JP2011222897A - Dust core, magnetic powder for dust core, and method for producing dust core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dust core obtained by pressure-molding metal powder, the dust core having high flux density and small loss, especially, small eddy current loss, and to provide magnetic powder for such a dust core and a method for producing the dust core.SOLUTION: The dust core is characterized in that Si particles (4) of equal to or less than 1.0 μm in mean particle size each having a surface oxide coating (8) so as to part particles of metal powder (3) consisting principally of Fe from each other are interposed. The magnetic powder for the dust core is coated with the Si particles of equal to or less than 1.0 μm in mean particle size having surface oxide coatings with a binder after adhesion. Further, the method of manufacturing such a dust core includes a preparation step of preparing composite powder comprising particles of the metal powder coated with the Si particles of equal to or less than 1.0 μm in mean particle size with the binder after the adhesion, a step of obtaining a pressure-molded body by pressure molding, and a heat treatment step of carrying out a hardening heat treatment on the pressure-molded body.

Description

  The present invention relates to a powder magnetic core, a magnetic powder for a powder magnetic core, and a method for producing a powder magnetic core, and more particularly, a powder magnetic core obtained by pressure-molding a metal powder containing iron as a main component, The present invention relates to a magnetic powder for a dust core and a method for producing a dust core.

  There is a dust core in which a binder is mixed with metal magnetic powder such as iron (Fe) and compression-molded. In order to reduce the iron loss that is an electric energy loss of the dust core, the coercive force is reduced to reduce the hysteresis loss, and the electrical resistance is increased to reduce the eddy current loss. The hysteresis loss is caused by plastic strain or residual stress applied to the metal magnetic powder during molding (compression molding), and can be reduced by performing heat treatment to remove these. On the other hand, the eddy current loss is due to the eddy current inside the magnetic core, and can be reduced by increasing the electric resistance of the magnetic core so as to suppress this.

  In particular, in order to reduce eddy current loss, an insulating surface layer is provided by diffusing silicon (Si) on the surface of the metallic magnetic powder made of Fe, and the electric resistance is increased by insulating the metallic magnetic powder grains. Powder magnetic core is known. For example, in Patent Document 1, a raw material metal magnetic powder provided with a predetermined amount of Si powder having an average particle diameter of 1 to 45 μm so as to cover the surface of a metal magnetic powder made of iron having an average particle diameter of 10 to 150 μm Is disclosed. When this raw metal magnetic powder is compressed into a predetermined shape and then sintered, Si diffuses inward from the surface of the metal magnetic powder made of Fe, and a concentrated layer of Si is formed on the surface of the metal magnetic powder. it can. Thereby, the metal magnetic powder particles are insulated from each other to increase the electric resistance of the dust core.

Further, the metal magnetic powder is made by utilizing a siliconizing treatment in which a silicon tetrachloride (SiCl ₄ ) gas or the like is reacted in a vapor phase with the metal magnetic powder made of Fe to form a Si concentrated layer on the surface of the metal magnetic powder. Also known is a dust core in which grains are insulated to increase electrical resistance. For example, in Patent Document 2, a metal magnetic powder having an average particle diameter of 1 to 500 μm is heated in a non-oxidizing atmosphere, and SiC is concentrated on the surface of the metal magnetic powder by introducing SiCl ₄ gas thereto. It is disclosed that the layer can be coated. A powder with a large specific surface area compared to a steel plate has high reactivity, and it is difficult to form a concentrated Si layer only on the surface layer, but it is said that this method can stably form this. Yes.

Incidentally, in the siliconizing treatment using the SiCl ₄ gas, the magnetic metal powder is corroded by chlorine contained in the SiCl ₄ gas, sometimes deteriorates the performance of the dust core. Also, handling of SiCl ₄ gas is difficult. Therefore, in Patent Document 3, Si powder or ferrosilicon powder is added to and mixed with Fe magnetic metal powder obtained by pulverization after pre-heat treatment without using SiCl ₄ gas, and heat treatment is performed in a hydrogen atmosphere. The method of doing is disclosed. When the heat-treated powder is further pulverized, a surface high Si layer-coated metal magnetic powder is obtained. In this regard, it is stated that by performing heat treatment at a predetermined temperature in a hydrogen atmosphere, a concentrated Si layer can be formed on the surface of the metal magnetic powder efficiently in a short time.

  Furthermore, Patent Document 2 also describes a dust core in which an insulating material such as a silicone resin or a phosphate is provided so as to cover the metal magnetic powder to increase the electric resistance. Together with the Si enriched layer on the surface of the metal magnetic powder, the metal magnetic powder particles can be insulated from each other to further increase the electric resistance.

