JP2011246812A - Method for producing powder for dust core and device for producing the powder for the dust core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing powder for a dust core and a device for producing the powder for the dust core, allowing improvement of productivity and quality of the powder for the dust core by preventing that secondary particles are generated in time of siliconizing treatment.SOLUTION: By bringing soft magnetic metal powder 21 into contact with silica dioxide holding member 22 coated by silica dioxide powder 23 while heating them, oxidation-reduction reaction between the soft magnetic metal powder 21 and the silica dioxide powder 23 is generated, and silicon disengaged from the silica dioxide powder 23 is made to diffuse and permeate into the surface of each soft magnetic metal powder 21 to form a silicon permeation layer on the surfaces of the soft magnetic metal powder 21.

Description

  The present invention relates to a method for producing a powder for a powder magnetic core and a powder production apparatus for a powder magnetic core for producing a powder for a powder magnetic core.

  The dust core is obtained by press-molding a dust core powder made of soft magnetic metal powder. Compared to the core material made by laminating electromagnetic steel sheets, the dust core has magnetic properties with less high frequency loss (hereinafter referred to as “iron loss”) depending on the frequency, and is suitable for shape variations. It has many advantages such as being able to cope with low cost and low material cost. Such a powder magnetic core is applied to, for example, a stator core and a rotor core of a vehicle drive motor, a reactor core constituting a power conversion circuit, and the like.

  For example, as shown in FIG. 14, the powder 101 for the powder magnetic core allows the silicon dioxide powder 103 to permeate and diffuse from the surface of the iron powder 102, thereby forming a silicon permeation layer 104 in which the silicon element is concentrated on the surface layer of the iron powder 102. The siliconization process to be performed is performed. In the siliconization treatment, the iron powder 102 and the silicon dioxide powder 103 are stirred and mixed to adhere the silicon dioxide powder 103 to the surface of the iron powder 102, and the mixed powder of the iron powder 102 and the silicon dioxide powder 103 is put into a furnace. Then, the mixed powder is heated to 1000 ° C. Then, the silicon element is detached from the silicon dioxide powder 103 and permeates and diffuses into the surface layer of the iron powder 102 to form the silicon permeation layer 104.

  When the silicon element is infiltrated to the center of the iron powder 102, the hardness of the powder 101 for dust core becomes high. In this case, when the dust core powder 101 is pressed and compacted, the dust core powder 101 is not deformed and the gap formed between the dust core powders 101 becomes larger. Density decreases. When the magnetic core density is low, there is a problem that the magnetic flux density is lowered. Therefore, it is preferable that the silicon permeation layer 104 has a distance X2 from the surface of the iron powder 102 to the center of the iron powder 102 that is less than 0.15 times the diameter D of the iron powder 102. However, if the silicon permeation layer 104 is thin or the silicon element concentration in the silicon permeation layer 104 is low, the contact portion of the iron powder 102 cannot be sufficiently insulated, and iron loss (mainly hysteresis loss and eddy current loss) is caused. Get higher. Therefore, the distance X2 and the concentration of the silicon permeation layer 104 formed on the powder 101 for dust core are very important in managing the specific resistance of the dust core (see, for example, Patent Document 1 and Patent Document 2). .

JP 2009-256750 A JP 2009-123774 A

  However, as shown in FIG. 15, the conventional method for manufacturing a powder for a powder magnetic core is to randomly extract 10 powders 101 for the powder magnetic core that are manufactured, and the silicon permeation layer 104 is iron from the surface of the iron powder 102. When the distance (distance from the surface) X2 formed toward the center of the powder 102 and the concentration of silicon element (Si concentration) in the silicon permeation layer were measured, the distance X2 from the surface and the Si concentration were between the powders. There was a lot of variation. Specifically, the extracted powder contained a powder having a poor silicification reaction (a powder having a low silicidation reaction amount) (see the graph described by a thin solid line in FIG. 15). Further, even if the powder is rich in the silicification reaction (powder having a high silicidation reaction amount) (see the graph described by the thick solid line in FIG. 15), the Si concentration on the surface of the iron powder 102 is about 2.0. The distance (thickness) X2 from the surface of the iron powder 102 of the silicon permeation layer 104 varies from about 4 μm to about 20 μm. Furthermore, the ratio of the Si concentration decreasing from the surface of the iron powder 102 of the silicon-penetrating layer 104 toward the center of the iron powder 102 varies greatly in the powder rich in the silicon immersion reaction. Therefore, in the conventional method for producing a powder for a powder magnetic core, it is not possible to cause each iron powder 102 to undergo a uniform silicidation reaction, and the silicon permeation layer 104 formed in each powder for a powder magnetic core 101 is made uniform. I couldn't plan. Therefore, when a portion having a small thickness (distance from the surface) X2 or a portion having a low Si concentration of the silicon permeation layer 104 formed on the powder 101 for dust core is in contact with each other at the time of compacting, insulation of the contact portion is performed. Therefore, there is a problem that the eddy current generated in the dust core becomes large and the specific resistance becomes low. Moreover, the powder 101 for a dust core having a large thickness (distance from the surface) X2 of the silicon-penetrating layer 104 is hard and causes a decrease in the core density and magnetic flux density.

  The reason why the thickness (distance from the surface) X2 and the Si concentration of the silicon-penetrating layer 104 varies between the powders 101 for powder magnetic cores by the conventional method for producing powders for powder magnetic cores is as follows. Since the mixed powder was heated without rotating the furnace in which the mixed powder was charged, the arrangement of the iron powder 102 and the silicon dioxide powder 103 did not change during the siliconization treatment, and there were a lot of silicon dioxide powder 103 around. In the iron powder 102, a large amount of silicon element penetrates and diffuses into the surface layer, and the thickness and the Si concentration of the silicon infiltrated layer 104 increase. This is considered to be because the amount permeating and diffusing into the silicon is small, and the thickness and the Si concentration of the silicon-penetrating layer 104 are small.

