JP2021082692A - Manufacturing method of dust core - Google Patents

Abstract

To provide a manufacturing method of a dust core which can obtain eddy current loss lowering effect larger than the influence on the hysteresis loss and has low iron loss.SOLUTION: A dust core is manufactured at least through a pressure molding step of molding soft magnetic powder into a molded body of a predetermined shape, and a molded body heat treatment step of heat-treating the molded body that has undergone the pressure molding step. In the molded body heat treatment step, the molded body is heat-treated in an atmosphere having oxygen concentration of 0.1% or more.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for producing a dust core.

A coil is an electromagnetic component that converts electrical energy into magnetic energy and stores and emits it. Coil is also called a reactor in electric power applications such as drive systems for hybrid vehicles, electric vehicles, and fuel cell vehicles, and is used in various applications such as booster circuits for vehicles. As the core of the coil, for example, a dust core is used. The dust core is formed by pressure molding soft magnetic powder.

The dust core is required to have a magnetic characteristic that a large magnetic flux density can be obtained with a small applied magnetic field and a magnetic characteristic that the energy loss due to a change in the magnetic flux density is small in order to improve the energy exchange efficiency and generate low heat. Examples of the magnetic characteristics related to the magnetic flux density include magnetic permeability (μ). As a magnetic property related to energy loss, iron loss (Pcv), which is also called core loss, can be mentioned. The iron loss (Pcv) is represented by the sum of the hysteresis loss (Ph) and the eddy current loss (Pe).

Japanese Patent No. 5435398

In order to reduce the eddy current loss, a technique of coating the periphery of the soft magnetic powder with an insulating material is known. However, if the insulating material is excessive in order to reduce the eddy current loss, the hysteresis loss may increase, and an effective iron loss lowering effect may not be obtained as compared with the increase in the insulating material. Therefore, a manufacturing method is desired in which the effect of reducing the eddy current loss is larger than the effect on the hysteresis loss and the iron loss can be reduced as a whole.

The present invention has been proposed to solve the above problems, and an object of the present invention is to provide a method for producing a dust core capable of obtaining an eddy current loss lowering effect larger than the influence on the hysteresis loss. To do.

In order to achieve the above object, the method for producing a dust core according to an embodiment of the present invention includes a pressure molding step of molding a soft magnetic powder into a molded product having a predetermined shape, and the molding through the pressure molding step. It is characterized by including a molded article heat treatment step of heat-treating the body in an atmosphere having an oxygen concentration of 0.1% or more.

By this method of manufacturing the dust core, the eddy current loss can be reduced without increasing the insulating material. Therefore, the eddy current loss can be reduced while maintaining the hysteresis loss, or the eddy current loss can be reduced so as to exceed the increase in the hysteresis loss, and the iron loss of the dust core is generally reduced. It is speculation, but not limited to this, by heat treatment in an atmosphere with an oxygen concentration of 0.1% or more, an oxide film is formed on the surface of the soft magnetic powder, and the specific resistance of the insulating layer is increased by this oxide film. It is considered that the magnetic domain is subdivided by this oxide film as the height increases, and the eddy current loss is reduced.

In the molded body heat treatment step, the heat treatment may be performed in an atmosphere having an oxygen concentration of 0.1% or more and 5% or less. When the oxygen concentration is 5% or less, the decrease in magnetic permeability can be stopped while receiving the maximum effect of reducing the eddy current loss, and the dust core achieves both low loss and high magnetic permeability. In the molded body heat treatment step, the heat treatment may be performed in an atmosphere having an oxygen concentration of 0.1% or more and 1% or less. When the oxygen concentration is 1% or less, the decrease in magnetic permeability can be further suppressed while receiving the effect of reducing the eddy current loss to the maximum, and the dust core has both low loss and high magnetic permeability.

Prior to the pressure molding step, a powder heat treatment step of heat-treating the soft magnetic powder at 500 ° C. or higher may be included. By using this powder heat treatment in combination, the eddy current loss can be further reduced, and a powder magnetic core with a lower iron loss can be realized.

