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

Abstract

To provide a powder magnetic core that can reduce carbon dioxide emissions generated during manufacturing of the powder magnetic core.SOLUTION: The present invention provides a powder magnetic core that includes recycled powder having an insulating film on surfaces of soft magnetic particles, the recycled powder being soft magnetic powder obtained by pulverizing a used powder magnetic core.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a powder magnetic core, a stator for a motor, a motor, and a method for manufacturing the powder magnetic core. [Background technology]

[0002] Conventionally, powder magnetic cores have been used as magnetic cores for electric devices such as motors and reactors. Powder magnetic cores are green compacts obtained by compressing soft magnetic powder having insulating films on the surfaces of soft magnetic particles. Patent Document 1 discloses a powder magnetic core used 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 and the coil, and sorting them by material. The magnetic core material described in Patent Documents 2 and 3 is an electromagnetic steel sheet such as a silicon steel sheet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 031209 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-124841 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-147608 Summary of the Invention [Problem to be solved by the invention]

[0005] It would be desirable to recover powder magnetic cores from used electrical equipment and recycle them. However, recycling of powder magnetic cores has not been carried out. Traditionally, powder magnetic cores have been manufactured using new soft magnetic powder as a raw material. New soft magnetic powder emits a large amount of carbon dioxide (CO2) during its manufacture. Therefore, it would be desirable to reduce the amount of new soft magnetic powder used, thereby reducing the CO2 emissions generated during the manufacture of powder magnetic cores, including the manufacture of soft magnetic powder.

[0006] An object of the present disclosure is to provide a powder magnetic core that can reduce CO2 emissions generated during the production of the powder magnetic core. [Means for solving the problem]

[0007] The powder magnetic core of the present disclosure includes recycled powder having insulating films on the surfaces of soft magnetic particles. The recycled powder is soft magnetic powder obtained by pulverizing used powder magnetic cores. [Effects of the Invention]

[0008] The powder magnetic core of the present disclosure can reduce CO2 emissions generated during the production of the powder magnetic core. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a partial cross-sectional view that schematically shows a powder magnetic core according to an embodiment. [Figure 2] FIG. 2 is a schematic perspective view showing an example of a powder magnetic core according to an embodiment. [Figure 3] FIG. 3 is a schematic perspective view showing another example of a powder magnetic core according to the embodiment. [Figure 4] FIG. 4 is a schematic perspective view showing yet another example of a powder magnetic core according to the embodiment. [Figure 5] FIG. 5 is a schematic perspective view of a motor stator according to the embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view of the motor according to the embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing an example of a crusher. [Figure 8] FIG. 8 is a graph showing the particle size distribution of the recycled powder and the new powder in Test Example 1. [Figure 9] FIG. 9 is a diagram schematically illustrating an insulating film of the recycled powder used as the raw material for the dust core of Sample No. 2 in Test Example 2. [Figure 10] FIG. 10 is a diagram schematically illustrating an insulating film of the recycled powder used as the raw material for the dust core of Sample No. 1 in Test Example 2. [Figure 11] FIG. 11 is a partially enlarged view of a cross section of the powder magnetic core of Sample No. 100 in Test Example 2. [Figure 12] FIG. 12 is a partially enlarged view of a cross section of the powder magnetic core of Sample No. 1 in Test Example 2. [Figure 13] FIG. 13 is a partially enlarged view of a cross section of the powder magnetic core of Sample No. 2 in Test Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] (1) The powder magnetic core of the present disclosure includes recycled powder having insulating films on the surfaces of soft magnetic particles. The recycled powder is soft magnetic powder obtained by pulverizing used powder magnetic cores.

[0012] By including recycled powder, the powder core of the present disclosure can reduce the amount of new soft magnetic powder used. The CO2 emissions required to obtain the recycled powder are less than the CO2 emissions required to manufacture new soft magnetic powder. Therefore, by using recycled powder as a raw material, the powder core of the present disclosure can reduce the CO2 emissions generated during the manufacture of the powder core.

[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 400 μm or less, and the insulating film may have an average thickness of 40 nm (nanometers) or more and 500 nm or less.

