JP7253202B2 - A method for producing a powder magnetic core, in which soft magnetic flat powder is insulated with a group of aluminum oxide fine particles, and the soft magnetic flat powder is bonded by friction bonding of the aluminum oxide fine particles. - Google Patents

Description

The present invention deposits a collection of fine crystals of an aluminum compound that deposits aluminum oxide by thermal decomposition in an organic compound, deposits the organic compound on the surface of a soft magnetic flat powder made of a metal or alloy, and furthermore, the organic compound is vaporized, the aluminum compound is thermally decomposed, and a group of aluminum oxide fine particles is deposited on the surface of the soft magnetic flat powder. After that, a mass of soft magnetic flat powder is filled into a mold, and the mass of soft magnetic flat powder is compressed by a press machine. When the repulsive force received by the press machine continues to increase, compression by the press machine is stopped. do. As a result, the aluminum oxide fine particles are bonded to the surface of the soft magnetic flat powder by frictional heat, and the aluminum oxide fine particles are bonded to each other by frictional heat, so that the soft magnetic flat powders are bonded to each other, and the soft magnetic flat powder is bonded. A method for manufacturing a powder magnetic core in which a compression-molded body consisting of an assembly is manufactured in a mold. In this manufacturing method, since compression by the pressing machine is stopped immediately before the soft magnetic flat powder is compressed, the soft magnetic flat powder is not plastically deformed. Therefore, the flat soft magnetic powder is not strained during processing, and the annealing treatment for restoring the holding force of the flat soft magnetic powder after forming the compact is unnecessary.

Powder magnetic cores are produced by filling a mass of soft magnetic powder with an insulated surface in a mold and compressing it, and then annealing the compression molded body in order to remove the processing strain of the soft magnetic powder generated during compression. , restores the coercive force of the soft magnetic powder to produce a dust core. Such powder magnetic cores are used as magnetic cores forming stators and rotors in motors, and magnetic cores forming reactors, noise filters, choke coils, and the like in power supply circuits. All of these electrical products are general-purpose products, and it is required that the manufacturing cost of the dust core be low.
In the soft magnetic powder whose surface is insulated, eddy currents are confined inside the soft magnetic powder during operation in an AC magnetic field. That is, eddy currents include eddy currents flowing in the soft magnetic powder and eddy currents flowing in the gaps between the soft magnetic powders. The higher, the lower the eddy currents of the latter. Since the eddy current loss is proportional to the square of the frequency of the alternating magnetic field, the higher the frequency, the greater the effect of reducing the eddy current loss. This eddy current loss results in energy loss during electromagnetic conversion, and this energy loss generates heat in the dust core. Therefore, by insulating the surface of the soft magnetic powder, heat generation of the powder magnetic core is reduced.
In addition, when the soft magnetic powder is compressed, the soft magnetic powder is plastically deformed, and processing distortion of the soft magnetic powder increases the holding force. As a result, the hysteresis loss of the soft magnetic powder increases, this hysteresis loss becomes energy loss during electromagnetic conversion, and this energy loss causes the dust core to generate heat. For this reason, the compression-molded body is annealed to restore the holding power of the soft magnetic powder to reduce the heat generation of the powder magnetic core made of the compression-molded body. Thus, energy loss during electromagnetic conversion consists of eddy current loss and hysteresis loss, and both are collectively referred to as iron loss of the dust core. Since the dust core generates heat due to the iron loss, it is necessary to insulate the soft magnetic powder and to anneal the compact.
By the way, the higher the magnetic permeability of the soft magnetic powder, the easier the soft magnetic powder is magnetized, and the easier the magnetic energy is taken into the dust core. Moreover, the magnetic energy of the magnetized dust core increases as the saturation magnetic flux density of the soft magnetic powder increases. However, there is no soft magnetic powder having both high permeability and high saturation magnetic flux density, and the comparison is relative. On the other hand, most dust cores are used at operating frequencies of 1-500 kHz and operating magnetic flux densities of 0.3-1.3 tesla. Therefore, according to the saturation magnetic flux density in the operating frequency range of the powder magnetic core, a powder magnetic core suitable for electrical products is used. On the other hand, the performance of the dust core depends on the frequency characteristics of the magnetic permeability of the soft magnetic powder and the saturation magnetic flux density of the soft magnetic powder. A method for producing a dust core that can be used as a raw material is preferred.
For example, a cobalt-based amorphous soft magnetic material has a high magnetic permeability but a small saturation magnetic flux density close to that of Mn-Zn ferrite. On the other hand, iron-based amorphous soft magnetic materials have a high saturation magnetic flux density but a low magnetic permeability. Iron powder has the highest saturation magnetic flux density among soft magnetic materials, but the lowest magnetic permeability. Furthermore, among permalloys, which are nickel-iron alloys, an alloy composed of 77% by mass of Ni, 14% by mass of Fe, 5% by mass of Cu, and 4% by mass of Mo has the highest magnetic permeability among the permalloys. The saturation magnetic flux density has an intermediate value of soft magnetic materials. In addition, Sendust (an alloy consisting of 9.6 mass% Fe, 5.6 mass% Si, and other parts Al, registered trademark of Tohoku University), which has the highest magnetic permeability among iron-silicon-aluminum alloys, has a magnetic permeability and saturation and magnetic flux density have intermediate values for soft magnetic materials. Mn-Zn ferrite, which is the cheapest material, has a high magnetic permeability but the lowest saturation magnetic flux density.
In addition to such soft magnetic materials, new thin ribbon materials are being developed by quenching amorphous alloys. For example, an amorphous alloy ribbon obtained by quenching a high-temperature solution composed of, for example, iron as a main component, silicone and boron, and trace amounts of copper and niobium, at a rate of 1,000,000°C/sec. is being developed. This amorphous quench ribbon is a material with relatively high magnetic permeability and saturation magnetic flux density (see Patent Document 1). Further, a thin ribbon made of an amorphous alloy has been developed, which has a magnetic permeability value close to that of sendust and a saturation magnetic flux density value close to that of silicon steel. This material is an alloy of high-concentration iron to which silicon, boron, phosphorus, and copper are added (see Patent Document 2).
On the other hand, among soft magnetic materials, Mn--Zn system ferrite and Ni--Zn system ferrite do not have ductility and malleability, and are brittle materials that are weak against impact, so they form a magnetic core with a sintered body. On the other hand, the volume resistivity of the Mn.Zn ferrite is 1×10 ³ Ω·cm, and the Ni—Zn ferrite is 1×10 ⁶ Ω·cm. Therefore, the eddy current flowing in the sintered body is small. All other soft magnetic materials are conductive metals or alloys, and the eddy current flowing inside the soft magnetic powder is large, so that the soft magnetic powder is insulated and the eddy current is trapped inside the soft magnetic powder. Also, metals or alloys have ductility and malleability, and are elastically and plastically deformed by compressive stress. Therefore, the surface of the soft magnetic powder made of metal or alloy is insulated, and a mass of soft magnetic powder made of metal or alloy with the surface insulated is compressed in a mold to entangle the plastically deformed soft magnetic powder. brings about mechanical strength to the compression molded body to obtain a powder magnetic core. The powder magnetic core in the present invention uses soft magnetic powder made of metal or alloy in order to compress a mass of soft magnetic powder in a mold.

As described above, in manufacturing a powder magnetic core, a mass of soft magnetic powder with an insulated surface is filled in a mold, and the mass of soft magnetic powder is simply compressed in the mold to produce a plastically deformed soft magnetic powder. A powder magnetic core with a certain mechanical strength is produced in a mold by entanglement of magnetic powder. In other words, when a group of soft magnetic powders is simply compressed, the phenomenon of plastic deformation of the soft magnetic powder and the plastic deformation of the soft magnetic powder form voids, and the soft magnetic powder rearranges to fill the voids. phenomena occur. The rearrangement of the soft magnetic powder ends with a relatively small compression pressure, but as the compression pressure increases, the plastic deformation of the soft magnetic powder progresses, the voids in the soft magnetic powder clusters are reduced, and the compression density increases. This increases the magnetic energy of the magnetized dust core. In addition, since the collection of soft magnetic powders has a certain particle size distribution, the soft magnetic powders with different particle sizes undergo plastic deformation at the same time, and the plastically deformed soft magnetic powders with different particle sizes are adjacent to each other. are entangled, and the entanglement of the soft magnetic powders progresses, so that the bonding between the soft magnetic powders progresses and the mechanical strength of the powder magnetic core is realized. Therefore, the powder magnetic core is composed of the soft magnetic powder that has undergone plastic deformation by simply compressing a collection of soft magnetic powder. However, as the plastic deformation of the soft magnetic powder progresses, the processing strain of the soft magnetic powder increases, thereby increasing the holding power of the soft magnetic powder and increasing the hysteresis loss of the soft magnetic powder. This causes the dust core to generate heat. This hysteresis loss is greater than the eddy current loss in the soft magnetic powder. Therefore, depending on the progress of plastic deformation, it is necessary to anneal the compression molded body at 500-800°C in a reducing atmosphere to remove the processing strain of the soft magnetic powder and return the holding power of the soft magnetic powder to its original value. There is On the other hand, the higher the hardness of the soft magnetic powder and the smaller the voids in the aggregate of the soft magnetic powder, the greater the compression pressure required, the greater the processing strain of the soft magnetic powder, and the higher the strain relief annealing temperature. . Therefore, in order to return the holding force of the soft magnetic powder to its original value, it is necessary to insulate the soft magnetic powder with an insulating material made of an inorganic material having high heat resistance. Therefore, the restoration of the holding force of the soft magnetic powder depends on the heat resistance of the material that insulates the soft magnetic powder. For example, in a powder magnetic core in which soft magnetic powder is insulated with a synthetic resin having low heat resistance, heat treatment at about 200° C. also serves to harden the resin, so there is almost no effect of restoring the coercive force.
On the other hand, if the soft magnetic powder is insulated with a highly heat-resistant inorganic material and the temperature of strain relief annealing is increased, the processing cost for insulating the soft magnetic powder and the annealing cost increase. As described above, the strain relief annealing process greatly affects the performance and manufacturing cost of the powder magnetic core. Therefore, a powder magnetic core manufacturing method that does not require strain relief annealing can produce a powder magnetic core with less hysteresis loss and at a low cost.
For example, atomized iron powder has a Vickers hardness of 75 to 87 HV, which is the lowest hardness among soft magnetic powders, and the compression density of the compact is close to 90% of the density of iron. Also, the annealing temperature for restoring the holding power is as low as 500-600°C. However, the atomized iron powder has a sharp drop in saturation magnetic flux density at frequencies above 1 kHz.
On the other hand, Sendust (registered trademark of Tohoku University) is magnetically annealed up to 1100° C. to remove impurities, but has a high Vickers hardness of 410-480 HV. On the other hand, the saturation magnetic flux density does not decrease in a relatively low frequency band exceeding 1 kHz, unlike iron powder. However, the annealing temperature for restoring the coercive force is as high as 600-700° C., and the processing and annealing costs for insulating the sendust are increased.
Further, the amorphous alloy ribbon is quenched at a rate of 100,000 to 1,000,000° C./second, and thus has a higher hardness. For example, the above-described amorphous alloy ribbon containing iron as a main component and to which silicone and boron are added has a high Vickers hardness of 720 HV, and the hardness does not significantly decrease even after annealing. Therefore, the annealing temperature to restore the coercive force is higher than Sendust, and the processing and annealing costs for insulating the amorphous alloy are more expensive than Sendust.
Therefore, if the soft magnetic powder is not plastically deformed when manufacturing the powder magnetic core, no working strain is generated, and strain relief annealing is not required. Also, the hysteresis loss of the soft magnetic powder does not increase. However, in order to achieve the mechanical strength of the compression molded body and to increase the compression density of the compression molded body, means other than plastic deformation of the soft magnetic powder are required. For this reason, first, it is necessary to proceed with the arrangement of the soft magnetic powder and create a cluster of soft magnetic powder that is densely accumulated. In addition, if the soft magnetic powder can be covered with an insulating material having high insulating properties, eddy currents flowing through the gaps between the soft magnetic powders can be reduced. Secondly, when compressing a group of soft magnetic powder covered with an insulator, if the insulators covering the soft magnetic powder are joined together, and the soft magnetic powders are joined together by joining the insulators together, Compression molded bodies can be formed. This eliminates the need to plastically deform the soft magnetic powder. Therefore, regardless of the hardness of the soft magnetic powder, the surface of the soft magnetic powder is insulated with an insulating material having a high insulating property, the clusters of the soft magnetic powder are rearranged and accumulated at high density, and the soft magnetic powder is compressed. When the insulators are bonded together, the insulators are bonded together, and the soft magnetic powders are bonded together. Become.
Therefore, the new powder magnetic core production method first uses all soft magnetic powder regardless of the hardness of the soft magnetic powder, and second, insulates the soft magnetic powder with a highly insulating substance, Thirdly, the clusters of soft magnetic powders are accumulated at high density. Fourthly, when the clusters of soft magnetic powders are compressed, the insulators are bonded together, and the soft magnetic powders are bonded together by bonding the insulators together. A method for manufacturing a powder magnetic core having these four characteristics is obtained. There is no such revolutionary method for manufacturing powder magnetic cores so far.

Japanese Patent Application Laid-Open No. 2001-300697 JP 2016-094651 A

Sanyo Special Steel Technical Report, Vol. 7 (2000) No. 1, pages 29-34 Powders and Metallurgy, Volume 47, Issue 7, Pages 711-716 Kawasaki Steel Engineering Report, 33 (2001) 4, pp. 184-187 Powders and Metallurgy, Volume 32, Issue 7, Pages 9-13 Kobe Steel Technical Report, Vol. 48, No. 3 (1998), pp. 25-28 Kobe Steel Technical Report, Vol. 50, No. 3 (2000), page 38 Kobe Steel Technical Report, Vol. 60, No. 2 (2010), page 82 Abstracts of the 42nd Annual Meeting of the Magnetics Society of Japan (2018), 13aC-3

