JP2020096167A - Dust core and method of manufacturing the same - Google Patents

Abstract

To provide a dust core that has both high permeability and high withstand voltage.SOLUTION: The dust core includes: a first powder 301 which is a soft magnetic composition powder, a second powder 302, and a third powder 303. The first powder 301 is a spherical powder having a flatness of 1.0 or more and 1.2 or less. The second powder 302 is an ellipsoidal powder having a flatness of 3.0 or more and 6.0 or less. Third powder 303 is a scaly powder with a flatness of more than 6.0.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to a dust core and a manufacturing method thereof.

In recent years, the electrification of vehicles has been spreading rapidly. Examples of electrified vehicles include hybrid vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (EVs). In such electrified vehicles, various electronic components and systems are required to be smaller and lighter in order to further improve fuel efficiency (electricity cost).

Further, driven by the market expansion of electrified vehicles, ever-higher performance is required for soft magnetic powders used in choke coils, reactors, transformers and the like and dust cores using the soft magnetic powders.

A powder magnetic core using this soft magnetic powder is required to have a high magnetic permeability, but for that purpose, it is necessary to pack the soft magnetic powder at a high density.

For example, Patent Document 1 discloses a method of filling a soft magnetic powder at a high density by mixing a thin-plate pulverized powder and a spherical powder obtained by an atomizing method.

FIG. 6A and FIG. 6B show the pulverized powder of the Fe-based amorphous alloy ribbon disclosed in Patent Document 1. The crushed powder is powder (powder) obtained by crushing a thin strip.

FIG. 6A is a diagram showing a pulverized powder 1 having a particle size of 50 μm or more. FIG. 6B is a diagram showing pulverized powder 2 having a particle size of 50 μm or less.

In Patent Document 1, Fe-based amorphous alloy ribbon (hereinafter, simply referred to as “thin ribbon”) pulverized powder and Fe-based amorphous alloy atomized spherical powder (hereinafter, simply referred to as “atomized spherical powder”) are used as main components. There is disclosed a dust magnetic core.

The particle size of the pulverized powder 1 shown in FIG. 6A is not less than twice the thickness of the ribbon (thickness 25 μm×2=50 μm) and not less than 6 times (thickness 25 μm×6=150 μm). The crushed powder 1 is 80% by mass or more of the total crushed powder.

The particle size of the pulverized powder 2 shown in FIG. 6B is not more than twice the thickness of the ribbon (thickness 25 μm×2=50 μm). The crushed powder 2 is 20% by mass or less of the total crushed powder.

In Patent Document 1, the particle diameters of the crushed powders 1 and 2 are the minimum values in the surface direction of the main surface of the powder crushed into a thin plate shape.

The particle size of the atomized spherical powder is 3 μm or more and ½ of the thickness of the ribbon (thickness 25 μm×1/2=12.5 μm) or less.

Japanese Patent No. 4944971

In order to fill the soft magnetic powder forming the dust core with a high density, it is necessary to perform pressure molding at a high pressure when manufacturing the dust core. However, since the soft magnetic powders come into contact with each other and the insulation between the powders cannot be maintained, the withstand voltage performance deteriorates.

In particular, when pressing a thin plate-shaped powder having a sharp edge as disclosed in Patent Document 1, the sharp edge bites into the adjacent powder, so that the powders are electrically connected. As a result, the withstand voltage performance is significantly deteriorated, and it becomes difficult to fill the battery with high density.

Further, since the thin plate-shaped powder is oriented in the flow direction at the time of pressure molding, when it is combined with the spherical powder as disclosed in Patent Document 1, it becomes difficult to fill the gap between the spherical powders, which is always high. Packing density is not obtained.

That is, with the method of Patent Document 1, it was not possible to obtain a dust core having both high magnetic permeability and high withstand voltage.

An object of one aspect of the present disclosure is to provide a dust core that achieves both high magnetic permeability and high withstand voltage, and a method for manufacturing the same.

A dust core according to an aspect of the present disclosure is a dust core containing a powder of a soft magnetic composition, and a spherical first powder having a flatness of 1.0 or more and 1.2 or less, and a flatness. Of 3.0 or more and 6.0 or less and an ellipsoidal second powder, and a scale-like third powder having a flatness of more than 6.0.

