WO2017033990A1

WO2017033990A1 - Magnetic core powder and method for producing dust core

Info

Publication number: WO2017033990A1
Application number: PCT/JP2016/074755
Authority: WO
Inventors: 哲隆加古; 大平　晃也
Original assignee: Ntn株式会社
Priority date: 2015-08-26
Filing date: 2016-08-25
Publication date: 2017-03-02

Abstract

This magnetic core powder A to be used to produce a dust core, contains: soft magnetic metal powder having individual particle surfaces coated with insulation coatings; and pure iron powder having individual particle surfaces not coated with insulation coatings. The insulating coatings coating the particle surfaces of the soft magnetic metal powder each have a softening point exceeding 700°C, and each contain 10-20 parts by mass of pure iron powder with respect to 100 parts by mass of the soft magnetic metal powder.

Description

Powder for magnetic core and method of manufacturing powder magnetic core

The present invention relates to a powder for a magnetic core used for producing a dust core, and a method of manufacturing the dust core.

A powder magnetic core is used as a core of an electromagnetic component such as a reactor or a choke coil, and normally, a soft magnetic metal powder which has been subjected to an insulation treatment (in which each particle surface is covered with an insulation film) It is obtained by compacting a green compact by compressing a powder serving as a main raw material (hereinafter referred to as “powder for magnetic core”) and then subjecting the green compact to a heat treatment (annealing treatment). Such a powder magnetic core has been used extensively in recent years because it has advantages such as a high degree of freedom in shape and easy to meet the demand for miniaturization and complicated shape.

By the way, in order to promote energy saving and the like in various fields, it is required to further improve the magnetic properties of the dust core (to achieve high magnetic flux density, high magnetic permeability, low iron loss, etc.). ing. As one of the technical means for satisfying such a demand, it is conceivable to devise in the composition of the powder for magnetic cores (see, for example,

Patent Documents

1 and 2 below).

If explaining it concretely, patent document 1 heat-processes to the powder compact of the powder for magnetic cores containing the pure iron powder to which insulation processing was given, Sendust alloy powder, and a binder, and said pure iron powder It has a main phase formed by adhesion and firing of Sendust alloy powder and a grain boundary phase formed around the main phase with the binder as the main component, and the proportion of Sendust alloy in the main phase is 5% by mass or more and less than 20% by mass And a dust core is disclosed. According to such a configuration, while maintaining the high magnetic flux density (saturation magnetic flux density) possessed by pure iron powder, a dust core having the characteristics of low iron loss possessed by Sendust alloy powder added and mixed in an appropriate amount (specifically It is possible to obtain a dust core having a magnetic flux density of 1 T or more at a magnetic field of 10 kA / m, a core loss of 20 W / kg or less at a magnetic flux density of 0.1 T and a frequency of 10 kHz.

Further, Patent Document 2 discloses a pressure of a powder for a magnetic core containing an alloy powder containing at least Fe, Si and Al (for example, Sendust powder), and a pure iron powder having a Vickers hardness of 1/3 or less of the above alloy powder. A powder magnetic core obtained by heat treatment of powder and having an occupied volume ratio of pure iron powder of 10 to 32 vol%, wherein the magnetic flux density at a magnetic field of 8 kA / m is 435 mT or more, the magnetic flux density 0.05 T, frequency A powder magnetic core having an iron loss at 20 kHz of 82 kW / m ³ or less is disclosed. In Patent Document 2, pure iron powder in which the particle surface is coated with an insulating film is used as a technical means for achieving low iron loss of the dust core (paragraphs 0035 and 0059 of the same document, etc.), An appropriate amount of lubricant is included in the mixed powder (paragraphs 0040, 0046, etc. in the same document), and the like.

International Publication WO2010 / 073590 Patent No. 5703749 gazette

As described above, in

Patent Documents

1 and 2, pure iron powder in which individual particle surfaces are coated with an insulation film by being subjected to insulation treatment, and alloy powder not subjected to insulation treatment (iron-based alloy A powder magnetic core is obtained by compressing the magnetic core powder obtained by mixing the powder and the powder. However, since the alloy powder has much higher hardness than pure iron powder, the above pure iron powder and the alloy powder are mutually different at the time of powder mixing for obtaining powder for magnetic core, compression of powder for magnetic core, etc. The contact may damage the insulating coating formed on the surface of the pure iron powder. In this case, since the insulation between the metal particles constituting the dust core is not properly secured, the eddy current loss increases, and the possibility that the dust core can not be sufficiently reduced in iron loss is increased.