Here, problems in realizing a new method for manufacturing a powder magnetic core are sorted out.
As described above, firstly, the soft magnetic powder is insulated with a highly insulating substance, secondly, the aggregate of the soft magnetic powder is densely accumulated, and thirdly, when compressing the aggregate of the soft magnetic powder, Insulators are bonded together, and soft magnetic powders are bonded together by bonding the insulators together. Compared to conventional dust cores, 1) less eddy current loss, 2) higher saturation magnetic flux density, 3) no increase in hysteresis loss, and 4) dust that reflects the magnetic properties of soft magnetic powder. A magnetic core can be manufactured. Therefore, the new manufacturing method should meet the following four requirements.
The first requirement is to evenly cover the soft magnetic powder with a highly insulating substance.
The second requirement is to rearrange the groups of soft magnetic powders so that the groups of soft magnetic powders have a high integration density and the surfaces of the soft magnetic powders overlap each other. That is, the arrangement is advanced so that the soft magnetic powder particles having a relatively small particle size enter the gaps between the clusters of the soft magnetic powder particles, and then the surfaces of the soft magnetic powder particles are overlapped. Furthermore, the surface of the soft magnetic powder, in which the surfaces of the soft magnetic powder overlap each other, is covered with an insulator. Also, the weight of the insulator is less than 1% of the weight of the soft magnetic powder. When a mass of soft magnetic powder with such a high integration density is compressed, the density of the green compact approaches the density of the soft magnetic powder. Accordingly, when the powder magnetic core is magnetized, the magnetic energy of the magnetized powder magnetic core is large. On the other hand, since the surface direction of the soft magnetic powder is the easy magnetization axis direction of the soft magnetic powder, when all the soft magnetic powders are superimposed face to face, the magnetic permeability of the dust core increases, making it easier to magnetize. As a result, the magnetic energy of the easily magnetized dust core is large.
The third requirement relates to the conditions under which the compression-molded body is created. That is, when a mass of soft magnetic powder coated with insulation is filled into a mold and the mass of soft magnetic powder is compressed with a press, first, the mass of soft magnetic powder coated with insulation is formed into the shape of the mold. be done. Second, the insulating material covering the soft magnetic powder continuously moves to fill the gaps in the aggregate of the soft magnetic powder. The degree of accumulation of the magnetic powder is further increased. Thirdly, when the insulators cannot move, the insulators come into contact with each other, frictional heat is generated at the contact portion, and the insulators are joined together by the frictional heat. Furthermore, by bonding the insulators together, the soft magnetic powders are bonded to each other, and a powder magnetic core composed of a collection of soft magnetic powders is manufactured in the mold. Fourth, when the insulators are brought into contact with each other and bonded by frictional heat, the repulsive force received by the press continues to increase, and at this point the compression by the press is stopped. As a result, the compression is stopped just before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed. Therefore, the hysteresis loss of the dust core does not increase.
Fourth, regardless of the hardness of the soft magnetic powder, all soft magnetic powders are used to manufacture the powder magnetic core while satisfying the above three requirements.
The method of processing the soft magnetic powder and the conditions related to the insulator to realize the above four requirements will be examined.
The first condition is to increase the density of the soft magnetic powder. That is, the clusters of soft magnetic powder are repeatedly moved in the liquid in the three directions of back and forth, left and right, and up and down to advance the arrangement of the soft magnetic particles in the liquid and increase the density of the clusters of soft magnetic powder. In other words, since the soft magnetic particles do not come into direct contact with each other in the liquid, the soft magnetic particles move easily. Therefore, when the cluster of soft magnetic powder is repeatedly moved in the three directions of back and forth, left and right, and up and down in the liquid, the soft magnetic powder having a relatively small particle size enters the gap of the cluster of soft magnetic powder. At the beginning, the arrangement in which the soft magnetic powder with a small particle size moves to the upper part of the cluster of soft magnetic powder advances. Finally, when the cluster of soft magnetic powder is moved vertically, the surfaces of the soft magnetic powder overlap each other.
The second condition concerns insulators. The insulator is fine particles having high insulating properties, high heat resistance, higher hardness than the soft magnetic powder, and a size three orders of magnitude smaller than the average particle diameter of the soft magnetic powder and two orders of magnitude smaller than the thickness of the soft magnetic powder, The weight of the aggregate of fine particles is less than 1% of the weight of the aggregate of soft magnetic powder. The soft magnetic powder is covered with fine particles having such properties, and the aggregate of the soft magnetic powder is compressed. When the microparticles receive compressive stress, they move continuously and fill the gaps between the soft magnetic particles. Further, when the fine particles continue to move, the adjacent soft magnetic particles move and rearrangement progresses, further increasing the degree of accumulation of the soft magnetic particles. Furthermore, when the particles cannot move, the particles come into contact with each other, and frictional heat is generated at the contact portion, and the particles are joined together by the frictional heat. The soft magnetic powder is bonded by bonding the fine particles together, and a powder magnetic core composed of a collection of the soft magnetic powder is manufactured in the mold. On the other hand, when the fine particles come into contact with each other and bond with each other by frictional heat, since the number of fine particles is extremely large, the repulsive force received by the pressing machine continues to increase, and at this point the compression by the pressing machine is stopped. As a result, the compression is stopped just before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed.
That is, the soft magnetic powder is evenly covered with a cluster of fine particles having the above properties, the soft magnetic powder cluster is filled in a mold, and the soft magnetic powder cluster is compressed with a press. At this time, first, the cluster of soft magnetic powder covered with the cluster of fine particles is molded into the shape of the mold. Second, the fine particles continuously move so as to fill the voids in the cluster of soft magnetic powder. Third, the soft magnetic powder adjacent to the fine particles also moves and rearranges, increasing the degree of accumulation of the soft magnetic powder. Fourth, when there is no space for the particles to move, the particles come into contact with each other. Since fine particles have high heat resistance and are hard, the fine particles are not destroyed by contact, and excessive frictional heat is generated at the portion where the fine particles come into contact with each other. At this point, the fine particles are strongly bonded to each other by frictional heat. In addition, the fine particles in contact with the surface of the soft magnetic powder generate excessive frictional heat at the portion that contacts the surface of the soft magnetic powder, and after the foreign matter or impurities in the contact portion are vaporized, the cleaned soft magnetic powder is removed. Firmly joins to the contact area by frictional heat. Fifth, when the reaction in which the fine particles are bonded to each other by frictional heat and the reaction in which the fine particles are bonded to the surface of the soft magnetic powder by frictional heat occur, the number of fine particles is extremely large, so the repulsive force against the applied pressure is increased. It continues to occur in the press machine, and at this point the compression by the press machine is stopped. As a result, the pressure is stopped immediately before the soft magnetic powder is compressed, and the soft magnetic powder is not plastically deformed.
The third condition is to manufacture dust cores using all soft magnetic powders.
By the way, in the conventional method of manufacturing a powder magnetic core, a mass of soft magnetic powder is simply compressed to promote plastic deformation of the soft magnetic powder. The mechanical strength required for the molded body was given. Therefore, when a group of soft magnetic powders having a high degree of accumulation in which the surfaces of the soft magnetic powders overlap each other is formed as described in the first condition, and the group of soft magnetic powders is compressed, the soft magnetic powders do not entangle with each other. For this reason, in the conventional method of manufacturing a powder magnetic core, a process for increasing the degree of accumulation of the soft magnetic powder is unnecessary, and the aggregate of the soft magnetic powder is simply compressed. On the other hand, in a new dust core manufacturing method, the soft magnetic powders that are overlapped face to face are joined together by joining the fine particles. Since the number of fine particles is extremely large, the powder magnetic core has a certain mechanical strength due to the joining of the fine particles by frictional heat.
Therefore, the above three conditions are reflected in the new powder magnetic core manufacturing method, and the manufactured powder magnetic core has higher saturation magnetic flux density and magnetic permeability than the conventional powder magnetic core, and has less eddy current loss. , there is no increase in hysteresis loss, the powder magnetic core has a certain mechanical strength, the powder magnetic core can be manufactured at low cost, and there are no restrictions on the shape and size of the powder magnetic core to be manufactured. It becomes a manufacturing method of powder magnetic core. Furthermore, if all soft magnetic powders can be used regardless of their hardness, dust cores reflecting the magnetic properties of the soft magnetic powders can be formed. In particular, since the frequency characteristics of the magnetic permeability differ depending on the material of the soft magnetic powder, it is possible to manufacture a powder magnetic core that is easily magnetized and absorbs magnetic energy even in a high frequency band. There are several problems in realizing this ideal manufacturing method, and these problems are the problems to be solved by the present invention. The problems of the present invention are described below.
The first issue is to use all soft magnetic powders as raw materials, process the clusters of soft magnetic powders in a liquid, promote the arrangement of soft magnetic powders, and create soft magnetic powders with high accumulation density and overlapping surfaces. Create a cluster in the liquid. The second problem is fine particles that are harder than soft magnetic powder, have excellent insulation properties, have high heat resistance, and are three orders of magnitude smaller than the average particle size of soft magnetic powder and two orders of magnitude smaller than the thickness of soft magnetic powder. is deposited on the surface of the soft magnetic powder. The third problem is to compress a group of soft magnetic powder covered with a group of fine particles, join the fine particles that are in contact with each other by frictional heat, and bond the soft magnetic powders together by joining the fine particles. The fourth problem is that the soft magnetic powder is not plastically deformed when the soft magnetic powder is compressed. The fifth problem is a manufacturing method in which the steps from the treatment of the soft magnetic powder in the liquid to the formation of the powder magnetic core are simple and continuous. The sixth problem is that there are no restrictions on the shape and size of the dust core. As a result, it has better performance than conventional powder magnetic cores, has mechanical strength equivalent to that of conventional powder magnetic cores, can be manufactured at a lower cost, and can be manufactured in various shapes and sizes. There are no restrictions on An object of the present invention is to realize a powder magnetic core manufacturing method that solves the six problems at the same time.

The soft magnetic flat powder is precipitated in the gaps between the flat surfaces of the soft magnetic flat powder, the aluminum oxide fine particles covering the soft magnetic flat powder are compressed, and the aluminum oxide fine particles are bonded to each other by frictional heat. A method for producing a powder magnetic core consisting of a collection of soft magnetic flat powders bonded together,
dispersing an aluminum compound that deposits aluminum oxide fine particles by thermal decomposition in methanol, wherein the weight of the aluminum oxide fine particles deposited is less than 1/100 of the weight of the aggregate of the soft magnetic flat powder; A methanol dispersion liquid of the aluminum compound is prepared, and the first property of dissolving or being miscible in methanol, the second property of having a viscosity higher than that of methanol, and the boiling point of the aluminum compound being higher than the boiling point of methanol. An organic compound having a third property lower than the thermal decomposition temperature is mixed with the methanol dispersion to prepare a mixed liquid. After that, a mixer equipped with a heating function is placed on a shaking table. , the mixer is filled with the mixed liquid and the cluster of the soft magnetic flat powder, the mixer is rotated and oscillated to disperse the cluster of the soft magnetic flat powder in the mixed liquid, and further vibrating Vibration in three directions, i.e., up and down, left and right, and back and forth, is repeatedly generated by the machine, and finally vibration in the vertical direction is generated. A collection of the soft magnetic flat powder in the mixer is repeatedly moved in the mixed liquid in the vibration direction, the soft magnetic flat powder is arranged in the mixed liquid, and finally a vertical vibration is applied. , the flat surfaces of the soft magnetic flat powder overlap each other through the mixed liquid, and a collection of the soft magnetic flat powder having the shape of the bottom surface is formed on the bottom surface of the mixer. By raising the temperature to the boiling point of methanol, a collection of fine crystals of the aluminum compound precipitates in the organic compound all at once, and the organic compound with the precipitated fine crystals of the aluminum compound adheres to the soft magnetic flat powder. , a collection of the soft magnetic flat powder, in which the flat surfaces of the soft magnetic flat powder overlap each other through the organic compound in which the fine crystals of the aluminum compound are precipitated, is formed on the bottom surface of the mixer in the shape of the bottom surface. a first step;
A mass of soft magnetic flat powder prepared in the first step is filled in a mold, and the mold is heated to a temperature at which the aluminum compound thermally decomposes, thereby first vaporizing the organic compound. Next, the fine crystals of the aluminum compound are thermally decomposed, and a group of aluminum oxide fine particles precipitates on the surface of the soft magnetic flat powder all at once, and the group of aluminum oxide fine particles covers the soft magnetic flat powder. After that, a presser applies a continuously increasing pressure to the aggregate of the soft magnetic flat powder, and when the repulsive force received by the press continues to increase, the pressurization by the press is stopped. As a result, first, the cluster of soft magnetic flat powder is molded into the shape of the mold, then the cluster of aluminum oxide fine particles precipitates in the gap between the flat surfaces of the soft magnetic flat powder, and further , the aluminum oxide fine particles continue to move to fill the gaps in the aggregate of the soft magnetic flat powder, and when the aluminum oxide fine particles become unable to move, the aluminum oxide fine particles in contact with the surface of the soft magnetic flat powder The surface of the soft magnetic flat powder is bonded by frictional heat, and the aluminum oxide fine particles that are in contact with each other are bonded by frictional heat at the contact portion, and the soft magnetic flat powder is bonded by the bonding of the aluminum oxide fine particles. and a second step in which a powder magnetic core composed of a collection of bonded soft magnetic flat powders is manufactured in the mold,
By continuously performing the above two steps, the soft magnetic flat powder is precipitated in the gaps between the flat surfaces of the soft magnetic flat powder, and the soft magnetic flat powder is bonded to each other by joining the aluminum oxide fine particles that cover the soft magnetic flat powder . and a method for producing a powder magnetic core, wherein a powder magnetic core is produced from an aggregate of the soft magnetic flat powder.