A dust core according to an aspect of the present disclosure is a dust core containing powder of a soft magnetic composition, has a surface smoothness of 1.1 or more and 2.0 or less, and a flatness of 1. A spherical first powder having a value of 0 or more and 1.2 or less and an ellipsoid having a surface smoothness of 1.7 or more and 2.5 or less and a flatness of 3.0 or more and 6.0 or less. -Like second powder and a scaly third powder having a surface smoothness of 3.4 or more and a flatness of more than 6.0.

A method for producing a dust core according to an aspect of the present disclosure rubs a soft magnetic composition against each other to produce a spherical first powder, an ellipsoidal second powder, and a scaly third powder. A step of heating the first powder, the second powder, and the third powder, and mixing the first powder, the second powder, and the third powder with a binder to produce granulated powder. And a step of filling the granulated powder into a predetermined mold, press-molding to obtain a green compact, and heating the green compact at a temperature at which the binder is cured. The first powder is a spherical powder having a flatness of 1.0 or more and 1.2 or less, and the second powder is an ellipsoid having a flatness of 3.0 or more and 6.0 or less. The third powder is a scaly powder having a flatness of more than 6.0.

A method for producing a dust core according to an aspect of the present disclosure rubs a soft magnetic composition against each other to produce a spherical first powder, an ellipsoidal second powder, and a scaly third powder. A step of heating the first powder, the second powder, and the third powder, and mixing the first powder, the second powder, and the third powder with a binder to produce granulated powder. And a step of filling the granulated powder into a predetermined mold, press-molding to obtain a green compact, and heating the green compact at a temperature at which the binder is cured. The first powder is a powder having a surface smoothness of 1.1 or more and 2.0 or less and a flatness of 1.0 or more and 1.2 or less, and the second powder is The surface smoothness is 1.7 or more and 2.5 or less, and the flatness is 3.0 or more and 6.0 or less. The third powder has a surface smoothness of 3.4 or more. And the flatness is greater than 6.0.

According to the present disclosure, it is possible to provide a dust core having both high magnetic permeability and high withstand voltage.

The figure which shows typically the manufacturing process of the soft magnetic powder which concerns on embodiment of this indication. The figure which shows typically the manufacturing process of the soft magnetic powder which concerns on embodiment of this indication. The figure which shows typically the manufacturing process of the soft magnetic powder which concerns on embodiment of this indication. The figure which shows typically an example of a structure of the cyclone mill which concerns on the Example of this indication. The figure which shows the SEM image of the soft magnetic powder which concerns on the Example of this indication. The figure which shows the particle size distribution of the soft magnetic powder which concerns on the Example of this indication. The figure which shows the SEM image of the cross section of the dust core which concerns on embodiment of this indication. The figure which shows the crushed powder (particle size 50 micrometers or more) of the Fe type|system|group amorphous alloy ribbon currently disclosed by patent document 1. The figure which shows the crushed powder (particle size 50 micrometers or less) of the Fe type|system|group amorphous alloy ribbon currently disclosed by patent document 1.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

<Method for producing soft magnetic powder>
A method for manufacturing soft magnetic powder according to the embodiment of the present disclosure will be described.

First, the alloy composition is melted by high-frequency heating or the like, and then cooled by a liquid quenching method to produce a thin strip or piece of an amorphous layer (step 1).

When carrying out the liquid quenching method, for example, a single-roll type amorphous manufacturing apparatus or a twin-roll type amorphous manufacturing apparatus used for manufacturing an Fe-based amorphous ribbon can be used.

In the following, the case of producing a thin ribbon of an amorphous layer (hereinafter, simply referred to as “thin ribbon”) will be described as an example, but it goes without saying that the following description also applies to the case of producing a thin piece.

Next, the thin strip obtained in step 1 is crushed to obtain crushed powder (step 2).

As a method of pulverizing the thin strips, for example, a method of using a cyclone mill so that the thin strips rub against each other can be mentioned. Details of this method will be described later with reference to FIG.

It is generally known that when a ribbon is heated and crystallized before pulverization, the ribbon becomes brittle and is easily pulverized. On the other hand, when heated, the hardness of the ribbon becomes high, which makes it difficult to grind the ribbon into small pieces. As a result, the proportion of the pulverized powder having a small particle diameter is reduced in the total pulverized powder.

