding chamber and/or the die comprises at least one surface which is curved in such a manner that an unwanted deformation of a sintered block, which has been obtained by sintering the magnetized compacted block in a sintering oven, whereby the unwanted deformation is given after a removal of the sintered block from the molding chamber, is compensated at least par tially.
The described apparatus is based on the idea that by choosing an appropriate geometric shape of the molding chamber and/or of the die, which both define the shape of the volume with which the sintered block is produced, deformations towards an undesired geometry can be reduced at least partially. This means that the deformations are not eliminated but they
"start" from an unwanted geometric shape and lead at least approximately to a desired geometric shape for the sintered block. Hence, a potential machining of the sintered block to wards a final permanent magnet (PM) can be accomplished with a minimum wastage of (typically expensive) magnetic material.
The mentioned unwanted deformation ( s ) may physically result from shrinking effects which may occur during or after the sintering process in the sintering oven. The sintering oven is typically external from the described apparatus. However, is may not be excluded that the described apparatus and the sintering oven may be combined into one and the same device.
A potential further physical reason for a deformation are in ternal magnetic forces resulting in magnetostriction. It is mentioned that irrespective of the physical reason for defor mation the extent of a deformation can be evaluated by means of test procedures for manufacturing sintered blocks. Based on the evaluated "test deformations" the at least one surface can be geometrically shaped in a proper manner.
The described "pre-accounting" of the deformation during man ufacturing by means of an appropriate "pre-shaping" of the molding chamber and/or the die may provide a maximum benefit for a manufacture in particular of a sintered Flux Focusing Permanent Magnet (FFPM) because for such a Permanent Magnet (PM) it is essential that its final geometric shape exactly corresponds to a desired geometric shape. However, the de scribed "deformation pre-accounting" principle is also appli cable for a parallel or radial magnetized PM With the de- scribed apparatus a sintered PM can be produced with an exact desired geometric shape even when during manufacturing there are given unwanted deformation and shrinkage effects.
According to an embodiment of the invention the molding cham ber comprises two opposing surfaces which are both curved. This may provide the advantage that expected and unwanted de formations can be compensated to a large extend. This holds true in particular for shrinkage effects which occur when the sintered block cools down after having been removed from the sintering oven.
According to a further embodiment of the invention, with re gard to a center of the molding chamber, a first surface is a convex surface and the second surface is a concave surface. This may provide the advantage that on the one hand the re spective surfaces of the molding chamber and/or of the die can be formed in an easy and reliable manner and on the other hand the pre-shaping can be realized in order to yield an ef fective deformation compensation.
According to a further embodiment of the invention the mag netic devices are designed in such a manner that the magnetic field within the molding chamber is associated with a spread angular distribution of magnetic flux lines.
The spread angular distribution of magnetic flux lines may be used in particular for causing, within the sintered block, a spread angular distribution of magnetic domain alignment di rections which may result in a focused magnetization of the sintered block. Thereby, outside from the bulk of the sin tered block a magnetic focal point or at least a magnetic fo cal region may be defined. In this point or in this region the magnetic flux density caused by the respective FFPM is increased as compared to points or regions outside from the focal point respectively the focal region. By designing an electric generator in such a manner that the focal point respectively the focal region is located within an airgap between a stator assembly and a rotor assembly the electric power which can be produced by the generator can be increased significantly.
According to a further embodiment of the invention the appa ratus further comprises a further magnetic device for gener ating a magnetic field acting on the powder being accommodat ed within the molding chamber.
Using, in addition to the two magnetic devices described above, a further magnetic device may allow to generate a highly spatially inhomogeneous magnetic field within the molding chamber. This may be in particular of advantage when a sintered magnet block for a FFPM is produced.
In case at least one of the now at least three magnetic de vices comprises at least one electromagnetic coil and a cur rent through the electromagnetic coil can be controlled there is given the opportunity to modify (the in-homogeneity of) the overall magnetic field by an appropriate current adjust ment. This may allow the described apparatus to be used for manufacturing sintered magnetic block with different flux fo cusing characteristics.
According to a further embodiment of the invention at least one of the two magnetic devices comprises (a) at least one electromagnetic coil for producing the magnetic field and (b) a magnetic yoke for guiding and/or for shaping the magnetic field being produced by the electromagnetic coil.
