JP2011135000A - Method of manufacturing dust core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust core which balances high specific permittivity with low eddy current. <P>SOLUTION: This method of manufacturing a dust core includes processes of: forming a compact using powder containing an iron constituent; firing the compact to form a fired body having resistivity <50 μΩm; and heat-treating the fired body in steam. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a dust core used in various electric devices. More specifically, the method for producing a dust core of the present invention relates to the method for improving the magnetic properties of a fired body formed by powder metallurgy.

  In recent years, an iron core material called a dust core has attracted attention as an electric device such as a motor. The dust core is produced by coating an iron-based powder with an insulator, adding a binder as necessary, and sequentially pressing and baking the mixture. According to such a technique, an iron core having a three-dimensional structure can be obtained unlike a conventional iron core manufactured from an electromagnetic steel sheet. Therefore, the range of the structural design of electrical equipment has been greatly expanded by the dust core.

  However, the use of a dust core for the iron core also has some drawbacks. For example, since the dust core is obtained by press-molding iron-based powder coated with an insulating film, a nonmagnetic component may be present between the iron powders, which may hinder the movement of the domain wall. For this reason, the magnetic permeability of the dust core is likely to be lower than that of an iron core made of an electromagnetic steel sheet.

  In order to increase the magnetic permeability in order to cope with such a situation, a method such as increasing the firing temperature after press molding can be considered. However, if the maximum relative magnetic permeability is increased to about 1000, the temperature is 500 ° C. or higher. Therefore, the insulating film is destroyed and eddy current loss increases.

  As described above, it has been impossible in the prior art to achieve both high maximum relative permeability of about 1000 and low eddy current loss.

  Therefore, in order to reduce eddy current loss, a method of forming an oxide layer on the powder surface by incorporating a predetermined amount or more of water vapor in the atmosphere at the stage of producing the powder by the atomizing method is disclosed.

For example, in Patent Document 1, when the particles of the soft magnetic material are manufactured by an atomizing method using a molten metal obtained by melting a soft magnetic material containing Fe as a main component, the conditions of the atomizing method are (a ) When the melting point of the soft magnetic material is Tm [° C.], the temperature of the molten metal is Tm + 200 ° C. or higher, and (b) is performed in a steam-containing atmosphere with a water vapor amount of 10 g / m ³ or higher. A method for producing an oxide-coated soft magnetic powder is disclosed in which a coating layer composed of an oxide formed by oxidizing the soft magnetic material is formed on the surface of the particles by filling.

  When this method is used, a highly durable oxide layer can be formed and eddy current loss can be reduced, but the oxide film is hard and the powder is difficult to deform during pressing. If pressing is not performed, a core having a high density, that is, a high saturation magnetic flux density and a magnetic permeability cannot be obtained. However, pressing at high pressure significantly reduces the durability of the mold and also increases the frequency of troubles when the green compact is extracted. Furthermore, when the formed oxide layer is pressed at a high pressure, a part thereof may be damaged. In this case, the damaged portion of the oxide layer is electrically connected, and as a result, eddy current loss cannot be reduced. As described above, Patent Document 1 does not disclose any technique for achieving both high maximum relative permeability and low eddy current loss.

  Also disclosed is a technique for taking measures such as adding an oxide layer repair process after pressing to enhance performance.

  For example, in Patent Document 2, a surface oxidation step of forming an oxide film on the surface of a soft magnetic powder containing iron as a main component, and a molded body having a predetermined shape by press-molding the soft magnetic powder having an oxide film formed on the surface thereof And a sintering step to sinter the soft magnetic powder compact by firing the soft magnetic powder compact. In the sintering step, the compact is treated with an inert gas. There is disclosed a method for producing a soft magnetic material, characterized by alternately repeating an oxidation treatment in contact with a weak oxidizing atmosphere gas mixed with a weak oxidizing gas and a degassing treatment for discharging the atmospheric gas out of the system. Yes.

  However, in this manufacturing method, there is a problem that the method becomes complicated due to the addition of the repair process of the oxide layer after pressing. Under these circumstances, high mass productivity cannot be realized when producing a dust core mainly for low frequency use that requires a high maximum relative permeability of about 1000. As described above, Patent Document 2 does not disclose any technique for achieving both high maximum relative permeability and low eddy current loss.

JP 2009-088496 A JP 2006-108475 A

  As described above, various methods for producing a dust core have been disclosed, and there is a demand for a method for producing a dust core that achieves both a high relative magnetic permeability and a low eddy current.

