JP2009302165A - Dust core and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust core having low loss by planarizing the surface of a soft magnetic powder, and performing insulation processing to improve an annealing temperature and to provide a manufacturing method thereof. <P>SOLUTION: The dust core includes a soft magnetic powder principally containing iron produced by a water atomizing method, and an insulator for covering the surface of the soft magnetic powder. The soft magnetic powder is subjected to planarization treatment, and pre-molding heat treatment for heating the powder at ≥700°C. Insulation treatment for covering the insulator is executed before or after the pre-molding heat treatment. After the insulation treatment, molding treatment for pressurizing and molding the soft magnetic powder is executed. After the molding treatment, annealing treatment for heating the powder at ≥550°C is executed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a dust core made of soft magnetic powder and a method for producing the same.

  Conventionally, choke coils have been used as electronic devices for control power supplies such as OA equipment, photovoltaic power generation systems, automobiles, and uninterruptible power supplies, and ferrite cores and dust cores have been used as the cores.

  Among these magnetic cores, the ferrite magnetic core has a drawback of low saturation density. On the other hand, a dust core produced by molding metal powder has a higher saturation magnetic flux density than soft magnetic ferrite, and therefore has excellent DC weight characteristics. In addition, due to demands such as improved energy exchange efficiency and low heat generation, the dust core requires magnetic properties that can obtain a large magnetic flux density with a small applied magnetic field and magnetic properties that have low energy loss due to changes in magnetic flux density. It is done.

  When the dust core is used in an alternating magnetic field, energy loss called iron loss occurs. This iron loss is expressed as the sum of hysteresis loss, eddy current loss, and abnormal eddy current. The main problems are hysteresis current and eddy current loss. This hysteresis loss is proportional to the operating frequency, and the eddy current loss is proportional to the square of the operating frequency. Therefore, the hysteresis loss is dominant in the low frequency region, and the eddy current loss is dominant in the high frequency region. The dust core is required to have magnetic characteristics that reduce the occurrence of this iron loss.

  In order to reduce the hysteresis loss of the dust core, it is only necessary to facilitate the movement of the domain wall. To that end, the retention of the soft magnetic powder may be reduced. By reducing this holding force, the initial permeability can be improved and the hysteresis loss can be reduced.

On the other hand, a high-density molded magnetic core has a high magnetic flux density. However, a powder magnetic core molded with high density generates a lot of distortion in the soft magnetic powder particles during molding. This distortion increases the holding power of the dust core and increases hysteresis loss.

  In order to remove this distortion, it is necessary to perform a tempering operation. In the soft magnetic powder containing iron as a main component, a high calcination temperature of 500 ° C. or higher is required to remove this distortion. However, at a high tempering temperature of 500 ° C. or higher, as described in Patent Document 1, as a conventional technique, when a phosphate-based insulating treatment is performed, the insulating coating is destroyed and burned out, and the vortex As a result, current loss increases.

  Therefore, an insulating coating excellent in heat resistance has been proposed. In Patent Document 2, a contrivance is made to increase heat resistance by performing a phosphate-based insulation treatment on iron powder and then applying a coating with a silicone resin thereon.

  In Patent Document 3, an insulating layer having a continuous and uniform thickness is formed on a spherical powder whose surface is flattened by a coating of rare earth fluoride, alkali metal fluoride, or alkaline earth metal fluoride. A manufacturing method in which the resistance value of the magnetic core is increased has been proposed.

JP2000-504785A JP 2006-5173 A JP2008-16670

  However, even in the method of coating a silicone resin on the phosphate-based film of Patent Document 2, if the temperature exceeds 600 ° C., the insulator is destroyed and eddy current loss increases. Also, in the manufacturing method in which a continuous and uniform thickness insulating layer is formed on a spherical powder whose surface is flattened as in Patent Document 3 and the resistance value of the dust core is increased, eddy current loss is There is no special consideration. Furthermore, in the method of Patent Document 3, since the heat treatment for removing processing strain is not performed after the flattening process, the hysteresis loss increases.

  The present invention has been proposed in order to solve the above-mentioned problems, and its purpose is to reduce the temperature of the smelting by improving the sintering temperature by performing an insulation treatment after the surface of the soft magnetic powder is flattened. It is to provide a lossy dust core and a manufacturing method thereof.