[0014] When the average particle size of the soft magnetic particles is 20 μm or more, it is easy to increase the density of the powder magnetic core. When the average particle size of the soft magnetic particles is 400 μm or less, it is easy to reduce the eddy current loss of the powder magnetic core. When the average thickness of the insulating film is 40 nm or more, it is easy to reduce the eddy current loss of the powder magnetic core. When the average thickness of the insulating film is 500 nm or less, the magnetic properties of the powder magnetic core can be improved.

[0015] (3) In the powder magnetic core of (1) or (2), the insulating film may have a plurality of cracks on the surface.

[0016] The presence of multiple cracks on the surface of the insulating film indicates that the soft magnetic powder is not new but recycled. Even if the insulating film has cracks, as long as the insulating film is not peeled off, the electrical insulation between the soft magnetic particles is maintained by the insulating film, and the increase in eddy current loss can be reduced.

[0017] (4) In any one of the powder magnetic cores (1) to (3) above, the insulating film may have an insulating layer containing phosphate, silica, or magnesia.

[0018] The insulating film tends to improve the electrical insulation between adjacent soft magnetic particles.

[0019] (5) In any of the powder magnetic cores (1) to (4) above, the mass ratio of the recycled powder to the mass of the powder magnetic core may be 1% by mass or more and 100% by mass or less.

[0020] By ensuring that the mass proportion of recycled powder is 1% by mass or more, it is possible to expect a reduction in CO2 emissions by reducing the amount of new soft magnetic powder used. The greater the mass proportion of recycled powder, the greater the CO2 reduction effect that can be expected. When the mass proportion of recycled powder is 100% by mass, the powder core contains only recycled powder 1. Because this powder core does not contain new soft magnetic powder, it has a high CO2 reduction effect.

[0021] (6) Any of the powder magnetic cores (1) to (5) above may contain new soft magnetic powder, and the mass ratio of the recycled powder to the total mass of the recycled powder and the new soft magnetic powder may be 1 mass% or more but less than 100 mass%.

[0022] By ensuring that the mass ratio of recycled powder is 1% by mass or more, it is possible to expect a reduction in CO2 emissions by reducing the amount of new soft magnetic powder used. By ensuring that the mass ratio of recycled powder is less than 100% by mass, it is possible to expect an improvement in magnetic properties by including new soft magnetic powder.

[0023] (7) In any of the powder magnetic cores (1) to (6) above, the soft magnetic particles may be formed from at least one metal selected from the group consisting of 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.

[0024] The soft magnetic particles are made of iron with a purity of 99% or higher, which facilitates the high density of the powder magnetic core.The soft magnetic particles are made of at least one metal selected from iron-silicon alloy, iron-silicon-aluminum alloy, iron-aluminum alloy, iron-nickel alloy, and iron-cobalt alloy, which facilitates the reduction of eddy current loss in the powder magnetic core.

[0025] (8) In any of the powder magnetic cores (1) to (7) above, the powder magnetic core may have a relative density of 85% or more.

[0026] By ensuring that the relative density of the powder magnetic core is 85% or higher, the magnetic properties of the powder magnetic core can be improved.

[0027] (9) A motor stator according to the present disclosure includes a powder magnetic core according to any one of (1) to (8) above and a coil.

[0028] The motor stator of the present disclosure includes the powder magnetic core of the present disclosure, and therefore can reduce CO2 emissions generated during production.

[0029] (10) A motor according to the present disclosure includes the motor stator and rotor described above in (9).

[0030] The motor of the present disclosure includes the motor stator of the present disclosure, and therefore can reduce CO2 emissions generated during manufacturing.

[0031] (11) A method for producing a powder magnetic core according to the present disclosure includes a step of recovering used powder magnetic cores containing soft magnetic powder having insulating films on the surfaces of the soft magnetic particles, a step of pulverizing the used powder magnetic cores to obtain recycled powder, and a step of compression-molding the recycled powder.

[0032] The method for producing a powder magnetic core according to the present disclosure can produce recycled powder by pulverizing used powder magnetic cores. By using recycled powder as a raw material, the method for producing a powder magnetic core according to the present disclosure can reduce CO2 emissions generated during the production of the powder magnetic core.

[0033] (12) In the method for producing a powder magnetic core according to (11) above, the soft magnetic particles may have an average particle size of 20 μm or more and 400 μm or less, and the insulating film may have an average thickness of 40 nm or more and 500 nm or less.