In view of the above situation, an object of the present invention is to enable stable production of a dust core with low core loss and high magnetic flux density and magnetic permeability.

The first invention of the present application invented to solve the above problems is a powder for a magnetic core used to produce a dust core, wherein the soft magnetic metal powder is coated with an insulating film on the surface of each particle. And an insulating film covering the particle surface of the soft magnetic metal powder including pure iron powder in which individual particle surfaces are not coated with the insulating film, the softening point of which exceeds 700 ° C .; 10 to 20 parts by mass of the pure iron powder is included with respect to 100 parts by mass of the metal powder.

As described above, soft magnetic metal powder (hereinafter also referred to as "coated metal powder") in which individual particle surfaces are coated with an insulating film, and individual particle surfaces are not coated with an insulating film, and the metal surface is not In the case of a powder for a magnetic core containing a pure iron powder exposed to the outside (hereinafter also referred to as "coated pure iron powder"), for example, an iron-based alloy powder having high hardness compared to pure iron powder Even when used as a base material, when obtaining a powder for a magnetic core by mixing a coated metal powder and a coated non-pure iron powder, and further, when forming a powder compact of the powder for a magnetic core, The possibility of damage to the insulating coating is reduced as much as possible. In addition to this, the insulating coating constituting the coated metal powder has a softening point exceeding 700.degree. In this case, for the purpose of appropriately removing the strain accumulated in the metal powder (obtaining a powder core having a low core loss), an annealing process with a heating temperature set, for example, in the range of about 600 to 700 ° C. is used for the core Even when applied to powder compacts, it is possible to prevent, as much as possible, the high iron loss of the dust core caused by the property change of the insulating film and the like.

In addition, if the content of the coated pure iron powder is insufficient, it becomes difficult to sufficiently increase the magnetic flux density and the magnetic permeability of the dust core, and if the content of the coated pure iron powder is too large, The contact between the particles constituting the powder makes it easy to increase the eddy current loss (iron loss) of the dust core. On the other hand, if 10 to 20 parts by mass of the pure iron powder without film is included with respect to 100 parts by mass of the film-coated metal powder, the occurrence of the various problems described above can be avoided as much as possible.

As described above, if the powder for a magnetic core according to the present invention is used, a dust core having low core loss and high magnetic flux density and magnetic permeability, specifically, iron loss at a magnetic flux density of 0.05 T and a frequency of 10 kHz It is possible to stably produce a dust core having a maximum magnetic permeability of 250 or more and a saturation magnetic flux density of 1.7 T or more at a magnetic field of 40 kA / m at 40 kW / m ³ or less.

In the above magnetic core powder, the soft magnetic metal powder (the base material of the metal powder with a film) is at least one selected from the group consisting of pure iron powder, silicon steel powder, permendur powder and iron-based nanocrystalline powder. It is preferable to do. Further, in order to obtain a powder magnetic core having a low core loss and a high magnetic flux density and permeability, it is preferable to set the thickness of the insulating coating to 1 to 100 nm.

The powder for a magnetic core according to the present invention may further contain 0.3 to 5 parts by mass of a solid lubricant with respect to 100 parts by mass of the coated metal powder.

Furthermore, in order to solve the above problems, in the present invention, as the second invention, each particle surface is an individual particle relative to 100 parts by mass of soft magnetic metal powder coated with an insulating film having a softening point exceeding 700 ° C. A compression molding process for obtaining a powder compact of the above-mentioned powder for a magnetic core by compressing the powder for a magnetic core formed by adding 10 to 20 parts by mass of pure iron powder whose surface is not coated with an insulating film; And a annealing step of heating at 600 ° C. or more and 700 ° C. or less.

According to such a manufacturing method, similarly to the first invention of the present application, a dust core having excellent magnetic characteristics can be mass-produced stably.

In the annealing step, it is preferable to heat the green compact in an inert atmosphere. Since the powder for magnetic core (powder compact thereof) contains pure iron powder not having an insulating film, when the annealing process is performed under a so-called active atmosphere such as oxygen atmosphere or air atmosphere, the pure iron powder is oxidized or expanded. It is because distortion will occur and the dust core will become high iron loss.

