JP7009425B2 - 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 (Ph) and the eddy current loss (Pe).

Japanese Unexamined Patent Publication No. 2009-147252

Generally, it is said that hysteresis loss and thus iron loss can be reduced by reducing the irregular structure occupying the crystal structure of the soft magnetic powder and increasing the DO ₃ structure which is a regular structure. It is known that when the temperature at which the powder is heat-treated is increased to a high temperature, the ratio of the irregular structure to the crystal structure of the powder decreases and the DO ₃ structure increases. Therefore, the powder is heat-treated at a high temperature of, for example, 900 ° C. to reduce the hysteresis loss.

However, as a result of diligent research, the present inventor, unlike the above-mentioned common general knowledge, leaves a certain degree of irregular structure by powder heat treatment, and as a result, hysteresis loss and thus iron loss are higher than in the case where the ratio of leaving irregular structure is small. We obtained the finding that it is possible to reduce the number of

In the method for producing a dust core of the present invention, a powder heat treatment step of heat-treating a soft magnetic powder made of FeSiAl alloy powder , which is a gas atomizing powder, at 500 ° C. or higher and 700 ° C. or lower, and the soft magnetic powder that has undergone the powder heat treatment step are added. In the crystal structure of the FeSiAl alloy powder that has undergone the powder heat treatment step, the steps include a molding step of forming a molded body by pressure molding and a annealing step of baking the molded body in the air at 600 ° C. or higher and 800 ° C. or lower . The crystal structure includes an irregular structure having an irregular structure, and the ratio of the irregular structure to the crystal structure is 5.70 wt% or more and 31.74 wt% or less.

According to the present invention, there is provided a soft magnetic powder capable of reducing hysteresis loss and thus iron 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. To do.

It is a flowchart which shows the manufacturing process of the dust core of this embodiment. It is a graph which shows the ratio of a powder heat treatment temperature and a DO3 structure _, a B2 structure and an irregular structure. It is a graph which shows the relationship between the ratio of an irregular structure, and iron loss Pcv. It is a graph which shows the relationship between the ratio of an irregular structure and the hysteresis loss Ph. It is a graph which shows the relationship between the coercive force Hc and iron loss Pcv.

(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. The method for manufacturing the dust core will be described with reference to the drawings. 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) insulation treatment step, (3) lubricant mixing step, (4) molding step, and (5). It has an annealing process.

(1) Powder heat treatment step (step S01)
The powder heat treatment step is a step of heat-treating the soft magnetic powder. The soft magnetic powder is made of FeSiAl alloy. By heat-treating the FeSiAl alloy powder, the crystal structure of the FeSiAl alloy powder is changed.

Specifically, the crystal structure of the FeSiAl alloy powder before the powder heat treatment has a DO ₃ structure and a B2 structure, which are regular structures, and an irregular structure, which is an irregular structure. Then, by heat-treating the FeSiAl alloy powder, the ratio of the irregular structure to the crystal structure of the FeSiAl alloy powder is reduced to 5.70 wt% or more and 31.74 wt% or less. The ratio of this irregular structure is calculated by X-ray diffraction by the Rietveld analysis method. Specifically, the determination is made based on the lattice constant calculated by X-ray diffraction. When the lattice constant is about 2.8 to 2.9, it is judged as an irregular structure, and when it is about 5.7, it is judged as a B2 structure and a _DO3 structure. In this way, the irregular structure can be detected from the difference in the lattice constant, and the ratio of the irregular structure to the entire crystal structure of the FeSiAl alloy powder can be calculated.

Further, the ratio of the irregular structure can be calculated from the arrangement position of the crystal structure detected by X-ray diffraction. That is, in the irregular structure, Fe atoms, Si atoms, and Al atoms are irregularly arranged in the body-centered cubic lattice structure (also referred to as “bcc structure”). On the other hand, in the DO ₃ structure, only Fe atoms are arranged at the positions of the apex and the center of the cubic unit cell in the bcc structure, and Si atoms and Al atoms are irregularly arranged at other positions. On the other hand, in the B2 structure, only Fe atoms are arranged at the apex of the unit cell, and Fe atoms, Si atoms and Al atoms are irregularly arranged at the body center position and other positions. As described above, from the difference in the crystal structure, each structure of the irregular structure, the B2 structure and the DO3 structure can be detected, and the ratio of the irregular structure to the entire crystal structure of the _FeSiAl alloy powder can be calculated.

