WO1996030144A1 - Soft magnetic anisotropic composite materials - Google Patents

Soft magnetic anisotropic composite materials Download PDF

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Publication number
WO1996030144A1
WO1996030144A1 PCT/SE1996/000397 SE9600397W WO9630144A1 WO 1996030144 A1 WO1996030144 A1 WO 1996030144A1 SE 9600397 W SE9600397 W SE 9600397W WO 9630144 A1 WO9630144 A1 WO 9630144A1
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Prior art keywords
particles
composite material
powder
essentially
resin
Prior art date
Application number
PCT/SE1996/000397
Other languages
French (fr)
Inventor
Mats Persson
Mats ALAKÜLA
Jan-Eric STÅHL
Tord Cedell
Original Assignee
Höganäs Ab
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Priority to AU51670/96A priority Critical patent/AU5167096A/en
Publication of WO1996030144A1 publication Critical patent/WO1996030144A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
    • C22C32/0094—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with organic materials as the main non-metallic constituent, e.g. resin
    • 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
    • H01F1/12—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 soft-magnetic materials
    • H01F1/14—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 soft-magnetic materials metals or alloys
    • H01F1/20—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder
    • H01F1/22—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together
    • H01F1/24—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together the particles being insulated
    • H01F1/26—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 soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together the particles being insulated by macromolecular organic substances

