JPH1083910A - Magnetic core and powder which is used for magnetic core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic core (magnetic core material), which is used for various choke coils or the like, has a high saturation magnetic flux density and a high electrical resistance, has a small hysteressis and eddy current loss and moreover, is excellent in corrosion resistance, and powder, which is used for this magnetic coil. SOLUTION: This magnetic core is obtained by a method wherein powders having a composition of the condition of n=2.5 to 6.0 and x=over 0.1 to less than 0.6 in Fen (Si1-x Crx ) are molded by compaction. It is more preferable that the above (x) is in a range of 0.2 to 0.5. The above powders comprise also ones, which have a flat shape and to concrete terms, have an aspect ratio of 5 or more. Moreover, these powders with the surfaces, which are covered with an inorganic insulating layer, are also comprised. The magnetic core obtainable by molding these powders by the compaction has a high saturation magnetic flux density, a high magnetic permeability and a high electrical resistance, is excellent in high-frequency characteristics and can be used at a high-frequency region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic core material used for, for example, a choke coil for a high-frequency switching power supply or a common mode choke coil used for a noise filter for an input circuit, that is, a magnetic core and a powder used for the core. About.

[0002]

2. Description of the Related Art Generally, a magnetic core 1 used for a choke coil for a high-frequency switching power supply is shown in FIG.
(A) has a donut shape (toroidal core) as shown in FIG. 2 (A), and a pair of half-ring-shaped magnetic cores 2 and 2 are attached to a common mode choke coil for noise filter as shown in FIG. Used facing each other. Each of the choke coils 1 and 2 has recently been used in a high-frequency region of 1 MHz or more, and is required to have excellent frequency characteristics. In order to cope with such a tendency, soft ferrite (MnO.Fe ₂ O ₃ , Zn.
Fe ₂ O ₃ ) or Fe powder, F
e-Ni PB permalloy or Fe-Si
A compact formed from a metal powder such as an Al-based sendust alloy is used.

However, the sintered body of the soft ferrite has a low magnetic flux density, and the one obtained by compacting Fe powder has a high saturation magnetic flux density, but has a low specific resistance and a large loss due to eddy current in the high frequency region. There is a disadvantage that. Also,
The one obtained by compacting Fe-Ni-based permalloy powder has the disadvantage that the amount of Ni used is large and the cost is high, and the saturation magnetic flux density is low. Further, Fe-Si-A
Powder compacted l-type sendust alloy powder has a certain level of saturation magnetic flux density and specific resistance, and has a small eddy current loss, but has a drawback of poor corrosion resistance.

[0004]

As described above, a magnetic core formed using a conventional metal powder or the like is used in the high frequency region in at least one of saturation magnetic flux density, specific resistance, and corrosion resistance. The characteristics required for a magnetic core for a choke coil are lacking. The present invention solves the above-mentioned problems of the conventional technology, and has a high practical magnetic core having excellent saturation magnetic flux density, high specific resistance, low hysteresis loss and eddy current loss, and excellent corrosion resistance, and is used for this. It is intended to provide a powder.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention has been made by paying attention to the composition and shape of metal powder used for molding a magnetic core. That is, in the magnetic core of the present invention, in F _n (Si _1-x Cr _x ), n = 2.
A powder having a composition of 5 to 6.0 and x = more than 0.1 to less than 0.6 is compacted. The above x is desirably in the range of 0.2 to 0.5. Here, the range n of Fe is to allow Si atoms and Cr atoms to penetrate into the crystal lattice of Fe. Further, when the range x of Cr is 0.1 or less, the electric resistance becomes small, eddy current is easily generated, the high frequency characteristics are reduced, and the corrosion resistance is also reduced. On the other hand, when x is 0.6 or more, the magnetic properties such as the intensity of the saturation magnetization and the magnetic permeability are deteriorated. Further, the range 1-x of Si is for securing the electric resistance at a certain level or more and reducing the eddy current loss.

[0006] The present invention is also directed to a flat shape in order to keep magnetic characteristics such as saturation magnetic flux density and magnetic permeability at a constant level.
A magnetic core characterized by compacting a metal powder having a (flake shape) is also proposed. The aspect ratio of the flat powder is desirably 5 or more. Further, an Fe—Si—Cr alloy having the above composition can be used for these metal powders. Furthermore, by coating the surface of the above powder or metal powder with an inorganic insulating layer, the electrical resistance of the magnetic core obtained by compacting them can be increased, and it can be used in a higher frequency region. Become. It is preferable that the insulating layer be used also as a binder for compacting, since the manufacturing process can be simplified. In addition, a flat-shaped powder for a magnetic core made of an Fe—Si—Cr alloy having the above composition is proposed. The aspect ratio of this powder is also desirably 5 or more. With such a powder, a magnetic core having each of the above properties can be reliably manufactured.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. In the composition of F _n (Si _1-x Cr _x ), n
And the alloys in which x was changed were each powdered by a water atomizing method, classified and classified to 100 mesh or less (average particle size of 7).
0 mesh). The coercive force H of each of these powders
c was measured by a VSM (vibrating sample magnetometer). In addition, in the state of the solid material before the atomization, each electric resistance was measured by a DC four-terminal method. Table 1 shows the measurement results.