JP-A-2005-060830 JP 2007-231330 A JP 2007-126696 A

  In the dust core, in order to increase the magnetic flux density, it is necessary to increase the molding density by compression molding. On the other hand, for example, as disclosed in Patent Document 1, the Si powder particles provided so as to cover the surface of the metal magnetic powder are easily detached, and the Si powder particles are dissipated by deformation caused by compression molding. In practice, it is difficult to form a coating layer of Si that can completely insulate each other. Also in Patent Documents 2 and 3, it is difficult to increase the electric resistance of the magnetic core by satisfactorily insulating the metal magnetic powder grains by destroying the concentrated Si layer formed by deformation caused by compression molding.

  The present invention has been made in view of such circumstances, and the object of the present invention is in a powder magnetic core obtained by pressure-molding a metal powder containing Fe as a main component, while the magnetic flux density is high, It is to provide a powder magnetic core having a small loss, particularly eddy current loss, and to provide a magnetic powder for such a powder magnetic core and a method for producing the powder magnetic core.

  The dust core according to the present invention is a dust core obtained by pressure-molding a metal powder mainly composed of Fe, and has an average particle diameter having a surface oxide film so as to separate the particles of the metal powder. Si particles of 1.0 μm or less are interposed.

  According to this invention, even if the Si particles are added in a smaller amount, the metal powder particles containing Fe as a main component are separated from each other, and the silicon particles, which are stable insulators, are used as the surface oxide film. Therefore, the metal magnetic powder particles are well insulated from each other. That is, the eddy current loss can be suppressed by increasing the electrical resistance of the magnetic core. In addition, since the metal powder particles can be brought close to each other with an average particle size of 1.0 μm or less between the particles, the molding density in compression molding can be increased, so that a high magnetic flux density can be achieved as a magnetic core.

  In the above-described invention, a glassy film containing a siloxane bond may be provided so as to separate the particles of the metal powder. According to this invention, the particles of the metal powder mainly composed of Fe are reliably separated from each other by the vitreous film which is an insulator having high affinity with Si particles having silicon dioxide as an insulator as a surface oxide film. Insulate the magnetic powder grains better. That is, the electric resistance of the magnetic core can be further increased to further suppress eddy current loss.

  In the above-described invention, the metal powder may be made of pure Fe. According to this invention, the metal powder particles are plastically deformed with pure Fe having a large plastic deformability, and then compression molding is performed to an interval between particles having an average particle size of 1.0 μm or less to increase the molding density. The magnetic core obtained can be given a high magnetic flux density. Further, the plastically deformed metal powder particles are reliably separated by Si particles, and the metal magnetic powder particles are well insulated by Si particles having silicon dioxide as an insulating oxide film as a surface oxide film. That is, the electric resistance of the magnetic core can be further increased to further suppress eddy current loss.

  In the above-described invention, the metal powder may be made of an Fe—Si alloy. According to this invention, the high magnetic permeability of the Fe—Si alloy can be imparted to the dust core. Further, the plastically deformed metal powder particles can be well insulated by Si particles having silicon dioxide as an insulator as a surface oxide film. That is, the electric resistance of the magnetic core can be further increased to further suppress eddy current loss.

  The magnetic powder for a dust core according to the present invention is a magnetic powder for a dust core made of a metal powder containing Fe as a main component, and Si particles having a surface oxide film and having an average particle diameter of 1.0 μm or less are described above. It is characterized by being adhered to the particle surface of the metal powder and coated with a binder.

  According to this invention, Si particles having silicon dioxide, which is a stable insulator, as a surface oxide film, can be applied without collapsing the state in which the Si particles are firmly and uniformly adhered to the surface of the metal powder mainly composed of Fe. The metal powder can be plastically deformed by pressure forming to obtain a dust core. That is, in the dust core, even if the Si particles are added in a smaller amount, the metal powder particles are surely separated from each other by the Si particles, and the silicon particles, which are stable insulators, are surfaced. Since it is provided as an oxide film, it is possible to increase electrical resistance and suppress eddy current loss. In addition, since the metal powder particles are compression-molded to an interval between particles having an average particle size of 1.0 μm or less to increase the molding density, a high magnetic flux density can be given to the obtained magnetic core.

  In the above-described invention, the metal powder may be made of pure Fe. According to this invention, the metal powder particles are plastically deformed with pure Fe having a large plastic deformability, and then compression molding is performed to an interval between particles having an average particle size of 1.0 μm or less to increase the molding density. Therefore, a dust core with a high magnetic flux density can be provided. In addition, the plastically deformed metal powder particles can be reliably separated from each other by Si particles having silicon dioxide as an insulator as a surface oxide film, and the metal magnetic powder particles can be better insulated. That is, it is possible to provide a dust core in which the electrical resistance of the magnetic core is further increased and eddy current loss is further suppressed.