  Accordingly, an object of the present invention is to provide a dust core that has both a high relative permeability and a low eddy current, and in particular, a dust powder having predetermined characteristics by subjecting a fired body to a specific heat treatment. It is to provide a technique for obtaining a core.

  The present invention includes a step of forming a green compact using a powder containing an iron component, a step of firing the green compact to form a fired body having a resistivity of less than 50 μΩ · m, and the fired body as water vapor. The present invention relates to a method for producing a dust core, which includes a step of heat treatment in the inside. The method for producing a dust core of the present invention is used for producing an iron core used in various electric devices.

  As for the manufacturing method of the powder core of this invention, it is desirable that the powder containing the said iron component is a pure iron powder. In the heat treatment, it is desirable that the treatment temperature is 120 ° C. or higher, the treatment humidity is 100%, and the treatment time is 100 to 200 hours.

  According to the method for manufacturing a dust core of the present invention, it is possible to realize both characteristics of relative permeability and eddy current loss at a high level by a predetermined heat treatment. For this reason, the dust core obtained by the manufacturing method of the present invention can be advantageously used as an iron core of various electric devices.

It is a graph which shows the relationship between the maximum specific permeability and heat processing time about the dust core of this invention. It is a graph which shows the relationship between magnetic flux density and heat processing time about the dust core of this invention. It is a graph which shows the relationship between the loss (hysteresis loss, eddy current loss, and these total) and heat processing time about the dust core of this invention.

  In view of the above problems, the inventor has earnestly studied about a technique for obtaining a dust core having predetermined characteristics, that is, high relative permeability and low eddy current, by sequentially performing press molding, firing and heat treatment of powder. ,investigated. In addition, in this study, when the three steps of press molding, firing, and heat treatment are completed, it is important to obtain a maximum maximum magnetic permeability of 1000 or more, and press molding and firing. In order to increase the undesired eddy current value of the fired body at the time when the process is completed, heat treatment is performed.

  As a result, if the resistivity of the fired body before heat treatment is less than 50 μΩ · m, the resistivity of the dust core can be effectively increased by heat treatment in a steam-containing atmosphere, and eddy current loss can be reduced. As a result, the inventors have found that a dust core having a high relative permeability and a low eddy current can be obtained. The present invention has been made in view of the above findings.

  The manufacturing method of the powder core of the present invention based on the above knowledge includes a green compact forming step, a firing step, and a heat treatment step. Below, each process is explained in full detail. The example shown below is an example of the present invention, and those skilled in the art can change the design as appropriate.

<Green compact formation process>
First, a powder containing an iron component (hereinafter sometimes referred to as “iron-based powder”) is prepared as a used powder. For example, pure iron powder, stainless steel powder, or the like can be used.

For example, when pure iron powder is used as these iron-based powders, Fe ₃ O ₄ (magnetite) is deposited on the powder surface in the heat treatment described later. Since the resistivity of magnetite is 50 μΩ · m or more, according to the above knowledge, as a result, the high relative permeability and the low eddy current of the dust core can be achieved at a high level.

  As the iron-based powder, those obtained by applying an insulating film to various powders obtained by various manufacturing methods such as an atomizing method and a reduction method can be applied. The insulating film is applied for the purpose of suppressing eddy current loss. Among these, it is preferable to apply the powder obtained by the water atomization method in terms of the high compressibility and low cost of the powder.

  The particle size of the iron-based powder can be determined by the magnetic flux density required for the dust core and the specific frequency region in which it is used. For example, when the magnetic flux density to be realized by the dust core is 1.0 to 2.0 T and the operating frequency region of the dust core is 50 to 400 Hz, the particle size of the iron-based powder is the average particle size. It is preferable to use a powder having a diameter of 100 μm to 200 μm.

  A predetermined binder is added to such powder and mixed. As the binder, an epoxy resin, a polyamide resin, or the like can be used. Particularly, when a polyamide resin is used, it is preferable in terms of increasing the strength.

  The mixing of the iron-based powder and the binder can be performed with a mixing rotator or the like with a binder mixing ratio of 0.005 to 5% by mass. In particular, the binder mixing ratio of 0.005 to 1% is preferable from the viewpoint of improving the magnetic flux density. Thus, the raw material containing an iron-type powder and a binder is obtained.

  Next, the raw material is press-molded using a predetermined mold. The shape of the mold is not particularly limited, and for example, a bearing-shaped mold can be used.

