JP5101848B2 - Method for producing soft magnetic powder and dust core using the soft magnetic powder - Google Patents

Description

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

  Dust cores can be manufactured at high yields for products with small and complex shapes, and because the electrical resistance inside the core can be increased, they are used in a wide range of fields such as noise filters, transformers, choke coils or motor cores. ing. This powder magnetic core is produced as follows, for example. That is, a soft magnetic powder composed mainly of Fe coated with an insulating film is mixed with a small amount of an organic resin binder, filled into a predetermined mold, and press-molded at a predetermined pressure using, for example, a press molding machine. Form green powder core. Next, the green is heat treated at a predetermined temperature to release the molding distortion accumulated at the time of molding to obtain a desired dust core. When the dust core produced in this way is used in an AC electric field, it is necessary that the soft magnetic powder be sufficiently insulated from each other in order to suppress power loss due to eddy currents and heat generation of circuit components. Become.

Therefore, as a method of coating the surface of the soft magnetic powder with an insulating film, for example, a phosphate containing aluminum and a heavy metal containing potassium or ammonium are mixed while stirring pure iron powder in a tumbling flow granulator. An insulating film aqueous solution containing a chromium salt is sprayed and then taken out from the apparatus, and then the soft magnetic powder is heat-treated at a predetermined temperature in the atmosphere and further dried (Patent Document 1). ).
Japanese Patent Laid-Open No. 2003-272911 (for example, see the description of Example 1)

  However, when a soft magnetic powder having an insulating film obtained by the above method is used to produce a powder magnetic core by press molding, there is a problem that the insulating film is easily damaged by the pressure during molding and the workability is low. . If the insulating film is damaged by the pressure during molding, the electrical resistivity of the soft magnetic powder is lowered, and the power loss due to eddy current is increased.

  Therefore, in view of the above points, a first object of the present invention is to provide a method for producing a soft magnetic powder having high insulation and high workability. A second object of the present invention is to provide a dust core having a small power loss due to an eddy current and a high magnetic permeability and a high saturation magnetic flux density.

In order to solve the above problems, a main component F e, a manufacturing method of the soft magnetic powder of the present invention whose surface is covered with an insulating film, an oxidation step of oxidizing the surface of the soft magnetic powder, the Mg The metal evaporating material is placed in the processing chamber and heated to evaporate the metal evaporating material to form a metal vapor atmosphere in the processing chamber, and the soft magnetic powder is kept in the processing chamber in a state kept below the temperature in the processing chamber. A film forming process for selectively depositing and depositing a metal evaporation material on the surface of the soft magnetic powder according to a temperature difference between the processing chamber and the soft magnetic powder while moving the soft magnetic powder in the processing chamber; A heat treatment step of heating the soft magnetic powder deposited with the metal evaporation material under a predetermined temperature to reduce the oxide film formed in the oxidation step to form an oxide insulating film containing magnesium on the surface of the soft magnetic powder ; It is characterized by including

  According to this, when a metal evaporation material containing Mg is arranged in the processing chamber and then this processing chamber is heated, an Mg metal vapor atmosphere is formed in the processing chamber. Next, for example, when a soft magnetic powder containing Fe as a main component is exposed to an air atmosphere, oxygen is adsorbed and an oxide film is formed on the surface of the soft magnetic powder. To do. When this soft magnetic powder is put into a processing chamber in which a metal vapor atmosphere is formed, metal atoms in the metal vapor atmosphere selectively adhere and deposit only on the surface of the soft magnetic powder. At that time, if the substrate is held for a predetermined time while being moved in the processing chamber, a thin film of a metal evaporation material is formed over the entire surface of the soft magnetic powder. Next, when the soft magnetic powder with metal atoms including Mg deposited on the surface is heated, the soft magnetic powder is reduced and a strong insulating film made of, for example, magnesium oxide is formed on the surface of the soft magnetic powder. As a result, the surface is covered with a strong insulating film, so that the insulating film is hardly damaged and a soft magnetic material having high insulating properties and workability can be obtained.

  In order to promote the oxidation of the surface of the soft magnetic powder, it is desirable to include an oxidation step of oxidizing the surface of the soft magnetic powder prior to the film forming step.

  If the metal vapor atmosphere is saturated in the processing chamber, the metal evaporation material may be formed at a high speed.

  Further, if the metal evaporation material contains Al, the adhesion to the soft magnetic material may be improved.