Supporting the electromagnetic coil in producing the magnetic field by providing a proper magnetic yoke may provide the ad vantage that the magnetic field respectively the magnetic flux (density) at least within selected regions of the mold ing chamber can be increased significantly. Further, by de signing the shape and/or the geometry of the magnetic yoke in a proper manner a spread angular distribution of magnetic flux lines can be produced which yields a desired focused flux magnetization design.
The magnetic yoke, which may also be denominated a pole piece, may be made from a ferromagnetic material, in particu lar from iron or cobalt iron for higher saturation. By con trast thereto, the mold may be made from a non-magnetic and in particular from a non-ferromagnetic material. A (current ly) preferred material is stainless steel. However, also oth er mold materials may be used provided that are mechanical stiff .
According to a further embodiment of the invention at least one of the magnetic devices comprises one electromagnetic coil and a further magnetic yoke or one magnetic yoke and a further electromagnetic coil.
By designing the respective magnetic coil in an asymmetric manner with regard to the number of coils and the number of magnetic yokes the generation of a magnetic field being asso ciated with a spread angular distribution of magnetic flux lines can be realized in an easy and effective manner. As mentioned already above such an in-homogenous magnetic field allows to manufacture FFPMs .
According to a further embodiment of the invention one of the two magnetic devices is a first magnetic device having a first magnetic yoke and the other one of the two magnetic de vices is a second magnetic device having a second magnetic yoke. With regard to the molding chamber the first magnetic yoke and the second magnetic yoke are located at opposing sides. Further, the first magnetic yoke has a first outer yoke surface facing the molding chamber and the second mag netic yoke has a second outer yoke surface facing the molding chamber. Furthermore, (with regard to the molding chamber) the first outer yoke surface is concave and the second outer yoke surface is con vex .
The described spatial design of the two magnetic yokes may provide the advantage that for manufacturing FFPMs a proper and well defined spread angular distribution of magnetic flux lines can be generated in an easy and effective manner. De pending on the specific application the bending of the outer yoke surfaces may be regular (without any corners and edges ("lumps and bumps") or irregular.
At least one of the outer yoke surfaces may have an at least approximately cylindrical shape. This causes a one dimension al (ID) magnetic flux focusing which results in a linearly extended focal region. Such a magnetic focusing corresponds to an 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 a two dimensional (2D) magnetic flux focusing which results at least approximately focal point. Such a magnetic focusing corresponds to an optical focusing by means of a spherical optical lens.
According to a further embodiment of the invention (a) the first outer yoke surface has (at least within a portion of the first outer yoke surface) a first radius and (b) the sec ond outer yoke surface has (at least within a portion of the second outer yoke surface) a second radius being different from the first radius. This may provide the advantage that higher alignment angle of the magnetic domain alignment di rections at and with regard to side edges of the sintered block can be realized.
According to a further aspect of the invention there is pro vided a method for manufacturing a sintered permanent magnet. The provided method comprises (a) filling a powder of perma nent magnet material into a molding chamber of a mold; (b) generating a magnetic field for magnetizing the power being accommodated within the molding chamber; (c) compacting the powder being accommodated within the molding chamber by means of a die, the magnetizing and compacting resulting in a mag netized compacted block of the powder; (d) sintering the mag netized compacted block in a sintering oven resulting in a sintered block; and (e) removing the sintered block from the sintering oven. The shape of the molding chamber is designed in such a manner that an unwanted deformation of the sintered block, which unwanted deformation is given after removing the sintered block from the sintering oven, is compensated at least partially.
Also the described method is based on the idea that unwanted deformation effects, which typically result from a shrinkage during sintering, can be compensated with pre-accounting by means of a properly shaped molding chamber being different to the shape of the finally manufactured sintered block.
Typically, the step of generating a magnetic field in order to obtain a magnetic alignment and the step of compacting the powder are accomplished at least partially at the same time.
The described procedure of deforming can occur after remov ing. However, internal stress resulting in the deformation can occur already before removing.
According to an embodiment of the invention the permanent magnet material comprises a rare earth material, in particu lar NdFeB. This may provide the advantage that very strong PMs can be manufactured without the need to produce a lot of wastage (of the typically very expensive rare earth material) for achieving a desired PM geometry.
In this respect it is mentioned that other compositions of the permanent magnet material may include ferrite and/or SmCo . According to a further aspect of the invention there is pro vided a sintered magnet being produced by carrying out a method as described above.
