阅读说明：本技术 压粉磁芯 (Dust core ) 是由 前出正人 小岛俊之 于 2018-07-04 设计创作，主要内容包括：本发明提供能够减少软磁性粉末的涡流损耗、特别是在高频区域中损耗小的压粉磁芯。为了实现上述目的,使用下述压粉磁芯,其含有软磁性组合物的粉末,其中,上述粉末的圆形度的最大值为0.5以上,平均值为0.2以上。另外,使用下述压粉磁芯,其含有软磁性组合物的粉末,其中,上述粉末含有粉碎粉和球状粉,上述粉碎粉的圆形度的最大值为0.5以上、平均值为0.2以上,上述球状粉的圆形度的最大值为0.9以上、平均值为0.5以上。(The invention provides a dust core which can reduce eddy current loss of soft magnetic powder, especially has small loss in a high frequency region. In order to achieve the above object, a dust core is used which contains a powder of a soft magnetic composition, wherein the powder has a maximum value of circularity of 0.5 or more and an average value of 0.2 or more. Further, a powder magnetic core is used, which contains a powder of a soft magnetic composition, wherein the powder contains a pulverized powder and a spherical powder, the maximum value of the circularity of the pulverized powder is 0.5 or more and the average value is 0.2 or more, and the maximum value of the circularity of the spherical powder is 0.9 or more and the average value is 0.5 or more.)

1. A powder magnetic core comprising a powder of a soft magnetic composition, wherein the powder comprises a pulverized powder and a spherical powder,

the maximum value of the circularity of the pulverized powder is 0.5 or more and the average value is 0.2 or more,

the spherical powder has a maximum value of 0.9 or more and an average value of 0.5 or more.

2. The dust core according to claim 1, wherein the maximum length of the pulverized powder is 50 μm or more and 100 μm or less,

The minimum value of the maximum length is 5 μm or less,

The average value of the maximum length is 5 μm or more and 9 μm or less.

3. The powder magnetic core according to claim 1, wherein the first powder having a particle diameter of the pulverized powder of more than 32 μm is 30% by weight or less of the pulverized powder.

4. The powder magnetic core according to claim 1, wherein the second powder having a particle size of the pulverized powder of 32 μm or less is 70% by weight or more of the pulverized powder.

5. The dust core according to claim 3, wherein the total oxygen amount of the first powder is 0.8 wt% or less.

6. The dust core according to claim 4, wherein the total oxygen amount of the second powder is 1.7% by weight or less.

7. The powder magnetic core according to claim 3, wherein the first powder has an insulating film of 10nm or more on a surface thereof.

8. The powder magnetic core according to claim 4, which contains not the second powder but a powder having a particle diameter of 32 μm or less of the first powder and the spherical powder.

9. The powder magnetic core according to claim 1, which contains not a first powder having a particle diameter of the pulverized powder of more than 32 μm, but a second powder having a particle diameter of the pulverized powder of 32 μm or less and a powder having a particle diameter of the spherical powder of more than 32 μm.

10. The powder magnetic core according to claim 1, wherein the spherical powder has a cumulative distribution D50% of particle diameters of 9 μm or less.

Technical Field

The present invention relates to a dust core using magnetic powder. In particular, the present invention relates to a dust core using soft magnetic powder for use in inductors such as choke coils, reactors, and transformers.

Background

In recent years, there has been a demand for electric driving and weight reduction of vehicles. In the process of making various electronic components smaller and lighter, soft magnetic powder used in choke coils, reactors, transformers, and the like, and dust cores using the soft magnetic powder, are required to have higher and higher performance.

In order to achieve reduction in size and weight of a powder magnetic core using the soft magnetic powder, a material is required to have high saturation magnetic flux density, low core loss (core lost), and further excellent dc superposition characteristics.

For example, patent document 1 describes a method of using a pulverized powder of an Fe-based amorphous alloy having a low magnetic core loss and excellent direct current superposition characteristics.

Fig. 1(a) and 1(b) show photographs of pulverized powder of a Fe-based amorphous alloy ribbon described in patent document 1. The powder is produced by pulverizing a thin strip.

FIG. 1(a) shows a first powder 1 having a particle diameter of 50 μm or more. FIG. 1(b) shows the second powder 2 having a particle size of 50 μm or less.

