JP2009164401A - Manufacturing method of dust core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust core which has high magnetic permeability and excellent DC superposition characteristics. <P>SOLUTION: Disclosed is the manufacturing method of the dust core in which metal magnetic particles are compression-molded, the manufacturing method of the dust core being characterized in that the metal magnetic particles are made of two kind of metal magnetic particles A and B differing in material and mean particle diameter, wherein the ratio of the mean particle diameters of the two kind of metal magnetic particles is 1:0.15 to 1:0.22 and the metal magnetic particles A have larger yield stress than the metal magnetic particles B. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a dust core. The dust core obtained by this manufacturing method is useful as a magnetic component used for a high-frequency transformer, a reactor, an inductor and the like mounted on a switching power supply.

  In recent years, various electronic devices have been reduced in size and weight, and reduction in power consumption has been demanded. Along with this, there is an increasing demand for miniaturization of switching power supplies mounted on electronic devices. In particular, switching power supplies used in notebook personal computers, small portable devices, thin CRTs, and flat panel displays are strongly required to be small and thin. However, in conventional switching power supplies, magnetic components such as transformers and reactors, which are main components, occupy a large volume, and there has been a limit to downsizing and thinning. Unless the volume of these magnetic components is reduced in size and thickness, it has been difficult to reduce the size and thickness of the switching power supply.

  Conventionally, in magnetic parts such as transformers and reactors used in such switching power supplies, metal magnetic materials such as sendust and permalloy, and oxide magnetic materials such as ferrite have been used as cores, that is, dust cores. .

  Metallic magnetic materials generally have a high saturation magnetic flux density and magnetic permeability, but have low electrical resistivity, so hysteresis loss and eddy current loss are particularly large in the high frequency region. Switching power supplies tend to be highly efficient and miniaturized by driving the circuit at a high frequency. However, it is difficult to use metallic magnetic materials for magnetic parts for switching power supplies due to the effects of eddy current loss. It was.

  On the other hand, an oxide magnetic material typified by ferrite has a higher electrical resistivity than a metal magnetic material, and therefore, an eddy current loss generated even in a high frequency region is small. However, when the transformer or the reactor is downsized, the magnetic field applied to the magnetic core becomes strong even if the current flowing through the coil is the same. In general, the saturation magnetic flux density of ferrite is smaller than that of a metal magnetic material, and when used as a magnetic component of a switching power supply, there is a limit to downsizing for the above reasons.

  As described above, with any conventional magnetic component, it has been difficult to satisfy both high frequency driving and miniaturization required for the magnetic component of the switching power supply, regardless of which material is used.

In recent years, various studies have been made to improve the low resistivity, which has a trade-off relationship, with respect to the above-described powder magnetic core material, which has a high saturation magnetic flux density and high magnetic permeability. For example, a dust core using particles formed with a coating film or particles of an oxide material having a high electrical resistivity, and a dust core made of a mixture of metal magnetic powder and a binder having high electrical insulation have been proposed (for example, , See Patent Literatures 1 to 6.)
According to these methods, the eddy current can be suppressed by increasing the electrical resistivity due to the effect of the nonmagnetic insulating film. That is, it can be used even in a high frequency band such as the MHz band.

That is, in Patent Document 1, the surface of the metallic magnetic material consisting of 1~10μm particles M-Fe _x O ₄ (where M = Ni, Mn, Zn, x ≦ 2) metal oxide represented by the spinel composition by A high-density sintered magnetic body that is coated with a magnetic material has been proposed.

  Further, in Patent Document 2, a ferromagnetic fine particle powder of a metal or an intermetallic compound having a ferrite layer coating formed by ultrasonic excitation ferrite plating on the surface is compression-molded, and the ferromagnetic material is passed through the ferrite layer. A composite magnetic material characterized in that a magnetic path is formed in a particle is proposed.

  In Patent Document 3, as a method for obtaining a soft magnetic molded body having a high density and a high specific resistance, soft magnetic metal particles, a high resistance material coated on the surface thereof, and a surface of the high resistance material There has been proposed a soft magnetic particle characterized in that it is composed of a phosphoric acid-based chemical conversion coating coated on the surface.