In the powder heat treatment step, for example, heating is performed in a vacuum atmosphere, an inert gas atmosphere, a non-oxidizing atmosphere, or an atmospheric atmosphere for 1 to 6 hours. Examples of the inert gas include H ₂ and N ₂ . The heat treatment temperature is preferably 500 ° C. or higher and 700 ° C. or lower. By setting the heat treatment temperature in this range, the ratio of the irregular structure to the crystal structure of the FeSiAl alloy powder can be reduced to 5.70 wt% or more and 31.74 wt% or less, and iron loss can be reduced. ..

The FeSiAl alloy powder is preferably a gas atomized powder. By using the gas atomized powder, the hysteresis loss can be effectively reduced. Further, the coercive force Hc of the FeSiAl alloy powder is preferably 0.43 A / cm or more and 1.81 A / cm or less. When the coercive force is set in this range, the hysteresis loss can be reduced.

(2) Insulation treatment step (step S02)
The insulation treatment step is a step of forming an insulating film on the surface of the FeSiAl alloy powder. As the insulating film, a silane coupling agent, a silicone oligomer, a silicone resin, or the like can be used. The insulation treatment step of the present embodiment includes two steps: (a) a silane coupling agent mixing step and (b) a silicone resin mixing step.

(A) Silane Coupling Agent Mixing Step The silane coupling agent mixing step is a step of mixing the silane coupling agent and coating the surface of the heat-treated FeSiAl alloy powder. As the type of silane coupling agent, aminosilane-based, epoxysilane-based, and isocyanate-based silane coupling agents can be used, and in particular, 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane. , Tris- (3-trimethoxysilylpropyl) isocyanurate is good.

The amount of the silane coupling agent added 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.

(B) Silicone Resin Mixing Step The silicone resin mixing step is a step of adding a predetermined amount of silicone resin to the FeSiAl alloy powder coated with a silane coupling agent and drying it at a predetermined temperature in an air atmosphere. By the silicone resin mixing step, a silicone resin layer is formed on the outside of the coating film made of the silane coupling agent.

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 type, methylphenyl type, propylphenyl type, epoxy resin modified type, alkyd resin modified type, polyester resin modified type, rubber type 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 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 addition amount is more than 3.0 wt%, the core expands and the density of the molded product decreases, and the magnetic permeability may decrease.

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 formation of the film becomes 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 shape retention is deteriorated, and the density and magnetic permeability of the molded product may decrease. The drying time is about 2 hours.

(3) Lubricant mixing step (step S03)
The lubricant mixing step is a step of adding a lubricant to the insulated FeSiAl alloy powder and mixing the mixture. By going through this step, the surface of the silicone resin layer is coated with the lubricant. As the lubricant, stearic acid and a metal salt thereof, and waxes such as ethylene bisstealamide, ethylene bisstealamide, and ethylene bisstearateamide can be used. By mixing the lubricant, the sliding between the powders can be improved, so that the molding density can be increased. Further, it is possible to reduce the pulling pressure of the upper punch during molding and prevent the generation of vertical streaks on the core wall surface due to the contact between the mold and the powder. The amount of the lubricant added is preferably about 0.1 wt% to 0.6 wt% with respect to the soft magnetic powder.

(4) Molding step (step S04)
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 (step S05)
In the annealing step, the insulating film coated with the soft magnetic powder at 600 ° C. or higher is destroyed in the N ₂ gas or N ₂ + H ₂ gas non-oxidizing atmosphere or in the air with respect to the molded product that has undergone the molding step. The heat treatment is performed at a temperature (for example, 800 ° C.) or lower. 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 to 5. Examples 1-5 and Comparative Example 1-4 were produced under the same conditions except for changing only the powder heat treatment temperature of (1) below.
(1) FeSiAl alloy powder having an average particle diameter of 19.8 μm (median diameter (D50)) was used. This FeSiAl alloy powder was heat-treated without heat treatment and at different heat treatment temperatures of 400 ° C. to 1000 ° C. As the conditions of the heat treatment, the heat treatment was performed for 2 hours in a nitrogen atmosphere.
(2) 1.0 wt% of a silane coupling agent was added to the heat-treated FeSiAl alloy powder, 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 FeSiAl alloy powder to which the silane coupling agent was added, 1.5 wt% of silicone resin (methylphenyl type) 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 (Acrawax (registered trademark)) was added in an amount of 0.5 wt% as a lubricant to the FeSiAl alloy 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 .
(5) Finally, the molded product prepared as described above was annealed in an atmospheric atmosphere at a temperature of 750 ° C. for 2 hours to prepare a dust core.