Definitions

  • the present invention concerns a new soft magnetic anisotropic composite material as well as a process for the preparation of this material.
  • the new composite material is characterized by high saturation flux density, high maximum permeability and low eddy current losses. These properties are the result of a considerably improved green density and indicate that the new composite material would be suitable for devices operating at power frequencies between 5.0 and 5000 Hz, e.g. relays, transformers, inductors and for magnetic shielding as well as for certain types of mo ⁇ tors. The material can also be used for devices opera ⁇ ting up to 50 kHz without significant eddy current losses.
  • the new high density composite material consists of compacted, flaky shaped iron particles bonded together by a non-magnetic organic resin, whereby the particles are aligned in an essentially parallel re ⁇ lationship.
  • the high density which in this context means a density above 7.4 q/crY , is mainly the result of the flaky form of the particles in combination with cer ⁇ tain process steps such as the soft annealing step de ⁇ scribed below.
  • the new material is a soft magnetic, amsotropic composite material, which essentially consists of compacted, essentially flaky shaped, electrically insulared particles, which have been prepared by cold rolling and disintegration of an essentially pure iron powder.
  • the particles are aligned in an essentially parallel relationship and bonded together by an organic polymer resin in an amount of 0.15 to 0.75 % by weight.
  • the diameter of the parti ⁇ cles is 3 to 35 times the thickness, preferably 5 to 20.
  • a characterizing feature of the new material is the high density of at least 7.4 g/cm 3 .
  • the present invention also concerns a process for the preparation of the composite material comprising the following steps:
  • the starting material for the process is suitably an iron powder prepared by a conventional method, such as atomisation or direct reduction of iron ore partic ⁇ les.
  • This powder is then annealed in order to reduce the content of impurities, such as carbon and oxygen, and to soften the iron.
  • This operation is preferably carried out in a reducing atmosphere at a temperature of about 750-1000°C.
  • the obtained powder contains less than C... % by weight of carbon. Powders of this type are avail ⁇ able from Hoganas AB, Sweden as ASC 100.29, which is ar. atomised powder containing less than 0.005 % by weight of carbon and NC 100.24 which is a sponge iron powder containing less than 0.01 % by weight of carbon.
  • the oxygen contents are approximately 0.09 and 0.40% by weight, respectively.
  • the annealed particles are ther. cold rolled into essentially flaky shape and disinte ⁇ grated such that the diameter of the particles are 3 tc 35 times the thickness and the maximum (diameter) par ⁇ ticle size is about 500 ⁇ m.
  • the flaky shaped particles thus obtained are then soft annealed at a temperature lr. the range of 700-900°C in a reducing e.g. H2 atmosphere. In contrast to previously used soft annealing processes
  • the annealing process according to the invention is carried out at lower temperature and no inert inorganic powder material, such as aluminia, has to be added before the heating in order to prevent sin- tering. As a consequence no step for removing the inert material is included in the process according to the present invention.
  • the carbon and oxygen contents of the annealed products are essentially the same as before this step.
  • the annea ⁇ led particles are subjected to an additional disintegra ⁇ tion step.
  • the iron flakes are then subjected to a phos ⁇ phoric acid treatment in aqueous solution.
  • the iron particles are subjected to the phosphoric acid at a temperature and for a time sufficient to form a thin electrically insulation layer around the individual iron flakes .
  • the powder is dried and mixed with an organic binder resin in an amount of less than 1 % by weight, preferably between 0.15 and 0.75% by weight and most preferably between 0.30 and 0.70 % by weight of the iron powder. If the binder content is less than 0.3 % the edge brittleness increases rapidly and makes the material hard to ma ⁇ chine.
  • the organic binder could be selected from ther- mosetting or thermoplastic resins and is preferably se ⁇ lected from the group consisting of epoxy resins such as Araldite, PPS (polyphenylene sulphide) or PEEK (polyetherether ketone) .
  • the mixture of iron flakes and organic binder is then fed into a pressing tool such that the flakes are aligned in the tool in a substantially parallel rela ⁇ tionship. This can be accomplished by allowing the flakes to fall freely into the die from a funnel which is positioned over the die, by vibrations, by magnetic alignment or combinations thereof.
  • the pressing tool could optionally be evacuated before the compaction of the flaky material, and, if the organic binder used is a thermoplastic resin, the material should be heated to a temperature above the melting point of the thermoplastic resin before the compacting step.
  • the evacuation step is especially preferred if very high densities are re ⁇ quired, and it has been found that va-cuum pressing in ⁇ creases the density by about 0.1 g/cm 3 which under cer- tain circumstances is of great importance.
  • the compacting step is carried out as a high-pressure isostatic or uniaxial pressing at pressures in the range of 400-1000 MPa.
  • the compacting temperatures vary depending on the type of binder and the intended use of the final product.
  • the compacting step could e.g. be carried out at 70°C and a curing step might be carried out at 70-100°C.
  • PPS and PEEK type of resins the compacting could be carried out at 300°C and the crosslinking at 400-450°C.
  • the compacting times are not critical but should be relatively short, such as 5-20 s, for economical reasons.
  • the compacted material When removed from the pressing tool, the compacted material is either stress relieved at an elevated tem ⁇ perature or subjected to an elevated temperature and subsequently to a controlled cooling.
  • the properties of the new material are unique and similar to those of stacked 35-50 ⁇ m thick sheets of pure iron separated by very thin electric isolators.
  • the mechanical properties of new material seem to have an optimum of about 150 MPa at a binder content of 0.35-0.50% by weight.
  • the invention is further illustrated by the follow ⁇ ing non-limiting example:
  • An atomised iron powder, ASC 100.29 (commercially available from Hoganas AB, Sweden) was used as base ma- terial for the new material according to the invention.
  • the base powder consisted of irregularly, uniaxially shaped particles, which were rolled between two steel rolls in such a way that virtually each particle without contact with other particles was subjected to a press force corresponding to 3 ton/cm. After rolling the pow ⁇ der was disintegrated in order to separate particles which have stuck to each other during rolling, in order to obtain a powder having a maximum particle size of 42C ⁇ m.
  • the obtained powder was in the form of flaky shape ⁇ particles having an average diameter of 250 ⁇ m and a thickness of 35 ⁇ m.
  • the powder was very hard as it has been subjected to strong deformation and, as a consequence, it was dif ⁇ ficult to compact.
  • the density when compacting at 800 MPa was 6.8 g/cm 3 .
  • the powder was soft annealed m a re ⁇ ducing H2 atmosphere at 750°C during 45 minutes. At th_r temperature the iron powder could be soft annealed es ⁇ sentially without risking that the powder particles s_* - tered together.
  • another disintegrating c the powder was carried out in order to restore its par ⁇ ticle size distribution without deforming the particle which would once more result in hardening due to defor ⁇ mation.
  • Bodies compacted with this powder had a densit y of 7.45 g/cm 3 (800 MPa) , which can be compared with thr_ density of the base material of 7.3 g/cm 3 .
  • a thin insulating layer on the ron flakes was prc- vided by subjecting the powder to a treatment with aque ⁇ ous phosphoric acid.
  • the oxygen and phosphorus contents of the obtained flakes were 0.41 and 0.02 % by weight, respectively.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Dispersion Chemistry (AREA)
  • Power Engineering (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Soft Magnetic Materials (AREA)

Abstract

The invention concerns a soft magnetic, anisotropic composite material essentially consisting of compacted, essentially flaky shaped, electrically insulated particles of essentially pure iron powder containing less than 0.01 % by weight of carbon, which particles are aligned in essentially parallel relationship and bonded together by an organic polymer resin. The new material is characterized by a green density of at least 7.4 g/cm3. The invention also concerns a process for the preparation of the new material as well as the use of the material for devices operating at power frequencies.