Patent document 1 describes a dust core including, as main components, a pulverized powder produced by pulverizing a ribbon of an Fe-based amorphous alloy and an atomized spherical powder of an Fe-based amorphous alloy. The first powder 1 having a particle size of more than 2 times (thickness 25 μm × 2: 50 μm) the thickness of the Fe-based amorphous alloy ribbon and not more than 6 times (thickness 25 μm × 6: 150 μm) is 80 mass% or more of the total pulverized powder.

The second powder 2 having a particle size of 2 times or less the thickness of the thin strip (thickness 25 μm × 2 ═ 50 μm) is 20 mass% or less of the total pulverized powder. Here, the particle diameter of the pulverized powder is the minimum value in the plane direction of the main surface of the pulverized powder pulverized into a thin plate.

The particle size of the atomized spherical powder is characterized by being 1/2 (25 μm × 1/2 is 12.5 μm) or less and 3 μm or more, which is a thin strip thickness.

Disclosure of Invention

Problems to be solved by the invention

However, in patent document 1, the proportion of the first powder 1 having a particle diameter 2 times or more the thickness of the ribbon (particle diameter 50 μm) is large, and therefore the electric resistance of the first powder 1 itself is reduced. Further, when the frequency reaches a high frequency (for example, 100kHz or more), the eddy current increases, and the eddy current loss rapidly increases. Thus, the loss of the dust core using the same increases.

The present invention has been made to solve the above conventional problems, and is intended to reduce eddy current loss of soft magnetic powder, and particularly to reduce loss in a high frequency region. The object is to provide a dust core which can obtain a high saturation magnetic flux density and excellent soft magnetic characteristics.

Means for solving the problems

In order to achieve the above object, a powder magnetic core containing a powder of a soft magnetic composition is used in which the maximum value of circularity of the powder is 0.5 or more and the average value is 0.2 or more.

In addition, a dust core containing a powder of a soft magnetic composition is used, wherein the powder contains a pulverized powder and a spherical powder, the maximum value of the circularity of the pulverized powder is 0.5 or more and the average value is 0.2 or more, and the maximum value of the circularity of the spherical powder is 0.9 or more and the average value is 0.5 or more.

ADVANTAGEOUS EFFECTS OF INVENTION

As described above, according to the means disclosed in the embodiment, the eddy current loss of the soft magnetic powder can be reduced, and particularly, the loss can be reduced in a high frequency region. Further, a powder magnetic core that can obtain a high saturation magnetic flux density and excellent soft magnetic characteristics can be provided.

Drawings

Fig. 1(a) is a diagram showing a soft magnetic powder having a particle size of 50 μm or more described in patent document 1, and fig. 1(b) is a diagram showing a soft magnetic powder having a particle size of 50 μm or less described in patent document 1.

Fig. 2(a) to 2(b) are views showing a process for producing a soft magnetic powder according to embodiment 1.

Fig. 3(a) is an SEM image showing the soft magnetic powder in example 1, and fig. 3(b) is an enlarged view of the region a in fig. 2 (a).

Fig. 4 is a particle size distribution diagram of the soft magnetic powder in embodiment 1.

Fig. 5(a) is an SEM image of a cross section of a powder magnetic core using a soft magnetic powder in embodiment 1, and fig. 5(B) is an enlarged view of a region B in fig. 5 (a).

Fig. 6 is a distribution diagram of circularity of the soft magnetic powder contained in the powder magnetic core in embodiment 1.

Fig. 7 is a distribution diagram of the maximum length of the soft magnetic powder contained in the powder magnetic core in embodiment 1.

Fig. 8 is a cross-sectional view of a powder magnetic core using soft magnetic powder obtained by mixing pulverized powder and spherical powder in embodiment 2.

Fig. 9(a) to 9(b) are views showing the steps of producing the soft magnetic pulverized powder of embodiment 2.

Fig. 10(a) is an SEM image showing the soft magnetic pulverized powder in embodiment 2, and fig. 10(b) is an enlarged view of region a in fig. 9 (a).

Fig. 11 is a particle size distribution diagram of the soft magnetic pulverized powder in embodiment 2.

Fig. 12 is a distribution diagram of the maximum length of the soft magnetic pulverized powder contained in the powder magnetic core in embodiment 2.

