Patent Application
20080102302
The present invention generally relates to a method for producing a dust core compact, and the dust core compact. More particularly, the present invention relates to a method for producing a dust core compact fabricated using soft magnetic powder, and the dust core compact.
Conventionally, there has been known a method for producing an annular magneto coil by combining a plurality of magneto coil components in a circumferential direction. The production method is disclosed in Japanese Patent Laying-Open No. 2003-235186 (Patent Document 1).
According to the method for producing a magnetogenerator disclosed in Patent Document 1, a plurality of magneto coil elements having recesses and projections formed at coupling portions are coupled to each other by engaging the recesses and projections with each other. The obtained magneto coil is placed within a housing, and thereafter the housing is cooled down. Since the housing shrinks as it cools down, the magneto coil is shrink-fitted on the inner peripheral surface of the housing.
In addition, mechanical structures and electric/electronic components such as the magneto coil described above have been fabricated from a dust core compact obtained by pressure-molding soft magnetic powder filled into a mold.
Patent Document 1: Japanese Patent Laying-Open No. 2003-235186
However, according to the production method disclosed in Patent Document 1, since the magneto coil element formed of a magnetic material such as a magnetic steel sheet may be formed with variations in dimensional accuracy, a gap or excess stress may be generated at the coupling portion between the magneto coil elements when the plurality of magneto coil elements are shrink-fitted on the inner peripheral surface of the housing. The generation of a gap or excess stress causes deterioration in magnetic properties of the magneto coil.
Further, when an attempt is made to obtain a complex-shaped structure such as a magneto coil as a one-piece structure by means of pressure forming, sufficient molding pressure may not be applied to some positions within a mold. In this case, the obtained dust core compact has uneven density, and thus cannot achieve desired magnetic properties.
Although there can be conceived a method of molding a plurality of dust core compact components each having a shape of a divided piece of a complete product and thereafter coupling them together by shrink-fitting or screwing, the method also causes a problem similar to that in the production method disclosed in Patent Document 1.
Consequently, one object of the present invention is to solve the aforementioned problems, and to provide a method for producing a dust core compact exhibiting a high strength and capable of being fabricated even when it has a complex shape, as well as to provide the dust core compact.
A method for producing a dust core compact includes the steps of: forming a compact component by pressure-forming a first soft magnetic powder having an average particle diameter Da under a pressure Pa; and forming a compact by pressure-forming a second soft magnetic powder having an average particle diameter Db and the compact component under a pressure Pb. Average particle diameter Da of the first soft magnetic powder and average particle diameter Db of the second soft magnetic powder satisfy relationship Da/Db≧2. Pressures Pa and Pb applied during the pressure forming satisfy relationship Pa/Pb≦1/2.
According to the method for producing a dust core compact configured as described above, a compact component is formed by subjecting the first soft magnetic powder to pressure forming (hereinafter also referred to as preparatory molding); and thereafter the compact component and the second soft magnetic powder are subjected to pressure forming (hereinafter also referred to as final molding) to mold the second soft magnetic powder and to bond the compact component and the second soft magnetic powder to obtain a compact. Therefore, even when the compact has a complex shape, the compact can easily be formed in that shape with even density.
On this occasion, since the preparatory molding is performed under relatively small pressure Pa satisfying the relationship Pa/Pb≦1/2, the compact component is formed with a gap of a certain degree provided between particles of the first soft magnetic powder. Thereby, particles of the second soft magnetic powder can be introduced into the gap by performing the final molding under relatively large pressure Pb satisfying the above relationship. In addition, since the second soft magnetic powder has relatively small average particle diameter Db satisfying the relationship Da/Db≧2, the particles of the second soft magnetic powder can easily be introduced into between the particles of the first soft magnetic powder. Consequently, the compact can be formed with the first and second soft magnetic powders intricately engaging with each other at a boundary position therebetween, thereby exhibiting excellent strength.
Preferably, the step of forming the compact component includes the step of forming the compact component by pressure-forming the first soft magnetic powder under pressure Pa of not more than 400 MPa. According to the method for producing a dust core compact configured as described above, the preparatory molding can be performed with a larger gap provided between the particles of the first soft magnetic powder. Thereby, the compact obtained by the final molding can exhibit a further improved strength.
Preferably, the step of forming the compact component includes the step of forming the compact component such that a surface thereof to be bonded to the second soft magnetic powder is shaped to have recesses and projections. According to the method for producing a dust core compact configured as described above, a contact area between the compact component and the second soft magnetic powder can be increased in the final molding. Thereby, the first and second soft magnetic powders can engage with each other more intricately, further improving the strength of the compact.
