Dust core, stator for motor, motor, and dust core manufacturing method

Abstract

This dust core is formed from a powder compact containing a powder having an insulating film on the surfaces of soft magnetic particles. The content ratio of iron oxide in an internal region located 3.0 mm or more inward from the surface of the powder compact is 0.1 mass% to 10.0 mass%.

Description

Powder magnetic core, motor stator, motor, and method for manufacturing powder magnetic core

[0001] The present disclosure relates to a powder magnetic core, a motor stator, a motor, and a method for manufacturing a powder magnetic core. This application claims priority based on Japanese Patent Application No. 2024-094683 filed on June 11, 2024, and Japanese Patent Application No. 2025-065316 filed on April 10, 2025. The entire contents of the aforementioned Japanese applications are incorporated herein by reference.

[0002] Conventionally, powder magnetic cores have been used as magnetic cores for electric devices such as motors and reactors. Powder magnetic cores are compacts formed by compressing soft magnetic powder having insulating films on the surfaces of soft magnetic particles. Patent Document 1 discloses a powder magnetic core for use in motors.

[0003] Patent Documents 2 and 3 disclose motor recycling methods. They describe crushing a stator consisting of a magnetic core and a coil, separating the magnetic core from the coil, and sorting the materials. The magnetic core material described in Patent Documents 2 and 3 is an electromagnetic steel sheet such as a silicon steel sheet.

[0004] International Publication No. 2019 / 031209 Japanese Patent Application Laid-Open No. 2007-124841 Japanese Patent Application Laid-Open No. 2012-147608

[0005] The powder magnetic core according to the present disclosure is formed from a powder compact containing soft magnetic particles having insulating films on their surfaces, wherein an internal region of the powder compact located at a depth of 3.0 mm or more from the surface thereof contains 0.1% by mass or more and 10.0% by mass or less of iron oxide.

[0006] FIG. 1 is a partial cross-sectional view schematically showing a powder magnetic core according to an embodiment. FIG. 2 is a schematic perspective view showing an example of a powder magnetic core according to an embodiment. FIG. 3 is a schematic perspective view showing another example of a powder magnetic core according to an embodiment. FIG. 4 is a schematic perspective view showing yet another example of a powder magnetic core according to an embodiment. FIG. 5 is a schematic perspective view of a stator for a motor according to an embodiment. FIG. 6 is a schematic cross-sectional view of a motor according to an embodiment. FIG. 7 is a schematic cross-sectional view showing an example of a pulverizer. FIG. 8 is a graph showing the particle size distributions of recycled powder and new powder in Test Example 1. FIG. 9 is a schematic view showing the insulating film of the recycled powder used as the raw material for the powder magnetic core of Sample No. 2 in Test Example 2. FIG. 10 is a schematic view showing the insulating film of the recycled powder used as the raw material for the powder magnetic core of Sample No. 1 in Test Example 2. FIG. 11 is a partially enlarged view of the cross section of the powder magnetic core of Sample No. 100 in Test Example 2. FIG. 12 is a partially enlarged view of the cross section of the powder magnetic core of Sample No. 1 in Test Example 2. 13 is a partially enlarged view of a cross section of the powder magnetic core of Sample No. 2 in Test Example 2.

[0007] It is desirable to recover powder magnetic cores from used electrical equipment and recycle them. However, the recycling of powder magnetic cores has not been carried out. Conventionally, powder magnetic cores have been manufactured using new soft magnetic powder as a raw material. New soft magnetic powder contains carbon dioxide (CO ２ Therefore, by reducing the amount of new soft magnetic powder used, the amount of CO emitted during the production of the powder core, including the production of the soft magnetic powder, can be reduced. ２ It is desirable to reduce emissions.

[0008] The present disclosure relates to CO generated during the production of a powder magnetic core. ２ One of the objects of the present invention is to provide a powder magnetic core that can reduce emissions.

[0009] The powder magnetic core of the present disclosure is characterized by the fact that CO generated during the production of the powder magnetic core ２ can reduce emissions.

[0010] First, embodiments of the present disclosure will be listed and described. In the following description, recycled powders A, B, C, and X may be used with the following meanings. Recycled powder A is a powder obtained by pulverizing only used powder cores that have been heat-treated in an oxygen-containing atmosphere (hereinafter simply referred to as an oxygen atmosphere). Recycled powder B is a powder obtained by pulverizing a used powder core that has been heat-treated in an oxygen atmosphere and a coil attached to the powder core, and classifying the pulverized powder through a specific sieve. Recycled powder C is a powder obtained by pulverizing a used powder core that has been heat-treated in an oxygen atmosphere, a coil attached to the powder core, and a resin mold covering at least one of the powder core and the coil, and classifying the pulverized powder through a specific sieve. Recycled powder X is a powder obtained by pulverizing only used powder cores that have been heat-treated in a nitrogen-containing atmosphere (hereinafter simply referred to as a nitrogen atmosphere).

[0011] (1) A powder magnetic core according to the present disclosure is formed from a powder compact containing soft magnetic particles having insulating films on their surfaces, wherein an iron oxide content in an internal region located 3.0 mm or more inward from the surface of the powder compact is 0.1% by mass or more and 10.0% by mass or less.

[0012] The powder magnetic core of the present disclosure, in which the content of iron oxide in the internal region is 0.1 mass % or more, contains recycled powder A. Therefore, the powder magnetic core of the present disclosure can reduce the amount of new soft magnetic powder used. ２ The CO emissions during the production of new soft magnetic powder ２ Therefore, by using recycled powder A as a raw material, the dust core of the present disclosure reduces the amount of CO emitted during the production of the dust core. ２ The powder magnetic core of the present disclosure, in which the content of iron oxide in the internal region falls within the above range, has superior strength compared to the powder magnetic core X produced using the recycled powder X.

[0013] (2) In the powder magnetic core of (1) above, the soft magnetic particles may have an average particle size of 20 μm (micrometers) or more, and the insulating film may have an average thickness of 40 nm (nanometers) or more.

[0014] When the average particle size of the soft magnetic particles is 20 μm or more, the density of the powder magnetic core can be easily increased. When the average thickness of the insulating film is 40 nm or more, the eddy current loss of the powder magnetic core can be easily reduced.

[0015] (3) In the powder magnetic core of (1) or (2), the insulating film may have an insulating layer containing phosphate, silica, or magnesia, and the soft magnetic particles may be formed of at least one metal selected from iron, iron-silicon alloy, iron-silicon-aluminum alloy, iron-aluminum alloy, iron-nickel alloy, and iron-cobalt alloy, each having a purity of 99% or more.

[0016] The insulating film is likely to improve electrical insulation between adjacent soft magnetic particles. The soft magnetic particles are made of iron with a purity of 99% or higher, which facilitates densification of the powder magnetic core. The soft magnetic particles are made of at least one metal selected from an iron-silicon alloy, an iron-silicon-aluminum alloy, an iron-aluminum alloy, an iron-nickel alloy, and an iron-cobalt alloy, which facilitates reduction of eddy current loss in the powder magnetic core.

[0017] (4) In any one of the powder magnetic cores (1) to (3) above, the mass ratio of the powder to the total mass of the powder and new soft magnetic powder may be 1 mass % or more and less than 100 mass %.

[0018] By setting the mass ratio of the powder to 1 mass % or more, CO ２ When the mass ratio of the powder is less than 100 mass %, the effect of improving magnetic properties and the effect of reducing eddy current loss due to the inclusion of new soft magnetic powder can be expected.

[0019] (5) A motor stator according to the present disclosure includes the powder magnetic core according to any one of (1) to (4) above and a coil.

[0020] The motor stator of the present disclosure includes the powder magnetic core of the present disclosure, and therefore reduces CO generated during manufacturing. ２ can reduce emissions.

[0021] (6) A motor according to the present disclosure includes the motor stator of (5) above and a rotor.

[0022] The motor of the present disclosure includes the motor stator of the present disclosure, and therefore reduces CO generated during manufacturing. ２ can reduce emissions.

[0023] (7) A method for producing a powder magnetic core according to the present disclosure includes the steps of recovering used powder magnetic cores containing soft magnetic powder having insulating films on the surfaces of soft magnetic particles, pulverizing the used powder magnetic cores to obtain recycled powder, compression-molding the recycled powder to produce a molded body, and heat-treating the molded body. The recovered used powder magnetic cores are heat-treated in an oxygen-containing atmosphere. The recycled powder contains 0.1% by mass or more and 10.0% by mass or less of iron oxide.