Fig. 13 is a cross-sectional view of a powder magnetic core using soft magnetic powder obtained by mixing pulverized powder and spherical powder in embodiment 3.

Fig. 14 is a cross-sectional view of a powder magnetic core using soft magnetic powder obtained by mixing pulverized powder and spherical powder in embodiment 4.

Detailed Description

(embodiment mode 1)

< production of Soft magnetic powder >

First, a method for manufacturing a powder magnetic core according to embodiment 1 will be described.

(1) The alloy composition is melted by high-frequency heating or the like, and a ribbon or a sheet of an amorphous layer is produced by a liquid quenching method. As a method for forming a thin ribbon of an amorphous layer, there is a liquid quenching method. As the liquid quenching method, a single-roll amorphous manufacturing apparatus or a twin-roll amorphous manufacturing apparatus used for manufacturing an Fe-based amorphous ribbon or the like can be used.

(2) Next, the ribbon or the sheet is pulverized and powdered. The pulverization of the thin strip or sheet may use a general pulverization device. For example, a ball mill, a pounder, a planetary mill, a cyclone mill, a jet mill, a rotary mill, or the like can be used.

At this time, when the ribbon is heated and crystallized, the ribbon becomes brittle and is easily crushed. However, the hardness of the ribbon becomes high, it becomes difficult to crush the ribbon into smaller pieces, and the proportion of the second powder 2 having a small particle size becomes small. Therefore, in the embodiment, by pulverizing the ribbon in an unheated state, the ribbon has low hardness and can be pulverized to be small, and the proportion of the second powder 2 having a small particle size can be increased.

In addition, by classifying the powder obtained by pulverization using a sieve, a soft magnetic powder having a desired particle size distribution can be obtained.

The mechanism of producing the pulverized powder of the present embodiment will be described with reference to fig. 2(a) and 2 (b). The soft magnetic ribbon 101 shown in fig. 2(a) is pulverized by a pulverizer such as a rotary mill. As a result, as shown in fig. 2(b), the surface of the powder 102 is cracked and gradually cut into fine particles 104. As a result, soft magnetic thin strip 101 becomes powder 102 having grinding marks 103 on the surface. The powder 102 is formed into a shape without edges and with rounded corners by surface cracking. The fine powder 104 also surface-cracks by the same mechanism, and has a rounded shape without edges.

(3) Next, the powder 102 and the fine powder 104 are subjected to a heat treatment to eliminate internal strain due to pulverization or to precipitate an α Fe crystal layer. Examples of the heat treatment apparatus include an air heater, a hot press, a lamp, a sheathed metal heater, a ceramic heater, and a rotary kiln.

In this case, rapid heating is preferably performed using a hot press or the like. Further, the crystallization of the powder 102 and the fine powder 104 progresses, and the surface of the powder 102 is further cracked. Thus, the proportion of the second powder 2 having a small particle diameter is increased.

< production of dust core >

(1) In the production of the dust core in embodiment 1, the soft magnetic powder 102, the fine powder 104, and a binder having good insulation properties and high heat resistance, such as a phenol resin or a silicone resin, are mixed to produce a granulated powder.

(2) Next, the granulated powder is filled in a mold having a desired shape and high heat resistance, and pressure-molded to obtain a green compact.

(3) Then, the powder magnetic core is heated at a temperature at which the binder is cured, thereby obtaining a powder magnetic core with low loss in a high frequency region.

< example 1>

An amorphous soft magnetic alloy powder was obtained by crushing a Fe-based amorphous alloy ribbon of fe73.5-Cu1-Nb3-Si 13.5-B9 (atomic%) prepared by a rapid cooling single roll method using a rotary mill. The crushing is as follows: after the coarse pulverization for 3 minutes, the usual pulverization for 20 minutes and the pulverization with cooling for 20 minutes were carried out.

Next, the soft magnetic alloy powder is heat-treated to remove internal strain due to pulverization and to precipitate an α Fe crystal layer. The heat treatment was carried out at 550 ℃ for 20 seconds under hot pressing.

Next, a silicone resin was mixed as a binder and granulated to produce granulated powder. Next, the granulated powder was put into a die, and a molding pressure of 4 ton/cm was set using an extruder²The pressure of (3) is increased to produce a green compact. The silicone resin is about 3 wt% of the soft magnetic powder.

