JP4609339B2 - Powder for powder magnetic core and method for producing powder magnetic core - Google Patents

Description

  The present invention relates to a dust core that can be used as various magnetic cores such as a motor and a reactor, a magnetic core powder suitable for manufacturing the dust core, and a method for manufacturing the same.

  There are many products that use electromagnetism around us, such as transformers, motors, generators, speakers, induction heaters, and various actuators. Many of these products use an alternating magnetic field, and the alternating magnetic field is usually generated by a coil having a magnetic core (soft magnet) disposed in the center. For this reason, the performance of the electromagnetic device depends on the performance of the coil, and the performance of the coil depends on the performance of the magnetic core. Therefore, it is very important to improve the performance of the magnetic core in order to improve the performance and size of the electromagnetic equipment.

  Such a magnetic core is first required to obtain a large magnetic flux density in an alternating magnetic field. Next, when used in an alternating magnetic field, it is required that the high frequency loss (iron loss) generated according to the frequency is small. The high-frequency loss includes eddy current loss, hysteresis loss, and residual loss. The main problems are eddy current loss and hysteresis loss.

  Further, in order to achieve the formability and miniaturization of the magnetic core according to the parts of the electromagnetic equipment, a dust core is being frequently used as the magnetic core instead of the conventional electromagnetic steel sheet. The dust core is obtained by pressure-molding magnetic powder having an insulating coating on the particle surface. By providing an insulating film, the specific resistance value can be increased to reduce eddy current loss, and magnetic properties such as magnetic flux density can be enhanced by increasing the density. Incidentally, the insulating film used for the dust core is disclosed in, for example, Patent Document 1 and Patent Document 2 below. Further, for example, the following Patent Document 3 discloses the formability of the dust core.

  In order to improve the performance of the powder magnetic core, it is certainly important to increase the magnetic flux density by increasing the density and to reduce the eddy current loss by securing the specific resistance value. However, recently, in order to further improve the energy efficiency and the like of the motor, there is a strong demand for reducing the loss due to the dust core. As described above, as a main loss due to the dust core, there is a hysteresis loss in addition to the eddy current loss. Reduction of this hysteresis loss is also very important. In particular, if a dust core is used only in the high frequency range of several tens to several hundreds of kHz, considering the use of the dust core in a frequency range lower than that, the hysteresis loss can be reduced. This is very important in reducing the overall loss of the magnetic core.

  In order to reduce the hysteresis loss, it is effective to reduce the coercive force of the dust core. This coercive force is affected by the strain (residual strain) remaining in the magnetic powder particles, and the coercive force increases when the strain is large. Since the dust core is obtained by pressure-molding magnetic powder, a residual strain is produced in the constituent particles more or less. Therefore, to reduce the hysteresis loss, it is effective to remove the residual strain once generated in the magnetic powder particles. In order to remove the strain, as described in Patent Document 3 below, heat treatment such as annealing is often performed. Although it depends on the composition of the magnetic powder, it is necessary to heat to 450 ° C. or higher, 500 ° C. or higher, and 700 ° C. or higher in order to sufficiently remove distortion with a powder magnetic core mainly composed of Fe.

  When the dust core is heated at high temperature, for example, the insulating coating made of phosphate described in Patent Document 1 and the insulating coating made of thermoplastic material described in Patent Document 2 are crystallized to cause sintering / aggregation or decomposition. It will be destroyed. As a result, even if the hysteresis loss can be reduced, the specific resistance value rapidly decreases and the eddy current loss increases rapidly, so that it is difficult to reduce the iron loss after all.

  Patent Document 3 discloses an example in which an annealing heat treatment at 700 ° C. × 1 hour is performed on a powder magnetic core made of a magnetic powder having a water glass insulating film formed on the surface thereof. When the specific resistance value described there is observed, a corresponding specific resistance value is ensured even after annealing. However, in this case, although the molding is performed at a high pressure of 1666 MPa, since the amount of water glass is large, in other words, because the insulating film is thick, the relative density is considerably low, and as a result, the magnetic flux density is also low. It has become. With this, it is impossible to achieve both improvement in magnetic characteristics and loss reduction of the dust core.