According to a further aspect of the invention there is pro vided an electromechanical transducer, in particular an elec tric generator. The electromechanical transducer comprises (a) a stator assembly and (b) a rotor assembly. The rotor as sembly comprises a support structure and at least one sin tered magnet as described above. The sintered magnet is mounted to the support structure.
The provided electromechanical transducer is based on the idea that it can be built up with a rotor assembly comprising a properly shaped sintered PM, which has been effectively manufactured without a lot of material wastage.
According to a further aspect of the invention there is pro vided a wind turbine for generating electrical power. The provided wind turbine comprises (a) a tower, (b) a wind ro tor, which is arranged at a top portion of the tower and which comprises at least one blade, and (c) an electro mechanical transducer as described above. The electro mechanical transducer is mechanically coupled with the wind rotor (110) .
The provided wind turbine, also denominated a wind energy in stallation, is based on the idea that the above described electromechanical transducer allows to realize the wind tur bine, with regard to PM material being used, in a cost saving manner. This may contribute for improving the attractiveness of wind turbine technology for regenerative power production compared to other technologies such as solar plants.
It has to be noted that embodiments of the invention have been described with reference to different subject matters.
In particular, some embodiments have been described with ref erence to method type claims whereas other embodiments have been described with reference to apparatus type claims. How ever, 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 re lating to different subject matters, in particular between features of the method type claims and features of the appa ratus type claims is considered as to be disclosed with this document .
The aspects defined above and further aspects of the present 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 embodi ment but to which the invention is not limited.
Brief Description of the Drawing
Figure 1 shows a wind turbine in accordance with an embodi ment of the present invention.
Figure 2 shows in a schematic representation the generator of the wind turbine of Figure 1.
Figure 3 shows a Flux Focusing Permanent Magnet (FFPM) pro duced in accordance with an embodiment of the inven tion.
Figure 4 shows an apparatus for manufacturing a sintered per manent magnet, the apparatus comprising (i) a mold having two opposing curved surfaces and (ii) two magnetic devices for ( inhomogeneously) magnetizing a sintered magnet block being within the mold.
Figure 5 shows an apparatus for manufacturing a sintered per manent magnet, the apparatus comprising (i) a mold and a die each having one curved surface and (ii) three magnetic devices for (inhomogeneously) magnet izing a sintered magnet block being within the mold. Figure 6 shows an apparatus for manufacturing a sintered per manent magnet with two magnetic yokes each having an outer yoke surface with a different curvature radi us .
Figure 7 illustrates the geometries of a mold, a sintered magnet block and the final PM in a known manufactur ing process for a sintered permanent magnet.
Figure 8 illustrates the geometries of a mold, a sintered magnet block and the final PM a manufacturing pro cess for a sintered permanent magnet in accordance with an embodiment of the invention.
Detailed Description
The illustration in the drawing is schematic. 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 are different from the corresponding reference signs only within the first digit. In order to avoid unnecessary repetitions elements or features which have already been elucidated with respect to a previously de scribed embodiment are not elucidated again at a later posi tion of the description.
Figure 1 shows a wind turbine 100 according to an embodiment of the invention. The wind turbine 100 comprises a tower 120 which is mounted on a non-depicted fundament. On top of the tower 120 there is arranged a nacelle 122. In between the tower 120 and the nacelle 122 there is provided a yaw angle adjustment device 121 which is capable of rotating the na celle 122 around a non-depicted vertical axis being aligned with the longitudinal extension of the tower 120. By control ling the yaw angle adjustment device 121 in an appropriate manner it can be made sure that during a normal operation of the wind turbine 100 the nacelle 122 is always properly aligned with the current wind direction. The wind turbine 100 further comprises a wind rotor 110 hav ing three blades 114. In the perspective of Figure 1 only two blades 114 are visible. The rotor 110 is rotatable around a rotational axis 110a. The blades 114, which are mounted at a hub 112, extend radially with respect to the rotational axis 110a.
In between the hub 112 and a blade 114 there is respectively provided a blade angle adjustment device 116 in order to ad just the blade pitch angle of each blade 114 by rotating the respective blade 114 around a non-depicted axis being aligned substantially parallel with the longitudinal extension of the respective blade 114. By controlling the blade angle adjust ment device 116 the blade pitch angle of the respective blade 114 can be adjusted in such a manner that at least when the wind is not too strong a maximum wind power can be retrieved from the available mechanical power of the wind driving the wind rotor 110.