Therefore, in the present embodiment, in the step 2, a method of crushing the ribbon without heating is adopted. As a result, the hardness of the ribbon becomes low, so that it can be crushed into small pieces. As a result, it is possible to increase the proportion of the pulverized powder having a small particle size in the total pulverized powder.

The pulverized powder obtained in step 2 may be classified, for example, using a sieve to obtain a pulverized powder having a desired particle size distribution.

Moreover, in the following description, the "crushed powder" is also referred to as "powder" or "particles".

Here, the manufacturing mechanism of the pulverized powder in the step 2 will be described with reference to FIGS. 1A to 1C.

The soft magnetic ribbon 101 shown in FIG. 1A (an example of a soft magnetic composition) may be any one having soft magnetic characteristics such as metal, alloy, silicon steel plate, amorphous, or nanocrystalline alloy.

When a cyclone mill is used, the soft magnetic ribbons 101 shown in FIG. 1A ride on the air flow, and the soft magnetic ribbons 101 rub against each other. As a result, the surface of the soft magnetic ribbon 101 is scraped off, and the powder 102 and the powder 103 shown in FIG. 1B are produced.

Further, by continuing the pulverization, the powder 102 and the powder 103 also come into the air stream, and the powders rub against each other. As a result, the surface of the powder 102 is scraped off, and the spherical powder 104 and the scaly powder 106 shown in FIG. 1C are generated. Further, the surface of the powder 103 is scraped off, and the ellipsoidal powder 105 and the scaly powder 106 shown in FIG. 1C are generated. The powder 106 is shavings scraped from the powder 102 or the powder 103.

The mechanism for producing crushed powder has been described above. Hereinafter, step 3 after step 2 will be described.

The pulverized powder obtained in the step 2 is heat-treated to remove the internal strain due to the pulverization or to precipitate the αFe crystal layer (step 3).

As the heat treatment device, for example, a hot air oven, a hot press, a lamp, a sheath heater (also referred to as a sheath heater), a ceramic heater, a rotary kiln, or the like can be used.

By the steps 1 to 3 described above, it is possible to manufacture a pulverized powder of the thin ribbon of the amorphous layer, that is, a soft magnetic powder.

<Manufacturing method of dust core>
A method for manufacturing the dust core according to the embodiment of the present disclosure will be described.

First, the soft magnetic powder produced in the above steps 1 to 3 is mixed with a binder to prepare granulated powder (step 11).

As the binder, a resin having good insulating properties and high heat resistance (for example, phenol resin or silicone resin) can be used.

Next, the granulated powder obtained in step 11 is filled in a mold having a desired shape and having high heat resistance, and pressure molding is performed to obtain a green compact (step 12).

Next, the green compact obtained in step 12 is heated at a temperature at which the binder hardens (step 13).

Through the steps 11 to 13 described above, a dust core having a high magnetic permeability can be manufactured.

(Example)
An example in which the method for manufacturing the soft magnetic powder and the method for manufacturing the dust core of the present embodiment described above are specifically implemented will be described below.

In this example, Fe73.5-Cu1-Nb3-Si13.5-B9 (atomic %) Fe-based amorphous alloy ribbon produced by the quenching single roll method was crushed using a cyclone mill to soften the amorphous layer. A magnetic alloy powder was obtained.

<Crushing mechanism by cyclone mill>
The crushing mechanism by the cyclone mill will be described with reference to FIG. FIG. 2 is a diagram schematically showing an example of the configuration of the cyclone mill 200 used in this example.

The cyclone mill 200 has a crushing chamber 201, a raw material input port 202, rotary blades 203 and 204, a discharge port 205, a rotary shaft 208, and a drive source 209.

The raw material charging port 202 is an opening through which the raw material 206 is charged, and communicates with the crushing chamber 201. The raw material 206 is, for example, the soft magnetic ribbon 101 shown in FIG. 1A.

The discharge port 205 is an opening communicating with the crushing chamber 201 and discharging the raw material particles 207 generated in the crushing chamber 201. A suction device (not shown) is provided outside the discharge port 205.

The crushing chamber 201 is a space where the raw material 206 is crushed.

Rotating blades 203 and 204 are provided in the crushing chamber 201. The rotary blades 203 and 204 are fixed to the rotary shaft 208, respectively. The rotating shaft 208 is given a rotational force by a drive source 209 (for example, a motor) and rotates as indicated by an arrow a. As a result, the rotary blades 203 and 204 also rotate.