[0024] The method for producing a powder magnetic core according to the present disclosure can produce a recycled powder magnetic core by using recycled powder A. By using recycled powder A as a raw material, the method for producing a powder magnetic core according to the present disclosure can reduce CO generated during the production of the powder magnetic core. ２ The method for producing a powder magnetic core according to the present disclosure can produce a powder magnetic core according to the present disclosure in which the iron oxide content in the internal region is 0.1% by mass or more and 10.0% by mass or less by using recycled powder A. The method for producing a powder magnetic core according to the present disclosure can produce a powder magnetic core superior in strength to the above powder magnetic core X.

[0025] (8) In the method for producing a powder magnetic core according to (7) above, the heat treatment step may be carried out in an atmosphere containing oxygen or an atmosphere containing nitrogen.

[0026] The method for producing a powder magnetic core according to (8) above can produce a powder magnetic core with high strength. The method for producing a powder magnetic core according to (8) above can produce a powder magnetic core with high strength if it is produced in an oxygen atmosphere, compared to a nitrogen atmosphere. The method for producing a powder magnetic core according to (8) above can produce a powder magnetic core with low iron loss if it is produced in a nitrogen atmosphere, compared to an oxygen atmosphere.

[0027] (9) In the method for producing a powder magnetic core according to (8) above, the oxygen concentration in the oxygen-containing atmosphere in the heat treatment step may be 100 ppm or more and 250,000 ppm or less by volume.

[0028] In the method for producing a powder magnetic core according to (9) above, by keeping the oxygen concentration within the above range, a powder magnetic core with high strength can be produced.

[0029] (10) In the method for producing a powder magnetic core according to (8) or (9), the temperature of the heat treatment may be 300° C. or higher and 900° C. or lower.

[0030] In the method for producing a powder magnetic core described above in (10), by setting the heat treatment temperature within the above range, it is possible to reduce the strain introduced into the soft magnetic particles by compression molding.

[0031] (11) In the method for producing a powder magnetic core according to any one of (7) to (10), the recovering step may recover a motor stator further including a coil attached to the used powder magnetic core. The step of obtaining the recycled powder includes a step of pulverizing the motor stator using a pulverizer equipped with a screen to obtain a pulverized product, and a step of classifying the pulverized product using a sieve. The screen has a plurality of openings. Each of the plurality of openings has a diameter of 1 mm or more and 15 mm or less. The sieve has a mesh size of less than 1 mm.

[0032] The pulverizer is equipped with a screen with openings each having a diameter within the above range, and by having the sieve openings within the above range, recycled powder B that meets the specified particle size and copper content ratio can be selected and obtained.

[0033] (12) In the method for producing a powder magnetic core according to any one of (7) to (11) above, the soft magnetic particles may have an average particle size of 20 μm or more, and the insulating film may have an average thickness of 40 nm or more.

[0034] When the average particle size of the soft magnetic particles is 20 μm or more, the density of the powder magnetic core can be easily increased. When the average thickness of the insulating film is 40 nm or more, the insulating film is less likely to peel off when the powder magnetic core is pulverized.

[0035] (13) In the method for producing a powder magnetic core according to any one of (7) to (12), the insulating film may have an insulating layer containing phosphate, silica, or magnesia, and the soft magnetic particles may be formed of at least one metal selected from iron, iron-silicon alloy, iron-silicon-aluminum alloy, iron-aluminum alloy, iron-nickel alloy, and iron-cobalt alloy, each having a purity of 99% or more.

[0036] The method for producing a powder magnetic core according to (13) above can produce a powder magnetic core that easily improves electrical insulation between adjacent soft magnetic particles. The method for producing a powder magnetic core according to (13) above can produce a high-density powder magnetic core because the soft magnetic particles are made of iron with a purity of 99% or more. The method for producing a powder magnetic core according to (13) above can produce a powder magnetic core that easily reduces eddy current loss because the soft magnetic particles are made of at least one metal selected from an iron-silicon alloy, an iron-silicon-aluminum alloy, an iron-aluminum alloy, an iron-nickel alloy, and an iron-cobalt alloy.

[0037] (14) In the method for producing a powder magnetic core according to any one of (7) to (13) above, in the compression molding step, a mixed powder containing new soft magnetic powder having an insulating film on the surface of the soft magnetic particles and the recycled powder may be compression molded.

[0038] By using a mixed powder containing new soft magnetic powder and recycled powder A, recycled powder B, or recycled powder C as a raw material, the magnetic properties of the powder core can be improved and the eddy current loss of the powder core can be reduced compared to when only recycled powder A, recycled powder B, or recycled powder C is used as a raw material.

[0039] [Details of the embodiments of the present disclosure] Specific examples of powder magnetic cores of the present disclosure are described below. The same reference numerals in the figures indicate the same objects. The sizes of components shown in each drawing are expressed for the purpose of clarifying the description and do not necessarily represent actual dimensional relationships. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0040] <Powder magnetic core> A powder magnetic core 10 according to an embodiment will be described with reference to Fig. 1 to Fig. 4. One of the features of the powder magnetic core 10 is that it contains recycled powder 1, as shown in Fig. 1. The powder magnetic core 10 is a powder magnetic core that has been recycled using the recycled powder 1 as a raw material.

[0041] <Recycled Powder> The recycled powder 1 has an insulating film 3 on the surface of soft magnetic particles 2. The recycled powder 1 is a soft magnetic powder obtained by pulverizing used dust cores.

[0042] [Soft Magnetic Particles] The soft magnetic particles 2 are formed of, for example, iron or an iron-based alloy. The iron has a purity of, for example, 99% or more. Iron with a purity of 99% or more contains 99% or more by mass of iron. The iron-based alloy is, for example, at least one selected from an iron-silicon alloy (silicon steel), an iron-silicon-aluminum alloy (sendust), an iron-aluminum alloy, an iron-nickel alloy (permalloy), and an iron-cobalt alloy. The soft magnetic particles 2 in this example are formed of iron with a purity of 99% or more. Iron with a purity of 99% or more is softer than an iron-based alloy. When the soft magnetic particles 2 are formed of iron with a purity of 99% or more, the powder core 10 can be easily densified by compression molding. Densifying the powder core 10 can improve the magnetic properties of the powder core 10. The magnetic properties include, for example, relative permeability and saturation magnetic flux density. An iron-based alloy has higher electrical resistance than iron. When the soft magnetic particles 2 are made of the iron-based alloy, eddy current loss that occurs when magnetic flux flows through the powder magnetic core 10 can be easily reduced.

[0043] <Average Particle Diameter> The average particle diameter of the soft magnetic particles 2 is, for example, 20 μm or more and 400 μm or less. When the average particle diameter of the soft magnetic particles 2 is 20 μm or more, the recycled powder 1 can be easily compression-molded, and the powder core 10 can be easily densified. By densifying the powder core 10, the magnetic properties of the powder core 10 can be improved. When the average particle diameter of the soft magnetic particles 2 is 45 μm or more, high magnetic properties are easily obtained. When the average particle diameter of the soft magnetic particles 2 is 90 μm or more, even higher magnetic properties are easily obtained. When the average particle diameter of the soft magnetic particles 2 is 150 μm or more, even higher magnetic properties are easily obtained. When the average particle diameter of the soft magnetic particles 2 is 200 μm or more, even higher magnetic properties are easily obtained. Furthermore, when the average particle diameter of the soft magnetic particles 2 is 400 μm or less, eddy current loss is easily reduced. When the average particle diameter of the soft magnetic particles 2 is 300 μm or less, eddy current loss is easily reduced even more. The average particle diameter of the soft magnetic particles 2 may be 45 μm or more and 300 μm or less, or even 90 μm or more and 300 μm or less.

[0044] The average particle size of the soft magnetic particles 2 can be determined as follows: The dust core 10 is pulverized into powder. The particle size distribution of the pulverized powder is measured using a laser diffraction particle size distribution analyzer. The sum of the values ​​obtained by multiplying the measured particle sizes by their frequencies is regarded as the average particle size of the soft magnetic particles 2. The frequency is the ratio of the number of particles in each particle size range to the total number of particles, expressed as a percentage. The particle size ranges are individual divisions obtained by dividing the entire range of particle sizes from the minimum to the maximum into specified particle size ranges. For example, the range of more than 15 μm to 25 μm or less is the 20 μm particle size range, the range of more than 25 μm to 35 μm or less is the 30 μm particle size range, and the range of more than 35 μm to 45 μm or less is the 40 μm particle size range. If the frequency of particles falling within the 20 μm particle size interval is 20%, the frequency of particles falling within the 30 μm particle size interval is 50%, and the frequency of particles falling within the 40 μm particle size interval is 30%, then the average particle size is (20 × 0.2) + (30 × 0.5) + (40 × 0.3) = 31 μm. In the above calculation example, for ease of understanding, the width of the particle size interval is set to 10 μm, but the width of the actual particle size interval is, for example, 5 μm or more and 40 μm or less.

