JP2007287848A - Magnetic core and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust core capable of obtaining an excellent magnetic characteristic such as permeability without performing annealing to remove a distortion generated between grains in press molding, and obtaining a mechanical strength. <P>SOLUTION: An electromagnetic steel plate previously molded in response to the shape of the inner wall of a mold is arranged inside the mold. Mixed powder obtained by mixing magnetic powder with a lubricant is put on the electromagnetic steel plate. Then the plate and the powder are integrally molded by warm pressing. Consequently, the magnetic core is obtained, where the surface part is formed with the electromagnetic steel plate and the inner part is formed with the press powder body of the magnetic powder. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to magnetic cores of various electric devices that have improved mechanical characteristics without deteriorating magnetic characteristics, and more particularly, to a technique for suppressing physical degradation and destruction during processing and use in a dust core for transformers and motors. .

  In recent years, miniaturization of electric / electronic devices has progressed, and accordingly, a compact and highly efficient powder magnetic core is required. Ferrite powder and ferromagnetic metal powder are used as the ferromagnetic powder for the dust core. The ferromagnetic metal powder has an advantage that the magnetic core can be downsized because the saturation magnetic flux density is higher than that of the ferrite powder, but has a disadvantage that the eddy current loss is increased because the electric resistance is small. In order to minimize this eddy current loss, an insulating film is formed on the surface of the ferromagnetic metal powder particles with an insulating material such as a resin or an inorganic material.

The dust core is distorted between particles during compression molding, so annealing is required, the magnetic permeability and core loss are degraded, the heat resistance and aging are adversely affected, and the manufacture of large products is difficult. There is a disadvantage that there is (see Patent Document 1).
A magnetic core that uses a silicone resin as a binder as disclosed in Patent Document 2 also has low heat resistance, especially in an environment exceeding 200 ° C., the shape stability of the magnetic core decreases, and the required mechanical properties and magnetic properties are reduced. There is a drawback that characteristics cannot be obtained.
Also, in the field of composite materials, there is one in which a molded powder molded body as shown in Patent Document 3 is pressed into the outside of the core material to integrally couple them. Due to the low strength, cracking occurred in the powder compact during press fitting, making it difficult to carry out.

Unlike a cast or sintered magnetic core, a dust core is made of a pressure-formed body of iron-based magnetic powder, and the bonding of each particle is mainly a mechanical bond accompanying plastic deformation and is metallurgically bonded. It is not a thing.
In the case of such a powder magnetic core having a weak binding force between powders, when incorporated in a circuit board for a component that vibrates violently, there is a problem that the function of the circuit board is lost due to the occurrence of cracks or chips due to vibration ( (See Patent Document 4).
Further, regarding the influence of eddy current, when the above-described powder magnetic core is used in a high frequency region, the insulation is insufficient, the specific resistance value is lowered, and the eddy current loss is increased. This increase in eddy current loss causes heat generation, and the resin binding the soft magnetic powder deteriorates, so that there is a disadvantage that a sufficient life of the dust core cannot be secured.

The dust core manufacturing method also has a problem that, for example, the silicone resin is thermally decomposed and reduced in weight, so that the binder between the ferromagnetic particles is reduced and the mechanical strength is reduced (see Patent Document 2). ).
In addition, when a dust core is made from gas atomized powder or atomized powder sprayed with both water and gas, the strength of the dust core is weak, and cracks and chipping occur during subsequent coil winding processing. There was a problem that it was likely to occur.
JP-A-2005-64422 JP 2000-49008 A JP 2004-197157 A JP-A-2005-116820

  An object of the present invention is to solve the above-described problems and provide a dust core having excellent mechanical properties (strength, impact resistance, dimensional stability, etc.).

