JP7079749B2 - Manufacturing method of dust core - Google Patents

Description

The present invention relates to a soft magnetic powder, a powder magnetic core composed of the soft magnetic powder, a method for producing a soft magnetic powder, and a method for producing a powder magnetic core.

The reactor is used in various applications such as a drive system for a hybrid vehicle, an electric vehicle, a fuel cell vehicle, and the like. As the core of this reactor, for example, a dust core is used. The dust core is formed by pressure molding the soft magnetic powder and the insulating film covering the soft magnetic powder.

The dust core is required to have a magnetic characteristic of low energy loss due to the demands for improved energy exchange efficiency and low heat generation. The magnetic property related to energy loss is specifically iron loss (Pcv). The iron loss (Pcv) is represented by the sum of the hysteresis loss (Phv) and the eddy current loss (Pev).

Japanese Unexamined Patent Publication No. 2018-133461

Conventionally, it has been said that when strain occurs in the particles of the soft magnetic powder, the coercive force of the soft magnetic powder increases and the hysteresis loss increases. Therefore, in the heat treatment of the soft magnetic powder, in order to remove the distortion in the particles of the soft magnetic powder and reduce the coercive force, the heat treatment is performed at a high temperature of, for example, 900 ° C. to reduce the hysteresis loss. However, in recent years, due to the diversification of reactor applications, further reduction of hysteresis loss is required.

An object of the present invention is to provide a soft magnetic powder capable of reducing hysteresis loss, a powder magnetic core composed of the soft magnetic powder, a method for producing the soft magnetic powder, and a method for producing the powder magnetic core. ..

As a result of diligent research, the present inventors have reduced hysteresis loss and thus iron loss as compared with the method of removing the strain in the particles of the soft magnetic powder by leaving a certain non-uniform strain in the particles of the soft magnetic powder. We obtained the finding that it is possible to reduce the amount of particles.

数式（１）のうち、βは積分幅、Ｄは結晶子の大きさ、θは回析角、λはＸ線の波長、ηは不均一歪、を表す。
The method for producing a dust core of the present invention is a powder heat treatment step in which a FeSiAl alloy powder is heat-treated at 500 ° C. or higher and 650 ° C. or lower in a nitrogen atmosphere, and the FeSiAl alloy powder that has undergone the powder heat treatment step is pressure-molded and molded. The following mathematical formula of the FeSiAl alloy powder, which comprises a molding step of producing a body and an annealing step of annealing the molded body at 600 ° C. or higher and 800 ° C. or lower, after the powder heat treatment step and before the molding step ( The value of the non-uniform strain η based on 1) is characterized by being 0.140% or more and 0.182% or less.

In the formula (1), β is the integral width, D is the size of the crystallite, θ is the diffraction angle, λ is the wavelength of the X-ray, and η is the non-uniform strain.

According to the present invention, it is possible to provide a soft magnetic powder capable of reducing hysteresis loss, a powder magnetic core composed of the soft magnetic powder, a soft magnetic powder, and a method for producing the powder magnetic core.

It is a flowchart which shows the manufacturing process of the dust core of this embodiment. It is a graph which shows the relationship between the heat treatment temperature of a powder, and a non-uniform strain in an Example. It is a graph which shows the relationship between the heat treatment temperature of a powder, and iron loss in an Example. It is a graph which shows the relationship between the heat treatment temperature of a powder, and a hysteresis loss in an Example. It is a graph which shows the relationship between the heat treatment temperature of a powder and an eddy current loss in an Example. It is a graph which shows the relationship between the heat treatment temperature of a powder and a coercive force in an Example.

(Embodiment)
The dust core of the present embodiment is formed as a core having a predetermined shape by pressure molding a soft magnetic powder heat-treated at a predetermined temperature. The dust core is used as the magnetic material of the reactor. A method for manufacturing this dust core will be described. FIG. 1 is a flowchart showing a manufacturing process of a dust core according to the present embodiment. As shown in FIG. 1, the powder magnetic core manufacturing method of the present embodiment includes (1) powder heat treatment step, (2) silicone oligomer layer forming step, (3) silicone resin layer forming step, and (4) molding step. (5) It has a baking step.