In addition, Patent Document 3 describes that, in the production process (atomization process) of the Fe—Si based magnetic powder, a SiO ₂ film is formed on the surface, which is preferable in increasing the electrical resistivity. . However, SiO ₂ film produced at this time is generated as more coatings 100 to 500 nm. When a powder magnetic core is produced using this magnetic powder, an increase in the relative density cannot be expected, and the magnetic flux density is not improved. In addition, when a relatively thick SiO ₂ film is formed before compacting, since the SiO ₂ film is destroyed when high-pressure molding is performed, the electrical resistivity of the dust core may decrease instead. . In order to recover and maintain the specific resistance of the dust core, heat treatment may be performed by adding silicone resin, etc., but in that case, the relative density and magnetic flux density of the dust core may be further reduced. It becomes. Therefore, it has been required to form an insulating film that is relatively thin and excellent in heat resistance and the like on the surface of the magnetic powder.

Therefore, in Patent Document 4 below, the insulating film formed on the surface of the magnetic powder is made relatively thin and excellent in heat resistance, etc., thereby achieving both high magnetic properties and low loss of the dust core. Obtained powders for dust cores are disclosed. That is, a powder magnetic core obtained by pressure-molding a magnetic core powder comprising a magnetic powder mainly composed of Fe and Si and an insulating coating formed on the particle surface of the magnetic powder, the insulating coating Is obtained by external oxidation treatment of the magnetic powder, and the specific oxygen amount (g / m ² ) indicating the oxygen amount (g) per unit surface area (m ² ) of the magnetic powder is 0.005 to 0.05 g / A powder magnetic core of m ² is disclosed. Since the insulating coating is thin and excellent in heat resistance, a powder magnetic core having a high magnetic flux density and a low hysteresis loss can be obtained by using a magnetic powder coated with the insulating coating.

  Further, in Patent Document 5 below, for the purpose of providing a composite magnetic body having excellent moldability and high heat treatment temperature to remove sufficient strain and providing magnetic properties, particularly core loss, at least a metal magnetic body and An invention is disclosed in which a composite magnetic body having a structure containing at least one oxide of a group A metal is used. Here, the group A metal is a single metal or an alloy containing at least one of Fe, Al, Ti, Sn, Si, Mn, Ta, Zr, Ca, and Zn. Group A metals are highly reducible, deprive oxygen from other oxides or atmospheres themselves and oxidize to become stable Group A metal oxides, insulate the periphery of metal magnetic powder, and reduce eddy current loss. be able to.

JP 2000-504785 gazette JP-A-5-209203 JP 2002-75720 A JP 2005-146315 A JP-A-10-208923

  However, the inventions of Patent Literature 4 and Patent Literature 5 are those in which magnetic powder is subjected to external oxidation treatment to obtain an insulating coating, and require “external oxidation”, that is, “gradual oxidation treatment (stabilization treatment)”. there were. These conventional techniques have the following problems.

(1) Although different metals or different metals and oxides are added to the magnetic metal powder, the metal content may diffuse into the magnetic metal powder, reducing the purity of the magnetic metal powder and deteriorating the purity. Worsens iron loss.

(2) If annealing (vacuum or atmosphere) is performed at a high temperature, the surface decarburization reaction proceeds and the surface SiO ₂ concentration becomes thin, so a slow oxidation treatment (about 850 ° C., H ₂ + N ₂ atmosphere) is added. The SiO ₂ concentration is increased. For this purpose, an “external oxidation”, that is, a “gradual oxidation treatment (stabilization treatment)” step is added to increase the cost.