Specific means of the present invention for solving such problems are as follows.
(1) An electromagnetic steel sheet that has been molded according to the shape of the inner wall of the mold in advance is placed inside the mold, and a mixed powder of magnetic powder and lubricant is put on the electromagnetic steel sheet, and these are integrated together warmly. A method for manufacturing a magnetic core, comprising press molding.
(2) The method for manufacturing a magnetic core according to (1), wherein the magnetic powder is an iron-based magnetic powder.
(3) The method for producing a magnetic core according to (1) or (2), wherein the lubricant is a fatty acid-based lubricant.
(4) The method for producing a magnetic core according to any one of (1) to (3), wherein a fatty acid lubricant is applied in advance to the inside of the mold.
(5) The method for producing a magnetic core according to any one of (1) to (4), wherein a temperature at the time of press forming in the warm is 150 ° C. or higher and 200 ° C. or lower.
(6) The method for manufacturing a magnetic core according to any one of (1) to (5), wherein the mold and the magnetic powder are heated to 150 ° C. or higher and 200 ° C. or lower in advance.
(7) A magnetic core characterized in that the surface portion is formed of a magnetic steel sheet, and the inside thereof is formed of a green compact of magnetic powder press-molded warm together with the magnetic steel sheet.
(8) The magnetic core according to (7), wherein the magnetic core is a magnetic core having a tooth portion, and a ratio of an occupied cross-sectional area of the electromagnetic steel sheet in the tooth tip end cross section is 10% or more and 50% or less. .

  According to the present invention, the surface portion of the magnetic core is formed of a magnetic steel sheet, and the inside thereof is formed of a green compact of magnetic powder integrally formed with the magnetic steel sheet, so that it has excellent magnetic properties such as magnetic permeability and mechanical properties. In particular, a magnetic core with improved crushing strength can be obtained.

  As described above, in order to improve the efficiency of motors, transformers, inductor cores, etc., reduce the size of the shape, etc., iron loss at the core has been reduced. The inventors of the present invention have conducted intensive research in order to effectively realize a technique for enhancing the mechanical characteristics without degrading the magnetic characteristics of the electrical steel sheet as much as possible. As a result, when a magnetic core was constructed by arranging magnetic steel sheets on the outer peripheral layer of the dust core, it was confirmed that the mechanical strength was improved, including the crushing strength, compared to the conventional dust core stator. It was found as a knowledge that a magnetic core without cracks can be obtained.

  Here, the crushing strength is a load when the magnetic core breaks when pressure is applied from above with the magnetic core standing in the radial direction. Further, as described below, in the present invention, the strength of the core was evaluated by the crushing strength. The ring used at that time is a molded body having a ring shape with an outer diameter of 28 mm, an inner diameter of 20 mm, and a height of 5 mm.

Next, the present invention based on the above findings will be described in more detail with reference to embodiments.
In the present invention, it is desirable to use an iron-based magnetic powder having a specific resistance of 0.7 μΩm or more as the magnetic powder. The specific resistance of magnetic powder is an eigenvalue that does not depend on the shape. If the powder core has the same shape, the larger the specific resistance, the smaller the eddy current loss. When the specific resistance ρ is less than 0.7 μΩm, This is because the loss cannot be sufficiently reduced.

  The iron-based magnetic powder is a ferromagnetic metal powder mainly composed of iron. The iron-based magnetic powder is preferably an iron powder made of pure iron. In this case, a high magnetic flux density can be easily obtained, and hysteresis loss can be reduced due to a decrease in coercive force. The purity of the pure iron is preferably 99% or more, more preferably 99.5% or more, or 99.8% or more. As such iron powder, for example, ASC100.29 manufactured by Höganäs can be used. This iron powder has components other than Fe of C: 0.001, Mn: 0.02, O: 0.08 (unit: mass%) or less, and has extremely few impurities compared to other commercially available iron powders, and has excellent compressibility. It is.