The present invention is a powder magnetic core obtained by molding a soft magnetic powder mainly composed of iron manufactured by a water atomization method and an insulator covering the surface of the soft magnetic powder, The powder is subjected to a pre- molding heat treatment in a non-oxidizing atmosphere at a temperature equal to or higher than 700 ° C. and below the temperature at which the soft magnetic powder starts sintering, and the surface thereof is coated with the insulator. in the forming process after the molded article, characterized in that it is produced by performing an annealing process at temperatures above 550 ° C..

  That is, the water atomization method known as a conventional method for producing soft magnetic powder is a kind of metal powder production, and a soft magnetic powder having a flat surface and relatively close to a sphere can be obtained. However, when the particle size of the powder to be produced is a certain size or larger (for example, an average particle size of 10 μm or more), protrusions and the like are formed on the surface, resulting in a powder having irregularities.

  Therefore, in the present invention, as a method for removing the unevenness, a ball mill or a bead mill for colliding the ball and the powder, a jet mill for colliding the powder, a high-speed air impact device for colliding the high-rotation rotor with the powder, etc. Is used to flatten the surface of the soft magnetic powder. At this time, the aspect ratio indicating the sphericity of the powder is set to 1.0 to 1.5.

In the present invention, the pre- molding heat treatment is performed in a non-oxidizing atmosphere while the temperature is not lower than 700 ° C. and not higher than the temperature at which the soft magnetic powder starts sintering. By this pre- molding heat treatment, it is possible to remove the processing strain during the water atomization method and the processing strain during the flattening treatment in the soft magnetic powder having a relatively large average particle diameter.

Furthermore, the present invention is characterized in that the annealing treatment after molding is performed at 550 ° C. or higher. That is, for the dust core after molding , a smelting operation is performed for the purpose of removing distortion at the time of molding, but in soft magnetic iron powder mainly composed of iron, to effectively remove this distortion, A high tempering temperature of 500 ° C. or higher is required. In addition, as this temperature, it is preferable that it is below the heat processing temperature before shaping | molding .

In the present invention, the surface of the soft magnetic powder produced by the water atomization method using a mixture of SiO ₂ powder, Al ₂ O ₃ powder, SiO ₂ powder, or Al ₂ O ₃ powder, which is an inorganic insulating powder, during the planarization treatment. To coat. At this time, the average particle diameter of primary particles such as SiO ₂ powder is preferably 2 to 20 nm. Further, the addition amount of SiO ₂ powder is desirably 0.5 wt% or less, and if it exceeds 0.5 wt%, it causes an increase in hysteresis loss due to a decrease in density, a decrease in maximum magnetic flux density, and a decrease in magnetic permeability.

In addition to adding an inorganic insulating powder such as SiO ₂ to the soft magnetic powder, the insulating treatment includes a silane coupling agent or organic material that is a heat-resistant protective film for the soft magnetic powder subjected to the planarization treatment. When a silicone resin as a binder is added, iron loss can be reduced as compared with the case where the insulation treatment is not performed.

Furthermore, in addition to the silane coupling agent and the silicone resin, or by performing insulation treatment with SiO ₂ powder which is an inorganic insulating material alone, eddy current loss can be further reduced.

  In the present invention, the soft magnetic powder preferably has an average particle size of 10 to 100 μm. That is, in the water atomization method, when the average particle size is 10 μm or less, a powder having a relatively flat surface and close to a sphere can be obtained. Therefore, it is not necessary to perform a flattening process on the soft magnetic powder in order to improve insulation. On the other hand, when the thickness is 10 μm or more, since there are irregularities such as protrusions on the surface, it is necessary to remove this in order to improve the insulating properties. Therefore, this particle size range is suitable for the present invention. On the other hand, when the average particle size is 100 μm or more, eddy current loss increases as the particle size increases.

  In addition, a method of manufacturing a low-loss powder magnetic core that improves the sintering temperature by performing an insulation treatment after the surface of the soft magnetic powder is planarized as described above is also an aspect of the present invention. is there.