数式（１）のうち、βは積分幅、Ｄは結晶子の大きさ（ｎｍ）、θは回析角（ｒａｄ）、λはＸ線の波長（ｎｍ）、ηは不均一歪（％）、を表す。なお、積分幅とは、Ｘ線回析で得られたピーク波形の面積をピーク高さで割った比である。 (1) Powder heat treatment step The powder heat treatment step is a step of increasing the non-uniform strain possessed by the crystal structure of the soft magnetic powder before the heat treatment by heat-treating the soft magnetic powder. Non-uniform strain is the variation in strain when observing an aggregate of tens of thousands of powders and looking from each crystal lattice plane. A large amount of non-uniform strain is a state in which the crystal structure of the soft magnetic powder has strain and there are many strains having different shapes. The non-uniform strain is calculated from the following mathematical formula (1) by X-ray diffraction of the crystal structure of the soft magnetic powder.

In formula (1), β is the integration width, D is the crystallite size (nm), θ is the diffraction angle (rad), λ is the X-ray wavelength (nm), and η is the non-uniform strain (%). Represents. The integrated width is a ratio obtained by dividing the area of the peak waveform obtained by X-ray diffraction by the peak height.

In the powder heat treatment step, heating is performed for 1 to 6 hours in a non-oxidizing atmosphere such as a vacuum atmosphere or an inert gas atmosphere. Examples of the inert gas include H ₂ and N ₂ . The heat treatment temperature is preferably 500 ° C. or higher and 650 ° C. or lower. By setting the heat treatment temperature in this range, the value (%) of the non-uniform strain η calculated from the above formula (1) can be set to 0.140 or more and 0.182 or less, and as will be described later, the hysteresis loss can be set. It is possible to reduce the iron loss and thus the iron loss.

The soft magnetic powder used in this embodiment is a soft magnetic powder containing iron as a main component, and is a permalloy (Fe-Ni alloy), a Si-containing iron alloy (Fe-Si alloy), and a sentust alloy (Fe-Si-). Al alloy), pure iron powder, etc. are used. The iron alloy may also contain Co, Al, Cr and 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 or 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, and may be a mixed powder of two or more types.

(2) Silicone oligomer layer forming step In the silicone oligomer layer forming step, a predetermined amount of silicone oligomer is added to the soft magnetic powder, and the mixture is dried in an air atmosphere at a predetermined temperature. By the silicone oligomer layer forming step, the silicone oligomer layer is formed on the outside of the soft magnetic powder.

The silicone oligomer has an alkoxysilyl group and does not have a reactive functional group, such as a methyl type or a methylphenyl type, or an epoxy type, an epoxymethyl type, a mercapto type or a mercapto having an alkoxysilyl group and a reactive functional group. Methyl-based, acrylic-methyl-based, methacrylic-methyl-based, vinylphenyl-based, and alicyclic epoxy-based ones having a reactive functional group without having an alkoxysilyl group 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 molecular weight of the silicone oligomer is preferably 100 to 4000. When the molecular weight is less than 100, it is liable to be broken down or disappear by thermal decomposition in the annealing step, and the soft magnetic powders are liable to be dielectrically broken down. On the other hand, when the molecular weight is larger than 4000, the film thickness becomes too thick and the magnetic characteristics deteriorate.

The amount of the silicone oligomer added is preferably 0.15 to 3.5 wt% with respect to the soft magnetic powder, and 0.5 to 1.25 wt% when the soft magnetic powder is an Fe—Ni alloy powder. Is more preferable. When the soft magnetic powder is Fe—Si alloy powder or pure iron powder, it is more preferably 0.15 to 3.5 wt%. If the amount added is less than 0.15 wt%, it does not function as an insulating film, and the eddy current loss increases and the magnetic characteristics deteriorate. If the amount added is more than 3.5 wt%, the core expands and the density of the molded product decreases, and the magnetic permeability decreases.

The drying temperature of the silicone oligomer layer is preferably 25 ° C. to 350 ° C., and more preferably 200 ° C. to 350 ° C. when the soft magnetic powder is an Fe—Ni alloy powder. When the soft magnetic powder is Fe—Si alloy powder or pure iron powder, 25 ° C to 350 ° C is more preferable. If the drying temperature is less than 25 ° C., the film formation is incomplete and the eddy current loss becomes high. On the other hand, if the drying temperature is higher than 350 ° C., the powder is oxidized and the hysteresis loss is increased, and the density and magnetic permeability of the molded product are lowered. The drying time is about 2 hours.