  In the above-described invention, the metal powder may be made of an Fe—Si alloy. According to this invention, the high magnetic permeability of the Fe—Si alloy can be imparted to the dust core. Further, even if the metal powder particles containing Si are difficult to be plastically deformed, the Si particles favorably bind the metal powder particles and facilitate the forming process. Can be compression-molded and well insulated. That is, the electric resistance of the magnetic core can be further increased to further suppress eddy current loss.

  In the above-described invention, the binder may be made of an alkoxy oligomer. According to this invention, in addition to separating the particles of the metal powder mainly composed of Fe from the Si particles having silicon dioxide as the surface oxide film as the surface oxide film, the Si particles include the siloxane bond derived from the alkoxy oligomer. Even with a glassy film having a high affinity, the metal powder particles can be separated from each other to provide a dust core with improved insulation. In other words, it is possible to provide a dust core with higher electrical resistance and further reduced eddy current loss.

  The method for producing a dust core according to the present invention is a method for producing a dust core obtained by press-molding a metal powder containing Fe as a main component, and Si particles having an average particle size of 1.0 μm or less are adhered. A preparation step of preparing a composite powder composed of metal powder particles coated with a binder, a step of obtaining a pressure-formed body by pressure molding, and a heat treatment step of curing and heat-treating the pressure-formed body. , Including.

  According to this invention, without destroying the state in which Si particles having silicon dioxide as a stable insulator as a surface oxide film are firmly and uniformly adhered to the surface of metal powder particles mainly composed of Fe. The metal powder particles can be plastically deformed by pressure forming to obtain a dust core. That is, in the obtained powder magnetic core, even if there is a smaller amount of Si particles, the metal powder particles are reliably separated by the Si particles, and the silicon particles are stable insulators. Is provided as a surface oxide film, the electrical resistance can be increased and eddy current loss can be suppressed. In addition, since the metal powder particles are compression-molded to an interval between particles having an average particle size of 1.0 μm or less to increase the molding density, a high magnetic flux density can be given to the obtained magnetic core.

  In the above-described invention, following the preparation step, a provisional drying step of drying at least a part of the composite powder may be included. According to this invention, the powder magnetic core can be pressure-molded without greatly moving or desorbing the Si particles adhered to the particle surface of the metal powder. They can be separated more reliably, and eddy current loss can be further suppressed. Moreover, the surface of Si particle | grains can be further oxidized with the water | moisture content etc. which are contained in composite powder, and an oxide film can be thickened.

  In the above-described invention, the binder may be made of an alkoxy oligomer. According to this invention, in addition to separating the particles of the metal powder mainly composed of Fe by the Si particles having silicon dioxide as an insulator as the surface oxide film, the Si particles containing an alkoxy oligomer-derived siloxane bond and Even with a glassy film having a high affinity, the particles of the metal powder are separated from each other to improve insulation. That is, the electric resistance of the magnetic core can be further increased to further suppress eddy current loss.

  In the above-described invention, the temporary drying step may be performed in a temperature range in which condensation dehydration of the alkoxy oligomer occurs. According to this invention, the surface oxide film made of silicon dioxide on the surface of the Si particles can be provided thicker due to moisture generated by condensation dehydration of the alkoxy oligomer. That is, the metal magnetic powder particles can be more reliably insulated from each other, the electric resistance of the magnetic core can be further increased, and eddy current loss can be further suppressed.

It is a perspective view which shows the powder magnetic core by this invention. It is an expanded sectional view which shows the powder magnetic core by this invention. It is process drawing which shows the manufacturing method of the powder magnetic core by this invention. It is sectional drawing which shows the adhesion state of the particle | grains of metal powder and Si particle | grains. It is a scanning electron micrograph of the magnetic powder for dust cores according to the present invention. It is sectional drawing which shows the magnetic powder for dust cores by this invention. It is a scanning electron micrograph of the cross section of the magnetic powder for dust cores by this invention. It is a list figure of the manufacturing conditions in an Example and a comparative example. It is a list of the magnetic characteristics in an Example and a comparative example.

  A dust core according to one embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, a powder magnetic core 1 obtained by pressure-molding metal powder is an annular core around which a primary winding 11 and a secondary winding 12 are wound. Such a dust core 1 can be used, for example, for a core of a transformer of a switching power supply mounted on an OA device or a vehicle, a magnetic core of a DC / DC motor, or the like. In addition, the shape of the powder magnetic core 1 can be changed as appropriate according to the application.