  According to the present invention as described above, the surface of the soft magnetic powder after the flattening treatment is covered with the inorganic insulating powder, so that the insulation is deteriorated even when the heat treatment is performed at a high temperature in the atmosphere. In addition, it is possible to provide a dust core and a method for manufacturing the dust core capable of reducing the influence of an increase in hysteresis loss due to oxidation or the like.

In the embodiment, a soft magnetic powder containing iron as a main component is subjected to a heat treatment after surface flattening, a silane coupling agent or a silicone resin is added, and then molded into a predetermined shape, which is made of nitrogen, hydrogen, or the like. It is characterized in that a dust core is produced by heat treatment in a non-oxidizing atmosphere. In this case, for the purpose of reducing eddy current loss to the soft magnetic powder, an insulating layer is formed on the surface of the soft magnetic powder by adding powder such as SiO ₂ .

  Hereafter, each process is demonstrated concretely. First, as a surface flattening step, in order to eliminate the irregularities on the surface of pure iron water atomized powder containing pure iron as a main component and having a particle size of 106 μm or less and an average particle size of 43 μm, a high-speed air current impact method is used. The surface is flattened. The water atomization method is a method in which a powder with a relatively flat surface and close to a sphere can be obtained. However, when the average particle size is 10 μm or more, irregularities such as protrusions are generated on the surface, so a surface flattening treatment is required. is there.

  This surface flattening treatment uses a device that gives mechanical energy such as impact, shear, shear stress, and friction to the pulverized particles that have been impacted by a rotor rotating at high speed. According to this type of device, the mechanical energy given to the pulverized particles and a part of the mechanical energy are accumulated in the solid particles, the activity and reactivity of the solid particles are increased, and the mechano- gen that causes a chemical reaction with surrounding substances. A chemical effect can be expressed.

Then, as pre- molding heat treatment, pure iron atomized powder subjected to surface flattening treatment was subjected to heat treatment at 900 ° C. for 2 hours in a hydrogen atmosphere. The reason why the heat treatment is performed at 900 ° C. is to remove the processing distortion during the water atomization method and the processing distortion during the flattening process. This is because even if the temperature is low, it is necessary to carry out at 700 ° C. or more, and a good effect can be obtained at 850 to 1000 ° C.

  Next, as an insulation treatment, a surface flattening treatment was performed, and the powder subjected to the heat treatment to remove the strain, 0.1% by mass of the silane coupling agent, and 1.0% by weight of the silicone resin were mixed in this order, and 180 ° C. Heat drying at a temperature of 2 hours. Add 0.2% by weight of zinc stearate as a lubricant and mix.

  In this way, by using zinc stearate, which is a metal salt of stearic acid, as a lubricant for insulation treatment, it becomes possible to increase the thermal decomposition rate of methyl groups depending on the type of metal, and tough silica even at lower temperatures A layer is formed.

  In this embodiment, by mixing an organic metal coupling agent (for example, a silane coupling agent) with respect to the soft magnetic powder in the insulation treatment, and forming a heat-resistant protective film on the surface of the soft magnetic alloy powder, Hysteresis loss can be remarkably reduced and iron loss can be reduced as compared with the case where the coupling agent is not used.

After the insulation treatment as described above, a molded body is formed by pressure molding at room temperature. Here, the added silicone resin acts as a binder during molding . Thereafter, the molded body, the dust core is manufactured by performing the baked net for 30 minutes at the molding prior to the heat treatment temperatures below under nitrogen.

  Next, Examples 1 to 13 of the present invention will be described below with reference to FIGS. 1 to 5 and Tables 1 to 5.

[1-1. Measurement item]
As measurement items, magnetic permeability and iron loss (core loss) are measured by the following method. The magnetic permeability was calculated from the inductance at 10 kHz and 0.5 V by applying a primary winding (20T) to the produced dust core and using an impedance analyzer.

  The iron loss was measured under the condition of maximum magnetic flux density Bm = 0.1 T using a BH analyzer with primary and secondary windings applied to the dust core. The hysteresis loss coefficient and eddy current loss coefficient are calculated from the measured iron loss by the following (1) to (3) using the least squares method on the iron loss frequency curve. I asked for it.