In the present invention, a group of soft magnetic flat powders in a liquid is repeatedly subjected to vibration in three directions, and finally, a vertical vibration is applied to advance the arrangement of the soft magnetic flat powders in the liquid. The flat surfaces of the flat powder are superimposed on each other. Next, a group of granular aluminum oxide fine particles having a size of 40 to 60 nm, which is three orders of magnitude smaller than the average particle size of the soft magnetic flat powder and two orders of magnitude smaller than the thickness of the soft magnetic flat powder, is placed on the surface of the soft magnetic flat powder. to precipitate. Furthermore, a mass of soft magnetic flat powder is filled into a mold, and the mass of soft magnetic flat powder is compressed with a press. When the repulsive force received by the press continues to increase, compression by the press is stopped. do. As a result, the aluminum oxide fine particles are bonded to the surface of the soft magnetic flat powder by frictional heat, the soft magnetic flat powder is insulated, and the aluminum oxide fine particles are bonded to each other by frictional heat. A powder magnetic core is produced in a mold by bonding together and consisting of a collection of the soft magnetic flat powders. Since a very large number of aluminum oxide fine particles are strongly bonded together by frictional heat, the powder magnetic core has the necessary mechanical strength. Further, when the repulsive force received by the press machine continues to increase , the compression by the press machine is stopped . The powder does not undergo plastic deformation. For this reason, strain relief annealing treatment of the powder magnetic core manufactured in the mold becomes unnecessary. In addition, since the soft magnetic flat powder is not plastically deformed, all soft magnetic flat powder can be used as a raw material for the powder magnetic core regardless of the hardness of the soft magnetic flat powder.
On the other hand, when the soft magnetic powder is flattened in the direction of the axis of easy magnetization, the diamagnetic field coefficient decreases, and the magnetic permeability of the flattened powder increases as the flatness increases. Therefore, when a powder magnetic core is produced using flat powder, all the flat powder surfaces overlap each other and are aligned in the direction of the easy axis of magnetization, which is the direction of the flat surface, so that the powder magnetic core is easily magnetized. Become. As a result, the magnetic permeability is increased, and a powder magnetic core having a saturation magnetic flux density close to that of the flat powder is formed in the mold. This powder magnetic core is easily magnetized regardless of the hardness of the soft magnetic powder, and absorbs a large amount of magnetic energy. Flattening of the soft magnetic powder does not rely on long-term batch processing using a ball mill, but by using an attritor treatment using a media-stirring mill, flattened powder can be obtained continuously in a short period of time and manufactured at low cost. be done. On the other hand, the working strain generated by flattening is eliminated by magnetic annealing.
By the way, the aluminum oxide Al ₂ O ₃ covering the surface of the soft magnetic flat powder brings the following excellent properties to the powder magnetic core. First, aluminum oxide is an excellent insulator, having a high volume resistivity of 10 ¹⁵ Ω·cm, a high dielectric breakdown voltage of 15 kV/mm, and no insulation frequency dependence. Therefore, the eddy current loss of the dust core is small even in the high frequency range. Secondly, the melting point of aluminum oxide is as high as 2072° C., the heat resistance is superior to that of soft magnetic flat powder, and the heat resistance is superior to that of conventional dust cores. Also, excessive frictional heat is generated at the portion where the fine particles come into contact with each other, and the fine particles are joined together by the frictional heat. Thirdly, aluminum oxide has a high Mohs hardness of 9, which is second only to diamond, and is harder than all soft magnetic flat powders, so all soft magnetic flat powders can be used for powder magnetic cores. In addition, when the aluminum oxide fine particles are stressed, they continue to move so as to fill the voids. When there are no gaps for movement, the microparticles come into contact with each other and frictional stress is generated in the contact area, but the microparticles do not break. Fourthly, aluminum oxide is resistant to acid and alkali, has better chemical resistance than flat soft magnetic powder, and has better chemical resistance than conventional powder magnetic cores. The density of aluminum oxide is 3.95 g/cm ³ , which is half the density of iron.
Here, a manufacturing method for manufacturing the powder magnetic core of the present invention will be described. A manufacturing method for manufacturing a powder magnetic core consists of the following seven steps.
An aluminum compound, which is inexpensive as a raw material, deposits aluminum oxide by a simple thermal decomposition process, and has a low thermal decomposition temperature of about 300° C., was used as a raw material for aluminum oxide. On the other hand, in order to cover the soft magnetic flat powder with aggregates of aluminum oxide fine particles, the first step is to disperse the aluminum compound in methanol and convert the aluminum compound into a liquid phase.
In order to cover the soft magnetic flat powder with aggregates of aluminum oxide fine particles, it is necessary to adhere a methanol dispersion of an aluminum compound to the surface of the soft magnetic flat powder. Therefore, the second step has a first property of being soluble or miscible with methanol, a second property having a viscosity higher than that of methanol, and a boiling point higher than the boiling point of methanol and the thermal decomposition temperature of the aluminum compound. An organic compound with a lower third property is mixed with the methanol dispersion to form a mixture.
In the third step, the mixed solution and the soft magnetic flat powder mass are charged into a mixer placed on a vibration table, and the mixer is rotated and oscillated so that the aluminum compound is mixed with methanol and an organic compound. and the soft magnetic flat powder is uniformly dispersed in the mixed liquid to prepare a mixture. Therefore, the mixed liquid adheres to the soft magnetic powder due to the viscosity of the mixed liquid.
In the fourth step, the vibration from the vibrator is transmitted to the mixer through the vibration table to vibrate the entire mixture. At this time, the soft magnetic flat powder is a powder having a constant aspect ratio, which is the ratio of the area to the thickness, and the density of the soft magnetic flat powder is nearly 10 times the density of the mixed liquid. The powder moves in the vibration direction in the mixed liquid with the flat surface facing upward. Further, since the soft magnetic flat powder having a relatively smaller particle size has a smaller mass, the soft magnetic flat powder having a smaller particle size moves more in the mixed liquid. Therefore, when the entire mixture is repeatedly vibrated in three directions, i.e., back and forth, left and right, and up and down, the soft magnetic flat powder moves repeatedly in three directions in the mixed liquid. At this time, the soft magnetic flat powder having a relatively small particle size is arranged to enter the gaps of the aggregate of the soft magnetic flat powder and to move upward in the aggregate of the soft magnetic flat powder. Gathering density increases. Finally, when vibration is applied in the vertical direction, the soft magnetic flat powders overlap each other with the flat surfaces facing upward through the liquid mixture. As a result, a cluster of soft magnetic flat powder having a high degree of accumulation in which the flat surfaces of the soft magnetic flat powder overlap each other is formed on the bottom surface of the mixer in the shape of the bottom surface. The vibration acceleration applied to the mixture depends on the amount of the soft magnetic flat powder to be filled, but since the mixed liquid has a low viscosity and the density of the soft magnetic flat powder is as high as 10 times the density of the mixed liquid, it is 0.2 It is about -0.4G. This solves the first problem described in paragraph 6.
The fifth step is to raise the temperature of the mixer to the boiling point of methanol. At this time, the fine crystals of the aluminum compound are precipitated all at once in the organic compound, the organic compound in which the fine crystals of the aluminum compound are precipitated adheres to the soft magnetic flat powder, and the organic compound in which the fine crystals of the aluminum compound are precipitated is formed. A collection of soft magnetic flat powders in which the flat surfaces of the soft magnetic flat powders overlap with each other is formed on the bottom surface of the mixer in the shape of the bottom surface. The vaporized methanol is recovered by a recovery machine and reused.
In the sixth step, the soft magnetic flat powder mass is transferred from the mixer to a mold, and the mold is heated to a temperature at which the aluminum compound is thermally decomposed. At this time, the organic compound is first vaporized, then the fine crystals of the aluminum compound are thermally decomposed, and a group of aluminum oxide fine particles precipitates on the surface of the soft magnetic flat powder all at once. Flat powder is covered. The aluminum oxide deposited by thermal decomposition of the aluminum compound is granular fine particles having a size of 40 to 60 nm, which is three orders of magnitude smaller than the average particle size of the soft magnetic flat powder and two orders of magnitude smaller than the thickness of the soft magnetic flat powder. This solves the second problem described in paragraph 6. The vaporized organic compound is recovered and reused.
In the seventh step, a pressing machine applies a continuously increasing pressure to the aggregate of the soft magnetic flat powder, and the compression is stopped when the repulsive force received by the pressing machine continues to increase. That is, at the time when a pressurizing pressure is applied to the aggregate of the soft magnetic flat powder, the aluminum oxide fine particles are not bonded to each other, and the aluminum oxide fine particles are not bonded to the soft magnetic flat powder. The collection of is molded into the shape of the mold. After that, when the applied pressure increases, since there are gaps in the aggregate of soft magnetic flat powder, the aluminum oxide fine particles continue to move so as to fill the gaps. In addition, as the aluminum oxide fine particles continue to move, the adjacent soft magnetic flat powder also moves, further increasing the degree of accumulation of the soft magnetic flat powder. Furthermore, when the applied pressure increases, the gaps through which the aluminum oxide fine particles can move disappear, the aluminum oxide fine particles come into contact with each other, excessive frictional heat is generated at the contact portions, and the aluminum oxide fine particles are joined by the frictional heat. At this time, since aluminum oxide is hard and has a high melting point, the fine particles are not destroyed even by friction between the fine particles. Soft magnetic flat powders are bonded to each other by bonding aluminum oxide fine particles to each other. Similarly, when the aluminum oxide fine particles in contact with the surface of the soft magnetic flat powder cannot move, excessive frictional heat is generated at the contact portion, and the aluminum oxide fine particles are bonded to the surface of the soft magnetic flat powder by the frictional heat. As a result, a powder magnetic core in which the soft magnetic flat powders are bonded to each other through the bonding of the aluminum oxide fine particles is produced in the mold. On the other hand, when the reaction in which the aluminum oxide fine particles are bonded to each other by frictional heat and the reaction in which the aluminum oxide fine particles are bonded to the surface of the soft magnetic flat powder by frictional heat, the number of aluminum oxide fine particles is extremely large. In order to cause the reaction of , a larger pressurizing pressure is required, and the repulsive force that the press receives continues to increase. At this point, that is, immediately after bonding of the aluminum oxide fine particles due to frictional heat occurs, the compression by the pressing machine is stopped. Therefore, the pressing pressure is stopped immediately before the soft magnetic flat powder is compressed, and the soft magnetic flat powder is not plastically deformed. This solves the third and fourth problems described in paragraph 6. Moreover, there are no restrictions on the size and shape of the mold that is filled with the aggregate of soft magnetic flat powder. This solves the sixth problem described in paragraph 6.
The dust core manufacturing method comprising the seven steps described above is a method in which simple treatments are continuously performed. This solves the fifth problem described in paragraph 6. As a result, all the problems to be solved by the present invention described in paragraph 6 have been solved.
The powder magnetic core manufactured by the manufacturing method described above provides the following effects.
First, since the soft magnetic flat powder has a high filling rate in the dust core, the saturation magnetic flux density of the dust core approaches the saturation magnetic flux density of the soft magnetic flat powder. Therefore, the magnetic energy of the magnetized dust core is large. That is, the arrangement of the soft magnetic flat powder was advanced, and a cluster of the soft magnetic flat powder having a high degree of accumulation in which the flat surfaces of the soft magnetic powder overlapped with each other through the mixed liquid was formed in the mixer. Furthermore, the soft magnetic flat powder covered with the aluminum oxide fine particles was made into a collection of soft magnetic flat powder with a high degree of accumulation in which the flat surfaces of the soft magnetic flat powder overlap each other. When this mass of soft magnetic flat powder is compressed with a press, the compression density of the compacted body approaches the density of the soft magnetic flat powder. In other words, when a mass of soft magnetic flat powder is compressed by a press, the mass of soft magnetic flat powder is first formed into the shape of the mold, and then the aluminum oxide fine particles continue to move to form the soft magnetic flat powder. In addition, when the aluminum oxide fine particles continue to move, the adjacent soft magnetic flat powder also moves, rearranges the soft magnetic flat powder, and increases the degree of accumulation of the soft magnetic flat powder. Further, when the aluminum oxide fine particles become unable to move, the aluminum oxide fine particles come into contact with each other, the aluminum oxide fine particles are bonded to each other by frictional heat, and the soft magnetic powder flats are bonded by the bonding of the aluminum oxide fine particles to each other. Also, the weight of the aluminum oxide fine particles is less than 1% of the weight of the aggregate of the soft magnetic flat powder. As a result, the compression density of the compression molded body approaches the density of the soft magnetic flat powder. Therefore, the saturation magnetic flux density of the dust core approaches the saturation magnetic flux density of the soft magnetic flake powder. In addition, since a collection of soft magnetic flat powder is mixed with a dispersion in which an aluminum compound is dispersed in a mixture of methanol and an organic compound, the shape, size, and particle size distribution of the soft magnetic flat powder used as a raw material are not restricted. do not have.
Secondly, the strain relief annealing treatment becomes unnecessary. Therefore, the coercive force of the flat soft magnetic powder forming the dust core remains unchanged, and the hysteresis loss in the dust core does not increase. Furthermore, since the soft magnetic flat powder is not plastically deformed, all soft magnetic flat powder can be used as a raw material regardless of hardness. In other words, the higher the hardness of the soft magnetic flat powder, the greater the pressure required to form the compact. As a result, the plastic deformation of the soft magnetic flat powder progresses, the distortion of the soft magnetic flat powder increases, the annealing temperature of the compression molded body rises, and it becomes difficult to restore the holding force of the soft magnetic flat powder. Alternatively, annealing costs increase. Therefore, the effect of eliminating the need for strain relief annealing is significant. That is, if the aluminum oxide fine particles cannot move when compressing the aggregate of the soft magnetic flat powder, the aluminum oxide fine particles come into contact with each other, and a reaction occurs in which the aluminum oxide fine particles are joined together by frictional heat. Further, the aluminum oxide fine particles come into contact with the surface of the soft magnetic flat powder, and frictional heat causes a reaction in which the aluminum oxide fine particles are bonded to the surface of the soft magnetic flat powder. When this friction reaction occurs, since the number of fine aluminum oxide particles is extremely large, the repulsive force received by the press continues to increase. to stop. Therefore, immediately before the flat soft magnetic powder is compressed, the pressure applied to the flat soft magnetic powder is stopped, the soft magnetic powder is not plastically deformed, and the holding force of the soft magnetic powder does not increase. In addition, since the soft magnetic powder is not plastically deformed, all soft magnetic flat powders can be used as raw materials for dust cores regardless of the hardness of the soft magnetic flat powder. As a result, the strain relief annealing process becomes unnecessary, and the manufacturing cost of the powder magnetic core can be reduced.
In other words, the conventional method for manufacturing a powder magnetic core is to apply an excessive pressure to the soft magnetic powder, sufficiently plastically deform the soft magnetic powder with high hardness, and plastically deform the voids in the soft magnetic powder. While filling with powder, plastically deformed soft magnetic powder is entangled with each other. As a result, the compression density of the compression molded body approached the density of the soft magnetic powder, and the mechanical strength required for the compression molded body was generated. On the other hand, in the present manufacturing method, the fine particles of aluminum oxide fill the voids in the clusters of the soft magnetic flat powder with a high integration density, and the aluminum oxide fine particles are bonded to each other by the heat of friction. , the soft magnetic flat powders were bonded together. Therefore, it is not necessary to plastically deform the flat soft magnetic powder.
Third, the soft magnetic powder is insulated with an insulator having higher insulation resistance than the conventional dust core, and the eddy current loss is smaller than that of the conventional dust core. That is, the aluminum oxide precipitated by the thermal decomposition of the aluminum compound is granular fine particles having a size of 40 to 60 nm, and these granular fine particles are laminated to insulate the soft magnetic flat powder. Since the aluminum oxide fine particles are granular, there are a large number of pores adjacent to the aluminum oxide fine particles, although the volume is smaller than that of the aluminum oxide fine particles. The voids are occupied by air with a volume resistivity of more than 10 ¹⁷ Ω·cm, which is two orders of magnitude higher than aluminum oxide. Therefore, an insulation resistance formed by a group of laminated aluminum oxide fine particles is formed by serially connecting a resistor made of aluminum oxide fine particles and a porous resistor made of air. Furthermore, the number of aluminum oxide fine particles and voids is extremely large. Therefore, the insulation resistance that insulates the flat soft magnetic powder is three orders of magnitude higher than the insulation resistance formed by bulk aluminum oxide based on the volume resistivity of 10 ¹⁵ Ω·cm. As a result, the insulating property is increased by three orders of magnitude compared to a powder magnetic core in which soft magnetic powder is insulated with a polymer material having a volume resistivity of 10 ¹⁴ -10 ¹⁵ Ω·cm. Moreover, the frequency dependence of the insulation resistance of both aluminum oxide and air is small. Therefore, the eddy current loss of the dust core is extremely small even in the high frequency range. This increases the imaginary part of the complex permeability of the dust core.
Fourthly, all of the soft magnetic flat powder is aligned in the direction of the flat surfaces, and the flat surfaces of the soft magnetic flat powder are overlapped and bonded via the aggregate of the aluminum oxide fine particles. The flat plane direction of the soft magnetic flat powder is the easy magnetization axis direction of the soft magnetic flat powder, and a powder magnetic core in which all the soft magnetic flat powder is aligned in the flat plane direction is easily magnetized and has an increased magnetic permeability. For this reason, the dust core is easily magnetized and easily captures magnetic energy.
Fifth, the flat soft magnetic powder is insulated by inexpensive means. In other words, the raw material for aluminum oxide is an inexpensive aluminum compound, and the organic compound is also a general-purpose industrial chemical. In addition, since aluminum oxide fine particles are generated by thermal decomposition at a temperature of about 300° C. in an air atmosphere, the soft magnetic flat powder can be insulated at low processing costs using inexpensive raw materials.
Sixthly, the manufacturing method for manufacturing the powder magnetic core is a manufacturing method in which a simple process consisting of seven steps as described above is continuously performed. In addition, strain relief annealing becomes unnecessary. As a result, the powder magnetic core can be manufactured at a low manufacturing cost.
Seventh, there are no restrictions on the shape and size of the powder magnetic core to be manufactured. In other words, there are no restrictions on the size and shape of the mold for filling the mass of soft magnetic flat powder, so there are no restrictions on the shape and size of the dust core.
Eighth, a powder magnetic core having a mechanical strength close to that of a conventional powder magnetic core is manufactured. In other words, the aluminum oxide fine particles are frictionally bonded to all the flat surfaces of the soft magnetic flat powder, and all the aluminum oxide fine particles that are in contact are frictionally bonded to each other. Since the number is extremely large, a mechanical strength close to that of conventional macro-bonding by plastic deformation of soft magnetic powder can be obtained. In other words, frictional heat is generated when an extremely large number of fine aluminum oxide particles bite into the surface of the soft magnetic flat powder, and all foreign matter present at the contact portion between the two is vaporized. After the contact portion is cleaned, the aluminum oxide fine particles is strongly bonded to the surface of the soft magnetic flat powder by frictional heat. In addition, when a large number of fine aluminum oxide particles come into contact with each other, frictional heat is generated at the contact area. to join firmly. Therefore, it is not necessary to plastically deform the soft magnetic flat powder.
As described above, according to the present manufacturing method, the powder magnetic core has higher saturation magnetic flux density, insulation, and magnetic permeability than conventional powder magnetic cores, less eddy current loss, and no increase in hysteresis loss. can be manufactured. As a result, the powder magnetic core can be manufactured at a lower cost than the conventional powder magnetic core while having better performance than the conventional powder magnetic core.

In the method for producing a powder magnetic core described in paragraph 7, the aluminum compound described in paragraph 7 is aluminum benzoate or aluminum naphthenate, and the organic compound described in paragraph 7 is vinyl carboxylates and acrylic esters. or any one type of ester consisting of methacrylic acid esters, or an organic compound of any one type of glycols or glycol ethers, or a liquid monomer consisting of styrene monomer, and using these substances, A method for producing a powder magnetic core, wherein the powder magnetic core is produced according to the method for producing a powder magnetic core described in paragraph 7.

A carboxylic acid metal compound that deposits a metal oxide upon thermal decomposition will be described. Among metal carboxylate compounds, there is a metal carboxylate compound in which an oxygen ion constituting a carboxyl group becomes a ligand and approaches a metal ion to form a coordinate bond. In this carboxylate metal compound, since the metal ion, which is the largest ion, approaches the oxygen ion and forms a coordinate bond, the distance between the two is shortened. This causes the oxygen ion coordinated to the metal ion to have the greatest distance to the covalently bonded ion on the opposite side of the metal ion. In a metal carboxylate compound having such molecular structural features, when the boiling point of the carboxylic acid constituting the metal carboxylate compound is exceeded, the oxygen ion that constitutes the carboxyl group covalently bonds with the ion covalently bonded on the opposite side of the metal ion. Bonds are cleaved first, decomposing into metal oxides and carboxylic acids. When the temperature is further increased, the carboxylic acid takes the heat of vaporization and vaporizes, and after the vaporization of the carboxylic acid is completed, the metal oxide is deposited. Among these carboxylic acid metal compounds, the carboxylic acid metal compounds that complete thermal decomposition at a relatively low temperature of about 300° C. are, in descending order of the boiling point of the carboxylic acid, metal acetate compounds, metal caprylate compounds, and metal benzoate compounds. , and metal naphthenate compounds. Accordingly, metal acetate compounds, metal caprylate compounds, metal benzoate compounds, and metal naphthenate compounds are metal compounds that deposit metal oxides upon thermal decomposition at relatively low temperatures.
On the other hand, in a metal carboxylate compound in which a carboxylate anion is covalently bonded to a metal ion, the bond between the oxygen ion and the metal ion is the longest among the bonds between the ions, so the metal is precipitated by thermal decomposition.
Among aluminum carboxylate compounds that deposit aluminum oxide upon thermal decomposition, aluminum acetate and aluminum caprylate deposit amorphous alumina upon thermal decomposition. Therefore, aluminum benzoate and aluminum naphthenate exist as raw materials for depositing aluminum oxide by thermal decomposition. The boiling point of benzoic acid is 249° C., and aluminum benzoate completes thermal decomposition at 310° C. in the air atmosphere to deposit aluminum oxide. Thermal decomposition is completed at 340° C. from the thermal decomposition temperature of aluminum naphthenate, and aluminum oxide is precipitated. Therefore, in the method for producing a powder magnetic core described in paragraph 7, aluminum benzoate or aluminum naphthenate is used as the aluminum compound. In the case of thermal decomposition of the aluminum carboxylate compound, the temperature at which thermal decomposition is completed is 50 to 60° C. lower in an air atmosphere than in a nitrogen atmosphere.
Next, an organic compound having a first property of being soluble or miscible with methanol, a second property of having a viscosity higher than that of methanol, and a third property of having a boiling point of higher than 65° C. and lower than 340° C. 7 It is used as an organic compound described in the paragraph.
Examples of such an organic compound include any one type of esters consisting of carboxylic acid vinyl esters, acrylic acid esters and methacrylic acid esters, or an organic compound of any one type of glycols and glycol ethers, or , liquid monomers consisting of styrene monomers. Therefore, any one of these organic compounds is used as the organic compound in the method for producing the powder magnetic core described in paragraph 7.
Therefore, aluminum benzoate or aluminum naphthenate is used as the aluminum compound described in paragraph 7 , and any one of carboxylic acid vinyl esters, acrylic esters, and methacrylic esters is used as the organic compound described in paragraph 7. Esters, or glycols, glycol ethers, or an organic compound of any one kind, or a liquid monomer consisting of a styrene monomer, and a powder magnetic core is produced according to the production method described in paragraph 7, it is easily magnetized. , a powder magnetic core with a large captured magnetic energy is produced in the mold.

It is explanatory drawing which expands and shows a part of cut surface of a powder magnetic core typically.