  As shown in the enlarged sectional view of the dust core 1 in FIG. 2, the dust core 1 is made of a metal powder 3 containing Fe as a main component. The metal powder 3 is preferably a material having a high magnetic permeability, and is selected from materials having a high plastic deformability in order to increase the molding density and increase the magnetic flux density as the magnetic core.

  As one example, the metal powder 3 is made of an Fe—Si alloy having a high magnetic permeability. As another example, the metal powder 3 is made of pure Fe having a lower magnetic permeability than that of the Fe—Si alloy but having a higher plastic deformability. As will be described later, the latter is more excellent for uniformly adhering the Si particles 4 to the surface of the metal powder 3 by van der Waals force (see FIGS. 4 to 7).

Adjacent particles of the metal powder 3 mainly composed of Fe are plastically deformed, but the Si particles 4 having a hard average particle diameter of 1.0 μm or less whose surface is covered with an oxide film 8 are so-called “spacers”. They are spaced apart without touching each other. Silicon dioxide (SiO ₂ ) is a stable insulator, and the plastically deformed metal powder particles are electrically independent. In this Si particle 4, a nano-order particle having an average particle size of 1.0 μm or less has a larger surface area ratio per mass than a normal particle, such as oxygen or water in the air. It is easily oxidized and its surface is easily covered with the oxide film 8.

  Since the particles of the metal powder 3 that is a magnetic material are electrically isolated and completely insulated with the Si particles 4 as an insulator in between, the electrical resistance of the dust core 1 can be increased, Eddy current loss can be suppressed. Moreover, since the particles of the metal powder 3 are compression-molded to an interval sandwiching particles having an average particle diameter of 1.0 μm or less using the Si particles 4 as spacers, as will be described in detail later, The molding density can be greatly increased. That is, a high magnetic flux density can be achieved.

  In addition, in the dust core 1, a glassy film 7 containing a siloxane bond and having a high affinity with the Si particles 4 is used to complement the particles of the metal powder 3 so as to complement the function of the Si particles 4 as a spacer. Given to be separated. The glassy film 7 is an insulator that is stable up to a high temperature, and the glassy film also provides insulation between the particles of the metal powder 3. In addition, as will be described later, the binder that forms the vitreous film 7 gives a lubricating action between the particles of the metal powder 3 in the process of pressure molding, and increases the plastic deformability between the particles of the metal powder 3, and It is possible to more reliably prevent the Si particles 4 adhered to the surface of the metal powder 3 from being detached, and to further increase the above-described insulation between the particles of the metal powder 3 that is a magnetic substance. That is, the electrical resistance of the dust core 1 is increased more reliably and eddy current loss is further reduced. Details of the glassy film 7 will be described later.

  Next, a method for manufacturing the above-described powder magnetic core 1 will be described with reference to FIGS. 4 to 7 and FIG.

  Prior to manufacturing the dust core 1, raw materials are prepared. For example, the metal powder 3 is prepared using a gas spray device, a water spray device, a centrifugal spray device, or the like. In the case of using a gas spraying device, it can be manufactured by a known powder manufacturing method in which a high-pressure gas is sprayed at high speed onto molten metal ejected from a nozzle after a metal material of a predetermined component is melted and solidified into fine particles in a space. Further, for example, Si particles 4 are prepared using a bead mill device, a ball mill device, an attritor mill device, or the like. Since the Si particles 4 are very fine particles having an average particle size of 1 μm or less as will be described later, the ratio of the surface area to the mass is large, and they are easily oxidized and ignited by oxygen or water in the atmosphere. In the above-mentioned apparatus, particles are obtained in an inert atmosphere, in a vacuum, or in a solvent. When taking out such particles from the atmosphere or solvent, the particles are gradually transferred to a state where the oxygen partial pressure is high, and the surface is made of thin silicon dioxide. An oxide film 8 was formed to obtain stable Si particles 4 even in the atmosphere.

  Subsequently, in the Si particle adhesion step (S1), the Si particles 4 having an average particle size of 1.0 μm or less are dispersed in a dispersion solvent such as acetone so as not to aggregate, and then mixed with the metal powder 3. Thereafter, the Si particles 4 are adhered to the surface of the metal powder 3 by drying. FIG. 4 schematically shows this. The Si particles 4 can be firmly and uniformly adhered to the surface of the metal powder 3 by van der Waals force acting between the fine Si particles 4 having an average particle size of 1.0 μm or less and the metal powder 3 particles. . Note that, when the metal powder 3 is pure Fe, the Si particles 4 tend to adhere to the surface of the metal powder 3 more easily than when the metal powder 3 is an Fe—Si alloy. Further, the adhesion tends to become stronger as the average particle size of the Si particles 4 becomes smaller.