(3) Silicone Resin Layer Forming Step In the silicone resin layer forming step, a predetermined amount of silicone resin is added to the soft magnetic powder on which the silicone oligomer layer is formed, and the mixture is dried in an air atmosphere at a predetermined temperature. By the silicone resin layer forming step, the silicone resin layer is formed on the outside of the silicone oligomer layer.

Silicone resin is a resin having a siloxane bond (Si—O—Si) as its main skeleton. By using a silicone resin, a film having excellent flexibility can be formed. As the silicone resin, methyl-based, methylphenyl-based, propylphenyl-based, epoxy resin-modified system, alkyd resin-modified system, polyester resin-modified system, rubber-based, and the like can be used. Among these, particularly when a methylphenyl-based silicone resin is used, it is possible to form a silicone resin layer having less heat loss and excellent heat resistance.

The amount of the silicone resin added is preferably 1.0 to 1.5 wt% with respect to the soft magnetic powder. If the amount added is less than 1.0 wt%, it does not function as an insulating film, and the eddy current loss increases and the magnetic characteristics deteriorate. If the amount added is more than 1.5 wt%, the core expands and the density of the molded product decreases, and the magnetic permeability decreases. By appropriately adjusting the amount of the silicone resin added to the silicone oligomer, a strong insulating film having high insulating performance can be formed, and in particular, the weight ratio of the silicone resin to the silicone oligomer is 1: 0.8 to 1: 3. In some cases, the strength and insulation performance are excellent.

The drying temperature of the silicone resin layer is preferably 100 ° C. to 400 ° C., and more preferably 200 ° C. to 300 ° C. when the soft magnetic powder is an Fe—Ni alloy powder. When the soft magnetic powder is an Fe—Si alloy powder, 100 ° C. to 400 ° C. is more preferable. When the soft magnetic powder is pure iron powder, 100 ° C. to 300 ° C. is more preferable. If the drying temperature is less than 100 ° C., the film formation is incomplete and the eddy current loss becomes high. On the other hand, if the drying temperature is higher than 400 ° C., the powder is oxidized and the hysteresis loss is increased, and the density and magnetic permeability of the molded product are lowered. The drying time is about 2 hours.

(4) Molding step In the molding step, a molded body is formed by pressure molding a soft magnetic powder having an insulating film formed on its surface. The pressure at the time of molding is 10 to 20 ton / cm ² , and it is preferably about 15 ton / cm ² on average.

(5) Annealing step In the annealing step, the molded product that has undergone the molding step is coated with a soft magnetic powder at 600 ° C. or higher in N ₂ gas or in an N ₂ + H ₂ gas non-oxidizing atmosphere or in the air. The heat treatment is performed at a temperature below the temperature at which the insulating film is destroyed (for example, 800 ° C.). A dust core is produced by going through this annealing step.

(Example)
Examples of the present invention will be described with reference to Table 1 and FIGS. 2-FIG. 6. Examples 1-4 and Comparative Examples 1-3 were prepared as follows. Specifically, Examples 1-4 and Comparative Example 1-3 are common to the following (2) to (5), and were produced by changing only the powder heat treatment temperature of the following (1).
(1) As the soft magnetic powder, FeSiAl alloy powder having an average particle diameter of 19.8 μm was used. The soft magnetic powder was heat treated for 2 hours in a nitrogen atmosphere without heat treatment and at different heat treatment temperatures of 500-750 ° C. Specifically, in Example 1-4, the heat treatment was performed in the range of 500 ° C. to 650 ° C. at intervals of 50 ° C. On the other hand, Comparative Example 1 did not undergo heat treatment, that is, did not go through the step (1). Comparative Examples 2 and 3 were heat-treated at 700 and 750 ° C., respectively.
(2) To the heat-treated soft magnetic powder, 0.5 wt% of a silicone oligomer was added, and the mixture was dried at 200 ° C. for 2 hours. Then, in order to crush the mass, sieving was performed with an opening of 250 μm.
(3) To the soft magnetic powder to which the silicone oligomer was added, 1.5 wt% of silicone resin was added, and the mixture was dried at 150 ° C. for 2 hours. Then, in order to crush the mass, sieving was performed with an opening of 250 μm.
(4) Ethylene bisstealamide used as a lubricant was added to the soft magnetic powder prepared as described above. Then, these were filled in a toroidal-shaped container having an outer diameter of 16.5 mm, an inner diameter of 11.0 mm, and a height of 5.0 mm to prepare a molded product at a molding pressure of 15 ton / cm ² . Two molded bodies, each of Example 1-4 and Comparative Example 1-3, were produced through these steps.
(5) Finally, two molded bodies prepared for each were annealed at a temperature of 700 ° C. to prepare a dust core. At this time, of the two molded products of Example 1-4 and Comparative Example 1-3, the annealing treatment was performed under two conditions, one in a nitrogen atmosphere and the other in the air.