As can be seen from Figure 1, within the nacelle 122 there is provided a gear box 124. The gear box 124 is used to convert the number of revolutions of the rotor 110 into a higher num ber of revolutions of a shaft 125, which is coupled in a known manner to an electromechanical transducer 130. The electromechanical transducer is a generator 130.
At this point it is pointed out that the gear box 124 is op tional and that the generator 140 may also be directly cou pled to the rotor 110 by the shaft 125 without changing the numbers of revolutions. In this case the wind turbine is a so caller Direct Drive (DD) wind turbine.
Further, a brake 126 is provided in order to stop the opera tion of the wind turbine 100 or in order to reduce the rota tional speed of the rotor 110 for instance in case of emer gency . The wind turbine 100 further comprises a control system 143 for operating the wind turbine 100 in a highly efficient man ner. Apart from controlling for instance the yaw angle ad justment device 121 the depicted control system 153 is also used for adjusting the blade pitch angle of the rotor blades 114 in an optimized manner.
In accordance with basic principles of electrical engineering the generator 130 comprises a stator assembly 135 and a rotor assembly 140. In the embodiment described here the generator 130 is realized in a so called "inner stator - outer rotor" configuration, wherein the rotor assembly 140 surrounds the stator assembly 135. This means that non-depicted permanent magnets respectively magnet assemblies of the rotor assembly 140 travel around an arrangement of a plurality of non- depicted coils of the inner stator assembly 135 which coils produce an induced current resulting from picking up a time varying magnetic flux from the traveling permanent magnets.
According to the embodiment described here each permanent magnet (PM) assembly comprises at least three sintered perma nent magnet devices which are made from a Nd-Fe-B material composition .
Figure 2 shows in a cross sectional view a schematic repre sentation of the generator 130. The generator 130 comprises a stator assembly 135. The stator assembly 135 comprises a sta tor support structure 237 comprising a stack of a plurality of lamination sheets and a plurality of stator windings 239 being accommodated within the stator support structure 237. The windings 239 are interconnected in a known manner by means of non-depicted electrical connections.
A rotor assembly 140 of the generator 130, which is separated from the stator assembly 135 by an air gap ag, comprises a rotor support structure 242 providing the mechanical base for mounting a plurality of sintered permanent magnets 250. In Figure 2 the rotational axis of the rotor assembly 140 is de nominated with reference numeral 230a.
In the exemplary embodiment described here at each angular position of the rotor assembly 140 there are arranged three sintered permanent magnets arranged next to each other. It is mentioned that in Figure 2 only three sintered permanent mag nets 250 being assigned to one angular position are depicted for the sake of ease of illustration. In reality, depending on the dimension of the generator 130, a plurality of sin tered permanent magnets 250 are mounted to the rotor support structure 242. The sintered permanent magnets 250 are prefer ably arranged in a matrix like structure around a curved sur face area of the support structure 242 having a basically cy lindrical geometry around the generator axis 240a.
As can be seen from Figure 2, the sintered permanent magnets 250 are not mounted directly to the rotor support structure 242. Instead, there is provided a back plate 244 made from a ferromagnetic material, e.g. iron. The back plate 244 is pro vided in order to ensure a proper guidance of magnetic flux. This significantly reduces in a beneficial manner the inten sity of magnetic stray fields.
Figure 3 shows a Flux Focusing Permanent Magnet (FFPM) 350 produced in accordance with an embodiment of the invention.
The FFPM 350 is magnetized in such a manner that there is given a spread angular distribution of magnetic domain align ment directions 352. According to the embodiment described here each magnetic domain alignment direction 352 follows a straight magnetization line. The straight lines are angled or inclined with respect to each other in a fan like manner. Specifically, the spread angular distribution of the straight magnetization lines produces, in the region above a main sur face 350a of the FFPM 350, a focal point 354 being character- ized by a local maximum of the magnetic field respectively the magnetic flux density produced by the FFPM 350.
According to the exemplary embodiment described here the de picted magnetic domain alignment pattern is symmetric with respect to a symmetry axis 354a. In this document the sym metry axis 354a is also denominated magnetic axis. The mag netic axis 354a is a normal axis to the main surface 350a, which runs through the focal point 354.