(Measurement item)
For Examples 1-5 and Comparative Examples 1-4 prepared as described above, the ratio of DO3 structure _, B2 structure and irregular structure to the crystal structure, lattice constant, coercive force Hc and iron loss Pcv (hysteresis loss Ph). And the eddy current loss Pe) was measured. The ratios of DO3 structure, B2 structure and irregular structure to the crystal structure, lattice constant and coercive force were calculated by measuring _FeSiAl alloy powder subjected to powder heat treatment at each temperature of (1) above.

The ratio and lattice constant of DO ₃ structure, B2 structure and irregular structure in the crystal structure are evaluated by X-ray diffraction to evaluate the crystal structure of FeSiAl alloy powder, and the lattice constant, DO ₃ structure, B2 structure and irregular structure are evaluated. The ratio of the structure was calculated. As the X-ray diffractometer, an apparatus manufactured by Bruker (BRUKER D2 PHASER 2nd Gen, X-ray: Cu-Kα ray) was used. The coercive force was measured with an HC meter (K-HC1000 manufactured by Tohoku Steel Co., Ltd.).

On the other hand, the iron loss Pcv is obtained by winding 16 turns of the primary winding and 8 turns of the secondary winding with a copper wire having a diameter of 0.5 mm on the prepared dust core after passing through the steps (1) to (5) above. Was wound and measured using a BH analyzer (Iwadori Measurement Co., Ltd .: SY-8219), which is a magnetic measuring instrument. The measurement conditions were a frequency of 100 kHz and a maximum magnetic flux density of Bm = 100 mT, 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 FIGS. 2 to 5. FIG. 2 is a graph showing the powder heat treatment temperature and the ratio of the DO ₃ structure, the B2 structure and the irregular structure. FIG. 3 is a graph showing the relationship between the ratio of irregular structures and iron loss Pcv. FIG. 4 is a graph showing the relationship between the ratio of irregular structures and the hysteresis loss Ph. FIG. 5 is a graph showing the relationship between the coercive force Hc and the iron loss Pcv.

(Relationship between irregular structure and iron loss)
As shown in Table 1 and FIG. 2, the ratio of the irregular structure to the crystal structure of the powder of Comparative Example 2 subjected to the powder heat treatment at 400 ° C. was the maximum at 40.13 wt%, and the heat treatment temperature was raised from this point to a high temperature. As a result, the proportion of irregular structures is decreasing. Then, when the powder heat treatment is performed at 1000 ° C., as shown in Comparative Example 4, the ratio of the irregular structure becomes 2.03 wt%, and it can be seen that the irregular structure occupies almost no powder.

Conventionally, it has been considered that iron loss Pcv can be reduced by eliminating the irregular structure occupying the crystal structure of the powder and increasing the DO ₃ structure which is a regular structure. Therefore, the powder heat treatment temperature was set to a high temperature of, for example, 900 ° C. or higher to remove the irregular structure occupying the crystal structure of the powder.

However, as shown in Table 1 and FIGS. 3 and 4, the iron loss Pcv tends to decrease as the heat treatment temperature is increased, as compared with 330 (kW / m ³ ) of Comparative Example 1 in which the powder heat treatment is not performed. However, when the powder heat treatment is performed at 850 ° C. or higher (Comparative Examples 3 and 4), the temperature becomes 343 (kW / m ³ ) or higher, and the iron loss increases as compared with Comparative Example 1. On the other hand, the iron loss of Example 1-5 subjected to the powder heat treatment in the range of 500 ° C. to 700 ° C. is smaller than that of Comparative Example 1-4. That is, when the ratio of the irregular structure is 5.70 wt% or more and 31.74 wt% or less, the iron loss Pcv is reduced. This is because, as shown in Table 1 and FIG. 4, in Example 1-5, the hysteresis loss Ph is reduced as compared with Comparative Example 1-4 while the eddy current loss Pe maintains a good value. Due to that.