  In Patent Document 4, a method of using a powder obtained by coating a soft magnetic metal particle with a highly insulating oxide powder (titania, silica, alumina, etc.), or mechanically repeating compression and shearing action on such powder. A method using a surface-fused powder to be loaded, and a method using a surface-fused powder obtained by mixing soft magnetic metal particles and an oxide powder have been proposed.

  In addition, the switching power supply circuit is required to have excellent direct current superposition characteristics. However, Patent Document 7 discloses a method of manufacturing a dust core that exhibits good direct current superposition characteristics using a metal magnetic material. Proposed. In other words, Sendust (Fe-Si-Al) alloy particles are flattened, shape anisotropy is developed, hard magnetization axes in the particles are generated in a direction perpendicular to the plane of the flat particles, and compressed while being oriented by a magnetic field. Molding and obtaining a powder magnetic core having a high demagnetizing field type in the magnetic path direction of the magnetic core. This suppresses saturation of the magnetic flux density against direct current excitation, provides no dust core, and provides a dust core with excellent direct current superposition characteristics to prevent coil current from increasing. There is an aim to do.

  Patent Documents 8 and 9 describe the production of a dust core using magnetic particles whose particle size distribution is changed so that the magnetic particles in the dust core are closely packed to improve the filling rate of the magnetic particles. A method has been proposed. That is, the surface of the Fe-Co based metal magnetic particle is coated with ferrite or coated with SiO2 fine particles to improve the electrical resistance, and the magnetic particle itself has two different particle size distributions. A technique for increasing the filling rate of magnetic particles in a powder magnetic core has been proposed.

  In Patent Document 10, two or more kinds of magnetic powders with different yield stresses of 1.5 times or more are mixed and molded at 200 MPa or more, so that the powder with small yield stress can be plastically deformed to increase the powder density. An inductor is disclosed.

JP-A-56-38402 WO03 / 015109 pamphlet JP 2001-85211 A JP 2003-332116 A JP 2003-303711 A JP 2001-307914 A JP 2001-68365 A JP 2003-306703 A Japanese Patent Laying-Open No. 2005-167097 JP 2006-294733 A Introduction to Powder Engineering by Shigeo Miwa, First Edition (published by Nikkan Kogyo Shimbun) p39-42

  However, in the manufacturing method of the dust core disclosed in Patent Documents 1 and 2 described above, there is a trade-off relationship between the improvement of the magnetic permeability and the improvement of the electric resistivity. A material that cannot be used and has a high resistivity has a permeability of about several tens to 80, and there is a problem that a high permeability cannot be obtained.

In addition, the method for producing a powder magnetic core disclosed in Patent Documents 3 to 6 uses a phosphoric acid-based chemical conversion coating film, a suspension containing SiO ₂ fine particles, a highly insulating silica-based binder, and the like. When the particles are mixed, a wet insulating film forming method is used in which a film is formed using a slurry-like treatment liquid. Although this insulation film formation method can increase the electrical resistance of the dust core, it is inferior in heat resistance and cannot be subjected to heat treatment at a temperature as high as necessary to remove the molding distortion of the particles. Cannot be improved. In addition, there is a possibility that chemical reaction with impurities in the particle mixture and corrosion of magnetic particles may occur, and there are disadvantages such as low strength and high production cost. For this reason, it can be said that the obtained dust core is difficult to apply to magnetic parts.

  For example, when Fe—Ni-based metal particles (untreated state, hereinafter referred to as “bare particles”) are pressed at a filling rate of 95% or more, the magnetic permeability is about 100 in the state after pressing. By heat-treating this material, the magnetic permeability can be improved to about 1000. However, in the case of bare particles, the resistivity decreases to almost the metal crystal level due to diffusion bonding at the interface between the particles, and the level is several tens of kHz. It can be used only in the frequency band up to.

Therefore, the use of particles formed of SiO ₂ coating with a bare particles of water glass method, resistivity after pressing exhibit greater resistivity and 1～100Omucm, permeability is about 30 to 70, higher Magnetic permeability cannot be obtained. When heat treatment at 600 to 1000 ° C. is performed to release the strain generated in the soft magnetic metal particles during press and increase the magnetic permeability, the magnetic permeability increases, but the resistivity decreases due to the breakdown of the insulating coating, and the frequency characteristics Has the disadvantage of getting worse. This is due to the fact that the metal magnetic particles and the insulating coating are interdiffused and the insulating properties of the insulating coating are significantly reduced. On the other hand, the permeability does not increase unless mutual diffusion occurs.