The iron-based magnetic powder may be a mixed powder composed of a plurality of powders suitable as a magnetic core material, or may be an alloy powder. The iron-based magnetic powder may be a granulated powder or a coarse powder. There is no limitation on the type of iron oxide, but examples include α-Fe ₂ O ₃ , γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and FeO ₂ . The specific resistance increases as the oxide film covers the entire particles of the iron-based magnetic powder and the film thickness increases. However, since the oxide film has a lower magnetism than iron, if the amount is too large, the magnetic flux density obtained in each magnetic field is also reduced.

In the present invention, there is no need to laminate the magnetic steel sheets and fix them by caulking, bolting or welding, and the magnetic powder as described above is filled on the magnetic steel sheets in the mold, and the magnetic powder and the magnetic steel sheets are filled. Are formed simultaneously to produce a magnetic core in which the outer surface of the compacted magnetic powder is covered with a magnetic steel sheet.
That is, as shown in FIG. 1, the electromagnetic steel sheet 2 is previously arranged inside the lower mold 1 in the filling step, and thereafter, a powder 3 in which iron-based magnetic powder and a lubricant are mixed is charged (of a Status). Next, in the forming step, the upper mold 2 is warmly pressed, and the magnetic powder and the electromagnetic steel sheet are press-molded at the same time (state b).

As the electrical steel sheet disposed in the mold, it is preferable to use one that is formed in advance according to the internal shape of the mold. In that case, a shape closer to the internal shape of the mold is desirable. However, it is possible to form the electromagnetic steel sheet simultaneously with the compression of the powder during press molding, and the shape may be more easily formed within the formable range. In addition, the electromagnetic steel sheet disposed in the mold may be integrated or divided. For example, the inner and outer side surfaces and the lower surface of the magnetic core can be formed separately and placed individually in the mold, or they can be joined together to form a mold It can also be placed inside. Moreover, what was shape | molded as an integral thing with a press may be used.
As shown in FIG. 1, the upper surface portion may be set and molded on the powder 3 filled with the electromagnetic steel sheet, or after the molding, the electromagnetic steel sheet may be joined to the upper surface of the molded body.

  For example, high-speed steel (high-speed tool steel) or cemented carbide can be used as the mold for molding. However, the mold inner surface is subjected to TiN coating treatment and the processed surface of the mold is hardened. It is good to use.

The lubricant mixed with the powder is preferably a fatty acid-based lubricant. Preferably, zinc stearate, aluminum stearate, molybdenum disulfide, or the like may be used.
Furthermore, when a fatty acid-based lubricant is applied to the inner surface of the magnetic steel sheet, filled with magnetic powder and processed warm, the lubricity between the inner surface of the magnetic steel sheet and the magnetic powder is improved, so that The penetration pressure can be reduced.

In the forming step, pressure is applied warmly, and magnetic powder (or magnetic powder and electromagnetic steel sheet) is formed into a shape suitable for the mold. “Warm” in the molding process means molding under an appropriate heating condition in consideration of iron-based magnetic powder, fatty acid-based lubricant, molding pressure and the like. In order to promote the reaction between the iron-based magnetic powder and the higher fatty acid-based lubricant, the molding temperature is preferably set to 100 ° C. or higher, and in order to prevent deterioration of the higher fatty acid-based lubricant, the molding temperature is preferably set to 200 ° C. or lower.
Further, it is preferable that the filling step is a step of filling the heated iron-based magnetic powder into the heated molding die. If both the iron-based magnetic powder and the molding die are heated, the iron-based magnetic powder and the fatty acid-based lubricant react stably in the subsequent molding process, and a uniform lubricating film is formed between them. Easy to be. Therefore, for example, it is preferable to heat both to 150 ° C. or more and 200 ° C. or less.

The degree of “pressing” in the molding process is appropriately determined according to the required characteristics of the powder magnetic core, the type of iron-based magnetic powder, oxide film and fatty acid-based lubricant, the material of the molding die, the inner surface properties, etc. .
However, in the case of the production method of the present invention, the molding can be performed under a molding pressure exceeding the conventional molding pressure. For example, the molding pressure can be 700 MPa or more.