< evaluation of core loss (core loss) >

The magnetic core loss at a frequency of 1MHz and a magnetic flux density of 25mT was measured for each of the obtained green compacts using a B-H analyzer. The standard of whether the magnetic core loss is qualified or not is set as 1300kW/m³The following. The reason for this is to achieve a core loss of a general metallic material or less. The magnetic core loss of the green compact of example 1, as measured by a B-H analyzer, was 1040kW/m³The qualification criterion is passed. A dust core with low loss in a high frequency region is obtained.

< shape of powder >

Fig. 3(a) shows an SEM image of the soft magnetic powder in example 1. Fig. 3(b) shows an enlarged image of the a region of fig. 3 (a). Powder 201 corresponds to powder 102, and powder 202 corresponds to fine powder 104. The powder 201 and the powder 202 have rounded shapes without edges based on the above-described pulverization mechanism.

< first powder 1 and second powder 2>

The first powder 1 having a particle size of more than 32 μm is 30 wt% or less of the whole pulverized powder. The second powder 2 having a particle size of 32 μm or less accounts for 70 wt% or more of the whole pulverized powder. Either one of them may be satisfied. The particle size was judged as whether or not the particle size could pass through an opening having a diameter of 32 μm. The same applies to the following.

Therefore, as shown in fig. 3(a), the following results are obtained: the first powder 1 is present in a certain amount and the second powder 2 is present in a large amount.

Next, fig. 4 shows the particle size distribution of the soft magnetic powder in example 1 and comparative example. In the comparative example, the pulverization time was set to be longer than that in example 1. The manufacturing conditions are described below for magnetic permeability. The particle size distribution was determined by means of the Microtrack MT3000(2) 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 example 1, the cumulative distribution was found to be 7 μm for D10%, about 14.6 μm for D50%, and 37.7 μm for D90%.

< dust core >

Fig. 5(a) shows an SEM image of a cross section of the powder magnetic core of example 1. Fig. 5(B) shows an enlarged image of the B region of fig. 5 (a). Powder 401 corresponds to powder 102. The powder 402 corresponds to the fine powder 104. Since powder 401 is pulverized by the above-described mechanism, the short side of powder 401 is substantially equal to the thickness of the soft magnetic ribbon of the raw material.

< distribution of circularity >

Fig. 6 shows the distribution of circularity of the powder of example 1. The distribution of circularity was calculated using WinRoof. In fig. 6, the horizontal axis represents circularity, and the vertical axis represents the frequency of existence of soft magnetic powder of each circularity.

The circularity is preferably 0.5 or more in maximum value and 0.2 or more in average value. Preferably, the circularity has a maximum value of 0.7 or more and an average value of 0.3 or more. Further, the maximum value of the circularity is preferably 0.8 or more and the average value is preferably 0.4 or more.

When the circularity is increased, the fluidity when the soft magnetic powder is filled into a mold is improved when the powder magnetic core is manufactured, and the void ratio of the powder magnetic core can be reduced. By decreasing the porosity, the proportion of the soft magnetic powder per unit volume increases, and soft magnetic properties such as saturation magnetic flux density and magnetic permeability of the dust core can be improved.

< maximum length of powder >

Fig. 7 shows the maximum length of the powder of example 1 (the longest length in the powder). The distribution of maximum length is calculated using WinRoof. In fig. 7, the horizontal axis represents the maximum length, and the vertical axis represents the frequency of existence of the soft magnetic powder of each maximum length.

The maximum value of the maximum length is 50 μm or more and 100 μm or less, the minimum value of the maximum length is 5 μm or less, and the average value of the maximum lengths is 6 μm or more and 9 μm or less.

The maximum length is preferably 50 μm to 80 μm in maximum, the minimum value is preferably 0.5 μm or less, and the average value is preferably 5 μm to 9 μm.

Further, the maximum value of the maximum length is preferably 50 μm or more and 60 μm or less.

When the maximum length is small, the particle diameter of the soft magnetic powder is small, and the electrical resistance of the soft magnetic powder can be increased. This can reduce eddy current at high frequency (for example, 100kHz or higher), and can reduce eddy current loss. Therefore, the loss of the dust core using the same can be reduced.

< porosity >

Further, the porosity of the powder magnetic core of example 1 was calculated by image analysis. The void ratio of the powder magnetic core of example 1 was 26.8%.