The soft magnetic powder may be a FeSiAl alloy powder. Further, even if an insulation treatment step of coating the soft magnetic powder with an insulating material and a lubricant addition step of adding a lubricant to the soft magnetic powder that has undergone the insulation treatment step are included before the pressure molding step. Good.

According to the present invention, it is possible to obtain an eddy current loss lowering effect larger than the effect on the hysteresis loss, and it is possible to obtain a dust core having a low iron loss.

It is a graph which shows the relationship between the oxygen concentration of the molded body heat treatment process, and the hysteresis loss Ph. It is a graph which shows the relationship between the oxygen concentration of the molded body heat treatment process, and the eddy current loss Pe. It is a graph which shows the relationship between the oxygen concentration of a molded body heat treatment process, and iron loss Pcv. It is a graph which shows the relationship between the oxygen concentration of the molded body heat treatment process, and the magnetic permeability μ.

Hereinafter, the method for producing the dust core according to the present embodiment will be described in detail. The present invention is not limited to the embodiments described below.

(Powder magnetic core)
The dust core is a magnetic material used in the core of a coil, which is also called an inductor and a reactor. This dust core is formed by pressure molding and annealing soft magnetic powder. The soft magnetic powder may contain an element that can be oxidized by annealing in a low-oxidizing atmosphere. Typically, the soft magnetic powder includes permalloy (Fe-Ni alloy) containing iron as a main component, a Si-containing iron alloy (Fe-Si alloy), a sendust alloy (Fe-Si-Al alloy), and an amorphous alloy. , Pure iron powder and the like.

The Si-containing iron alloy may contain Co, Al, Cr or Mn. When permalloy (Fe—Ni alloy) is used, the ratio of Ni to Fe is preferably 50:50 or 25:75, but other ratios may be used. For example, Fe-80Ni and Fe-36Ni may be used. In addition to Fe and Ni, Si, Cr, Mo, Cu, Nb, Ta and the like may be contained. Examples of the Fe-Si alloy powder include Fe-3.5% Si alloy powder and Fe-6.5% Si alloy powder, but the ratio of Si to Fe is other than 3.5% and 6.5%. It may be. Pure iron powder contains 99% or more of Fe. The soft magnetic powder is not limited to one type, but may be a mixed powder of two or more types.

This soft magnetic powder may be produced by a pulverization method or an atomization method. The atomizing method may be any of a water atomizing method, a gas atomizing method, and a water gas atomizing method. The water atomization method is currently the most available and low cost. When the water atomization method is used, it is preferable because the particle shape is distorted and it is easy to improve the mechanical strength of the powder molded product obtained by pressure-molding the particle shape. The gas atomizing method is preferable because it can effectively reduce the hysteresis loss.

Further, the soft magnetic powder may be coated with an insulating layer by adhering an insulating material to the outside. That is, the soft magnetic powder means to include either a soft magnetic powder on which an insulating layer is not formed or a soft magnetic powder on which an insulating layer is formed. The insulating material may be attached so as to cover the entire outside of the soft magnetic powder, or may be attached so as to cover a part of the soft magnetic powder. That is, the insulating material adheres to the soft magnetic powder so that the soft magnetic powder adheres to the surface of each particle, the soft magnetic powder adheres to the surface of the agglomerates, or both of these aspects are mixed. Further, the insulating material may be adhered to the entire circumference of the particle surface or the aggregate surface, may be dispersed and adhered in a dot shape, or may be dispersed and adhered in a lump shape. ..

Examples of the insulating material include a silane coupling agent, a silicone oligomer, a silicone resin, or a mixture thereof. For example, as the insulating material, the silane coupling agent and the silicone resin may be attached to the outside of the soft magnetic powder, or the silicone oligomer and the silicone resin may be attached to the outside of the soft magnetic powder. When a plurality of types of insulating materials adhere to the outside of the soft magnetic powder, the insulating layer made of the plurality of types of insulating materials may be divided into individual layers for each type, or a single layer in which each type is mixed. It may be.

As the silane coupling agent, aminosilane-based, epoxysilane-based, and isocyanurate-based silane coupling agents can be used, and in particular, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and tris. -(3-Trimethoxysilylpropyl) isocyanurate is preferred.