  Moreover, in the manufacturing method of the powder magnetic core currently disclosed by patent document 7, there exists a subject in the cost at the time of particle processing and compression molding, and shape controllability, and it is unpreferable on production. In addition, Sendust alloy particles are generally hard, the particles themselves are poorly deformable, and if a large amount of binder is not used, the compactability of the powder compact itself is poor, so the filling rate deteriorates and it is difficult to improve the magnetic properties. .

  Moreover, in the manufacturing method of the powder magnetic core currently disclosed by patent document 8, 9, the particle | grains from which a particle size differs consist of the same composition. That is, since all the particles have the same hardness, if pressure is applied until close-packing is obtained during molding, there is no escape of force, so a large stress is applied to all particles, and high temperature is used to eliminate the molding distortion that occurs due to this stress. Heat treatment at is required. Further, even if the metal magnetic particles have an insulating coating on the surface, the insulating coating has a problem that it is easily broken due to the stress.

  If the heat treatment is performed at a temperature of about 1,000 ° C., a high magnetic permeability can be obtained, but the high frequency characteristics are poor and it is difficult to apply to high frequency devices such as inductors. In addition, the granulation process and the molding process are complicated, resulting in poor productivity and high production costs.

  As described above, in any of the above methods, there is a trade-off relationship between magnetic permeability improvement and electrical resistivity improvement. This is related to the fact that generally spherical particles are used as the insulating coated magnetic particles used. In other words, if the magnetic particles are spherical, the demagnetizing field between the particles and the porosity between the particles are large, so the magnetic permeability does not increase, or heat treatment is performed to reduce the demagnetizing field and the insulation coating and the magnetic particles If they are interdiffused, the resistivity will decrease.

  On the other hand, when flat particles are used as magnetic particles, the demagnetizing field increases in the direction perpendicular to the flat surface and decreases in the horizontal direction, so there is a possibility that the permeability can be increased without mutual diffusion. . However, the flat direction of these flat particles is in various directions when placed in a mold. If this is pressed as it is, the direction of all particles cannot be completely controlled, such as making the flat surface horizontal or perpendicular to the direction of the magnetic field, and in the end, only the characteristics at the same level as when using spherical particles are used. I can't get it.

  In addition, in the method of manufacturing a powder magnetic core disclosed in Patent Document 10, although the numerical values related to the examples are given for the particle size ratio and mixing ratio of the two types of magnetic powder, an appropriate particle size ratio and mixing It is not shown how to determine the ratio. If the particle size ratio and the mixing ratio are not appropriate, the following problems occur. (Regarding the mixing ratio, Table 2.4 of Non-Patent Document 1 shows the Hudson filling porosity for two types of spheres.)

  That is, if the number of particles having a small yield stress is small, the filling rate cannot be increased unless the particles having a large yield stress are plastically deformed. If there are too many particles with a small yield stress, it is necessary to plastically deform to particles with a small yield stress. If the particle size ratio is inappropriate, the filling rate before pressurization is low, so it is necessary to place many particles with low yield stress in the gaps between particles with large yield stress. However, there is a problem that excessive pressure is applied to bring the particles into the gap, or particles that do not reach the gap come out and the final filling rate cannot be increased.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a dust core having high magnetic permeability and good DC superposition characteristics.

  That is, the method for producing a dust core of the present invention is a method for producing a dust core in which metal magnetic particles are compression-molded. The metal magnetic particles are made of two types of metal magnetic particles A and B having different materials and average particle sizes. The ratio of the average particle diameter of the two types of metal magnetic particles is 1: 0.15 to 1: 0.22, and the metal magnetic particles A having a large average particle diameter have a low yield stress. It is characterized by being larger than the yield stress of the magnetic particles B.

  According to the present invention, it is possible to obtain a powder magnetic core with a highly increased filling rate of magnetic particles, a high magnetic permeability, a high magnetic permeability particularly in a high frequency band, and an excellent DC superposition characteristic. A powder magnetic core can be provided.