When the rotary blades 203 and 204 rotate, the air flow 210 and the circulation flows 211 and 212 are constantly generated.

The airflow 210 is an airflow from the inlet side of the crushing chamber 201 to the outlet side of the crushing chamber 201 through the inside of the crushing chamber 201.

The circulation flow 211 is an air flow that circulates along the surface of the rotary blade 203.

The circulation flow 212 is an air flow that circulates along the surface of the rotary blades 204.

The flow of charging the raw material 206 into the cyclone mill 200 having such a configuration to obtain the raw material particles 207 will be described below.

The raw material 206 input from the raw material input port 202 rides on the air flow 210 and flows into the crushing chamber 201.

On the other hand, the rest of the raw material 206 flowing into the crushing chamber 201 rides on the circulating flow 211 or the circulating flow 212 and moves inside the crushing chamber 201. At this time, the raw material 206 riding on the circulating flow 211 and the raw material 206 riding on the circulating flow 212 rub against each other and are ground. The raw material particles 207 are generated by this friction pulverization. The raw material particles 207 generated here are, for example, the powders 104, 105, and 106 shown in FIG. 1C.

The fine powder (for example, the powder 106 shown in FIG. 1C) of the raw material particles 207 is flown out of the crushing chamber 201 along with the air flow 210, and is collected from the discharge port 205 by the suction force of the suction device (not shown). ..

In this embodiment, the crushing execution time is 50 minutes. That is, the raw material 206 (soft magnetic ribbon 101) was charged from the raw material charging port 202 while rotating the rotary blades 203 and 204 for 50 minutes. As a result, the raw material 206 riding on the circulating flow 211 and the raw material 206 riding on the circulating flow 212 rub against each other, the surface of each raw material 206 is scraped off, and the final atomic particles 207 are shown in FIG. 1C. The indicated powders 104, 105, 106 were produced.

The powder 106, which is a fine powder, collects in the axial direction of the rotary shaft 208 (central portions of the rotary blades 203 and 204), flows along the air flow 210 and flows out from the crushing chamber 201, and is discharged from the discharge port 205 by the suction force of the suction device. It was In this way, only the powder 106 having a constant particle size could be continuously collected. The recovered powder 106 was scaly.

On the other hand, the powders 104 and 105, which are particles larger than the powder 106, stay in the grinding chamber 201 while riding on the circulating flow 211 or the circulating flow 212 and scraping off the surface. That is, the powder 106 is generated from the powders 104 and 105 also during this retention. This powder 106 was also collected from the discharge port 205 as in the above.

When the crushing was completed (after 50 minutes had elapsed), the spherical powder 104 without corners and the ellipsoidal powder 105 without corners remained in the grinding chamber 201.

In this embodiment, the crushing time is set to 50 minutes, but it can be appropriately adjusted according to the desired shape and particle size. Further, in the present embodiment, the case where the powders 104 to 106 are manufactured by using the cyclone mill 200 has been described as an example, but the powders 104 to 106 may be manufactured by another device or another method.

Further, in this embodiment, as the cyclone mill 200, a 150S, single motor manufactured by Shizuoka Co., Ltd. was used. The rotation speed is preferably 11,000 to 15,000 rpm, and the optimum value is 15,000 rpm. Therefore, in this example, the rotation speed of 15000 rpm was used.

When a planetary ball mill, an attritor, a sample mill, or a vibration mill is used, spherical powder or ellipsoidal powder cannot be formed (particles do not have sharp corners), and the average particle size of the powder exceeds 20 μm. When a mixer mill is used, the average particle size of the powder is on the order of 10 μm, but spherical powder or ellipsoidal powder cannot be obtained (particles cannot have sharp corners). Also, it cannot be crushed with a jet mill.

The following treatments were performed on the powders 104, 105 and 106 obtained as described above.

First, the powders 104, 105 and 106 were heat-treated to remove the internal strain due to pulverization and to precipitate an αFe crystal layer. As the heat treatment, hot pressing was used to heat the powders 104, 105 and 106 at 560° C. for 2 seconds.

Next, the powders 104, 105 and 106 were mixed so as to satisfy the powder 104+powder 105:powder 106=90% by weight:10% by weight to prepare a mixed powder.