The porosity (portion other than the soft magnetic powder) of the dust core is preferably 30% or less. Preferably 20% or less. More preferably 10% or less.

When the porosity is small, the proportion of the soft magnetic powder per unit volume increases, and soft magnetic properties such as saturation magnetic flux density and magnetic permeability of the powder magnetic core can be improved.

< particle size and oxygen amount >

The total oxygen amount in the soft magnetic powder was measured as follows. First, only the graphite crucible is heated in an inert gas atmosphere (helium gas or the like) to a temperature at which the soft magnetic powder is melted. Next, oxygen in the soft magnetic powder reacts with graphite to become carbon monoxide. The carbon monoxide is active in infrared absorption and can therefore be detected by infrared absorption.

By the above measurement method, the total oxygen amount of the powder of example 1 was 1.01%. The total oxygen content of the first powder 1 is preferably 0.8 wt% or less and the total oxygen content of the second powder 2 is preferably 1.7 wt% or less.

The total oxygen content of the first powder 1 is 0.4 wt% or less, and the total oxygen content of the second powder 2 is more preferably 0.8 wt% or less.

Further, it is more preferable that the total oxygen amount of the first powder 1 is 0.2 wt% or less and the total oxygen amount of the second powder 2 is 0.4 wt% or less.

When the oxygen amount is small, the ratio of the soft magnetic powder oxidized becomes small, and the ratio of the soft magnetic powder exhibiting good soft magnetic properties becomes large. This improves the soft magnetic properties such as saturation magnetic flux density and magnetic permeability of the powder magnetic core. Further, the loss can be reduced.

< effects >

In the case of pulverization utilizing cracking of the powder surface, the powder has no corners and rounded corners, and the particle size distribution in which the first powder 1 and the second powder 2 are present in a large amount can be easily controlled.

By not performing the embrittlement treatment by the heat treatment before the pulverization, the powder is easily cracked at the time of the pulverization. When heat treatment is performed for the purpose of making the ribbon brittle, the hardness of the ribbon increases, and conversely, the ribbon is difficult to crush. That is, it becomes difficult for cracking to occur.

This makes it possible to obtain a powder magnetic core in which the fluidity is good when the soft magnetic powder is filled into the mold, and the second powder 2 can enter between the first powders 1. Therefore, the void ratio of the dust core can be reduced. By decreasing the porosity, the proportion of the soft magnetic powder per unit volume is increased, and the soft magnetic properties such as the saturation magnetic flux density and the magnetic permeability of the dust core can be improved.

Further, since the first powder 1 is 30 wt% or less of the total pulverized powder and the second powder 2 is 70 wt% or more of the total pulverized powder, the electrical resistance of the pulverized powder becomes large, and eddy current can be reduced at a high frequency (for example, 100kHz or more), and eddy current loss can be reduced. Therefore, the loss of the dust core using the soft magnetic powder can be reduced.

(magnetic permeability)

Next, the magnetic permeability of the powder magnetic core was examined.

< evaluation of core loss (magnetic permeability) >

The magnetic permeability at a frequency of 100kHz was measured for each of the obtained compacts using an impedance analyzer. The criterion of whether the magnetic permeability is qualified or not is set to be more than 22. The reason is to achieve a magnetic permeability or higher for the same kind of metal-based material. The sample of example 1 was measured using an impedance analyzer. The magnetic permeability of example 1 was 24.0, and the standard for the acceptability was satisfied, and a dust core having excellent magnetic properties was obtained.

< example 1>

The production was performed under the conditions described above. In general, the pulverization time is 20 minutes, and the pulverization time with cooling is 20 minutes. For pulverization with cooling, pulverization is performed while cooling a motor and a pulverization container of a pulverizer with a spot cooler. Kept at an average of 65 ℃ by cooling. The ordinary pulverization for 2.5 minutes and the pulverization for 2.5 minutes with cooling were repeated 8 times.

< comparative example >

The total micronization time was set to 60 minutes. The pulverization time was usually 20 minutes, and the cooling pulverization time was 50 minutes. Except for this, the same conditions as in example 1 were used. The average was 80 ℃. In addition, the pulverization for 1 minute and the cooling for 2 minutes were repeated 20 times.