In the compression molding step, the powder for magnetic core is preferably compression molded with a pressure of 980 MPa or more. This is for densifying the green compact and obtaining a dust core having excellent strength and magnetic properties.

Further, in the manufacturing method of the above configuration, the thickness of the insulating coating is preferably 1 to 100 nm, and the powder for a magnetic core is used with respect to 100 parts by mass of the soft magnetic metal powder in which the individual particle surfaces are covered with the insulating coating. It is preferable to further include 0.3 to 5 parts by mass of a solid lubricant.

As described above, according to the present invention, it is possible to stably produce (mass-produce) a dust core having low core loss and high magnetic flux density and magnetic permeability.

It is a figure which shows the initial stage of a compression molding process typically. It is a figure which shows typically the middle step of a compression molding process. It is a schematic perspective view of the core for choke coils which is an example of a dust core. It is a figure which shows the test result of a confirmatory test.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The powder A for a magnetic core according to the present invention (see FIG. 1A) is used as a raw material powder for producing a dust core such as a core 1 for a choke coil (see FIG. 2). And the core 1 as a powder magnetic core is manufactured through a powder mixing process, a compression-molding process, and an annealing process in order, for example. Each step will be described in detail below.

Powder mixing process
In this powder mixing step, a plurality of types of powders are mixed to obtain a powder A for a magnetic core for producing a dust core. Here, for the soft magnetic metal powder (hereinafter also referred to as "coated metal powder") in which individual particle surfaces are covered with an insulating film, the individual particle surfaces are not covered with the insulating film, and the metal surface is external A powder for magnetic core A is obtained by adding and mixing a predetermined amount of pure iron powder (hereinafter also referred to as "coated pure iron powder") exposed to the solid lubricant and a solid lubricant.

Examples of the soft magnetic metal powder to be a base material of the coated metal powder include, in addition to pure iron powder having a purity of 97% or more, silicon steel (Fe-Si) powder, sendust (Fe-Al-Si) powder, Fe- At least one selected from the group of iron-based alloy powders represented by Al alloy powder, permalloy (Fe-Ni) powder, permendur (Fe-Co) powder, etc., iron-based amorphous powder, iron-based nanocrystalline powder, etc. Can be used. Among these, pure iron powder, silicon steel powder, permendur powder and iron-based nanocrystalline powder are selected from among these because they have the advantage of easily obtaining a powder magnetic core having both high magnetic flux density and magnetic permeability. It is preferable to use any one or a mixture of two or more.

The soft magnetic metal powder has its particle size (strictly speaking, it is an average particle size based on the number, and here it is a value measured by a laser diffraction / disturbance method. The same applies to the case of “particle size” hereinafter). Even if it is too small or, conversely, too large, it is difficult to obtain a high density green compact and, consequently, a dust core excellent in mechanical strength and magnetic properties. Specifically, when a soft magnetic metal powder having a particle diameter as small as 40 μm or less is used, it becomes difficult to compact the powder for the magnetic core at a high density, and the hysteresis loss of the powder magnetic core (Iron loss) tends to be large. On the other hand, when a large particle size soft magnetic metal powder having a particle size exceeding 100 μm is used, the eddy current loss (iron loss) of the dust core tends to be large. Therefore, as the soft magnetic metal powder, one having a particle size of 40 μm to 100 μm is used.

As an insulating film to be provided on the particle surface of the soft magnetic metal powder, one having heat resistance such that no damage or property change occurs when the green compact is heated in the annealing step described later, specifically, it is softened A point whose temperature exceeds 700 ° C. is selected. As the insulating film having such heat resistance, for example, a phosphate film containing at least one element selected from the group of Zn, Fe, Mn and Ca, B, Ca, Mg, Al, Si, Ti, An oxide film containing at least one element selected from the group of V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Mo and Bi, a crystal separated from a swellable layered clay mineral It is possible to adopt a film made of an aggregate or the like. The insulating film may have a single-layer structure or a two-layer structure (laminated structure), and in the case of a two-layer structure, for example, a laminate of a phospho-oxide film and a silicone resin film, It is possible to employ a laminate of a phosphorylated oxidized film and a film composed of an aggregate of crystals cleaved from a swellable layered clay mineral.