  Subsequently, in the coating step (S2), first, a binder described later is dissolved in a solvent, and the powder 2 obtained by adhering the Si particles 4 to the surface of the metal powder 3 is added and mixed, and then dried. Thus, the magnetic powder 5 for dust core is obtained. The magnetic powder 5 for a dust core can be obtained by previously mixing the Si particles 4 with a binder and mixing it with the metal powder 3.

  As shown in FIGS. 5 to 7, in the magnetic powder 5 for a dust core, the Si particles 4 on which the film 8 is formed adhere to the metal powder 3 and are embedded in the binder film 9 that covers the metal powder 3. It has entered.

  By the way, the binder improves its workability without collapsing the powder 2 obtained by adhering the Si particles 4 to the surface of the metal powder 3 in the pressure forming step (S4) described later, It is provided to fix the magnetic powder 5 for the powder magnetic core in the shape of the powder magnetic core 1. Further, in a heat treatment step (S5) described later, a glassy film 7 is formed on the surface of the metal powder 3 particles, and the particles of the metal powder 3 are bonded to each other so that the Si particles 4 are fixed to the surface of the metal powder 3. Thus, it may be given for the purpose of complementing the function of the Si particles 4 as a spacer. One example of such a binder is an alkoxysilyl group which is a silicon binder having a high affinity with Si particles 4 and provides a glassy film containing a siloxane bond having a high insulating property after the heat treatment step (S4). Is a binder composed of an alkoxy oligomer.

  Next, in the temporary drying step (S3), the magnetic powder 5 for dust core is heated and included so as to be processed into the desired shape of the dust core 1 in the pressure forming step (S4) described later. Moisture generated by condensation and dehydration of alkoxy oligomers is volatilized and removed. In the composite powder after temporary drying obtained in this way, even if the metal powder 3 is plastically deformed in the pressure forming step (S4) described later, the Si particles 4 are largely moved from the surface of the metal powder 3 and removed. The dust core 1 can be formed without being separated.

  In the temporary drying step (S3), moisture generated by drying the binder and a solvent contained in the composite powder further oxidize the surface of the Si particles 4. That is, the Si particles 4 having a thin oxide film are first adhered to the particles of the metal powder 3 by van der Waals force and then further oxidized to form a thick oxide film 8 on the surface of the Si particles 4. . Thereby, in the powder magnetic core 1 finally obtained, the insulation of the particles of the metal powder 3 can be made more reliable.

  Subsequently, in the pressure molding step (S4), the composite powder of the magnetic powder 5 for dust core is pressure molded to obtain a pressure molded body. Using a known press machine, the desired shape of the dust core 1 is formed. The metal powder 3 is plastically deformed by being given a lubricating action by a binder, and is compression-molded to an interval between which the Si particles 4 are sandwiched. Therefore, the molding density of the pressure molded body can be increased. That is, the magnetic flux density of the obtained magnetic core can be made higher. Due to the lubricating action by the binder and the adhesion action of the Si particles 4, the Si particles 4 are not easily detached from the metal powder 3, and the particles of the metal powder 3 can be more reliably insulated from each other in the finally obtained dust core 1. it can.

  Subsequently, in the heat treatment step (S5), the pressure-molded body is heat-treated and the binder is cured to obtain the dust core 1. By increasing the molding density in the pressure molding step (S4), the binder completely covers the metal powder 3. If the binder is made of an alkoxy oligomer containing an alkoxysilyl group as described above, a glassy film 7 having high insulating properties is provided between the particles of the metal powder 3 by this heat treatment. The particles of the powder 3 are insulated more reliably.

  Thus, the dust core 1 is obtained. In the dust core 1, as described above, eddy current loss can be suppressed and a high magnetic flux density can be achieved.

[Evaluation test]
Next, the dust core 1 was manufactured by the above-described manufacturing method under a plurality of manufacturing conditions shown in FIG. 8, and the magnetic characteristics were evaluated. The results are shown in FIG. Some details of the manufacturing method are as follows.

  As shown in FIG. 1, the dust core 1 used for the evaluation is a ring-shaped core having an outer diameter of 28 mm, an inner diameter of 20 mm, and a height of 5 mm.