Figure 4 shows an apparatus 460 for manufacturing a block in the form of pressed magnet powder that can be sintered in an oven and become a sintered permanent magnet. Specifically, the apparatus 460 is used for magnetizing and compacting a powder of magnetic material 495. A subsequent sintering of a resulting magnetized compacted block is carried out in a non- depicted sintering oven. The apparatus 460 comprises a mold 470 within which a molding chamber 472 is formed. The molding chamber 472 can be closed by a non-depicted die, which is used for compacting the powder of magnetic material 495, which in accordance with usual procedures for manufacturing sintered magnets has to be filled into the molding chamber 472. The non-depicted die performs a movement along a direc tion being perpendicular to the plane of drawing.
The apparatus 460 further comprises means for producing a magnetic field which is applied to the compacted powder 495 during the sintering process. These magnetic field production means include a first magnetic device 461 and the second mag netic device 464. In the embodiment shown in Figure 4, the first magnetic device 461 produces a magnetic North pole N and the second magnetic device 464 produces a magnetic South pole S. In accordance with known apparatuses the first mag netic device comprises (i) a first electromagnetic coil 462 for generating a magnetic field and (ii) a first magnetic yoke 463 for guiding and/or for shaping the magnetic field (lines) being present within the molding chamber 472. Corre- spondingly, the second magnetic device 464 comprises (i) a second electromagnetic coil 465 and (ii) a second magnetic yoke 466.
According to the exemplary embodiment described here the first magnetic yoke 463 being assigned to the North pole and the second magnetic yoke 466 being assigned to the South pole have a different geometry. Specifically, the bending radii of the outer surfaces of the two magnetic yokes 463, 466 is dif ferent from each other. This has the effect that within the molding chamber 472 there will be provided an inhomogeneous magnetic field respectively magnetic flux which results in an inhomogeneous magnetization of the powder 495. This inhomoge neous magnetization may result in a spread angular distribu tion of magnetic domain alignment directions 352 as shown in Figure 3.
As can be seen from Figure 4, according to the embodiment de scribed here the molding chamber 472 comprises a geometry which is different from a cuboid. Hence, the cross section of the molding chamber 432 depicted in Figure 4 is not a rectan gle. Specifically, according to the embodiment described here a lower first surface 470a of the mold 470 is curved in a convex manner (with regard to a central point the molding chamber 472) . Further, an opposing upper second surface 470b of the mold 470 is curved in a concave manner (again with re spect to a central point the molding chamber 472) .
Such a shaping of the molding chamber 472 will, at a first glance, result in a geometry of the produced sintered block which geometry deviates from a typically desired cuboid shape of a permanent magnet (PM) . However, when taking into account (at a second glance) undesired deformations with regularly occur during a forthcoming sintering process and/or during a subsequent cool down period of a sintered magnet block the geometry of the molding chamber 472 can pre-account such de formations. Hence, a molding chamber 472 with properly shaped curved surfaces 470a, 470b can lead to at least approximately perfectly shaped cuboid sintered PM bodies. Hence, when fi nalizing or further processing a sintered PM block towards a PM piece with a cuboid shape there will be less PM material which has to be removed from the sintered PM block. This makes the manufacturing of single permanent magnets very ef fective, in particular from an economical point of view, be cause there is less material which has to be machined away and which, although it could be recycled, typically repre sents a wastage material.
It is pointed out that the described pre-accounting of defor mations can be realized not only with PM which are supposed to be of cuboid shape. By appropriately shaping the inner surface (s) of the molding chamber 472 magnetized compacted blocks can be produced which have, after completing a defor mation procedure, at least approximately a desired shape re spectively geometry. Hence, in some applications the molding chamber may be defined not only by two but by three or more curved surfaces.
Figure 5 shows an apparatus 560 for manufacturing a magnet block from magnet powder ready for sintering in an oven in accordance with a further embodiment of the invention.
In accordance with the embodiment shown in Figure 4a non cuboid molding chamber 572 is formed by two curved surfaces, a first curved surface 570a of a mold 570 and a second curved surface 570b of the mold 570. A non-depicted die is used for compacting powder of magnetic material 595 filled into the molding chamber 572. The movement of the die is along a di rection perpendicular to the plane of drawing.