  In press molding, in order to obtain high compressibility and to suppress friction between the inner surface of the mold and the green compact when the green compact is drawn out, a lubricant is applied to the inner surface of the mold in advance. It is preferable to keep it. As the lubricant, for example, zinc stearate, ethylene bisstearoamide, potassium dihydrogen phosphate, or the like can be used, and an electrostatic coating method or the like can be applied as a specific coating mode.

  Moreover, as press molding conditions, it can be set as holding stress 600-1500 Mpa, and it is especially preferable at a point which prevents the lifetime reduction of a metal mold | die while making a core high density to make holding stress 800-1000 MPa.

  A predetermined green compact can be obtained as described above.

<Baking process>
The green compact containing the binder obtained as described above is fired. Firing can be performed in a predetermined firing furnace in an air or nitrogen atmosphere at a holding temperature of 200 to 600 ° C. and a holding time of 10 to 120 minutes.

  Under such conditions, in particular, the holding temperature of 300 to 550 ° C. suppresses breakage of the insulating film due to heat and suppresses eddy current loss, and the relative permeability increases due to relaxation of internal strain. This is preferable in that the hysteresis loss is reduced.

  As described above, a predetermined fired body can be obtained.

  The resistivity of the fired body can be measured by, for example, a normal four-terminal method.

<Heat treatment process>
The fired body obtained as described above is heat-treated. The heat treatment can be performed with a predetermined heat treatment apparatus at a humidity of 100%, a holding temperature of 100 to 550 ° C., and a holding time of 10 minutes to 200 hours.

  As described above, a predetermined dust core can be obtained.

  The effects of the present invention are demonstrated below by examples. The following examples are merely representative examples for explaining the present invention, and do not limit the present invention in any way.

<Preparation of powder core>
A pure iron powder with a phosphate film manufactured by Höganäs was mixed with a binder to obtain a raw material containing an iron-based powder and a binder.

  Next, the raw material was press-molded using a mold (a ring shape having an outer diameter of 35 mm, an inner diameter of 25 mm, and a height of 5 mm). In press molding, in view of high compressibility and the like, a lubricant was applied in advance to the inner surface of the mold.

  Here, the green compact of the example of the present invention was obtained by setting the press molding condition to a holding stress of 980 MPa.

  Next, the green compact was fired at a holding temperature of 500 ° C. in an air atmosphere in a firing furnace to obtain a fired body of the present invention example.

Here, the maximum relative magnetic permeability (definition: maximum value of B / (μ ₀ H)) of the fired body was measured with an apparatus BH analyzer SY-8232 manufactured by Iwatatsu Measurement Co., Ltd., which was 985, and the resistivity (RS / L: R is the measured resistance value, S is the cross-sectional area of the measurement region, and L is 7 μΩ · m when the length of the measurement region is measured by the four-terminal method.

  Furthermore, heat treatment was performed with a heat treatment apparatus manufactured by ESPEC Co., Ltd. at a humidity of 100%, a holding temperature of 120 ° C., and a holding time of 200 minutes, to obtain a dust core of the present invention example.

<Evaluation of magnetic properties>
With respect to the dust core obtained as described above, the maximum relative permeability (the maximum value of B / (μ ₀ H)), the magnetic flux density, the hysteresis loss, and the eddy current loss were measured.

  The maximum specific permeability, magnetic flux density, and loss were measured using an apparatus BH analyzer SY-8232 manufactured by Iwatatsu Keiki Co., Ltd. The loss was separated into hysteresis loss and eddy current loss by the two-frequency method. These results are shown in FIGS.

  According to FIGS. 1-3, only the eddy current can be reduced by changing the maximum relative magnetic permeability, the magnetic flux density, and the hysteresis loss by the heat treatment applied to the fired body. Thereby, it can be seen that the powder core subjected to the heat treatment can achieve both high relative permeability and low eddy current loss.

  According to the method for manufacturing a dust core of the present invention, it is possible to obtain a dust core that has both a high relative permeability and a low eddy current loss. Accordingly, the present invention is promising in that it can be applied to the manufacture of iron cores that are required to have higher magnetic properties.

Claims (3)

Forming a green compact using a powder containing an iron component;
A method for producing a dust core, comprising: firing the green compact to form a fired body having a resistivity of less than 50 μΩ · m; and heat treating the fired body in water vapor.   The method for producing a dust core according to claim 1, wherein the powder containing the iron component is pure iron powder.   In the said heat processing, processing temperature is 120 degreeC or more, processing humidity is 100%, and processing time is 100 to 200 hours, The manufacturing method of the powder core of Claim 1 or 2 characterized by the above-mentioned.

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