Examples of the silicone oligomer include methyl-based and methylphenyl-based silicone oligomers having an alkoxysilyl group and no reactive functional group, and epoxy-based, epoxymethyl-based and mercapto-based silicone oligomers having an alkoxysilyl group and a reactive functional group. Instead of mercaptomethyl-based, acrylic-methyl-based, methacryl-methyl-based, vinylphenyl-based, or alkoxysilyl group, an alicyclic epoxy-based having a reactive functional group or the like can be used. In particular, a thick and hard insulating layer can be formed by using a methyl-based or methylphenyl-based silicone oligomer. Further, in consideration of the ease of forming the silicone oligomer layer, a methyl type or a methylphenyl type having a relatively low viscosity may be used.

The silicone resin is a resin having a siloxane bond (Si—O—Si) as a main skeleton, and can form an insulating layer having excellent flexibility. As the silicone resin, a methyl-based, methylphenyl-based, propylphenyl-based, epoxy resin-modified system, alkyd resin-modified system, polyester resin-modified system, rubber-based, or the like can be typically used. Among these, in particular, when a methylphenyl-based silicone resin is used, an insulating layer having little heat loss and excellent heat resistance can be formed.

In addition, various additives may be added to the soft magnetic powder. For example, inorganic insulating powders such as alumina powder, magnesia powder, silica powder, titania powder and zirconia powder, and condensed metal phosphates such as condensed aluminum phosphate, condensed calcium phosphate and condensed magnesium phosphate may be added.

(Manufacturing method of dust core)
This dust core is manufactured through at least a pressure molding step of soft magnetic powder and a molded body heat treatment step also called annealing. Prior to the pressure molding step, at least one of a powder heat treatment step of heat-treating the soft magnetic powder, an insulation treatment step of coating the soft magnetic powder with an insulating material, and a lubricant addition step of adding a lubricant may be performed. .. When the powder heat treatment step and the insulation treatment step are included, the powder heat treatment step is the first step. When the lubricant addition step is included, the lubricant addition step is a step immediately before the pressure molding step. That is, when all the steps are executed, the powder heat treatment step, the insulation treatment step, the lubricant addition step, the pressure molding step and the molded body heat treatment step are executed in this order on the soft magnetic powder.

(Powder heat treatment process)
In the powder heat treatment step, the soft magnetic powder is heated in a non-oxidizing atmosphere or an atmospheric atmosphere. The non-oxidizing atmosphere is preferably a vacuum atmosphere or an inert gas atmosphere. Examples of the inert gas include H ₂ and N ₂ . The heating time is, for example, about 1 to 6 hours. In this powder heat treatment step, it is preferable to heat the soft magnetic powder in a temperature environment of 500 ° C. or higher and 700 ° C. or lower. In this powder heat treatment step, when the soft magnetic powder is heated in a temperature environment of 500 ° C. or higher and 700 ° C. or lower, the effect of reducing the hysteresis loss can be obtained. It is speculation, and the reason for reducing the hysteresis loss is considered to be as follows, although it is not limited to this mechanism.

That is, when the soft magnetic powder is heated in a temperature environment of 500 ° C. or higher and 700 ° C. or lower, an irregular structure occupying the crystal structure of the soft magnetic powder remains at a ratio of 5.70 wt% or more and 31.74 wt% or less. Then, the strain generated by the pressure molding step is likely to occur in multiple directions, and the atoms are likely to move in the crystal in multiple directions in the molded body heat treatment step. Therefore, in the heat treatment step of the molded product, it is considered that the crystal structure of the soft magnetic powder tends to return to a regular structure and the hysteresis loss is reduced.

On the other hand, when the soft magnetic powder is heated in a temperature environment of less than 500 ° C., the proportion of irregular structures becomes too large, and when the soft magnetic powder is heated in a temperature environment of more than 700 ° C., the proportion of irregular structures becomes small. Pass. If the proportion of irregular structures becomes too large, it cannot return to the regular structure, and if the proportion of irregular structures becomes too small, strain tends to occur in one direction along the pressurizing direction, and one atom is present. It can move only in one direction, it cannot move in multiple directions, and it is considered difficult to arrange it in a regular structure. The regular structures are, for example, a DO ₃ structure and a B ₂ structure.