Embodiment 1
This embodiment relates to the organic compound in the method for producing the powder magnetic core described in paragraph 7, and the organic compound has a first property of being dissolved or mixed with methanol and a second property of having a viscosity higher than that of methanol. , the boiling point of which is higher than 65°C and lower than 340°C, which is the boiling point of methanol.
Examples of such organic compounds include one type of organic compound belonging to any one of vinyl carboxylates, acrylic esters, and methacrylic esters, glycols, and glycol ethers, or styrene. There are liquid monomers consisting of monomers.
Carboxylic acid vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl piperate, octyl Vinyl carboxylates such as vinyl acid, vinyl monochloroacetate, vinyl adipate, vinyl crotonate, and vinyl benzoate.
For example, carboxylic acid vinyl esters with a low boiling point include vinyl acetate, which has a chemical formula of _CH3COO -CH= _CH2 , dissolves in methanol, has a higher viscosity than methanol, and has a boiling point of 72.7°C. . Vinyl acetate is an ester obtained by reacting acetic acid with vinyl alcohol, and is an inexpensive organic compound used as a raw material for the synthesis of polyvinyl acetate. Since vinyl acetate is easily polymerized by light or heat, a small amount of polymerization inhibitor (also referred to as a polymerization inhibitor) is added.
Furthermore, vinyl monochloroacetate has the chemical formula Cl--CH ₂ COO--CH=CH ₂ , dissolves in methanol, and has a boiling point of 136°C. Monochlorovinyl acetate is an inexpensive organic compound used as a cross-linking site for acrylic rubber.
Acrylic esters are acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate.
For example, acrylic esters with a low boiling point include methyl acrylate, which has a chemical formula of CH ₂ =CH-COOCH ₃ , dissolves in methanol, and has a boiling point of 80°C. Methyl acrylate is an inexpensive organic compound used as a raw material for acrylic resins. Since methyl acrylate is a substance that easily polymerizes, a small amount of stabilizer is added.
Furthermore, butyl acrylate has a chemical formula of CH ₂ =CH-COOC ₄ H ₉ , dissolves in methanol, and has a boiling point of 148°C. Butyl acrylate is an ester obtained by reacting acrylic acid and n-butanol, and is an inexpensive organic compound used as a raw material for fiber treatment agents, adhesives, paints, synthetic resins, acrylic rubbers, and emulsions. Methyl acrylate is a substance that easily polymerizes, and a small amount of stabilizer is added.
Methacrylic acid esters are methacrylic acid esters such as ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, alkyl methacrylate, tridecyl methacrylate, and stearyl methacrylate. .
For example, methacrylic acid esters with a low boiling point include ethyl methacrylate, which has a chemical formula of H ₂ C=C(CH ₃ )COOC ₂ H ₅ , dissolves in methanol, and has a boiling point of 117°C. Ethyl methacrylate is an inexpensive organic compound used as a raw material for pigments, paints, adhesives, fiber treatment agents, molding materials, and dental materials. Ethyl methacrylate is a substance that easily polymerizes, and a small amount of stabilizer is added.
Furthermore, n-butyl methacrylate has _a chemical formula of _CH2C ( _CH3 )COO( _CH2 ) _3CH3 , is soluble in methanol, and has a boiling point of 163.5°C. n-Butyl methacrylate is an inexpensive organic compound used as a raw material for paints, dispersants, and fiber treatment agents. Since n-butyl methacrylate is easily polymerized by light or heat, a small amount of polymerization inhibitor is added.
Glycols are a type of alcohol, and are compounds having a structure in which two carbon atoms of a chain aliphatic hydrocarbon are substituted with one hydroxy group each. Glycols with a low boiling point include ethylene glycol, which has a chemical formula of C ₂ H ₄ (OH) ₂ , is miscible with methanol, and has a boiling point of 197.3°C. Ethylene glycol is an inexpensive organic compound that is widely used as a solvent, antifreeze, and synthetic raw material.
Furthermore, diethylene glycol, whose chemical formula is O(CH ₂ CH ₂ OH) ₂ , is miscible with methanol and has a boiling point of 244.3°C. Diethylene glycol is an inexpensive organic compound used in antifreeze, brake fluid, lubricants, inks, tobacco moisturizers, fabric softeners, cork plasticizers, adhesives, paper, packaging materials, and paints. be.
Propylene glycol, whose chemical formula is CH ₃ CHOHCH ₂ OH, is miscible with methanol and has a boiling point of 188.2°C. Propylene glycol is used as a moisturizer, lubricant, emulsifier, antifreeze liquid, intermediate raw material for plastics, solvent, etc. In addition, it is highly moisturizing and antifungal, so it is used to improve the quality of pharmaceuticals, cosmetics, noodles and rice balls. It is an inexpensive organic compound that is widely used as a drug.
Furthermore, dipropylene glycol, which has the chemical formula [ _CH3CH (OH) _CH2 ] _2O , is miscible with methanol and has a boiling point of 232.2°C. Dipropylene glycol is an inexpensive organic compound that is used as an intermediate raw material for polyester resins, hydraulic oil for hydraulic equipment, antifreeze liquid, raw material for printing ink, and the like.
Tripropylene glycol has a chemical formula of [CH ₃ CH(OH)CH ₂ ] ₂ O, is miscible with methanol, and has a boiling point of 265°C. Tripropylene glycol is used as a raw material for lubricating oil and cutting oil, a raw material for polyurethane and acrylic acid ester intermediates, a paint and ink solvent, an antifreeze liquid, a feed additive, an intermediate raw material for polyester resin, and a solvent for water-soluble oils. It is an inexpensive organic compound that contains
Furthermore, glycol ethers have both an ether group and a hydroxyl group in one molecule, and are highly soluble in water, many organic solvents, and resins, and most glycol ethers dissolve in methanol. There are three types of glycol ethers: Ethylene glycol-based ethers and propylene glycol-based ethers are inexpensive and are used in paints, inks, dyes, photocopying fluids, detergents, electrolytes, soluble oils, hydraulic fluids, brake fluids, refrigerants, antifreeze agents, etc. organic compounds. Dialkyl glycols are also inexpensive organic compounds that are used as reaction solvents, separation extractants, polymerization solvents, antidegradants and stabilizers, electrolytes in batteries and capacitors, and the like.
For example, an ethylene glycol-based ether with a low boiling point is ethylene glycol monomethyl ether, which has the chemical formula CH ₃ O—(CH ₂ CH ₂ O)—H, dissolves in methanol, and has a boiling point of 124.5°C. . Ethylene glycol monoisopropyl ether has a chemical formula of (CH ₃ ) ₂ CHO—(CH ₂ CH ₂ O)—H, dissolves in methanol, and has a boiling point of 141.8°C.
Also, among ethylene glycol-based ethers with high boiling points, there is triethylene glycol monobutyl ether, which has a chemical formula of C ₄ H ₉ O—(CH ₂ CH ₂ O) ₃ —H, dissolves in methanol, and has a boiling point of 271. 2°C. Diethylene glycol mono-2-ethylhexyl ether has a chemical formula of C ₂ H ₅ —C ₄ H ₉ CHCH ₂ O—(CH ₂ CH ₂ O) ₂ —H, dissolves in methanol, and has a boiling point of 272°C. .
In addition, propylene glycol-based ethers with low boiling points include propylene glycol monomethyl ether, which has the chemical formula of CH ₃ —CH ₃ O—(CH ₂ CHO) ₂ —H, dissolves in methanol, and has a boiling point of 121°C. .
Also, among propylene glycol-based ethers with a high boiling point, there is tripropylene glycol monobutyl ether, which has a chemical formula of CH ₃ —C ₄ H ₉ —(CH ₂ CHO) ₃ —H, dissolves in methanol, and has a boiling point of 274°C. is.
In addition, dialkyl glycols with low boiling points include ethylene glycol dimethyl ether, which has the chemical formula CH ₃ O—(CH ₂ CHO)—CH ₃ , dissolves in methanol, and has a boiling point of 85.2°C.
In addition, among dialkyl glycols with high boiling points, there is diethylene glycol dibutyl ether, which has a chemical formula of C ₄ H ₉ O—(CH ₂ CH ₂ O) ₂ —C ₄ H ₉ , dissolves in methanol, and has a boiling point of 274°C. be.
Furthermore, the styrene monomer is a liquid monomer with a chemical formula of C ₆ H ₅ CH=CH ₂ , miscible with methanol, and having a boiling point of 145°C. Styrene monomers are inexpensive organic compounds that are raw materials for synthetic resin materials such as polystyrene, foamed polystyrene, acrylonitrile-styrene, acrylonitrile-butadiene-styrene, and unsaturated polyesters. Since the styrene monomer readily polymerizes, a small amount of polymerization inhibitor is added.
As described above, any one type of esters consisting of carboxylic acid vinyl esters, acrylic acid esters, and methacrylic acid esters, or one type of organic compound belonging to any one of glycols and glycol ethers There are organic compounds that have the above three properties. Also, the styrene monomer has the above three properties. Therefore, these organic compounds are used as organic compounds in the method for producing a powder magnetic core described in paragraph 7.

Embodiment 2
The present embodiment relates to soft magnetic powder used as a raw material for dust cores. The soft magnetic powder is selected based on the operating frequency range of the electrical product in which the powder magnetic core is mounted and the magnitude of the magnetic flux density of the powder magnetic core in this frequency range. On the other hand, in order to increase the saturation magnetic flux density of the dust core, it is necessary to increase the filling rate of the soft magnetic powder in the dust core. In order to increase the filling rate of the soft magnetic powder, it is necessary to apply a large pressure to the aggregate of the soft magnetic powder to promote plastic deformation of the soft magnetic powder. Therefore, since most soft magnetic powders have high hardness, the soft magnetic powder is annealed in advance to reduce the hardness of the soft magnetic powder. In addition, since the soft magnetic powder that has undergone plastic deformation has an increased coercive force, magnetic annealing of the dust core restores the coercive force of the soft magnetic powder to reduce the core loss of the dust core.
A dust core that forms a stator or rotor in a motor has a low operating frequency but a high saturation magnetic flux density. For such applications, pure iron powder, which has the highest saturation magnetic flux density among soft magnetic powders, is used. On the contrary, powder magnetic cores constituting reactors, noise filters, choke coils, etc. in power supply circuits have a high operating frequency but a low saturation magnetic flux density. Fe--Si alloy powder, Fe--Si--Al alloy powder, and Fe--Ni alloy powder are used for such applications. Amorphous alloy powders have a wide variety of magnetic properties, and since they have individual properties depending on the composition of the alloy, they are not dealt with here.
Pure iron powder has a saturation magnetic flux density of 2.2 tesla, which is the highest among soft magnetic powders. The packing density in the powder magnetic core is high, and the saturation magnetic flux density of the powder magnetic core is further increased. For this reason, it is used in dust cores that make up stators and rotors of motors that require magnetic energy. For example, atomized iron powder with a Vickers hardness of 75 to 87 HV has the lowest hardness among soft magnetic powders, and the compression density of a compression molded body using hydrogen-annealed atomized iron powder is 90% of the density of iron. close to On the other hand, the reduced iron powder has a Vickers hardness of 160 to 210 HV, which is more than double the hardness of the atomized iron powder, but it is a porous body with many voids and is therefore easily plastically deformed. However, in manufacturing the dust core, the hardness is reduced by hydrogen annealing. On the other hand, pure iron powder has the lowest magnetic permeability among the soft magnetic powders, and has the disadvantage that it is difficult to capture magnetic energy into the dust core. Moreover, the holding force is as large as 80 A/m, and the hysteresis loss is large. Furthermore, it is a conductor having a volume resistivity of 1×10 ⁻⁵ Ω·cm.
On the other hand, when silicon is added to iron, the magnetic permeability increases, but if the silicon content exceeds 5% by mass, it becomes extremely brittle. be. In addition, when silicon is added to iron, the electrical resistance increases, but the volume resistivity of the 3% by mass Fe—Si alloy is 5×10 ⁻⁵ Ω·cm, which is conductive. The 3% by mass Fe—Si alloy has a high coercive force of 65 A/m and a large hysteresis loss, but a high saturation magnetic flux density of 1.3 tesla. Moreover, it has a Vickers hardness of 180 to 205 HV, and is used as a raw material for powder magnetic cores after the hardness is reduced by annealing. As described above, the magnetic properties of the Fe--Si alloy are close to those of the reduced iron powder, but since it is less susceptible to corrosion than the reduced iron powder, the Fe--Si alloy, like the pure iron powder, is used as a compressor for motor stators and rotors. Used for powder magnetic cores.
Furthermore, Permalloy, which is an Fe—Ni alloy in which nickel is added to iron, has a significantly higher magnetic permeability than iron, but a lower saturation magnetic flux density. Also, the higher the nickel content, the higher the price, so the nickel content is suppressed to 50% by mass or less. In addition, magnetic annealing is performed at 1100° C. in a hydrogen atmosphere for about 3 hours to remove impurities and adjust the magnetic properties of permalloy. Here, the properties are shown as a representative permalloy containing 45% by mass of nickel. DC magnetic properties include an initial permeability of 3000, a saturation magnetic flux density of 1.4 tesla, and a coercive force of 16 A/m. . In terms of AC magnetic properties, permalloy with a plate thickness of 0.1 mm has an effective magnetic permeability of 3000 at 1 kHz and 2500 at 3 kHz. In addition, its physical properties include a density of 8.25 g/cm ³ , which is about 5% higher than that of iron, a volume resistivity of 5×10 ⁻⁵ Ω·cm, which is conductive, and a magnetic Curie point of 420° C., which is 350% higher than that of iron. °C, and the hardness is 60-90 HRB in Rockwell hardness (corresponding to 110-190 HV in Vickers hardness). Therefore, permalloy is used for transformer cores, motor cores, and iron cores for relays because it is excellent in AC magnetic permeability and saturation magnetic flux density.
Further, the Fe--Si--Al system alloy obtained by adding silicon and aluminum to iron has high hardness and is brittle, so it is easily pulverized. In particular, Sendust (registered trademark of Tohoku University), which has a composition of Fe-10 mass% Si-6 mass% Al, has a magnetic permeability of 1.2 × 10 ⁵ and is easily magnetized, and has a coercive force of 0.1 A / m. , the hysteresis loss is small, and the saturation magnetic flux density is 1 tesla, which is close to permalloy. Also, it is a conductor having a volume resistivity of 8×10 ⁻⁵ Ω·cm. On the other hand, the Vickers hardness is as high as 410 HV, and although the hardness is lowered by annealing, the filling rate is not as high as that of pure iron powder. In addition, when a powder magnetic core made of sendust is used at 80-120°C, the iron loss increases from that at room temperature, and the heat generated by the iron loss further increases the iron loss. there were. However, recently, it has been found that by setting the composition of Fe-8.8% by mass Si-6.0% by mass Al, the iron loss decreases and the temperature coefficient of the iron loss becomes negative (Non-Patent Document 1 reference).
Furthermore, among the electromagnetic stainless steels in which chromium, aluminum and molybdenum are added to iron, the electromagnetic stainless steel composed of Fe-13% by mass Cr-0.2% by mass Al-1% by mass Mo has a large magnetic permeability, The holding force is as large as 85 A/m and the hysteresis loss is large. On the other hand, the magnetic flux density is 1.35 Tesla, which is comparable to permalloy. Further, it has a Rockwell hardness of 70 HRB (corresponding to 130 HV in Vickers hardness), which is harder than atomized iron powder and softer than reduced iron powder. Moreover, it is excellent in corrosion resistance. For this reason, electromagnetic stainless steel is used for electromagnetic valves of automobiles because of its excellent response to pulsed magnetic fields. It is also a conductor with a volume resistivity of 6.5×10 ⁻⁵ Ω·cm.
The characteristics of soft magnetic powders having representative compositions have been described above for various types of soft magnetic powders. Since any soft magnetic powder is a conductor, it is necessary to insulate the soft magnetic powder. Eddy current loss can be remarkably reduced by insulating the soft magnetic powder with a collection of fine aluminum oxide particles having high heat resistance and insulating properties according to the present invention. Moreover, annealing at a temperature exceeding 800° C. is possible, and the hysteresis loss of the powder magnetic core can be reduced. In order to bring the density of the powder magnetic core closer to the density of the soft magnetic powder, the soft magnetic powder is preliminarily annealed to lower its hardness. Therefore, the present invention is highly effective in producing a powder magnetic core without plastically deforming the soft magnetic particles by stacking the soft magnetic particles having an increased degree of accumulation face-to-face and compressing the aggregate of the soft magnetic particles.