As described above, as a result of diligent research, the present inventors contradict the conventional idea that iron loss Pcv can be reduced by intentionally leaving an irregular structure in the crystal structure of the powder in the heat treatment process of the powder. I got the knowledge. Then, as described above, when the ratio of the irregular structure is 5.70 wt% or more and 31.74 wt% or less, the iron loss Pcv is reduced as compared with the case where the ratio of the irregular structure is smaller than 5.70 wt%.

This is because the crystal structure of the powder is intentionally left with an irregular structure, which makes it easier for the atoms to move in the crystal during the annealing process for producing the dust core, and the crystal structure is regular. It is presumed that this is because it tends to have a DO ₃ structure. Generally, in the case of producing a dust core, pressure is applied to obtain a molded body, so that the pressure causes distortion in the crystal structure of the powder, resulting in an irregular structure. After that, by annealing the molded body, this strain is removed, and the crystal structure of the powder is returned to the DO ₃ structure, which is a regular structure, in order to reduce the iron loss Pcv.

As in the conventional case, if the ratio of the DO ₃ structure having a regular structure is increased at the stage of the powder heat treatment step, the pressurizing direction is unidirectional, so that strain is likely to occur in one direction along the pressurizing direction. Therefore, when the compact is annealed, the atoms can move only in one direction, cannot move in multiple directions, and it is difficult to arrange them in a regular structure. Therefore, in the crystal structure of the dust core after annealing, it is difficult to obtain a complete DO ₃ structure, and there is a limit to the reduction of iron loss.

On the other hand, as in the present invention, by intentionally leaving the irregular structure in the above numerical range at the time point after the powder heat treatment, strain generated during pressurization is likely to occur in the molded product in multiple directions. In addition, it also retains an irregular structure, allowing atoms to move in multiple directions. Therefore, when the compact is annealed in the annealing step, the atoms move in multiple directions and tend to be arranged in a regular structure. That is, the dust core produced through the annealing step tends to have a DO ₃ structure, which is a regular structure. Therefore, it is presumed that the hysteresis loss and eventually the iron loss can be reduced.

(Relationship between irregular structure and coercive force)
As shown in Table 1 and FIG. 5, the coercive force Hc decreases when the heat treatment temperature of the powder is increased. Conventionally, it has been considered that the hysteresis loss Ph is reduced by reducing the proportion of irregular structures in the powder and reducing the coercive force Hc.

Certainly, the iron loss tends to decrease from 3.89 in Comparative Example 1 to 0.53 (A / cm) in Example 4, which has the highest value of coercive force Hc. However, when the coercive force Hc reaches 0.43 (A / cm), the iron loss Pcv tends to increase, and rather, the coercive force Hc of Comparative Examples 3 and 4 having a low coercive force Hc has the highest coercive force. The iron loss is increased as compared with the high comparative example 1.

From this, it can be seen that there is a limit to reducing the iron loss Pcv only by reducing the coercive force Hc. In this embodiment, it is shown that the iron loss Pcv can be particularly reduced by setting the coercive force Hc to 0.43 (A / cm) or more and 1.81 (A / cm) or less. ..

(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 insulation treatment step includes (a) a silane coupling agent mixing step, and (a) the silane coupling agent is mixed in the silane coupling agent mixing step, but the present invention is not limited thereto. For example, a silicone oligomer may be mixed instead of the silane coupling agent. Examples of the silicone oligomer include methyl and methylphenyl groups 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. Mercaptomethyl-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.

Claims (1)

A powder heat treatment process in which a soft magnetic powder composed of FeSiAl alloy powder , which is a gas atomized powder, is heat-treated at 500 ° C. or higher and 700 ° C. or lower, and a powder heat treatment step .
A molding step of forming a molded product by pressure molding the soft magnetic powder that has undergone the powder heat treatment step,
An annealing step of annealing the molded product in the atmosphere at 600 ° C. or higher and 800 ° C. or lower.
Including
The crystal structure of the FeSiAl alloy powder that has undergone the powder heat treatment step includes an irregular structure in which the crystal structure becomes an irregular structure.
The ratio of the irregular structure to the crystal structure is 5.70 wt% or more and 31.74 wt% or less.
A method for manufacturing a dust core .

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