  The method for producing a dust core of the present invention uses two types of metal magnetic particles A and B. The metal magnetic particles include soft iron, Fe-Si alloys, Fe-Si-Al alloys (Sendust, etc.), Fe-Ni alloys (Permalloy, Supermalloy, etc.), Fe-Co alloys, etc. A magnetic material can be mentioned. In the present invention, two types of soft ferromagnets having different yield stresses are selected from these, and the average particle diameter of the metal magnetic particles (A) having the larger yield stress is selected from that of the other metal magnetic particles (B). Larger than that. The difference in yield stress is determined by measuring the particle filling rate of the molded body when each metal particle is press-molded alone, thereby determining the degree of difficulty of plastic deformation of the metal particles, that is, the magnitude of the yield stress. be able to.

  The ratio of the average particle diameter of the metal magnetic particles A and B is 1: 0.15 to 1: 0.22. By making the ratio of the average particle diameters in this way, the particles B enter the gaps between the particles A even before pressurization (before plastic deformation), and the amount of the particles B existing in the gaps between the particles A is reduced. It is possible to reduce the pressure at the time of compacting and to increase the filling rate after pressurization.

  These metal magnetic particles A and B are mixed so as to be as uniform as possible, and the mixture is compression-molded to form a dust core. The mixing ratio of the metal magnetic particles A and B is preferably 1: 0.35 or the amount of the metal magnetic particles B is larger than this. This is because it is known that the porosity when close-packed using only particles of the same particle size is 0.2595, so the voids formed during the close-packing of metal magnetic particles A The volume ratio of A and B is set to (1-0.2595): 0.2595≈1: 0.35 with the intention of filling with metal magnetic particles B, or the amount of metal magnetic particles B is I tried to make it a lot.

  As a compression molding method, using a mold, for example, uniaxial compression molding that compresses and compresses in the vertical direction, compression rolling molding, soft magnetic particles having an electrically insulating nonmagnetic coating are packed in a rubber mold and the like from all directions. Hydrostatic compression molding that compresses and compresses, warm uniaxial compression molding that performs these in warm, warm hydrostatic compression molding (WIP), hot uniaxial compression molding that performs hot, and hot hydrostatic compression molding ( Any compression molding method generally employed for compression molding of oxide-coated metal magnetic particles such as HIP) can be employed.

  In the present invention, it is preferable to heat-treat the obtained green compact. Molding distortion of the dust core molded by heat treatment disappears, the permeability is improved, the permeability is high (μ ′ (the real part of the permeability) is large), and the loss is small (μ ” (A small imaginary part of magnetic permeability) can be obtained.The maximum temperature of the heat treatment is preferably 400 to 700 ° C. If the maximum temperature of the heat treatment is high, the distortion of the particles can be removed. However, μ ′ can be raised, but since the resistivity also decreases due to diffusion between particles, an optimum temperature may be set from the necessary values of μ ′ and ρ (resistivity).

  The atmosphere during the heat treatment is preferably performed under an inert gas atmosphere such as nitrogen or argon or under vacuum in order to prevent oxidation of particles.

  From the viewpoint of improving the high frequency characteristics, it is preferable that an insulating coating is formed on the surface of the metal magnetic particles. This insulating coating is preferably made of a metal oxide. If a coating is provided, the occupancy of the magnetic material is reduced by that amount, and the magnetic permeability is reduced. Therefore, it is preferable that the insulating coating is thin. In view of the balance between high frequency characteristics and magnetic permeability, the thickness of the insulating coating is preferably 5 to 30 nm. It is preferable that this insulating coating adheres uniformly to the surface of the metal magnetic particles.

  The insulating film can be formed by a wet film forming method, but may be a film (dry insulating film) formed by a dry film forming method. According to the dry film forming method, the coating material is not made into a slurry as in the wet method, so that it is possible to prevent contamination with impurities, nonuniformity, composition change, and corrosion due to halogen ions.

  Examples of the dry film forming method include a vapor deposition method, a sputtering method, an ablation method, a mechanofusion method, and the like, and any method can be used.