The apparatus 560 differs from the apparatus 460 shown in Figure 4 in that a spatially inhomogeneous magnetic field / flux within the molding chamber 572 is not only produced with two but with three magnetic devices. Specifically, the appa ratus 560 comprises two magnetic devices 561 and 567 which both produce, from the perspective of the powder 595 to be magnetized, a magnetic North pole. Further, the apparatus 560 comprises one magnetic device 564 which produces, from the perspective of the powder 595 to be magnetized, a magnetic South pole. Each one of the magnetic devices 561, 564 and 567 comprises one electromagnetic coil (see reference numerals 562, 565, and 568) and one magnetic yoke (see reference nu merals 563, 566, and 569) .
Figure 6 shows in accordance with a further embodiment of the invention an apparatus 660 for manufacturing a sintered per manent magnet from a powder of magnetic material 695. In this embodiment a spatially inhomogeneous magnetic field / flux within a molding chamber 672 is produced with two magnetic devices having differently shaped magnetic yokes. Specifical ly, a first magnetic device producing a magnetic North pole comprises a first magnetic yoke 663 and a second magnetic de vice producing a magnetic South pole comprises a second mag netic yoke 666. As can be seen from the Figure 6, the first magnetic yoke 663 has an outer (convex) curved yoke surface 663a having a first radius R1 and the second magnetic yoke 666 has an outer (concave) curved yoke surface 666a having a second radius R2. The corresponding magnetic field lines or magnetic flux lines are denominated with reference numeral 630.
Although not obligatory for producing a proper spatially in homogeneous magnetic field / flux, in the embodiment de scribed here the second (concave) radius R2 is bigger than the first (convex) radius R1. By properly selecting the two radii R1 and R2 the focusing strength respectively the focal length of a produced FFPM can be adjusted.
Figures 7 and 8 illustrate for different sintered PM manufac turing processes the geometries of a mold, a sintered magnet block and the final PM which is installed in an electric gen- erator. Figure 7 shows these geometries for a known manufac- turing process whereas Figure 8 shows these geometries for manufacturing process in accordance with an embodiment of the invention .
Figures 7a and 8a show, as a reference, the final PM piece 250 which is to be produced. According to the exemplary em bodiment described here the final PM piece 250 has a cuboid shape. As mentioned above, the desired final shape can also deviate from a pure cuboid. For instance, the desired shape can have rounded corners or edges.
Figures 7b and 8b show the geometry of a molding chamber 772, 872 which is used for the compacting and magnetizing process of magnetic powder material. The molding chamber 772 has a cuboid shape whereas the shape of the molding chamber 872 is non-cuboid because it comprises two curved opposing surfaces.
Figures 7c and 8c show the geometric size relation between a produced sintered PM block which has undergone a deformation after it (a) has been removed from the respective molding chamber 772, 872, (b) has been sintered in a sintering oven, and (c) has been removed from the sintering oven. The sin tered PM block 775, which has been produced by means of the (known) cuboid molding chamber 770 and a known sintering oven and which has undergone deformation effects, strongly differs from a cuboid shape. By contrast thereto, the sintered PM block 875 which has been produced by means of the non-cuboid but curved molding chamber 870 and which has also undergone deformation effects has a shape of a cuboid or at least a shape which deviates only with a small extend from the de sired cuboid shape.
Figures 7d and 8d show the (volume) difference between (i) the final PM piece 250 and (ii) the produced sintered PM bod ies 775, 875. It can be seen that the PM material wastage for producing the final PM piece 250 from the curved sintered PM block 775 is significantly larger than the PM material wast- age for producing the final PM piece 250 from the at least approximately cuboid sintered PM block 875. Since a lot of PM material wastage increases the manufacturing costs for PM magnet pieces the pre-accounting of deformations by means of an appropriate curved shaping of the molding chamber is an effective measure for making the production of sintered PM pieces (economically) more effective.
It should be noted that the term "comprising" does not ex- elude other elements or steps and the use of articles "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

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 molding chamber (472, 572,
672) for receiving a powder of a permanent magnet material (495, 595, 695);
at least two magnetic devices (461, 464; 561, 564) for generating a magnetic field for magnetizing the powder (495, 595, 695) being accommodated within the molding chamber (472, 572, 672); and
at least one die for compacting the powder (495, 595,
695) being accommodated within the molding chamber (472, 572, 672) ,
the magnetizing and compacting resulting in a magnetized com pacted block of the powder (495, 595, 695); wherein
the molding chamber (472, 572, 672) and/or the die comprises at least one surface (470a, 470b; 570a, 570b) which is curved in such a manner that an unwanted deformation of a sintered block (885), which has been obtained by sintering the magnet ized compacted block in a sintering oven, whereby the unwant ed deformation is given after a removal of the sintered block (885) from the sintering oven, is compensated at least par tially.