(Insulation process)
In the insulation treatment step, an insulating layer made of an insulating material is formed on the outside of the soft magnetic powder. In the insulation treatment step of forming the single-layer insulating layer on the outside of the soft magnetic powder, all the insulating materials included in the insulating layer are mixed with the soft magnetic powder and dried by heating. In the insulation treatment step of forming an insulating layer divided into layers for each type of insulating material on the outside of the soft magnetic powder, mixing of the soft magnetic powder and the insulating material and heat drying are repeated in order from the lower layer to the outermost surface layer. When mixing the soft magnetic powder with other materials, use a mixer (W type, V type), a pot mill, etc., and at this time, mix the soft magnetic powder so that internal strain does not enter. Is preferable.

The silane coupling agent is preferably 0.25 wt% to 1.0 wt% with respect to the soft magnetic powder. By setting the addition amount of the silane coupling agent within this range, the standard deviation, magnetic characteristics, and strength characteristics of the density of the molded dust core can be improved. The drying temperature of the silane coupling agent is 25 ° C to 200 ° C. This is because if the drying temperature is lower than 25 ° C., the solvent may remain and the film may be incomplete. On the other hand, if the drying temperature is higher than 200 ° C., decomposition may proceed and the film may not be formed. The drying time is about 2 hours.

The silicone oligomer is preferably 0.25 wt% to 2.0 wt% with respect to the soft magnetic powder. If the amount added is less than 0.25 wt%, it does not function as an insulating film, and the eddy current loss increases, resulting in an increase in loss. If the amount added is more than 2.0 wt%, the dust core expands, resulting in a decrease in strength. The drying temperature of the silicone oligomer is preferably 25 ° C to 350 ° C. If the drying temperature is less than 25 ° C., the formation of the film is incomplete, the eddy current loss becomes high, and the loss increases. On the other hand, if the drying temperature is higher than 350 ° C., the hysteresis loss increases due to the oxidation of the powder, and the loss increases. The drying time is about 2 hours.

The silicone resin is preferably 1.0 to 3.0 wt% with respect to the soft magnetic powder. This is because if the amount added is less than 1.0 wt%, it does not function as an insulating film, and the magnetic characteristics may deteriorate due to an increase in eddy current loss. This is because if the amount added is more than 3.0 wt%, the core expands and the density of the molded product decreases, which may reduce the magnetic permeability. The drying temperature of the silicone resin is preferably 100 ° C to 200 ° C. This is because if the drying temperature is less than 100 ° C., the film formation may be incomplete and the eddy current loss may increase. On the other hand, if the drying temperature is higher than 200 ° C., the powder becomes an inorganic substance and does not play a role as a binder, the retention of the powder becomes poor, and the density and magnetic permeability of the molded product may decrease. The drying time is about 2 hours.

(Lubricant addition process)
The lubricant mixing step is a step of adding a lubricant to the obtained soft magnetic powder and mixing the mixture. By this mixing step, the surface of the insulating layer is coated with a lubricant. As the lubricant, stearic acid and a metal salt thereof, and waxes such as ethylene bisstealamide and ethylene bisstearateamide can be used. By mixing the lubricant, the sliding between the soft magnetic powders is improved, the density at the time of mixing is improved, and the molding density is increased. Further, by mixing the lubricant, the withdrawal pressure of the upper punch during molding is reduced, and the generation of vertical streaks on the core wall surface due to the contact between the mold and the powder is suppressed.

(Pressure molding process)
In the molding step, a molded product is formed by pressure molding the soft magnetic powder. The pressure at the time of molding is 10 to 20 ton / cm ² , and the average pressure is preferably about 12 to ^{15 ton / cm 2.}

(Mold body heat treatment process)
In the molded body heat treatment step, the molded body that has undergone the pressure molding step is heated to remove strain. The temperature range of the heating environment is preferably 650 ° C. or higher and 850 ° C. or lower. If it is less than 650 ° C., the effect of strain removal becomes limited. If the temperature exceeds 850 ° C., the insulating layer made of the insulating material is destroyed, and the effect of reducing the eddy current loss caused by the insulating layer made of the insulating material is diminished.