Examples of swellable layered clay minerals that can be used as a material for forming the insulating coating include kaolinite minerals such as halloysite, kaolinite, enderite, dickite and nacrite, and antigorite minerals such as antigorite and chrysotile, Smectite minerals such as montmorillonite, beidellite, nontronite, saponite, hectorite, soconite, stevensite, vermiculite minerals such as vermiculite, mica group minerals such as muscovite and phlogopite mica, micalite such as margarite and tetrasilylic mica Group minerals and the like. The layered mineral exemplified above may be selected and used alone or in combination of two or more.

The thicker the film thickness of the insulating film, the more difficult it is to obtain a powder magnetic core having a high density, and consequently, a powder magnetic core having excellent mechanical strength and magnetic properties (especially permeability). On the other hand, the thinner the film thickness of the insulating film, the higher the magnetic permeability of the powder magnetic core, but if the film thickness of the insulating film is too thin, the insulating film may be damaged when the powder for magnetic core is compression molded. The possibilities increase. Therefore, the film thickness of the insulating film is preferably 1 nm or more and 100 nm or less, and more preferably 1 nm or more and 20 nm or less.

The pure iron powder (coated pure iron powder) contained in the powder for magnetic core A is not particularly limited as long as it is generally available, but the purity is 97% or more and the atomizing method (gas atomizing method or water atomizing method) (Manufactured by atomized pure iron powder) are preferred. This is advantageous in reducing the loss and increasing the magnetic permeability of the dust core as the purity of iron is higher, and the iron powder produced by the atomization method may be produced by other production methods (for example, It is derived from being advantageous in enhancing the strength and magnetic properties of the powder core, as it is superior in removability of strain and plastic deformation (compression formability) compared to iron powder manufactured by reduction method and electrolysis method). Do.

For the same reason as setting the preferable particle size range for the soft magnetic metal powder which is the base material of the metal powder with a film, the pure iron powder with a film diameter of 40 μm to 100 μm is also used. Is preferred. However, if the particle sizes of the coated metal powder (soft magnetic metal powder) and the coated pure iron powder differ greatly, the powder A for the magnetic core, and in turn the coated pure iron powder (particles of the coated pure iron powder) becomes uniform in the structure of the dust core. There is a concern that the eddy current loss may increase due to the contact between particles of the pure iron powder without segregation. Therefore, as the non-coated pure iron powder, it is preferable to select and use one having the same particle size as that of the coated metal powder even within the above-mentioned particle size range.

There is no particular limitation on the solid lubricant to be included in the powder for magnetic core A, and there is no particular limitation, for example, metal soaps such as aluminum stearate and zinc stearate, amide waxes such as stearic acid amide and bis stearic acid amide, graphite and molybdenum disulfide At least one selected from the group of inorganic solid lubricants and the like can be used. By including a solid lubricant in the powder A for magnetic cores, the friction force between the molding die used for the compression molding process to be described later and the powder A for magnetic cores, and between the metal particles constituting the powder A for magnetic cores Since the frictional force can be reduced, the compressibility of the green compact can be improved, and also the durable life of the molding die can be improved.

The above-described coated pure iron powder and solid lubricant are added in an amount of 10 to 20 parts by mass and 0.3 to 5 parts by mass with respect to 100 parts by weight of the coated metal powder, respectively. In short, the powder for magnetic core A contains 10 to 20 parts by mass of pure iron powder without film and 0.3 to 5 parts by mass of solid lubricant with respect to 100 parts by mass of the coated metal powder.

The addition amount of the coated pure iron powder is set in the above range because, when the added amount of the coated pure iron powder is less than 10% by mass, the magnetic characteristics improvement effect of the powder magnetic core by including the powder (pressure In the case where the magnetic flux density and magnetic permeability of the powder core may not be sufficiently enjoyed, and the amount of the pure iron-free coated film exceeds 20% by mass, the particles of the powder contact each other, This is because the eddy current loss (iron loss) of the dust core is likely to increase.