Description

SOFT MAGNETIC ANISOTROPIC COMPOSITE MATERIALS
The present invention concerns a new soft magnetic anisotropic composite material as well as a process for the preparation of this material.
The new composite material is characterized by high saturation flux density, high maximum permeability and low eddy current losses. These properties are the result of a considerably improved green density and indicate that the new composite material would be suitable for devices operating at power frequencies between 5.0 and 5000 Hz, e.g. relays, transformers, inductors and for magnetic shielding as well as for certain types of mo¬ tors. The material can also be used for devices opera¬ ting up to 50 kHz without significant eddy current losses. In brief, the new high density composite material consists of compacted, flaky shaped iron particles bonded together by a non-magnetic organic resin, whereby the particles are aligned in an essentially parallel re¬ lationship. The high density, which in this context means a density above 7.4 q/crY , is mainly the result of the flaky form of the particles in combination with cer¬ tain process steps such as the soft annealing step de¬ scribed below.
Materials of flaky shaped particles have previously been proposed for magnetic applications. Specifically, and contrary to the present invention, these materials are intended for static magnetic components such as mag¬ netic cores. Thus the US patents 2 937 964 and 3 255 052 both concern magnetic cores made of flaky shaped parti- cles of a nickel based alloy which also includes iron and molybdenum. According to the US patents the parti¬ cles are insulated by a plurality of layers including i . a. silicate. The article "Compressed Iron Motor Core for Electric Motors" by Kiyoshi Fukui et al. in IEEE Trans- actions on Magnetics, September 1972, describes the use of flaky electrolytic iron and spherical atomised iron powders of different sizes in compressed iron powder cores for small electric motors. The article "A lami¬ nated flake-iron powder material for use at audio and ultrasonic frequencies", Soft magnetic materials in
Telecommunications, Pergamon Press, London 1953 pp 268 - 277 discloses an flaky shaped iron powder having a den¬ sity of about 7.0
Figure imgf000004_0001
which is taught not to be useful for power frequencies. According to the present invention the new material is a soft magnetic, amsotropic composite material, which essentially consists of compacted, essentially flaky shaped, electrically insulared particles, which have been prepared by cold rolling and disintegration of an essentially pure iron powder. The particles are aligned in an essentially parallel relationship and bonded together by an organic polymer resin in an amount of 0.15 to 0.75 % by weight. The diameter of the parti¬ cles is 3 to 35 times the thickness, preferably 5 to 20. A characterizing feature of the new material is the high density of at least 7.4 g/cm3.
The present invention also concerns a process for the preparation of the composite material comprising the following steps:
a) cold rolling essentially pure iron powder into es¬ sentially flake shaped particles, b) disintegration of the rolled powder to a maximum particle size of 500 micron c) soft annealing the resulting powder at a temperature of 700 to 900 °C in a reducing atmosphere, such as H2 atmosphere, d) disintegrating of the annealed powder in order to obtain essentially the same particle size distribution as in step b) e) mixing the powder with an organic binder resin, f) feeding the obtained mixture into a pressing tool such that the flakes are aligned in the tool in a substantially parallel relationship, g) compacting the material, h) removing the compacted material from the pressing tool and, optionally, i) stress relieving the material at an elevated temperature.
The starting material for the process is suitably an iron powder prepared by a conventional method, such as atomisation or direct reduction of iron ore partic¬ les. This powder is then annealed in order to reduce the content of impurities, such as carbon and oxygen, and to soften the iron. This operation is preferably carried out in a reducing atmosphere at a temperature of about 750-1000°C. The obtained powder contains less than C... % by weight of carbon. Powders of this type are avail¬ able from Hoganas AB, Sweden as ASC 100.29, which is ar. atomised powder containing less than 0.005 % by weight of carbon and NC 100.24 which is a sponge iron powder containing less than 0.01 % by weight of carbon. The oxygen contents are approximately 0.09 and 0.40% by weight, respectively. The annealed particles are ther. cold rolled into essentially flaky shape and disinte¬ grated such that the diameter of the particles are 3 tc 35 times the thickness and the maximum (diameter) par¬ ticle size is about 500 μm. The flaky shaped particles thus obtained are then soft annealed at a temperature lr. the range of 700-900°C in a reducing e.g. H2 atmosphere. In contrast to previously used soft annealing processes
BAD ORIGINAL in this field, the annealing process according to the invention is carried out at lower temperature and no inert inorganic powder material, such as aluminia, has to be added before the heating in order to prevent sin- tering. As a consequence no step for removing the inert material is included in the process according to the present invention. After the soft annealing step the carbon and oxygen contents of the annealed products are essentially the same as before this step. In order to secure the correct particle size distribution the annea¬ led particles are subjected to an additional disintegra¬ tion step. According to a preferred embodiment of the invention the iron flakes are then subjected to a phos¬ phoric acid treatment in aqueous solution. The iron particles are subjected to the phosphoric acid at a temperature and for a time sufficient to form a thin electrically insulation layer around the individual iron flakes .