Further, in this heat treatment step of the molded product, the molded product is heated in an oxidizing atmosphere having an oxygen concentration of 0.1% or more in volume concentration. The gas composition other than oxygen in the atmosphere is not particularly limited, and may be nitrogen, for example. When the oxygen concentration in the heating environment is 0.1% or more, the eddy current loss of the dust core is sharply reduced as compared with the hysteresis loss of the dust core. Therefore, even if the hysteresis loss is increased by the heat treatment step of the molded product, the eddy current loss is reduced more than the increase in the hysteresis loss, and the iron loss is generally lowered. It is speculation, but not limited to this, when the oxygen concentration in the heating environment is 0.1% or more in the heat treatment process of the molded body, an oxide film is formed on the surface of the soft magnetic powder, and this oxide film forms an oxide film on the insulating layer. It is considered that the specific resistance increases and the magnetic domain is subdivided by this oxide film to reduce the eddy current loss.

Here, it is more preferable that the heat treatment of the molded product in an oxidizing atmosphere having an oxygen concentration of 0.1% or more and the powder heat treatment step in a temperature environment of 500 ° C. or more are used in combination. The powder magnetic core produced by combining the molded body heat treatment step and the powder heat treatment step tends to have a lower eddy current loss than the powder magnetic core without the powder heat treatment step.

This oxygen concentration is preferably determined in the range of 1% or less in terms of volume concentration. When the oxygen concentration is 1% or more, the eddy current loss tends to level off even if the oxygen concentration is increased. On the other hand, when the oxygen concentration is increased, the thickness of the oxide film on the surface of the soft magnetic powder changes according to the oxygen concentration, so that the magnetic permeability continues to decrease as the oxygen concentration increases. When the oxygen concentration is 1% or less, the effect of reducing the eddy current loss can be maximized and the decrease in magnetic permeability can be suppressed. Therefore, both high magnetic permeability of the dust core and low iron loss can be achieved. However, depending on the presence or absence of powder heat treatment and the temperature, the eddy current loss decreases up to an oxygen concentration of 5%, and the eddy current loss may level off even if the oxygen concentration at which the oxygen concentration becomes 5% or more is increased. Therefore, the upper limit of the oxygen concentration is acceptable as long as the volume concentration is at least 5% or less.

Hereinafter, the present invention will be described in more detail based on Examples. The present invention is not limited to the following examples.

As the soft magnetic powder, a FeSiAl alloy powder having an average particle diameter (D50) of 19 μm obtained by the gas atomization method was used. Unless otherwise specified, the average particle size shall refer to D50, that is, the median diameter. This FeSiAl alloy powder was powder heat treated. In the powder heat treatment, the FeSiAl alloy powder was heated at a temperature of 500 ° C. for 2 hours in a nitrogen atmosphere.

The FeSiAl alloy powder after the powder heat treatment was insulated. In the insulation treatment step, a silane coupling agent and a silicone resin were first mixed with the FeSiAl alloy powder. The silane coupling agent was mixed at a ratio of 1.0 wt% with respect to the total amount of the FeSiAl alloy powder. The silicone resin was mixed at a ratio of 1.6 wt% with respect to the total amount of the FeSiAl alloy powder. After mixing, the mixture of FeSiAl alloy powder, silane coupling agent and silicone resin was heated in a temperature environment of 150 ° C. for 2 hours, and the mixture was dried by this heating. The dried mixture was passed through a 250 μm sieve.

The FeSiAl alloy powder that had undergone the insulation treatment was subjected to a lubricant addition treatment. In this lubricant addition step, ethylene bisstealamide (Acrawax (registered trademark)) was mixed as a lubricant. Ethylene bisstealamide was mixed at a ratio of 0.5 wt% with respect to the total amount of FeSiAl alloy powder before the insulation treatment step. After mixing, the mixture of FeSiAl alloy powder and ethylene bisstealamide that had undergone insulation treatment was heated in a temperature environment of 150 ° C. for 2 hours, and the mixture was dried by this heating. The dried mixture was passed through a 250 μm sieve.