Pc = Kh × f + Ke × f2 (1)
Ph = Kh × f (2)
Pe = Ke × f2 (3)
Pc: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: Frequency Ph: Hysteresis loss Pe: Eddy current loss

[1-2. First characteristic comparison (pre- molding heat treatment and flattening treatment)]
The sample used for the first characteristic comparison was prepared as follows. Comparative examples 1 to 5 and Example 1 were conducted by subjecting water atomized powder of pure iron (average particle size 43 μm) classified to a particle size of 106 μm or less to surface treatment, pre- molding heat treatment, and annealing treatment as shown in Table 1. ~ 3 samples were prepared. These samples were mixed in the order of 0.1% by mass of a silane coupling agent and 1.0% by weight of a silicone resin, dried and heated (180 ° C., 2 hours), and then zinc stearate as a lubricant was added in an amount of 0.0. 2% by weight was added and mixed.

  This was press-molded at a pressure of 1000 MPa at room temperature to produce a dust core having a ring shape with an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 7 mm. These powder magnetic cores were heat-treated (purified) for 30 minutes in nitrogen.

In Comparative Example 1, the flattening treatment and the pre- molding heat treatment at 900 ° C. were not performed on the pure iron water atomized powder. In Comparative Example 2, a pure iron water atomized powder was subjected to a phosphate film treatment without being subjected to a flattening treatment and a pre- molding heat treatment at 900 ° C.

In Comparative Example 3, the surface of the pure atomized water atomized powder was flattened by the impact method in high-speed air current without performing the pre- molding heat treatment at 900 ° C. For surface flattening, the rotor of the impact method in high-speed air current was set to 4800 revolutions / minute and the time was 3 minutes (Condition 1).

In Comparative Example 4, the surface of the pure iron water atomized powder was flattened by a high-speed air-flow impact method without performing a pre- molding heat treatment at 900 ° C. For surface flattening, the rotor of the impact method in high-speed air current was set to 6400 revolutions / minute and the time was 3 minutes (Condition 2).

In Comparative Example 5, the surface of the pure atomized water atomized powder was flattened by a high-speed air current impact method without performing a pre- molding heat treatment at 900 ° C. For surface flattening, the rotor of the impact method in high-speed air current was set to 8000 revolutions / minute and the time was 3 minutes (Condition 3).

In Example 1, the surface of the pure iron water atomized powder was flattened and then subjected to pre- molding heat treatment at 900 ° C. for 2 hours in a hydrogen atmosphere. The surface flattening was performed by the high-speed air current impact method, and the rotor of the high-speed air current impact method was set to 4800 revolutions / minute and the time was 3 minutes (Condition 1).

In Example 2, the surface of the pure iron water atomized powder was flattened and then subjected to pre- molding heat treatment at 900 ° C. for 2 hours in a hydrogen atmosphere. Surface flattening was performed by a high-speed air current impact method, and the rotor of the high-speed air current impact method was 6400 revolutions / minute and the time was 3 minutes (Condition 2).

In Example 3, the pure atomized water atomized powder was subjected to pre- molding heat treatment at 900 ° C. for 2 hours in a hydrogen atmosphere after the surface was flattened. Surface flattening was performed by a high-speed air current impact method, and the rotor of the high-speed air current impact method was set at 8000 revolutions / minute and the time was 3 minutes (Condition 3).

Table 1 is a table showing the relationship between density, magnetic permeability, and iron loss (eddy current loss, hysteresis loss) for Comparative Examples 1 to 5 and Examples 1 to 3. In addition, FIG. 1 shows the case where the surface is flattened with a high-speed air impact method (rotor rotation speed 6400 times / minute (condition 2)) with respect to pure iron water atomized powder, and the surface is not flattened. It is a drawing substitute photograph which shows the mode of the surface of the powder at the time.

As can be seen from the above, in Comparative Example 1 in which the flattening treatment and the pre- molding heat treatment at 900 ° C. were not performed, the eddy current loss was greatly increased by 550 ° C. purification. Further, in Comparative Example 2 in which the flattening treatment and the pre- molding heat treatment at 900 ° C. were not performed and the phosphate film treatment was performed, the eddy current loss increased greatly at 600 ° C. purification.