(Measurement item)
Non-uniform strain, coercive force and iron loss were measured for Examples 1-4 and Comparative Example 1-3 prepared as described above. The non-uniform strain was calculated from the above equation (1) using X-ray diffraction. As the X-ray diffractometer, a fully automatic X-ray diffractometer (manufactured by Rigaku Co., Ltd .: Cu tube, X-ray wavelength λ = 0.154 nm) was used.

The coercive force was measured with an HC meter (K-HC1000 manufactured by Tohoku Steel Co., Ltd.). For iron loss, a copper wire of φ0.5 mm is wound around the powder magnetic core with 20 turns of the primary winding and 20 turns of the secondary winding, and the BH analyzer (Iwadori Measurement Co., Ltd .: SY) is a magnetic measuring instrument. -8219) was used for measurement. The measurement conditions were a frequency of 100 kHz and a maximum magnetic flux density of Bm = 100 T, and the hysteresis loss (Ph) and the eddy current loss (Pe) were calculated. This calculation was performed by calculating the hysteresis loss coefficient (Kh) and the eddy current loss coefficient (Ke) by the least squares method using the following equations (1) to (3) for the frequency curve of the loss.

Pcv = Kh × f + Ke × f ² ... (1)
Ph = Kh × 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

The above measurement results are shown in Table 1 and FIG. 2-5. FIG. 2 is a graph showing the relationship between the heat treatment temperature of the powder and the non-uniform strain. FIG. 3 is a graph showing the relationship between the heat treatment temperature of the powder and the iron loss Pcv. FIG. 4 is a graph showing the relationship between the heat treatment temperature of the powder and the hysteresis loss Ph. FIG. 5 is a graph showing the relationship between the heat treatment temperature of the powder and the eddy current loss Pe. FIG. 6 is a graph showing the relationship between the heat treatment temperature of the powder and the coercive force Hc.

(Relationship between non-uniform strain and iron loss)
As shown in Table 1 and FIG. 2, the non-uniform strain η tends to increase from Comparative Example 1 without heat treatment to Example 2 in which the non-uniform strain η has a maximum of 0.182. When the heat treatment temperature of Example 2 exceeds 550 ° C, the non-uniform strain η gradually decreases, and the non-uniform strain η of Example 4 having a heat treatment temperature of 650 ° C becomes 0.140. Further, when the heat treatment temperature is raised, the non-uniform strain η of Comparative Example 2 having a heat treatment temperature of 700 ° C. is sharply reduced to 0.060, which is less than half of that of Example 4 having a heat treatment temperature of 650 ° C.

Conventionally, it has been considered that the strain of the powder, which was present before the heat treatment, is gradually reduced after the heating by performing the heat treatment of the powder. However, as a result of diligent research, the present inventors further increased the non-uniform strain state of the non-uniform strain η generated in the powder before the heat treatment by applying heat, and the heat treatment temperature was 550 ° C. It was found that in (Example 2), the increase in the non-uniform strain state settled down, and then the increase tended to decrease, and when the temperature exceeded 650 ° C., the non-uniform strain η decreased extremely.

The iron loss Pcv of Example 1-4 subjected to the annealing treatment in the atmosphere is smaller than that of the iron loss Pcv of Comparative Example 1-3. That is, as shown in FIGS. 3 to 5, in Examples 1-4, the eddy current loss Pe was a good value, and the hysteresis loss tended to be reduced as compared with Comparative Example 1-3. , Iron loss Pcv is reduced.

In particular, the reduction of iron loss Pcv is remarkable when the annealing treatment is performed in a nitrogen atmosphere. The iron loss Pcv of Example 1-4 is 300 (kW / m ³ ) or less, whereas that of Comparative Example 1-3 exceeds 350 (kW / m ³ ) even in Comparative Example 2 having the best numerical value. In Comparative Examples 1 and 3, it exceeds 400 (kW / m ³ ). This is because the hysteresis loss Ph of Example 1-4 could be significantly reduced as compared with the hysteresis loss Ph of Comparative Example 1-3. Specifically, the hysteresis loss Ph of Example 1-4 is due to the fact that the hysteresis loss Ph of Comparative Example 1-3 can be reduced to 80% or less of that of Comparative Example 2, which has the lowest hysteresis loss Ph.

