JP2011157591A - Method for producing powder for dust core and apparatus for producing powder for dust core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing powder for dust core, in which secondary particles are prevented from being produced upon siliconizing treatment, to improve the quality and productivity of the powder for dust core, and an apparatus for producing the powder for dust core. <P>SOLUTION: In the method for producing the powder 28 for dust core, the operation of heating a powdery mixture 23 of iron powder 24 and silicon dioxide powder 22 to a soaking temperature upon heating required for eliminating a silicon element from the silicon dioxide powder 22 so as to be diffused and penetrated in the iron powder 24, without stirring, and thereafter, stirring the powdery mixture 23 in a state where the heated powdery mixture 23 is cooled to a soaking temperature upon cooling at which the silicon dioxide powder 22 is not sintered, is repeatedly performed to form a silicon-penetrated layer 25 having the silicon element diffused and penetrated in the surface layer of the iron powder 24. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a dust core powder manufacturing method and a dust core powder manufacturing apparatus for manufacturing a dust core powder.

  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. 13, the powder 101 for the powder magnetic core diffuses and diffuses the silicon dioxide powder 103 from the surface of the iron powder 102, thereby forming a silicon-permeable 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 201, so that the silicon permeation layer 104 is formed.

  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, in the conventional powder magnetic core powder manufacturing method, as shown in FIG. 14, ten manufactured powder magnetic core powders 101 are taken out at random, and the silicon permeation layer 104 is iron powder from the surface of the iron powder 102. When the distance (distance from the surface) X2 formed toward the center of 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 increased greatly between the powders. It was scattered. 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. 14). Moreover, even if the powder is rich in silicification reaction (powder having a high silicidation reaction amount) (see the graph described by the thick solid line in FIG. 14), the Si concentration on the surface of the iron powder 102 is about 2.0. In addition, the distance (thickness) X2 from the surface of the iron powder 102 of the silicon permeation layer 104 is dispersed to 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 powder magnetic core powder manufacturing method, each iron powder 102 cannot be subjected to a uniform silicon reaction, and the silicon permeation layer 104 formed in each powder magnetic core powder 101 is made uniform. I couldn't. 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 powder manufacturing method for powder magnetic cores is that 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 was a lot of silicon dioxide powder 103 around the iron. In the 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 probably because the amount of permeation and diffusion is small, and the thickness and Si concentration of the silicon permeation layer 104 are small.

  Therefore, 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 as shown in FIGS. 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 powder magnetic core powder manufacturing method was carried out and the product was taken out from the furnace 105, as shown in FIG. 16, the iron powder 102 and the silicon dioxide powder 103 were hardened into dumplings into 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. Particularly, in the powder core manufacturing method, as shown in FIGS. 15 and 17, the furnace 105 is continuously rotated for 1 hour in a state where the mixed powder is heated to 1000 ° C., and the iron powder 102 and the silicon dioxide powder 103. The mixed powder 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 powder manufacturing method for powder magnetic cores, and the powder manufacturing apparatus for powder magnetic cores.

In order to solve the above problems, a method for manufacturing a powder magnetic core according to one aspect of the present invention includes a soft magnetic metal powder and silicon dioxide in a powder magnetic core manufacturing method for manufacturing a powder magnetic core powder. Heat treatment step of heating the mixed powder of the siliconizing powder to a soaking temperature necessary for heating so that silicon element is detached from the siliconizing powder and diffused and penetrates into the soft magnetic metal powder without stirring. And in the state of cooling the heated mixed powder to a cooling soaking temperature at which the powder for siliconization does not sinter, a stirring step at the cooling soaking temperature for stirring the mixed powder, By repeating the heat treatment step and the stirring step at the soaking temperature during cooling, a silicon permeation layer in which the silicon element is diffused and permeated into the surface layer of the soft magnetic metal powder is formed.
When the siliconizing powder is silicon dioxide powder, it is preferable that the soaking temperature during heating is 1000 ° C. and the soaking temperature during cooling is 700 ° C.

  In the method for producing a powder for a powder magnetic core according to the above aspect, the cumulative time obtained by accumulating the heating time in the heat treatment step is the distance from the surface of the soft magnetic metal powder of the silicon-penetrating layer is the diameter of the soft magnetic metal powder. It is preferable that it is equal to the processing time for heating the mixed powder so as to be less than 0.15 times.