  The present invention has been made in view of such circumstances, and (1) to obtain a material capable of further reducing hysteresis loss (his loss) and eddy current loss (eddy loss) of a dust core, (2 ) When high-temperature vacuum annealing is performed, sintering between the powders is suppressed, and the powder can be easily crushed (especially effective for powders having a large contact area such as flat powder), and (3) slow oxidation The purpose is to eliminate the need for processing (stabilization processing), simplify the process, and contribute to cost reduction.

  The present inventor adds hysteresis metal loss (His loss) and eddy current loss (eddy current) by adding a mixture of specific metal oxides when vacuum-annealing Fe-Si powder or Fe-Al-Si powder at high temperature. It can be reduced at the same time, and at the same time, it can be easily pulverized by suppressing sintering of powders for powder magnetic cores (especially effective for powders with large contact areas such as flat powders) The present invention has been reached.

That is, first, the present invention relates to a magnetic powder mainly composed of iron (Fe) and silicon (Si), or iron (Fe), aluminum (Al) and silicon (Si), and a particle surface of the magnetic powder. The present invention relates to a powder for a powder magnetic core comprising an insulating coating and / or insulating particles formed on the insulating coating, and the insulating coating and / or insulating particles are SiO ₂ powder, Al ₂ O ₃ powder, CaO powder, MgO powder. , TiO ₂ powder, Fe ₂ O ₃ powder, K ₂ O powder, and Na ₂ O ₃ powder, which is a composite oxide of at least two kinds of metal oxide powders.

In addition, the present invention is formed on the particle surface of magnetic powder having iron (Fe) and silicon (Si) or iron (Fe), aluminum (Al) and silicon (Si) as main components, and the magnetic powder. It is an invention of a powder for a powder magnetic core comprising an insulating coating and / or insulating particles and a binding resin formed on these surfaces, wherein the insulating coating and / or the insulating particles are SiO ₂ powder, Al ₂ O A composite oxide of at least two metal oxide powders selected from the group consisting of ₃ powder, CaO powder, MgO powder, TiO ₂ powder, Fe ₂ O ₃ powder, K ₂ O powder, and Na ₂ O ₃ powder It is characterized by that.

In the powder for a powder magnetic core of the present invention, the metal oxide powder is particularly preferably a combination of SiO ₂ powder and MgO powder.

  In the powder for powder magnetic core of the present invention, as the binding resin, an organic resin such as silicone resin, thermoplastic polyimide, polyphenylene sulfide, or an inorganic binder such as water glass can be used. Among these, a silicone resin is preferably exemplified.

  Secondly, the present invention is a dust core obtained by pressure-molding and heat-treating the above powder for dust core.

3rdly, this invention is invention of the manufacturing method of the powder for powder magnetic cores, and iron (Fe) and silicon (Si), or iron (Fe), aluminum (Al), and silicon (Si) as a main component. At least two kinds selected from the group consisting of SiO ₂ powder, Al ₂ O ₃ powder, CaO powder, MgO powder, TiO ₂ powder, Fe ₂ O ₃ powder, K ₂ O powder, and Na ₂ O ₃ powder The first mixing step of adding and mixing the above metal oxide powder, the powder annealing step of vacuum annealing the mixed powder, and the second mixing of adding and mixing a binding resin to the vacuum annealed mixed powder Process.

In the method for producing a powder for a powder magnetic core of the present invention, a combination of SiO ₂ powder and MgO powder is preferable as the metal oxide powder, and a silicone resin is preferable as the binding resin, as described above.

  4thly, this invention is invention of the manufacturing method of a powder magnetic core, the process of pressure-molding this powder for powder magnetic cores after the manufacturing process of said powder for powder magnetic cores, and this molded object And a heat treatment step.