[0034] When the average particle size of the soft magnetic particles is 20 μm or more, it is easy to increase the density of the powder magnetic core. When the average particle size of the soft magnetic particles is 400 μm or less, it is easy to reduce the eddy current loss of the powder magnetic core. 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. When the average thickness of the insulating film is 500 nm or less, the magnetic properties of the powder magnetic core can be improved.

[0035] (13) The method for producing a powder magnetic core according to (11) or (12) above may have the following configuration: In the step of obtaining the recycled powder, the used powder magnetic core is pulverized using a pulverizer equipped with a screen. The screen has a plurality of openings, each of which has a diameter of 1 mm or more and 15 mm or less.

[0036] By pulverizing the powder magnetic core using a pulverizer equipped with a screen, recycled powder can be easily obtained.

[0037] (14) In the method for producing a powder magnetic core according to any one of (11) to (13) above, the step of obtaining the recycled powder may include a step of pulverizing the used powder magnetic core, classifying the pulverized product using a sieve, and a step of sorting the recycled powder using a magnet.

[0038] According to the above process, recycled powder of a predetermined particle size can be obtained by selection.

[0039] (15) In the method for producing a powder magnetic core according to any one of (11) to (14) above, in the compression molding step, a lubricant may be added to the recycled powder in a content of 0.1% by mass or more and 1.0% by mass or less.

[0040] By adding a lubricant to the recycled powder, the lubricity of the recycled powder during compression molding can be improved, making it easier to achieve a high density powder core.

[0041] (16) In the method for producing a powder magnetic core according to any one of (11) to (15) 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.

[0042] By using a mixed powder containing new soft magnetic powder and recycled powder as a 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 a raw material.

[0043] [Details of the embodiments of the present disclosure] Specific examples of powder magnetic cores according to the present disclosure are described below. The same reference numerals in the drawings indicate the same objects. The sizes of components shown in the drawings are shown for the purpose of clarifying the description and do not necessarily represent the actual dimensional relationships. It should be noted that the present invention is not limited to these examples, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0044] <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 recycled powder magnetic core that uses the recycled powder 1 as a raw material.

[0045] <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.

[0046] [Soft magnetic particles] The soft magnetic particles 2 are made 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 made 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 made 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. 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 above iron-based alloy, eddy current loss that occurs when magnetic flux flows through the powder magnetic core 10 can be easily reduced.

[0047] <Average particle size> 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 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 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 even more easily reduced. 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.

[0048] 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 average particle size of the soft magnetic particles 2 is determined by multiplying the measured particle sizes by their frequency. The frequency is the percentage of the number of particles in each particle size range to the total number of particles. A particle size range is an individual division into a specified particle size range that divides the entire range from the minimum to the maximum particle size. For example, the range from greater than 15 μm to less than 25 μm is defined as the 20 μm particle size range, the range from greater than 25 μm to less than 35 μm is defined as the 30 μm particle size range, and the range from greater than 35 μm to less than 45 μm is defined as 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, between 5 μm and 40 μm.

[0049] [Insulating film] The insulating film 3 provides electrical insulation between adjacent soft magnetic particles 2. By providing the insulating film 3 on the surfaces 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 from, for example, phosphate, silica, or magnesia. The phosphate is, for example, zinc phosphate, iron phosphate, manganese phosphate, or calcium phosphate.

[0050] The insulating film 3 may have a single-layer structure with only one type of insulating layer, or a multilayer structure with two or more types of insulating layers stacked. The multilayer insulating film 3 may have an insulating layer containing phosphate, silica, or magnesia. The insulating layer containing phosphate has high adhesion to the soft magnetic particles 2. Furthermore, the insulating layer containing phosphate is easily deformed. The insulating film 3 having the 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. The insulating layer containing silica or magnesia is hard. The insulating film 3 having the 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, if the material of the first insulating layer is phosphate, the material of the second insulating layer is silica or magnesia. If 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, and the second insulating layer is made of silica.

[0051] <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. This allows for improved magnetic properties of the powder magnetic core. 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 better 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.

[0052] 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.

[0053] The relative density of the powder core 10 is, for example, 85% or more. The higher the relative density of the powder core, 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 taken as the true density.

[0054] 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.