  In order to solve the above problems, a powder magnetic core manufacturing apparatus according to one aspect of the present invention includes a soft magnetic metal powder and silicon dioxide in a powder magnetic core manufacturing apparatus for manufacturing a powder magnetic core powder. A mixed powder of powder for siliconization is charged, and is held rotatably about an axis, and a driving force is applied to the rotary furnace in which a stirring member is erected on the inner wall. A motor, a heater for heating the rotary furnace, and a controller for controlling the heating operation of the heater and the driving of the motor, the controller desorbing silicon element from the siliconization powder and When heating the rotary furnace to a soaking temperature required for diffusion and penetration into the soft magnetic metal powder, the motor is stopped and the rotary furnace is stopped, while the heated mixed powder is immersed in the immersion powder. The silicon powder does not sinter When cooling to the cooling time of soaking temperature, the drives the motor, the operation of rotating the rotary furnace, but for repeated.

  The powder manufacturing apparatus for a powder magnetic core according to the above aspect includes a temperature sensor that measures an internal temperature of the rotary furnace, and the controller determines whether the internal temperature of the rotary furnace is based on temperature measurement data of the temperature sensor. It is preferable to feedback control the heating operation of the heater so as to stabilize the soaking temperature during heating.

The powder magnetic core powder manufacturing method and the powder magnetic core powder manufacturing apparatus according to the above aspect are a mixture of a soft magnetic metal powder and silicon dioxide powder containing silicon dioxide. Heating to a soaking temperature required for diffusion and penetration into the magnetic metal powder (for example, when the siliconizing powder is a silicon dioxide powder, the soaking temperature is preferably 1000 ° C.). When doing so, the rotary furnace is stationary and the mixed powder is not stirred. Therefore, at the time of this heat treatment, the siliconizing powder is not sintered, and only the process of diffusing and penetrating from the surface of the soft magnetic metal powder by desorption of silicon element from the siliconizing powder proceeds. Thereafter, a soaking temperature at which the siliconized powder does not sinter the heated mixed powder (for example, when the siliconized powder is a silicon dioxide powder, the soaking temperature at cooling may be 700 ° C. The mixed powder is agitated by rotating the rotary furnace in the cooled state. In this way, since the mixed powder is cooled to the soaking temperature during cooling and then the mixed powder is heated, the powder for siliconization is not pressurized and sintered during stirring. Then, after the cooling process, the heating process is performed again. By stirring the mixed powder during the cooling treatment, the silicon powder is uniformly attached to the surface of the soft magnetic metal powder. During the heat treatment, the silicon element is uniformly diffused and penetrated into each soft magnetic metal powder. The distance from the surface of the soft magnetic powder and the silicon concentration of the silicon permeation layer formed on the surface layer of the powder become uniform. Therefore, according to the powder magnetic core powder manufacturing method and the powder magnetic core powder manufacturing apparatus of the above aspect, secondary particles are not generated during the siliconization treatment, so that the quality and productivity of the powder for the powder magnetic core can be improved. Can do.

  In the method for producing a powder for a powder magnetic core according to the above aspect, the cumulative time obtained by accumulating the heating time in the heat treatment step is 0.15 of the diameter of the soft magnetic metal powder. Since it is equal to the processing time for heating the mixed powder so as to be less than twice, the hardness of the powder for powder magnetic core can be adjusted so as not to lower the magnetic core density and magnetic flux density of the powder magnetic core.

  The powder manufacturing apparatus for a powder magnetic core according to the above aspect includes a temperature sensor that measures the internal temperature of the rotary furnace, and the controller uses the temperature measurement data of the temperature sensor to determine whether the internal temperature of the rotary furnace is a soaking temperature during heating. As the heating operation of the heater is feedback controlled so that it is stable, the soaking temperature during heating in each heating process is controlled to a constant level even when heating and cooling processes are repeated. Can be prevented.

It is a schematic block diagram of the powder manufacturing apparatus for dust cores according to the embodiment of the present invention. It is a longitudinal cross-sectional view of a rotary furnace. It is a figure explaining a siliconization process, Comprising: The mixed powder injection | throwing-in process is shown. It is a figure explaining a siliconization process, Comprising: A heat processing process is shown. It is an image figure of a silicification reaction. It is a figure explaining a siliconization process, Comprising: A heater removal process is shown. It is a figure explaining a siliconization process, Comprising: The stirring process at the time of soaking | uniform-heating temperature is shown. It is an image figure which shows the cross section of the powder for dust cores. It is a figure for demonstrating the silicon immersion reaction in the powder manufacturing method for dust cores. It is a figure which shows the conditions of the siliconization process in a comparative example and an Example. It is a figure which shows the yield rate of a comparative example and an Example. 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 an Example according to powder for powder magnetic cores. 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.