Magnetic powder containing iron (Fe) and silicon (Si), or iron (Fe), aluminum (Al) and silicon (Si) as main components, SiO ₂ powder, Al ₂ O ₃ powder, CaO powder, MgO powder, Adding and mixing at least two metal oxide powders selected from the group consisting of TiO ₂ powder, Fe ₂ O ₃ powder, K ₂ O powder, and Na ₂ O ₃ powder, and vacuum annealing the mixed powder Thus, an insulating coating and / or insulating particles made of a composite oxide of these metal oxide powders are formed on the surface of the magnetic powder particles. As a result, carbon (C), which is an impurity in the metal magnetic powder, is removed (decarburization: hysteresis loss loss is reduced) and the insulation coating on the surface of the metal magnetic powder is stabilized (inhibition of decrease in the concentration of insulating oxide on the powder surface: eddy current) Loss suppression).

FIG. 1 is a schematic diagram showing a conventional and decarburization process of the present invention. FIG. 1A shows a conventional decarburization process when a metal oxide is coated on a magnetic powder, and a surface of an Fe—Si—C powder containing carbon as an impurity is coated with SiO ₂ powder. During powder vacuum annealing, C in the magnetic powder is
SiO ₂ + 2C = Si + 2CO
C + H ₂ O → CO + H ₂
By this reaction, CO and H ₂ gas are diffused. Some SiO ₂ stays forming a thin film on the surface of the magnetic powder.

FIG. 1B is a decarburization process of the present invention when two or more specific metal oxides (SiO ₂ and MgO) are coated on magnetic powder, and Fe—Si—C powder containing carbon as an impurity. The surface is coated with SiO ₂ and MgO powder.

As a result, not only the existing SiO _{2 on the} surface of the magnetic powder but also an oxide can be added to actively cause a decarburization reaction. Further, SiO ₂ and MgO remain on the surface of the magnetic powder, and the stability of the SiO ₂ film after the addition of the silicone resin as the binder is improved.

  The powder for powder magnetic core of the present invention has a thin and uniform composite metal oxide coating (insulating coating) formed on the surface of an Fe-Si or Fe-Al-Si magnetic powder. It is. First, since this insulating film is thin, it is possible to increase the density of the powder magnetic core, and consequently improve the magnetic properties of the powder magnetic core. In addition, since this insulating film is uniform and excellent in heat resistance, even when heat treatment is performed, it does not break down so much and the specific resistance value of the dust core does not decrease rapidly.

  Accordingly, a powder magnetic core obtained by heat-treating a powder compact that is pressure-molded using the magnetic core powder of the present invention has a low magnetic resistance by suppressing the rapid decrease in specific resistance in addition to high magnetic properties by high density. It is possible to simultaneously secure eddy current loss and reduce hysteresis loss caused by a decrease in coercive force. That is, according to the dust core of the present invention, improvement of magnetic characteristics and reduction of iron loss can be achieved at a very high level.

The “powder vacuum annealing” performed in the present invention is a magnetic powder containing Fe and Si as main components, SiO ₂ powder, Al ₂ O ₃ powder, CaO powder, MgO powder, TiO ₂ powder, Fe ₂ O ₃ powder, K ₂ O powder, and a mixture of at least two or more metal oxide powder selected from _Na 2 _{O 3} powder ^group, 10 ^-2 to 10 -4 Torr, it is preferable to vacuum annealing at 800 to 1000 ° C. . By this “powder vacuum annealing”, a magnetic core powder having an insulating coating formed on the surface of the magnetic powder is obtained.
Details such as the form of the excellent insulating film and the generation mechanism are not clear.

(1) Insulating coating The insulating coating of the present invention formed on the surface of Fe-Si based magnetic powder is a silicon resin coating that is stably generated by metal oxides such as silicon dioxide (SiO ₂ ) and magnesium oxide (MgO). However, at present, the composition and structure have not been elucidated in detail.
Moreover, this insulating film is excellent in heat resistance. When the powder magnetic core made of Fe-Si magnetic powder is heat-treated, even if the temperature is set to 450 ° C. or higher, 500 ° C. or higher, 600 ° C. or higher, or 700 ° C. or higher, it is not completely destroyed.