[0055] By including recycled powder 1, the powder core 10 can reduce the amount of new soft magnetic powder used. A powder core 10 manufactured using recycled powder 1 as a raw material can reduce CO2 emissions generated during the manufacture of the powder core 10. The powder core 10 may further include new soft magnetic powder. The new soft magnetic powder has an insulating film on the surface of the soft magnetic particles. The structure of the new soft magnetic powder is basically the same as the structure of the recycled powder described above. The new soft magnetic powder is unused soft magnetic powder in the manufactured state. 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.

[0056] The mass proportion of the recycled powder 1 relative to the mass of the powder core 10 is, for example, 1% by mass or more and 100% by mass or less. When the mass proportion of the recycled powder is 1% by mass or more, a CO2 reduction effect can be expected by reducing the amount of new soft magnetic powder used. This CO2 reduction effect can be expected the greater the mass proportion of the recycled powder. When the mass proportion of the recycled powder 1 is 100% by mass, the powder core 10 contains only the recycled powder 1. In other words, this powder core 10 is manufactured using only the recycled powder 1 as a raw material. Because it does not contain new soft magnetic powder, the CO2 reduction effect is high.

[0057] The mass proportion of the recycled powder 1 relative to the total mass of the recycled powder 1 and the new soft magnetic powder is, for example, 1% by mass or more and less than 100% by mass. When the mass proportion of the recycled powder 1 is 1% by mass or more, the amount of new soft magnetic powder used can be reduced, which is expected to reduce CO2 emissions. When the mass proportion of the recycled powder 1 is less than 100% by mass, the magnetic properties can be improved by including new soft magnetic powder. The greater the mass proportion of the recycled powder 1, the greater the CO2 reduction effect. The mass proportion of the recycled powder 1 may be, for example, 5% by mass or more, 10% by mass or more, 20% by mass or more, 40% by mass or more, 50% by mass or more, 70% by mass or more, or even 90% by mass or more.

[0058] 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 in an annular arrangement 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 can be appropriately determined depending on the specifications of the motor. The shape of the teeth 30 can be selected from any shape, such as a quadrangular prism, trapezoidal prism, or the like, in addition to a triangular prism.

[0059] 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 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 top 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.

[0060] 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.

[0061] 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.

[0062] <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 coils 210 are arranged on each of the teeth 30.

[0063] <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 arranged facing each other in a direction along a rotation axis 330.

[0064] 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 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.

[0065] The stator 200 and the rotor 250 are housed in a cylindrical case 310. Disk-shaped plates 320 are attached to both ends of the case 310. A through-hole is formed in the center of each plate 320, and a rotating shaft 330 passes through the case 310. The stator 200 is fixed to the case 310 by fitting the outer peripheral surface of the yoke 20 into the inner peripheral surface of the case 310. An annular bearing 340 that rotatably supports the rotating shaft 330 is attached to the inner peripheral surface of the yoke 20.

[0066] <Method of manufacturing powder magnetic cores> 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 pulverization step, and a pressing step. Each step will be described in detail below.

[0067] <Recovery process> The recovery process is a process of recovering used powder magnetic cores. 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 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 the core has actually been used as an electrical device. Used powder magnetic cores may also be cores that have been manufactured as powder magnetic cores and then collected without being used as electrical equipment. In other words, a core that has once been molded from soft magnetic powder is included in the category of used powder magnetic cores, regardless of whether it has been used as an actual 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.

[0068] 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 to prevent peeling of the insulating film when the powder magnetic core is pulverized in the pulverization step described below.

[0069] Used powder magnetic cores are collected from used electrical equipment. Used powder magnetic cores may still have accessories such as coils attached, or may remain covered in a resin mold. Therefore, there is no need to remove the coils or other accessories from the used powder magnetic cores, or to remove the resin mold.

[0070] <Crushing process> The pulverization process is a process in which used powder cores are pulverized to obtain recycled powder. The recycled powder is soft magnetic powder contained in used powder cores. In powder cores, adjacent soft magnetic particles are not metallurgically bonded to each other. The inventors discovered that when a powder core is pulverized, the soft magnetic particles separate from each other 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 core before pulverization. In other words, even when the powder core is pulverized, the particle size of the soft magnetic powder is substantially maintained. If the insulating film in a used powder core is thin, the insulating film may peel off due to the impact caused when the powder core is pulverized. If the insulating film is thick, cracks may occur in the insulating film when the powder 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 core is pulverized.