Moreover, it was based on the verification result of the present inventors shown to the following Table 1 that the addition amount of the solid lubricant was set to said range. That is, the present inventors prepare a plurality of types of magnetic core powders different in addition amount (only) of the solid lubricant, and compression molding each magnetic core powder under the same conditions to obtain a green compact. Thereafter, the green density of each green compact, and the magnetic flux density (magnetic flux density at a magnetic field of 10 kA / m) of a green powder core obtained by annealing each green compact were measured. And when the addition amount of a solid lubricant is less than 0.3 mass%, the improvement effect of the durable life of a molding die can not fully be received, and especially the addition amount of a solid lubricant is 0.2. It became clear that adhesion to the metal mold of the powder for magnetic cores occurred when it became about mass%, and it was not possible to form a green compact of a predetermined shape. On the other hand, as apparent from Table 1 below, as the addition amount of the solid lubricant is increased, the proportion of the metal powder relative to the powder for the magnetic core relatively decreases, so that the magnetic properties of the dust core, particularly the magnetic flux Density decreases. And when the addition amount of a solid lubricant exceeds 5 mass%, it will become impossible to obtain the dust core which has desired magnetic flux density.

[Compression molding process]
In the compression molding process, a cylindrical (ring-shaped) green compact serving as a base of the core 1 is compression molded using a molding die 10 as schematically shown in FIGS. 1A and 1B. That is, as shown in FIG. 1A, after the powder filling portion (cavity) 15 defined by the core pin 11, the die 12 and the lower punch 14 is filled with the powder A for a magnetic core, as shown in FIG. Is moved relatively close to the lower punch 14 to compress the powder for magnetic core A to obtain a green compact A '. The molding pressure of the powder for magnetic core A is 800 MPa or more, preferably 980 MPa or more. However, when the molding pressure exceeds 2000 MPa, the durable life of the molding die 10 is reduced, and the possibility of damage to the insulating coating and the like is increased. Therefore, the molding pressure is set to 800 to 2000 MPa, more preferably 980 to 2000 MPa.

[Annealing process]
In the annealing step, an annealing process is performed in which the green compact A ′ placed in an appropriate atmosphere is heated at a predetermined temperature for a predetermined time. The annealing treatment temperature of the green compact A ′ is 600 ° C. or more and 700 ° C. or less, preferably 650 ° C. or more and 700 ° C. or less. If the annealing temperature is less than 600 ° C., there is a possibility that the strain removal effect by performing the annealing can not be sufficiently obtained, and if the annealing temperature exceeds 700 ° C., the adjacent coating is produced. This is because particles of the pure iron powder may be bonded (sintered) to each other, which may increase eddy current loss. The heating time (annealing treatment time) of the green compact A1 ′ depends on the size of the green compact A ′, but the heating time (for example, 5 ̃) of the core portion of the green compact A ′ can be sufficiently heated. 60 minutes). In addition, the annealing treatment is performed in an inert atmosphere such as nitrogen or argon. This is to prevent, as much as possible, the high iron loss of the dust core due to the oxidation and expansion of the coated pure iron powder contained in the green compact A ′.

And, by applying the annealing treatment as described above, the strain accumulated in the particles of the coated metal powder and the coated pure iron powder is appropriately removed, and the core 1 as a dust core having excellent magnetic properties is obtained. .

In summary, in the present invention, a soft magnetic metal powder (coated metal powder) in which individual particle surfaces are coated with an insulating film, and individual particle surfaces are not coated with an insulating film, and the metal surface is not Powder A for a magnetic core including a pure iron powder (coated pure iron powder) exposed to the outside, wherein the insulating coating constituting the coated metal powder has a softening point exceeding 700 ° C., and the coated metal powder A green compact A 'is compression molded using a magnetic core powder A to which 10 to 20 parts by mass of a coated pure iron powder is added per 100 parts by mass, and then the green compact A' is annealed. The core 1 as a dust core was obtained.

As described above, in the case of powder A for a magnetic core containing coated metal powder and coated pure iron powder, an iron-based alloy powder having a higher hardness than pure iron powder is used as a base material of coated metal powder. Even in the powder mixing process for obtaining the powder A for the magnetic core, and the compression molding process for molding the green compact A ′ of the powder A for the magnetic core, the possibility of damage to the insulating coating is reduced as much as possible. Be In addition to this, the insulating coating constituting the coated metal powder has a softening point exceeding 700.degree. In this case, even if the green compact A ′ is subjected to an annealing process at a heating temperature set in the range of 600 ° C. to 700 ° C. as described above, high core loss of the core 1 caused by the characteristic change of the insulating film is obtained. It can be prevented as much as possible.