After undergoing a powder heat treatment step, an insulation treatment step, and a lubricant addition step, the FeSiAl alloy powder was subjected to a pressure molding treatment. In the pressure molding process, pressure molding was performed at ^{15 ton / cm 2 at room temperature using a mold.} As a result, a compact magnetic core molded body having an outer diameter of 16.5 mm, an inner diameter of 11.0 mm and a height of 5 mm was obtained.

A plurality of molded bodies that have undergone the pressure molding step were prepared in order to perform heat treatment of the molded body at different oxygen concentrations. In the molded body heat treatment step, each molded body was heated in an oxidizing atmosphere having an oxygen concentration of 0.001%, 0.01%, 0.1%, 1%, 5% and 21% by volume. In this molded body heat treatment step, the molded body was heated at 700 ° C. for 2 hours in these oxidizing atmospheres.

Further, a powder magnetic core without powder heat treatment, a powder magnetic core powder heat-treated at 600 ° C., and a powder magnetic core powder heat-treated at 680 ° C. were separately produced to obtain magnetic permeability μ, iron loss Pcv, hysteresis loss Ph, and eddy current loss. Pe was measured. These powder magnetic cores are subjected to a compact heat treatment step under an oxidizing atmosphere having oxygen concentrations of 0.001%, 0.01%, 0.1%, 1%, 5% and 21%, except for the presence or absence of powder heat treatment and the temperature. It was produced by the same manufacturing method and under the same conditions as the powder magnetic core that had been powder-heat-treated in a heating environment of 500 ° C.

The magnetic permeability μ, iron loss Pcv, hysteresis loss Ph, and eddy current loss Pe of these dust cores were measured. At the time of measurement, a reactor having a dust core as a core was prepared. When measuring the magnetic permeability μ, a copper wire having a diameter of 0.5 mm was wound around the dust core for 30 turns. In measuring the loss, a copper wire having a diameter of 0.5 mm was wound around the dust core for 30 turns as the primary winding and 3 turns as the secondary winding.

Then, by using an LCR meter (Agilent Technology: 4284A), the magnetic permeability μ was calculated from the inductance at 10 kHz and 1.0 V. ^{In addition, the iron loss Pcv (kw / m 3} ) is measured under the measurement conditions of a frequency of 100 kHz and a maximum magnetic flux density Bm of 100 mT using a BH analyzer (Iwadori Measurement Co., Ltd .: SY-8219), which is a magnetic measuring device. Was done.

Further, the hysteresis loss Ph (kw / m ³ ) and the eddy current loss Pe (kw / m ³ ) were calculated from the measurement result of the iron loss Pcv. Hysteresis loss Ph (kw / m ³ ) and eddy current loss Pe (kw / m ³ ) are obtained by using the following equations (1) to (3) as the minimum square method for the hysteresis loss coefficient (Kh) of the iron loss Pcv frequency curve. ), The eddy current loss coefficient (Ke) was calculated.
Pcv = Kh x f + Ke x f ² ... (1)
Ph = Kh x f ... (2)
Pe = Ke × f ² ... (3)
Pcv: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: Frequency Ph: Hysteresis loss Pe: Eddy current loss

Table 1 below shows the magnetic permeability μ, iron loss Pcv, hysteresis loss Ph, and eddy current loss Pe of each of the produced dust cores.
(Table 1)

In addition, the graphs of FIGS. 1 to 4 were created according to Table 1 above. FIG. 1 is a graph showing the relationship between the oxygen concentration in the molded body heat treatment step and the hysteresis loss Ph, and FIG. 2 is a graph showing the relationship between the oxygen concentration in the molded body heat treatment step and the eddy current loss Pe. FIG. 3 is a graph showing the relationship between the oxygen concentration in the molded body heat treatment step and the iron loss Pcv, and FIG. 4 is a graph showing the relationship between the oxygen concentration in the molded body heat treatment step and the magnetic permeability μ.