  The metal powder 3 is an Fe powder having an average particle diameter (D50) = 51 μm (actual measurement value) unless otherwise specified (Examples 10 to 12 and Comparative Example 3). Further, the Si particles 4 are powders having an average particle diameter (D50) = 0.2 μm unless otherwise specified (Examples 12 to 15, Comparative Examples 2 and 3). That is, the particle size ratio between the metal powder 3 and the Si particles 4 calculated from the measured value is 0.004, which will be described later. The Si particles 4 are wet pulverized in a dispersion solvent using a bead mill apparatus, then the dispersion solvent is removed in a vacuum dryer, and then gradually transferred to a state where the oxygen partial pressure is high, and the surface is made of silicon dioxide. It is obtained by stabilizing while forming the oxide film 8.

  In the Si particle adhesion step (S1) and the coating step (S2), a binder made of an alkoxy oligomer was dissolved in an acetone solvent, and the metal powder 3 and the Si particles 4 were mixed at a predetermined Si ratio (see FIG. 8). . When this is stirred and dried, the magnetic powder 5 for a dust core is obtained. The ratio of the binder mass to the total mass of the metal powder 3 and Si particles 4 (binder ratio) was 1% unless otherwise specified (Example 9).

  In the temporary drying step (S3), unless otherwise specified (Example 6), the magnetic powder 5 for dust core is heated in a reduced pressure atmosphere at a temperature of 200 ° C. for 10 minutes at which the alkoxy oligomer of the binder undergoes condensation dehydration. did.

In the pressure molding step (S4), the magnetic powder 5 for dust core after temporary drying is filled in a mold for molding a shape as shown in FIG. 1, and 15 ton / cm ² is given at 100 ° C., Press-press molding was performed.

  In the heat treatment step (S5), in order to change the alkoxysilyl group of the binder into a vitreous having a siloxane bond, the pressure-molded body was placed in a nitrogen atmosphere at 550 ° C., 0 unless otherwise specified (Examples 7 and 8). Heated for 5 hours.

  An 80-turn primary winding 11 and a 20-turn secondary winding 12 made of enameled wire were wound around the dust core 1 obtained as described above. In the evaluation, an alternating current BH measuring device was used to measure a magnetic flux density (B10k) at an applied magnetic field of 10 kA / m by applying a sinusoidal alternating magnetic field having an excitation magnetic flux density of 0.2 T and a frequency of 10 kHz. The result shown in was obtained.

First, in Comparative Example 1, since Si particles 4 are not added, the ratio of Fe having high plastic deformability in the powder magnetic core 1 is high, and the density by pressure molding can be made relatively high. That is, a density of 7.29 (g / cm ³ ) and a magnetic flux density of 1.55 (T) could be obtained. On the other hand, the specific resistance was 2.2 × 10 ² (μΩ · m), and the core loss (loss) was 4086 kW / m ³ . It is considered that the Si particles 4 do not act as the spacer described above, and only the insulation between the particles of the metal powder 3 by the vitreous film 7 can be given.

On the other hand, as in Examples 1 to 4, the ratio of the mass of the Si particles 4 to the total mass of the metal powder 3 and the Si particles 4 (Si ratio) is in the range of 0.1 to 2.0%. In addition, when Si particles 4 are added, the density by pressure molding becomes lower than that of Comparative Example 1. That is, the density was 6.90 to 7.17 (g / cm ³ ), but the magnetic flux density was 1.45 to 1.48 (T), which was not inferior to Comparative Example 1. . On the other hand, since the Si particles 4 provide insulation between the particles of the metal powder 3 together with the vitreous film 7, the specific resistance is 6.0 × 10 ^{5 to} 2.8 × 10 ⁶ (μΩ · m). Compared to Example 1, it was very high. That is, the core loss can be suppressed to 698 to 990 kW / m ^3, which is much smaller than that of Comparative Example 1.

Further, as in Example 5, when the Si ratio is increased to about 3.0% and the Si particles 4 are added, the density by pressure molding is lowered. That is, the density was 6.61 (g / cm ³ ), and the magnetic flux density was 1.17 (T). Further, although the specific resistance was 8.8 × 10 ⁵ (μΩ · m), the core loss was 1030 kW / m ³ , which is higher than those in Examples 3 and 4 having a low Si ratio.

  From the above, there is a preferable range in which both the magnetic flux density and the core loss due to the Si ratio can be improved at the same time under the manufacturing conditions of the above-described pressure forming step (S4). This is about 0.1 to 3.0% by mass.

By the way, when the average particle diameter (D50) of the Si particles 4 is increased to 1.2 μm as in Comparative Example 2, the density is 7.10 (g / cm ³ ) and the magnetic flux density is 1.45 (T). It was. On the other hand, the specific resistance was as low as 4.5 × 10 ² (μΩ · m), and the core loss was 2831 kW / m ³ , which was higher than that in Example 3. That is, in the Si particles 4 having a large average particle diameter, the van der Waals force acting between the particles of the metal powder 3 is weak and it is difficult for the particles of the metal powder 3 to adhere to the surface. As a result, it is considered that the Si particles 4 are moved in the pressure forming step (S4), and the contact between the particles of the metal powder 3 is increased.