[0008]

[Table 1]

From the results shown in Table 1, it was found that each coercive force of each invention example was as small as 11 Oe or less, and that the hysteresis loss was small. On the other hand, it was found that each coercive force of the comparative example was as large as 12 Oe or more, and that the steresis loss was large. The electric resistance of each invention example is 80 μΩ only for No.5.
Cm, and others are at a high level of 110 μΩ · cm or more, and eddy current hardly occurs. On the other hand, each electric resistance of the comparative example has a high level of 100 μΩ · cm or more, while a low level of 75 to 60 μΩ · cm,
There were variations. In addition, the solid material before powdering in each case was 60
Table 1 also shows the results of measuring the corrosion resistance after 96 hours in an atmosphere at 95 ° C and a relative humidity of 95%. Here, indicates that almost no rusting was observed, Δ indicates that scattered spot-like rust was observed, and X indicates that where planar rust was observed. From the results shown in Table 1, some of the examples of the invention were marked with a triangle, but most of them were marked with excellent corrosion resistance. On the other hand, those of the comparative examples were roughly marked, but some were marked with x and were inferior in corrosion resistance. This corrosion resistance is considered to depend on the content of Cr in the powder alloy of each example. From the above, it is understood that the powder of each invention example has a small coercive force, a high electric resistance of a certain level or more, and also has excellent corrosion resistance. Therefore, a magnetic core compacted using these powders can be reduced in hysteresis and eddy current loss.

Next, Fe ₃ (Si _0.75 Cr _0.25 ) and Fe ₅
Each alloy powder of 100 mesh or less (average particle size of 70 mesh or less) having two kinds of compositions of (Si _0.6 Cr _0.4 ) was obtained by a water atomizing method. Inorganic binder made of water glass (about 2 wt% of powder) on the surface of each of these powders
Was coated with a blend or the like, and pressed into a donut shape (outer diameter 28 mm × inner diameter 16 mm × height 5 mm) as shown in FIG. 3 (A). The green density after molding is about 6.0 g / cm each.
³ , and the transverse rupture strength was about 60 MPa. These two types of compacts were placed in a reducing atmosphere containing hydrogen,
Heat treatment was performed at 0 to 600 [deg.] C. to remove C and O and to remove internal strains received during the atomization. On the other hand, as a comparative example, a sendust alloy (Fe-9.6 wt% S
Using i-5.4 wt% Al) powder, binder coating, compacting, and heat treatment were performed in the same manner as described above.

The core loss (including both the eddy current loss and the hysteresis loss) of these three types of compacts was measured for each of the heat treatment temperatures using an AC BH analyzer. The result was plotted on the graph of FIG. From each graph in FIG.
In the case of the invention examples, in the range of 200 ℃ or more,
Only a fraction of the core loss of the comparative example was observed. From this, it is understood that according to the magnetic core using the powder compact of each invention example, excellent characteristics in which both the eddy current loss and the hysteresis loss are small can be obtained. In addition, it is clear from Table 1 that each of the invention examples has both high electric resistance and excellent corrosion resistance. In addition, the water glass of the binder may be replaced with a silicon resin of 1 to 3 wt% or the like, and both have an insulating function.

Further, Fe ₃ (Si _0.75 Cr _0.25 ) and Fe ₅
Alloy powders of 100 mesh or less (average particle size of 70 mesh or less) having two compositions of (Si _0.6 Cr _0.4 ) were obtained by a water atomizing method. These powders were put into an attritor together with toluene and iron balls, and each of them was subjected to continuous pulverization for 15 hours to obtain flat powders each having a thickness of about 1 μm. The aspect ratios of these flat powders were all in the range of about 5.0 to 50.0. Each of these flat powders was compacted together with a binder into the same donut shape (outer diameter 28 mm × inner diameter 16 mm × height 5 mm) (the compact density after compaction: about 6.2 g / cm ³ , bending strength; About 80 MPa). Further, in a reducing atmosphere containing hydrogen, heat treatment was performed at 200 to 600 ° C. to remove C and O, and to remove internal strains received during the above-mentioned atomization and pulverization. On the other hand, as a comparative example, Sendust alloy
(Fe-9.6wt% Si-5.4wt% Al) powder,
The pulverization, compacting, and heat treatment were performed in the same manner as described above. The core loss (including both the eddy current loss and the hysteresis loss) of these three types of compacts was measured for each of the heat treatment temperatures using an AC B-H analyzer. The result was plotted on the graph of FIG.