(2) Magnetic powder As described above, the magnetic powder targeted in the present invention is an Fe-Si-based or Fe-Al-Si-based magnetic powder mainly composed of Fe and Si. Fe-Si-based and Fe-Al-Si-based magnetic powders are frequently used as soft magnetic powders because of their relatively high electrical resistivity and relatively low cost. The amount of Si is determined by the balance with the specific resistance value, magnetic flux density, strength, high frequency characteristics, superposition characteristics, etc. required for the dust core. For example, the Si amount is preferably 1 to 10% by mass. If the amount of Si is too small, the electrical resistivity is small and eddy current loss cannot be reduced. If the amount of Si is too large, the magnetic properties are deteriorated or the formability is lowered, which is not preferable. In the case of the present invention, the Si content is preferably 0.5 to 4.0%, more preferably 1.0 to 3.0%, from the viewpoint of moldability of the magnetic powder during high pressure molding.

  The Fe-Si-based and Fe-Al-Si-based magnetic powder may be an alloy powder composed of a predetermined amount of Si, the remaining Fe, and inevitable impurities, and is not limited to the binary system, but may be aluminum (Al), tin (Sn). ), Nickel (Ni), cobalt (Co) or the like may be included as appropriate.

  The magnetic powder may be atomized powder such as gas atomized or water atomized, or pulverized powder obtained by pulverizing an alloy ingot with a ball mill or the like. However, a pulverized powder having a different shape of each particle than the atomized powder made of spherical particles can provide a high-strength and high-strength powder magnetic core due to the shape effect.

  The particle size of the magnetic powder is preferably 20 to 300 μm, more preferably 50 to 200 μm, from the viewpoint of increasing the density of the dust core. From the viewpoint of reducing eddy current loss, the smaller the particle size, the better, for example, 50 μm or less. On the other hand, from the viewpoint of reducing the hysteresis loss, it is preferable to make the particle diameter coarse, for example, 100 μm or more. The magnetic powder can be easily classified by a sieving method or the like, but the particle size may be considered as an average particle size with a mass accumulation of 50%.

(3) Characteristics of the dust core Since the dust core of the present invention is made of a magnetic powder coated with a thin and heat-resistant insulating film, it has high magnetic characteristics due to high density, eddy current loss and hysteresis loss. It can be excellent on both sides.

(4) Molding of the dust core The dust core of the present invention is obtained, for example, through a filling step of filling the core powder into a molding die and a molding step of pressing the core powder. The magnetic core powder to be filled in the molding die may be a mixed powder obtained by adding a silane coupling agent, another insulating agent, or the like to the magnetic powder with the insulating coating of the present invention. Pressure molding of magnetic core powder (including the above mixed powder) filled in a molding die is a general molding method in which an internal lubricant or the like is mixed in the powder regardless of whether it is cold, warm or hot. May be performed. However, from the viewpoint of improving the magnetic characteristics by increasing the density of the powder magnetic core, it is more preferable to employ the mold lubrication warm pressing method described below. As a result, even if the molding pressure is increased, no galling occurs between the inner surface of the molding die and the magnetic powder, and the release pressure does not become excessive, and a reduction in the mold life can be suppressed. And it becomes possible to mass-produce high-density powder magnetic cores not at the test level but at the industrial level.

  The degree of pressurization in the molding process is appropriately selected according to the specifications of the powder magnetic core, manufacturing equipment, etc., but when using the above mold lubrication warm press molding method, it is under a high pressure that exceeds the conventional molding pressure. Can be molded. For this reason, even if it is hard Fe-Si system magnetic powder, a high-density powder magnetic core can be obtained easily. The molding pressure can be, for example, 700 MPa or more, 785 MPa or more, 1000 MPa or more, 1500 MPa or more, 2000 MPa, or even 2500 MPa. The higher the molding pressure, the higher the density magnetic core. However, 2000 MPa or less is usually sufficient. This is because if the high-pressure molding is performed, the density of the powder magnetic core approaches the true density, and further increase in density cannot be substantially desired, and there is no need for it in consideration of the mold life and productivity. Therefore, for example, the molding pressure is preferably 980 to 2000 MPa.