After the phosphoric acid treatment the powder is dried and mixed with an organic binder resin in an amount of less than 1 % by weight, preferably between 0.15 and 0.75% by weight and most preferably between 0.30 and 0.70 % by weight of the iron powder. If the binder content is less than 0.3 % the edge brittleness increases rapidly and makes the material hard to ma¬ chine. The organic binder could be selected from ther- mosetting or thermoplastic resins and is preferably se¬ lected from the group consisting of epoxy resins such as Araldite, PPS (polyphenylene sulphide) or PEEK (polyetherether ketone) .
The mixture of iron flakes and organic binder is then fed into a pressing tool such that the flakes are aligned in the tool in a substantially parallel rela¬ tionship. This can be accomplished by allowing the flakes to fall freely into the die from a funnel which is positioned over the die, by vibrations, by magnetic alignment or combinations thereof. The pressing tool could optionally be evacuated before the compaction of the flaky material, and, if the organic binder used is a thermoplastic resin, the material should be heated to a temperature above the melting point of the thermoplastic resin before the compacting step. The evacuation step is especially preferred if very high densities are re¬ quired, and it has been found that va-cuum pressing in¬ creases the density by about 0.1 g/cm3 which under cer- tain circumstances is of great importance. Generally, the compacting step is carried out as a high-pressure isostatic or uniaxial pressing at pressures in the range of 400-1000 MPa. The compacting temperatures vary depending on the type of binder and the intended use of the final product. For epoxy resins the compacting step could e.g. be carried out at 70°C and a curing step might be carried out at 70-100°C. For PPS and PEEK type of resins the compacting could be carried out at 300°C and the crosslinking at 400-450°C. The compacting times are not critical but should be relatively short, such as 5-20 s, for economical reasons.
When removed from the pressing tool, the compacted material is either stress relieved at an elevated tem¬ perature or subjected to an elevated temperature and subsequently to a controlled cooling.
Due to the high densities, up to 7.58 g/cm3, the properties of the new material are unique and similar to those of stacked 35-50 μm thick sheets of pure iron separated by very thin electric isolators. Thus, the bandwidth of the soft magnetic composite material can be as high as 100 kHz, the saturation flux density more than 1.9 Tesla and the maximum permeability, μmax. •= 400. The mechanical properties of new material seem to have an optimum of about 150 MPa at a binder content of 0.35-0.50% by weight. The invention is further illustrated by the follow¬ ing non-limiting example:
An atomised iron powder, ASC 100.29 (commercially available from Hoganas AB, Sweden) was used as base ma- terial for the new material according to the invention. The base powder consisted of irregularly, uniaxially shaped particles, which were rolled between two steel rolls in such a way that virtually each particle without contact with other particles was subjected to a press force corresponding to 3 ton/cm. After rolling the pow¬ der was disintegrated in order to separate particles which have stuck to each other during rolling, in order to obtain a powder having a maximum particle size of 42C μm. The obtained powder was in the form of flaky shapeα particles having an average diameter of 250 μm and a thickness of 35 μm.
The powder was very hard as it has been subjected to strong deformation and, as a consequence, it was dif¬ ficult to compact. The density when compacting at 800 MPa was 6.8 g/cm3. The powder was soft annealed m a re¬ ducing H2 atmosphere at 750°C during 45 minutes. At th_r temperature the iron powder could be soft annealed es¬ sentially without risking that the powder particles s_* - tered together. After the annealing step another disintegrating c: the powder was carried out in order to restore its par¬ ticle size distribution without deforming the particle which would once more result in hardening due to defor¬ mation. Bodies compacted with this powder had a density of 7.45 g/cm3 (800 MPa) , which can be compared with thr_ density of the base material of 7.3 g/cm3.
A thin insulating layer on the ron flakes was prc- vided by subjecting the powder to a treatment with aque¬ ous phosphoric acid. The oxygen and phosphorus contents of the obtained flakes were 0.41 and 0.02 % by weight, respectively.
BAD ORIGINAL The obtained powder was subsequently mixed with different amounts (from 0.2 to 1.0% by weight) of Araldite LY 5052, an epoxy resin available from Ciba- Geigy, and was compacted to ring cores for measuring of magnetic properties. After the compacting operation the ring cores were heated (80°C, 2 h) , for curing of the epoxy binder. By compacting (800 MPa) the powder mixture in vacuum in an uniaxial tool a density of 7.58 g/cm3 was obtained when the content of epoxy binder was 0.6% by weight. On average the vacuum compacting gave 0.1 g/cm3 higher densities than conventional compacting in uniaxial tools. Densities of at least 7.4 g/cm3 were ob¬ served for all components based on powders having an epoxy content between 0.2 and 0.7 also with conventional compacting.
A comparison between the results obtained with the material according to the present invention and a con¬ ventional material is given below.
Figure imgf000009_0001