In example 1 and comparative example, the pulverization time was changed. In example 1 in which the total pulverization time was short, the particle diameter was large, the magnetic permeability was high, and the magnetic properties were good. The longer the pulverization time, the smaller the particle size becomes. When the particle diameter is small, the ratio of the oxide layer to the volume occupied by the particles becomes large, and the magnetic permeability becomes low.

As a result, the particle diameter d 50% is larger than 10.7. mu.m, preferably 13 to 17 μm.

[ Table 1]

(embodiment mode 2)

Fig. 8 shows a cross section of a powder magnetic core using soft magnetic powder obtained by mixing pulverized powder and spherical powder in embodiment 2 of the present invention. The first powder 501 and the second powder 502 are pulverized powders, and the spherical powder 503 is a spherical powder.

The first powder 501 is a pulverized powder having a particle size of more than 32 μm and is 30 wt% or less of the total pulverized powder, and the second powder 502 is a pulverized powder having a particle size of 32 μm or less and is 70 wt% or more of the total pulverized powder.

The spherical powder 503 is a spherical powder having a cumulative distribution D50% of particle diameter of 9 μm or less, and occupies 1 to 30 vol% of the powder magnetic core.

The insulating film 504 is an insulating film having high resistance formed on the surface of the first powder 501. The thickness of the insulating film 504 is larger than that of the natural oxide film (10nm to 20 nm). In addition, the insulating film 504 is formed by heat treatment to combine the constituent elements of the first powder 501 with those of the insulating filmOxygen in the atmosphere is combined to form FeO and Fe₂O₃、Fe₃O₄、Al₂O₃、SiO₂And the like. Alternatively, SiO is formed by a chemical method or a physical method₂、Al₂O₂、TiO₂And the like.

Next, a method for manufacturing a powder magnetic core according to embodiment 2 will be described.

< production of first powder 501 and second powder 502 >

(preparation of pulverized powder)

(1) The alloy composition is melted by high-frequency heating or the like, and a ribbon or a sheet of an amorphous layer is produced by a liquid quenching method. As a liquid quenching method for producing a ribbon of an amorphous layer, a single-roll amorphous production apparatus or a twin-roll amorphous production apparatus used for producing an Fe-based amorphous ribbon or the like can be used.

(2) Next, the ribbon or the sheet is pulverized and powdered. The pulverization of the thin strip or sheet may use a general pulverization device. For example, a ball mill, a pounder, a planetary mill, a cyclone mill, a jet mill, a rotary mill, or the like can be used.

In this case, when the ribbon is heated and crystallized, the ribbon becomes brittle and is easily crushed. However, the hardness of the ribbon becomes high, it becomes difficult to crush the ribbon into small particles, and the proportion of the crushed powder having small particle size becomes small. Therefore, in the embodiment, by pulverizing the ribbon in an unheated state, the ribbon has low hardness and can be pulverized to a small size, and the proportion of pulverized powder having a small particle size is increased.

In addition, by classifying the powder obtained by pulverization using a sieve, a pulverized powder having a soft magnetic property with a desired particle size distribution can be obtained.

The mechanism of producing the pulverized powder of the present embodiment will be described with reference to fig. 9(a) and 9 (b). The soft magnetic ribbon 601 shown in fig. 9(a) is pulverized by a pulverizer such as a rotary mill. As a result, as shown in fig. 9(b), the surface of the powder 602 is cracked and gradually cut into fine powder 604, and the powder 602 has grinding marks 603 on the surface. The powder 602 is fractured into a shape without corners and with rounded corners by surface cracking. The fine powder 604 also has surface cracks by the same mechanism, and has a rounded shape without edges. Here, the powder 602 corresponds to the first powder 501, and the fine powder 604 corresponds to the second powder 502.

(3) Next, the pulverized powder (powder) of the ribbon or the sheet is subjected to a heat treatment to remove internal strain due to the pulverization or to precipitate an α Fe crystal layer. Examples of the heat treatment apparatus include an air heater, a hot press, a lamp, a sheathed metal heater, a ceramic heater, and a rotary kiln. In this case, rapid heating is preferably performed using a hot press or the like. This is because crystallization proceeds further, and cracking of the surface of the powder 602 proceeds further. Therefore, the proportion of the pulverized powder having a small particle size is increased.