  By the way, when the magnetic core powder is pressure-molded, residual stress and residual strain are generated inside. In order to remove this, it is preferable to perform a heat treatment step of heating and gradually cooling the powder compact after the molding step. Thereby, the coercive force of the dust core is reduced, and the hysteresis loss is reduced. In addition, a good dust core such as followability to an alternating magnetic field can be obtained. The residual strain removed in the annealing step may be strain accumulated in the magnetic powder particles before the molding step.

  Residual strain and the like are effectively removed as the heat treatment temperature increases. However, if the heat treatment temperature is too high, at least partial destruction occurs even in the heat-resistant insulating film of the present invention. Therefore, it is preferable to determine the heat treatment temperature in consideration of the heat resistance of the insulating coating. For example, when the heat treatment temperature is 450 to 800 ° C., it is preferable to achieve both the removal of residual strain and the protection of the insulating film. The heating time is 1 to 300 minutes, preferably 5 to 60 minutes, in view of the effect and economy.

The atmosphere during the heat treatment is preferably a non-oxidizing atmosphere. For example, a vacuum atmosphere or an inert gas atmosphere. The reason why the heat treatment process is performed in a non-oxidizing atmosphere is to prevent the powder magnetic core and the magnetic powder constituting the powder core from being excessively oxidized and deteriorating the magnetic characteristics and electrical characteristics. Specifically, there is a case where a scale of FeO or a Fe ₂ SiO ₄ layer is generated. Further, when heating is necessary for the formation of the second insulating film, that is, when the second insulating film is baked, it is efficient and preferable that the heat treatment process is also used as the heat treatment of the second insulating film.

(5) Use of dust core The dust core of the present invention can be used for various electromagnetic devices such as motors (particularly, cores and yokes), actuators, transformers, induction heaters (IH), and speakers. In particular, the dust core made of the magnetic powder coated according to the present invention can reduce hysteresis loss due to annealing or the like with high magnetic flux density, and is effective for devices used in a relatively low frequency range.

Hereinafter, the present invention will be described more specifically with reference to examples.
[1. Manufacturing process]
(Example)
(1) Raw material powder Fe-Si water atomized powder or gas atomized powder (2) Mixing treatment Fe-1 wt% Si powder + SiO ₂ powder (0.14 wt%, particle size: 25.6 μm) + MgO powder (0.7 wt%, Particle size: 3.8 μm) Mixing (3) Powder annealing treatment 1100 ° C. × 4 h, treatment in vacuum (vacuum degree: 10 ⁻² Pa) (4) Coating treatment 0.2% by weight of silicone resin to Fe—Si powder Mixing, stirring and drying (5) Powder molding Molding at a surface pressure of 1600 MPa using mold lubrication warm molding method (6) Heat treatment 675 ° C x 45 min, treatment in N ₂ atmosphere

(Comparative example)
For comparison, without mixing SiO ₂ powder and MgO powder into the Fe—Si powder of (2) above, (3) powder annealing treatment → (4) coating treatment → (5) powder molding → (6 ) Heat treatment was performed.

[2. Carbon reduction effect by annealing treatment]
When the powder was annealed under the above conditions, the amount of carbon and the amount of oxygen were reduced. FIG. 2 shows a comparison of the carbon content of the untreated powder and the SiO ₂ powder + MgO powder mixed annealing powder obtained in the examples of the present invention. FIG. 3 shows a comparison of the oxygen content of the untreated powder and the SiO ₂ powder + MgO powder mixed annealing powder obtained in the example of the present invention.
2 and 3 show that decarbonization and deoxygenation are significant according to the present invention.