  As described above, in the present invention, since the molded dust core is covered with the magnetic steel sheet, it is possible to prevent the dust portion from being cracked or chipped due to an external impact. In particular, the surface cracking due to the springback, which has been a problem in the past, does not occur in the present invention because the electromagnetic steel sheet as a single piece is firmly adhered to the powder surface that has been compacted. Moreover, since the dispersion of force due to vibration is also promoted by the steel plate, cracks due to slight holes can be prevented. By using an electromagnetic steel sheet in this way, the brittleness that was a problem of the dust core can be eliminated. The electromagnetic steel sheet is a material having high permeability and low iron loss, and does not deteriorate the magnetic properties of the dust core.

The present invention is characterized in that the outside of the compacted magnetic powder is surrounded by a magnetic steel sheet, but the volume ratio of the whole magnetic steel sheet to the magnetic powder is the tip of the tooth in the case of a magnetic core. The ratio of the cross-sectional area occupied by the magnetic steel sheet in the cross section is preferably 10% or more and 50% or less.
Here, as shown in FIG. 3, the ratio of the occupied cross-sectional area of the electromagnetic steel sheet is represented by (electromagnetic steel sheet cross-sectional area) / (total cross-sectional area) in the cross-section at the tooth tip.
FIG. 4 shows changes in crushing strength and iron loss with respect to the ratio of the occupied cross-sectional area of the electrical steel sheet. From FIG. 4, as the occupied sectional area increases, the crushing strength and high-frequency iron loss (W1 / 10k) also increase. However, when the cross-sectional area exceeds 50%, the increase rate of the iron loss increases from the crushing strength. Come. Therefore, the ratio of the electrical steel sheet is specified to be not less than 10% and not more than 50% with a remarkable increase in strength.
Hereinafter, the present invention will be further described by examples.

A magnetic steel sheet pre-formed into a shape that matches the mold shape is placed along the inner wall of the high-speed steel mold (the mold shape is not shown), as shown in FIG. A mixture of magnetic powder ASC 100.29 manufactured by the company and a fatty acid lubricant (zinc stearate) was filled. At that time, a mold and magnetic powder heated in advance to a heating temperature of 150 ° C. were used. Subsequently, the temperature at the time of press-molding was set to 200 ° C. and pressure-molded to prepare a magnetic core. At that time, the amount of the electromagnetic steel sheet disposed inside the mold was variously adjusted to obtain a magnetic core having a ratio of the electromagnetic steel sheet of 10% to 50%.
In addition, as a comparative example, a core (magnetic powder core) formed using only the dust core using the above powder was also prepared.

The rotor was put into the obtained magnetic core, and the iron loss was measured using a wattmeter based on the current and voltage input from the outside. The frequencies were 50 Hz and 2 kHz, and the magnetic flux density of the yoke was 1.0T.
Similarly to the core, ring-shaped rings each having an outer diameter of 28 mm, an inner diameter of 20 mm, and a height of 5 mm were prepared, and the crushing strength was examined.
Table 1 shows the obtained magnetic properties and crushing strength.

In the present invention, by increasing the proportion of the electrical steel sheet from 10% to 50%, the crushing strength can be strengthened more than twice as compared with the magnetic core of the comparative example. Moreover, the iron loss showed the characteristics of the magnetic steel sheet in the commercial frequency range of W10 / 50, and the iron loss of the magnetic core of the present invention was lower than that of the magnetic powder magnetic core of the comparative example. On the other hand, the iron loss W10 / 2k at a frequency of 2 kHz was slightly higher in the magnetic core of the present invention than in the magnetic powder magnetic core of the comparative example.
Therefore, although the iron loss slightly increased at high frequencies, the low frequency iron loss including the magnetic flux density was improved, the strength was increased, and a magnetic core having desired characteristics could be produced.