Next, the mixed powder and a silicone resin as a binder were mixed to produce granulated powder. The silicone resin was about 3% by weight of the mixed powder.

Next, the granulated powder was put into a mold and pressure-molded using a press at a molding pressure of 4 ton/cm ² to produce a green compact.

<Evaluation of initial permeability>
The initial magnetic permeability at a frequency of 100 kHz was measured for the green compact obtained as described above using an impedance analyzer. Here, the acceptance standard of the initial magnetic permeability was set to 19 or more. The reason is that the loss was set to be equal to or higher than the initial magnetic permeability of a general metal-based material having the same degree. Then, as a result of measurement with an impedance analyzer, the initial magnetic permeability was 21. Therefore, the pass/fail criteria can be cleared and high magnetic permeability can be realized.

<Shape of soft magnetic powder>
The shape of the soft magnetic powder obtained in this example will be described with reference to FIG. FIG. 3 is a view showing an SEM (Scanning Electron Microscope) image of the soft magnetic powder according to this example.

In FIG. 3, the first powder 301 corresponds to the powder 104 shown in FIG. 1C, the second powder 302 corresponds to the powder 105 shown in FIG. 1C, and the third powder 303 is the powder shown in FIG. 1C. It corresponds to 106.

As shown in FIG. 3, the first powder 301 was spherical, the second powder 302 was ellipsoidal, and the third powder 303 was scaly.

<Particle size distribution of soft magnetic powder>
The particle size of the first powder 301 was larger than 32 μm. The first powder 301 was 36% by weight of the total crushed powder.

The particle size of the second powder 302 was 32 μm or less. The second powder 302 was 54% by weight of the total crushed powder.

The particle size of the third powder 303 was 32 μm or less. Further, the third powder 303 was 10% by weight of the total crushed powder.

The particle size was measured by determining whether each of the first powder 301, the second powder 302, and the third powder 303 passes through an opening having a diameter of 32 μm.

Table 1 shows a summary of the characteristics of the first powder 301, the second powder 302, and the third powder 303 described above.

In order to increase the packing density of the soft magnetic powder, in the present embodiment, as described above, the first powder 301, the first powder 301, the second powder:the third powder=90 wt%: The second powder 302 and the third powder 303 were mixed. More specifically, the respective powders were mixed so that the first powder 301:the second powder 302:the third powder 303=36% by weight:54% by weight:10% by weight.

Since the fine powder may impede the flow of the powder at the time of pressure molding and the packing density of the powder may not be increased, the weight ratio of the third powder 303, which is the finest among the soft magnetic powders, is the total pulverized powder. Is preferably 50% by weight or less. Further speaking, the weight ratio of the third powder 303 is preferably 30% by weight or less of the total pulverized powder. Further speaking, the weight ratio of the third powder 303 is preferably 20% by weight or less of the total crushed powder.

On the other hand, the total weight ratio of the first powder 301 and the second powder 302 is preferably 50% by weight or more of the total pulverized powder. Further, in order to increase the packing density of the soft magnetic powder, it is preferable to make the proportion of the second powder 302 having a small particle diameter larger than that of the first powder 301 having a large particle diameter. That is, when the first powder 301, the second powder 302, and the third powder 303 are mixed, it is preferable that the second powder 302 be larger than the first powder 301.

From the above, in the present embodiment, as shown in FIG. 3, a certain number of first powders 301 having a particle size larger than 32 μm are present, and the second powder 302 and the third powder 303 having a particle size of 32 μm or less are also constant. There were a few.

The particle size distribution of the soft magnetic powder of this example is shown in FIG. The particle size distribution shown in FIG. 4 was measured by Microtrac MT3000II series. In FIG. 4, the horizontal axis represents the particle size, and the vertical axis represents the frequency of existence of the soft magnetic powder of each particle size. In the cumulative distribution, D10% was about 9 μm, D50% was about 29 μm, and D90% was about 59 μm.

<Details of particle size>
The particle size of each of the first powder 301, the second powder 302, and the third powder 303 is as described above, but each particle size will be described in more detail below.