Embodiment 3
This embodiment is an embodiment of a powder magnetic core produced using atomized iron powder and reduced iron powder, which are the cheapest materials among soft magnetic powders, and is described in Non-Patent Document 2. In addition, the superiority of the method for manufacturing the dust core of the present invention will be explained from two types of embodiments of the dust core. The atomized iron powder used in Non-Patent Document 2 has a Vickers hardness of 100, and the reduced iron powder has a Vickers hardness of 60, both of which are lower than the iron powder used as an abrasive. For this reason, it is considered that the hardness of the produced iron powder was further reduced by hydrogen annealing.
The initial magnetic permeability of the iron powder varies depending on the manufacturing conditions of the iron powder and the concentration of impurities such as silicon and manganese. The reduced iron powder used in Non-Patent Document 2 has a silicon concentration of 0.05% by mass and a manganese concentration of 0.25% by mass. In contrast, the atomized iron powder used in Non-Patent Document 2 has a silicon concentration as low as 0.01% by mass and a manganese concentration as low as 0.04% by mass. Therefore, the initial magnetic permeability of the reduced iron powder is higher than that of the atomized iron powder.
To manufacture the dust core, 0.75% by mass of epoxy resin as an insulating material and 0.5% by mass of zinc stearate as a lubricating material are added to both iron powders, and two types of 490 MPa and 686 MPa are produced. Pressurization was applied to form a ring shape having an outer diameter of 38 mm, an inner diameter of 25 mm, and a thickness of 6.2 mm. After that, the green compact was heat-treated at 180° C. in the atmosphere to cure the epoxy resin and produce a powder magnetic core. Zinc stearate has a melting point of 140° C., liquefies when the epoxy resin is polymerized, and functions as a lubricant.
Epoxy resin has a volume resistivity of 10 ¹⁵ Ω·cm and is excellent in insulating properties, but its heat resistance is lower than 200°C. Zinc stearate also thermally decomposes at 420° C. into toxic carbon monoxide, carbon dioxide, zinc oxide gases and solid particles. Therefore, the manufactured powder magnetic core has a heat resistance lower than 200° C. and cannot be annealed to restore the coercive force. In addition, both iron powders are undergoing plastic deformation due to the magnitude of the applied pressure. However, since heat treatment at 180° C. has no annealing effect, the hysteresis loss of the dust core is large.
A dust core made of reduced iron powder pressurized at 490 MPa has a density of 6.74 g/cm ³ , which corresponds to a filling rate of 85.8%, and a DC initial magnetic permeability of 71.1. . A dust core made of reduced iron powder pressurized at 686 MPa has a density of 6.95 g/cm ³ , a filling rate of 88.4%, and an initial DC permeability of 75.7. . On the other hand, a powder magnetic core made of atomized iron powder pressurized at 490 MPa has a density of 6.87 g/cm ³ , which corresponds to a filling rate of 87.4% and an initial magnetic permeability of 64 g/cm 3 . .2. A dust core made of atomized iron powder pressurized at 686 MPa has a density of 7.06 g/cm ³ , a filling rate of 89.8%, and an initial DC permeability of 68.7. .
The AC initial magnetic permeability of the powder magnetic core made of reduced iron powder is 74 at 10 kHz, and the initial magnetic permeability gradually decreases as the frequency increases, and the rate of decrease increases from around 300 kHz. On the other hand, the AC initial permeability of the dust core made of the atomized iron powder is the frequency characteristic obtained by shifting the initial permeability of the dust core of the reduced iron powder downward by 10. is shown.
Furthermore, regarding the compaction behavior of the iron powders when the two types of iron powders are pressurized, the two types of iron powders show similar characteristics in terms of the rate of reduction in porosity with respect to the pressurization pressure. The decrease in porosity is due to plastic deformation and rearrangement of the iron powder. For the two types of iron powder, the rearrangement of the iron powder is completed at a pressure of 100 MPa, and plastic deformation is started from a pressure of around 50 MPa. Therefore, at pressures up to about 50 MPa, the voids are reduced due to the rearrangement of the iron powder. The voids are reduced by plastic deformation of the iron powder. Therefore, in the powder magnetic core manufactured by applying a pressing pressure of 490 MPa, the plastic deformation of the iron powder has sufficiently progressed. Therefore, the hysteresis loss of the powder magnetic core increases.
Here, the measurement results of two types of powder magnetic cores are examined.
First, regarding the compression density of the compression molded body, the atomized iron powder has a higher compression density with respect to the same pressing pressure. However, the difference in compacted density is only 2%. On the other hand, the Vickers hardness of the reduced iron powder used is 0.6 times that of the atomized iron powder used, and is easily plastically deformed. However, both iron powders start to undergo plastic deformation at a pressure of around 50 MPa, and at a pressure of 490 MPa, the plastic deformation of both iron powders has progressed sufficiently. Therefore, the difference in hardness of the iron powder has little effect on the difference in compression density. On the other hand, the reduced iron powder is a porous body with many voids and is easily crushed by the applied pressure, but the plastically deformed iron powder has a high porosity. Therefore, it is considered that the difference in compaction density is due to the high porosity of the reduced iron powder after plastic deformation.
Second, the initial DC permeability of the reduced iron powder is 10% higher than that of the atomized iron powder. Furthermore, the initial magnetic permeability of alternating current from 10 kHz to 1 MHz is 15% higher in the powder magnetic core made of reduced iron powder than in the powder magnetic core made of atomized iron powder. As described above, the reduced iron powder has a high impurity concentration of silicon and manganese, and thus has a high initial magnetic permeability. Furthermore, the initial permeability increased due to the flattening effect of the reduced iron powder. In other words, the atomized iron powder has an irregular contour and isotropically deforms when pressurized. On the other hand, the reduced iron powder also has an irregular outline, but since it is a porous body, the reduced iron powder is easily crushed in the pressurizing direction and easily deformed in the direction perpendicular to the pressurizing direction. In other words, the reduced iron powder was deformed in the plane direction, which is the direction of the axis of easy magnetization, and the demagnetizing field coefficient decreased, and the initial magnetic permeability of the reduced iron powder increased. This phenomenon is similar to the phenomenon that magnetic permeability increases when soft magnetic powder is flattened.
Third, since the plastic deformation of the two types of iron powder starts at around 50 MPa, the plastic deformation of the two types of iron powder progresses at a pressure of 490 MPa, and the iron powder with increased holding power is compacted. A magnetic core is formed. However, the heat treatment of the powder magnetic core is 180° C., which is the curing treatment temperature of the epoxy resin. Therefore, the heat treatment at 180° C. has no annealing effect to restore the holding power. In addition, the contours of the two types of iron powder are irregular and do not have shape anisotropy. A pressure of 490 MPa is required in order to compress such a mass of iron powder and achieve the mechanical strength necessary for a compression molded body. The applied pressure promotes plastic deformation of the iron powder, and the entanglement of the iron powder realizes the mechanical strength required for the compression-molded body. However, the hysteresis loss of the dust core increases.
Here, the superiority of the powder magnetic core manufacturing method of the present invention over the results of two types of powder magnetic cores will be described.
Firstly, if the iron powder is insulated by a collection of aluminum oxide fine particles, the heat resistance is higher than that of the iron powder, so strain relief annealing becomes possible, and the holding power of the iron powder is restored. In addition, the aggregates of aluminum oxide fine particles fill the gaps between the iron powders and the gaps between the reduced iron powders, increasing the compaction density. Contributes to the realization of mechanical strength as a magnetic core. In addition, since the aluminum oxide fine particles bonded by frictional heat fill the gaps between the iron powders, the eddy current flowing through the gaps between the iron powders is reduced.
Secondly, even if the iron powder has an irregular shape, if the iron powder mass is made into a mass of iron powder that overlaps with each other, and the mass of iron powder is compressed, the gap between the iron powder that overlaps with each other narrows. , the compression density increases. In addition, since all the iron powders overlap each other and the easy axis of magnetization is in the plane direction, the dust core is easily magnetized and the initial permeability of the iron powder increases.
Thirdly, if the applied pressure is stopped before the iron powder is plastically deformed and the iron powders are joined together through the joining of the aluminum oxide fine particles, the hysteresis loss in the powder magnetic core does not increase, and the pressure is reduced. Powder magnetic cores have the required mechanical strength.
As a result, the dust core manufactured using the atomized iron powder and the reduced iron powder according to the method for manufacturing a dust core of the present invention has increased initial permeability, reduced eddy current loss, and no increase in hysteresis loss.

Embodiment 4
This embodiment is an embodiment for comparing the performance of a dust core manufactured using reduced iron powder and a dust core manufactured using flat reduced iron powder, and is described in Non-Patent Document 3. . In addition, the superiority of the method for manufacturing the dust core of the present invention will be explained from two types of embodiments of the dust core.
To both iron powders, 1% by mass of epoxy resin was added as an insulating material, and 0.1% by mass of zinc stearate was added as a lubricating material. After that, the green compact was heat-treated at 180° C. in the air for 30 minutes to harden the epoxy resin to produce a green powder magnetic core. Even if the heat treatment is performed at 180° C. for 30 minutes, the retention force of the reduced iron powder cannot be restored, and the hysteresis loss in the dust core is large.
In a powder magnetic core manufactured at a pressurization pressure of 490 MPa, the flat reduced iron powder has a compaction density of 6.93 g/cm ³ , a filling rate of 88.0%, and an initial DC permeability of 94.9. On the other hand, the reduced iron powder has a compaction density of 6.74 g/cm ³ , a filling rate of 85.7%, and an initial DC magnetic permeability of 72.1. In addition, in the powder magnetic core manufactured at a pressurization pressure of 686 MPa, the flat reduced iron powder has a compaction density of 7.09 g/cm ³ , a filling rate of 90.0%, and a direct current initial magnetic permeability of 99.1. . On the other hand, the reduced iron powder has a compaction density of 6.97 g/cm ³ , a filling rate of 88.5%, and an initial DC magnetic permeability of 78.1. For any of the reduced iron powders, increasing the compressive stress increases the compressive density and the direct current initial magnetic permeability.
In addition, the powder magnetic core compressed at a pressure of 686 MPa has an alternating initial magnetic permeability of 100 at 10 to 200 kHz. The initial permeability is 80, and the initial permeability is increased by 20%. In the range of 200 kHz-1 MHz, the higher the frequency, the smaller the difference in the initial magnetic permeability.
In addition, the iron loss at a magnetic flux density of 50 mT is smaller for the dust core using flat reduced iron powder than for the dust core using reduced iron powder, and the difference between the two increases as the frequency increases. spread. In other words, although both iron powders are insulated with the same material and the same mass number, the iron loss of the dust core using flat reduced iron powder is smaller.
Here, the measurement results of two types of powder magnetic cores are examined.
First, the gaps between the flat reduced iron powders in the compression molded body using the flat reduced iron powder became relatively narrower than when the reduced iron powder was used, and the compression density increased. However, the difference in compacted density is only 2-3%. In addition, the ratio of the filling rate in the powder magnetic core manufactured with a pressure of 686 MPa and the filling rate in the powder magnetic core manufactured with a pressure of 490 MPa is While it is 1.023 for the magnetic core, it is 1.033 for the dust core using reduced iron powder. If all the flattened reduced iron powders are overlapped with each other, the above-mentioned difference in the compaction density will be wider than 2 to 3%, and the filling rate ratio in the case of using the flattened reduced iron powder will be 1.023. get bigger. Therefore, the flattened reduced iron powder that overlapped with each other remains partially. On the other hand, if all the flattened reduced iron powders are overlapped with each other, there arises a problem that the mechanical strength required for the powder magnetic core cannot be achieved. For this reason, a mass of flat reduced iron powder was simply compressed.
Secondly, in the dust core using the flat reduced iron powder, compared with the dust core using the reduced iron powder, the DC initial magnetic permeability increased by 31% at a pressure of 490 MPa, and increased by 686 MPa. 27% increase in pressure. Also, in the powder magnetic core produced at a pressure of 686 MPa, the initial magnetic permeability increased by 20% at a frequency of 10-200 kHz. That is, when pressure is applied to the flat reduced iron powder, the flat reduced iron powder is crushed, and the flat reduced iron powder having a certain proportion is deformed in the flat plane direction and the flatness increases. Since this flat plane direction is the direction of easy axis of magnetization, the initial magnetic permeability increased due to the flattening effect. Therefore, a difference in initial magnetic permeability appeared between the dust core using the flat reduced iron powder and the dust core using the reduced iron powder.
Thirdly, the iron loss in the dust core is due to the shape of the reduced iron powder being irregular and the shape of the flattened reduced iron powder being flattened in the surface direction. In other words, the gaps between the flat reduced iron powders in the compression-molded body made of the flat reduced iron powder were narrowed, and the compression density was increased. When the gap between the flat reduced iron powders becomes narrower, the insulation between the adjacent flat reduced iron powders becomes higher, and the eddy current flowing through the gap between the flat reduced iron powders decreases. The eddy current loss of the core was smaller than that of the dust core using the reduced iron powder.
Here, the superiority of the powder magnetic core manufacturing method of the present invention over the results of two types of powder magnetic cores will be described.
First, if the reduced iron powder is insulated with a collection of fine aluminum oxide particles that have higher heat resistance than the reduced iron powder, strain relief annealing becomes possible, the holding force is restored, and the hysteresis loss of the powder magnetic core is reduced. Decrease. In addition, the aggregate of aluminum oxide fine particles, which are three orders of magnitude smaller than the epoxy resin pellets, fills the gaps between the reduced iron powders and the gaps between the reduced iron powders, increasing the compaction density. In addition, the fine aluminum oxide particles filling the gaps and voids are bonded to each other by frictional heat, and the mechanical strength of the powder magnetic core is realized. This eliminates the need for plastic deformation of the reduced iron powder and flattened reduced iron powder, and reduces the hysteresis loss of the dust core.
Secondly, even if the reduced iron powder has an irregular shape, if the aggregate of the reduced iron powder is made into an aggregate of iron powder with a high degree of accumulation overlapping the faces, and the aggregate of the reduced iron powder is compressed, all of the reduced iron powder can be obtained. As for , the gaps between the reduced iron powders that overlap each other are narrowed, and the compaction density is increased. In the case of flat reduced iron powder, since a group of flat reduced iron powders in which the flat surfaces overlap each other is compressed, the compression density is further increased. In addition, since all the reduced iron powder or all the flattened reduced iron powders are aligned in the flat plane direction, the initial magnetic permeability of the powder magnetic core is further increased. In addition, the gaps between the reduced iron powders or the gaps between the flat reduced iron powders become narrower, and the narrowed gaps are filled with highly insulating aluminum oxide fine particles, further reducing the eddy current flowing through the gaps. As a result, the initial permeability increases.
Third, if the pressure is stopped before both iron powders are plastically deformed, and the two iron powders are bonded together via the bonding of the aluminum oxide fine particles, the hysteresis loss in the powder magnetic core does not increase. , and the dust core has the necessary mechanical strength.
As a result, the dust core manufactured using the reduced iron powder and the flat reduced iron powder according to the method for manufacturing a dust core of the present invention has an increased initial permeability, a reduced eddy current loss, and no increase in hysteresis loss. .