[0071] 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.

[0072] [Crusher] Used powder magnetic cores can be pulverized using a known pulverizer. The pulverizer used is, for example, a cutter-type pulverizer, a hammer-type pulverizer, or a chain-type pulverizer. A cutter-type pulverizer pulverizes the powder magnetic cores by scraping them off with a rotating blade. A hammer-type pulverizer pulverizes the powder magnetic cores by smashing them with a rotating hammer. A chain-type pulverizer pulverizes the powder magnetic cores by smashing them with a rotating chain.

[0073] The powder magnetic cores 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 magnetic cores 10 are fed into the pulverization chamber 110 through the inlet 111. The rotary blade 120 is disposed within the pulverization chamber 110. The rotary blade 120 is attached to a rotary shaft 121. A plurality of rotary blades 120 are attached in a line along the rotary shaft 121. The rotary blades 120 rotate as the rotary shaft 121 rotates. The fixed blade 130 is disposed within the pulverization chamber 110. A predetermined clearance is provided between the rotary blade 120 and the fixed blade 130. The powder magnetic 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 crushed material sheared by the rotary blade 120 and the fixed blade 130 is crushed and crushed between the rotary blade 120 and the screen 140.

[0074] 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. When the diameter of the openings 141 is 2 mm or more and 10 mm or less, the powder cores 10 are easily pulverized and the recycled powder 1 is easily obtained. The diameter of the openings 141 may be 2 mm or more and 10 mm or less.

[0075] When a used powder core 10 with a coil attached or resin molded is pulverized, the powder core 10 is pulverized to a particle size similar to that of the soft magnetic powder used as the raw material. In contrast, the coil and resin mold are pulverized to a size similar to the diameter of the openings 141 in the screen 140. The particle size of the recycled powder 1 obtained by pulverizing the powder core 10 is sufficiently smaller than the size of the pulverized coil and resin mold. Therefore, the recycled powder 1 and the pulverized coil and resin mold can be easily separated using a sieve. Furthermore, since the recycled powder 1 is attracted to a magnet, it may also be separated using a magnet.

[0076] The pulverization step may include a step of classifying the pulverized powder obtained by pulverizing the powder core 10 using a sieve, and a step of sorting the recycled powder 1 using a magnet. By performing the sieving step and the magnetic sorting step, only recycled powder 1 having a predetermined particle size can be selected and obtained.

[0077] <Pressing process> The pressing process is a process in which the recycled powder is compression molded. 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 to 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.

[0078] 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 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.

[0079] In the pressing process, only recycled powder may be compression-molded, or a mixed powder containing new soft magnetic powder and recycled powder may be compression-molded. Using a mixed powder containing new soft magnetic powder and recycled powder as a raw material can improve the magnetic properties of the powder core and reduce the eddy current loss of the powder core compared to using only recycled powder as a raw material. When using a mixed powder 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 and less than 100 mass%. By using a mass ratio of recycled powder of 1 mass% or more, the amount of new soft magnetic powder used can be reduced, thereby expected to reduce CO2 emissions. By using a mass ratio of recycled powder of less than 100 mass%, the magnetic properties can be improved by including new soft magnetic powder. The greater the mass ratio of recycled powder, the greater the CO2 reduction effect. From the viewpoint of CO2 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 the same as the mass proportion of the recycled powder in the mixed powder used as a raw material.

[0080] <Heat treatment process> The method for producing a powder magnetic core may include a heat treatment step after the pressing step. The heat treatment step is a step of heat-treating the compacted powder magnetic core. By heat-treating the powder magnetic core, it is possible to remove the strain introduced into the soft magnetic particles by the compaction, thereby improving the magnetic properties of the powder magnetic core. The heat treatment temperature is, for example, 300°C or higher and 900°C or lower. The lubricant added in the pressing step is eliminated by the heat treatment.

[0081] [Test Example 1] The particle size distribution of the recycled powder obtained by crushing the powder magnetic core was investigated.

[0082] The dust core was manufactured using new soft magnetic powder as a raw material. Hereinafter, 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 that 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.

[0083] The powder magnetic core is a circular stator core as 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.