Conventionally, it has been considered that iron loss can be reduced by eliminating the strain in the soft magnetic powder. Therefore, the heat treatment temperature of the powder is a temperature at which distortion in the powder can be eliminated, for example, a high temperature of about 900 ° C.

However, as shown above, the iron loss Pcv of Examples 1-4 is lower than that of Comparative Examples 2 and 3. That is, the iron loss Pcv is reduced in Examples 1-4 in which the heat treatment temperature of the powder is lower than in Comparative Examples 2 and 3. That is, in the present invention, contrary to the conventional idea, the iron loss Pcv is reduced by intentionally leaving a non-uniform strain. Then, when the non-uniform strain η is in the range of 0.140 or more and 0.182 or less, the iron loss Pcv is reduced. In other words, when the heat treatment temperature of the powder is in the range of 500 ° C. or higher and 650 or lower, the iron loss Pcv is reduced.

(Relationship between non-uniform strain and coercive force)
As shown in Table 1 and FIG. 6, the coercive force Hc decreases when the heat treatment temperature of the powder is increased. Conventionally, it has been considered that the hysteresis loss is reduced by removing the strain in the powder and reducing the coercive force Hc. Certainly, the iron loss Pcv and the hysteresis loss Ph are reduced in Comparative Examples 2 and 3 as compared with Comparative Example 1 in which the heat treatment is not performed.

However, as shown above, in Examples 1-4 having a large coercive force Hc, the hysteresis loss and the iron loss Pcv are reduced as compared with Comparative Examples 2 and 3. From this, it can be seen that there is a limit to reducing the iron loss Pcv and the hysteresis loss Ph simply by reducing the coercive force Hc. Then, in this embodiment, by reducing the coercive force Hc to a certain extent and setting the value of the non-uniform strain η to 0.140 or more and 0.182 or less, the iron loss is lower than simply reducing the coercive force Hc. It was shown that it can be planned. It is presumed that if the strain is left in the soft magnetic powder, the width of the magnetic domain in the crystal of the powder is narrowed, which leads to the reduction of the hysteresis loss.

(Other embodiments)
Although embodiments of the present invention have been described herein, this embodiment is presented as an example and is not intended to limit the scope of the invention. The above-described embodiment can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the scope of the invention. The embodiments and variations thereof are included in the scope of the invention described in the claims and the equivalent scope thereof, as are included in the scope and gist of the invention.

In the present embodiment, the silicone oligomer layer forming step is performed after the powder heat treatment step, but the inorganic insulating powder adhesion step may be provided after the powder heat treatment step and before the silicone oligomer layer forming step. The step of adhering the inorganic insulating powder is a step of mixing the soft magnetic powder and the inorganic insulating powder. Mixing is performed using a mixer (W type, V type), a pot mill or the like, and at this time, the powder is mixed so as not to contain internal strain. As described above, the inorganic insulating powder layer can be attached to the surface of the soft magnetic powder. By adhering the inorganic insulating powder to the surface of the soft magnetic powder, it is possible to insulate between the soft magnetic powders and raise the heat treatment temperature. The inorganic insulating powder is preferably at least one of alumina powder, magnesia powder, silica powder, titania powder, and zirconia powder.

Claims (1)

A powder heat treatment step of heat-treating FeSiAl alloy powder at 500 ° C. or higher and 650 ° C. or lower in a nitrogen atmosphere.
A molding step of forming a molded body by pressure molding the FeSiAl alloy powder that has undergone the powder heat treatment step, and a molding step.
An annealing step of annealing the molded product at 600 ° C. or higher and 800 ° C. or lower,
Have,
The value of the non-uniform strain η based on the following mathematical formula (1) of the FeSiAl alloy powder after the powder heat treatment step and before the molding step is
Must be 0.140% or more and 0.182% or less
A method for manufacturing a dust core.

In the formula (1), β is the integral width, D is the crystallite size, θ is the diffraction angle, λ is the wavelength of the X-ray, and η is the non-uniform strain.

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