[0045] [Insulating Film] The insulating film 3 provides electrical insulation between adjacent soft magnetic particles 2. By providing the insulating film 3 on the surface of the soft magnetic particles 2, the electrical resistance of the powder core 10 can be increased and the eddy current loss of the powder core 10 can be reduced. The insulating film 3 is formed of, for example, phosphate, silica, or magnesia. The phosphate is, for example, zinc phosphate, iron phosphate, manganese phosphate, or calcium phosphate.

[0046] The insulating film 3 may have a single-layer structure having only one type of insulating layer, or a multilayer structure having two or more types of insulating layers stacked together. The multilayer insulating film 3 may have an insulating layer containing phosphate, silica, or magnesia. An insulating layer containing phosphate has high adhesion to the soft magnetic particles 2. Furthermore, an insulating layer containing phosphate is easily deformed. An insulating film 3 having an insulating layer containing phosphate easily follows the deformation of the soft magnetic particles 2 when the recycled powder 1 is compression-molded, and therefore is less likely to peel off. An insulating layer containing silica or magnesia is hard. An insulating film 3 having an insulating layer containing silica or magnesia is less likely to be damaged or become too thin when the recycled powder 1 is compression-molded. When the insulating film 3 has a two-layer structure, it has a first insulating layer and a second insulating layer in this order. The first insulating layer is in contact with the surface of the soft magnetic particles 2. The second insulating layer is disposed on the first insulating layer and in contact with the first insulating layer. For example, the first insulating layer contains phosphate or silica, and the second insulating layer contains any of phosphate, silica, and magnesia. Specifically, when the material of the first insulating layer is phosphate, the material of the second insulating layer is silica or magnesia. When the material of the first insulating layer is silica, the material of the second insulating layer is phosphate or magnesia. The insulating film 3 in this example has a two-layer structure in which the first insulating layer and the second insulating layer are stacked in order. In this example, the first insulating layer is made of phosphate. The second insulating layer is made of silica.

[0047] <Average Thickness> Generally, the average thickness of the insulating film of the soft magnetic powder contained in a conventional powder magnetic core is 20 nm or more and 30 nm or less. In the powder magnetic core 10 of the embodiment, the average thickness of the insulating film 3 is, for example, 40 nm or more and 500 nm or less. When the average thickness of the insulating film 3 is 40 nm or more, the eddy current loss of the powder magnetic core 10 is easily reduced. Furthermore, when the average thickness of the insulating film 3 is 40 nm or more, the insulating film 3 is less likely to peel off, making it easier to achieve the effect of reducing eddy current loss by the insulating film 3. When the average thickness of the insulating film 3 is 500 nm or less, the proportion of the soft magnetic particles 2 contained in the powder magnetic core 10 does not become too small. Therefore, the magnetic properties of the powder magnetic core 10 can be improved. The average thickness of the insulating film 3 may be 50 nm or more and 400 nm or less, 80 nm or more and 350 nm or less, or even 100 nm or more and 300 nm or less. When the average thickness of the insulating film 3 is 50 nm or more and 400 nm or less, high magnetic properties are easily obtained. If the average thickness of the insulating film 3 is 80 nm or more and 350 nm or less, the variation in magnetic properties is likely to be small, and if it is 100 nm or more and 300 nm or less, the variation in magnetic properties is small and higher magnetic properties are likely to be obtained. The average thickness of the insulating film 3 may be 120 nm or more, 150 nm or more, or even 200 nm or more. The thickness of the insulating film 3 is the combined thickness of all the insulating layers that make up the insulating film 3.

[0048] The average thickness of the insulating film 3 can be determined as follows. The cross section of the powder magnetic core 10 is observed using a microscope, and the observed image is subjected to image analysis. The microscope is a scanning electron microscope (SEM) or a transmission electron microscope (TEM), for example. The number of fields of view observed is 20 or more. The magnification is, for example, 50,000 times or more and 200,000 times or less. The average thickness of the insulating film 3 in each field of view is determined by image analysis. In each field of view, the thickness of the insulating film 3 is measured at five or more locations and the average is determined. The average thickness of the insulating film 3 in all fields of view, 20 or more, is determined, and the average is taken as the average thickness of the insulating film 3.

[0049] In dust cores made from new soft magnetic powder, cracks and peeling of the insulating film are almost never observed. As will be described later with reference to Figures 10 and 12, the insulating film 3 of the recycled powder 1 has cracks 3c, but almost no peeling is observed. In this way, the presence or absence of multiple cracks 3c on the surface of the insulating film 3 can be used as an indicator to determine whether the powder is recycled or not.

[0050] The powder magnetic core 10 contains iron oxide in an internal region located 3.0 mm or more inward from the surface. The content of iron oxide in the internal region is 0.1% by mass or more and 10.0% by mass or less. The iron oxide may be, for example, Fe ３ O ４ , Fe ２ O ３ , FeO, FeOOH, and FeOH. The iron oxide content refers to the total content of these iron oxides. A content of iron oxide of 0.1% by mass or more in the internal region is one indicator that the powder core is produced using recycled powder obtained by pulverizing a powder core heat-treated in an oxygen-containing atmosphere (hereinafter simply referred to as an oxygen atmosphere) in the powder core manufacturing method described below. When a powder core produced using new soft magnetic powder is heat-treated in an oxygen atmosphere, iron may be partially oxidized in the external region located less than 3.0 mm from the surface of the powder core, resulting in the generation of iron oxide in the external region. However, oxygen has difficulty penetrating the internal region of the powder core, so iron is not oxidized in the internal region, and iron oxide is therefore unlikely to be generated in the internal region. In other words, a powder core having an iron oxide content of 0.1% by mass or more in the internal region can only be produced by using recycled powder 1 obtained by pulverizing a powder core heat-treated in an oxygen atmosphere. The powder magnetic core 10 has an iron oxide content of 0.1% by mass or more and 10.0% by mass or less in the internal region, and therefore has superior strength compared to the powder magnetic core X produced using the above-described recycled powder X. The iron oxide content of the internal region may be 0.1% by mass or more and 7.0% by mass or less, or 0.1% by mass or more and 5.0% by mass or less.

[0051] The iron oxide content in the internal region was measured as follows: A cross section of the powder magnetic core was taken, and ten randomly selected points in the internal region were subjected to component analysis by X-ray diffraction (XRD) to measure the iron oxide content at each measurement point. The average value of all measurement points was taken as the iron oxide content in the internal region.

[0052] [Small Copper Pieces] The recycled powder 1 may further contain small copper pieces 4. In the method for producing a powder magnetic core described below, when recycled powder obtained by pulverizing a used powder magnetic core and a coil together is used as a raw material, the powder magnetic core 10 contains small copper pieces 4. The small copper pieces 4 are mainly arranged between the soft magnetic particles 2. The average length of the small copper pieces 4 is, for example, larger than the average particle diameter of the soft magnetic particles 2 and is approximately the same as the diameter of the openings in the screen described below. The method for measuring the average length of the small copper pieces 4 is the same as the method for measuring the average particle diameter of the soft magnetic particles 2. The copper content of the entire powder magnetic core 10 is, for example, 0.01% by mass or more and 5.00% by mass or less. A powder magnetic core 10 having a copper content of 0.01% by mass or more is one indicator that the powder magnetic core is produced using recycled powder 1 obtained by pulverizing a used powder magnetic core and a coil together and classifying it using a specific sieve. When the copper content is 0.01% by mass or more and 5.00% by mass or less, the iron loss is less likely to increase compared to powder core A produced using recycled powder A. The copper content may be 0.015% by mass or more and 4.50% by mass or less, or 0.02% by mass or more and 4.00% by mass or less.