  Then, as shown in FIGS. 16 and 18, the inventors put a mixed powder obtained by stirring and mixing iron powder 102 having an average particle diameter of 200 μm and silicon dioxide powder 103 having an average particle diameter of 50 nm into a furnace 105, and The powder for a magnetic core is manufactured by heating 105 and then stirring the mixed powder continuously for 1 hour by rotating the furnace 105 while adjusting the internal temperature of the furnace 105 to 1000 ° C. Tried. As a result, the inventors believe that the silicon dioxide powder 103 is uniformly attached around the iron powder 102 while changing the arrangement during the silicidation treatment, and a uniform silicification reaction can be generated in each iron powder 102. It was.

  However, when the above method for producing a powder for a powder magnetic core was carried out and the product was taken out from the furnace 105, as shown in FIG. 17, the iron powder 102 and the silicon dioxide powder 103 were solidified in a dumpling shape to form secondary particles 110. It had become. The secondary particles 110 were sintered with silicon dioxide powder 103 (see dot portion) to combine a plurality of iron powders 102, and the diameters ranged from 600 μm to 700 μm. The reason why the secondary particles 110 are formed is considered as follows.

  It is known that sintering begins at a temperature of about two-thirds of the melting point. The melting point of silicon dioxide is 1600 ° C. ± 75 ° C. On the other hand, the heating temperature of the mixed powder during the siliconizing treatment is about 1000 ° C. Accordingly, the heating temperature of the mixed powder of 1000 ° C. corresponds to a temperature that is about two thirds of the melting point of silicon dioxide. By heating the mixed powder to 1000 ° C., silicon element is detached from the silicon dioxide powder 103 adhering to the surface of the iron powder 102 and diffuses and penetrates into the iron powder 102. The material moves and sintering occurs. Sintering also occurs in the silicon dioxide powder 103 that is diffusion bonded to the surface of the iron powder 102, so that the iron powders 102 are bonded together via the sintered silicon dioxide powder 103. In particular, as shown in FIGS. 16 and 18, the above method for producing a powder for a powder magnetic core is such that the furnace 105 is continuously rotated for 1 hour while the mixed powder is heated to 1000 ° C., and the iron powder 102 and the silicon dioxide powder. The mixed powder of 103 is repeatedly dropped from a high place to a low place and stirred. In this case, the silicon dioxide powder 103 in the low place is compressed by the weight of the mixed powder falling from above, and the sintering is promoted. As described above, when the mixed powder is simply stirred while being heated to 1000 ° C. during the siliconization treatment, the silicon dioxide powder 103 is pressure-sintered to generate secondary particles 110. As a result, the quality and productivity of the powder for powder magnetic cores have deteriorated.

  The present invention has been made to solve the above-mentioned problems, and prevents the generation of secondary particles during the siliconization treatment, and improves the quality and productivity of the powder for powder magnetic core. It aims at providing the manufacturing method of the powder for powder magnetic cores, and the powder manufacturing apparatus for powder magnetic cores.

  In order to solve the above problems, a method for producing a powder for a powder magnetic core according to an aspect of the present invention is the method for producing a powder for a powder magnetic core, wherein the soft magnetic metal powder and the silicon dioxide powder coated with the silicon dioxide powder are used. By bringing the silicon holding member into contact with heating, an oxidation-reduction reaction occurs between the soft magnetic metal powder and the silicon dioxide powder, and the silicon element detached from the silicon dioxide powder is diffused on the surface of the soft magnetic metal powder. A silicon infiltration layer is formed on the surface of the soft magnetic metal powder by infiltration.

  In the method for producing a powder for a powder magnetic core according to the above aspect, the silicon dioxide holding member is a sintering preventing material whose surface is coated with silicon dioxide powder, wherein the silicon dioxide holding member prevents sintering, and the soft magnetic metal It is preferable to mix the powder and the anti-sintering material and stir with heating.

  In the method for producing a powder for a powder magnetic core according to the above aspect, the silicon dioxide holding member is an inner wall of a rotary furnace coated with silicon dioxide powder, and the soft magnetic metal powder and sintering for preventing sintering are performed. It is preferable that the preventive material is put into the rotary furnace and heated and stirred.

In the method for producing a powder for a powder magnetic core according to the above aspect, the sintering preventing material has an average particle size smaller than that of the soft magnetic metal powder and does not react with the soft magnetic metal powder and the silicon dioxide powder. It is preferable.
For example, the sintering preventing material is preferably alumina (Al ₂ O ₃ ) or zirconia (ZrO ₂ ).

  In the method for producing a powder for a powder magnetic core according to the above aspect, it is preferable that an average particle diameter of the sintering preventing material is 7 μm to 30 μm.

  In order to solve the above problems, a powder magnetic core manufacturing apparatus according to an aspect of the present invention is a powder magnetic core powder manufacturing apparatus for manufacturing a powder magnetic core, wherein the powder magnetic core is rotatably held and heated. A rotary furnace made of a conductive material, a driving means for applying a rotational force to the rotary furnace, and a heating means for heating the rotary furnace, wherein the rotary furnace comprises a soft magnetic metal powder, a surface Is mixed with a sintering inhibitor coated with silicon dioxide powder.

  In the powder magnetic core manufacturing apparatus of the above aspect, the average particle diameter of the sintering preventing material is preferably 7 μm to 30 μm.