On the other hand, in Comparative Examples 3 to 5 in which the surface was flattened by the high-speed air-flow impact method without performing the pre- molding heat treatment at 900 ° C., the eddy current was higher than that in Comparative Example 2 even if the sample was purified at 600 ° C. Loss is reduced, but hysteresis loss is increased. In contrast, after the surface planarization, in a hydrogen atmosphere, for 2 hours at 900 ° C., forming before the heat treatment the Examples 1 to 3 was performed, by performing the molding before the heat treatment, reduction of hysteresis loss, Toru Magnetic susceptibility is improved. This is considered that the applied force generated at the time of surface flattening was removed.

[1-3. Second characteristic comparison (presence / absence of heat treatment before molding and presence / absence of flattening treatment)]
A sample used in the second characteristic comparison was prepared as follows. The surface treatment, first heat treatment, and second heat treatment as shown in Tables 2 and 3 were performed on water atomized powder of pure iron (average particle size 43 μm) classified to a particle size of 106 μm or less. A sample of Example 4 was produced. These samples were mixed in the order of 0.1% by mass of a silane coupling agent and 1.0% by weight of a silicone resin, dried and heated (180 ° C., 2 hours), and then zinc stearate as a lubricant was added in an amount of 0.0. 2% by weight was added and mixed.

  This was press-molded at a pressure of 1000 MPa at room temperature to produce a dust core having a ring shape with an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 7 mm. These powder magnetic cores were subjected to a sinter treatment at a temperature of 400 ° C. to 625 ° C. for 30 minutes in nitrogen.

In Comparative Example 6, the flattening treatment and the pre- molding heat treatment were not performed on the water atomized powder of pure iron. In Comparative Example 7, a pure iron water atomized powder was subjected to a phosphate film treatment without being subjected to a flattening treatment and a pre- molding heat treatment.

In Example 4, the pure atomized water atomized powder was subjected to a pre- molding heat treatment at 900 ° C. for 2 hours in a hydrogen atmosphere after the surface was flattened. Surface flattening was performed by a high-speed air current impact method, and the rotor of the high-speed air current impact method was 4800 revolutions / minute and the time was 3 minutes.

Table 2 is a table showing the relationship between density, magnetic permeability, and iron loss (eddy current loss, hysteresis loss) for Comparative Examples 6 and 7 and Example 4. FIG. 2 is a graph showing the relationship between the total loss and the heat treatment temperature for Comparative Examples 6 and 7 and Example 4. FIG. 3 shows the relationship between eddy current loss and heat treatment temperature for Comparative Examples 6 and 7 and Example 4. FIG. 4 shows the relationship between hysteresis loss and heat treatment temperature for Comparative Examples 6 and 7 and Example 4.

As can be seen from the above, in Comparative Example 6 where the flattening treatment and the pre- molding heat treatment were not performed on the water atomized powder of pure iron, the eddy current loss increased rapidly when the annealing treatment temperature reached 550 ° C. did. Moreover, even in the comparative example 7 in which pure iron water atomized powder was not subjected to flattening treatment and pre- molding heat treatment and subjected to phosphate film treatment, when the annealing treatment temperature reached 600 ° C., eddy current loss occurred. Increased rapidly. Along with this, it can be seen that the total loss increased in the same way.

For these, for water atomized powder of pure iron, after surface planarization, at a hydrogen atmosphere, for 2 hours at 900 ° C., in Example 4 was molded prior to heat treatment, and ShoJun at 625 ° C. However, since the eddy current loss does not increase, the total loss does not increase, and the hysteresis loss is reduced and the magnetic permeability is improved. This is considered that the stress which generate | occur | produces at the time of surface planarization was removed.

[1-4. Third characteristic comparison (with or without addition of SiO ₂ powder)]
The sample used for the third characteristic comparison was prepared as follows. The surface treatment, the first heat treatment, and the second heat treatment as shown in Tables 3 and 4 were performed on the pure iron water atomized powder (average particle size 43 μm) classified to a particle size of 106 μm or less. A sample was prepared. For these samples, 0.1% by mass of silane coupling agent and 1.0% by weight of silicone resin were mixed in this order, and after drying and heating (180 ° C., 2 hours), 0% zinc stearate as a lubricant was added. Add 2% by weight and mix.