Further, in FIGS. 1 to 4, the series plotted with circles are the powder magnetic cores without powder heat treatment, and the series plotted with triangles are the pressures subjected to powder heat treatment in a heating environment of 500 ° C. It is a powder core. The series plotted with diamonds are the dust cores that have been powder heat treated in a heating environment of 600 ° C, and the series plotted by the squares are the powder cores that have been powder heat treated in a heating environment of 680 ° C. is there.

As shown in Table 1 and FIG. 1, the correlation between the increase / decrease in oxygen concentration and the increase / decrease in hysteresis loss Ph is low. In other words, the hysteresis loss Ph is maintained within a predetermined range regardless of the oxygen concentration. On the other hand, as shown in Table 1 and FIG. 2, when the oxygen concentration is 0.01% and 0.1%, the eddy current loss Pe when the oxygen concentration is 0.1% is sharply reduced. The effect of lowering the eddy current loss Pe continues at an oxygen concentration of 0.1% or more. That is, it was confirmed that the eddy current loss Pe sharply decreased when the oxygen concentration became 0.1% or more. From these, as shown in Table 1 and FIG. 3, it was confirmed that when the oxygen concentration was 0.1% or more, the iron loss Pcv decreased and a low-loss dust core was obtained.

Further, as shown in Table 1 and FIG. 2, when the powder heat treatment was omitted, the eddy current loss Pe when the oxygen concentration was 0.1% or more was ^{142.5 kW / m 3 on average.} On the other hand, when powder heat treatment at 500 ° C. or higher is used in combination, the eddy current loss Pe when the oxygen concentration is 0.1% or higher is 80.5 kW / m ³ , 95 kW / m ^{3 and 73.25 kW / m on average.} It was ^3. From these, it was confirmed that the eddy current loss Pe was further reduced by using the powder heat treatment step in a temperature environment of 500 ° C. or higher and the molded product heat treatment having an oxygen concentration of 0.1% or more in combination.

Further, as shown in Table 1 and FIG. 2, the eddy current loss Pe is minimized when the oxygen concentration is 1%, and the oxygen concentration is 1% or more, except for the dust core whose powder heat treatment temperature is 600 ° C. It was confirmed that it was almost flat. Further, as shown in Table 1 and FIG. 2, in the powder magnetic core in which the temperature of the powder heat treatment was 600 ° C., the eddy current loss Pe decreased up to the oxygen concentration of 5%, and most of the powder heat treatment had an oxygen concentration of 5% or more. It was confirmed that it would level off.

On the other hand, as shown in Table 1 and FIG. 4, there is a range in which the eddy current loss Pe is flat, whereas the magnetic permeability μ is consistently decreased according to the oxygen concentration. Therefore, it was confirmed that when the oxygen concentration is at least 5% or less, both low eddy current loss Pe and high magnetic permeability μ can be achieved. Further, it was confirmed that when the oxygen concentration is 1% or less, the low eddy current loss Pe and the high magnetic permeability μ can be more reliably achieved at the same time.

Claims (6)

A pressure molding process that molds soft magnetic powder into a molded body of a predetermined shape,
A molded body heat treatment step of heat-treating the molded body that has undergone the pressure molding step in an atmosphere having an oxygen concentration of 0.1% or more.
Including,
A method for producing a dust core. In the molded body heat treatment step, heat treatment is performed in an atmosphere having an oxygen concentration of 0.1% or more and 5% or less.
The method for producing a dust core according to claim 1. In the molded body heat treatment step, heat treatment is performed in an atmosphere having an oxygen concentration of 0.1% or more and 1% or less.
The method for producing a dust core according to claim 1. A powder heat treatment step of heat-treating the soft magnetic powder at 500 ° C. or higher is included before the pressure molding step.
The method for producing a dust core according to any one of claims 1 to 3. The soft magnetic powder is a FeSiAl alloy powder.
The method for producing a dust core according to any one of claims 1 to 4. Insulation treatment step of coating the soft magnetic powder with an insulating material and
A lubricant addition step of adding a lubricant to the soft magnetic powder that has undergone the insulation treatment step,
Before the pressure molding step,
The method for producing a dust core according to any one of claims 1 to 5.

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