[0053] [Resin Particles] The recycled powder 1 may further contain resin particles 5. In the method for producing a powder magnetic core described below, when recycled powder obtained by pulverizing a used powder magnetic core, a coil, and a resin mold together is used as a raw material, the powder magnetic core 10 contains resin particles 5. The resin particles 5 are mainly disposed between the soft magnetic particles 2. The resin particles 5 tend to improve electrical insulation between adjacent soft magnetic particles 2. The average particle diameter of the resin particles 5 is, for example, the same as that of the soft magnetic particles 2. The method for measuring the average particle diameter of the resin particles 5 is the same as that for the soft magnetic particles 2. The carbon content of the powder magnetic core 10 as a whole can be considered to be the resin content of the powder magnetic core 10 as a whole. The carbon content is, for example, 0.05% by mass or more and 1.00% by mass or less. Powder core 10 having a carbon content of 0.05% by mass or more is one indicator of a powder core made using recycled powder 1 obtained by crushing used powder cores, coils, and resin molds together and classifying them using a specific sieve. By having a carbon content of 0.05% by mass or more and 1.00% by mass or less, iron loss is less likely to increase compared to powder core A. The carbon content may be 0.05% by mass or more and 0.80% by mass or less, or 0.06% by mass or more and 0.70% by mass or less.

[0054] The total content of elements excluding iron, copper, and carbon in the entire powder magnetic core 10 is, for example, 0.50% by mass or more and 1.00% by mass or less. When the total content is 0.50% by mass or more and 1.00% by mass or less, iron loss is less likely to increase compared to the powder magnetic core A. The total content may be 0.55% by mass or more and 0.98% by mass or less, or 0.60% by mass or more and 0.96% by mass or less.

[0055] The content ratio of each element and the total content ratio can be measured by high-frequency inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0056] The powder magnetic core 10 contains the recycled powder 1, which allows the amount of new soft magnetic powder used to be reduced. The powder magnetic core 10 manufactured using the recycled powder 1 as a raw material reduces the amount of CO generated during the manufacturing of the powder magnetic core 10. ２The amount of discharged material can be reduced. The powder core 10 may further contain new soft magnetic powder. The new soft magnetic powder has an insulating film on the surface of the soft magnetic particles. The configuration of the new soft magnetic powder is basically the same as the configuration of the recycled powder 1 described above. The new soft magnetic powder is unused soft magnetic powder in the state in which it is manufactured. By including new soft magnetic powder in the powder core 10, the magnetic properties of the powder core 10 can be improved and the eddy current loss of the powder core 10 can be reduced.

[0057] The mass ratio of the recycled powder 1 to the mass of the powder magnetic core 10 is, for example, 1 mass % or more and 100 mass % or less. By making the mass ratio of the recycled powder 1 1 mass % or more, the amount of new soft magnetic powder used can be reduced, thereby reducing CO ２ This CO ２ The greater the mass proportion of recycled powder 1, the greater the expected reduction effect. When the mass proportion of recycled powder 1 is 100 mass%, the powder core 10 contains only recycled powder 1. In other words, this powder core 10 is manufactured using only recycled powder 1 as a raw material. Since it does not contain new soft magnetic powder, CO ２ The reduction effect is high.

[0058] The mass ratio of the recycled powder 1 to the total mass of the recycled powder 1 and the new soft magnetic powder is, for example, 1 mass % or more and less than 100 mass %. By making the mass ratio of the recycled powder 1 1 mass % or more, the amount of new soft magnetic powder used can be reduced, thereby reducing CO ２ By setting the mass ratio of the recycled powder 1 to less than 100 mass %, it is possible to expect an improvement in magnetic properties due to the inclusion of new soft magnetic powder. The greater the mass ratio of the recycled powder 1, the greater the reduction in CO ２ The mass proportion of the recycled powder 1 may be, for example, 5 mass% or more, 10 mass% or more, 20 mass% or more, 40 mass% or more, 50 mass% or more, 70 mass% or more, or even 90 mass% or more.

[0059] The relative density of the powder core 10 is, for example, 85% or more. The higher the relative density of the powder core 10, the better the magnetic properties of the powder core 10. When the relative density of the powder core 10 is 85% or more, high magnetic properties are easily obtained. The powder core 10 having high magnetic properties contributes to improving the performance of electrical equipment such as motors and reactors. The relative density of the powder core 10 may be 90% or more, 93% or more, or even 95% or more. The upper limit of the relative density of the powder core 10 is not particularly limited, but is, for example, 99%. The relative density is the apparent density divided by the true density, expressed as a percentage. Here, the theoretical density of the soft magnetic powder is referred to as the true density. Since the content of materials other than the soft magnetic powder in the powder core 10 is very small, the theoretical density of the soft magnetic powder can be considered the true density.

[0060] The powder magnetic core 10 can have various shapes depending on the application. The powder magnetic core 10 can be used as a magnetic core for electric devices such as motors and reactors. The powder magnetic core 10a shown in FIG. 2 is a circular stator core used in the stator of an axial gap motor. The powder magnetic core 10a includes a yoke 20 and teeth 30. The yoke 20 and teeth 30 are integrally molded. The yoke 20 has an annular plate shape. A plurality of teeth 30 are equally spaced and arranged in a ring shape on the upper surface of the yoke 20. Each tooth 30 protrudes from the upper surface of the yoke 20. The teeth 30 have a cylindrical shape. In this example, there are 12 teeth 30. The teeth 30 in this example have a triangular prism shape. A coil (not shown) is attached to the outer periphery of each tooth 30. The number of teeth 30 is not particularly limited and is set appropriately depending on the specifications of the motor. The shape of the teeth 30 may be any shape other than a triangular prism, such as a trapezoidal prism or other quadrangular prism.

[0061] The powder magnetic core 10b shown in FIG. 3 is a split core obtained by splitting the stator core described above with reference to FIG. 2 around the axis. The split core constitutes a part of the stator core. The stator core is formed by combining the split cores in an annular shape. The powder magnetic core 10b includes a fan-shaped yoke 20 and a triangular prism-shaped tooth 30 protruding from the upper surface of the yoke 20. There is one tooth 30. In this example, the annular stator core is formed by combining 12 powder magnetic cores 10b.

[0062] The powder magnetic core 10c shown in Fig. 4 is another example of a split core obtained by splitting the stator core described above with reference to Fig. 2 around the axis. In the powder magnetic core 10c, three teeth 30 are arranged on one yoke 20. The yoke 20 has a fan-like shape. The teeth 30 have a triangular prism-like shape. In this example, a circular stator core is formed by combining four powder magnetic cores 10c.

[0063] The powder core 10 may include a resin mold (not shown). The resin mold covers at least a portion of the powder core 10. The resin mold is provided, for example, on a portion of the powder core 10 that comes into contact with the coil. The resin mold may be provided so as to cover the coil arranged on the powder core 10. In this case, the coil can be integrated with the powder core 10 by the resin mold. The resin mold is formed of, for example, at least one resin selected from the group consisting of epoxy resin, acrylic resin, fluorine resin, and polyimide resin.

[0064] <Motor Stator> A motor stator 200 according to an embodiment will be described with reference to FIG. 5 . Hereinafter, the motor stator may be simply referred to as a "stator." The stator 200 shown in FIG. 5 is used in an axial gap motor. The stator 200 includes a powder magnetic core 10 and a coil 210. The powder magnetic core 10 shown in FIG. 5 has the same configuration as the powder magnetic core 10a shown in FIG. 2. The coil 210 is disposed on each tooth 30. The coil 210 includes a cylindrical portion formed by winding a wire. The winding includes a conductor made of copper or a copper alloy and an insulating coating provided on the outer periphery of the conductor.

[0065] <Motor> A motor 300 according to an embodiment will be described with reference to Fig. 6. The motor 300 includes a stator 200 and a rotor 250. The motor 300 shown in Fig. 6 is an axial gap motor in which the stator 200 and the rotor 250 are disposed facing each other in a direction along a rotation axis 330.

[0066] The rotor 250 is arranged to face the end faces of each tooth 30 of the stator 200. The rotor 250 includes a plurality of flat magnets 260 and an annular retaining plate 270 that supports these magnets 260. The end faces of each tooth 30 and each magnet 260 face each other at a predetermined interval in a direction along the rotation shaft 330. The retaining plate 270 is fixed to the rotation shaft 330 and rotates together with the rotation shaft 330. Each magnet 260 is embedded in the retaining plate 270. The plurality of magnets 260 are arranged at equal intervals around the axis of the rotation shaft 330. Each magnet 260 is magnetized in a direction along the rotation shaft 330. The magnetization directions of adjacent magnets 260 are opposite to each other.

[0067] Stator 200 and rotor 250 are housed in a cylindrical case 310. Disk-shaped plates 320 are attached to both ends of case 310. A through-hole is formed in the center of each plate 320, and a rotating shaft 330 passes through case 310. Stator 200 is fixed to case 310 by fitting the outer peripheral surface of yoke 20 into the inner peripheral surface of case 310. An annular bearing 340 that rotatably supports rotating shaft 330 is attached to the inner peripheral surface of yoke 20.