  This was press-molded at a pressure of 1000 MPa at room temperature to produce a dust core having a ring shape with an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 7 mm. And these powder magnetic cores were tempered in nitrogen at a temperature of 625 ° C. for 30 minutes.

In Example 5, the surface of an iron atomized powder of pure iron was flattened and then subjected to pre- molding heat treatment at 900 ° C. for 2 hours in a hydrogen atmosphere. Surface flattening was performed by a high-speed air current impact method, and the rotor of the high-speed air current impact method was 4800 revolutions / minute and the time was 3 minutes.

In Examples 6 to 8, 0.05 to 0.25 wt% of SiO ₂ fine powder (specific surface area 300 m ² / g, average particle size 7 nm) was added to pure iron water atomized powder to flatten the surface. Then, pre- molding heat treatment was performed at 900 ° C. for 2 hours in a hydrogen atmosphere. Surface flattening was performed by a high-speed air current impact method, and the rotor of the high-speed air current impact method was 4800 revolutions / minute and the time was 3 minutes.

In Example 9, the surface of the pure iron water atomized powder was flattened and then subjected to pre- molding heat treatment at 900 ° C. for 2 hours in a hydrogen atmosphere. Surface flattening was performed by a high-speed air current impact method, and the rotor of the high-speed air current impact method was 4800 revolutions / minute and the time was 3 minutes.

In Examples 10 to 12, 0.05 to 0.25 wt% of SiO ₂ fine powder (specific surface area 300 m ² / g, average particle diameter 7 nm) was added to pure iron water atomized powder to flatten the surface. Then, pre- molding heat treatment was performed at 900 ° C. for 2 hours in a hydrogen atmosphere. Surface flattening was performed by a high-speed airflow impact method, and the rotor of the high-speed airflow impact method was 6400 rotations / minute and the time was 3 minutes.

Tables 3 and 4 are tables showing the relationship among density, magnetic permeability, and iron loss (eddy current loss and hysteresis loss) for Examples 5 to 12. Further, FIG. 5 is a diagram showing a relationship between the addition amount and the eddy current loss of the SiO ₂ powder for Example 5-12.

As can be seen from the above, compared to the case where the SiO ₂ powder is not added by adding the SiO ₂ fine powder to the pure atomized water atomized powder and performing the pre- molding heat treatment after the surface flattening. Thus, eddy current loss can be further reduced. The amount of the SiO ₂ fine powder is desirably 0.5 wt% or less, and if it exceeds this, the density will decrease. As the inorganic insulating powder, _Al 2 _{O 3} powder and SiO ₂ powder and _Al 2 _{O 3} may be a mixture of powder instead of SiO ₂ powder.

[1-5. Fourth characteristic comparison (presence / absence of heat treatment before forming and flattening treatment when soft magnetic powder is Fe-Si alloy water atomized powder)]
A sample used in the fourth characteristic comparison was prepared as follows. Surface treatment, first heat treatment, and second heat treatment as shown in Table 5 were performed on Fe-Si alloy water atomized powder (average particle diameter 42 μm) having a Si component of 6.5% classified to a particle size of 106 μm or less. The samples of Comparative Example 8 and Example 13 were prepared. These samples were mixed with 0.75% by weight of silicone resin, dried and heated at a temperature of 180 ° C. for 2 hours, and then mixed with 0.2% by weight of zinc stearate as a lubricant.

  This was press-molded at a pressure of 1700 MPa at room temperature to produce a dust core having a ring shape with an outer diameter of 16 mm, an inner diameter of 8 mm, and a height of 7 mm. And these powder magnetic cores were tempered in nitrogen at a temperature of 700 ° C. for 30 minutes.

In Comparative Example 8, the flattening treatment and the pre- molding heat treatment at 900 ° C. were not performed on the water atomized powder of the Fe—Si alloy whose Si component was 6.5%. In Example 13, a water atomized powder of pure iron of Fe-Si alloy having a Si component of 6.5% was subjected to a pre- molding heat treatment at 900 ° C. for 2 hours in a hydrogen atmosphere after surface flattening. It is what I did. Surface flattening was performed by a high-speed air current impact method, and the rotor of the high-speed air current impact method was 6400 revolutions / minute and the time was 3 minutes (Condition 2).