  In order to solve the above-mentioned problems, a dust core according to claim 5 is formed by press-molding soft magnetic powder obtained by the manufacturing method according to any one of claims 1 to 4, and then heat treatment at a predetermined temperature. It is characterized by giving. By using a soft magnetic material coated with a strong insulating film, this strong insulating film plays a role as a lubricant, and at the time of manufacturing, the density becomes high and distortion is difficult to occur, and the electric resistivity is high, The power loss due to the eddy current can be reduced, and in addition, it has high magnetic permeability and high saturation magnetic flux density.

  As described above, in the method for producing a soft magnetic powder of the present invention, a soft magnetic material having high insulation and workability is obtained, and the dust core of the present invention has a small power loss due to eddy currents. In addition, it has the effect of having high magnetic permeability and high saturation magnetic flux density.

  Referring to FIGS. 1 and 2, reference numeral 1 denotes a processing apparatus suitable for carrying out the manufacturing method of the present invention. The processing apparatus 1 includes a vacuum chamber 11 having a substantially hexagonal cross section that constitutes a processing chamber 10. The vacuum chamber 11 is attached to a support means 2 composed of a pedestal 21 installed on the floor and support plates 22a and 22b provided at a predetermined interval and perpendicular to the pedestal 21.

  The rotating shafts 23a and 23b are provided with bearings (not shown) at predetermined height positions from the pedestals 21 of the supporting plates 22a and 22b so as to protrude toward the inside of the supporting plates 22a and 22b and on the same horizontal line. ), And one end of each of the rotating shafts 23a and 23b having the cooling means 231 is connected to the side walls 11a and 11b of the vacuum chamber 11, respectively. A pulley 24 is provided at the other end of one rotating shaft 23 a protruding from one support plate 22 a, and between this pulley 24 and a pulley 32 provided on a rotating shaft 31 of the motor 3 provided on the base 21. The belt V is hung. Accordingly, when the motor 3 is operated to rotate the rotation shafts 23a and 23b, the vacuum chamber 11 can rotate about the rotation shafts 23a and 23b at a predetermined rotation speed (for example, 1 rpm).

  On the outer periphery of the vacuum chamber 11, there is provided a stainless steel heat insulating material 41 provided with a reflection surface on the inner side so as to cover substantially the whole, and an electric heater having a nichrome filament is provided inside the heat insulating material 41. 42 is arranged to constitute the heating means 4. Then, after the vacuum chamber 11 is depressurized as described later, the processing chamber 10 can be heated to a predetermined temperature substantially uniformly by heating the vacuum chamber 11 with the heating means 4.

  Openings are respectively provided in the upper surface and the lower surface of the vacuum chamber 11, and open / close valves 5a and 5b are attached to the respective openings. Each of the on-off valves 5a and 5b is a butterfly valve having a known structure, for example, and has valve bodies 51 attached to the openings on the upper surface and the lower surface of the vacuum chamber 11, respectively. In the valve main body 51, a rotatable circular valve body and a valve seat on which the valve body is seated are provided. Then, a drive shaft (not shown) provided in the valve body 51 is operated manually or electrically, so that the valve body is located between the valve closing position where the valve body is seated on the valve seat and the valve opening position where the valve body is separated from the valve seat. It can be opened and closed by turning the valve body.

An exhaust pipe 6 or a hopper 7 provided with a coupling (not shown) at one end is detachably attached to the valve body 51 on the side facing the vacuum chamber 11. The other end of the bellows-like exhaust pipe 6 is connected to a vacuum exhaust means 61 including a turbo molecular pump, a cryopump, a diffusion pump, a rotary pump, and the like. Then, when the exhaust pipe 6 is connected to the valve body 51 of one of the on-off plates 5b at the closed position of both the on-off valves 5a, 5b, the vacuum exhaust means 61 is activated and the on-off valve 5b is opened, the processing chamber 10 is opened. The pressure can be reduced to a predetermined pressure (eg, 1 × 10 ⁻⁵ Pa).

On the other hand, the hopper 7 is made of a metal that can be hermetically sealed, and the inside constitutes the preparation chamber 70. The chute portion 71 below the hopper 7 is provided with another open / close valve 72 including a rotatable circular valve body and a valve seat on which the valve body is seated. 70 is sealed. When the raw material described later is put into the processing chamber 10, after the raw material is stored in the hopper 70, an exhaust pipe (not shown) is connected to the tip of the chute portion 71 to operate the vacuum exhaust means and open the on-off valve 72. Then, the preparation chamber 70 is depressurized to a predetermined pressure (for example, 1 × 10 ⁻³ Pa).

