JP6882375B2 - Mixed powder for dust core and powder magnetic core - Google Patents

Description

The present invention relates to a powder magnetic core mixed powder in which a soft magnetic powder having an insulating film formed on the surface and a lubricant are mixed, and a powder magnetic core formed by compression molding using the powder magnetic core mixed powder. It is a thing.

Electromagnetic steel sheets, dust cores, soft ferrites, etc. are used for the iron cores of electromagnetic devices used in alternating magnetic fields such as noise filters and reactors. In both cases, it is necessary to suppress the eddy current generated in the iron core by the alternating magnetic field, but the eddy current is suppressed by forming an insulating film on the plate surface of the electromagnetic steel plate and on the powder surface of the dust core. .. Further, since soft ferrite is an oxide, the electrical resistance of the material itself is high, and it is not necessary to form an insulating film.

Among these, in recent years, it has become particularly common to use a dust core formed by compression molding soft magnetic powder as an iron core of an electromagnetic device. The dust core is formed by compression molding a soft magnetic powder having an insulating film formed on its surface, but its magnetic properties largely depend on the density of the molded body, and in order to obtain high magnetic properties, particles It is necessary to mold at high density while ensuring electrical insulation between them.

Here, the magnetic characteristics refer to magnetic flux density, magnetic permeability, iron loss, etc., but when electrical insulation between particles is ensured, interparticle eddy current loss generated between particles is suppressed. The eddy current loss is only the intraparticle eddy current loss generated inside the particle, and the eddy current loss is suppressed to the minimum. Therefore, as for the characteristics of the dust core obtained by compression-molding the soft magnetic powder coated with the insulating film, the DC magnetic characteristics typified by the magnetic flux density and the magnetic permeability are important characteristics.

Since the saturation magnetic flux density is proportional to the amount of iron, it depends on the density of the molded product. In addition, since the magnetic permeability is the slope of the initial magnetization curve and is an index indicating the ease of passage of the magnetic flux, the magnetic permeability increases as the number of voids serving as the reluctance decreases, and the magnetic permeability is formed in the same manner as the saturation magnetic flux density. The higher the body density, the higher the value.

Further, a high magnetic permeability means that the magnetic flux density in a certain exciting magnetic field is high, and not only the saturated magnetic flux density but also the magnetic flux density is improved by increasing the molded body density. Therefore, in order to improve the DC magnetic characteristics, it is most important to increase the density of the molded product.

As described above, the powder magnetic core is obtained by compression molding a soft magnetic powder on which an insulating film is formed, and is obtained by filling the soft magnetic powder in a mold and compressing it under pressure. A lubricant is used during molding to prevent seizure with the mold.

There are roughly two types of usage of lubricants when producing dust cores. The first is internal lubrication molding (mixed lubrication molding) in which a lubricant is directly mixed with the soft magnetic powder or the soft magnetic powder is coated with a lubricant, and the other is a lubricant applied to the inner surface of the mold. Mold lubrication molding. Further, since mold lubrication molding has a problem that it is difficult to form a complicated shape, there is also a method of using internal lubrication in which a lubricant is mixed with a soft magnetic powder when producing a molded body having a complicated shape.

Mold lubrication molding has the advantage of obtaining a high molded body density because it does not contain a lubricant inside the molded body, but there are restrictions on the shape of the molded body because the lubricant is applied to the inner wall surface of the mold. It is not a suitable method for molding complex shapes. On the other hand, internal lubrication molding has a problem that a high molded body density cannot be obtained. Under such circumstances, the development of a technique for increasing the density of molded bodies has been awaited even if internal lubrication molding suitable for molding complicated shapes is adopted.

The techniques described in Patent Document 1 and Patent Document 2 are known as examples of using a lubricant when producing a powder compact, but the lubricant used in these prior arts is an organic type. Lubricant only.