  In order to solve the above problems, a powder magnetic core manufacturing apparatus according to an aspect of the present invention is a powder magnetic core powder manufacturing apparatus for manufacturing a powder magnetic core, wherein the powder magnetic core is rotatably held and heated. A rotary furnace made of a conductive material; a driving means for applying a rotational force to the rotary furnace; and a heating means for heating the rotary furnace, wherein the rotary furnace coats an inner wall with silicon dioxide powder. Then, a mixed powder of soft magnetic metal powder and an anti-sintering material is introduced.

  The powder magnetic core powder manufacturing method and the powder magnetic core powder manufacturing apparatus according to the above aspect include, for example, a mixed powder of a soft magnetic metal powder and a sintering inhibitor whose surface is coated with silicon dioxide powder in a rotary furnace. Then, the rotary furnace is rotated while being heated by a heating means, and the soft magnetic metal powder and the anti-sintering material are stirred and mixed. In this case, the soft magnetic metal powder comes into contact with the silicon oxide powder coated on the surface of the anti-sintering material and generates an oxidation-reduction reaction. By this oxidation-reduction reaction, silicon element is desorbed from the silicon dioxide powder and diffuses and penetrates into the surface of the soft magnetic metal powder, thereby forming a silicon permeation layer on the surface of the soft magnetic metal powder. The silicon dioxide powder is prevented from sintering by the sintering inhibitor. Therefore, even if the rotary furnace is rotated in a heated state and the mixed powder is stirred and mixed, the soft magnetic metal powder is bonded through the silicon dioxide powder or the silicon dioxide powder is sintered together. No secondary particles are produced. Further, silicon dioxide powder as a sintering preventing material is successively supplied to the surface of the soft magnetic powder by stirring and mixing the mixed powder, so that a silicon permeation layer is uniformly formed on the surface of each soft magnetic metal powder. Therefore, according to the method for manufacturing a powder for a powder magnetic core and the powder core manufacturing apparatus for the powder magnetic core, secondary particles are prevented from being generated during the siliconization treatment, and the quality and productivity of the powder for the powder magnetic core are improved. Can be made.

  The method for manufacturing a powder for a powder magnetic core and the powder core manufacturing apparatus for a powder magnetic core according to the above aspect include, for example, putting a mixed powder of a soft magnetic metal powder and an antisintering material into a rotary furnace and heating the rotary furnace with heating means. The soft magnetic metal powder and the sintering preventing material are stirred and mixed while rotating. In this case, the soft magnetic metal powder comes into contact with the silicon dioxide powder coated on the inner wall of the rotary furnace and generates an oxidation-reduction reaction. By this oxidation-reduction reaction, silicon element is desorbed from the silicon dioxide powder and diffuses and penetrates into the surface of the soft magnetic metal powder, thereby forming a silicon permeation layer on the surface of the soft magnetic metal powder. The silicon dioxide powder is prevented from sintering by the sintering inhibitor. Therefore, secondary particles are not generated by binding of the soft magnetic metal powder via the silicon dioxide powder or sintering of the silicon dioxide powder. Further, the soft magnetic powder changes the position of contact with the silicon dioxide powder coated on the inner wall of the rotary furnace when the mixed powder is agitated and mixed, so that a silicon permeation layer is uniformly formed on the surface of each soft magnetic metal powder. Therefore, according to the method for manufacturing a powder for a powder magnetic core and the powder core manufacturing apparatus for the powder magnetic core, secondary particles are prevented from being generated during the siliconization treatment, and the quality and productivity of the powder for the powder magnetic core are improved. Can be made.

  The powder for the powder magnetic core of the above aspect has an average particle size smaller than that of the soft magnetic metal powder and does not react with the soft magnetic metal powder and silicon dioxide powder. Even if the mixture is stirred and mixed, the sintering preventing material spreads between the soft magnetic metal powders, and sintering of the silicon dioxide powder can be prevented.

  In addition, by setting the average particle size of the sintering preventing material to 7 μm to 30 μm, segregation of the soft magnetic metal powder and the sintering preventing material and sintering of the silicon dioxide powder are surely prevented, and the powder magnetic core is used. The quality and productivity of the powder can be further improved.

It is a schematic block diagram of the powder manufacturing apparatus for dust cores according to the first embodiment of the present invention. It is a longitudinal cross-sectional view of a rotary furnace. It is an image figure which shows the cross section of a sintering prevention material. It is an image figure which shows the positional relationship of carbon-iron metal powder and a sintering prevention material. It is an image figure of a siliconization process. It is an image figure which shows the cross section of the powder for dust cores. It is a figure which shows the conditions of the siliconization process in a comparative example and Example 1. FIG. It is a figure which shows the yield rate of a comparative example and Example 1. FIG. It is a graph which shows the result of having investigated the distance of the silicon osmosis | permeation layer formed toward the center part of iron powder from the surface of iron powder about the powder for powder magnetic cores of Example 1 according to powder for powder magnetic cores. It is a graph which shows the measurement aspect of an average particle diameter. It is a graph which shows the relationship between the average particle diameter of the sintering prevention material in Example 2, and a yield. It is a longitudinal cross-sectional view of the rotary furnace which concerns on 2nd Embodiment of this invention and is used with the powder manufacturing apparatus for powder magnetic cores. It is the A section enlarged view of FIG. It is an image figure of a siliconization process. It is a graph which shows the result of having investigated the distance of the silicon osmosis | permeation layer formed toward the center part of iron powder from the surface of iron powder according to the powder for powder magnetic cores. It is an image figure of the process heated while stirring mixed powder. It is drawing which made the micrograph of the powder for powder magnetic cores obtained when heating mixed powder while stirring. It is a conceptual diagram of the apparatus heated while stirring mixed powder.

  Next, one embodiment of a powder magnetic core powder manufacturing method according to the present invention will be described with reference to the drawings.