Claims

1. Soft magnetic, amsotropic composite material essentially consisting of compacted, essentially flaky shaped, electrically insulated particles of essentially pure iron powder containing less than 0.01 % by weight of carbon, which particles are aligned in essentially parallel relationship and bonded together by an organic polymer resin characterized by a green density of at least 7.4 g/cm3 at a compaction pressure of 800 MPa. 2. Composite material according to claim 1, wherein in the particles have a ratio diameter to thickness of 3 to 35 and an average thickness of 10-100 μm and an average diameter of 200-500 μm.
3. Composite material according to claim 1 or 2 wherein the organic polymer is present in an amount of less than 0.75, preferably between 0.30 and 0.70 % by weight of the iron powder. . Composite material according to any of the claims 1-3, wherein the electrically insulated flaky particles originate from atomised particles of essen¬ tially pure iron coated with an insulating layer.
5. Composite material according to any of the claims 1 - 4, c h a r a c t e r i z e d in that the or¬ ganic polymer resin is a thermoplastic or thermosetting resin.
6. Composite material according to claim 5, c h a r a c t e r i z e d in that the organic polymer is an epoxy resin.
7. Process for the preparation of a soft magnetic, amsotropic composite material according to any of the preceding claims, c h a r a c t e r i z e d by the fol¬ lowing steps:
a) cold rolling essentially pure iron powder into es- sentially flake shaped particles, b) disintegration of the rolled powder to a maximum particle size of 500 micron c) soft annealing the resulting powder at a temperature of 700 to 900 °C in a reducing atmosphere d) disintegrating of the annealed powder in order to obtain essentially the same particle size distribution as in step b) e) mixing the powder with an organic binder resin, f) feeding the obtained mixture into a pressing tool such that the flakes are aligned in the tool in a substantially parallel relationship, g) compacting the material, h) removing the compacted material from the pressing tool and, optionally, i) stress relieving the material at an elevated temperature.
8. Process according to claim 7 wherein the com- pacting step f) is carried out under reduced pressure or vacuum.
9. Process according to claim 7 or 8 wherein the particles of step d) are first subjected to a treatment with an aqueous solution of phosphoric acid at a tem- perature and for a time sufficient to form an insulating layer on the particles and subsequently dried.
10. Process according to claim 7 to 9 wherein the amount of binder is in the range of 0.15 to 0.75 % by weight of the iron powder. 11. Process according to any of the claims 7 to 10 wherein the binder is a thermosetting or thermoplastic resin.
12. Process according to claim 11 wherein the ther¬ mosetting resin is an epoxy resin. 13. Process according to claim 11 wherein the binder is a thermoplastic resin and the mixture in the pressing tool is subjected to a temperature above the melting point of the thermoplastic resin.
14. Process according to any of the claims 7 to 13 wherein the compacted material of step f) is subjected to an increased temperature and a subsequent controlled cooling. 15. Starting material for the preparation of soft magnetic, amsotropic composite material according to any of the claims 1-6, c h a r a c t e r i z e d in that it consists of flaky shaped particles of essentially pure iron containing less than 0.01 % oy weight of car- bon wherein the particles have a ratio diameter to thickness of 3 to 35, an average thickness of 10-100 μm and an average diameter of 200-500 μm optionally elec¬ trically insulated by an oxide layer.
16. Use of a composite material according to any of the claims 1 to 6 for devices operating at power fre¬ quencies, such as relays, transformers, inductors, mo¬ tors and for magnetic shielding
17. Use according to claim 16 for devices operating between 50 and 5000 Hz.
PCT/SE1996/000397 1995-03-28 1996-03-27 Soft magnetic anisotropic composite materials WO1996030144A1 (en)