In the same manner as in Example 1, magnetic steel sheets were respectively arranged so as to have various cross-sectional area ratios inside the high-speed steel mold, and magnetic powder MBS478 (iron-based magnetic powder) manufactured by Mitsubishi Materials Corporation and fatty acid-based lubricant were contained therein. A mixture of (molybdenum disulfide) was filled and molded. The mold used at that time was a cemented carbide mold whose inner surface was TiN coated. In addition, a fatty acid lubricant (molybdenum disulfide) was applied in advance to the inner surface of the electromagnetic steel sheet. Furthermore, press molding was performed at a temperature of 100 ° C. during press molding. At that time, a mold and magnetic powder previously heated at a heating temperature of 200 ° C. were used. In addition, as a comparative example, a core (magnetic powder core) formed using only the dust core using the above powder was also prepared.
The core loss and crushing strength of the obtained magnetic core were measured in the same manner as in Example 1.
Table 2 shows the obtained magnetic characteristics and crushing strength.

By increasing the proportion of the electrical steel sheet from 20% to 50%, the crushing strength could be increased more than twice. Moreover, the iron loss showed the characteristics of the magnetic steel sheet in the commercial frequency range of W10 / 50, and the iron loss of the magnetic core of the present invention was lower than that of the magnetic powder magnetic core. On the other hand, the iron loss W10 / 2k at a high frequency of 2 kHz was slightly higher in the magnetic core of the present invention than in the magnetic powder magnetic core of the comparative example.
Therefore, although the iron loss slightly increased at high frequencies, the low frequency iron loss including the magnetic flux density was improved, the strength was increased, and a magnetic core having desired characteristics could be produced.

As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to these cases, and it goes without saying that various additions or modifications can be made by those skilled in the art.
For example, in the above description, the application of magnetic powder made by Hoganas or Mitsubishi Materials was used as the stator material, but the present invention is not limited to this case. For example, any magnetic powder can be applied.

It is a conceptual diagram of the manufacturing method of the magnetic core of this invention. It is a figure which shows an example of manufacture of the magnetic core of this invention. It is a figure which shows the structure of the magnetic core of this invention. It is a figure which shows the relationship between the volume of the magnetic steel sheet which occupies for a magnetic core, the crushing strength, and an iron loss.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lower die 2 Magnetic steel plate 3 Powder which mixed iron type magnetic powder and lubricant 4 Upper die

Claims (8)

  A magnetic steel sheet that has been molded according to the shape of the inner wall of the mold in advance is placed inside the mold, and a mixed powder of magnetic powder and lubricant is placed on the electromagnetic steel sheet, and these are press-molded together warmly. A method of manufacturing a magnetic core characterized by the above.   The method of manufacturing a magnetic core according to claim 1, wherein the magnetic powder is an iron-based magnetic powder.   The method for manufacturing a magnetic core according to claim 1, wherein the lubricant is a fatty acid-based lubricant.   The method of manufacturing a magnetic core according to any one of claims 1 to 3, wherein a fatty acid-based lubricant is applied in advance to the inner wall of the mold.   The method for manufacturing a magnetic core according to any one of claims 1 to 4, wherein a temperature at which the hot pressing is performed is 150 ° C or higher and 200 ° C or lower.   The method for manufacturing a magnetic core according to any one of claims 1 to 5, wherein the mold and the magnetic powder are previously heated to 150 ° C or higher and 200 ° C or lower.   A magnetic core characterized in that a surface portion is formed of a magnetic steel sheet, and the inside thereof is formed of a green compact of a magnetic powder press-molded warm together with the magnetic steel sheet.   The magnetic core according to claim 7, wherein the magnetic core is a magnetic core having a tooth portion, and a ratio of an occupied cross-sectional area of the magnetic steel sheet in a tooth tip end cross section is 10% or more and 50% or less.

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