(First embodiment)
<Schematic configuration of powder for powder magnetic core>
FIG. 6 is an image view showing a cross section of the powder 28 for dust core.
The powder 28 for dust core has a silicon permeation layer 25 formed on the surface layer of the iron powder 24 in order to ensure insulation of the iron powder 24 (an example of soft magnetic metal powder), and further covers the surface of the iron powder 24. Thus, the silicone coating layer 27 is formed.

<Schematic configuration of powder manufacturing apparatus for dust core>
FIG. 1 is a schematic configuration diagram of a powder magnetic core manufacturing apparatus 1 according to an embodiment of the present invention.
The powder magnetic core manufacturing apparatus 1 is used in a siliconizing treatment process in which a silicon permeation layer 25 is formed on the surface layer of the iron powder 24 among the processes of manufacturing the powder 28 for a powder magnetic core.

  The powder manufacturing apparatus 1 for a dust core includes a hollow cylindrical rotary furnace 2. The rotary furnace 2 is made of a material (for example, SUS310S) that has high thermal conductivity and is difficult to chemically react. The rotary furnace 2 has rotary shafts 3 and 4 fixed to both end faces, and is rotatably held by a support (not shown) via the rotary shafts 3 and 4. A motor (not shown) is connected to the rotary shaft 3 so as to apply a rotational force to the rotary furnace 2 via the rotary shaft 3.

  In the rotary furnace 2, a mixed powder 20 obtained by stirring and mixing a carbon-iron metal powder 21 (an example of a soft magnetic metal powder) and a sintering preventing material 22 (an example of a silicon dioxide holding member) for preventing sintering is mixed. An inlet 5 for feeding and an outlet 6 for taking out the powder 26 subjected to the siliconization treatment are provided. A heater 7 is wound around the outer peripheral surface of the rotary furnace 2 so that the mixed powder 20 is heated through the rotary furnace 2.

  A flow path is provided inside the rotary shafts 3 and 4. The flow path of the rotating shaft 3 is connected to an atmospheric gas supply source (not shown) and supplies the atmospheric gas into the rotary furnace 2. The flow path of the rotating shaft 4 is connected to an exhaust pump (not shown) and exhausts the gas in the rotary furnace 2.

FIG. 2 is a longitudinal sectional view of the rotary furnace 2.
A plurality (three in this case) of stirring plates 10 are fixedly provided on the inner wall of the rotary furnace 2. The stirring plate 10 is a linear plate material made of a material (for example, SUS310S) that has high thermal conductivity and is difficult to chemically react. The stirring plate 10 has substantially the same length as the entire length of the rotary furnace 2. The stirring plate 10 is parallel to the axis of the rotary furnace 2, is evenly arranged in the circumferential direction of the vertical section of the rotary furnace 2, and stands up toward the center of the rotary furnace 2. As a result, when the rotary furnace 2 is rotated by a motor (not shown), the material supplied to the rotary furnace 2 can be scooped up and dropped one after another by the stirring plate 10 and stirred. Inside the rotary furnace 2, a temperature sensor 8 for measuring the temperature in the rotary furnace 2 is attached.

<Configuration of anti-sintering material>
FIG. 3 is an image view showing a cross section of the sintering preventing material 22.
The sintering preventing material 22 is coated on the outer peripheral surface with silicon dioxide powder 23. The silicon dioxide powder 23 is fixed to the entire outer peripheral surface of the sintering preventing material 22 with an adhesive. The sintering preventing material 22 preferably has an average particle size smaller than the average particle size of the carbon-iron metal powder 21. In general, the kinetic energy of the powder is affected by the particle size, and by making the average particle size of the sintering preventing material 22 smaller than the average particle size of the carbon-iron metal powder 21, the sintering preventing material 22 It is because it becomes easy to enter between the carbon-iron metal powders 21 and contact between the iron powders can be prevented. Moreover, it is preferable that the sintering preventing material 22 does not react with the carbon-iron metal powder 21 (iron powder 24) and the silicon dioxide powder 23. This is because the amounts of the carbon-iron metal powder 21 and the silicon dioxide powder 23 are controlled so that the silicon permeation layer 25 can be appropriately formed on the iron powder 24. In this embodiment, aluminum powder (Al ₂ O ₃ powder) is used for the sintering preventing material 22.

  On the other hand, the silicon dioxide powder 23 has an average particle size smaller than the average particle size of the anti-sintering material 22 and is adhered to the entire surface of the anti-sintering material 22 with almost no gap. The silicon dioxide powder 23 preferably has an average particle size of 1 μm or less. This is because when the average particle diameter of the silicon dioxide powder 23 exceeds 1 μm, the contact area with the carbon-iron metal powder 21 becomes small, and the reaction rate of diffusing and penetrating the surface of the carbon-iron metal powder 21 becomes slow. In particular, the silicon dioxide powder 23 preferably has an average particle diameter of 50 nm in order to facilitate diffusion and penetration into the carbon-iron metal powder 21.

<Method for producing powder for powder magnetic core>
Next, a method for producing a powder for a dust core will be described.
First, the mixed powder 20 obtained by stirring and mixing the carbon-iron metal powder 21 and the sintering preventing material 22 is charged into the rotary furnace 2 from the charging port 5. Then, an atmospheric gas (for example, a mixed gas of 30% hydrogen (H ₂ ) with respect to the supply amount of argon (Ar) and Ar) is supplied to the rotary furnace 2 and exhaust is started. Then, the rotary furnace 2 is heated by the heater 7.