In this example, the average particle size of the first powder 301 having a particle size larger than 32 μm was about 47 μm. The average particle size of the second powder 302 having a particle size of 32 μm or less was about 16 μm. The average particle size of the third powder having a particle size of 32 μm or less was about 8 μm. The average particle size as used herein is a numerical value of D50% of the cumulative particle size distribution measured by Microtrac MT3000II series.

In order to increase the packing density of the soft magnetic powder, the relationship among the average particle diameters of the first powder 301, the second powder 302, and the third powder 303 is that the average particle diameter of the first powder 301>the second powder 302. It is preferable that the average particle size>the average particle size of the third powder 301 is satisfied.

Further, if the average particle diameters of the first powder 301, the second powder 302, and the third powder 303 are too different, the fine third powder 303 impedes the flow of the powder at the time of pressure molding, and the powder is filled. In some cases, the density cannot be increased.

Therefore, the average particle diameter of the first powder 301 is preferably 30 μm or more and 60 μm or less. Furthermore, the average particle size of the first powder 301 is preferably 40 μm or more and 50 μm or less.

The average particle size of the second powder 302 is preferably 10 μm or more and 20 μm or less.

The average particle size of the third powder 303 is preferably 4 μm or more and 12 μm or less.

<Dust core>
FIG. 5 shows an SEM image of a cross section of a dust core manufactured using the soft magnetic powder of this example.

The cross section 501 is a cross section of the first powder 301 (the powder 104 shown in FIG. 1C). The cross section 502 is a cross section of the second powder 302 (powder 105 shown in FIG. 1C). The cross section 503 is a cross section of the third powder 303 (the powder 106 shown in FIG. 1C).

Since the first powder 301 is spherical as described above, the cross section 501 of the first powder 301 was circular as shown in FIG. Further, since the second powder 302 has an ellipsoidal shape as described above, the cross section 502 of the second powder 302 has an elliptical shape as shown in FIG. Further, since the third powder 303 has a scaly shape as described above, the cross section 503 of the third powder 303 had a scaly shape as shown in FIG.

Further, by using the cyclone mill 200, the powder of the soft magnetic composition is retained and the powders collide with each other, so that the temperature of the powder surface rises and an Fe oxide film is formed on the powder surface. The thickness of the Fe oxide film was 20 nm or less when pulverization was performed with an oxygen concentration of 0.1% (N2 purge). The thickness of the Fe oxide film is preferably 20 nm or less, more preferably 10 nm or less.

Since the pulverization method of the cyclone mill 200 is a method in which the powder particles collide with each other, the Fe oxide film thickness on the powder surface can be made smaller than that in the pulverization method in which the powder particles collide with a blade or a ball. Further, by pulverizing in a low oxygen concentration, the Fe oxide film thickness can be made thin, and the soft magnetic characteristics of the dust core can be improved.

<Surface smoothness>
The surface smoothness of each of the first powder 301, the second powder 302, and the third powder 303 will be described.

The surface smoothness is a true spherical surface having a completely smooth surface having an actual surface area S1 of a particle (powder) having the same volume equivalent diameter D as the particle (powder) and a surface roughness Ra of 0. It is a value divided by the surface area S2 of the particles. The closer the surface smoothness to 1, the smoother the surface of the particles.

The surface area S1 can be measured by, for example, a gas adsorption type specific surface area meter. The surface area S2 can be obtained by calculating the surface area of a sphere having the volume equivalent diameter D as a diameter.

In this example, the surface smoothness of the first powder 301 was 1.616, the surface smoothness of the second powder 302 was 2.138, and the surface smoothness of the third powder 303 was 4.268. ..

By reducing the surface smoothness, the frictional resistance between particles is reduced, so that good fluidity can be obtained. In particular, at the time of manufacturing the dust core, it is suppressed that the thermosetting resin (an example of the binder) mixed with the soft magnetic powder does not enter the fine irregularities on the surface of the soft magnetic powder and does not contribute to the flow. It becomes possible to perform pressure molding with a small amount of thermosetting resin. Therefore, the packing density of the soft magnetic powder can be increased. Therefore, the ratio of the soft magnetic powder per unit volume is increased, and the soft magnetic characteristics such as the saturation magnetic flux density and the magnetic permeability of the dust core can be improved.

The effect of increasing the packing density of the soft magnetic powder by reducing the surface smoothness can be sufficiently obtained if the surface smoothness is 1.1 or more. In addition, the production of particles having a surface smoothness of less than 1.1 is costly.