  As a raw material of the soft magnetic powder containing Fe as a main component, for example, pure iron powder finely pulverized to an average particle diameter of 20 μm to 400 μm is used. On the other hand, the metal evaporating material M is an alloy obtained by adding Al to Mg in order to improve the adhesion with Mg or pure iron powder. The metal evaporating material M is stored in a storage chamber 12 provided on the inner wall of the vacuum chamber 11 so as to be positioned on the same line of the rotary shafts 23a and 23b. The storage chamber 12 is composed of a cylindrical member, and a flange 12a is provided on a surface opened inside the vacuum chamber 11 so as to cover a part of the opening. Thereby, when the vacuum chamber 11 is rotated, the metal evaporating material M arranged in the storage chamber 12 can be prevented from jumping out into the processing chamber 10 by the flange 12a. At least two storage chambers 12 are arranged at equal intervals in the circumferential direction on the inner wall of the vacuum chamber 11, and surround the periphery of the raw material charged into the processing chamber 10 through the on-off valves 5a and 5b. You may form cyclically | annularly over the whole inner wall face of the vacuum chamber 12, so that M may be arrange | positioned.

  Next, a method for producing soft magnetic powder using the processing apparatus 1 and production of a dust core using the soft magnetic powder will be described. The granular metal evaporation material M is accommodated in the storage chamber 12 at the open position of one of the on-off valves 5a located above the vacuum chamber 11. The total amount of the metal evaporating material M stored in the storage chamber 12 is the time required for forming the metal evaporating material M with a predetermined film thickness on the surface of the raw material so that the yield of the metal evaporating material M is increased. It is necessary to continue the metal vapor atmosphere in the vacuum chamber 11.

Next, after closing one open / close valve 5a and connecting the exhaust pipe 6 to the valve body 51 of the other lower open / close valve 5b, the vacuum exhaust means 61 is operated and the drive shaft is operated to open / close the other open / close valve 5b. The valve 5b is opened. Then, the processing chamber 10 is depressurized to a predetermined pressure (for example, 1 to 1 × 10 ⁻² Pa) according to the type of the metal evaporation material M stored in the storage chamber 12, and then the heating unit 4 is operated to set the predetermined temperature ( For example, the processing chamber 10 is heated to 370 to 650 ° C. At a temperature lower than 300 ° C., the vapor pressure at which Mg can be deposited and deposited at high speed on the surface of the raw material put into the vacuum chamber 11 is not reached. On the other hand, when the temperature exceeds 800 ° C., the deposition time on the raw material becomes extremely short.

When the processing chamber 10 reaches a predetermined temperature, a metal vapor atmosphere having a predetermined vapor pressure (in the case of Mg, for example, a vapor pressure of 0.13 Pa at 370 ° C.) is formed in the processing chamber 10. While a metal vapor atmosphere is formed in the processing chamber 10, in the preparation chamber 70 of the hopper 7, after the raw material, for example, pure iron powder is stored, the preparation chamber 70 is heated to a predetermined temperature (for example, by a heating unit (not shown)) under atmospheric pressure. 250 ° C.) and held for a predetermined time (for example, 1 hour) to oxidize the surface of the pure iron powder (by this, the surface of the pure iron powder is covered with an oxide film of Fe ₂ O ₃ (FIG. 2 (a))). When the oxidation process is completed, an exhaust pipe (not shown) is connected to the tip of the chute 71, the vacuum exhaust means is operated, the on-off valve 72 is opened, and the preparation chamber 70 has a predetermined pressure (for example, 1 × 10 ⁻² Pa). ) Until the pressure is reduced. In this case, the temperature of the pure iron powder becomes 200 ° C.

  Next, when the formation of the metal vapor atmosphere in the processing chamber 10 and the oxidation treatment in the preparation chamber 70 are finished, the on-off valve 72 is closed and the exhaust pipe is removed from the tip of the chute portion 71. Then, an inert gas such as Ar is introduced through a gas introduction means (not shown) so that a pressure difference of two digits or more is generated between the processing chamber 10 and the preparation chamber 70, and the pressure in the preparation chamber 70 is set to a predetermined value. (For example, 1000 Pa).