  Simultaneously with the start of heating, the rotary furnace 2 is rotated by driving a motor (not shown). As the rotating furnace 2 rotates, as shown in FIG. 2, the mixed powder 20 is scooped up from the bottom to a predetermined height by the stirring plate 10, and is slid down to the bottom, and the carbon-iron metal powder 21 and the sintering preventing material 22. Are mixed and stirred, and a siliconizing treatment is performed. During this siliconization process, the temperature in the rotary furnace 2 is feedback-controlled based on temperature measurement data detected by the temperature sensor 8 and maintained at 1000 ° C.

  As shown in FIG. 5, the mixed powder 20 heated in the rotary furnace 2 causes an oxidation-reduction reaction between the silicon dioxide powder 23 and the carbon-iron metal powder 21 coated on the surface of the sintering preventing material 22, The silicon element is desorbed from the silicon dioxide powder 23, and carbon monoxide (CO) gas is generated. The detached silicon element permeates from the surface of the carbon-iron metal powder 21 and diffuses into the carbon-iron metal powder 21 to form a silicon permeation layer 25 on the surface layer of the carbon-iron metal powder 21. As the heating time elapses, silicon element is concentrated on the surface layer of the carbon-iron metal powder 21. On the other hand, the generated CO gas is exhausted to the outside of the rotary furnace 2 through the flow path in the rotary shaft 4 and is replaced with the processing gas. Therefore, the pressure and atmosphere in the rotary furnace 2 are kept constant. Such a siliconization treatment is performed in a desorption / diffusion atmosphere in which the reaction generation rate at which silicon element is desorbed from the silicon dioxide powder 23 is faster than the diffusion rate at which it penetrates and diffuses into the surface layer of the carbon-iron metal powder 21. The carbon-iron metal powder 21 approaches the high-purity iron powder 24 as the oxidation-reduction reaction proceeds and the carbon element is removed, and the powder 26 subjected to the siliconization treatment is generated.

Here, the positional relationship between the carbon-iron metal powder 21 and the sintering preventing material 22 when the mixed powder 20 is stirred and mixed will be described. FIG. 4 is an image diagram showing a positional relationship between the carbon-iron metal powder 21 and the sintering preventing material 22.
By stirring, the carbon-iron metal powder 21 is prevented from entering the other carbon-iron metal powder 21 and coming into contact with the other carbon-iron metal powder 21. More specifically, since the sintering preventing material 22 has an average particle size smaller than that of the carbon-iron metal powder 21, it enters between the carbon-iron metal powders 21 and the carbon-iron metal powders 21 come into contact with each other. prevent. The entire surface of the sintering preventing material 22 is coated with silicon dioxide powder 23. Therefore, the carbon-iron metal powder 21 whose outer peripheral surface is covered with the sintering preventing material 22 is in contact with the silicon dioxide powder 23 on the entire surface. Moreover, due to the stirring accompanying the rotation of the rotary furnace 2, the sintering preventing material 22 that contacts the surface of the carbon-iron metal powder 21 is constantly replaced, and the silicon dioxide powder 23 continues to be supplied to the surface of the carbon-iron metal powder 21. Therefore, the silicification reaction proceeds uniformly on the surface of each carbon-iron metal powder 21 (iron powder 24).

  When the mixed powder 20 is heated and mixed with the heater 7, the silicon dioxide powder 23 is first diffusion bonded to the surface of the carbon-iron metal powder 21 and gradually diffuses and penetrates into the surface of the carbon-iron metal powder 21. To go. The silicon dioxide powder 23 coated on the sintering preventing material 22 is heated by the heater 7 mounted on the outer peripheral surface of the rotary furnace 2, but the sintering preventing material 22 prevents the silicon dioxide powder 23 from sintering. It is out. Therefore, the carbon-iron metal powder 21 is not combined with the other carbon-iron metal powder 21 through the silicon dioxide powder 23 diffusion-bonded to the surface. Further, the sintering preventing material 22 is not bonded via the silicon dioxide powder 23. That is, even if the mixed powder 20 is stirred and mixed while heating, secondary particles are not generated.

  When the rotary furnace 2 is rotated while being heated for a predetermined heating time (for example, 1 hour), the supply and exhaust of the atmospheric gas, the heating by the heater 7, and the rotation of the rotary furnace 2 are stopped. The heating time is preferably set so that the distance X1 of the silicon-penetrating layer 25 from the surface of the iron powder 24 is less than 0.15 times the diameter D of the iron powder 24 (see FIG. 6). This is because the hardness of the powder core powder 28 can be adjusted so as not to lower the magnetic core density and magnetic flux density of the powder magnetic core obtained by powder molding the powder core powder 28.

  After confirming that the internal temperature of the rotary furnace 2 has decreased to room temperature, the operator takes out the powder 26 (see FIG. 5) subjected to the siliconization treatment from the outlet 6 of the rotary furnace 2.

  The powder 26 that has been subjected to the siliconization treatment as described above is subjected to a coating treatment. In the coating treatment, for example, a powder 26 that has been subjected to a siliconization treatment in a solution obtained by dissolving a silicone resin in ethanol is added and stirred. After stirring for a predetermined time, the ethanol is further stirred while evaporating, and the silicone resin is fixed to the surface of the powder 26 subjected to the siliconization treatment. Thereby, the powder 28 for powder magnetic core (refer FIG. 6) by which the silicon penetration layer 25 was covered with the silicone coating layer 27 is produced | generated.

<Method of manufacturing a dust core>
Next, a method for producing a dust core by compacting the dust core powder 28 produced as described above will be described.
The powder 28 for powder magnetic core is filled in a punch die having a cavity of a predetermined shape such as a motor core, and the powder 28 for powder magnetic core 28 is pressed by applying a predetermined pressure and a predetermined heat. The pressure-molded body is taken out of the cavity and subjected to a high-temperature annealing process in order to remove processing distortion generated inside. Thereby, the dust core of a predetermined shape is manufactured. The dust core produced in this way uses the powder 28 for the dust core that forms the silicon permeation layer 25 on the surface layer of the iron powder 24 within a range of 0.15 times or less the diameter D of the iron powder 24. Therefore, the powder magnetic core powder 28 is appropriately deformed during pressure molding, and the magnetic core density and magnetic flux density are high.