On the other hand, Patent Documents 3 to 5 and the like disclose examples of using an organic lubricant and a solid lubricant in combination when manufacturing a sliding component used at a high temperature such as a valve guide. However, the point of these techniques is to leave the solid lubricant even after sintering, and it is not an attempt to improve the compressibility and the density of the molded product.

Japanese Unexamined Patent Publication No. 2012-111987 Japanese Unexamined Patent Publication No. 2012-67334 Japanese Unexamined Patent Publication No. 2003-183701 Japanese Unexamined Patent Publication No. 2008-20123 JP-A-2010-216016

The present invention has been made to solve the above-mentioned conventional problems, and even if internal lubrication molding is adopted in the production of the dust core, the powder density can be increased and the powder magnetic core having excellent magnetic properties can be used. It is an object of the present invention to provide a mixed powder for a powder magnetic core capable of producing the above, and a powder magnetic core produced by using the mixed powder for a powder magnetic core.

The powder magnetic core mixed powder of the present invention is a powder magnetic core mixed powder in which a soft magnetic powder coated with an insulating film, a lubricant and a solid lubricant are mixed, and the content of the lubricant is 0. .1% by mass or more and 0.8% by mass or less, the content of the solid lubricant is 0.01% by mass or more and 0.2% by mass or less, and the total content of the lubricant and the solid lubricant is the amount is not less than 0.28 wt%, the lubricant is I density 2.0 g / cm ³ or less der, an organic-based lubricant comprising an organic compound having 12 or more of the linear structure of carbon The solid lubricant is a mixed powder for a dust core, which is an inorganic compound having a density of 4.0 g / cm ^{3 or more.}

Further, the insulating film is preferably a phosphoric acid-based film.

Further, the solid lubricant is preferably in the form of a powder having a particle size of 20 nm or more and 20 μm or less.

Further, the powder magnetic core of the present invention is a powder magnetic core characterized in that it is produced by compression-molding the mixed powder for powder magnetic core and then heating and annealing.

According to the present invention, even if internal lubrication molding is adopted in the production of the dust core, the density of the molded body can be increased and the dust core having excellent magnetic characteristics can be obtained.

It is a graph which illustrates the relationship between the compact density of a dust core and the molding pressure at the time of compression molding. It is a graph which illustrates the relationship between the compact density of a dust core, the magnetic permeability and the magnetic flux density. It is a graph which illustrates the relationship between the compact density of a dust core which mixed solid lubricants having various particle diameters, and the molding pressure at the time of compression molding.

It was explained earlier that the characteristics of the dust core are the DC magnetic characteristics represented by the magnetic flux density and the magnetic permeability. However, in order to improve the DC magnetic characteristics of the dust core, the magnetic material per unit volume It is necessary to increase the amount of magnetic resistance and reduce the voids and non-magnetic substances that become magnetic resistance, and it is important to mold the dust core at high density.

Lubricants are necessary substances for molding, but they are not magnetic materials. Therefore, it is useful to reduce the amount of lubricant as much as possible in order to obtain high magnetic properties. That is, it leads to high magnetic properties. It is possible to consider increasing the molding pressure to reduce the voids without reducing the lubricant, but it will cause process problems such as an increase in the load on the mold, so it is not adopted. Can not.

As described above, since the lubricant is a material necessary for preventing seizure with the mold during molding, the amount that can be reduced is limited, and it is necessary to achieve both moldability and reduction of the amount of lubricant. Is.

In view of this background, the present inventors diligently studied research, experiments, and the like, and focused on the volume of the lubricant. In order to reduce the volume of the lubricant, it is effective to use a high-density lubricant, and by replacing a part of the lubricant used as the lubricant with a high-density solid lubricant, the moldability We have found that it is possible to reduce the amount of lubricant at the same time, and succeeded in completing the present invention.

In addition, as a result of examining the insulating film that covers the surface of the soft magnetic powder, it was found that the inorganic insulating film, especially the phosphoric acid-based film, has lubricity, and the soft film coated with the phosphoric acid-based film. It was also found that the amount of lubricant can be reduced more effectively by using magnetic powder as the material for the dust core.