  In this state, after the tip of the chute portion 71 of the hopper 7 is connected to the valve body 51 of the one on-off valve 5a located on the upper side, when the on-off valves 5a and 72 are opened, the pure iron in the preparation chamber 70 is opened. Powder is thrown into the processing chamber 10 through the on-off valves 72 and 5a by its own weight. In this case, since there is a pressure difference between the processing chamber 10 and the preparation chamber 70, the inert gas enters the processing chamber 10 from the preparation chamber 70 into the processing chamber 10, and the pressure in the processing chamber 10 increases. Thus, although the evaporation is temporarily stopped (the operation of the heating means 4 is not stopped), it is possible to prevent the metal atoms in the metal evaporation atmosphere from entering the preparation chamber 70 side.

Next, when the introduction of pure iron powder into the processing chamber 10 is completed, the on-off valves 5a and 72 are closed to isolate the processing chamber 10 and the preparation chamber 70 from each other, and then the hopper 7 is removed. When the pressure in the vacuum chamber 11 evacuated through the vacuum evacuation means reaches a predetermined value (for example, 1 × 10 ⁻² Pa) again, the metal evaporation material M is re-evaporated and the metal vapor enters the processing chamber 10. An atmosphere is formed. When the metal vapor atmosphere is formed, the on-off valve 5b is closed, the exhaust pipe 6 is removed, the motor 3 is operated, and the vacuum chamber 11 is rotated at a predetermined number of revolutions and held for a predetermined time. As a result, due to the temperature difference between the pure iron powder lower than the temperature inside the processing chamber 10 and the processing chamber 10, metal atoms in the metal vapor atmosphere adhere to and deposit on the surface of the pure iron powder at high speed and selectively. And the metal evaporation material M is formed into a film over the whole surface by rotating the vacuum chamber 11 and moving the pure iron powder in the processing chamber 10.

Next, after holding for a predetermined time, the rotation of the vacuum chamber 11 and the operation of the heating means 4 are stopped, and an inert gas such as Ar is introduced through a gas introduction means (not shown) to cause metal vapor in the processing chamber 10 Stop the formation of the atmosphere. Then, the exhaust pipe 6 is connected to the valve main body 51 of the lower other on-off valve 5b, the vacuum exhaust means 61 is operated, and the other on-off valve 5b is opened, so that a predetermined pressure (10 × 10 ⁻³ Pa ) The processing chamber 10 is again depressurized.

Next, the heating means 4 is operated again to heat the processing chamber 10, and heat treatment is performed at a predetermined temperature (for example, 400 to 600 ° C.) for a predetermined time (for example, 1 hour). As a result, the oxide film (Fe ₂ O ₃ ) covering the surface of the pure iron powder is reduced, and a strong insulating film such as magnesium oxide, aluminum oxide or magnesia spinel is formed on the surface of the soft magnetic powder. A material is obtained (see FIG. 2 (b)). Then, an inert gas such as Ar is introduced into the processing chamber 10 through a gas introducing means (not shown), the processing chamber 10 is vented, and the soft magnetic material is rapidly cooled. Thereafter, a collection container (not shown) is connected to the valve body 51 of the on-off valve 5b located on the lower side, and the on-off valve 5b is opened to collect the soft magnetic material.

  Next, the soft magnetic powder obtained by the above-described series of treatments is filled into a predetermined mold, and is pressed at a predetermined pressure using a press molding machine having a known structure to form a green powder core. The green is then subjected to a heat treatment at a predetermined temperature to release the molding distortion accumulated during molding, and a desired dust core is produced. As a result, the surface of the soft magnetic powder is covered with a strong insulating film, so that the insulating film is not easily damaged by the pressure during molding during press molding, and the workability is high. Further, since the insulation between the soft magnetic materials is high, the electrical resistivity is high, the power loss due to eddy current can be reduced, and furthermore, the magnetic permeability and the saturation magnetic flux density are high.

  As raw materials, 100 kg of each pure iron powder having an average particle size of 20, 40, 100, 200, 300 and 400 μm was prepared, and after forming an insulating film using the processing apparatus 1, a press molding machine was used. A core-shaped powder magnetic core for a motor was obtained.