Therefore, the surface smoothness of the first powder 301 is preferably 1.1 or more and 2.0 or less. The surface smoothness of the second powder 302 is preferably 1.7 or more and 2.5 or less. The surface smoothness of the third powder 303 is preferably 3.4 or more.

<Flatness>
The flatness of each of the first powder 301, the second powder 302, and the third powder 303 will be described.

The flatness is a value obtained by dividing the maximum half axis among the three half axes of the ellipsoid by the minimum half axis. The closer the flatness is to 1.0, the closer the shape is to a sphere.

In the present example, most of the first powders 301 had a flatness of 1.0 or more and 1.2 or less. In addition, the majority of the second powder 302 has a flatness of 3.0 or more and 6.0 or less. In addition, the majority of the third powder 303 has a flatness of more than 6.0.

At the time of pressure molding, the powder having a flatness of 1.2 or more is arranged with its longitudinal direction aligned with the flow direction of the powder. Therefore, the projected area of the powder having a flatness of 1.2 or more as viewed from the flow direction is smaller than the projected area of the substantially spherical powder having a flatness of less than 1.2, which reduces the flow resistance. be able to. That is, the pressure during pressure molding can be reduced.

Therefore, when manufacturing a dust core formed by mixing soft magnetic particles with a thermosetting resin (an example of a binder), it is possible to mold a mixture having a higher resin viscosity and a reduced resin amount. The packing density of the soft magnetic powder can be increased.

With the second powder 302 and the third powder 303 having a surface smoothness larger than that of the first powder 301, the fluidity of the binder can be improved by increasing the flatness thereof. Therefore, the second powder 302 can enter between the first powders 301 with a small amount of binder. In addition, the third powder 303 can enter between the second powders 302 with a small amount of binder.

The flatness has a greater effect than the surface smoothness due to the above-described effects. This is because the flatness has a larger effect on the outer shape than the surface smoothness. Further, if the pulverization time is lengthened, the flatness of the particles does not change significantly, but the surface is gradually scraped due to the collision of the powders, and the surface smoothness becomes smaller. Further, when manufacturing a dust core, the flatness is more important than the surface smoothness in order to obtain good fluidity of the binder.

From the above, the ratio of the soft magnetic powder per unit volume is increased, and the soft magnetic characteristics such as the saturation magnetic flux density and magnetic permeability of the dust core can be improved.

<Effect>
According to the friction pulverization used in the present embodiment and the present example, the spherical first powder 301 having a particle size larger than 32 μm, the ellipsoidal second powder 302 having a particle size of 32 μm or less, and the particle size The particle size distribution of the flaky third powder 303 having a particle size of 32 μm or less can be easily controlled.

In the present embodiment and the present example, the spherical first powder 301 having a surface smoothness of 1.1 or more and 2.0 or less and a flatness of 1.0 or more and 1.2 or less. And an ellipsoidal second powder 302 having a surface smoothness of 1.7 or more and 2.5 or less and a flatness of 3.0 or more and 6.0 or less, and a surface smoothness of 3. A powder magnetic core containing a scaly third powder 303 having a flatness of 4 or more and a flatness of more than 6.0 is produced.

With this, at the time of manufacturing the dust core, good fluidity can be obtained with a small amount of binder, the second powder 302 can enter between the first powders 301, and the third powder 303 between the second powders 302. Can enter. Therefore, the packing density of the soft magnetic powder can be increased. Therefore, the ratio of the soft magnetic powder per unit volume increases, and the soft magnetic characteristics such as the saturation magnetic flux density and the magnetic permeability of the dust core can be improved.

Furthermore, the soft magnetic powder of the present embodiment is spherical or ellipsoidal, and does not have a corner like an edge. Therefore, it is possible to improve the withstand voltage performance without causing conduction between the powders by cutting into adjacent powders. Further, the flaky powder may have corners, but since it has a small particle size, it does not bite into the adjacent powder and electric field concentration occurs, so that the withstand voltage performance is not deteriorated.

From the above, in the present embodiment and the present embodiment, it is possible to fill the soft magnetic powder with high density while ensuring the insulating property between the soft magnetic powders. Therefore, it is possible to provide a dust core having both high magnetic permeability and high withstand voltage.