In addition, if the content of the coated pure iron powder is insufficient, it becomes difficult to sufficiently increase the magnetic flux density and the magnetic permeability of the core 1, and if the content of the coated pure iron powder is too large, Although the eddy current loss (iron loss) of the core 1 tends to increase due to the contact between the particles constituting the powder, 10 to 20 parts by mass of the pure iron powder is included with respect to 100 parts by mass of the coated metal powder. The occurrence of the various problems described above can be avoided as much as possible.

From the above, according to the present invention, a dust core having a low core loss and high magnetic flux density and magnetic permeability (core 1), specifically, a magnetic flux density of 0.05 T and an iron loss at a frequency of 10 kHz of 40 kW A powder magnetic core (core 1) having a maximum magnetic permeability of 250 or more and a saturation magnetic flux density of 1.7 T or more at a magnetic field of 40 kA / m can be stably produced at / m ³ or less.

As mentioned above, although the manufacturing method of the powder magnetic core (core 1) using powder A for magnetic cores and powder A for this magnetic cores which concern on embodiment of this invention was demonstrated, the range which does not deviate from the summary of this invention to these. It is possible to make appropriate changes.

For example, in the compression molding process, a mold lubrication molding method in which a lubricant such as zinc stearate is attached to the inner wall surface (the defining surface of the cavity 15) of the mold 10, and the mold 10 at a predetermined temperature (maximum The green compact A ′ may be compression molded by employing either or both of the warm molding methods of heating to about 120 ° C.). Further, as the molding die 10, in particular, the one in which the defining surface of the cavity 15 is coated with a hard film such as DLC or titanium aluminum nitride (TiAlN) may be used. If the above means is adopted, it is easy to obtain a green compact A 'of higher density.

Verification tests were conducted to demonstrate the utility of the present invention. In carrying out the test, a ring-shaped test piece (Example 1-8) manufactured by applying the present invention and a ring-shaped test piece (Comparative Example 1-9) manufactured without applying the present invention are prepared. did. And about each ring-shaped test piece, (1) magnetic flux density, (2) magnetic permeability (maximum magnetic permeability), (3) iron loss, and (4) radial crushing strength were evaluated in five steps. Hereinafter, first, the confirmation method and evaluation point of the evaluation items of the above (1) to (4) will be described.

(1) Magnetic flux density and (2) Maximum permeability [Confirmation method]
The magnetic flux density at a magnetic field of 40 kA / m was measured using a direct current BH measuring device (SK-110 manufactured by Metron Giken Co., Ltd.), and the maximum permeability was simultaneously calculated. As the magnetic flux density and the maximum magnetic permeability are preferably as high as possible, the following evaluation points were given according to the measured value and the calculated value.
[Evaluation point of magnetic flux density]
5 points: 1.9 T or more 4 points: 1.8 T or more and less than 1.9 T 3 points: 1.7 T or more and less than 1.8 T 2 points: 1.6 T or more and less than 1.7 T 1 point: less than 1.6 T [maximum permeability Evaluation point of magnetic permeability]
5 points: 300 or more 4 points: 275 or more and less than 300 3 points: 250 or more and less than 275 2 points: 225 or more and less than 250 1 point: less than 225

(3) Iron loss [confirmation method]
The iron loss at a magnetic flux density of 0.05 T and a frequency of 10 kHz was measured using an AC BH measuring instrument (BH analyzer SY-8218 manufactured by Iwatsugumi Co., Ltd.). As the core loss is preferably as small as possible, the following evaluation points were given according to the measured values.
[Evaluation points]
5 points: 25 kW / ^{m 3} less than 4 points: 25 kW / ^{m 3} or more 30 kW / ^{m 3} less than 3 points: 30 kW / ^{m 3} or more 40 kW / ^{m 3} less than 2 points: 40 kW / ^{m 3} or more 50 kW / ^{m 3} less than 1 point: 50 kW / m ³ or more

(4) Bearing ring strength [confirmation method]
The compressive force (compression speed 1.0 mm / min) in the diameter reduction direction was applied to the outer peripheral surface of the ring-shaped test piece using a precision universal tester autograph manufactured by Shimadzu Corporation, and the compressive force was divided by the fracture cross-sectional area The value was taken as the crushing strength. As the radial crushing strength is preferably as high as possible, the following evaluation points were given according to the calculated value.
[Evaluation points]
5 points: 60 MPa or more 4 points: 50 MPa or more and less than 60 MPa 3 points: 40 MPa or more and less than 50 MPa 2 points: 30 MPa or more and less than 40 MPa 1 point: less than 30 MPa