<Schematic configuration of powder for powder magnetic core>
FIG. 8 is an image diagram showing a cross section of the powder 28 for a powder magnetic core.
The powder 28 for the powder magnetic core is an oxidation-reduction between the carbon-iron metal powder 21 and the silicon dioxide powder 22 (an example of a siliconizing powder) in order to ensure insulation of the iron powder 24 (an example of a soft magnetic metal powder). A silicon permeation layer 25 is formed on the surface layer of the iron powder 24 by the reaction. And the powder 28 for powder magnetic cores is formed with a silicone coating layer 27 so as to cover the surface of the iron powder 24, and the insulation is further enhanced.

<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 the support columns 5 and 6 via the rotary shafts 3 and 4. A motor 7 is connected to the rotary shaft 3, and a rotational force is applied to the rotary furnace 2 through the rotary shaft 3. The motor 7 is connected to the controller 8, and is controlled for a rotation operation (rotation amount, rotation speed, rotation time, etc.) for rotating the rotary furnace 2 and a rotation stop operation for stopping the rotation of the rotary furnace 2.

  The rotary furnace 2 is provided with an opening / closing door 9 that can be opened and closed. In the rotary furnace 2, powder is supplied and taken out via the open / close door 9. On the inner wall of the rotary furnace 2, a plurality of (here, three) stirring plates 10 made of a straight plate material are fixed. 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 the motor 7, the powder supplied inside can be scooped up and dropped one after another by the stirring plate 10 and stirred.

  Inside the rotating shaft 4, two flow paths are formed along the axis of the rotating shaft 4. A supply pipe 11 for supplying a processing gas for generating an atmosphere during the silicidation process is connected to one flow path of the rotary shaft 4, and gas is exhausted from the rotary furnace 2 to the other flow path. The exhaust pipe 16 is connected. The supply pipe 11 is provided with a supply valve 13 for controlling the supply amount of the processing gas supplied from the gas supply source 12. The exhaust pipe 16 is provided with an exhaust valve 17 for controlling an exhaust amount for exhausting gas from the rotary furnace 2. The supply valve 13 and the exhaust valve 17 are connected to the controller 8 and the valve opening degree is controlled.

FIG. 2 is a longitudinal sectional view of the rotary furnace 2.
A heater 14 is attached to the outer peripheral surface of the rotary furnace 2 so that the powder in the rotary furnace 2 can be heated. The heater 14 includes a first heater member 14A and a second heater member 14B. The heater 14 is detached from the rotary furnace 2 by dividing the first and second heater members 14A and 14B, and the powder in the rotary furnace 2 can be cooled to the outside air. A temperature sensor 15 for measuring the temperature in the rotary furnace 2 is attached to the inner wall of the rotary furnace 2. The first and second heater members 14 </ b> A and 14 </ b> B and the temperature sensor 15 are connected to the controller 8. The controller 8 controls the heating operation of the first and second heater members 14A and 14B so as to feedback control the inside of the rotary furnace 2 to a predetermined temperature based on the measured temperature data measured by the temperature sensor 15. Further, the controller 8 controls the connecting operation and the dividing operation of the first and second heater members 14A and 14B, and controls the heating and cooling of the mixed powder 23.

<Method for producing powder for powder magnetic core>
Next, a method for producing a powder for a dust core will be described. FIG. 3 is a diagram for explaining the siliconizing treatment and shows a mixed powder charging step. FIG. 4 is a diagram for explaining the siliconization treatment and shows a heat treatment step. FIG. 5 is an image diagram of the silicon immersion reaction. FIG. 6 is a diagram for explaining the siliconizing process and shows a heater removing step. FIG. 7 is a view for explaining the siliconization treatment and shows a stirring step at the time of cooling soaking temperature. FIG. 8 is an image diagram showing a cross section of the powder 28 for a powder magnetic core. FIG. 9 is a diagram for explaining a silicon immersion reaction in the method for producing a powder for a powder magnetic core.
First, the silicon dioxide powder 22 is added to the carbon-iron metal powder 21 and mixed and stirred to adhere the silicon dioxide powder 22 to the outer peripheral surface of the carbon-iron metal powder 21. Then, as shown in FIG. 3, the open / close door 9 of the rotary furnace 2 is opened, and the mixed powder 23 of the carbon-iron metal powder 21 and the silicon dioxide powder 22 is put into the rotary furnace 2 to seal the open / close door 9. .