The powder magnetic core mixed powder of the present invention is composed of a soft magnetic powder coated with an insulating film and a lubricant and a solid lubricant as lubricants. Hereinafter, the soft magnetic powder, the insulating film, the lubricant, and the solid lubricant will be described in detail in this order.

(Soft magnetic powder)
As the soft magnetic powder, an iron-based soft magnetic powder can be exemplified. This iron-based soft magnetic powder is a ferromagnetic metal powder, and specifically, pure iron powder, iron-based alloy powder (Fe-Al alloy, Fe-Si alloy, Sendust, Permalloy, etc.), amorphous powder, etc. Is.

Such soft magnetic powder can be obtained, for example, by forming fine particles by an atomizing method, reducing the powder, and then pulverizing the powder. In the present invention, in principle, any particle size used for ordinary powder metallurgy can exert its action and effect regardless of the particle size distribution.

However, since the present invention is intended to improve the compressibility when molding into a molded product while suppressing a predetermined iron loss, the iron-based soft magnetic powder used has a large particle size component (for example, for example). It is preferable that the iron-based soft magnetic powder contains a slightly larger particle size (250 μm or more and 600 μm or less) than usual. For example, an iron-based soft magnetic powder having a particle size distribution as shown in Table 1 can be exemplified.

The particle size distribution of the iron-based soft magnetic powder shown in Table 1 is screened in accordance with the "Metal powder sieving analysis test method" (JPMA PO2-1992) specified by the Japan Powder Metallurgical Industry Association. Can be obtained by Specifically, it can be obtained by first sieving using a sieve having a mesh size of 600 μm, and then sieving using a sieve having a mesh size of 250 μm to 45 μm corresponding to the particle size shown in Table 1. Can be done.

(Insulating film)
An insulating film is formed on the surface of the soft magnetic powder to suppress eddy currents. This insulating film is preferably an inorganic insulating film, and typical examples of the inorganic insulating film include a phosphoric acid-based film (phosphoric acid-based chemical conversion film) and a chromium-based chemical conversion film. In particular, the phosphoric acid-based film has good wettability to the soft magnetic powder, can uniformly coat the surface of the soft magnetic powder, and has lubricity. Therefore, the phosphoric acid-based film is used as an insulating film in the present invention. More suitable.

The insulating film may be an organic insulating film made of an organic material such as silicone, or a double film consisting of an organic insulating film made of an organic material such as silicone and an inorganic insulating film such as a phosphoric acid film. It may be.

For the phosphoric acid-based film, for example, water: 1000 parts by mass, H ₃ PO ₄ : 193 parts by mass, MgO: 31 parts by mass, and H ₃ BO ₃ : 30 parts by mass are mixed and further diluted 20 times with water. It is possible to form a treatment liquid for a phosphoric acid-based film on the surface of the soft magnetic powder by mixing 5 parts by mass of this treatment liquid with 100 parts by mass of the soft magnetic powder and drying at 200 ° C. in the air. it can. The thickness of this phosphoric acid-based film is 10 to 100 nm.

(Glidant)
Among the lubricants mixed in the powder molding, examples of the lubricant include organic lubricants made of an organic compound having a linear structure having _{12 or more carbon atoms (−CH 2−).} In addition to metal stearic acid salts such as zinc stearate, organic lubricants such as hydrocarbon-based, fatty acid-based, higher alcohol-based, aliphatic amide-based, metal soap-based, and ester-based lubricants can be exemplified. Can include the following organic lubricants.

Examples of hydrocarbon-based lubricants include liquid paraffin, paraffin wax, and synthetic polyethylene wax. Examples of fatty acid-based and higher alcohol-based lubricants include stearic acid and stearyl alcohol, which are relatively inexpensive and low-toxic. And so on.