[Example 1]
FIG. 7 is a diagram showing the conditions of the siliconizing treatment in the comparative example and Example 1.
In Example 1, the siliconizing treatment was performed under the following conditions. A carbon-iron metal powder (iron powder) having an average particle diameter of 150 to 212 μm and a specific gravity of 7.8, an average particle diameter of 1 μm and a specific gravity of 2.2, and having an average particle diameter of 50 nm and a specific gravity on the surface Al ₂ O ₃ powder (sintering preventive material) having an average particle diameter of 1 μm coated with 2.2 g / cm ³ of silicon dioxide powder is composed of 97 to 95% by weight of iron powder and 3 to 5% by weight of silicon dioxide powder. And mixing the mixed powder into a rotary furnace, and then supplying a mixed gas of 30% hydrogen (H ₂ ) to the rotary furnace with respect to the supply amount of argon (Ar) and Ar. Exhaust from. Then, the rotary furnace is heated to 1000 ° C. The rotary furnace is continuously rotated at a rotational speed of 25 rpm for 1 hour of the processing time while being maintained at 1000 ° C. Thereafter, heating and rotation of the rotary furnace are stopped, and the siliconization process is completed.

On the other hand, in the comparative example, the siliconizing treatment was performed under the following conditions. 95-97% by weight of iron powder having an average particle size of 150 to 212 μm and a specific gravity of 7.8, and silicon dioxide powder having an average particle size of 50 nm and a specific gravity of 2.2 were stirred and mixed at a ratio of 3 to 5% by weight. After the mixed powder is put into the rotary furnace, a mixed gas of 30% hydrogen (H ₂ ) is supplied to the rotary furnace with respect to the supply amount of argon (Ar) and Ar, and the rotary furnace is heated at the same time as the rotary furnace is rotated. Let The rotary furnace is continuously rotated for 1 hour during the processing time while maintaining the internal temperature at 1000 ° C. Thereafter, heating and rotation of the rotary furnace are stopped, and the siliconization process is completed.

<About the yield of Example 1 and a comparative example>
The inventor examined the yield of Example 1 and the comparative example. FIG. 8 shows the experimental results. Here, as the yield is closer to 0%, the generation rate of secondary particles generated by sintering the silicon dioxide powder is higher, and as the yield is closer to 100%, the generation rate of secondary particles is lower (in powder form). )
The yield of the comparative example was about 5%. That is, in the comparative example, the mixed powder of the iron powder and the silicon dioxide powder was almost converted into secondary particles when the siliconization treatment was performed.
On the other hand, the yield of Example 1 was almost 100%. That is, in Example 1, even if the mixed powder of the iron powder and the anti-sintering material coated with the silicon dioxide powder on the surface is subjected to the same siliconization treatment as in the comparative example, it is hardly converted into secondary particles. A fine powdery magnetic core powder could be produced by forming a silicon permeation layer on the surface of each iron powder.

  From the above experimental results, during the silicidation treatment, a mixture of an anti-sintering material coated with silicon dioxide powder and carbon-iron metal powder was put into the rotary furnace, and then the rotary furnace was heated to the processing temperature. It was proved that, if rotated in this state, a silicon-penetrating layer can be formed on the iron powder without generating secondary particles, and the productivity of the powder for powder magnetic core is improved.

<Regarding the uniformization of the silicon-permeable layer>
The inventors took out 10 powders at random from Example 1, cut them, and observed the cut surfaces with an electron microscope. And the distance of the silicon osmosis | permeation layer formed toward the center part of iron powder from the surface of iron powder was measured according to the powder for powder magnetic cores. The measurement results are shown in FIG.

  As shown in FIG. 9, iron powder and silicon dioxide powder all cause a redox reaction in all of the randomly extracted powders. Each powder was converged in a range where the Si concentration on the surface of the iron powder was 4.0% or more and 6.0% or less. Each powder had substantially the same rate of decrease in Si concentration from the surface of the iron powder toward the center of the iron powder. Furthermore, each powder has a distance from the surface of the iron powder of the silicon-permeable layer (thickness of the silicon-permeable layer) of about 20 μm, and the distance from the surface of the iron powder of the silicon-permeable layer is made uniform between the powders. It was.

  Therefore, at the time of the siliconization treatment, a mixture of an anti-sintering material whose surface is coated with silicon dioxide powder and a carbon-iron metal powder is put into a rotary furnace, and then the rotary furnace is rotated while being heated to the processing temperature. As a result, it was proved that a powder for a magnetic core having a uniform silicon permeation layer formed on the surface layer of each iron powder can be produced, and the quality of the powder for a powder magnetic core is improved.

[Example 2]
Next, Example 2 will be described. In Example 2, the siliconizing treatment was performed in the same procedure as in Example 1 while changing only the average particle size of the sintering preventing material among the experimental conditions of Example 1. Therefore, also in Example 2, the average particle diameter of the carbon-iron metal powder (iron powder) is 150 to 212 μm, and the average particle diameter of the silicon dioxide powder is 50 nm.

<Measurement of average particle size>
First, the average particle size measurement mode implemented by the inventors will be described with reference to FIG. The numerical value of “average particle diameter” in the present specification is determined by this measurement mode.
The inventors prepared several sieves with different openings. Then, the particles to be measured were passed through each sieve. At this time, as shown in FIG. 10, the weight percentage (% by weight) of the particles that passed through the openings was measured for each sieve. The diameter of the openings when the weight percentage of the particles that passed through the openings was 50% of the total (see the one-dot chain line in the figure) was taken as the average particle diameter of the particles.