From each graph of FIG. 2, in each of the invention examples, the core loss is 1000 Kw / m ^{3 in} the range of 300 ° C. or more.
And the core loss was only a few to a tenth of the core loss of the comparative example. Moreover, in this range, the core loss was smaller than that of each of the non-flattened invention examples shown in FIG. In particular, among the magnetic cores using powders having an aspect ratio of 5 or more, those with Fe ₃ (Si _0.75 Cr _0.25 ) were remarkable. This is a similar alloy composition,
When the powder has a flat shape, the path of the magnetic flux passing through the inside is longer than that of a spherical or lump shape, and the demagnetizing field generated in the opposite direction is smaller, so that the hysteresis loss is reduced. It is presumed that. From these, it is understood that according to the magnetic core of the compacted body made of the flat powder of each of the invention examples, excellent characteristics in which both the eddy current loss and the hysteresis loss are further reduced can be obtained. Further, it is apparent from Table 1 that each of the invention examples has both high electric resistance and excellent corrosion resistance.

The present invention is not limited to the above embodiments. The pulverization of the alloy is not limited to the atomization method, and the ingot may be formed into a flat powder by a mechanical pulverization method using a jaw crusher, a hammer mill, and a ball mill. Also, compacting is performed by pressing
In addition to the method of molding the powder and the binder filled in the mold with a (compressor) at a pressure of several 100 MPa, extrusion molding in which the powder with the binder added is extruded from a die, and the inside of a cavity surrounded by a rubber mold and a core metal A method such as hydraulic molding, in which a powder and a binder are filled into the mixture and pressure is applied to the surrounding liquid to form the mixture, may be used.

Further, in addition to the above, the alloy composition of the powder may be, for example, C in a range where carbides such as SiC are not formed (about 0.1 watts).
(t% or less) to soften the powder and facilitate flattening of the powder. Further, the strength of the alloy powder is improved by adding 1 to 2 wt% of Ni or Mn, or Ni or Mn is added.
Can be added up to about 10% by weight to improve the corrosion resistance and heat resistance in combination with Cr. The insulating layer may be a dedicated material different from the binder, and the surface of the powder may be coated by dipping or showering.

[0016]

According to the magnetic core of the present invention described above, a high saturation magnetic flux density and a good magnetic permeability can be obtained due to a small hysteresis loss, an electric resistance is high, and an eddy current loss can be reduced. A magnetic core having excellent characteristics in the region can be provided. In particular, a magnetic core obtained by compacting a flat metal powder can exert more excellent effects on the above-described respective characteristics. In addition, since it has excellent corrosion resistance, the above-described effects can be maintained for a long time even in a severe use environment. Further, according to the powder of the present invention, the above-mentioned magnetic core is surely and easily,
Moreover, it can be mass-produced and provided at low cost.

[Brief description of the drawings]

FIG. 1 is a graph in which core losses of a magnetic core using a powder of the present invention and a magnetic core of a comparative example are plotted at respective heat treatment temperatures.

FIG. 2 is a graph plotting the core loss of the magnetic core using the flat powder of the present invention and the core of the comparative example for each heat treatment temperature.

FIGS. 3A and 3B are perspective views each showing a general shape of a magnetic core.

[Explanation of symbols]

 1,2 ………………… Core

[Table 1]

Claims (7)

[Claims] 1. A _{Fe n (Si 1-x Cr} x), n = 2.
A magnetic core obtained by compacting a powder having a composition of 5 to 6.0 and x = more than 0.1 to less than 0.6. 2. The magnetic core according to claim 1, wherein x = 0.2 to 0.5 in the composition. 3. A magnetic core obtained by compacting a flat metal powder. 4. The magnetic core according to claim 3, wherein the metal powder has an aspect ratio of 5 or more. 5. The method according to claim 1, wherein the composition of the metal powder is F _n (Si _1-x
(Cr _x ), n = 2.5-6.0, x = more than 0.1-0.5.
The magnetic core according to claim 3 or 4, wherein the number is less than 6. 6. The magnetic core according to claim 1, wherein the surface of the powder or the metal powder is covered with an inorganic insulating layer. 7. In F _n (Si _1-x Cr _x ), n = 2.
A powder for a magnetic core, having a composition of 5 to 6.0, x = more than 0.1 to less than 0.6, and having a flat shape.