Examples of the aliphatic amide-based lubricant include fatty acid amides of stearic acid amides, oleic acid amides and erucic acid amides, and alkylene fatty acid amides of methylene bisstearic acid amides and ethylene bisstearic acid amides.

Further, as the metal soap-based lubricant, among metal soaps, metal stearate is mainly used, and zinc stearate, calcium stearate, lithium stearate and the like can be mentioned.

Examples of the ester-based lubricant include stearic acid monoglyceride, which is a fatty acid ester of alcohol.

In the present invention, one or more of the above-mentioned organic lubricants can be selected and used as the lubricant.

The content of these lubricants in the powder magnetic core mixed powder of the present invention is 0.1% by mass or more and 0.8% by mass or less. If the content is less than 0.1% by mass, seizure with the mold will occur during compaction molding. On the other hand, if it exceeds 0.8% by mass, the density of the compact becomes low, and it becomes impossible to obtain a dust core having excellent magnetic characteristics.

(Solid lubricant)
Examples of the solid lubricant to be mixed with the lubricant during powder compaction include an inorganic lubricant having ^{a density of 4.0 g / cm 3 or more.} Specific examples include molybdenum disulfide (MoS ₂ ) and zinc oxide (ZnO). In the present invention, one or more of the above-mentioned inorganic lubricants can be selected and used as the solid lubricant.

The density of the lubricant among the lubricants is 2.0 g / cm ³ or less, but the amount of the lubricant cannot be effectively reduced unless the density of the solid lubricant is twice or more that of the lubricant. For this reason, the density of the solid lubricant should be 4.0 g / cm ³ or more.

The particle size of the solid lubricant is preferably 20 nm or more and 20 μm or less. If the particle size of the solid lubricant is less than 20 nm, the solid lubricant gets into the unevenness of the surface of the soft magnetic powder and the gaps between the soft magnetic powders, and cannot exert the lubricating function. On the other hand, if the particle size of the solid lubricant exceeds 20 μm, the number of particles of the solid lubricant is reduced, and it is not possible to contribute to the reduction of friction between the soft magnetic powders and the reduction of friction between the soft magnetic powders and the mold.

The content of these solid lubricants in the powder magnetic core mixed powder of the present invention is 0.01% by mass or more and 0.2% by mass or less. If the content is less than 0.01% by mass, the replacement of the lubricant with a solid lubricant becomes insufficient, and the DC magnetic characteristics cannot be improved. On the other hand, if it exceeds 0.2% by mass, the total amount of the lubricant added to maintain the extraction property increases, so that the density of the molded product decreases and the saturation magnetic flux density decreases.

(Powder magnetic core)
Further, the powder magnetic core of the present invention is compression-molded in a mold using a soft magnetic powder coated with an insulating film and a mixed powder for a powder magnetic core in which a lubricant and a solid lubricant are mixed. It can be produced by heating and annealing.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples as well as the present invention, and the present invention is carried out with appropriate modifications to the extent that it can be adapted to the gist of the present invention. It is also possible, all of which are within the technical scope of the invention.

Pure iron powder (manufactured by Kobe Steel: Magmel (registered trademark) ML35N) was used as the soft magnetic powder, and a phosphoric acid-based film to be an insulating film was formed on the surface thereof. The formation of the phosphate coating, as a phosphate coating treatment liquid, water: 1000 parts by weight, H ₃ PO _4: 193 parts by weight, MgO: 31 parts by mass, H ₃ BO _3: mixing 30 parts by weight Then, it was used as a stock solution, and a treatment solution having a different concentration was used by appropriately diluting it with water up to 20 times in order to change the electric resistance. A phosphoric acid-based film was formed on the surface of the pure iron powder by mixing 5 parts by mass of the treatment liquid with 100 parts by mass of the pure iron powder and drying at 200 ° C. in the air.