2. The apparatus (460, 560, 660) as set forth in the preced ing claim, wherein
the molding chamber (472, 572, 672) comprises two opposing surfaces (470a, 470b; 570a, 570b) which are both curved.
3. The apparatus (460, 560, 660) as set forth in the preced ing claim, wherein
with regard to a center of the molding chamber (472, 572,
672) a first surface is a convex surface (470a, 570a) and the second surface is a concave surface (470b, 570b) .
4. The apparatus (460, 560, 660) as set forth in any one of the preceding claims, wherein
the magnetic devices (461, 464) are designed in such a manner that the magnetic field (630) within the molding chamber is associated with a spread angular distribution of magnetic flux lines .
5. The apparatus (560) as set forth in any one of the preced ing claims, further comprising
a further magnetic device (567) for generating a magnet ic field (630) acting on the powder (595) being accommodated within the molding chamber.
6. The apparatus (460, 560, 660) as set forth in 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 produc ing the magnetic field (630) and
a magnetic yoke (463, 466; 563, 566) for guiding and/or for shaping the magnetic field being produced by the electro magnetic coil (462, 465; 562, 565).
7. The apparatus as set forth in the preceding claim, wherein at least one of the magnetic devices comprises one electro magnetic coil and a further magnetic yoke or one magnetic yoke and a further electromagnetic coil.
8. The apparatus (460, 560, 660) as set forth in any one of the two preceding claims, wherein
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 one 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 regard to the molding chamber (472, 572, 672) the first magnetic yoke (463, 563, 663) and the second magnetic yoke (466, 566, 666) are located at opposing sides, the first magnetic yoke (463, 563, 663) has a first outer yoke surface (663a) facing the molding chamber (672),
the second magnetic yoke (466, 566, 666) has a second outer yoke surface (666a) facing the molding chamber (466, 566,
666) , and
the first outer yoke surface (663a) is concave and the second outer yoke surface (666a) is convex.
9. The apparatus (460, 560, 660) as set forth in the preced ing claim, wherein
the first outer yoke surface (663a) has a first radius (Rl) and the second outer yoke surface (666a) has a second radius (R2) being different from the first radius (Rl) .
10. A method for manufacturing a sintered permanent magnet (250, 350), the method comprising
filling a powder of permanent magnet material (495, 595, 695) into a molding chamber (472, 572, 672) of a mold (470, 570); generating a magnetic field (630) for magnetizing the power (495, 595, 695) being accommodated within the molding chamber (472, 572, 672);
compacting the powder (495, 595, 695) being accommodated within the molding chamber (472, 572, 672) by means of a die, the magnetizing and compacting resulting in a magnetized com pacted block of the powder (495, 595, 695);
sintering the magnetized compacted block in a sintering oven resulting in a sintered block (885); and
removing the sintered block (885) from the sintering oven; wherein the shape of the molding chamber (472, 572, 672) is designed in such a manner that an unwanted deformation of the sintered block (885), which unwanted deformation is given af ter removing the sintered block (885) from the sintering ov en, is compensated at least partially.
11. The method as set forth in the preceding claim, wherein the permanent magnet material (495, 595, 695) comprises a ra re earth material, in particular NdFeB.
12. Sintered magnet (250, 350) being produced by carrying out a method as set forth in the preceding claim.
13. An electromechanical transducer (140), in particular an electric generator (130), the electromechanical transducer
(130) comprising
a stator assembly (135), and
a rotor assembly (140) comprising
a support structure (242) and
at least one sintered magnet (250, 350) as set forth in the preceding claim, wherein the sintered mag net (250, 350) is mounted to the support structure
(242) . 14. A wind turbine (100) for generating electrical power, the wind turbine (100) comprising
a tower (120) ,
a wind rotor (110), which is arranged at a top portion of the tower (120) and which comprises at least one blade (114), and
an electromechanical transducer (130) as set forth in the preceding claim, wherein the electromechanical transducer (130) is mechanically coupled with the wind rotor (110) .
EP19733947.6A 2019-04-23 2019-05-20 Manufacturing sintered permanent magnets with a reduced deformation Withdrawn EP3939058A2 (en)

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