[3. Iron loss reduction effect]
FIG. 4 shows the iron loss of the eddy current loss and hysteresis loss of the untreated powder, the powder simply vacuum-annealed, and the SiO ₂ powder + MgO powder mixed annealing powder obtained in the example of the present invention. Comparison is shown.
From the results shown in FIG. 4, the hysteresis loss is reduced by vacuum annealing the received powder at 1100 ° C. by reducing the amount of C and increasing the crystal grain size, but the SiO ₂ concentration on the powder surface is reduced and eddy current loss is reduced. Gets worse. In contrast, when SiO ₂ and MgO under the above conditions are added and vacuum annealing is performed, hysteresis loss and eddy current loss can be reduced.

From the above, it can be seen that the following effects can be obtained by the present invention.
(1) Impurities (carbon) in the metal magnetic powder are reduced, and hysteresis loss is reduced.
(2) The crystal grains in the powder are coarsened and the hysteresis loss is reduced.
(3) Since an oxide is present on the powder surface, an insulating film formed by a silicone resin coating is stably generated, and eddy current loss is reduced.
(4) Since SiO ₂ and MgO are also sintering inhibitors, they prevent powders from sticking and sintering during heat treatment at high temperatures and facilitate the powder crushing. This is particularly effective for a powder having a large surface area such as a flat powder and a large contact area between the powders.

  When producing a powder magnetic core, two or more kinds of specific metal oxide powders are added to and mixed with the magnetic powder, and the mixed powder is subjected to vacuum annealing, whereby these metals are formed on the particle surface of the magnetic powder. By forming an insulating film and / or insulating particles composed of a composite oxide of oxide powder, carbon (C), which is an impurity of the metal magnetic powder, is removed (decarburization: hysteresis loss loss reduction) and the surface of the metal magnetic powder is removed. It is possible to achieve both stabilization of the insulating coating (suppression of decrease in the insulating oxide concentration on the powder surface: suppression of eddy current loss). Further, since the gradual oxidation treatment (stabilization treatment) required in the prior art is unnecessary, the process is simplified and the cost is reduced.

The decarburization process of the prior art and the present invention is schematically shown. FIG. 1 (a) shows a conventional decarburization process when a metal powder is coated with a metal oxide, and FIG. 1 (b) shows two or more specific metal oxides (SiO ₂ and MgO) on the magnetic powder. ) Is the decarburization process of the present invention. The contrast of the carbon content of the untreated powder and the SiO ₂ powder + MgO powder mixed annealing powder obtained in the examples of the present invention is shown. It shows a comparison of oxygen of SiO ₂ powder + MgO powder mix annealing powder obtained in Example untreated flour and the present invention. And untreated flour, simply a powder was subjected to vacuum annealing, the SiO ₂ powder + MgO powder mix annealing powder obtained in Example of the present invention, the contrast of an iron loss of the combined eddy-current loss and hysteresis loss shown.

Claims (4)

Magnetic powder containing iron (Fe) and silicon (Si), or iron (Fe), aluminum (Al) and silicon (Si) as main components, SiO ₂ powder, Al ₂ O ₃ powder, CaO powder, MgO powder, A first mixing step of adding and mixing at least two kinds of metal oxide powders selected from the group of TiO ₂ powder, Fe ₂ O ₃ powder, K ₂ O powder, and Na ₂ O ₃ powder; and the mixed powder A powder annealing step of decarburizing the magnetic powder by vacuum annealing and a second mixing step of adding and mixing a binding resin to the vacuum annealed mixed powder. Powder manufacturing method. Process for the preparation of powder for a dust core according to claim 1, wherein the metal oxide powder is a combination of SiO ₂ powder and MgO powder. The method for producing a powder for a powder magnetic core according to claim 1 or 2 , wherein the binding resin is a silicone resin. A powder magnetic core comprising a step of pressure-molding the powder for powder magnetic core and a step of heat-treating the compact after the step of producing the powder for powder magnetic core according to any one of claims 1 to 3. Manufacturing method.

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