Table 5 is a table showing the relationship between density, magnetic permeability, and iron loss (eddy current loss, hysteresis loss) for Comparative Example 8 and Example 13.

From the above, in Comparative Example 8 in which the flattening treatment and the pre- molding heat treatment were not performed on the water atomized powder of the Fe—Si alloy having the Si component of 6.5%, the aspect ratio was 1.7. When annealing temperature is performed at 700 ° C., both eddy current loss and hysteresis loss increase.

On the other hand, the surface of the Fe-Si alloy water atomized powder having a Si component of 6.5% was flattened, and then pre- molding heat treatment was performed at 900 ° C. for 2 hours in a hydrogen atmosphere. Surface flattening at this time was performed by a high-speed air current impact method, and the rotor of the high-speed air current impact method was 6400 revolutions / minute and the time was 3 minutes. As a result, the aspect ratio of Example 13 is 1.3, and eddy current loss does not increase even if it is purified at 700 ° C. Therefore, total loss does not increase, and hysteresis loss is reduced and magnetic permeability is improved. This is considered that the stress which generate | occur | produces at the time of surface planarization was removed.

[Other embodiments]
As another example of the present embodiment, the first heat treatment temperature may be a temperature other than 900 ° C. Specifically, if it is 700 ° C. or more and not more than the temperature at which the soft magnetic powder starts sintering, it is possible to remove the processing strain during the water atomization method and the processing strain during the flattening process.

In the embodiment of the present invention, a drawing-substituting photograph showing the surface of the soft magnetic powder that has been subjected to a surface flattening treatment by a high-speed air-flow impact method. The graph which showed the relationship between the heat processing temperature in a 2nd Example, and total loss. The graph which showed the heat processing temperature in 2nd Example, and the relationship between eddy current loss. The graph which showed the relationship between the heat processing temperature and hysteresis loss in 2nd Example. Graph showing the relationship between the added amount and the eddy current loss and the total loss of the SiO ₂ powder in the third embodiment forms embodiment.

Claims (6)

A powder magnetic core formed by molding a soft magnetic powder mainly composed of iron produced by a water atomization method and an insulator covering the surface of the soft magnetic powder,
The soft magnetic powder is subjected to pre-molding heat treatment in a non-oxidizing atmosphere at a temperature equal to or higher than 700 ° C. and below the temperature at which the soft magnetic powder starts sintering, and the surface thereof is coated with the insulator. And
A dust core produced by subjecting the molded product after the molding treatment to an annealing treatment at a temperature of 550 ° C or higher. _2. The pressure according to claim 1, wherein the flattening treatment is performed by coating with an inorganic insulating powder, such as SiO ₂ powder, Al ₂ O ₃ powder, or a mixture of SiO ₂ powder and Al ₂ O ₃ powder. Powder magnetic core.   The powder magnetic core according to claim 1, wherein the soft magnetic powder has an average particle size of 10 to 100 μm. A method for producing a powder magnetic core comprising a soft magnetic powder mainly composed of iron produced by a water atomizing method and an insulator covering the surface of the soft magnetic powder,
The surface of the soft magnetic powder is subjected to a flattening process, and the soft magnetic powder after the flattening process is heated in a non-oxidizing atmosphere at a temperature of 700 ° C. or more and a temperature at which the soft magnetic powder starts sintering. Perform pre-molding heat treatment,
In any of the steps before and after the pre-molding heat treatment, an insulating treatment for covering the surface of the soft magnetic powder with the insulator is performed,
Performing a molding process for pressure-molding the insulated soft magnetic powder,
A method for producing a powder magnetic core, comprising subjecting a molded product after the molding treatment to an annealing treatment at a temperature of 550 ° C. or higher. During the flattening treatment, the soft magnetic powder is treated with SiO ₂ powder, Al ₂ O ₃ powder, which is an inorganic insulating powder, or a mixture of SiO ₂ powder and Al ₂ O ₃ powder. The manufacturing method of the powder magnetic core of Claim 4.   6. The method of manufacturing a dust core according to claim 4, wherein the soft magnetic powder has an average particle size of 10 to 100 [mu] m.