[0068] <Method for manufacturing powder magnetic core> The powder magnetic core 10 can be manufactured by a method for manufacturing a powder magnetic core according to an embodiment. The method for manufacturing a powder magnetic core can manufacture recycled powder by pulverizing used powder magnetic cores. The method for manufacturing a powder magnetic core includes a recovery step, a recycled powder preparation step, a pressing step, and a heat treatment step. Each step will be described in detail below.

[0069] <Recovery Process> The recovery process is a process of recovering used powder magnetic cores. Used powder magnetic cores are powder magnetic cores that have been heat-treated in an oxygen atmosphere. The recovery process may also be a process of recovering motor stators. The motor stators include used powder magnetic cores and coils attached to the used powder magnetic cores. The motor stators may further include a resin mold that covers at least one of the used powder magnetic cores and the coils. The used powder magnetic cores are recovered from used electrical equipment. Used powder magnetic cores may be recovered with accessories such as coils still attached to the recovered powder magnetic cores, or with at least one of the used powder magnetic cores and the coil still covered by a resin mold. When the used powder magnetic cores and coils are pulverized together in the recycled powder production process described below, it is not necessary to completely remove the coils from the used powder magnetic cores. In this case, the productivity of the powder magnetic cores is superior to that of recovering powder magnetic cores from which the accessories and resin molds have been completely removed. In the recycled powder production process described below, when the used powder core, coil, and resin mold are crushed together, it is not necessary to completely remove the resin mold from at least one of the used powder core and coil. In this case, the productivity of the powder core is superior compared to when the powder core is recovered from which the accessories and resin mold have been completely removed.

[0070] Used powder magnetic cores contain soft magnetic powder having insulating films on the surfaces of the soft magnetic particles. The composition of the soft magnetic powder in used powder magnetic cores is basically the same as the composition of the recycled powder 1 described above. Used powder magnetic cores may be powder magnetic cores that have never been recycled, or may be powder magnetic cores that have been recycled at least once. A powder magnetic core that has never been recycled is a powder magnetic core manufactured using only new soft magnetic powder as raw materials. A recycled powder magnetic core is a powder magnetic core that contains recycled powder. Here, "used" does not necessarily mean that it has actually been used as an electrical device. Used powder magnetic cores may also be powder magnetic cores that have been manufactured as powder magnetic cores and then collected without being used as electrical equipment. In other words, anything that has been molded from soft magnetic powder into a powder magnetic core is included in the category of used powder magnetic cores, regardless of whether it has actually been used as an electrical device. Used powder magnetic cores may also be powder magnetic cores that have been collected as defective products during the production of powder magnetic cores.

[0071] Used powder magnetic cores are powder magnetic cores that have been heat-treated in an oxygen atmosphere, and therefore generally have iron oxide present in an outer region located less than 3.0 mm from the surface of the powder magnetic core. The iron oxide content in the outer region is 20.0% by mass or more and 70.0% by mass or less. When a used powder magnetic core is a powder magnetic core that has been heat-treated in an oxygen atmosphere and has never been recycled, iron oxide is present in the outer region, but iron oxide is substantially absent in an inner region located 3.0 mm or more inward from the surface of the powder magnetic core. On the other hand, when a used powder magnetic core is a powder magnetic core that has been heat-treated in an oxygen atmosphere and recycled at least once, iron oxide is also present in an inner region located 3.0 mm or more inward from the surface of the powder magnetic core. The iron oxide content in the inner region is 0.1% by mass or more and 10.0% by mass or less. That is, depending on whether or not iron oxide is present in the internal region, it can be determined whether or not a used powder magnetic core has been heat-treated in an oxygen atmosphere and recycled at least once.

[0072] The average particle diameter of the soft magnetic particles in the used powder magnetic core is, for example, 20 μm or more and 400 μm or less. The average particle diameter of the soft magnetic particles may be 45 μm or more and 300 μm or less, or even 90 μm or more and 300 μm or less. The average thickness of the insulating film in the used powder magnetic core is, for example, 40 nm or more and 500 nm or less. The average thickness of the insulating film may be 50 nm or more and 400 nm or less, 80 nm or more and 350 nm or less, or even 100 nm or more and 300 nm or less. Generally, the average thickness of the insulating film in conventional powder magnetic cores is 20 nm or more and 30 nm or less. In the manufacturing method for a powder magnetic core of the embodiment, the average thickness of the insulating film is set to 40 nm or more and 500 nm or less in order to make it less likely for the insulating film to peel off when the powder magnetic core is pulverized in the pulverization step described below.

[0073] <Recycled Powder Production Process> The recycled powder production process is a process of obtaining recycled powder by at least performing a pulverization process. The recycled powder contains 0.1% by mass or more and 10.0% by mass or less of iron oxide. In the pulverization process, the object to be pulverized is pulverized. The object to be pulverized is pulverized object A, pulverized object B, or pulverized object C. The pulverized object A is only a used powder core. The pulverized object B is a used powder core and a coil attached to the powder core. The pulverized object C is a used powder core, a coil attached to the powder core, and a resin mold covering at least one of the powder core and the coil. If the object to be pulverized is pulverized object B or pulverized object C, a classification process is performed after the pulverization process. In the classification process, the pulverized product obtained by pulverizing pulverized object B or pulverized object C is classified using a sieve. The recycled powder is pulverized powder A, pulverized powder B, or pulverized powder C. Recycled powder A is a powder obtained by pulverizing pulverization target A, and is the soft magnetic powder contained in used powder cores. Recycled powder B is a powder obtained by pulverizing and classifying pulverization target B, and contains the soft magnetic powder contained in used powder cores and copper flakes. Recycled powder C is a powder obtained by pulverizing and classifying pulverization target C, and contains the soft magnetic powder contained in used powder cores, copper flakes, and resin powder.

[0074] In a powder magnetic core, adjacent soft magnetic particles are not metallurgically bonded to each other. The inventors discovered that when a powder magnetic core is pulverized, the soft magnetic particles separate and become dispersed, i.e., powdered, and that the particle size of the powdered particles is substantially the same as the particle size of the soft magnetic powder contained in the powder magnetic core before pulverization. In other words, even when a powder magnetic core is pulverized, the particle size of the soft magnetic powder is substantially maintained. If the insulating film in a used powder magnetic core is thin, the insulating film may peel off due to the impact when the powder magnetic core is pulverized. If the insulating film is thick, cracks may occur in the insulating film when the powder magnetic core is pulverized, but peeling of the insulating film is unlikely to occur. If the average thickness of the insulating film before pulverization is 40 nm or more, the insulating film is unlikely to peel off when the powder magnetic core is pulverized.

[0075] The average particle diameter of the recycled powder is, for example, 20 μm or more and 400 μm or less. The average particle diameter of the recycled powder is the average particle diameter of soft magnetic particles including an insulating film. The average particle diameter of the recycled powder is the particle diameter D50 at which the cumulative mass is 50% in the particle size distribution measured by a laser diffraction particle size distribution analyzer. The average particle diameter of the recycled powder may be 45 μm or more and 300 μm or less, or even 90 μm or more and 300 μm or less. The average thickness of the insulating film in the recycled powder is, for example, 40 nm or more and 500 nm or less. The average thickness of the insulating film in the recycled powder may be 50 nm or more and 400 nm or less, 80 nm or more and 350 nm or less, or even 100 nm or more and 300 nm or less.

[0076] [Crusher] A known crusher can be used to crush the object to be crushed. Crushers used include, for example, a cutter-type crusher, a hammer-type crusher, or a chain-type crusher. A cutter-type crusher crushes the object to be crushed by scraping it off with a rotating blade. A hammer-type crusher crushes the object to be crushed by smashing it with a rotating hammer. A chain-type crusher crushes the object to be crushed by smashing it with a rotating chain.