  Then, a siliconization process is performed on the mixed powder 23. As shown in FIG. 9, the siliconization treatment of the present embodiment adjusts the internal temperature of the rotary furnace 2 to the soaking temperature during heating and the soaking temperature during cooling, and the internal temperature of the rotary furnace 2 is equal to the soaking temperature during cooling. Only when it is, the rotary furnace 2 is rotated and the mixed powder 23 is stirred and mixed.

More specifically, the controller 8 opens the supply valve 13 and the exhaust valve 17, and performs processing for promoting the oxidation-reduction reaction of the carbon-iron metal powder 21 and the silicon dioxide powder 22 from the gas supply source 12 to the rotary furnace 2. A gas (here, a mixed gas of argon (Ar) and hydrogen (H ₂ )) is supplied. Then, as shown in FIG. 4, the controller 8 attaches the first and second heater members 14 </ b> A and 14 </ b> B to the outer peripheral surface of the rotary furnace 2, and the first and second heaters are stationary in a state where the rotary furnace 2 is not rotated. The mixed powder 23 is heated via the rotary furnace 2 by the members 14A and 14B. The controller 8 constantly measures the internal temperature of the rotary furnace 2 with the temperature sensor 15. When the controller 8 detects from the temperature measurement data of the temperature sensor 15 that the internal temperature of the rotary furnace 2 has reached the soaking temperature during heating, the controller 8 keeps the rotary furnace 2 stationary without rotating. The heating operation of the first and second heater members 14A and 14B is controlled so as to maintain the heat temperature. Here, the soaking temperature during heating refers to a temperature necessary for detaching the silicon element from the silicon dioxide powder 22 and allowing it to diffuse and penetrate into the iron powder 24.

  By this heat treatment, as shown in FIG. 5, the silicon dioxide powder 22 and the carbon-iron metal powder 21 generate an oxidation-reduction reaction, and the silicon element is desorbed from the silicon dioxide powder 22, and carbon monoxide (CO). Gas is generated. The detached silicon element penetrates from the surface of the iron powder 24 and diffuses into the iron powder 24 to form a silicon permeation layer 25 on the surface layer of the iron powder 24. As the heating time elapses, the silicon element is concentrated on the surface layer of the iron powder 24. On the other hand, the generated CO gas is discharged to the outside of the rotary furnace 2 through the exhaust pipe 16, and the pressure in the rotary furnace 2 is 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 22 is faster than the diffusion rate at which the silicon powder 24 penetrates and diffuses into the surface layer of the iron powder 24.

  Since the rotary furnace 2 is not rotated while the mixed powder 23 is heated to the soaking temperature during heating, the heated silicon dioxide powder 22 is not compressed by the stirring of the mixed powder 23. In addition, the heating time t1 for heating the mixed powder 23 at the soaking temperature is limited to a predetermined distance from the surface of the iron powder 24 in order to limit the movement of the substance between the silicon dioxide powders 22 and prevent sintering. (The distance of 0.15 times the diameter D of the iron powder 24) is set to a part of the processing time required. Therefore, at the time of the heat treatment, in the rotary furnace 2, only the silicon element desorbs and diffuses and penetrates from the silicon dioxide powder 22 adhering to the surface of the carbon-iron metal powder 21, and the silicon dioxide powder 22 is sintered. do not do.

  As shown in FIG. 9, when the internal temperature of the rotary furnace 2 is maintained at the heating soaking temperature for a predetermined heating time t1, the controller 8, as shown in FIG. 6, the first and second heater members 14A, 14B is divided and the heater 14 is removed from the rotary furnace 2. Then, the rotary furnace 2 is exposed to the outside air, and the internal temperature decreases. Also at this time, the rotary furnace 2 is not rotated. Therefore, the mixed powder 23 is not stirred and the silicon dioxide powder 22 is not sintered.