<Relationship between average particle size and yield>
The relationship between the average particle size of the sintering preventing material obtained in Example 2 and the yield will be described with reference to FIG.
As shown in FIG. 11, it was found that when the average particle size of the sintering preventing material is 30 μm or more, the yield is significantly reduced. This is because when the average particle size of the sintering preventing material is too large for the average particle size of iron powder of 150 to 212 μm, the iron powder and the sintering preventing material are not uniformly mixed, and segregation occurs. This is probably because of this. In this state where the iron powder and the anti-sintering material are segregated, the silicon dioxide powder coated on the surface of the anti-sintering material is less likely to cause an oxidation-reduction reaction with the iron powder, resulting in a silicidation reaction rate and yield. Decreasing problems will occur. Therefore, it is preferable that the average particle diameter of the sintering preventing material is 30 μm or less (about 1/5 or less of the average particle diameter of iron powder in terms of ratio).

  On the other hand, it was found that even when the average particle size of the sintering preventing material is 7 μm or less (particularly when it is 1 μm or less), the yield decreases. This is because if the average particle size of the sintering preventing material is too small for the average particle size of the silicon dioxide powder, the surface of the sintering preventing material is not closely coated with the silicon dioxide powder. This is thought to be due to the tendency of crystallization. When sintering is likely to occur in this way, the generation rate of secondary particles increases, resulting in a problem that yield decreases. Therefore, the average particle diameter of the sintering preventing material is preferably 7 μm or more (in terms of the ratio, it is about 140 times or more the average particle diameter of the silicon dioxide powder).

From the above experimental results, when the conditions of Example 2, that is, the average particle diameter of the iron powder is 150 to 212 μm and the average particle diameter of the silicon dioxide powder is 50 nm, the average particle diameter of the sintering inhibitor is 7 It can be confirmed that by setting the thickness to ~ 30 μm, segregation of iron powder and anti-sintering material and sintering of silicon dioxide powder can be surely prevented, and the quality and productivity of powder for powder magnetic core can be improved. It was.
In addition, when the conditions different from Example 2, that is, when the average particle diameter of iron powder or silicon oxide powder is changed, the selection range of the average particle diameter of the sintering preventing material may be changed according to the change ratio. . Specifically, with respect to the average particle diameter after the change of the iron powder or silicon oxide powder, the average particle diameter of the sintering preventing material is about 1/5 or less of the average particle diameter of the iron powder, and the silicon dioxide powder. What is necessary is just to select so that it may become about 140 times or more of the average particle diameter of. Thereby, segregation of the iron powder and the sintering preventing material and sintering of the silicon dioxide powder can be reliably prevented, and the quality and productivity of the powder for the dust core can be improved.

(Second Embodiment)
Subsequently, a second embodiment of the present invention will be described. FIG. 12 is a longitudinal sectional view of a rotary furnace 34 used in the powder core manufacturing apparatus 30 according to the second embodiment of the present invention. FIG. 13 is an enlarged view of a portion A in FIG. Note that the silicon dioxide film 33 shown in FIG. 12 is shown thicker than it actually is to make it easier to see in the drawing.
The present embodiment is different from the first embodiment in that the “silicon dioxide holding member” is configured by the inner wall of the rotary furnace 34 coated with the silicon dioxide powder 23, and the rest is the same as the first embodiment. The configuration is common. Here, the difference from the first embodiment will be mainly described, and the points common to the first embodiment will be denoted by the same reference numerals in the drawings, and the description will be omitted as appropriate.

  As shown in FIG. 12, the inner wall of the rotary furnace 34 and the surfaces of the stirring plate 10 and the temperature sensor 8 are covered with a silicon dioxide film 33. As shown in FIG. 13, the silicon dioxide film 33 is formed by fixing the silicon dioxide powder 23 on the inner wall of the rotary furnace 34 and the surfaces of the stirring plate 10 and the temperature sensor 8 so as not to be peeled off by an adhesive or the like.

  In such a powder magnetic core manufacturing apparatus 30, a mixed powder 32 of the carbon-iron metal powder 21 and the sintering preventing material 31 is input. The anti-sintering material 31 has the same configuration as the anti-sintering material 22 of the first embodiment except that the outer peripheral surface is not coated with the silicon dioxide powder 23. In the powder core manufacturing apparatus 30 for powder magnetic cores, heating by the heater 7 is started in a state where the rotary furnace 34 is not rotated after the supply and exhaust of the processing gas are started. When the temperature sensor 8 detects a predetermined processing temperature, the rotary furnace 34 is rotated, and the mixed powder 32 is stirred and mixed by the stirring plate 10.

  The carbon-iron metal powder 21 rolls on the silicon dioxide film 33 and comes into contact with the silicon dioxide powder 23 of the silicon dioxide film 33 at the time of stirring and mixing. The carbon-iron metal powder 21 and the silicon dioxide powder 23 are heated to a predetermined processing temperature (for example, 1000 ° C.) by the heat of the heater 7. For this reason, the carbon-iron metal powder 21 and the silicon dioxide powder 23 undergo a redox reaction, and the silicon element desorbed from the silicon dioxide powder 23 diffuses and permeates the surface of the carbon-iron metal powder 21 and also generates CO gas. To do. The carbon-iron metal powder 21 is put into the rotary furnace 34 together with the sintering preventing material 31. Therefore, even if the silicon dioxide powder 23 diffusion-bonded to the surface of the carbon-iron metal powder 21 is heated to a predetermined processing temperature, the silicon dioxide powder 23 is sintered with the other silicon dioxide powder 23 by the sintering preventing material 31. It is prevented. That is, the silicon dioxide powder 23 is sintered with the carbon-iron metal powder 21 as a nucleus, and secondary particles are prevented from growing like a snowman.

