JP2003068514A - Powder magnetic core and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder magnetic core which contains a good amount of powder made of Fe-Co alloy having an especially high magnetic flux density among soft magnetism materials, and has a good electric insulation property provided by an insulation binder while making the best use of the high magnetic flux density, and also to provide a method for manufacturing the same. SOLUTION: In the powder magnetic core, the chief of which is soft magnetism alloy powder and the remaining parts of which are the insulation binder and air gap, the soft magnetism alloy powder consists of 10 to 70 wt.% of Co, at most 10 wt.% of at least one kind of element selected among B, C, Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zr, Nb, and Mo, and Fe and inevitable impurities for the remaining part. The volume occupancy rate of the soft magnetism alloy powder is 95 vol.% or above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust core and a method for producing the same, and more specifically, it contains a large amount of powder of an Fe--Co alloy having a particularly high magnetic flux density among soft magnetic alloy materials. The present invention relates to a dust core having good electrical insulation while making use of a high magnetic flux density, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Dust cores can be manufactured with a high yield even if the target product is small and has a complicated shape. Currently, for example, for choke coils of switching power supplies, solenoid valves such as noise filters and injectors. It is used for the core of. This dust core is manufactured as follows.

First, soft magnetic alloy powder having a predetermined composition is manufactured by applying mechanical pulverization, atomizing method, liquid super-quenching method or the like. Then, the soft magnetic alloy powder is uniformly mixed with a predetermined amount of an insulating material and a binder component to coat the surface of the soft magnetic alloy powder with these materials, thereby increasing the electrical resistivity of the powder magnetic core for manufacturing. Measures are taken to raise the height.

In the following description, the above-mentioned insulating material and binder component are collectively referred to as "insulating binder". Next, the obtained mixture is filled in a mold and then molded at a predetermined pressure at room temperature to manufacture a green body of a dust core. Finally, the green body is heat-treated to release the molding strain accumulated at the time of molding to obtain the target dust core.

As the soft magnetic alloy used as the material for the powder magnetic core, the obtained powder magnetic core has good moldability, so that pure Fe, Fe-Si-Al system, Fe-N are used.
i-based and Fe-Si based soft magnetic alloys are widely used.

[0006]

In recent years, along with the miniaturization of the above-mentioned products, it has been desired to develop a dust core having a higher magnetic flux density. To respond to this, for example, Fe
Since the Fe-Co alloy represented by -49% Co-2% V (permenjer) has the highest magnetic flux density among soft magnetic materials, the Fe-Co alloy is used as a dust core. It is being considered to be used as a raw material.

However, the above-mentioned manufacturing method is
When applied to a Co-based alloy, since the Fe-Co-based alloy is hard, the molding density cannot be increased even if ordinary die molding is performed at room temperature.
The volume occupancy of the Co-based alloy powder does not increase. As a result, Fe--C is also obtained in the obtained dust core.
The o-based alloy powder has a low volume occupancy, and there is a problem that such a dust core cannot achieve a desired magnetic flux density.

By solving the above problems, the present invention provides Fe-C, which has a particularly high magnetic flux density among soft magnetic materials.
An object of the present invention is to provide a powder magnetic core which contains a large amount of powder of an o-based alloy and has a good electric insulating property by an insulating binder while making use of its high magnetic flux density, and a manufacturing method thereof.

[0009]

In order to achieve the above object, in the present invention, a soft magnetic alloy powder is used as a main component, and the balance is an insulating binder and voids. Is Co: 10 to 70 mass%, B, C, Al, Si, Ti, V, Cr, Mn, N
At least one selected from the group consisting of i, Cu, Zr, Nb, and Mo: 10 mass% or less, the balance consisting of Fe and unavoidable impurities, and the volume occupancy of the soft magnetic alloy powder is 95 vol% or more. A powder magnetic core is provided.

Further, in the present invention, a mixture of the soft magnetic alloy powder and the insulating binder is heated to 700 ° C.
The method for producing a powder magnetic core according to claim 1, which includes the step of press-molding as described above. The press molding is preferably performed by any one of a uniaxial pressing method, a hot isostatic pressing method, an upset method, and an extrusion method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The dust core of the present invention is Co: 10.
~ 70 mass%, B, C, Al, Si, Ti, V, Cr,
At least one selected from the group of Mn, Ni, Cu, Zr, Nb, and Mo: 10 mass% or less, and a soft magnetic alloy powder consisting of the balance of Fe and unavoidable impurities, and an insulating binder described later are molded, It is a bulk body manufactured by further heat treatment. Therefore, this dust core has a skeleton structure in which soft magnetic alloy powder is coated with an insulating binder and simultaneously bound to each other, and has a structure structure in which fine pores are distributed as voids. .

The reasons why each component composition of the soft magnetic alloy powder is limited in the dust core of the present invention are as follows. Co: 10 to 70% by mass When the Co content is less than 10% by mass, the magnetic flux density of the alloy itself is low, so that a dust core manufactured using such an alloy powder achieves a desired magnetic flux density. I can't. Further, when the content ratio of Co exceeds 70 mass%, the magnetic flux density of the alloy itself is saturated and Co is expensive, which is rather disadvantageous in terms of cost.