  As shown in FIG. 9, when the controller 8 detects that the internal temperature of the rotary furnace 2 has reached the soaking temperature during cooling based on the temperature measurement data of the temperature sensor 15, the controller 8 drives the motor 7, as shown in FIG. 7. Thus, the rotary furnace 2 is started to rotate. Here, the soaking temperature during cooling refers to a temperature at which the silicon dioxide powder 22 is not sintered. For example, the soaking temperature during cooling is desirably set to a temperature that is half the melting point of the silicon dioxide powder 22. Due to the rotation of the rotary furnace 2, the mixed powder 23 is scooped up from the bottom of the rotary furnace 2 to a predetermined height by the stirring plate 10, and then slid down from the stirring plate 10 inclined downward to the bottom of the rotary furnace 2. Is repeated and stirred. In this case, the mixed powder 23 at the bottom is pressed by the weight of the mixed powder falling from above, but since the mixed powder 23 is cooled to the soaking temperature at the time of cooling, the silicon dioxide powder 22 is added. The powder state is maintained without pressure sintering. Further, the iron powder 24 is not bonded via the silicon dioxide powder 22. That is, secondary particles are not generated when the mixed powder 23 is stirred. This cooling process is performed for a predetermined cooling time t2 necessary for uniformly adhering the silicon dioxide powder 22 to the surface of the iron powder 24 by stirring accompanying the rotation of the rotary furnace 2.

  As shown in FIG. 9, when the rotary furnace 2 is rotated while maintaining the internal temperature of the rotary furnace 2 at the cooling soaking temperature for a predetermined cooling time t <b> 2, the controller 8, as shown in FIG. 4, 7 is stopped, and the rotary furnace 2 is stopped. Then, the controller 8 reattaches the first and second heater members 14A and 14B to the outer peripheral surface of the rotary furnace 2, and rotates the first and second heater members 14A and 14B while the rotary furnace 2 is stationary. The furnace 2 and the mixed powder 23 are heated, and the above heat treatment is performed again. At the time of this heat treatment, the silicon dioxide powder 22 is uniformly attached to the surface of each iron powder 24 by stirring during the cooling treatment, so that the silicon immersion reaction proceeds uniformly on the surface of each iron powder 24.

  The controller 8 forms the silicon permeation layer 25 on the surface layer of the iron powder 24 by repeatedly performing the heat treatment and the cooling treatment. In this case, as shown in FIG. 9, the cumulative time obtained by accumulating the heating time t1 is such that the distance X1 from the surface of the iron powder 24 of the silicon infiltration layer 25 is less than 0.15 times the diameter D of the iron powder 24. As described above (see FIG. 8), it is desirable that the processing time for heating the mixed powder 23 is equal. In this way, by controlling the heat treatment in the siliconization treatment according to the treatment time required for the siliconization treatment, the magnetic core density and magnetic flux density of the dust core formed by dusting the dust core powder 28 are not reduced. In addition, the hardness of the powder 28 for powder magnetic core can be adjusted. When the heating process and the cooling process are finished, the controller 8 closes the supply valve 13 and the exhaust valve 17 while the rotary furnace 2 is stationary. After confirming that the internal temperature of the rotary furnace 2 has dropped to room temperature, the operator opens the door 9 and takes out the powder 26 (see FIG. 5) subjected to the siliconization treatment from the rotary furnace 2.

  The powder 26 subjected to the siliconization treatment increases the distance X1 of the silicon-penetrating layer 25 formed from the surface of the iron powder 24 toward the center of the iron powder 24 each time the heat treatment is repeated during the siliconization treatment. In addition, the silicon element concentration (Si concentration) of the silicon permeation layer 25 is increased. And by making the silicon dioxide powder 22 uniformly adhere to the surface of the iron powder 24 by stirring at the time of the cooling treatment, in each powder 26, the distance X1 from the surface of the iron powder 24 of the silicon permeation layer 25 is increased. The concentration of the silicon permeation layer 25 is progressing uniformly.

  In each heating process, the controller 8 feedback-controls the heating operation of the heater 14 based on the temperature measurement data of the temperature sensor 15 so that the internal temperature of the rotary furnace 2 is stabilized at the heating soaking temperature. To do. Therefore, even when the controller 8 repeats the heat treatment and the cooling treatment, the soaking temperature during heating in each heat treatment can be controlled to be constant, and the generation of secondary particles can be prevented.