<Example 1>
1 to 5 schematically show the steps of this example. First, as shown in FIG. 1, substantially spherical metal magnetic particles 11 made of cobalt iron (Fe—Co alloy, weight ratio 50:50), which is an Fe—Co alloy formed by a water atomization method, are classified by sieving. Then, only particles (metal magnetic particles A) having an average particle diameter of 8 μm were extracted. Next, the substantially spherical metal magnetic particles 12 made of supermalloy (Fe—Ni—Mo alloy, weight ratio 17: 78: 5), which is an Fe—Ni alloy formed by the water atomization method, are classified by sieving, Only particles having an average particle diameter of 1.4 μm (metal magnetic particles B) were extracted. Here, the yield stress of the metal magnetic particles B is smaller than the yield stress of the metal magnetic particles A, and the metal magnetic particles B are more easily plastically deformed.

  Since 1.4 μm / 8 μm = 0.175, the particle size ratio 8 μm: 0.14 μm between the metal magnetic particles A and the metal magnetic particles B is close to 1: 0.1716. This is a particle size ratio for closest packing of particles calculated from a theoretical formula for the ideal model. According to the calculation results of Hudson shown in Non-Patent Document 1 (considering up to secondary particles), the packing bulk density is highest when the ratio is 1: 0.1716, and a value close to 90% is obtained. It is. However, considering that good magnetic properties can be obtained if the filling rate is 85% or more (porosity 15% or less), a porosity of 15% or less is obtained in Table 2.4 of Non-Patent Document 1: The particle size ratio may be in the range of 0.15 to 1: 0.22.

Next, as shown in FIG. 2, the metal magnetic particles A11 and the metal magnetic particles B12 having different average particle diameters are mixed and stirred by a mixer. In this example, the automatic mortar 13 was used and stirred / mixed for 20 minutes. The mixing ratio (volume ratio) of metal magnetic particles A11 and metal magnetic particles B12 is 1: 0.35 so that the number of metal magnetic particles B is slightly larger, and a predetermined amount is set in consideration of the density of each particle. Weighed.
Regarding the mixing time, if it was too long, the mixed powder could be separated or plastically deformed, so it was kept in the tens of minutes.

  Next, as shown in FIG. 3, the mixed particles are put into a ring core molding die 14, and vibration is applied to the die containing the mixed particles, whereby metal magnetic particles are formed in the gaps between the metal magnetic particles A <b> 11. Packed so that particle B12 was present.

Next, as shown in FIG. 4, it was molded into a ring core shape having an inner diameter of 3 mmφ, an outer diameter of 8 mmφ, and a height of about 3 mm by uniaxial pressing of 1177 MPa (12 ton / cm ² ).
The obtained ring core is shown in FIG. 5 (a), and the particle filling state is shown in FIG. 5 (b). As can be seen in FIG. 5B, the particle filling rate in the molded body is significantly improved from about 90% in the case of molding using particles having a single particle size.

  Next, this ring core compact was put in an electric muffle furnace and heat-treated under conditions of a maximum temperature of 500 ° C. and a heat treatment time (holding time at the maximum temperature) of 2 hours. In order to prevent the oxidation of the particles, the atmosphere was vacuum (vacuum degree 0.001 Pa).

  The effective permeability μ ′ of the complex permeability μ = μ ′ + iμ ″ measured by the BH analyzer in the frequency region of 1 kHz to 10 MHz is wound around the ring core for 5 turns. 21 and the DC superposition characteristics thereof are shown in FIG.

<Comparative Example 1>
A similar ring core was molded and heat-treated in the same manner as in Example 1 except that only the metal magnetic particles A11 were used as the metal magnetic particles. The primary and secondary windings are wound around the obtained ring core for 5 turns, respectively, and the effective permeability μ ′ of the complex permeability μ = μ ′ + iμ ″ measured in the frequency region of 1 kHz to 10 MHz with a BH analyzer is obtained. This is indicated by 22 in FIG. 6 and its DC superposition characteristics are indicated by 26 in FIG.

<Comparative example 2>
A similar ring core was formed and heat-treated in the same manner as in Example 1 except that only the metal magnetic particle B12 was used as the metal magnetic particle. The primary and secondary windings are wound around the obtained ring core for 5 turns, respectively, and the effective permeability μ ′ of the complex permeability μ = μ ′ + iμ ″ measured in the frequency region of 1 kHz to 10 MHz with a BH analyzer is obtained. This is indicated by 23 in FIG. 6 and its DC superposition characteristics are indicated by 27 in FIG.