[0077] The object to be pulverized may be pulverized using a pulverizer equipped with a screen. An example of a pulverizer 100 will be described with reference to FIG. 7 . FIG. 7 is a schematic diagram of the configuration of the pulverizer 100. The pulverizer 100 is a cutter-type pulverizer. The pulverizer 100 includes a pulverization chamber 110, a rotary blade 120, a fixed blade 130, and a screen 140. The pulverization chamber 110 has an inlet 111. Used powder cores 10 are loaded into the pulverization chamber 110 through the inlet 111. Although not shown, in the case of pulverization object B, a coil is attached to the loaded powder core 10, and in the case of pulverization object C, a coil and a resin mold are attached to the loaded powder core 10. The rotary blade 120 is disposed in the pulverization chamber 110. The rotary blade 120 is attached to a rotation shaft 121. A plurality of rotary blades 120 are attached in a row along the rotation shaft 121. The rotary blade 120 rotates as the rotary shaft 121 rotates. The fixed blade 130 is disposed in the crushing chamber 110. A predetermined clearance is provided between the rotary blade 120 and the fixed blade 130. The powder core 10 is sheared by the rotary blade 120 and the fixed blade 130. The screen 140 is attached to the discharge outlet of the crushing chamber 110. The pulverized material sheared by the rotary blade 120 and the fixed blade 130 is crushed and pulverized between the rotary blade 120 and the screen 140.

[0078] The screen 140 is a plate having a plurality of openings 141. The powder cores 10 are pulverized to a size that can pass through the openings 141. As described above, when the powder cores 10 are pulverized, the soft magnetic particles break down into powder. The recycled powder 1 obtained by pulverizing the powder cores 10 is discharged through the openings 141. The shape of each opening 141 is, for example, circular. The diameter of each of the plurality of openings 141 can be selected appropriately depending on the size of the powder cores 10 to be pulverized. The diameter of the openings 141 is, for example, 1 mm or more and 15 mm or less. By having the diameter of the openings 141 be 1 mm or more and 15 mm or less, the powder cores 10 can be easily pulverized and the recycled powder 1 can be easily obtained. The diameter of the openings 141 may be 2 mm or more and 10 mm or less.

[0079] When crushing object B or crushing object C is crushed, the powder core 10 is crushed to a particle size approximately equal to the particle size of the soft magnetic powder used as the raw material. In contrast, the coil and resin mold are crushed to a size approximately equal to the diameter of the openings 141 in the screen 140.

[0080] [Sieving] The soft magnetic powder obtained through the openings 141 of the screen 140 and the copper pieces obtained by crushing the coil are classified using a sieve. The sieve used has a mesh size of, for example, less than 1 mm. A mesh size of less than 1 mm allows for the selection and acquisition of only recycled powder 1 that meets the specified particle size and copper content. The soft magnetic powder obtained through the openings 141 of the screen 140, the copper pieces obtained by crushing the coil, and the resin powder obtained by crushing the resin mold may also be classified using a sieve. The mesh size of this sieve is also less than 1 mm, allowing for the selection and acquisition of only recycled powder 1 that meets the specified particle size, copper content, and resin content. The sieve mesh size may be 800 μm or less or 700 μm or less. The sieve mesh size is, for example, 400 μm or more. That is, the sieve opening may be 400 μm or more and less than 1 mm, 400 μm or more and 800 μm or less, or 400 μm or more and 700 μm or less.

[0081] The recycled powder preparation step may further include a step of attracting the mixed powder classified by the sieve with a magnet to select the soft magnetic powder.

[0082] <Pressing Process> The pressing process is a process of compression molding the recycled powder. By compression molding the recycled powder, a recycled powder core is obtained. When the average particle diameter of the recycled powder is 20 μm or more and 400 μm or less, the recycled powder is easy to handle and compression mold. The higher the molding pressure when compressing the recycled powder, the higher the density of the powder core can be. The molding pressure is, for example, 500 MPa or more and 1500 MPa or less.

[0083] In the pressing process, a lubricant may be added to the recycled powder before compression molding. Adding a lubricant can improve the lubricity of the recycled powder during compression molding, facilitating the densification of the powder core. Solid lubricants such as fatty acid amides and metal soaps can be used as the lubricant. Examples of fatty acid amides include stearic acid amide and ethylene bisstearic acid amide. Examples of metal soaps include metal stearates such as zinc stearate and lithium stearate. The lubricant content is, for example, 0.1% by mass or more and 1.0% by mass or less, where the total of the recycled powder and the lubricant is 100% by mass. A lubricant content of 0.1% by mass or more can sufficiently improve the lubricity of the recycled powder, thereby enabling the densification of the powder core. A lubricant content of 1.0% by mass or less can prevent a decrease in the proportion of soft magnetic powder contained in the powder core, thereby improving the magnetic properties of the powder core. The lubricant content may be 0.3% by mass or more and 0.6% by mass or less.

[0084] In the pressing step, only the recycled powder may be compression molded, or a mixed powder containing new soft magnetic powder and recycled powder may be compression molded. By using a mixed powder containing new soft magnetic powder and recycled powder as the raw material, it is possible to improve the magnetic properties of the powder core and reduce the eddy current loss of the powder core compared to when only recycled powder is used as the raw material.

[0085] When the used powder cores to be collected are powder cores made using recycled powder obtained by pulverizing a powder core heat-treated in an oxygen atmosphere, pulverizing the used powder cores may increase the iron oxide content of the recycled powder. Furthermore, when the used powder cores to be collected are powder cores made using recycled powder B, pulverizing and classifying the used powder cores and coils together may increase the copper content of the recycled powder. When the used powder cores to be collected are powder cores made using recycled powder C, pulverizing and classifying the used powder cores, coils, and resin molds together may increase the copper content and carbon content of the recycled powder. In these cases, it is preferable to increase the amount of new soft magnetic powder in the mixed powder. As a result, the iron oxide content of the mixed powder can be reduced, and the iron oxide content in the inner region of the produced powder core can be reduced to 8.0 mass% or less. Furthermore, the copper content in the mixed powder can be set to 4.00% by mass or less, and the carbon content in the mixed powder can be set to 0.80% by mass or less.

[0086] When the mixed powder is used as a raw material, the mass ratio of the recycled powder to the total mass of the recycled powder and new soft magnetic powder is, for example, 1 mass % or more but less than 100 mass %. By making the mass ratio of the recycled powder 1 mass % or more, the amount of new soft magnetic powder used can be reduced, thereby reducing CO ２ By setting the mass ratio of recycled powder to less than 100 mass %, it is possible to expect an improvement in magnetic properties due to the inclusion of new soft magnetic powder. The greater the mass ratio of recycled powder, the greater the reduction in CO ２ The effect of reducing CO ２From the viewpoint of the reduction effect, the mass proportion of the recycled powder may be, for example, 5 mass% or more, 10 mass% or more, 20 mass% or more, 40 mass% or more, 50 mass% or more, 70 mass% or more, or even 90 mass% or more. The mass proportion of the recycled powder in the mixed powder is maintained even after compression molding. In other words, the mass proportion of the recycled powder in the powder core manufactured using the mixed powder as a raw material is equivalent to the mass proportion of the recycled powder in the mixed powder used as a raw material.

[0087] <Heat Treatment Step> The heat treatment step is a step of heat treating the compression-molded compact. Heat treating the compact can reduce the distortion introduced into the soft magnetic particles by compression molding. This can improve the magnetic properties of the powder magnetic core. The heat treatment atmosphere is an oxygen atmosphere or a nitrogen atmosphere. An oxygen atmosphere tends to increase the strength of the powder magnetic core compared to a nitrogen atmosphere. A nitrogen atmosphere tends to reduce the iron loss of the powder magnetic core compared to an oxygen atmosphere. The oxygen concentration in the oxygen atmosphere is, for example, 100 ppm or more and 250,000 ppm or less by volume. The heat treatment temperature is, for example, 300°C or more and 900°C or less. The lubricant added in the pressing step is lost by the heat treatment.

[0088] Test Example 1 The particle size distribution of recycled powder A1 obtained by pulverizing a dust core was examined.

[0089] The dust core was manufactured using new soft magnetic powder as a raw material. Hereinafter, the new soft magnetic powder will be referred to as "new powder." The new powder is iron powder with an insulating film on the surface of soft magnetic particles made of iron. The soft magnetic particles are made of iron with a purity of 99% or more. The average particle diameter of the soft magnetic particles was approximately 250 μm. The insulating film has a two-layer structure consisting of a first insulating layer, which is the inner layer, and a second insulating layer, which is the outer layer, stacked in this order. The first insulating layer is made of phosphate. The second insulating layer is made of silica. The average thickness of the insulating film was approximately 80 nm.

[0090] The powder magnetic core is a circular stator core shown in Figure 2. The outer diameter d of the stator core is approximately 52 mm. The thickness t of the stator core is approximately 19 mm. The thickness t of the stator core is the total thickness of the yoke and the teeth.