Note that the present disclosure is not limited to the above description of the embodiments, and various modifications can be made without departing from the spirit of the present disclosure.

INDUSTRIAL APPLICABILITY The dust core and the manufacturing method thereof according to the present disclosure are useful for dust cores using soft magnetic powder used in inductors such as choke coils, reactors, and transformers.

1, 2 Ground powder 101 Soft magnetic ribbon 102, 103, 104, 105, 106 Powder 201 Grinding chamber 202 Raw material inlet 203, 204 Rotor blade 205 Discharge port 206 Raw material 207 Raw material particles 501, 502, 503 Cross section 301 First powder 302 second powder 303 third powder

Claims (17)

A dust core containing powder of a soft magnetic composition,
A spherical first powder having a flatness of 1.0 or more and 1.2 or less;
An ellipsoidal second powder having a flatness of 3.0 or more and 6.0 or less;
And a scale-like third powder having a flatness of more than 6.0.
Dust core. The average particle size of the first powder is 30 μm or more and 60 μm or less,
The dust core according to claim 1. The average particle size of the second powder is 10 μm or more and 20 μm or less,
The dust core according to claim 1 or 2. The average particle size of the third powder is 4 μm or more and 12 μm or less,
The dust core according to any one of claims 1 to 3. The weight ratio of the third powder is 50 wt% or less of the total powder,
The dust core according to any one of claims 1 to 4. The total weight ratio of the first powder and the second powder is 50% by weight or more of the total powder,
The dust core according to any one of claims 1 to 5. The second powder is more than the first powder,
The dust core according to any one of claims 1 to 6. A dust core containing powder of a soft magnetic composition,
A spherical first powder having a surface smoothness of 1.1 or more and 2.0 or less and a flatness of 1.0 or more and 1.2 or less;
An ellipsoidal second powder having a surface smoothness of 1.7 or more and 2.5 or less and a flatness of 3.0 or more and 6.0 or less;
And a scale-like third powder having a surface smoothness of 3.4 or more and a flatness of more than 6.0.
Dust core. The average particle size of the first powder is 30 μm or more and 60 μm or less,
The dust core according to claim 8. The average particle size of the second powder is 10 μm or more and 20 μm or less,
The dust core according to claim 8 or 9. The average particle size of the third powder is 4 μm or more and 12 μm or less,
The dust core according to any one of claims 8 to 10. The weight ratio of the third powder is 50 wt% or less of the total powder,
The dust core according to any one of claims 8 to 11. The total weight ratio of the first powder and the second powder is 50% by weight or more of the total powder,
The dust core according to any one of claims 8 to 12. The second powder is more than the first powder,
The dust core according to any one of claims 8 to 13. An Fe oxide film having a thickness of 20 nm or less is provided on the surfaces of the first powder, the second powder, and the third powder.
The dust core according to any one of claims 1 to 14. Rubbing the soft magnetic compositions against each other to produce a spherical first powder, an ellipsoidal second powder, and a scaly third powder,
Heating the first powder, the second powder, and the third powder;
Mixing the first powder, the second powder, and the third powder with a binder to produce granulated powder;
A step of filling the granulated powder in a predetermined mold and press-molding to obtain a green compact;
Heating the green compact at a temperature at which the binder hardens,
The first powder is a spherical powder having a flatness of 1.0 or more and 1.2 or less,
The second powder is an ellipsoidal powder having a flatness of 3.0 or more and 6.0 or less,
The third powder is a flaky powder having a flatness of more than 6.0.
Manufacturing method of dust core. Rubbing the soft magnetic compositions against each other to produce a spherical first powder, an ellipsoidal second powder, and a scaly third powder,
Heating the first powder, the second powder, and the third powder;
Mixing the first powder, the second powder, and the third powder with a binder to produce granulated powder;
A step of filling the granulated powder in a predetermined mold and press-molding to obtain a green compact;
Heating the green compact at a temperature at which the binder hardens,
The first powder is a powder having a surface smoothness of 1.1 or more and 2.0 or less and a flatness of 1.0 or more and 1.2 or less,
The second powder is a powder having a surface smoothness of 1.7 or more and 2.5 or less and a flatness of 3.0 or more and 6.0 or less,
The third powder is a powder having a surface smoothness of 3.4 or more and a flatness of more than 6.0.
Manufacturing method of dust core.