Embodiment 5
This embodiment is an embodiment of a powder magnetic core manufactured using atomized iron powder, and is described in Non-Patent Document 4. Also, the superiority of the method for manufacturing the dust core of the present invention will be explained from the embodiment of the dust core.
0.5% by weight of epoxy resin powder was added to the atomized iron powder, and four pressures of 196 to 686 MPa were applied in a floating die type mold, and the outer diameter was 38 mm, the inner diameter was 25 mm, and the height was 6.5 mm, and then cured at 150° C. for 1 hour to produce four dust cores. Curing at 150° C. does not have the annealing effect of restoring the holding power of the atomized iron powder.
The powder magnetic core molded under a pressure of 196 MPa has a filling rate of 76% and an initial DC magnetic permeability of 49. The powder magnetic core molded under a pressure of 294 MPa has a filling rate of 81% and an initial DC magnetic permeability of 60. The powder magnetic core molded under a pressure of 490 MPa has a filling rate of 87% and an initial magnetic permeability of 72 for direct current. The powder magnetic core molded under a pressure of 686 MPa has a filling rate of 91% and an initial DC magnetic permeability of 78.
On the other hand, the powder magnetic core made of atomized iron powder described in Non-Patent Document 2 has a filling rate of 87.4% when a pressure of 490 MPa is applied, and an initial magnetic permeability of direct current is 64.2. Met. The powder magnetic core to which a pressurization pressure of 686 MPa was applied had a filling rate of 89.8% and an initial DC magnetic permeability of 68.7. Compared to the powder magnetic core described in Non-Patent Document 4, at the same pressurization pressure, the value of the filling factor is close, but the DC magnetic permeability is small. The reason for this depends on the impurity concentration. The concentration of silicon in Non-Patent Document 2 is 0.01% by mass, and the concentration of manganese is 0.04% by mass. On the other hand, in Non-Patent Document 4, the concentration of silicon is as high as 0.029% by mass and the concentration of manganese is as high as 0.069% by mass. The atomized iron powder of Non-Patent Document 4 has a high initial permeability due to high concentrations of silicon and manganese.
Further, the atomized iron powder used for the dust core described in Non-Patent Document 2 has a smaller particle size than the atomized iron powder used for the dust core described in Non-Patent Document 4. For example, in the atomized iron powder described in Non-Patent Document 2, there is no atomized iron powder with a particle size larger than 180 μm. In addition, atomized iron powder with a particle size of 45 μm or less accounts for 23%. On the other hand, in the atomized iron powder described in Non-Patent Document 4, the atomized iron powder with a particle size of 200-250 μm contains 11.2%, and the atomized iron powder with a particle size of 250-325 μm contains 20.1%. , atomized iron powder having a particle size of 325 μm or more accounts for 23.2%. Also, atomized iron powder with a particle size of 80 μm or less is only 0.1%.
Furthermore, as the applied pressure increases, the values of the real and imaginary parts of the complex permeability gradually increase, and the frequency at which the values of the real and imaginary parts of the complex permeability begin to decrease gradually decreases. Side-shifting results are shown. At a pressure of 294 MPa, the real part has a value of 80 up to around 500 kHz. Also, the real part gradually decreases as the frequency increases from 500 kHz. On the other hand, the imaginary part of the complex permeability gradually increases from around 60 kHz, has a peak value of 20 in the frequency region over 1 MHz, and overlaps the real part at frequencies over 200 MHz.
Here, the measurement results of the powder magnetic core are examined.
First, consider the compacted density results. It is expected that the smaller the particle size of the atomized iron powder used for the powder magnetic core, the higher the compression density. The atomized iron powder used in Non-Patent Document 2 clearly has a smaller particle size than the atomized iron powder used in Non-Patent Document 4. Despite the apparent difference in particle size, there is little difference in the packing ratio of the dust cores. On the other hand, the atomized iron powder begins to undergo plastic deformation at a pressure of around 50 MPa, and at a pressure of 490 MPa, the plastic deformation of the atomized iron powder has progressed considerably. Therefore, the plastic deformation of the iron powder progressed, and despite the difference in the particle size distribution of the iron powder, the filling rate of the iron powder did not change. That is, in order to obtain the mechanical strength necessary for the powder magnetic core, the atomized iron powder was compressed with a pressure of about 490 MPa. However, the iron powder that has undergone plastic deformation has an increased holding power for the iron powder, resulting in an increased hysteresis loss. Furthermore, curing at 150° C. for 1 hour does not restore the retention of the iron powder.
Second, we consider the complex permeability results. Like the reduced iron powder, the atomized iron powder has an irregular contour, but unlike the reduced iron powder, it is not porous. As the pressure applied to the insulated mass of atomized iron powder is increased, the gap between the atomized iron powder particles becomes narrower, the eddy current flowing in the gap becomes smaller, and the eddy current loss is reduced. As a result, the values of the real part and the imaginary part of the complex magnetic permeability increased with increasing applied pressure. Further, although the atomized iron powder is not porous, the flattening of the atomized iron powder progresses and the flattening rate increases as the pressure is increased. As a result, the values of the real and imaginary parts of the complex permeability increased. That is, the proportion of the atomized iron powder deformed in the plane direction, which is the direction of easy magnetization, increased, the flatness increased, and the values of the real part and the imaginary part of the complex permeability of the atomized iron powder increased.
Here, the superiority of the powder magnetic core manufacturing method of the present invention over the results of two types of powder magnetic cores will be described.
First, a powder magnetic core was composed of atomized iron powder with advanced plastic deformation. As a result, the holding force of the atomized iron powder increases as the plastic deformation progresses, and the hysteresis loss increases as the holding force increases. In order to restore the holding power of the atomized iron powder, annealing in a hydrogen atmosphere at a temperature higher than 500°C is required, and the material used to insulate the atomized iron powder must have heat resistance higher than 500°C. If the atomized iron powder is insulated with the aluminum oxide fine particles of the present invention, the heat resistance is higher than the heat resistance of the atomized iron powder, so strain relief annealing is possible, the holding force is restored, and the hysteresis of the powder magnetic core. loss is reduced.
Secondly, if the insulating material is composed of the aluminum oxide fine particles of the present invention, the size of the fine particles is three orders of magnitude smaller than that of the epoxy resin pellets, so that the gaps between the atomized iron powders are further narrowed, and the narrowed gaps are treated as insulation. are filled with aluminum oxide particulates with high V, resulting in even less eddy currents flowing through the gap. This further increases the values of the real and imaginary parts of the complex permeability. In addition, the compression density increases, and the saturation magnetic flux density of the powder magnetic core increases.
Thirdly, in the method for manufacturing a powder magnetic core of the present invention, a mass of atomized iron powder is made into a mass of atomized iron powder having a high degree of accumulation and overlapping faces, and the mass of atomized iron powder is compressed. As a result, the surfaces are overlapped and compressed, the gaps between the atomized iron powders are narrowed, and the narrowed gaps are filled with highly insulating aluminum oxide fine particles. This further reduces the eddy currents flowing through the gap and further increases the values of the real and imaginary parts of the complex permeability.
Fourth, if the applied pressure is stopped before the atomized iron powder is plastically deformed and the atomized iron powders are bonded to each other through the bonding of the aluminum oxide fine particles, the hysteresis loss in the powder magnetic core does not increase. , the dust core has the required mechanical strength.
As a result, the powder magnetic core manufactured by using the atomized iron powder and according to the method for manufacturing the powder magnetic core of the present invention has increased initial magnetic permeability, reduced eddy current loss, and no increase in hysteresis loss.

Embodiment 6
This embodiment is an embodiment of a powder magnetic core manufactured using flat atomized iron powder, and is described in Non-Patent Document 5. Also, the superiority of the method for manufacturing the dust core of the present invention will be explained from the embodiment of the dust core.
A ring having an outer diameter of 36 mm, an inner diameter of 24 mm, and a thickness of 5 mm was obtained by using flat atomized iron powder and flat atomized iron powder insulated with three kinds of insulating materials, and applying a pressure of 490 MPa in each case. Four types of dust cores having different shapes were produced. The first insulated flat atomized iron powder was made by adding 0.8% by weight of a synthetic resin to the iron powder. The second insulated flat atomized iron powder was obtained by mixing an aqueous solution of phosphoric acid, boric acid, and magnesium oxide with the flat atomized iron powder, and then drying the mixture. The third insulated flat atomized iron powder was obtained by adding 0.8% by weight of synthetic resin to the second insulated flat atomized iron powder, and insulating the iron powder with a double insulating layer.
The phosphoric acid used to insulate the flat atomized iron powder has a melting point of 42.35°C, and changes to diphosphate H ₄ P ₂ O ₇ at 200°C and metaphosphoric acid (HPO ₃ ) _n at 300°C or higher. do. Also, boric acid changes to metaborate HBO ₂ at 100°C, tetraborate H ₂ B ₄ O ₇ at 140°C, and glassy boric oxide B ₂ O ₃ at 300°C. On the other hand, magnesium oxide has a melting point of 2852° C. and is excellent in heat resistance. In addition, since the four types of powder magnetic cores are manufactured by applying a pressure of 490 MPa to a mass of flat atomized iron powder, plastic deformation of the atomized iron powder starts at a pressure of around 50 MPa. , the plastic deformation of the flat atomized iron powder that constitutes the four types of powder magnetic cores is progressing. On the other hand, due to the heat resistance of magnesium oxide, it is possible to carry out hydrogen annealing at a temperature higher than 500°C. However, since the four types of powder magnetic cores were not subjected to hydrogen annealing, the four types of powder magnetic cores had a large hysteresis loss.
First, the compacted density results are described. The dust core made of flat atomized iron powder has a density of 7.10 g/cm ³ and a filling rate of 90%. This packing rate is 3% higher than that of the powder magnetic core manufactured by using the atomized iron powder described in Non-Patent Document 4 and applying the same pressure of 490 MPa. As a result, the flattening effect of the atomized iron powder appeared in the increase of the compaction density. In addition, the filling rate is 2% higher than that of the powder magnetic core manufactured by using the flat reduced iron powder described in Non-Patent Document 3 and applying the same pressurization pressure of 490 MPa. This result shows that the temperature at which the flat atomized iron powder is hydrogen-annealed is higher than the hydrogen annealing temperature of the flat reduced iron powder described in Non-Patent Document 3, and the hardness of the flat atomized iron powder is lower than the hardness of the flat reduced iron powder. I think it depends. Furthermore, the density of the dust core made from the first insulated iron powder is 6.90 g/ ^cm3 , and the density of the dust core made from the second insulated iron powder is 7.04 g/cm3. ³ , and the density of the dust core made from the third insulated iron powder is 6.83 g/cm ³ .
Next, the results of the resistivity of four types of powder magnetic cores will be described. As for the insulating effect of the insulator, the first insulator has no insulating effect, the second insulator has a slight insulating effect, and the third insulator has an insulating effect.
Furthermore, the results of eddy current loss of four types of dust cores will be described. The eddy current loss is large in the order of the dust core made of only iron powder, the dust core made of the first insulator, the dust core made of the third insulator, and the dust core made of the second insulator. Although the difference in eddy current loss between the dust core made of the third insulator and the dust core made of the second insulator is small, the dust core made only of iron powder and the first insulator The difference in eddy current loss is large compared to a powder magnetic core made of
Here, the results for dust cores are examined.
First, consider the compacted density results. The densities of the three types of powder magnetic cores insulated from the flat atomized iron powder are lower than the densities of the powder magnetic cores produced only from the iron powder. In other words, the insulator does not sufficiently fill the gaps formed by the plastically deformed flat atomized iron powder. Since the outline of the flat atomized iron powder is irregular, and not all the flat surfaces of the atomized iron powder overlap each other, and because the flat atomized iron powder consists of powders of various sizes, compression molding is possible when pressure is applied. Many cavities are formed in the body. On the other hand, since each of the three types of insulating materials has a certain size, the voids could not be filled and the compression density decreased. In addition, the decrease in the density of the dust core made from the second insulated iron powder is the same as the dust core made from the first insulated iron powder and the dust core made from the third insulated iron powder. Less than the decrease in compaction density with the powder magnetic core. The reason for this is that the crushed resin pellets are larger in particle size than the magnesium oxide powder, and the crushed resin pellets are an obstacle to filling the voids.
Second, consider the resistivity results. The first insulator is made by adding only 0.8% by weight of synthetic resin to iron powder, and since the synthetic resin pellets have a certain size, the crushed synthetic resin pellets are flat atomized iron powder. The insulation effect was not obtained because some of the flat atomized iron powders were in direct contact with each other without filling the gaps between them. On the other hand, when flat atomized iron powder covered with a double insulating layer is compressed, the magnesium oxide powder, which is harder than the synthetic resin pellets, comes into contact with the synthetic resin pellets, making them finer. Fine pieces of synthetic resin pellets that are pulverized into particles smaller than the first insulator and magnesium oxide powder enter the gaps between the flat atomized iron powders. Since the insulation between the two is high, insulation has progressed.
Third, consider the consequences of eddy current losses. In the powder magnetic core made of the first insulating material, similar to the result of the compaction density, since the resin pellets are large, the gaps between the flat atomized iron powders are not completely filled, and some of the flat atomized iron powders are separated from each other. Direct contact resulted in an eddy current loss similar to that of a dust core made of iron powder only. On the other hand, the powder magnetic core made of the third insulator and the powder magnetic core made of the second insulator have a volume resistivity of 2×10 ¹⁶ Ω·cm, which is high insulation, and an average particle diameter of Magnesium oxide powder of 1.3 μm and bits of synthetic resin pellets were present in the interstices between the iron powders to reduce eddy current losses.
Here, the superiority of the powder magnetic core manufacturing method of the present invention over the results of two types of powder magnetic cores will be described.
First, from the results of the compression density described above, the smaller the size of the insulator that insulates the flat atomized iron powder, the more the gaps between the atomized iron powders are filled with the insulator, and the lower the compression density is suppressed. rice field. Therefore, the size of the aluminum oxide fine particles of 40 to 60 nm in the present invention is two orders of magnitude smaller than that of the magnesium oxide powder having an average particle size of 1.3 μm, so that the reduction in compaction density can be suppressed. Also, the gaps between the flat atomized iron powders are reliably insulated, and the eddy current flowing through the gaps is reduced. As a result, the values of the real and imaginary parts of the complex permeability increase.
Secondly, if the flat atomized iron powder is insulated with a group of granular aluminum oxide fine particles of 40 to 60 nm as in the present invention, the gaps between the flat atomized iron powders are filled with the aluminum oxide fine particles, As the compaction density increases, the insulation resistance of the gap increases remarkably due to the enormous number of granular aluminum oxide particles and pores. This significantly reduces the eddy currents flowing through the gap and reduces the eddy current losses in the dust core. Moreover, the values of the real part and the imaginary part of the complex magnetic permeability increase according to the degree of decrease in the eddy current loss.
Third, as in the present invention, by compressing a group of flat atomized iron powders that overlap with each other, the gaps between the flat atomized iron powders are reliably insulated, the eddy current flowing through the gaps is reduced, and , the compression density increases. In addition, since all the flattened atomized iron powders overlap each other and are aligned in the plane direction, which is the direction of the axis of easy magnetization, the powder magnetic core is easily magnetized and the magnetic permeability of the powder magnetic core increases.
Fourthly, as in the present invention, if the pressure is stopped before the flat atomized iron powder is plastically deformed and the flat atomized iron powders are joined together via the joining of the aluminum oxide fine particles, the powder magnetic core can be Hysteresis losses are not increased and the dust core has the required mechanical strength.
As a result, the dust core manufactured by using the flat atomized iron powder and according to the method for manufacturing a dust core of the present invention has increased initial permeability, reduced eddy current loss, and no increase in hysteresis loss.

Embodiments of four types of powder magnetic cores manufactured using atomized iron powder, flat atomized iron powder, reduced iron powder, and flat reduced iron powder have been described. In the powder magnetic core of the embodiment, since the iron powder is insulated with an insulating material having low heat resistance, hydrogen annealing of the iron powder is impossible. In addition, since the powder magnetic core was formed from iron powder that had undergone plastic deformation, the hysteresis loss of the powder magnetic core increased. Furthermore, the heat treatment temperature is as low as 180° C., and there is no annealing effect for plastically deformed iron powder. Compared with such a powder magnetic core, the powder magnetic core produced by the method for producing a powder magnetic core of the present invention has the following two advantages.
First, the surface of the iron powder was insulated with a collection of fine particles of aluminum oxide. This provides the following four effects. First, the melting point of aluminum oxide is higher than that of iron powder, and the heat resistance of the powder magnetic core is the heat resistance of the iron powder. As a result, the dust core can be annealed in hydrogen, the holding force of the iron powder is restored, and the hysteresis loss of the dust core is reduced. Secondly, aluminum oxide is granular microparticles of 40-60 nm, and when a mass of iron powder covered with aluminum oxide microparticles is compressed, the aluminum oxide microparticles move to fill the voids in the mass of iron powder. Furthermore, the aluminum oxide fine particles are bonded to each other by frictional heat at the contact portion, and the dust core has the necessary mechanical strength due to the bonding of the extremely large number of aluminum oxide fine particles. Thirdly, aluminum oxide is an excellent insulator, and a large number of fine aluminum oxide particles and pores fill the gaps between the iron powders, resulting in a significant increase in the insulation resistance of the gaps. As a result, the eddy currents flowing in the gaps between the iron powders are significantly reduced, the AC magnetic permeability of the powder magnetic core is increased, and the powder magnetic core is easily magnetized in the corresponding frequency band. Fourth, aluminum oxide is a hard substance next to diamond and has an extremely high melting point. Therefore, when aluminum oxide fine particles come into contact with each other, the fine particles are not destroyed, and excessive frictional heat is generated at the contact area, are joined by frictional heat. Since an extremely large number of aluminum oxide fine particles exist in the mass of iron powder to be compressed, when the aluminum oxide fine particles are bonded together, the repulsive force compressing the mass of iron powder increases, and the compression is stopped at this point. be able to. As a result, the iron powder is not plastically deformed and the hysteresis loss of the dust core is not increased.
Secondly, a process is performed on the mass of iron powder to form a mass of iron powder in which the surfaces of the iron powder overlap each other. This provides the following three effects. First, the gaps between the iron powders are narrowed, which increases the compression density of the compact and increases the saturation magnetic flux density of the dust core. Secondly, the narrowed gaps between the iron powders are filled with aggregates of aluminum oxide fine particles, the eddy current flowing in the gaps between the iron powders is reduced, and the eddy current loss of the powder magnetic core is reduced. This increases the initial magnetic permeability of alternating current, making it easier to magnetize the dust core in the corresponding frequency band. Third, when a group of iron powders whose faces overlap each other is compressed, the iron powders are deformed in the direction of the easy magnetization axis perpendicular to the faces, so the initial magnetic permeability of alternating current increases, and the dust core in the corresponding frequency band becomes easily magnetized.