After that, pure iron powder having a phosphoric acid-based film formed on the surface, a lubricant (stearic acid amide or lauric acid amide), and a solid lubricant (ZnO or MoS ₂ having a particle size of 0.5 μm) only in the invention example were added. As shown in Table 2, a dust core was produced by mixing with different contents and performing dust molding by internal lubrication molding.

The molded body density, extraction pressure, magnetic permeability, and magnetic flux density of the various powder magnetic cores produced were determined by measurement.

The molded body density was calculated from the volume and mass by measuring the mass and dimensions of the rectangular parallelepiped test piece as it was molded (before heat treatment). The size of the rectangular parallelepiped test piece is 12.7 mm × 31.75 mm × thickness about 5 mm, and the mass of powder (single weight) to be filled is 15 g.

The thickness of the rectangular parallelepiped test piece is set to "about" because the thickness changes depending on the molding pressure. The molded body density shown in Table 2 is the molded body density when the molding pressure is 900 MPa. is there. The height of the columnar molded body and the thickness of the ring-shaped test piece, which will be described later, are also referred to as "about" for the same reason.

The extraction pressure is an average value when three columnar compacts having a diameter of 25 mm and a height of about 25 mm and a unit weight of 83 g are produced at a molding pressure of 588 MPa and the pressure at the time of extraction is measured. This extraction pressure must be 30 MPa or less.

For the magnetic permeability and magnetic flux density, a ring-shaped test piece having an outer diameter of 45 mm, an inner diameter of 33 mm, a thickness of about 5 mm, and a single weight of 31 g was prepared, held in the air at 350 ° C. for 20 minutes, air-cooled, and then manufactured by Metron Giken. It was measured using a magnetic measuring instrument. The magnetic permeability shown here is the maximum magnetic permeability, and was measured at a primary winding number of 200, a secondary winding number of 50, and a maximum exciting magnetic field of 10000 A / m. The magnetic flux density is the magnetic flux density when the exciting magnetic field is 10000 A / m.

The molded body density, punching pressure, magnetic permeability, and magnetic flux density obtained by these measurements are shown in Table 2 and FIGS. 1 to 3. The molded body density shown in Table 2 is the molded body density when the molding pressure is 900 MPa. Further, the test data shown in Table 2 and the test data shown in FIGS. 1 to 3 have some variations because the test batches are different.

(Relationship between molded body density, magnetic permeability and magnetic flux density)
According to Table 2 and FIG. 1, when comparing Comparative Example 4 and Invention Example 1 in which the total mass of the lubricant was 0.3% by mass, a part of the lubricant was replaced with a high-density solid lubricant. In the first invention example, the density of the molded body is higher.

Further, according to Table 2 and FIG. 2, when comparing Comparative Example 4 and Invention Example 1 in which the total mass of the lubricant is 0.3% by mass, a part of the lubricant is changed from a lubricant to a solid lubricant having a high density. The replaced invention example 1 has higher magnetic permeability and magnetic flux density. From this test result, it can be seen that increasing the molding density improves the magnetic permeability and the magnetic flux density.

(Effect of particle size of solid lubricant)
FIG. 3 shows the effect of the particle size of the solid lubricant (zinc oxide) in Invention Example 1 on the molding density. According to FIG. 3, it can be seen that the density of the molded product is higher in any case of the particle size of zinc oxide as compared with Comparative Example 4 in which all the lubricants are used as lubricants.

In particular, zinc oxide having a particle size of 20 nm (0.02 μm), 0.5 μm, and 11 μm has a higher molded body density than Comparative Example 4 at all molding pressures, and among them, zinc oxide It can be said that the one having a particle size of about 0.5 μm is the most preferable.

The particle size of zinc oxide can be measured with a measuring instrument using laser diffraction (for example, Microtrac). The particle size indicates a particle size D50 of 50% in terms of production frequency.