<Comparative Example 3>
A mixed particle was obtained in the same manner as in Example 1 except that the average particle diameter of the metal magnetic particle 11 made of cobalt iron and the metal magnetic particle 12 made of supermalloy was the same 8 μm, and a ring core was formed using this mixed particle. Heat treated. The primary and secondary windings are wound around the obtained ring core for 5 turns, respectively, and the effective permeability μ ′ of the complex permeability μ = μ ′ + iμ ″ measured in the frequency region of 1 kHz to 10 MHz with a BH analyzer is obtained. The direct current superimposition characteristics are shown at 24 in FIG. 6 and at 28 in FIG.

  As is apparent from FIG. 6, the initial permeability of the ring core of Comparative Example 1 is as low as about 80, and the initial permeability of the ring core of Comparative Example 3 is as low as about 160. The initial permeability of the ring core of Comparative Example 2 is about 220. In Comparative Examples 1 and 2, the magnetic permeability starts to decrease from about 20 kHz. Regarding the DC superposition characteristics, as shown in FIG. 7, the ring core of Comparative Example 1 maintains the initial value up to about 2000 A / m because the saturation magnetic flux density of the Fe—Co alloy is large. Magnetic susceptibility is as low as about 80. In the ring core of Comparative Example 2, the initial value of the magnetic permeability is high, but since the saturation magnetic flux density is small, the magnetic permeability rapidly decreases as the superimposed magnetic field increases. The ring core of Comparative Example 3 is excellent in DC superposition characteristics, but the magnetic permeability is not high enough. On the other hand, the filling rate of the ring core of Example 1 is improved, so that the initial value of the magnetic permeability is improved to about 180, and the direct current superposition characteristics are excellent.

<Example 2>
The same metal magnetic particles A11 and metal magnetic particles B12 as in Example 1 were obtained. In this example, an SiO ₂ film was formed on the surfaces of both the metal magnetic particles A11 and the metal magnetic particles B12 using a water glass method so that the average film thickness was 10 nm. That is, soft magnetic metal particles are put into an aqueous solution in which water glass having a composition of Na ₂ O.xSiO ₂ .nH ₂ O (x = 2 to 4) (the aqueous solution of this water glass shows alkalinity) is dissolved in water. Was added to the solution and hydrolyzed by controlling the pH to attach gel-like silicic acid (H ₂ SiO ₃ ) to the surface of the soft magnetic metal particles. Thereafter, the SiO ₂ film was formed by drying the soft magnetic metal particles. The film thickness of the SiO ₂ film was controlled to 20 nm by adjusting the concentration of the water glass aqueous solution.

  A ring core was formed and heat-treated in the same manner as in Example 1 except that these particles were used as the metal magnetic particles A and B. The resistivity at this time was 10 Ωcm.

  The effective permeability μ ′ of the complex permeability μ = μ ′ + iμ ″ measured in the frequency range of 1 kHz to 10 MHz with the BH analyzer by winding the primary and secondary windings 5 turns on this ring core is shown in FIG. 31.

<Comparative example 4>
An insulating film is formed on the surface in the same manner as in Example 2 except that only the metal magnetic particles A11 are used as the metal magnetic particles, and the same method as in Example 2 except that this metal magnetic particle having an insulating film is used. A ring core was molded and heat treated. The primary and secondary windings are wound around the obtained ring core for 5 turns, respectively, and the effective permeability μ ′ of the complex permeability μ = μ ′ + iμ ″ measured in the frequency region of 1 kHz to 10 MHz with a BH analyzer is obtained. It is shown at 32 in FIG.

<Comparative Example 5>
An insulating film is formed on the surface in the same manner as in Example 2 except that only the metal magnetic particles B12 are used as the metal magnetic particles, and the same manner as in Example 2 except that this metal magnetic particle having an insulating film is used. A ring core was molded and heat treated. The primary and secondary windings are wound around the obtained ring core for 5 turns, respectively, and the effective permeability μ ′ of the complex permeability μ = μ ′ + iμ ″ measured in the frequency region of 1 kHz to 10 MHz with a BH analyzer is obtained. This is shown at 33 in FIG.

<Comparative Example 6>
A mixed particle was obtained in the same manner as in Example 1 except that the average particle diameter of the metal magnetic particle 11 made of cobalt iron and the metal magnetic particle 12 made of supermalloy was the same 8 μm, and a ring core was formed using this mixed particle. Heat treated. The primary and secondary windings are wound around the obtained ring core for 5 turns, respectively, and the effective permeability μ ′ of the complex permeability μ = μ ′ + iμ ″ measured in the frequency region of 1 kHz to 10 MHz with a BH analyzer is obtained. It is shown at 34 in FIG.