[0091] A plurality of powder magnetic cores, each without a coil or resin molded part, were prepared and heat-treated in an oxygen atmosphere. The plurality of powder magnetic cores were pulverized using a pulverizer to obtain recycled powder A1. The pulverizer used was the SF-1 model manufactured by Sanriki Seisakusho Co., Ltd. This pulverizer was a cutter-type pulverizer equipped with a screen 140 shown in FIG. 7. Each of the plurality of openings 141 formed in the screen 140 had a diameter of 5 mm. The rotation speed of the rotary blade was approximately 1000 rpm (revolutions per minute).

[0092] The particle size distribution of recycled powder A1 was measured using a laser diffraction particle size distribution analyzer. The laser diffraction particle size distribution analyzer used was an MT3300EX manufactured by Nikkiso Co., Ltd. The particle size distribution of recycled powder A1 is shown in Figure 8. Figure 8 also shows the particle size distribution of new powder. The particle size distribution of recycled powder A1 was obtained by taking three samples from recycled powder A1 and averaging the particle size distributions of these samples. The particle size distribution of new powder was measured at the raw material stage. Figure 8 shows the particle size distribution based on mass. The horizontal axis of Figure 8 is particle diameter [μm], and the vertical axis is frequency [mass%]. The solid line graph shows the particle size distribution of recycled powder A1, and the dashed line graph shows the particle size distribution of new powder.

[0093] The particle diameters D10, D50, and D90 of the recycled powder A1 and the new powder were determined. Particle diameter D10 is the particle diameter at which the cumulative mass is 10%. Particle diameter D50 is the particle diameter at which the cumulative mass is 50%. Particle diameter D90 is the particle diameter at which the cumulative mass is 90%. The results are shown in Table 1.

[0094]

[0095] 8 and Table 1, the particle size distribution of the recycled powder A1 obtained by pulverizing the powder magnetic core is almost the same as the particle size distribution of the new powder at the raw material stage. This shows that by pulverizing the used powder magnetic core, it is possible to pulverize it to a particle size similar to that of the soft magnetic powder used as the raw material.

[0096] The particle size distributions of recycled powders B1 and B2 and recycled powders C1 and C2 were also investigated in the same manner as recycled powder A1. Recycled powder B1 was prepared in the same manner as recycled powder A1, except that the powder core and coil heat-treated in an oxygen atmosphere were pulverized together and the resulting powder was sieved. The coil conductor was made of copper. The sieve had a mesh size of 500 μm. Recycled powder B2 was prepared in the same manner as recycled powder B1, except that the diameter of each opening 141 in the screen 140 was 8 mm. Recycled powder C1 was prepared in the same manner as recycled powder A1, except that the powder core and coil heat-treated in an oxygen atmosphere, and the resin mold were pulverized together and the resulting powder was sieved. The resin mold was made of epoxy resin. Recycled powder C2 was prepared in the same manner as recycled powder C1, except that the diameter of each opening 141 in the screen 140 was 8 mm. Although not shown in the figures, it was found that the particle size distributions of the recycled powders B1 and B2 and the recycled powders C1 and C2 were almost the same as the particle size distribution of the new powder at the raw material stage. This shows that whether the used powder core and coil are pulverized together, or the used powder core, coil, and resin mold are pulverized together, it is possible to produce a recycled powder having a particle size similar to that of the soft magnetic powder used as the raw material by classifying it with a sieve.

[0097] The components of recycled powders B1, B2, C1, and C2 were measured by ICP-OES, and the results are shown in Table 2.

[0098]

[0099] As shown in Table 2, it was found that by pulverizing the powder core and the coil together, or by pulverizing the powder core, the coil, and the resin mold together and then classifying them using a specific sieve, the copper content satisfies 0.01% by mass or more and 5.00% by mass or less, the carbon content satisfies 0.05% by mass or more and 1.00% by mass or less, and the total content of elements excluding iron, copper, and carbon satisfies 0.50% by mass or more and 1.00% by mass or less.

[0100] Test Example 2 Powder magnetic cores were produced using either recycled powder A1 or A2 or new powder, and the losses of these powder magnetic cores were evaluated.

[0101] <Sample No. 1> Sample No. 1 is a powder magnetic core using recycled powder A1 from Test Example 1 as the raw material. In Sample No. 1, the average thickness of the insulating film at the raw material stage was approximately 80 nm. The powder magnetic core of Sample No. 1 was manufactured as follows. 0.3 mass% of lubricant was added to the recycled powder. The recycled powder was compression-molded to obtain a powder magnetic core. The molding pressure was approximately 850 MPa. The compression-molded powder magnetic core was heat-treated in an oxygen atmosphere. The oxygen concentration in the atmosphere was 210,000 ppm by volume. The heat treatment temperature was 600°C, and the holding time was 15 minutes. The manufactured powder magnetic core was a ring-shaped toroidal core.

[0102] <Sample No. 2> The powder magnetic core of Sample No. 2 was produced in the same manner as the powder magnetic core of Sample No. 1, except that recycled powder A2, which had a different average insulating film thickness from that of Sample No. 1, was used as the raw material. Recycled powder A2 of Sample No. 2 was obtained by pulverizing a powder magnetic core, as with Sample No. 1. However, in Sample No. 2, the average thickness of the insulating film at the raw material stage was approximately 25 nm.

[0103] <Sample No. 100> The dust core of Sample No. 100 was produced in the same manner as the dust core of Sample No. 1, except that only new powder was used as the raw material. In Sample No. 100, the average thickness of the insulating film of the new powder was approximately 25 nm.

[0104] <<Loss in Powder Core>> The loss in the powder core of each sample was measured. The loss in the powder core was measured as follows. A primary coil and a secondary coil were wound around the powder core. The number of turns in the primary coil was 300, and the number of turns in the secondary coil was 30. The iron loss when a current was passed through the primary coil to magnetize the powder core was measured using the secondary coil. The measured loss in the powder core is the iron loss [W / kg] at a frequency of 1 kHz and a magnetic flux density of 1.0 T. The loss in each of the powder cores of Sample No. 1 and Sample No. 2 is shown below. The loss in the powder core is shown as a ratio based on the loss in the powder core of Sample No. 100. Sample No. 1: 112% Sample No. 2: 442%

[0105] The loss of the powder core of Sample No. 1, which used recycled powder A1 with an average insulating film thickness of approximately 80 nm as its raw material, was increased by 12% compared to the loss of the powder core of Sample No. 100. In contrast, the loss of the powder core of Sample No. 2, which used recycled powder A2 with an average insulating film thickness of approximately 25 nm as its raw material, was increased by 342% compared to the loss of the powder core of Sample No. 100. The loss of the powder core of Sample No. 1 was almost the same as the loss of the powder core of Sample No. 100. This shows that the powder core of Sample No. 1 has performance equivalent to that of the powder core of Sample No. 100.

[0106] <Evaluation of Insulating Film> The recycled powders A1 and A2 used as raw materials for the powder cores of Sample No. 1 and Sample No. 2 were observed using an SEM. The state of the insulating film on the surface of the soft magnetic particles was examined. The SEM magnification was 3000x. Figures 9 and 10 are plan views of the insulating film 3. As shown in Figure 9, Sample No. 2 had cracked portions 3c and many peeled portions 3f where the insulating film 3 had partially peeled off. In Figure 9, the peeled portions 3f are indicated by hatching. As shown in Figure 10, Sample No. 1 had fine cracks in the insulating film 3 and many cracked portions 3c in the insulating film 3. Although many cracks were observed in Sample No. 1, almost no peeling of the insulating film 3 was observed. This suggests that the thicker the insulating film, the less likely it is to peel off when the powder core is pulverized.

[0107] The state of the insulating film in each powder magnetic core sample was examined. The state of the insulating film was observed by observing the cross section of the powder magnetic core using a SEM. The SEM magnification was 1000x. FIG. 11 is a schematic enlarged view of the cross section of the powder magnetic core of Sample No. 100. As shown in FIG. 11, in Sample No. 100, the surface of the soft magnetic particles 2 was covered with an insulating film 3. FIG. 12 is a schematic enlarged view of the cross section of the powder magnetic core of Sample No. 1. As shown in FIG. 12, in Sample No. 1, cracks 3c were present in the insulating film 3, but almost no peeling of the insulating film 3 was observed. FIG. 13 is a schematic enlarged view of the cross section of the powder magnetic core of Sample No. 2. As shown in FIG. 13, in Sample No. 2, many peeling portions 3f were present in the insulating film 3.