(Effect of reducing extraction pressure by phosphoric acid-based film)
Soft magnetic powder and stearic acid amide as a lubricant are mixed in an amount of 0.3% by mass and compression molded at a molding pressure of 600 MPa to prepare a cylindrical molded body having a diameter of 25 mm and a height of about 25 mm. Pressure and compact density were measured. The soft magnetic powder used in the test had no film on the surface. No. 1 and No. 1 in which an oxide film was formed on the surface by water treatment. 2. No. 1 having a phosphoric acid-based film formed on the surface. There are three types of three. The test results are shown in Table 3.

According to Table 3, No. No. No film was formed on the surface of the soft magnetic powder. While the extraction pressure of No. 1 was 30 MPa, No. 1 in which an oxide film was formed on the surface of the soft magnetic powder by water treatment. In No. 2, the molded product could not be extracted even when the extraction pressure was set to 50 MPa. On the other hand, No. 1 having a phosphoric acid-based film formed on the surface. The extraction pressure of No. 3 is 21 MPa, and it can be seen that forming a phosphoric acid-based film on the surface of the soft magnetic powder is effective in reducing the extraction pressure.

Generally, when molding a sintered part or the like, a lubricant of 0.5% by mass or more, preferably 0.75% by mass or more is usually mixed with the soft magnetic powder, but an inorganic such as a phosphoric acid-based film or the like is used. Since the system insulating film has lubricity, the extraction pressure is low and the density of the molded body can be improved even if the lubricant is reduced to 0.3% by mass or less.

Solid lubricants have a higher melting point than organic lubricants used as lubricants and are considered to be inferior in lubricity because they do not melt during compression molding, but inorganic insulating films such as phosphoric acid-based films have lubricity. Therefore, as shown in Invention Example 4 of Table 2, even if 0.2% by mass of a solid lubricant having poor lubricity is added, the extraction pressure does not increase.

(Effect of solid lubricant content)
According to Table 2, when the total mass of the lubricant is 0.28% by mass and the same Comparative Example 5 and Invention Examples 5 to 9 are compared, even if 0.01% by mass is replaced with the solid lubricant, the molded body density It was found that the magnetic permeability and magnetic flux density were improved, and even when 0.1% by mass was replaced with a solid lubricant, the extraction pressure was within the allowable range of 30 MPa or less, and the molded product density, magnetic permeability and magnetic flux density were high. You can see that it is improving.

Adding 0.2% by mass of a solid lubricant is also effective in improving the density of the molded body, the magnetic permeability, and the magnetic flux density. The density of zinc oxide is 5.6 g / cm ³ , which is 4 to 5 times the density of lubricants such as stearic acid amide and lauric acid amide, which is about 1.2 g / cm ³ , so the lubricant is 0.1% by mass. On the other hand, it is considered that addition of at least 0.4% by mass is effective, but as described above, it is preferable that the total mass of the lubricant is small, so it is desirable to add 0.2% by mass or less.

Claims (4)

A mixed powder for a dust core, which is a mixture of a soft magnetic powder coated with an insulating film and a lubricant and a solid lubricant.
The content of the lubricant is 0.1% by mass or more and 0.8% by mass or less.
The content of the solid lubricant is 0.01% by mass or more and 0.2% by mass or less.
The total content of the lubricant and the solid lubricant is 0.28% by mass or more.
The lubricant, I density 2.0 g / cm ³ or less der, an organic lubricant comprising an organic compound having 12 or more of the linear structure of carbon,
The solid lubricant is a mixed powder for a dust core, which is an inorganic compound having a density of 4.0 g / cm ^{3 or more.} The mixed powder for a dust core according to claim 1, wherein the insulating film is a phosphoric acid-based film. The mixed powder for a dust core according to claim 1 or 2 , wherein the solid lubricant is in the form of a powder having a particle size of 20 nm or more and 20 μm or less. A dust core, which is produced by compression-molding the mixed powder for a powder magnetic core according to any one of claims 1 to 3 and then heating and annealing.

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