Here, the complex magnetic permeability of the soft magnetic material will be explained. When a powder magnetic core is wound and an alternating current is applied to excite the powder magnetic core, hysteresis loss occurs due to the soft magnetic material forming the powder magnetic core. When the structure of this powder magnetic core is represented by an electric circuit, the winding forms the L component and the powder magnetic core forms the R component, so the impedance is represented by R+jωL. If this relationship is applied to the magnetic permeability, the magnetic permeability is expressed by Equation (1). In this case, μ′ is the real part of the complex permeability and represents the inductance component, and μ″ is the imaginary part of the complex permeability and represents the resistance component.
(Formula 1) μ=μ′−jμ″
On the other hand, when a high-frequency alternating current is passed through the powder magnetic core, the magnetic permeability of the soft magnetic material is such that the magnetic flux density B cannot follow changes in the magnetic field H, resulting in a phase lag. At this time, the L component (μ') decreases and the R component (μ'') increases. This case was explained in the behavior of the complex magnetic permeability in the flat powder described above.
The relationship between the magnetic permeability and the complex magnetic permeability when B=μH, which is the definition of the magnetic permeability μ represented by the relationship between the magnetic field strength H and the magnetic flux density B, is given by Equation (2). Therefore, if at least one of the real part μ′ and the imaginary part μ″ increases, the magnetic permeability μ increases. The increase in magnetic permeability μ makes the dust core more magnetized, and magnetic energy based on the product of the saturation magnetic flux density and the applied magnetic field is taken into the dust core.
(Formula 2) μ={(μ′) ² +(μ″) ² } ^1/2

Example 1
In this embodiment, the flat atomized iron powder obtained by flattening the atomized iron powder is insulated with a group of fine particles of aluminum oxide, and the insulated group of flat atomized iron powder is compressed in a mold to form a powder magnetic core. is manufactured in a mold.
290PC-2 manufactured by Kobe Steel, Ltd. was used as the flat atomized iron powder. This flattened iron powder is obtained by flattening atomized iron powder (300M manufactured by Kobe Steel, Ltd.). The impurity concentration of the atomized iron powder (300M) is 0.01% by weight of silicon and 0.19% by weight of manganese (according to Non-Patent Document 6). The manganese concentration is higher than the impurity concentration of the atomized iron powder. Therefore, the initial magnetic permeability of the atomized iron powder (300M) is slightly higher.
Aluminum benzoate Al(C ₆ H ₅ COO) ₃ (for example, a product of Mitsuwa Chemicals Co., Ltd.) was used as a raw material for aluminum oxide. Furthermore, as an organic compound, diethylene glycol (a product of Junsei Chemical Co., Ltd., for example) having a boiling point of 244° C. and a viscosity of 30 mPas at 25° C., which is nearly 50 times the viscosity of methanol, was used. In addition, as a mixer, a device with a built-in far-infrared heater that simultaneously performs diffusion mixing by rotation and movement mixing by shaking (for example, rocking mixer RMH-HT of Aichi Electric Co., Ltd.) is used. A vibration exciter was added to the bottom of the machine.
31 g (corresponding to 0.08 mol) of aluminum benzoate was dispersed in 1 liter of methanol, and this methanol dispersion was mixed with 200 cc of diethylene glycol to prepare a mixed solution. Therefore, the viscosity of the mixture is nearly ten times that of methanol. Next, a mixer was placed on a vibration table, and the mixed liquid and 1 kg of the flat atomized iron powder were put into the mixer, and mixing and shaking were repeated by the mixer to prepare a mixture. Therefore, the volume occupied by methanol in the mixture is eight times the volume occupied by flat atomized iron powder. Further, when 31 g of aluminum benzoate is thermally decomposed, 8 g of aluminum oxide is deposited, and the ratio of the weight of aluminum oxide to the weight of flat atomized iron powder corresponds to 0.008. Next, a vibratory acceleration of 0.3 G in three directions, front and back, left and right, and up and down, is repeatedly generated by a vibration exciter, the vibration is transmitted to the mixture in the mixer through the vibration table, and finally, from 0.3 G An up-and-down vibrational acceleration of about Furthermore, the temperature of the mixer was raised to 65° C., which is the boiling point of methanol, to vaporize the methanol. The vaporized methanol is recovered and reused. After that, the capsule in the mixer was removed, and the mixture in which methanol was vaporized was taken out from the capsule and filled into a mold. The mold has a shape for molding a ring-shaped body having an outer diameter of 40 mm, an inner diameter of 25 mm, and a thickness of 6 mm.
Next, the mold was heated to 310° C. at a heating rate of 20° C./min and held for 1 minute. This caused first the diethylene glycol to vaporize and then the aluminum benzoate to pyrolyze. Vaporized diethylene glycol is recovered and reused. After that, the pressing machine generates a pressurizing pressure that increases at a rate of 10 MPa / min, applies the pressurizing pressure to the mixture in the mold, and starts compression when the repulsive force received by the press continues to increase. It was stopped and a dust core was produced in the mold. After that, the dust core was taken out from the mold.
Next, the performance of the produced powder magnetic core was measured. This result is compared with two types of dust cores described in Non-Patent Document 5. The first dust core is a ring-shaped dust core produced by pressing flat atomized iron powder (290PC-2) at a pressure of 490 MPa. In the second powder magnetic core, the surface of the flat atomized iron powder (290PC-2) is insulated with phosphoric acid, boric acid, and magnesium oxide, and 0.8% by weight of synthetic resin is added, and two types of insulators are added. It is a powder magnetic core formed by compacting a mass of flat atomized iron powders insulated by , under a pressure of 490 MPa.
First, the weight of the powder magnetic core was measured, and the density of the powder magnetic core was obtained from the volume of the powder magnetic core. The density was 7.3 g/ ^cm3 . On the other hand, the density of the first dust core described in Non-Patent Document 5 is 7.1 g/cm ³ and the compression density of the second dust core is 6.84 g/cm ³ . The density of the produced powder magnetic core is higher than the density of the two types of powder magnetic cores described in Non-Patent Document 5. The reason for this is that the gaps between the flat atomized iron powders are narrowed by laying all the flat atomized iron powders on top of each other, and the aluminum oxide fine particles fill the gaps in the clusters of the flat atomized iron powders. and the effect that the degree of accumulation of the flat atomized iron powder increases with the movement of the aluminum oxide fine particles.
Furthermore, the specific resistance of the dust core was measured. A copper plate was attached to both surfaces of the powder magnetic core via a conductive paste, and the copper plate was pressed to measure the specific resistance. The specific resistance of the produced powder magnetic core was 38 Ω·cm. On the other hand, the second dust core described in Non-Patent Document 5 has a specific resistance of 21 Ω·cm. The specific resistance of the produced powder magnetic core is higher than that of the second powder magnetic core described in Non-Patent Document 5. The reason for this is that the surfaces of the flat atomized iron powders that are overlapped with each other are covered with aggregates of aluminum oxide fine particles and holes having extremely high insulation resistance, and by compressing the aggregates of the flat atomized iron powders, This is because the aluminum oxide fine particles and the vacancies filled the overlapping slight gaps, and the aluminum oxide fine particles and the vacancies filled the gaps between the adjacent flat atomized iron powders.
Next, using a BH analyzer, SY-8218/SY-8218 manufactured by Iwasaki Tsushinki Co., Ltd., the eddy current loss of the produced powder magnetic core was determined. Eddy current losses at a magnetic flux density of 50 mT were 1 kW/m ³ at 10 kHz and 100 kW/m ³ at 100 kHz. This value is ⅛ of the eddy current loss of the second dust core described in Non-Patent Document 5. The reason for this is that the clusters of aluminum oxide fine particles with extremely high insulation resistance and voids fill the slight gaps between the flat surfaces overlapping with each other, and also fill the gaps between adjacent flat atomized iron powders, resulting in flat atomized iron powder. This is due to the reduced eddy currents flowing through the powder gaps.
Furthermore, Model No. of Keycom Co., Ltd. is used as a magnetic material measurement system. Using per, the frequency characteristic of magnetic permeability was measured. In a magnetic field of 8 A/m, the initial magnetic permeability of the produced dust core was 80 up to around 10 kHz and 65 around 100 kHz. On the other hand, the initial magnetic permeability of the first dust core described in Non-Patent Document 5 is 82 up to around 10 kHz and 68 around 100 kHz in a magnetic field of 8 A/m. The initial magnetic permeability of the second dust core has a value of 65 near 10 kHz and a value of 63 near 100 kHz in a magnetic field of 8 A/m. The initial magnetic permeability of the powder magnetic core is higher than those of the two types of powder magnetic cores described in Non-Patent Document 5. The reason for this is that all of the flat atomized iron powder is aligned in the flat plane direction, which is the direction of the easy axis of magnetization, and the collection of aluminum oxide fine particles with extremely high insulation resistance and the air holes causes the flat planes to overlap each other. This is because the gaps between adjacent flat atomized iron powders are filled, and the eddy current flowing through the gaps between the flat atomized iron powders is reduced.
In addition, using a simple iron loss measuring instrument manufactured by Toei Kogyo Co., Ltd., the iron loss of the produced powder magnetic core was measured under the measurement conditions of an excitation magnetic flux density of 1 T and an excitation frequency of 100 to 800 Hz. Iron losses were 6 W/kg at 100 Hz, 13 W/kg at 200 Hz, 28 W/kg at 400 Hz and 56 W/kg at 800 Hz.
On the other hand, in Non-Patent Document 7, atomized iron powder (300NH of Kobe Steel, Ltd.) is insulated with a two-layer coating of a phosphoric acid-based inorganic insulating coating and a silicone resin, and this powder is heated to 130 ° C. and molded with mold lubrication. describes a powder magnetic core obtained by forming a ring-shaped powder magnetic core at 1176 MPa according to the method and then performing magnetic annealing at 500° C. for 30 minutes in a nitrogen atmosphere. The annealing temperature is restricted to 550° C. due to the heat resistance of the insulator. According to Non-Patent Document 7, the compressed density is 7.61 g/cm ³ and the filling rate reaches 97% because the applied pressure is as high as 1176 MPa. On the other hand, the atomized iron powder pressurized at 1176 MPa is sufficiently plastically deformed. Therefore, magnetic annealing at 500° C. only partially reduces the hysteresis loss of the dust core. In addition, the iron loss of the powder magnetic core under the measurement conditions of an excitation magnetic flux density of 1.5 T and an excitation frequency of 200 to 700 Hz is 5 W/kg at 50 Hz, 12 W/kg at 100 Hz, 23 W/kg at 200 Hz, 50 W/kg at 400 Hz and 100 W/kg at 700 Hz.
The iron loss of the manufactured powder magnetic core is about 1/2 of the powder magnetic core described in Non-Patent Document 7. The reason for this is that the produced dust core has less eddy current flowing through the gaps between the flat atomized iron powders than the eddy current flowing through the gaps between the atomized iron powders described in Non-Patent Document 7, and the flat atomized iron powders is not plastically deformed and the retention force of the flat atomized iron powder is not increased.
Next, the produced powder magnetic core was dropped from a height of 2 m onto the floor, but the powder magnetic core was not destroyed. Therefore, the produced powder magnetic core has the required mechanical strength. The reason for this is that the extremely large number of aluminum oxide fine particles are bonded to each other by frictional heat.
Furthermore, observation and analysis of the manufactured powder magnetic core were performed. The produced powder magnetic core was cut into two in the thickness direction, and the cut surface was observed with an electron microscope. As an electron microscope, an ultra-low accelerating voltage SEM manufactured by JFE Techno-Research Corporation was used. This apparatus is capable of observation with an extremely low accelerating voltage from 100 volts, and has the feature of directly observing a sample without forming a conductive coating on the sample.
First, a secondary electron beam between 900 and 1000 V of the reflected electron beam was taken out, image processing was performed, and the cut surface was observed. Flat atomized iron powder overlapped with each other on flat surfaces, and granular fine particles with a size of 40 to 60 nm were stacked to form 13 to 17 layers, evenly filling gaps between flat surfaces. Next, the energy and intensity of the characteristic X-rays were subjected to image processing, and the types of elements constituting the granular fine particles and their distribution states were analyzed. Both aluminum atoms and oxygen atoms were uniformly distributed, and no particular uneven distribution was observed. For this reason, it was confirmed that the granular fine particles of aluminum oxide evenly filled the gaps between the flat atomized iron powders overlapping the flat surfaces. FIG. 1 schematically shows a state in which a part of the cut surface is enlarged. 1 is flat atomized iron powder and 2 is fine particles of aluminum oxide.
As described above, the dust core produced using the flat atomized iron powder has a higher compaction density and an increased insulation resistance than the dust core produced by the conventional manufacturing method using the flat atomized iron powder. The eddy current loss was small, the initial magnetic permeability increased, and the flat atomized iron powder retention force did not increase, and it had the necessary mechanical strength.

Example 2
In this embodiment, the flat reduced iron powder obtained by flattening the reduced iron powder is insulated with a group of fine particles of aluminum oxide, and the insulated group of flat reduced iron powder is compressed in a mold to form a powder magnetic core. is manufactured in a mold.
MG150D manufactured by JFE Steel Corporation was used as the flat reduced iron powder. This flat reduced iron powder is obtained by flattening reduced iron powder (MG270H manufactured by JFE Steel Corporation), and is the flat reduced iron powder described in Non-Patent Document 3.
Further, as in Example 1, aluminum benzoate was used as the raw material of aluminum oxide, diethylene glycol was used as the organic compound, and the same apparatus was used as the mixer.
Further, in the same manner as in Example 1, 31 g of aluminum benzoate was dispersed in 1 liter of methanol, and this methanol dispersion was mixed with 200 cc of diethylene glycol to prepare a mixed solution. Next, a mixer was placed on a vibration table, and the mixed liquid and 1 kg of flat reduced iron powder were put into the mixer, and mixing and shaking were repeated by the mixer to prepare a mixture. Next, a vibratory acceleration of 0.3 G in three directions of front and back, left and right, and up and down was repeatedly generated by a vibrator, and finally a vertical vibration acceleration of 0.3 G was applied to the mixture. Furthermore, the temperature of the mixer was raised to 65° C. to vaporize the methanol. Thereafter, the capsule in the mixer was removed, and the mixture in which methanol was vaporized was taken out from the capsule and filled into the same mold as in Example 1.
Next, as in Example 1, the mold was heated to 310° C. and held for 1 minute. Thereafter, in the same manner as in Example 1, the pressing machine generated a pressurizing pressure increasing at a rate of 10 MPa/min, and the pressurizing pressure was applied to the mixture in the mold, and the repulsive force received by the press continued. Compression was stopped at the time when the core was increased, and a powder magnetic core was produced in the mold. After that, the dust core was taken out from the mold.
Next, the performance of the produced powder magnetic core was measured. This result is compared with the dust core described in Non-Patent Document 3. MG150D was used as flat reduced iron powder for both powder magnetic cores.
First, the weight of the powder magnetic core was measured, and the density of the powder magnetic core was obtained from the volume of the powder magnetic core. The density was 7.2 g/ ^cm3 . On the other hand, the density of the powder magnetic core described in Non-Patent Document 3 is 6.93 g/cm ³ . The reason why the density of the produced dust core is higher than that of the dust core described in Non-Patent Document 3 is that, as in Example 1, all the flattened reduced iron powders are overlapped with their flat surfaces, The effect of narrowing the gaps between the flat reduced iron powders, the effect of the aluminum oxide fine particles filling the gaps in the collection of the flat reduced iron powders, and the degree of accumulation of the flat reduced iron powders along with the movement of the aluminum oxide fine particles depends on the effect of heightened Furthermore, in the dust core described in Non-Patent Document 3, since the flat reduced iron powder is a porous body, the cured epoxy resin cannot fill all the voids in the flat reduced iron powder, and the dust core density decreased.
Next, a BH analyzer manufactured by Denshi Jiki Kogyo Co., Ltd. was used to measure the initial magnetic permeability at direct current. The initial magnetic permeability of the produced powder magnetic core was 100 at direct current. On the other hand, the powder magnetic core described in Non-Patent Document 3 has an initial magnetic permeability at direct current of 94.9.
Also, the apparatus of Example 1 was used to measure the initial magnetic permeability with an alternating current. The manufactured powder magnetic core was 100 up to around 200 kHz, gradually decreased beyond 200 kHz, and was 67 at 1 MHz. On the other hand, the dust core described in Non-Patent Document 3 was 94.9 up to around 200 kHz, and after 200 kHz it gradually decreased to 63 at 1 MHz.
The reason why the initial magnetic permeability of the produced powder magnetic core is higher than the initial magnetic permeability described in Non-Patent Document 3 is that, as in Example 1, all the flattened reduced iron powders are placed in flat planes in the direction of the easy axis of magnetization. The effect of aligning in the direction and the collection of aluminum oxide fine particles and holes with extremely high insulation resistance fill the slight gaps between the flat surfaces overlapping each other, and also fill the gaps between the adjacent flat reduced iron powders, This is because the eddy current flowing through the gaps between the flat reduced iron powders has decreased.
Using the apparatus of Example 1, the iron loss of the dust core was measured under the measurement conditions of an excitation magnetic flux density of 50 mT and an excitation frequency of 20-100 kHz. The iron loss of the manufactured dust core is about half the iron loss of the dust core described in Non-Patent Document 3 at 20 kHz, and the iron loss of the dust core described in Non-Patent Document 3 at 50 kHz. It was about 1/4, and about 1/5 of the iron loss of the dust core described in Non-Patent Document 3 at 100 kHz. Note that the iron loss described in Non-Patent Document 3 is based on a pressure of 686 MPa instead of 490 MPa for pressurizing a mass of flat reduced iron powder.
As compared with the results of Example 1, the iron loss results differ from the iron loss of the dust core described in Non-Patent Document 3 as the frequency increases. The reason for this is that the epoxy resin that insulates the flat reduced iron powders described in Non-Patent Document 3 does not fill the gaps between the flat reduced iron powders, and some of the flat reduced iron powders are in direct contact with each other. This is due to eddy current losses flowing through the gaps between powders. In other words, if all the flat reduced iron powders overlap with each other, the mechanical strength required for the powder magnetic core cannot be achieved, so the collection of flat reduced iron powders was simply compressed. This brings some of the flat reduced iron powder into direct contact. As a result, since the eddy current loss is proportional to the square of the frequency, the higher the frequency, the greater the eddy current loss of the dust core described in Non-Patent Document 3. In addition, since the iron loss at 20 kHz is about half the iron loss of the dust core described in Non-Patent Document 3, the hysteresis loss of the flattened reduced iron powder increases when manufacturing the dust core. Depends on the effect it didn't have. In other words, the powder magnetic core described in Non-Patent Document 3 was heat-treated at 180°C for 30 minutes, but at 180°C under pressure of 686 MPa, the working strain of the flattened reduced iron powder in which plastic deformation progressed was The hysteresis loss of the powder magnetic core is increasing due to the increase in the coercive force of the flat reduced iron powder.
Next, the powder magnetic core was dropped from a height of 2 m onto the floor in the same manner as in Example 1, but the powder magnetic core was not destroyed. Therefore, the dust core has the required mechanical strength. The reason for this is that the extremely large number of aluminum oxide fine particles are bonded to each other by frictional heat.
Furthermore, in the same manner as in Example 1, the manufactured powder magnetic core was cut into two in the thickness direction, and the cut surfaces were observed with an electron microscope. As in Example 1, it was confirmed that the granular fine particles of aluminum oxide evenly filled the gaps between the flat reduced iron powders overlapping the flat surfaces.
As described above, the dust core produced using the flat reduced iron powder has a higher compression density and an increased insulation resistance than the dust core produced by the conventional manufacturing method using the flat reduced iron powder. The eddy current loss was small, the initial magnetic permeability was increased, the holding force of flat atomized iron powder was not increased, and the required mechanical strength was obtained.