  The powder 26 that has been subjected to the siliconization treatment as described above is subjected to a coating treatment. In the coating treatment, the powder 26 is put into a solution in which a silicone resin is dissolved in ethanol and stirred. After stirring for a predetermined time, stirring is performed while further evaporating ethanol, and the silicone resin is fixed to the surface of the powder 26. Thereby, the powder 28 for dust cores in which the silicon permeation layer 25 is covered with the silicone coating layer 27 is 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. Further, the powder magnetic core uses the powder 28 for the powder magnetic core in which the distance X1 of the silicon-permeable layer 25 from the surface of the iron powder 24 and the Si concentration distribution in the silicon-permeable layer 25 are made uniform among the powders. Insulation is ensured at the contact surface of the powder 28 for the powder magnetic core, eddy current is reduced, and the specific resistance is increased.

FIG. 10 is a diagram showing conditions for the siliconizing treatment in the comparative example and the example.
In the examples, the siliconizing treatment was performed under the following conditions. 95 to 97% by weight of 1.5% by weight carbon steel powder (iron powder) having an average particle size of 150 to 212 μm, and 3 to 5% by weight of silicon dioxide powder having an average particle size of 50 nm and a specific gravity of 2.2 After the mixed powder stirred and mixed at a ratio is put into the rotary furnace 2, 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. Heat in a stationary state. After the rotary furnace 2 is kept stationary, the internal temperature of the rotary furnace 2 is maintained at 1000 ° C., the soaking temperature during heating for 15 minutes, and then the internal temperature of the rotary furnace 2 reaches 700 ° C., the soaking temperature during cooling. The rotary furnace 2 is cooled to And in the state which maintained the internal temperature of the rotary furnace 2 at 700 degreeC, the rotary furnace 2 is rotated for 1 minute, and mixed powder is stirred. At this time, the rotary furnace 2 is rotated at a rotational speed of 25 rpm. Thereafter, the rotation of the rotary furnace 2 is stopped, and the rotary furnace 2 is heated to 1000 ° C. The above heat treatment and cooling agitation treatment are repeated four times each, and when the cumulative time of the heating time for performing the heat treatment reaches 1 hour of the treatment time, the heating and rotation of the rotary furnace 2 are stopped, and the siliconization treatment is finished. .

On the other hand, in the comparative example, the siliconizing treatment was performed under the following conditions. 95 to 97% by weight of 1.5% by weight carbon steel powder (iron powder) having an average particle size of 150 to 212 μm, and 3 to 5% by weight of silicon dioxide powder having an average particle size of 50 nm and a specific gravity of 2.2 After the mixed powder stirred and mixed at a ratio is put into the rotary furnace 2, 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. Heat in a stationary state. When the internal temperature of the rotary furnace 2 rises to the processing temperature of 1000 ° C., the rotary furnace 2 is rotated. The rotary furnace 2 is continuously rotated for 1 hour of the processing time while maintaining the internal temperature at 1000 ° C. Thereafter, heating and rotation of the rotary furnace 2 are stopped, and the siliconization process is completed.

<About the yield of an Example and a comparative example>
The inventor examined the yield of the example and the comparative example. 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, most of the mixed powder supplied to the rotary furnace 2 was converted into secondary particles.
On the other hand, the yield of the example was about 90%. In other words, in the example, the mixed powder supplied to the rotary furnace 2 hardly forms secondary particles, and a silicon-penetrating layer is formed on the surface of each iron powder to produce a fine powdery powder magnetic core powder. did it.

  From the above experimental results, during the silicidation treatment, if the internal temperature of the rotary furnace 2 is lowered to the cooling soaking temperature (700 ° C.) at which the silicon dioxide powder is not sintered, the rotary furnace 2 is rotated. It was proved that the mixed powder can be stirred 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 the examples, 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. 12, iron powder and silicon dioxide powder generate oxidation-reduction reactions 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 silicidation process, the rotary furnace 2 is heated to 1000 ° C. while the rotary furnace 2 is stationary, so that the silicification process proceeds, and then the rotary furnace 2 is cooled to 700 ° C., By repeating the operation of rotating the rotary furnace 2 and stirring and mixing the mixed powder, it is possible to produce a powder for a powder magnetic core in which the silicon permeation layer formed on the surface layer of each iron powder is uniform, and the quality of the powder for the powder magnetic core Proved to improve.