B, C, Al, Si, Ti, V, Cr, M
At least one selected from the group consisting of n, Ni, Cu, Zr, Nb, and Mo: 10 mass% or less. B, C, Al, Si, Ti, V, Cr, Mn, Ni, C
u, Zr, Nb and Mo respectively have the role of increasing the electrical resistivity of the alloy and improving the magnetic properties. However, if these elements are contained in a total amount of 10% by mass or more,
Since the magnetic flux density of the alloy decreases, the upper limit of the content of these elements is 10% by mass. The preferred content of these elements is 5% by mass or less.

Among these elements, Al, Si,
Ti, V, Cr and Mn are preferable because they have a large effect as described above. Further, in the dust core of the present invention, the volume ratio occupied by the soft magnetic alloy powder is 95% by volume or more in the above-mentioned texture structure. Therefore, the ratio of the total volume of the insulating binder, which is the rest of the dust core, and the entire volume of the void is less than 5% by volume. This is because if the volume ratio of the soft magnetic alloy powder is less than 95% by volume, the dust core cannot achieve the desired magnetic flux density.

The magnetic flux density of the dust core of the present invention is preferably 1.4 T or more in an applied magnetic field of 10,000 A / m. Further, the electric resistivity of the dust core of the present invention is preferably 2000 μΩcm or more. This is because if the electrical resistivity is less than 2000 μΩcm, the core loss of the dust core increases.

The dust core of the present invention can be manufactured as follows. First, as a raw material, a soft magnetic alloy powder, a material having the above-described component composition is prepared. This soft magnetic alloy powder can be manufactured by mixing respective component powders in a predetermined ratio and then manufacturing the melt to prepare an alloy melt having a predetermined composition ratio, and applying the atomizing method to the melt. It is also possible to manufacture the ribbon by applying the melt quenching method to the melt and then crush it.

Then, the soft magnetic alloy powder and the insulating binder are mixed to obtain a mixture in which the insulating binder covers the entire surface or a part of the surface of the soft magnetic alloy powder. The insulating binder used at this time is particularly limited as long as it has binding ability and can maintain the insulating property even when subjected to press molding treatment and strain relief annealing at a predetermined temperature described later. is not.
As such an insulating binder, for example, water glass,
Mention may be made of silicone resins, oxides such as aluminum oxide and silicon oxide, and nitrides such as boron nitride.

At this time, the mixing amount of the insulating binder is preferably set to 0.1 to 5 parts by mass with respect to 100 parts by mass of the soft magnetic alloy powder. If the amount is less than 0.1 parts by mass, the soft magnetic alloy powder cannot be sufficiently covered, and the electrical insulation of the obtained powder magnetic core deteriorates. Also,
When the mixing amount of the insulating binder is more than 5 parts by mass, the volume occupancy rate of the soft magnetic alloy powder in the dust core becomes small, and the magnetic flux density of the dust core decreases.

In the present invention, the resulting mixture contains 70
Press molding is performed at a temperature of 0 ° C. or higher to obtain a green body. Then, after the green body is machined into a predetermined shape, strain relief annealing is performed in an inert atmosphere such as Ar to remove the strain accumulated during the press molding and the machining. As a result, the green body becomes a dust core containing 95% by volume or more of soft magnetic alloy powder having a predetermined composition in volume occupancy.

In this press-forming process, when the temperature is less than 700 ° C., the volume occupancy of the soft magnetic alloy powder in the green body is less than 95% by volume. Therefore, the volume occupancy of the obtained dust core is also the same. Is less than 95% by volume, and as a result, the desired magnetic flux density cannot be obtained. Therefore, the press molding temperature is set to 700 ° C. or higher.

The press molding is not particularly limited as long as it is carried out at a temperature of 700 ° C. or higher, and for example, any one of a hot isostatic press, a uniaxial press, an extrusion press and an upset press is suitable. Can be done. In addition, as a press molding method, a uniaxial press,
When either one of the extrusion press and the upset press is selected, it is preferable to preform the mixture at room temperature and press-form the preform prior to press-forming.

[0022]

EXAMPLES Examples 1 to 2 and Comparative Example 1 Soft magnetic alloy powders were produced from the molten alloys having the predetermined compositions shown in Table 1 by the gas atomizing method. 1 part by mass of a silicone resin as an insulating binder was added to and mixed with 99 parts by mass of the obtained soft magnetic alloy powder, and the mixture was sealed in a mild steel can. Then, the can was subjected to hot isostatic pressing at a pressure and temperature shown in Table 1 for about 2 hours to obtain a green body from the mixture. The obtained green body was machined into a ring shape with an outer diameter of 28 mm, an inner diameter of 20 mm, and a height of 5 mm.
Strain relief annealing treatment was carried out for 2 hours in an Ar atmosphere at 0 ° C. to obtain a dust core.