Further, the first and second soft magnetic powders each include a plurality of metal magnetic particles and an insulating coating film surrounding a surface of each of the plurality of metal magnetic particles. In the method for producing a dust core compact configured as described above, surfaces of the first and second soft magnetic powders are covered with the insulating coating film, and thus metal bonding between the particles cannot be attained when the pressure forming is performed. Consequently, the present invention, which improves the strength of the compact by the effect of physical engagement between the first magnetic powder and the second soft magnetic powder, can be utilized more effectively.
Preferably, the method for producing a dust core compact further includes the step of heat-treating the compact at a temperature of not less than 200° C. and not more than 500° C. after the step of forming the compact. According to the method for producing a dust core compact configured as described above, the heat treatment of the compact at a temperature of not less than 200° C. can eliminate an interface between the insulating coating films bonded to each other by the pressure forming, and thus the compact can exhibit a further improved strength. In addition, by setting the temperature for the heat treatment at not more than 500° C., insulation breakdown of the insulating coating film by heat can be suppressed. Thereby, the insulating coating film can sufficiently serve as an insulating layer between the metal magnetic particles.
A dust core compact according to the present invention is a dust core compact fabricated using any of the methods for producing a dust core compact described above. In the dust core compact, the particles constituting the second soft magnetic powder engage the particles constituting the first soft magnetic powder at a boundary position between the first soft magnetic powder and the second soft magnetic powder. According to the dust core compact configured as described above, the dust core compact has a structure in which the particles of the first and second soft magnetic powders engage with each other at the boundary position therebetween, and thus excellent bond strength can be achieved at that position.
As described above, according to the present invention, a method for producing a dust core compact exhibiting a high strength and capable of being fabricated even when it has a complex shape, and the dust core compact can be provided.
21, 31 soft magnetic powder, 22 compact component, 41 compact.
Embodiments of the present invention will be described with reference to the drawings.
Referring to
The metal magnetic particle is made of, for example, iron (Fe), an iron (Fe)-silicon (Si) based alloy, an iron (Fe)-nitrogen (N) based alloy, an iron (Fe)-nickel (Ni) based alloy, an iron (Fe)-carbon (C) based alloy, an iron (Fe)-boron (B) based alloy, an iron (Fe)-cobalt (Co) based alloy, an iron (Fe)-phosphorus (P) based alloy, an iron (Fe)-nickel (Ni)-cobalt (Co) based alloy, and an iron (Fe)-aluminum (Al)-silicon (Si) based alloy. The metal magnetic particle may be made of a single metal, or may be an alloy.
The insulating coating film is formed by treating the metal magnetic particle with phosphoric acid. Further, the insulating coating film preferably contains an oxide. As the insulating coating film containing an oxide, an oxide insulator can be used, such as iron phosphate containing phosphorus and iron, manganese phosphate, zinc phosphate, calcium phosphate, silicon oxide, titanium oxide, aluminum oxide, or zirconia oxide. The insulating coating film may cover the metal magnetic particle in one layer, or in multiple layers.
The insulating coating film serves as an insulating layer between the metal magnetic particles. By covering the metal magnetic particle with the insulating coating film, the dust core to be obtained can have an increased electric resistivity ρ. This can suppress eddy current from flowing between the metal magnetic particles, and reduce core loss of the dust core due to occurrence of the eddy current.
Next, prepared soft magnetic powder 21 is filled into a die 10 of a molding apparatus and pressure-formed under a pressure Pa (a preparatory molding step). On this occasion, pressure Pa is preferably not more than 400 MPa. Further, the pressure forming is preferably performed in an inert gas atmosphere or a reduced-pressure atmosphere, which can suppress soft magnetic powder 21 from being oxidized by oxygen in the atmosphere. Referring to
Referring to
Referring to
Further, since pressure Pb satisfies the relationship described above relative to pressure Pa applied during the preparatory molding, the distance between the particles of soft magnetic powder 21 obtained by the preparatory molding is further reduced when the final molding is performed. Thereby, a junction location between compact component 22 and soft magnetic powder 31 can obtain a state where the particles of soft magnetic powders 21 and 31 intricately engage with each other.
Referring to
Finally, compact 41 is appropriately worked by such as extrusion, cutting, or the like, to be completed as the dust core.
The method for producing a dust core compact in the first embodiment of the present invention includes the steps of: forming compact component 22 by pressure-forming soft magnetic powder 21 as the first soft magnetic powder having average particle diameter Da under pressure Pa; and forming compact 41 by pressure-forming soft magnetic powder 31 as the second soft magnetic powder having average particle diameter Db and compact component 22 under pressure Pb. Average particle diameter Da of soft magnetic powder 21 and average particle diameter Db of soft magnetic powder 31 satisfy the relationship Da/Db≧2. Pressures Pa and Pb applied during the pressure forming satisfy the relationship Pa/Pb≦1/2.