In Example 6, the temporary drying step (S3) is omitted from Example 3. However, the density was 7.00 (g / cm ³ ), and the magnetic flux density was 1.44 (T), almost unchanged from Example 3. On the other hand, the specific resistance was 9.8 × 10 ⁵ (μΩ · m), which was slightly higher than Example 3, and the core loss was slightly higher at 1121 kW / m ³ . As described above, it is considered that the binder did not provide a plastic deformation lubrication action of the metal powder 3 and the Si particles 4 did not function as a spacer between the metal powder 3 particles. That is, in order to increase the magnetic flux density and further suppress the core loss, it is preferable to perform the temporary drying step (S3).

Furthermore, in Examples 7 and 8, the temperature of the heat treatment step (S5) was increased to 700 and 850 ° C. compared to Example 3. Then, the densities of 7.10 and 7.15 (g / cm ³ ) and the magnetic flux densities of 1.45 and 1.46 (T) were almost the same as in Example 3. On the other hand, the specific resistance tends to be 5.9 × 10 ⁴ and 5.0 × 10 ⁴ (μΩ · m), which is smaller than that of Example 3, but the core loss tends to be low, 655 and 607 kW / m ^3. It was. This is because, due to the high heat treatment temperature, the crystal grains of the metal powder 3 are coarsened to reduce the hysteresis loss, and a stronger glassy film is formed so as to separate the particles of the metal powder 3, thereby obtaining high insulation. Think. That is, it is preferable to raise the temperature of the heat treatment step (S5) to a predetermined temperature, and as a result of further examination of details, it is preferably in the range of 500 to 1150 ° C, more preferably in the range of 700 to 850 ° C.

Furthermore, in Example 9, compared with Example 3, the binder ratio was lowered to 0.1%. In this case, the density was 7.03 (g / cm ³ ) and the magnetic flux density was 1.44 (T), and there was almost no change from Example 3. On the other hand, the specific resistance was 9.2 × 10 ⁵ (μΩ · m) and the core loss was 856 kW / m ^3, which was higher than that of Example 3. There was no significant increase in core loss.

Furthermore, in Example 10, compared with Example 3, the average particle diameter (D50) of Fe of the metal powder 3 was increased to 102 μm. That is, the particle size ratio between the metal powder 3 and the Si particles 4 (average particle size of Si / average particle size of Fe) was set to 0.002 and smaller than 0.004. Also in this case, a density of 7.52 (g / cm ³ ) and a magnetic flux density of 1.58 (T), which were higher than those of Example 3, were obtained. The specific resistance is 9.5 × 10 ⁵ (μΩ · m), the core loss is 833 kW / m ³ , and the core loss is slightly larger than that of the third embodiment.

Furthermore, in Example 11, compared with Example 3, the average particle diameter (D50) of Fe of the metal powder 3 was reduced to 1.2 μm. That is, the particle size ratio between the metal powder 3 and the Si particles 4 was 0.167, which was larger than 0.004. In this case, the density was 6.49 (g / cm ³ ) and the magnetic flux density 1.12 (T), and the magnetic flux density was lower than that in Example 3. The specific resistance is 8.9 × 10 ⁵ (μΩ · m), the core loss is 948 kW / m ³ , and the core loss is slightly larger than that of the third embodiment.

Furthermore, in Example 12, as in Example 11, the average particle diameter (D50) of Fe of the metal powder 3 was reduced to 1.2 μm, and the average particle diameter (D50) of the Si particles 4 was 0.3 μm. Increased. That is, the particle size ratio between the metal powder 3 and the Si particles 4 was 0.250, which was larger than 0.167 in Example 11. In this case, the density was 6.56 (g / cm ³ ) and the magnetic flux density was 1.10 (T), and almost no change from Example 11. On the other hand, the specific resistance was 2.6 × 10 ³ (μΩ · m), and the core loss was 2256 kW / m ^3, which was larger than those in Examples 3 and 11.