[0108] The reason why the loss of the powder core of Sample No. 1 was smaller than the loss of the powder core of Sample No. 2 is thought to be as follows. In the powder core of Sample No. 1, as shown in FIG. 12 , cracks 3c exist in the insulating film 3, but the insulating film 3 maintains electrical insulation between the soft magnetic particles 2. This is thought to be why the increase in eddy current loss was reduced in the powder core of Sample No. 1. In contrast, in the powder core of Sample No. 2, as shown in FIG. 13 , peelings 3f exist in the insulating film 3, which reduces electrical insulation between the soft magnetic particles 2. This is thought to be why the eddy current loss increased in the powder core of Sample No. 2.

[0109] The oxide content in the internal region of each powder magnetic core sample was measured using the method described above. As a result, the oxide content in the internal region of both powder magnetic cores Sample No. 1 and Sample No. 2 was within the range of 0.1 mass % or more and 10.0 mass % or less. On the other hand, the oxide content in the internal region of powder magnetic core Sample No. 100 was less than 0.1 mass %.

[0110] Test Example 3 Powder magnetic cores were produced using at least one of recycled powder B1 and new soft magnetic powder, and the loss and strength of these powder magnetic cores were evaluated.

[0111] <Samples No. 3 to 5> The powder core of Sample No. 3 was produced in the same manner as the powder core of Sample No. 1, except that recycled powder B1 was used as the raw material. As described above, the average thickness of the insulating film at the raw material stage was approximately 80 nm. The powder core of Sample No. 4 was produced in the same manner as the powder core of Sample No. 3, except that a mixed powder of recycled powder B1 and new powder was used as the raw material. The content of recycled powder B1 in the mixed powder was 50 mass% and the content of new powder was 50 mass%. The powder core of Sample No. 5 was produced in the same manner as the powder core of Sample No. 3, except that new powder was used as the raw material.

[0112] <Samples No. 6 to No. 8> The powder magnetic cores of Samples No. 6 to No. 8 were produced in the same manner as the powder magnetic cores of Samples No. 3 to No. 5, except that the heat treatment was carried out in a nitrogen atmosphere. The nitrogen concentration in the atmosphere was 1 ppm by volume. The heat treatment temperature was 600°C, and the holding time was 15 minutes.

[0113] <Samples No. 9 to 11> The powder core of Sample No. 9 was produced in the same manner as Sample No. 3, except that recycled powder X was used as the raw material. Recycled powder X was obtained in the same manner as recycled powder A1, except that a powder core heat-treated in a nitrogen atmosphere was pulverized. The powder core of Sample No. 10 was produced in the same manner as Sample No. 9, except that a mixed powder of recycled powder X and new powder was used as the raw material. The content of recycled powder X in the mixed powder was 50 mass%, and the content of new powder was 50 mass%. The powder core of Sample No. 11 was produced in the same manner as Sample No. 9, except that new powder was used as the raw material. The new powder used in Sample No. 11 was different from the new powder used in Sample No. 5.

[0114] <Samples No. 12 to 14> The powder magnetic cores of Samples No. 12 to 14 were manufactured in the same manner as Samples No. 9 to 11, except that the heat treatment was performed in a nitrogen atmosphere. The heat treatment conditions were the same as those for Sample No. 6. The new powder used in Sample No. 14 was different from the new powder used in Sample No. 8.

[0115] <<Loss of Powder Magnetic Core>> The loss of the powder magnetic core of each sample was measured in the same manner as in Test Example 2. The results are shown in Table 3.

[0116] <<Evaluation of Strength>> The strength of each powder magnetic core sample was measured. The measured strength of the powder magnetic core is the radial crushing strength. The radial crushing strength was measured in accordance with "JIS Z 2507:2000." Specifically, two plates were placed radially opposite the ring-shaped powder magnetic core, the test piece was sandwiched between these plates, and a load was applied to one of the plates. The maximum load at which the ring-shaped powder magnetic core broke was then determined, and this maximum load (average of n = 3) was evaluated as the radial crushing strength (MPa). The results are shown in Table 3.

[0117]

[0118] The radial crushing strengths of the powder cores of Samples No. 3 and 4 were higher than that of Sample No. 5. The radial crushing strength of the powder core of Sample No. 3 was higher than that of Sample No. 9, and the radial crushing strength of the powder core of Sample No. 4 was higher than that of Sample No. 10. The radial crushing strength of the powder cores of Samples No. 6 and 7 was higher than that of Sample No. 8. The radial crushing strength of the powder core of Sample No. 6 was higher than that of Sample No. 12, and the radial crushing strength of the powder core of Sample No. 7 was higher than that of Sample No. 13. The loss of the powder core of Sample No. 6 was smaller than that of Sample No. 3. The loss of the powder magnetic core of sample No. 7 was smaller than the loss of the powder magnetic core of sample No. 4.

[0119] REFERENCE SIGNS LIST 1 recycled powder 2 soft magnetic particles 3 insulating film 3f peeled portion, 3c cracked portion 4 copper pieces 5 resin particles 10, 10a, 10b, 10c powder core 20 yoke 30 teeth 100 crusher 110 crushing chamber, 111 inlet 120 rotating blade, 121 rotating shaft 130 fixed blade 140 screen, 141 opening 200 motor stator (stator), 210 coil 250 rotor, 260 magnet, 270 holding plate 300 motor 310 case, 320 plate, 330 rotating shaft, 340 bearing d outer diameter, t thickness

Claims

1. Formed from a compact containing powder having an insulating film on the surface of soft magnetic particles, The soft magnetic particles containing iron oxide are located in an internal region at least 3.0 mm inward from the surface of the compacted powder. The content of iron oxide in the internal region is 0.1% by mass or more and 10.0% by mass or less. Powder magnetic core.

2. The average particle diameter of the soft magnetic particles is 20 μm or more. The powdered magnetic core according to claim 1, wherein the average thickness of the insulating film is 40 nm or more.

3. The insulating film has an insulating layer containing phosphate, silica, or magnesia. The powdered magnetic core according to claim 1 or 2, wherein the soft magnetic particles are formed from at least one metal selected from iron, iron-silicon alloy, iron-silicon-aluminum alloy, iron-aluminum alloy, iron-nickel alloy, and iron-cobalt alloy with a purity of 99% or more.

4. A powdered magnetic core according to claim 1 or claim 2, and a coil, comprising Motor stator.

5. A motor comprising a stator and a rotor as described in claim 4, Motor.

6. A process for recovering used compacted magnetic cores containing soft magnetic powder having an insulating film on the surface of soft magnetic particles, The process involves crushing the used compacted magnetic core to obtain recycled powder, A step of producing a molded body by compressing and molding the recycled powder, The process includes a step of heat-treating the molded body, The recovered used compacted magnetic core is a compacted magnetic core that has been heat-treated in an oxygen-containing atmosphere. The recycled powder contains 0.1% by mass or more and 10.0% by mass or less of iron oxide. A method for manufacturing compacted magnetic cores.

7. The method for manufacturing a compacted magnetic core according to claim 6, wherein the heat treatment step is carried out in an atmosphere containing oxygen or nitrogen.

8. The method for manufacturing a compacted magnetic core according to claim 7, wherein the oxygen concentration in the oxygen-containing atmosphere during the heat treatment step is 100 ppm or more and 250,000 ppm or less by volume.

9. The method for manufacturing a compacted magnetic core according to claim 7 or claim 8, wherein the temperature of the heat treatment is 300°C or more and 900°C or less.

10. In the recovery process described above, the motor stator, which further includes the coil attached to the used powdered magnetic core, is recovered. The process of obtaining the recycled powder is as follows: A step of obtaining pulverized material by crushing the motor stator with a pulverizer equipped with a screen, The process includes classifying the pulverized material by sieving, The screen has a plurality of openings, The diameter of each of the aforementioned multiple openings is 1 mm or more and 15 mm or less. The method for manufacturing a compacted magnetic core according to any one of claims 6 to 8, wherein the mesh opening of the sieve is less than 1 mm.

11. The average particle diameter of the soft magnetic particles is 20 μm or more. A method for manufacturing a compacted magnetic core according to any one of claims 6 to 8, wherein the average thickness of the insulating film is 40 nm or more.

12. The insulating film has an insulating layer containing phosphate, silica, or magnesia. The method for manufacturing a compacted magnetic core according to any one of claims 6 to 8, wherein the soft magnetic particles are formed from at least one metal selected from iron, iron-silicon alloy, iron-silicon-aluminum alloy, iron-aluminum alloy, iron-nickel alloy, and iron-cobalt alloy with a purity of 99% or more.

13. The method for manufacturing a compacted magnetic core according to any one of claims 6 to 8, wherein the compression molding step involves compressing a mixed powder containing new soft magnetic powder having an insulating film on the surface of soft magnetic particles and the recycled powder.