(production of spherical powder 503)

For spherical powder, amorphous powder is produced by gas atomization, water atomization, or the like. Then, the steel sheet is heat-treated to remove internal strain or to precipitate an α Fe crystal phase.

Alternatively, the surface of the pulverized powder produced as described above may be mechanically ground so as to be spherical or remelted by thermal plasma.

< production of powder magnetic core by mixing pulverized powder and spherical powder 503 >

(1) In the production of the powder magnetic core according to embodiment 2, the first powder 501, the second powder 502, the spherical powder 503, and a binder having good insulation properties and high heat resistance, such as a phenol resin or a silicone resin, are mixed with a mixer to produce a granulated powder. Here, the powder obtained by mixing the pulverized powder and the spherical powder 503 is soft magnetic powder.

(2) The granulated powder is filled in a mold having a desired shape and high heat resistance, and is pressure-molded to obtain a green compact.

(3) Then, the powder magnetic core is heated at a temperature at which the binder is cured, thereby obtaining a powder magnetic core with low loss in a high frequency region.

(example 2)

An Fe-based amorphous alloy ribbon of fe73.5-Cu1-Nb3-Si 13.5-B9 (atomic%) produced by a rapid cooling single roll method was pulverized by a rotary mill to obtain soft magnetic pulverized powder of an amorphous layer. The pulverization was carried out for 3 minutes, followed by coarse pulverization and fine pulverization for 40 minutes.

As the spherical powder 503, Fe-Si-Cr-B (particle size: 5 μm) manufactured by EPSONATMIX was used.

Next, the pulverized powder is heat-treated to remove internal strain due to pulverization and to precipitate an α Fe crystal layer. As for the heat treatment, heating was performed at 550 ℃ for 20 seconds under hot pressing.

Next, the soft magnetic powder obtained by mixing the pulverized powder and the spherical powder 503 was mixed with a silicone resin as a binder, and granulated to produce a granulated powder.

Next, the granulated powder was put into a die, and a molding pressure was set to 4 ton/cm using an extruder²The pressure of (3) is increased to produce a green compact. In the soft magnetic powder obtained by mixing the pulverized powder and the spherical powder 503, the ratio of the pulverized powder to the spherical powder 503 was set to 9: 1 (weight ratio). The silicone resin is about 3% by weight of the soft magnetic powder obtained by mixing the pulverized powder and the spherical powder 503.

The magnetic core loss at a frequency of 1MHz and a magnetic flux density of 25mT was measured for each of the obtained green compacts using a B-H analyzer. The standard of whether the magnetic core loss is qualified or not reaches 1300kW/m³The following criteria for acceptability are met. The standard of pass or fail is to be equal to or less than the core loss of the conventional metallic material. This provides a powder magnetic core with low loss in the high-frequency range.

< shape of pulverized powder >

Fig. 10(a) shows an SEM image of the soft magnetic pulverized powder in example 2. Fig. 10(b) shows an enlarged image of the a region of fig. 10 (a). The first powder 701 is the powder 602 in fig. 9(b), and the second powder 702 is the fine powder 604 in fig. 9 (b). The first powder 701 and the second powder 702 are formed into a shape having no edges and rounded corners by the above-described pulverization mechanism.

< pulverized powder having particle size of 32 μm or more >

The first powder 701 is a pulverized powder having a particle size of more than 32 μm. The first powder 701 is 30 wt% or less of the total pulverized powder. The second powder 702 is a pulverized powder having a particle size of 32 μm or less. The second powder 702 is 70% by weight or more of the total pulverized powder. Either of them may be used. The particle size was judged as whether or not the particle size could pass through an opening having a diameter of 32 μm. The same applies hereinafter.

Therefore, as shown in fig. 10(a), the particle size distribution is such that a certain amount of the first powder 701 is present and a large amount of the second powder 702 is present.

Next, fig. 11 shows the particle size distribution of the soft magnetic pulverized powder in example 2. The particle size distribution was determined by means of the Microtrack MT3000(2) series. In fig. 11, the horizontal axis represents the particle size, and the vertical axis represents the frequency of existence of the soft magnetic pulverized powder having each particle size. In the cumulative distribution, D10% was 7 μm, D50% was 14.6 μm, and D90% was 37.7. mu.m.

< circularity of pulverized powder and spherical powder 503 >

The circularity distribution of the pulverized powder was calculated using WinRoof.