Furthermore, in Comparative Example 3, the average particle diameter (D50) of the Si particles 4 is reduced to 6.8 μm and the average particle diameter (D50) of the Si particles 4 is smaller than that of Example 3 in the nano order. The size was further increased to 1.8 μm. That is, the particle size ratio between the metal powder 3 and the Si particles 4 was 0.265, slightly larger than that of Example 12. In this case, a density of 6.76 (g / cm ³ ) and a magnetic flux density of 1.28 (T), which were higher than those of Examples 11 and 12, were obtained. On the other hand, the specific resistance is 3.4 × 10 ² (μΩ · m), and the core loss is 3012 kW / m ³ , which is abruptly larger than Example 12 as well as Example 3 and Example 11. Oops. In other words, in order to prevent an abrupt increase in core loss, at least the Si particles 4 are made to be nano-order fine particles of 1.0 μm or less, and the particle size difference with respect to this is large so that they can be easily adhered. It is preferable to use a metal powder 3 having a large particle size such that the ratio is 0.25 or less. For example, the average particle diameter (D50) of the metal powder 3 particles is preferably 1 to 300 μm.

By the way, in Example 13 and 14, the alloy which consists of Fe-3Si and Fe-6.5Si whose magnetic permeability is higher than pure Fe was used for the metal powder 3 with respect to Example 3. Then, since the plastic deformability of the metal powder 3 is lowered by solid solution strengthening compared to pure Fe, the density 7.28 and 6.53 (g / cm ³ ) and the magnetic flux densities 1.38 and 1.10 (T) The magnetic flux density tended to be lower than in Example 3. On the other hand, the specific resistance is 1.6 × 10 ⁶ and 7.1 × 10 ⁵ (μΩ · m), which is equal to or higher than that of Example 3, and the core loss is 400 and 350 kW / m ³ which is much higher than that of Example 3. I was able to make it smaller.

On the other hand, in Example 15, an alloy made of Fe-10Si was used for the metal powder 3 as compared to Example 3. That is, the ratio of Si to Fe of the metal powder 3 was increased as compared with Examples 13 and 14. Then, the specific resistance was 3.2 × 10 ⁵ (μΩ · m), and the core loss was 300 kW / m ³ , which was even smaller than in Examples 13 and 14. On the other hand, the magnetic flux density was as small as 0.71 (T) while the density was 6.53 (g / cm ³ ), which was almost the same as in Example 14.

  From the above, it can be seen that increasing the Si ratio of the Fe—Si alloy used for the metal powder 3 increases the magnetic flux density but also tends to increase the core loss. That is, the metal powder 3 may not be pure Fe, but may be an Fe—Si alloy. When the metal powder 3 is an Fe—Si alloy, Si is preferably 10% by mass or less, and 6.5%. More preferably, it is as follows.

  So far, representative embodiments and modifications based on the embodiments have been described. However, the present invention is not necessarily limited thereto, and those skilled in the art will not depart from the scope of the appended claims. Various alternative embodiments and modifications can be found.

DESCRIPTION OF SYMBOLS 1 Powder magnetic core 3 Metal powder 4 Si particle 5 Magnetic powder 7 for powder magnetic core Glassy film 8 Oxide film

Claims (12)

  A powder magnetic core obtained by pressure-molding a metal powder containing Fe as a main component, wherein Si particles having an average particle size of 1.0 μm or less having a surface oxide film so as to separate the particles of the metal powder. A dust core characterized by being interposed.   2. The dust core according to claim 1, further comprising a vitreous film containing a siloxane bond so as to separate the particles of the metal powder.   The dust core according to claim 1, wherein the metal powder is made of pure Fe.   The dust core according to claim 1 or 2, wherein the metal powder is made of an Fe-Si alloy.   A magnetic powder for a powder magnetic core comprising a metal powder containing Fe as a main component, wherein Si particles having a surface oxide film and having an average particle size of 1.0 μm or less are adhered to the particle surface of the metal powder, and a binder is used. A magnetic powder for a dust core, which is coated with the powder.   6. The magnetic powder for a dust core according to claim 5, wherein the metal powder is made of pure Fe.   6. The magnetic powder for a dust core according to claim 5, wherein the metal powder is made of an Fe-Si alloy.   The magnetic powder for a dust core according to claim 5, wherein the binder is made of an alkoxy oligomer. A method for producing a powder magnetic core obtained by pressure molding metal powder containing Fe as a main component,
A preparation step of preparing a composite powder composed of particles of the metal powder in which Si particles having an average particle size of 1.0 μm or less are adhered and coated with a binder;
Obtaining a pressure molded body by pressure molding; and
A heat treatment step of heat-treating the pressure-formed body.   The method for manufacturing a dust core according to claim 9, further comprising a temporary drying step of drying at least a part of the composite powder following the preparation step.   The method for manufacturing a dust core according to claim 10, wherein the binder is made of an alkoxy oligomer.   The method for producing a dust core according to claim 11, wherein the temporary drying step is performed in a temperature range in which condensation dehydration of the alkoxy oligomer occurs.