According to the method for producing a dust core compact configured as described above, compact 41 having a final shape is fabricated by two molding steps, that is, the preparatory molding step and the final molding step. Therefore, even when compact 41 has a complex shape, that shape can easily be attained. Further, since compact 41 is fabricated by pressure-forming compact component 22 and soft magnetic powder 31 during the final molding, there is no need to use an adhesive or the like. Accordingly, compact 41 has no nonmagnetic layer such as an adhesive therein, and thus a dust core having excellent magnetic properties can be obtained.
Further, by controlling the average particle diameters of soft magnetic powders 21 and 31 and the pressures applied during the preparatory molding and the final molding to satisfy appropriate relationships, the junction location between compact component 22 and soft magnetic powder 31 can obtain the state where the particles of soft magnetic powders 21 and 31 intricately engage with each other. Thereby, both powders are firmly bonded, and excellent bond strength can be achieved.
The method for producing a dust core compact in the present embodiment can be used to fabricate a dust core, a choke coil, a switching power supply element, a magnetic head, various types of motor components, a solenoid for automobile, various types of magnetic sensors and electromagnetic valves, and the like. Further, without being limited to these magnetic components, the method can also be used to subject such as iron powder having no insulating coating film to pressure forming to fabricate a mechanical component.
Referring to
The method for producing a dust core compact in accordance with the present invention was evaluated by an example described below.
Iron powder coated with phosphate manufactured by Hoeganaes Japan K.K. (product name: “Somaloy 550”, average particle diameter Da=265 μm) was prepared as soft magnetic powder 21. Further, iron powder coated with phosphate manufactured by Hoeganaes Japan K.K. (product name: “Somaloy 500”, average particle diameter: 110 μm) was classified using sieves to prepare samples A to C of the iron powder coated with phosphate, having different average particle diameters, as soft magnetic powder 31. On this occasion, the classification was performed using sieves with a mesh size of 200 mesh, 147 mesh, and 80 mesh. Average particle diameters Db of samples A to C of the iron powder coated with phosphate were measured by laser scattering and diffraction, using Microtrac (manufactured by Nikkiso Co., Ltd.). Table 1 shows average particle diameter Db for each sample obtained by the measurement, and a value of Da/Db.
Next, the preparatory molding step and the final molding step were performed in accordance with the procedure described below, using a molding apparatus having a cylindrical pressurizing space with a diameter of 20 mm. Firstly, an appropriate die lubricant was applied on the inner wall of a die in the molding apparatus, and the iron powder coated with phosphate “Somaloy 550” as soft magnetic powder 21 was filled into the pressurizing space. Thereafter, pressure forming was performed with applied pressure Pa changed in the range between 1 ton/cm2 and 12 ton/cm2 to fabricate a plurality of compact components 22 molded under different applied pressures (the preparatory molding step).
Next, samples A to C of the iron powder coated with phosphate “Somaloy 500” as soft magnetic powder 31 were filled upon the obtained compact component 22. Thereafter, pressure forming was performed under applied pressure Pb of 12 ton/cm2 to prepare compact 41 (the final molding step). On this occasion, there were some cases where bonding between compact component 22 and samples A to C of the iron powder coated with phosphate was not achieved depending on the combination thereof.
Further, iron powder manufactured by Hoeganaes Japan K.K. (product name: “ABC100. 30”, average particle diameter Da=110 μm, having no insulating coating film) was prepared. This powder was also classified using sieves to prepare sample D of the iron powder as soft magnetic powder 21 and sample E of the iron powder as soft magnetic powder 31 having different particle diameters. On this occasion, sample D of the iron powder was obtained by the classification using a sieve with a mesh size of 115 mesh (124 μm), and sample E of the iron powder was obtained by the classification using a sieve with a mesh size of 200 mesh (74 μm). Average particle diameter Da of sample D of the iron powder and average particle diameter Db of sample E of the iron powder were measured by laser scattering and diffraction, using Microtrac (manufactured by Nikkiso Co., Ltd.). Table 2 shows average particle diameter Da of sample D and average particle diameter Db of sample E obtained by the measurement, along with a value of Da/Db.
Next, the preparatory molding step described above was performed using sample D of the iron powder (average particle diameter Da=138 μm) prepared as soft magnetic powder 21 to fabricate a plurality of compact components 22 molded under different applied pressures. Further, the final molding step described above was performed using sample E of the iron powder (average particle diameter Db=58 μm) prepared as soft magnetic powder 31 to fabricate compact 41.
As can be seen in
It should be understood that the disclosed embodiments and example above are, in all respects, by way of illustration only and are not by way of limitation. The scope of the present invention is set forth by the claims rather than the above description, and is intended to cover all the modifications within a spirit and scope equivalent to those of the claims.
The present invention is mainly utilized for manufacturing magnetic components such as a dust core, a choke coil, a switching power supply element, a magnetic head, various types of motor components, a solenoid for automobile, various types of magnetic sensors and electromagnetic valves, as well as manufacturing mechanical components.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-273522 | Sep 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/17126 | 9/16/2005 | WO | 00 | 3/21/2007 |