Examples 3 to 6 and Comparative Examples 2 to 4 Soft magnetic alloy powders were produced from the molten alloys having the predetermined compositions shown in Table 1 by the water atomizing method. 1 part of water glass as an insulating binder was added to 99 parts by mass of the obtained soft magnetic alloy powder.
By adding parts by mass and mixing, and subjecting this mixture to press molding at room temperature, a cylindrical preform having an outer diameter of 20 mm and a height of 10 mm was prepared. Then, this preform was subjected to a uniaxial press molding treatment at the pressure and temperature shown in Table 1 to make the preform a green body. By machining the obtained green body, the outer diameter is 20 mm and the inner diameter is 1
After forming a ring shape having a height of 2 mm and a height of 5 mm, the green body was subjected to a strain relief annealing treatment in which it was held in an Ar atmosphere at a temperature of 700 ° C. for 2 hours to obtain a dust core.

Examples 7 to 8 and Comparative Example 5 Except that an alloy melt having a predetermined composition shown in Table 1 was used and that the preform was subjected to extrusion press forming treatment at the pressure and temperature shown in Table 1. Manufactured a dust core in the same manner as in Examples 3 to 6. Examples 9 to 10 and Comparative Example 6 Upset was performed by using the alloy melt having the predetermined composition shown in Table 1, using aluminum oxide as the insulating binder, and the preform at the pressure and temperature shown in Table 1. A dust core was manufactured in the same manner as in Examples 3 to 6 except that the press molding process was performed.

The characteristics of each of the powder magnetic cores obtained above were examined according to the following specifications. (1) Volume occupancy rate (volume%) of the soft magnetic alloy powder in the dust core: The volume density of the dust core is measured, and calculated from the amount of addition of the insulating binder and the specific gravity. (2) Magnetic flux density: DC BH tracer is used and applied magnetic field is 1
Measure the magnetic flux density at 0000 A / m.

(3) Electric resistivity: Measured as DC resistance by the four-terminal method. The above results are summarized in Table 1.

[0027]

[Table 1]

Comparative Examples 7 to 11 Alloys having the component compositions shown in Table 2 were melted, and the ingots were sequentially subjected to forging and hot rolling to a thickness of 5 mm. Then, the obtained rolled material is machined into a ring shape with an outer diameter of 28 mm, an inner diameter of 20 mm and a height of 5 mm, and then the rolled material is strain-relieved and annealed for 2 hours in an Ar atmosphere at a temperature of 800 ° C. A magnetic core made of an ingot was processed.

The characteristics of the above items (2) and (3) were examined for these magnetic cores, and the results are summarized in Table 2.

[0030]

[Table 2]

As is clear from Table 1, in the powder magnetic core of the example which was press-molded at a temperature of 700 ° C. or higher, the soft magnetic alloy powder had a volume occupancy ratio of 95% by volume or more. In the dust core of the comparative example that was press-molded at 700 ° C. or less, the volume occupancy of the soft magnetic alloy powder was less than 95% by volume. The magnetic flux density of the powder magnetic core of the example is somewhat higher than that of the comparative example made of the same soft magnetic alloy powder as that of the example, although it varies somewhat depending on the composition of the soft magnetic alloy powder and the press molding conditions.

In particular, in the dust core of Example 4 containing permendur as the soft magnetic alloy powder, the magnetic flux density was 1.91T, which is about 70% that of the dust core of Comparative Example 3. A large maximum value of the magnetic flux density of a dust core using a soft magnetic powder made of a conventional Fe-Si alloy.
It is about 60% larger than 2T. Further, as is clear from Table 1 and Table 2, the dust core of the present invention has a higher electric resistivity than the magnetic core of the comparative example made of the ingot material, and has a good electric insulation property. For example, the electrical resistivity of Example 1 is 7,000 μΩcm, whereas the electrical resistivity of Comparative Example 7 is 7 μΩcm.

[0033]

As is clear from the above description, in the dust core of the present invention, the volume occupancy of the soft magnetic alloy powder is 95.
Since it is at least volume%, the magnetic flux density is high, and since it contains an insulating binder, the electric insulation is also good. Therefore, the dust core of the present invention is useful as, for example, a core for an electromagnetic valve such as an injector, which is required to have a strong attractive force even if it is small, and its industrial value is great.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4K018 AA10 AA24 AA40 AB10 CA02                       CA11 CA12 EA01 EA11 EA31                       EA44 KA44                 5E041 AA11 AA14 AA19 CA03

Claims (3)

[Claims] 1. A powder magnetic core mainly composed of a soft magnetic alloy powder, the balance of which comprises an insulating binder and voids, wherein the soft magnetic alloy powder is Co: 10 to 70 mass%, B,
C, Al, Si, Ti, V, Cr, Mn, Ni, Cu,
At least one selected from the group consisting of Zr, Nb and Mo: 1
A dust core comprising 0 mass% or less, the balance being Fe and inevitable impurities, and the volume occupancy of the soft magnetic alloy powder being 95 vol% or more. 2. The method of manufacturing a dust core according to claim 1, further comprising press-molding a mixture of the soft magnetic alloy powder and the insulating binder at a temperature of 700 ° C. or higher. 3. The method for producing a dust core according to claim 2, wherein the press molding is performed by any one of a uniaxial pressing method, a hot isostatic pressing method, an upset method, and an extrusion method.