  Therefore, the powder magnetic core powder manufacturing apparatus 30 according to the present embodiment can prevent the generation of secondary particles during the siliconization treatment, and can improve the quality and productivity of the powder for the powder magnetic core.

The present invention is not limited to the above embodiment, and various applications are possible.
(1) For example, in the above embodiment, the anti-sintering materials 22 and 31 were using Al ₂ O ₃ powder, carbon - average particle diameter is smaller than the iron metal powder 21 (iron powder 24), carbon - ferrous metal As long as it does not react with the powder 21 (iron powder 24) or the silicon dioxide powder 23, the sintering preventing materials 22 and 31 are not limited thereto. For example, the sintering preventing materials 22 and 31 may be zirconia (ZrO ₂ ) or the like.
(2) For example, in the above embodiment, the inside of the rotary furnace 2 is filled with a mixed gas obtained by mixing Ar and 30% hydrogen with respect to the supply amount of Ar. It is good also as an atmosphere. Further, the siliconizing treatment may be performed in a reduced pressure atmosphere, or in a low gas partial pressure, specifically in a low carbon monoxide (CO) atmosphere or in a low nitrogen (N ₂ ) atmosphere. The processing gas may be another gas such as carbon gas as long as it promotes the oxidation-reduction reaction between the soft magnetic metal powder and the silicon immersion powder.
(3) For example, in the above embodiment, the stirring plate 10 fixed to the inner wall of the rotary furnace 2 is provided in a straight line parallel to the axis of the rotary furnace 2, but the stirring is fixed to the inner wall of the rotary furnace 2. The plate may be provided in a spiral shape. In this case, since the mixed powder supplied to the rotary furnace 2 is placed on a spiral stirring plate and gradually falls as the rotary furnace 2 rotates, the mixed powder at the bottom of the rotary furnace 2 is dropped from above. It becomes difficult to be compressed by the weight of the powder. As a result, it is possible to more reliably prevent the mixed powder from becoming secondary particles and improve the yield of the powder for the powder magnetic core.
(4) For example, in the said embodiment, although the carbon-iron metal powder 21 was raised as an example of a soft magnetic metal powder, Fe-Si alloy, Fe-Al alloy, Fe-Si-Al alloy, titanium, aluminum etc. were used. Soft magnetic metal powder may be used.

DESCRIPTION OF SYMBOLS 1,30 Powder manufacturing apparatus 2 for powder magnetic cores Rotary furnace 7 Heater 8 Temperature sensor 10 Stirring plate 20 Mixed powder 21 Carbon-iron metal powder (an example of soft magnetic metal powder)
22 Sintering prevention material 23 Silicon dioxide powder (an example of powder for siliconization)
24 Iron powder (an example of soft magnetic metal powder)
25 Silicon penetration layer 28 Powder 31 for powder magnetic core Sintering prevention material 33 Silicon dioxide film 34 Rotary furnace (silicon dioxide holding member)

Claims (8)

In the method for producing a powder for a dust core,
By bringing the soft magnetic metal powder and the silicon dioxide holding member coated with the silicon dioxide powder into contact with heating, an oxidation-reduction reaction between the soft magnetic metal powder and the silicon dioxide powder is generated. A method for producing a powder for a powder magnetic core, comprising diffusing and infiltrating the detached silicon element into the surface of the soft magnetic metal powder to form a silicon infiltration layer on the surface of the soft magnetic metal powder. In the manufacturing method of the powder for powder magnetic cores described in claim 1,
The silicon dioxide holding member is for preventing sintering, and is a sintering preventing material whose surface is coated with silicon dioxide powder,
A method for producing a powder for a powder magnetic core, comprising mixing the soft magnetic metal powder and the anti-sintering material and stirring with heating. In the manufacturing method of the powder for powder magnetic cores described in claim 1,
The silicon dioxide holding member is an inner wall of a rotary furnace coated with silicon dioxide powder,
A method for producing a powder for a powder magnetic core, wherein the soft magnetic metal powder and a sintering preventing material for preventing sintering are put into the rotary furnace and heated and stirred. In the manufacturing method of the powder for powder magnetic cores described in Claim 2 or Claim 3,
The method for producing a powder for a powder magnetic core, wherein the sintering preventing material has an average particle size smaller than that of the soft magnetic metal powder and does not react with the soft magnetic metal powder and the silicon dioxide powder. . In the manufacturing method of the powder for powder magnetic cores described in claim 4,
The method for producing a powder for a powder magnetic core, wherein an average particle diameter of the anti-sintering material is 7 μm to 30 μm. In the powder core production apparatus for dust core for producing the powder for dust core,
A rotary furnace made of a material that is rotatably held and has thermal conductivity;
Drive means for applying a rotational force to the rotary furnace;
Heating means for heating the rotary furnace,
The powder manufacturing apparatus for a powder magnetic core, wherein the rotary furnace is charged with a mixed powder of a soft magnetic metal powder and a sintering preventing material whose surface is coated with a silicon dioxide powder. In the powder magnetic core production apparatus according to claim 6,
The powder manufacturing apparatus for a powder magnetic core according to claim 1, wherein an average particle size of the anti-sintering material is 7 μm to 30 μm. In the powder core production apparatus for dust core for producing the powder for dust core,
A rotary furnace made of a material that is rotatably held and has thermal conductivity;
Drive means for applying a rotational force to the rotary furnace;
Heating means for heating the rotary furnace,
An apparatus for producing a powder for a dust core, wherein the rotary furnace has an inner wall coated with silicon dioxide powder, and a mixed powder of a soft magnetic metal powder and an anti-sintering material is introduced.

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