[0084] A plurality of dust cores were prepared. The dust cores were pulverized using a pulverizer to obtain recycled powder. 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).

[0085] The particle size distribution of the recycled powder was measured using a laser diffraction particle size analyzer. The laser diffraction particle size analyzer used was the MT3300EX manufactured by Nikkiso Co., Ltd. Figure 8 shows the particle size distribution of the recycled powder. Figure 8 also shows the particle size distribution of the new powder. The particle size distribution of the recycled powder was determined by taking three samples from the recycled powder and averaging the particle size distributions of these samples. The particle size distribution of the 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 the recycled powder, and the dashed line graph shows the particle size distribution of the new powder.

[0086] The particle diameters D10, D50, and D90 of the recycled powder and 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.

[0087] [Table 1]

[0088] As shown in Fig. 8 and Table 1, the particle size distribution of the recycled powder obtained by crushing powder cores is nearly the same as that of the new powder at the raw material stage. This shows that by crushing used powder cores, it is possible to crush them to a particle size similar to that of the soft magnetic powder used as the raw material.

[0089] [Test Example 2] Powder cores were manufactured using recycled powder and new powder, and the losses of these powder cores were evaluated.

[0090] <Sample No. 1> Sample No. 1 is a powder magnetic core using the recycled powder of Test Example 1 as the raw material. In Sample No. 1, the average thickness of the insulating film at the raw material stage is 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. 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.

[0091] <Sample No. 2> Sample No. 2 is a dust core that uses recycled powder as its raw material. Like sample No. 1, the recycled powder for sample No. 2 was obtained by crushing a dust core. However, in sample No. 2, the average thickness of the insulating film at the raw material stage was approximately 25 nm. Sample No. 2 dust core was manufactured in the same manner as sample No. 1 dust core, except that recycled powder with an insulating film average thickness different from that of sample No. 1 was used.

[0092] <Sample No. 100> Sample No. 100 is a powder magnetic core manufactured using only new powder as a raw material. In Sample No. 100, the average thickness of the insulating film of the new powder is approximately 25 nm. Sample No. 100 powder magnetic core was manufactured in the same manner as Sample No. 1 powder magnetic core, except that new powder was used as a raw material.

[0093] <Losses in powder magnetic cores> The loss of each powder core sample was measured. The loss of the powder core was measured as follows: A primary coil and a secondary coil were wound around the powder core. The primary coil had 300 turns, and the secondary coil had 30 turns. Current was passed through the primary coil to magnetize the powder core, and the iron loss was measured using the secondary coil. The measured loss of 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 of each powder core for sample No. 1 and sample No. 2 is shown below. The loss of the powder core is shown as a ratio based on the loss of the powder core for sample No. 100. Sample No. 1: 112% Sample No. 2: 442%

[0094] The loss of sample No. 1, which uses recycled powder with an average insulating film thickness of approximately 80 nm as its raw material, was 12% higher than the loss of sample No. 100. In contrast, the loss of sample No. 2, which uses recycled powder with an average insulating film thickness of approximately 25 nm as its raw material, was 342% higher than the loss of sample No. 100. The loss of sample No. 1 is almost the same as that of sample No. 100. This shows that sample No. 1 has performance equivalent to that of sample No. 100.

[0095] <Evaluation of insulating films> The recycled powder used as the raw material for the powder cores of Samples No. 1 and No. 2 was 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 planar views of the insulating film 3. As shown in Figure 9, Sample No. 2 had cracks 3c and many peeled areas 3f where the insulating film 3 had partially peeled off. In Figure 9, the peeled areas 3f are indicated by hatching. As shown in Figure 10, Sample No. 1 had fine cracks in the insulating film 3 and many cracked areas 3c. Although many cracks were observed in the insulating film 3 of 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 crushed.

[0096] The state of the insulating film in each powder core sample was examined. The cross section of the powder core was observed using an SEM at 1000x magnification. Figure 11 is a schematic enlarged view of the cross section of the powder core of sample No. 100. As shown in Figure 11, in sample No. 100, the surface of the soft magnetic particles 2 was covered with an insulating film 3. Figure 12 is a schematic enlarged view of the cross section of the powder core of sample No. 1. As shown in Figure 12, in sample No. 1, cracks 3c were found in the insulating film 3, but almost no peeling of the insulating film 3 was observed. Figure 13 is a schematic enlarged view of the cross section of the powder core of sample No. 2. As shown in Figure 13, in sample No. 2, many peelings 3f were found in the insulating film 3.