  The ring cores of Example 2 and Comparative Examples 4 to 6, which are dust cores using metal magnetic particles having an insulating coating, are excellent in high frequency characteristics because they do not decrease on the high frequency side. The ring core of Example 2 has a permeability of about 30 or 50, and the ring core of Comparative Example 6 has a low permeability of about 45, whereas the permeability of the ring core of Example 2 is about 90, and can maintain a high permeability up to a high frequency band. It can be seen that was obtained by this example.

  As is clear from the above results, according to the present invention, magnetic metal particles having different particle sizes and yield stresses can be mixed and used so that the magnetic particles can be filled at a high filling rate, and the pressure can be reliably increased. It is possible to increase the permeability of the powder magnetic core, improve the high frequency characteristics, and the DC superposition characteristics. Moreover, if an insulating coating is provided on the metal magnetic particles, a dust core having a higher resistivity can be obtained.

  The dust core according to the present invention can be used as a core material for inductors and transformers. Compared to a conventional ferrite core material, the same magnetic core can be obtained with a small volume, miniaturization and thinning. It becomes possible. As a result, it is possible to make an unprecedented small and thin inductor and transformer and a switching power supply using them as a power source for a notebook personal computer, a small portable device, a thin CRT, a television and the like.

In the process schematic diagram of Example 1, it is a figure which shows the process of obtaining the particle | grains of a predetermined particle diameter by classification. In the process schematic diagram of Example 1, it is a figure which shows the process of mixing and stirring metal magnetic particle A11 and metal magnetic particle B12 from which average particle diameter differs with a mixer. In the process schematic diagram of Example 1, it is a figure which shows the state which put the said mixed particle in the metal mold | die 14. FIG. It is a figure which shows a compression process among the process schematic diagrams of Example 1. FIG. In the process schematic diagram of Example 1, it is a figure which shows the shape | molded powder magnetic core (a) and its particle | grain filling condition (b). It is a figure which shows the frequency characteristic of the magnetic permeability of the ring core obtained in Example 1 and Comparative Examples 1-3. It is a figure which shows the direct current | flow superimposition characteristic of the magnetic permeability of the ring core obtained in Example 1 and Comparative Examples 1-3. It is a figure which shows the frequency characteristic of the magnetic permeability of the ring core obtained in Example 2 and Comparative Examples 4-6.

Explanation of symbols

11 Metal Magnetic Particle A
12 Metal Magnetic Particle B
13 Automatic Mortar 14 Mold 21 Permeability-Frequency Curve of Ring Core of Example 1 22 Permeability-Frequency Curve of Ring Core of Comparative Example 23 Permeability-Frequency Curve of Ring Core of Comparative Example 24 24 Permeation of Ring Core of Comparative Example 3 Magnetic permeability-frequency curve 25 Magnetic permeability-DC magnetic field curve of the ring core of Example 1 26 Magnetic permeability-DC magnetic field curve of the ring core of Comparative Example 27 Magnetic permeability-DC magnetic field curve of the ring core of Comparative Example 28 28 of the ring core of Comparative Example 3 Permeability-DC magnetic field curve 31 Permeability-frequency curve of the ring core of Example 2 32 Permeability-frequency curve of the ring core of Comparative Example 4 33 Permeability-frequency curve of the ring core of Comparative Example 34 34 Permeation of the ring core of Comparative Example 6 Magnetic susceptibility-frequency curve

Claims (2)

  In the method of manufacturing a powder magnetic core in which metal magnetic particles are compression-molded, the metal magnetic particles are composed of two types of metal magnetic particles A and B having different materials and average particle sizes, and the average particle of the two types of metal magnetic particles The ratio of diameters is 1: 0.15 to 1: 0.22, and the yield stress of the metal magnetic particles A having a large average particle diameter is larger than the yield stress of the metal magnetic particles B having a small average particle diameter. Manufacturing method of a dust core.   2. The method of manufacturing a dust core according to claim 1, wherein an insulating coating is formed on the surface of the metal magnetic particles A.

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