Prior to the film formation process, an oxidation treatment was performed in the preparation chamber 70. In this case, the temperature of the preparation chamber 70 was set to 250 ° C., and the processing time was 1 hour. On the other hand, as the metal evaporation material M in the film forming process, an alloy obtained by mixing Mg and Al at a composition ratio of 3: 7 was used, and a granular material was stored in the storage chamber 12. Further, after the processing chamber 10 is evacuated to 1 × 10 ⁻³ Pa, the temperature of the processing chamber 10 is set to 400 ° C. by the heating means 4, and a metal vapor atmosphere having a vapor pressure of 1 Pa is set in the processing chamber 10. Formed. Then, after the pure iron powder was put into the processing chamber 10 in which the vapor atmosphere of Mg and Al was formed, a film forming process was performed for 2 minutes to obtain a thin film having an average of 100 nm. In this case, the vacuum chamber 11 was rotated at a rotation speed of 1 rpm.

  Next, after the formation of the Mg and Al vapor atmosphere is stopped, the processing chamber 10 is decompressed again, the heating means 4 is operated again, and the pure iron powder on which the Mg and Al metal film is formed is heat-treated. To obtain a soft magnetic powder. In this case, the temperature of the processing chamber 10 was set to 700 ° C., and the processing time was 1 hour.

Next, the above soft magnetic powder was molded into a core magnetic powder core with a molding pressure of 6 t / cm ² , and the furnace temperature was set to 650 ° C. and the treatment time was 30 minutes in the heating furnace. Annealing was performed for removal.
(Comparative Example 1)

  As in Example 1, 100 kg of each pure iron powder having an average particle size of 20, 40, 100, 200, 300 and 400 μm was prepared, and after forming an insulating film by phosphoric acid treatment, a press molding machine was used. A powder magnetic core having a core shape for a motor was obtained.

  As the phosphoric acid treatment, a commercially available phosphoric acid-based treatment solution was added by 5% by weight to each of the above powders, mixed and dried. As a result, a phosphate insulating film having a thickness of 500 to 700 nm was obtained.

  Next, under the same conditions as in Example 1, it was molded into a motor core-shaped dust core, and the furnace temperature was set to 650 ° C. and the treatment time was 30 minutes in the heating furnace, and annealing was performed for strain relief. .

  FIG. 3 is a table showing various characteristics of the magnetic flux density, magnetic permeability, resistance value, and iron loss of each dust core obtained in Example 1 and Comparative Example 1. According to this, in the comparative example 1, it turns out that an electrical resistance value is 0.05-0.2 microhm and the iron loss exceeds 150 W / Kg. On the other hand, in Example 1, each soft soft magnetic powder is covered with a strong insulating film, so that an electric resistance value that is two orders of magnitude higher than that of Comparative Example 1 is obtained, and the iron loss is also an order of magnitude lower. I know that there is.

1 is a diagram schematically illustrating a configuration of a film forming apparatus of the present invention. The figure explaining the manufacture procedure of the soft soft magnetic powder of this invention. The figure which shows the characteristic of the powder magnetic core obtained in Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processing apparatus 10 Processing chamber 3 Drive means 4 Heating means 70 Preparation chamber M Metal evaporation material

Claims (4)

A method for producing a soft magnetic powder comprising Fe as a main component and having a surface coated with an insulating film,
An oxidation process for oxidizing the surface of the soft magnetic powder;
A metal evaporating material containing Mg is placed in a processing chamber and heated to evaporate the metal evaporating material to form a metal vapor atmosphere in the processing chamber, and the soft magnetic powder is processed in a state kept below the temperature in the processing chamber. A film forming step of selectively depositing and depositing a metal evaporation material on the surface of the soft magnetic powder according to a temperature difference between the processing chamber and the soft magnetic powder while moving the soft magnetic powder in the processing chamber;
A heat treatment process in which a soft magnetic powder having a metal evaporation material adhered and deposited on the surface is heated at a predetermined temperature, and the oxide film formed in the oxidation process is reduced to form an oxide insulating film containing magnesium on the surface of the soft magnetic powder ; A process for producing a soft magnetic powder, comprising: The metal vapor atmosphere, the manufacturing method of the soft magnetic powder of claim 1 Symbol mounting, characterized in that a saturated state in the processing chamber. The method for producing a soft magnetic powder according to claim 1 or 2, wherein the metal evaporation material contains Al. A powder magnetic core, wherein the soft magnetic powder obtained by the production method according to any one of claims 1 to 3 is pressure-molded and then subjected to a heat treatment at a predetermined temperature.

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