Next, methods for producing ring-shaped test pieces according to Example 1-8 and Comparative Example 1-9 will be described.
Example 1
First, 100 parts by mass of pure iron powder (Somaloy 110i / 70 μm in average particle diameter manufactured by Haganes Japan) coated with an iron phosphate film as an insulating film is coated with an insulating film. 10 parts by mass of atomized pure iron powder (MH28N manufactured by Kobe Steel Co., Ltd./number average particle diameter 90 μm) and 0.3% by mass of bis (stearic acid amide) as a solid lubricant are added. Were mixed to obtain a powder for magnetic core. Then, the powder for magnetic core filled in the cavity of the molding die is compressed at a molding pressure of 1176 MPa (molding temperature is normal temperature), and the outer diameter size, inner diameter size and thickness are 20 mm, 12 mm and 7 mm respectively I got a body. Finally, annealing treatment (650 ° C. × 30 min) was applied to the ring-shaped green compact under a nitrogen atmosphere to obtain a ring-shaped test piece as Example 1.
Example 2
The same as Example 1 except that the addition amount of the pure iron powder in which each particle surface is not coated with the insulating film is changed to 20 parts by mass.
[Example 3]
The same as Example 1 except that the molding pressure of the powder for magnetic core was 980 MPa.
Example 4
The same as Example 1 except that the molding pressure of the powder for a magnetic core was set to 1960 MPa.
[Example 5]
The same as Example 1 except that the molding temperature was 120 ° C.
[Example 6]
The same as Example 1 except that the treatment temperature of the annealing treatment was 600 ° C.
[Example 7]
The same as Example 1 except that the treatment temperature of the annealing treatment was 700 ° C.
[Example 8]
The pure iron powder in which each particle surface is not coated with the insulating film is changed from the atomized pure iron powder described above to a flat electrolytic pure iron powder (Myron PM250 manufactured by Toho Zinc Co., Ltd./number average particle diameter 90 μm) The same as Example 1 except for the above.
Comparative Example 1
The same as Example 1 except that the addition of pure iron powder in which individual particle surfaces are not coated with the insulating film is omitted.
Comparative Example 2
The same as Example 1 except that the addition amount of the pure iron powder in which each particle surface is not coated with the insulating film is 5 parts by mass.
Comparative Example 3
The same as Example 1 except that the addition amount of the pure iron powder in which each particle surface is not coated with the insulating film is 25 parts by mass.
Comparative Example 4
The same as Example 1 except that the molding pressure of the powder for magnetic core was 784 MPa.
Comparative Example 5
The same as Example 1 except that the molding temperature was 150 ° C.
Comparative Example 6
The same as Example 1 except that the treatment temperature of the annealing treatment was 550 ° C.
Comparative Example 7
The same as Example 1 except that the treatment temperature of the annealing treatment was 750 ° C.
Comparative Example 8
The same as Example 1 except that the annealing treatment was performed in the air atmosphere.
Comparative Example 9
Except that the pure iron powder whose individual particle surface is not coated with the insulating film is changed from the atomized pure iron powder described above to a flat electrolytic pure iron powder (Myron PG manufactured by Toho Zinc Co., Ltd. / number average particle diameter 40 μm) Is the same as in Example 1.

FIG. 3 simply shows a method of producing ring-shaped test pieces according to Example 1-8 and Comparative Example 1-9, and (1) magnetic flux density, (2) magnetic permeability of each ring-shaped test piece, The evaluation points of (3) iron loss and (4) radial crushing strength are shown.

As is clear from FIG. 3, all of the examples 1-8 have excellent magnetic characteristics such as high magnetic flux density, high magnetic permeability, and low core loss because all the evaluation items have three or more evaluation points. It can be said that it is a high quality powder magnetic core which also has high strength while being high quality. On the other hand, in Comparative Example 1-9, since the evaluation points of at least one evaluation item of the magnetic flux density, the magnetic permeability and the iron loss are 2 points or less, it can be said that there is a problem in some magnetic characteristics. Hereafter, based on the test result of a confirmatory test, it considers easily.