[0097] The reason why the loss in the powder core of sample No. 1 was smaller than the loss in 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. It is therefore thought that 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 the electrical insulation between the soft magnetic particles 2. It is therefore thought that the eddy current loss increased in the powder core of sample No. 2. [Explanation of symbols]

[0098] 1. Recycled powder 2 Soft magnetic particles 3. Insulating film 3f Peeling area, 3c Cracked area 10, 10a, 10b, 10c powder magnetic core 20 York 30 Teeth 100 Crusher 110 Grinding chamber, 111 Feeding port 120 Rotary Blade 130 Fixed blade 140 Screen, 141 Aperture 200 Motor stator (stator), 210 Coil 250 rotor, 260 magnet, 270 retaining plate, 300 motor 310 case, 320 plate, 330 rotating shaft, 340 bearing d: outer diameter, t: thickness

Claims

1. The recycled powder includes soft magnetic particles having an insulating film on the surface thereof, The recycled powder is a soft magnetic powder obtained by pulverizing used powder magnetic cores. Powder magnetic core.

2. the average particle size of the soft magnetic particles is 20 μm or more and 400 μm or less, 2. The powder magnetic core according to claim 1, wherein the insulating film has an average thickness of 40 nm or more and 500 nm or less.

3. The powder magnetic core according to claim 1 or 2, wherein the insulating film has a plurality of cracks on a surface thereof.

4. The powder magnetic core according to claim 1 or 2, wherein the insulating film has an insulating layer containing phosphate, silica, or magnesia.

5. 3. The powder magnetic core according to claim 1, wherein a mass ratio of the recycled powder to a mass of the powder magnetic core is 1 mass% or more and 100 mass% or less.

6. Contains new soft magnetic powder, 3. The powder magnetic core according to claim 1, wherein a mass ratio of the recycled powder to a total mass of the recycled powder and the new soft magnetic powder is 1 mass % or more and less than 100 mass %.

7. 3. The powder magnetic core according to claim 1, wherein the soft magnetic particles are formed of at least one metal selected from the group consisting of 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.

8. 3. The powder magnetic core according to claim 1, wherein the powder magnetic core has a relative density of 85% or more.

9. A magnetic core according to claim 1 or 2, comprising: a powder magnetic core; and a coil. Stator for motor.

10. A motor comprising the stator for a motor according to claim 9 and a rotor. Motor.

11. a step 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 core to obtain recycled powder; and compressing the recycled powder. A method for manufacturing a powder magnetic core.

12. the average particle size of the soft magnetic particles is 20 μm or more and 400 μm or less, The method for producing a powder magnetic core according to claim 11, wherein the insulating film has an average thickness of 40 nm or more and 500 nm or less.

13. In the step of obtaining the recycled powder, the used powder core is pulverized using a pulverizer equipped with a screen, the screen has a plurality of openings; The method for producing a powder magnetic core according to claim 11 or 12, wherein the diameter of each of the plurality of openings is 1 mm or more and 15 mm or less.

14. 13. The method for producing a powder magnetic core according to claim 11 or 12, wherein the step of obtaining the recycled powder includes a step of pulverizing the used powder magnetic core, classifying the pulverized product using a sieve, and a step of sorting the recycled powder using a magnet.

15. The method for producing a powder magnetic core according to claim 11 or 12, wherein in the compression molding, a lubricant is added to the recycled powder in a content of 0.1 mass % or more and 1.0 mass % or less.

16. 13. The method for producing a powder magnetic core according to claim 11 or 12, wherein the compression molding step includes compression molding a mixed powder containing new soft magnetic powder having insulating films on surfaces of soft magnetic particles and the recycled powder.

17. The soft magnetic particles have an insulating film on the surface thereof, The insulating film has a plurality of cracks on the surface thereof, the insulating film has an insulating layer containing phosphate, silica, or magnesia; the soft magnetic particles are 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; Recycled powder.

18. the average particle size of the soft magnetic particles is 20 μm or more and 400 μm or less, The recycled powder according to claim 17, wherein the insulating film has an average thickness of 40 nm or more and 500 nm or less.

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