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2331859A (en) * 1997-11-28 1999-06-02 Asea Brown Boveri Magnetic cores for rotating electric machines
EP0997915A2 (en) * 1998-10-30 2000-05-03 Kawasaki Steel Corporation Flat-paticle iron powder, method for making the same and powder magnetic core using the same
WO2002100580A1 (en) * 2001-06-13 2002-12-19 Höganäs Ab Method of preparation of high density soft magnetic products
EP1486990A2 (en) * 2003-06-03 2004-12-15 Sumitomo Electric Industries, Ltd. Composite magnetic material and manufacturing method thereof
WO2005023464A1 (en) * 2003-09-09 2005-03-17 Höganäs Ab Iron based soft magnetic powder
DE102004009297B4 (en) * 2003-02-27 2005-12-01 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.), Kobe Binder for powder metallurgy, powder mixture for powder metallurgy and method for the production of the same
EP1570564B1 (en) * 2002-12-04 2010-07-28 Robert Bosch Gmbh Electric machine, in particular brushless synchronous motor

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US2937964A (en) * 1957-07-23 1960-05-24 Adams Edmond Magnetic flake core
US4543208A (en) * 1982-12-27 1985-09-24 Tokyo Shibaura Denki Kabushiki Kaisha Magnetic core and method of producing the same
DE3439397C2 (en) * 1984-10-27 1990-01-18 Vacuumschmelze Gmbh, 6450 Hanau, De
DE3907090A1 (en) * 1989-03-04 1990-09-06 Vacuumschmelze Gmbh Process for the powder metallurgical production of a soft magnetic body

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Publication number Priority date Publication date Assignee Title
US2937964A (en) * 1957-07-23 1960-05-24 Adams Edmond Magnetic flake core
US4543208A (en) * 1982-12-27 1985-09-24 Tokyo Shibaura Denki Kabushiki Kaisha Magnetic core and method of producing the same
DE3439397C2 (en) * 1984-10-27 1990-01-18 Vacuumschmelze Gmbh, 6450 Hanau, De
DE3907090A1 (en) * 1989-03-04 1990-09-06 Vacuumschmelze Gmbh Process for the powder metallurgical production of a soft magnetic body

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Title
SOFT MAGNETIC MATERIALS IN TELECOMMUNICATIONS, PERGAMON PRESS, LONDON, 1953, CAMPBELL G. et al., "A Laminated Flake Iron Powder Material for Use at Audio and Ultrasonic Frequencies", pages 268-277. *

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2331859A (en) * 1997-11-28 1999-06-02 Asea Brown Boveri Magnetic cores for rotating electric machines
EP0997915A2 (en) * 1998-10-30 2000-05-03 Kawasaki Steel Corporation Flat-paticle iron powder, method for making the same and powder magnetic core using the same
EP0997915A3 (en) * 1998-10-30 2000-06-21 Kawasaki Steel Corporation Flat-paticle iron powder, method for making the same and powder magnetic core using the same
CN1326648C (en) * 2001-06-13 2007-07-18 赫加奈斯公司 Method for preparation of high density soft magnetic products
US6503444B1 (en) 2001-06-13 2003-01-07 Höganäs Ab High density soft magnetic products and method for the preparation thereof
WO2002100580A1 (en) * 2001-06-13 2002-12-19 Höganäs Ab Method of preparation of high density soft magnetic products
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