First, from the evaluation points of Example 1-2 and Comparative Example 1-3, the soft magnetic metal powder subjected to the insulation treatment is a pure iron powder (coated pure iron powder) not subjected to the insulation treatment. It is understood that the use of the powder for magnetic core added quantitatively is effective in realizing a dust core having a low core loss, a high magnetic flux density and a high magnetic permeability and a high strength. The reason why the test piece according to Example 1-2 has a higher strength than the test piece according to Comparative Example 1-2 is mainly due to the use of powder for a magnetic core in which the amount of addition of the pure iron powder coated with a film is large. It is guessed that it is because it produced. That is, since the pure iron powder is relatively soft, when the powder for the magnetic core is compressed, the particles are complexly entangled in a complicated manner, and with the execution of the annealing treatment at a predetermined temperature, the coated pure iron powder The test piece according to Example 1-2 manufactured using the powder for a magnetic core having a relatively large amount of addition of the coated pure iron powder is, for example, because the sintering of the particles of each other is started, Comparative Example 1 It is presumed that the strength was higher than the test piece according to -2.

Further, from the evaluation points of Example 3-4 and Comparative Example 4, it is effective to set the molding pressure of the powder for magnetic core in a predetermined range in order to achieve high magnetic flux density and high magnetic permeability of the dust core. It is understood that there is. Further, from the evaluation points of Example 5 and Comparative Example 5, it is understood that raising the molding temperature (the temperature of the molding die) to a predetermined temperature is effective in enhancing the magnetic characteristics of the dust core. Ru. In addition, from the evaluation points of Example 6-7 and Comparative Example 6-8, it is possible to appropriately set the conditions (treatment temperature and atmosphere) of the annealing treatment to reduce the iron loss and increase the magnetic flux density of the dust core. And it is understood that it is effective in achieving high permeability. Further, from the evaluation points of Examples 1 and 8 and Comparative Example 9, the powder type (and the particle diameter) of the pure iron powder not subjected to the insulation treatment to be added to the soft magnetic metal powder subjected to the insulation treatment is appropriate It is understood that it is important to select the above in order to improve the magnetic properties of the dust core (in particular, to reduce the iron loss).

As described above, the powder for magnetic core and the method for producing a dust core according to the present invention are extremely useful, which can make it possible to produce a high quality dust core having both high magnetic properties and strength.

1 core (dust magnetic core)
10 Mold A powder for magnetic core

Claims

A soft magnetic metal powder for use as a powder for a magnetic core, which is used to produce a dust core, wherein individual particle surfaces are coated with an insulating film, and pure iron powder wherein the individual particle surfaces are not coated with an insulating film Including
The insulating film coating the particle surface of the soft magnetic metal powder has a softening point exceeding 700 ° C.,
A powder for a magnetic core, comprising 10 to 20 parts by mass of the pure iron powder with respect to 100 parts by mass of the soft magnetic metal powder.
The powder for a magnetic core according to claim 1, wherein the soft magnetic metal powder is at least one selected from the group consisting of pure iron powder, silicon steel powder, permendur powder and iron-based nanocrystalline powder.
The powder for a magnetic core according to claim 1 or 2, wherein the thickness of the insulating film is 1 to 100 nm.
The powder for a magnetic core according to any one of claims 1 to 3, further comprising 0.3 to 5 parts by mass of a solid lubricant with respect to 100 parts by mass of the soft magnetic metal powder.
10 to 20 parts by mass of pure iron powder in which each particle surface is not coated with an insulation film relative to 100 parts by mass of soft magnetic metal powder coated with an insulation film whose softening point exceeds 700 ° C. A compression molding step of obtaining a green compact of the magnetic core powder by compressing the magnetic core powder formed by the addition;
And an annealing step of heating the green compact at 600 ° C. or more and 700 ° C. or less.
The method of manufacturing a dust core according to claim 5, wherein the green compact is heated in an inert atmosphere in the annealing step.
The method of manufacturing a dust core according to claim 5 or 6, wherein the powder for magnetic core is compressed with a pressure of 980 MPa or more in the compression molding step.
The method for producing a dust core according to any one of claims 5 to 7, wherein the thickness of the insulating film is 1 to 100 nm.
The method for manufacturing a dust core according to any one of claims 5 to 8, wherein the powder for a magnetic core further comprises 0.3 to 5 parts by mass of a solid lubricant with respect to 100 parts by mass of the soft magnetic metal powder. .