The present invention is not limited to the above embodiment, and various applications are possible.
(1) For example, in the above embodiment, the inside of the rotary furnace 2 is filled with a mixed gas obtained by mixing 30% hydrogen with Ar and 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.
(2) 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.
(3) For example, in the above embodiment, the first and second heater members 14A and 14B are removed from the rotary furnace 2 to cool the rotary furnace 2 to the outside, but the heater 14 is always attached to the rotary furnace 2, A cooling water channel may be provided in the rotary furnace 2. In this case, the control of the soaking temperature during cooling can be performed more easily and accurately.
(4) For example, in the above embodiment, the iron powder 24 is raised as an example of the soft magnetic metal powder, but Fe-Si alloy, Fe-Al alloy, Fe-Si-Al alloy, titanium, aluminum and the like are used as the soft magnetic metal. It may be a powder.
(5) For example, in the said embodiment, although the silicon dioxide powder 22 was mentioned as an example of the powder for silicification, the powder containing at least silicon dioxide, and the powder containing either one or both of a metal carbide or a carbon allotrope, Alternatively, a mixed powder obtained by mixing silicon powder or a powder containing silicon dioxide and a silicon carbide powder may be used as a siliconizing powder. Alternatively, an iron-based powder containing at least an oxygen element may be used as the soft magnetic powder, and a powder containing at least a carbon element may be used as the siliconizing powder.

DESCRIPTION OF SYMBOLS 1 Powder manufacturing apparatus for dust cores 2 Rotary furnace 7 Motor 8 Controller 10 Stirring plate 14 Heater 15 Temperature sensor 21 Iron powder (an example of soft magnetic metal powder)
22 Silicon dioxide powder (an example of siliconized powder)
23 Mixed powder 25 Silicon permeation layer 28 Powder for powder magnetic core

Claims (5)

In the method for producing a powder for a powder magnetic core for producing a powder for a powder magnetic core,
During the heating necessary for diffusing and infiltrating the soft magnetic metal powder by detaching the silicon element from the silicon powder without stirring the mixed powder of the silicon powder containing the soft magnetic metal powder and silicon dioxide. A heat treatment step of heating to a soaking temperature;
In the state where the heated powder mixture is cooled to a cooling soaking temperature at which the siliconization powder does not sinter, the stirring step is performed at the cooling soaking temperature for stirring the mixed powder.
By forming the silicon-penetrated layer in which the silicon element is diffused and permeated into the surface layer of the soft magnetic metal powder by repeatedly performing the heat treatment step and the stirring step at the soaking temperature at the time of cooling, the green compact is characterized in that Magnetic core powder manufacturing method. In the method for producing a powder for a powder magnetic core according to claim 1,
The cumulative time obtained by accumulating the heating time in the heat treatment step is such that the distance of the silicon-penetrating layer from the surface of the soft magnetic metal powder is less than 0.15 times the diameter of the soft magnetic metal powder. A method for producing a powder for a powder magnetic core, characterized by being equal to a processing time for heating the mixed powder. In the method for producing a powder for a powder magnetic core according to claim 1 or 2,
The siliconizing powder is silicon dioxide powder,
The soaking temperature during heating is 1000 ° C.,
The method for producing a powder for a powder magnetic core, wherein the soaking temperature during cooling is 700 ° C. In the powder manufacturing apparatus for the powder magnetic core for manufacturing the powder for the powder magnetic core,
A rotary furnace in which a mixed powder of siliconizing powder containing soft magnetic metal powder and silicon dioxide is charged, is held rotatably about an axis, and a stirring member is erected on an inner wall;
A motor for applying a driving force to the rotary furnace;
A heater for heating the rotary furnace;
A controller for controlling the heating operation of the heater and the driving of the motor;
When the controller heats the rotary furnace to a soaking temperature required for heating so that silicon element is desorbed from the siliconization powder and diffused and penetrates into the soft magnetic metal powder, the motor is stopped, While cooling the rotary furnace, when cooling the heated mixed powder to a cooling soaking temperature at which the siliconization powder does not sinter, the motor is driven to rotate the rotary furnace, A powder manufacturing apparatus for a powder magnetic core, characterized by being repeatedly performed. In the powder magnetic core manufacturing apparatus according to claim 4,
A temperature sensor for measuring the internal temperature of the rotary furnace,
The controller performs feedback control on the heating operation of the heater based on temperature measurement data of the temperature sensor so that the internal temperature of the rotary furnace is stabilized at the soaking temperature during heating. Powder manufacturing equipment for powder magnetic cores.

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