Example 3
In this embodiment, flat sendust powder is used as flat soft magnetic powder having a high hardness, the flat sendust powder is insulated with a group of aluminum oxide fine particles, and the insulated flat sendust powder is compressed in a mold. , is an embodiment of manufacturing a powder magnetic core in a mold.
Flat sendust powder (a product of Tokin Co., Ltd.) was obtained by flattening water-atomized sendust powder, and then annealing it in an argon gas atmosphere at 650° C. for 2 hours to remove distortion due to flattening. The iron powder has an average length of 40 μm and an average thickness of 1.5 μm. The flat sendust powder has a high hardness, and in order to plastically deform the flat sendust powder, a higher pressure than the above-described pressure for plastically deforming the flat iron powder is applied. This increases the hysteresis loss of the dust core.
Further, as in Example 1, aluminum benzoate was used as the raw material of aluminum oxide, diethylene glycol was used as the organic compound, and the same apparatus was used as the mixer.
Further, in the same manner as in Example 1, 31 g of aluminum benzoate was dispersed in 1 liter of methanol, and this methanol dispersion was mixed with 200 cc of diethylene glycol to prepare a mixed solution. Next, a mixer was placed on a vibration table, and the mixed liquid and 1 kg of flat sendust powder were put into the mixer, and mixing and shaking were repeated by the mixer to prepare a mixture. Next, a vibratory acceleration of 0.3 G in three directions of front and back, left and right, and up and down was repeatedly generated by a vibrator, and finally a vertical vibration acceleration of 0.3 G was applied to the mixture. Furthermore, the temperature of the mixer was raised to 65° C. to vaporize the methanol. Thereafter, the capsule in the mixer was removed, and the mixture in which methanol was vaporized was taken out from the capsule and filled into the same mold as in Example 1.
Next, the performance of the produced powder magnetic core was measured. This result is compared with the powder magnetic core using flat sendust powder described in Non-Patent Document 8. In addition, the powder magnetic core described in Non-Patent Document 8 is formed by forming a slurry obtained by mixing a silicone resin, a thickener, and a solvent into a flat powder into a sheet, and pressing and heat-treating the obtained sheet. was applied to produce a dust core. In addition, although silicone resin has excellent insulating properties like epoxy resin, its heat resistance is lower than 250 ° C., and heat treatment cannot restore the holding power of flat sendust powder, and the hysteresis loss in the powder magnetic core is big.
First, the weight of the powder magnetic core was measured, and the filling rate of the powder magnetic core was obtained from the volume of the powder magnetic core. The filling rate was 82% by weight. On the other hand, the packing rate of the powder magnetic core described in Non-Patent Document 8 is 70% by weight. The large difference in filling rate is due to the following reasons.
Looking at the cross-sectional photograph of the powder magnetic core published in Non-Patent Document 8, many voids are formed. Furthermore, most of the voids are formed above and below the flat sendust powder having a relatively large particle size. Therefore, when the slurry was formed into a sheet, voids were formed in the sheet, and the voids were further expanded as the sheet was then press-molded. As a result, the packing rate of the dust core was lowered. In other words, if the flat sendust powder is only formed into a sheet, the clusters of the flat sendust powder are not rearranged, so the density of the clusters of the flat sendust powder is low. Cheap. Moreover, in the photograph of the cross section of the powder magnetic core, most of the flat sendust powder is deformed in an undulating manner with the flat surface facing up and down. In other words, the flat sendust powder has a high hardness, and when a dust core is produced, a large pressure is applied to sufficiently plastically deform the flat sendust powder. strength occurs. Therefore, since a mass of flat sendust powder in which voids were formed was compressed by applying a large pressure, most of the flat sendust powder was deformed in an undulating manner with its flat surface facing up and down. This further enlarged the void. On the other hand, the heat resistance of the insulating material is lower than 250 ° C., and the heat treatment of the dust core cannot restore the holding power of the flat sendust powder, and the hysteresis loss of the dust core published in Non-Patent Document 8 is big. On the other hand, when all the flat soft magnetic powders are arranged in the flat plane direction as in Example 3, the plastically deformed flat sendust powder is less likely to entangle, and the required mechanical strength of the powder magnetic core is not achieved.
On the other hand, in the dust core of Example 3, the mixture of the flat sendust powder and the liquid mixture was repeatedly vibrated in three directions and finally vibrated in the vertical direction. For this reason, the flat surface of the flat sendust powder having a relatively small particle size faces up, and the arrangement in which it enters the gaps of the aggregate of the flat sendust powder and the arrangement in which it moves upward in the aggregate of the flat sendust powder progresses. The degree of accumulation of powder clusters increases. Finally, when vibration is applied in the vertical direction, all the flat sendust powders face upward and the flat surfaces overlap each other. As a result, the packing rate of the powder magnetic core of Example 3 was increased.
Next, using the apparatus of Example 1, the complex magnetic permeability was measured with an alternating current. The manufactured dust core had a real part value of 400 up to around 10 MHz, which gradually decreased beyond 10 MHz, dropped to a value of 210 around 300 MHz, and overlapped with the imaginary part. The imaginary part increased from around 3 MHz, reached a peak value of 210 around 300 MHz, and gradually decreased from 300 MHz. The conductivity of sendust is 1.25×10 ⁶ S/m, and the skin thickness of sendust with a relative magnetic permeability of 400 at 10 MHz is 2.25 μm. This value corresponds to an insulating value obtained by laminating 7 to 8 layers of fine aluminum oxide particles of 50 nm on an average thickness of flat sendust powder of 1.5 μm to a similar thickness. Therefore, in Example 3, since all the flat sendust powders insulated with a group of aluminum oxide fine particles were superimposed between flat surfaces, a reduced eddy current flows through the gap between flat surfaces with high insulation. In addition, the imaginary part of the complex permeability increased due to the reduction of the eddy current. In addition, since all the flat sendust powders were arranged in the flat plane direction, which is the direction of easy magnetization, the real part of the complex magnetic permeability had a constant value.
On the other hand, the powder magnetic core published in Non-Patent Document 8 has a value of 280 up to around 5 MHz, gradually decreases beyond 5 MHz, and drops to a value of 130 around 500 MHz, overlapping with the imaginary part. rice field. The imaginary part increased from around 2 MHz, increased to a value of 130 around 500 MHz, and overlapped with the real part. That is, the powder magnetic core published in Non-Patent Document 8 has many voids as described above, and most of the flat sendust powder is deformed in an undulating manner with the flat surface in the vertical direction. there is Further, the silicone resin, the thickener and the solvent added to the flat sendust powder are adsorbed to the flat sendust powder with an adhesive force depending on the concentration of the thickener. After the heat treatment, the silicone resin is cured and the thickener and solvent are volatilized. Therefore, in the portion where the larger gap is formed, when the flat sendust powder is deformed in an undulating manner, part of the insulator is separated from the flat sendust powder, and the flat sendust powders come into direct contact with each other. As a result, eddy currents flow in the gaps between the flat sendust powders. As a result, the value of the imaginary part of the complex permeability of the powder magnetic core published in Non-Patent Document 8 was 0.6 times the value of the imaginary part of the complex permeability of the powder magnetic core in Example 3. In addition, in the dust core disclosed in Non-Patent Document 8, all the flat sendust powders were deformed in an undulating manner, and many gaps were formed in the gaps between the flat sendust powders. On the other hand, in the dust core of Example 3, all the flat sendust powders were aligned in the flat plane direction, which is the easy axis direction of magnetization. was 1.4 times the value of the real part of the complex permeability of the dust core.
Next, the powder magnetic core was dropped from a height of 2 m onto the floor in the same manner as in Example 1, but the powder magnetic core was not destroyed. Therefore, the dust core has the required mechanical strength. The reason for this is that the extremely large number of aluminum oxide fine particles are bonded to each other by frictional heat.
Furthermore, in the same manner as in Example 1, the produced powder magnetic core was cut into two in the thickness direction, and the cut surfaces were observed with an electron microscope. As in Example 1, it was confirmed that the granular fine particles of aluminum oxide evenly filled the gaps between the flat sendust powders overlapping the flat surfaces.
As described above, the powder magnetic core produced using the flat sendust powder has a higher compression density, an increased insulation resistance, and a higher eddy current than the powder magnetic core produced by the conventional manufacturing method using the flat sendust powder. The loss was small, the initial magnetic permeability increased, the holding force of flat atomized iron powder did not increase, and the required mechanical strength was obtained.

A comparison was made between the performance of the powder magnetic cores in the above three examples and the performance of the powder magnetic core produced by the conventional manufacturing method. The powder magnetic cores in the examples are superior to the powder magnetic cores produced by the conventional manufacturing method in the following items.
First, the density of the powder magnetic cores in the examples is higher than the density of the powder magnetic cores produced by the conventional manufacturing method. The reason for this is that all the flat soft magnetic powders are superimposed with their flat surfaces to narrow the gaps between the flat soft magnetic powders, and the aluminum oxide fine particles fill the gaps in the clusters of the flat soft magnetic powders. This is because when the soft magnetic powder mass was compressed, the aluminum oxide microparticles moved, and the movement of the microparticles further increased the degree of accumulation of the flat soft magnetic powder. As a result, the saturation magnetic flux density of the powder magnetic core in the example becomes higher than the saturation magnetic flux density of the powder magnetic core produced by the conventional manufacturing method, and the magnetic energy of the magnetized powder magnetic core is large.
Secondly, the magnetic permeability of the powder magnetic core in the example had a higher value than the magnetic permeability of the powder magnetic core produced by the conventional manufacturing method. The reason for this is that all the flat soft magnetic powders are aligned in the direction of the flat surface, which is the direction of the easy axis of magnetization, and the aggregation of aluminum oxide fine particles with extremely high insulation resistance and fine holes is the basis for the separation of the flat soft magnetic powders. This is due to filling the gap and reducing eddy currents flowing through the gap. As a result, the powder magnetic cores in the examples are easier to magnetize than the powder magnetic cores produced by the conventional manufacturing method.
Third, the iron loss of the powder magnetic cores in the examples is smaller than that of the powder magnetic cores produced by the conventional manufacturing method. The reason for this is that the flat soft magnetic powder is not plastically deformed when manufacturing the dust core, so the hysteresis loss of the flat soft magnetic powder does not increase, and the eddy current flowing through the gap between the flat soft magnetic powders is reduced. Depends on what you did. As a result, the powder magnetic cores in the examples generate less heat than the powder magnetic cores produced by the conventional manufacturing method. In other words, in the dust cores of Examples, a large number of fine aluminum oxide particles are frictionally bonded to each other, thereby imparting mechanical strength to the dust cores. On the other hand, in the dust core produced by the conventional manufacturing method, the flat soft magnetic powder is sufficiently plastically deformed, and the plastically deformed flat soft magnetic powder is entangled with each other, thereby imparting mechanical strength to the dust core. Furthermore, since the powder magnetic core in the conventional manufacturing method insulates the flat soft magnetic powder with an insulator with low heat resistance, magnetic annealing is performed on the powder magnetic core to restore the holding power of the plastically deformed flat soft magnetic powder. can't
As described above, the method for producing a powder magnetic core in the present invention firstly uses all soft magnetic powders regardless of the hardness of the soft magnetic powders, and secondly, aluminum oxide fine particles with high insulating properties. Third, the groups of soft magnetic powder are densely accumulated so that their surfaces overlap each other. Fourth, when the groups of soft magnetic powder are compressed, the aluminum oxide fine particles are This is an epoch-making method for producing a powder magnetic core, in which the soft magnetic powders are bonded together by frictional heat, and by frictional heat bonding between aluminum oxide fine particles.

1 flat atomized iron powder 2 fine particles of aluminum oxide

Claims (2)

The soft magnetic flat powder is precipitated in the gaps between the flat surfaces of the soft magnetic flat powder, the aluminum oxide fine particles covering the soft magnetic flat powder are compressed, and the aluminum oxide fine particles are bonded to each other by frictional heat. A method for producing a powder magnetic core consisting of a collection of soft magnetic flat powders bonded together,
dispersing an aluminum compound that deposits aluminum oxide fine particles by thermal decomposition in methanol, wherein the weight of the aluminum oxide fine particles deposited is less than 1/100 of the weight of the aggregate of the soft magnetic flat powder; A methanol dispersion liquid of the aluminum compound is prepared, and the first property of dissolving or being miscible in methanol, the second property of having a viscosity higher than that of methanol, and the boiling point of the aluminum compound being higher than the boiling point of methanol. An organic compound having a third property lower than the thermal decomposition temperature is mixed with the methanol dispersion to prepare a mixed liquid. After that, a mixer equipped with a heating function is placed on a shaking table. , the mixer is filled with the mixed liquid and the cluster of the soft magnetic flat powder, the mixer is rotated and oscillated to disperse the cluster of the soft magnetic flat powder in the mixed liquid, and further vibrating Vibration in three directions, i.e., up and down, left and right, and back and forth, is repeatedly generated by the machine, and finally vibration in the vertical direction is generated. A collection of the soft magnetic flat powder in the mixer is repeatedly moved in the mixed liquid in the vibration direction, the soft magnetic flat powder is arranged in the mixed liquid, and finally a vertical vibration is applied. , the flat surfaces of the soft magnetic flat powder overlap each other through the mixed liquid, and a collection of the soft magnetic flat powder having the shape of the bottom surface is formed on the bottom surface of the mixer. By raising the temperature to the boiling point of methanol, a collection of fine crystals of the aluminum compound precipitates in the organic compound all at once, and the organic compound with the precipitated fine crystals of the aluminum compound adheres to the soft magnetic flat powder. , a collection of the soft magnetic flat powder, in which the flat surfaces of the soft magnetic flat powder overlap each other through the organic compound in which the fine crystals of the aluminum compound are precipitated, is formed on the bottom surface of the mixer in the shape of the bottom surface. a first step;
A mass of soft magnetic flat powder prepared in the first step is filled in a mold, and the mold is heated to a temperature at which the aluminum compound thermally decomposes, thereby first vaporizing the organic compound. Next, the fine crystals of the aluminum compound are thermally decomposed, and a group of aluminum oxide fine particles precipitates on the surface of the soft magnetic flat powder all at once, and the group of aluminum oxide fine particles covers the soft magnetic flat powder. After that, a presser applies a continuously increasing pressure to the aggregate of the soft magnetic flat powder, and when the repulsive force received by the press continues to increase, the pressurization by the press is stopped. As a result, first, the cluster of soft magnetic flat powder is molded into the shape of the mold, then the cluster of aluminum oxide fine particles precipitates in the gap between the flat surfaces of the soft magnetic flat powder, and further , the aluminum oxide fine particles continue to move to fill the gaps in the aggregate of the soft magnetic flat powder, and when the aluminum oxide fine particles become unable to move, the aluminum oxide fine particles in contact with the surface of the soft magnetic flat powder The surface of the soft magnetic flat powder is bonded by frictional heat, and the aluminum oxide fine particles that are in contact with each other are bonded by frictional heat at the contact portion, and the soft magnetic flat powder is bonded by the bonding of the aluminum oxide fine particles. and a second step in which a powder magnetic core composed of a collection of bonded soft magnetic flat powders is manufactured in the mold,
By continuously performing the above two steps, the soft magnetic flat powder is precipitated in the gaps between the flat surfaces of the soft magnetic flat powder, and the soft magnetic flat powder is bonded to each other by joining the aluminum oxide fine particles that cover the soft magnetic flat powder . and a method for producing a powder magnetic core, in which a powder magnetic core is produced from a collection of soft magnetic flat powders. In the method for producing a dust core according to claim 1, the aluminum compound according to claim 1 is aluminum benzoate or aluminum naphthenate, and the organic compound according to claim 1 is carboxylic acid vinyl esters. , acrylic esters, or methacrylic esters, or organic compounds of glycols or glycol ethers, or liquid monomers consisting of styrene monomers. A method for manufacturing a dust core, comprising using a substance and manufacturing a dust core according to the method for manufacturing a dust core according to claim 1.

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