JPH05326240A - Dust core and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a dust core having high mu (permeability) by orienting easy axis of magnetization of ferromagnetic powder along the flux of magnetic circuit. CONSTITUTION:Ferromagnetic powder, e.g. Fe-Si-Al based alloy powder, is admixed with a binder, e.g. an epoxy resin powder, and the mixture is filled in a die and subsequently compression molded and cured in magnetic field. The ferromagnetic powder to be employed has magnetically anisotropic flat shape where the ratio between long axis length and short axis length is about 10. Applying direction of magnetic field is set in parallel with the magnetic path at the time of compression molding. This method produces a dust core having higher relative dust density and mu than conventional ones. Powder can be oriented in parallel with the magnetic path by applying magnetic field in parallel with the magnetic path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust core used in inductors such as transformers and noise filters, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A dust core has been used in the field of this type. Conventional powder magnetic cores have a constant μ even if a direct current is superposed and have better frequency characteristics of μ compared to metal wound cores, but their initial permeability μ _i is low and their applications are limited. It was being done. For example, as a noise filter, an inductor having a magnetic core having a μ as high as possible is required, and a magnetic core having a high μ even when a direct current is superposed is required. The current dust core cannot meet this requirement. Moreover, although the wound core of the metal ribbon has a high μ, it cannot be used as a noise filter in a portion where the magnetization is saturated by a slight magnetic field and the current is superposed. Similar problems occur when the magnetic core material is ferrite.

Recently, a study has been made on increasing the switching frequency of a power supply, and accordingly, the use of a dust core in a transformer is being studied. However, in the conventional dust core, μ
Is running out.

[0004]

A conventional dust core uses a crushed powder of a metal ingot or a powder produced by atomization. These powders have a spherical shape or an isotropic shape close thereto. Therefore, the demagnetizing field coefficient of the obtained dust core is large, and the dust density is difficult to increase, so that it is difficult to improve μ.

Therefore, a technical problem of the present invention is to solve the above-mentioned problems and to provide a dust core having a high μ and a method for manufacturing the same.

[0006]

As a result of various investigations, the present inventors have found that in order to solve the above-mentioned problems, a magnetically anisotropic shape, specifically, a long axis length and a short axis Molding a dust core by using flat or acicular powder with a ratio of length greater than 1 and orienting the easy axis (long axis) of the powder parallel to the magnetic path. Has been found to be advantageous for improving μ. Furthermore, they have found that in order to orient this powder parallel to the magnetic path, it can be obtained by molding while applying a magnetic field so as to be parallel to the magnetic path.

That is, according to the present invention, there is provided a green compact containing a ferromagnetic powder having magnetic anisotropy, wherein the easy axis of magnetization of the ferromagnetic powder is oriented along the magnetic flux of the magnetic circuit. A powder magnetic core characterized by being present.

According to the present invention, when a ferromagnetic powder having magnetic anisotropy is formed by applying a forming pressure in a magnetic field, the magnetic field is applied along the direction of the magnetic flux of the magnetic circuit. A method for producing a dust core, characterized by orienting the easy axis of magnetization of a ferromagnetic powder, is obtained.

According to the present invention, in the method for producing a dust core, the method for producing a dust core is characterized in that molding is performed so that a load direction of the molding pressure and a magnetic field applying direction are orthogonal to each other. Is obtained.

By the way, since the shape of the powder of the present invention is not isotropic (for example, flat or needle-like), the gap between the powders is smaller than that when the powder having an isotropic shape is used, and the green compact density is obtained. It is possible to raise. Also, the effect of the demagnetizing field due to the shape is reduced. Further, since the direction of easy magnetization is aligned with the magnetic path, μ of the dust core is increased.

Here, in the present invention, when a toroidal-shaped dust core is manufactured, a large current is applied to the center of the green compact to form a magnetic circuit of the dust core. A high-performance dust core can be obtained by molding while inducing a magnetic field in the direction of magnetic flux.

That is, according to the present invention, in any one of the above-described methods for manufacturing a dust core, the dust core has a toroidal shape, and an electric conductor is provided at the center during molding. A method for producing a powder magnetic core is obtained, which is characterized by energizing and applying a magnetic field to the formed powder compact.

This is because the magnetic field induced by the current causes the easy axis (long axis) of the magnetically anisotropic powder to be oriented in the direction of the magnetic flux of the magnetic circuit, as described above.

In the embodiments of the present invention described below, only flat powders have been described, but the same effect can be expected even when acicular powders are used. Further, in the embodiments described below, only the method of inserting the mixture of the magnetic powder and the binder into the mold, compression-molding and heat-curing the mixture, but naturally other means may be used. The same effect can be expected.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) Fe-Si as a ferromagnetic powder
-Al (L) alloy powder is mixed with epoxy resin powder as a binder, inserted into a mold, and compression molded at a molding pressure of 10 ton / cm ² in a magnetic field or no magnetic field.
It was cured at a temperature of 0 to 200 ° C. As the ferromagnetic powder according to Example 1 of the present invention, a flat powder having a ratio of the major axis length to the minor axis length of about 10 and a magnetically anisotropic shape is used. For comparison, as a ferromagnetic powder according to the conventional example, a powder having a ratio of major axis length to minor axis length of about 1 and a magnetically isotropic shape was used for comparison. The direction of the magnetic field applied during compression molding was parallel to the magnetic path, and the magnetic field strength was 10 kOe.

Table 1 shows the magnetic permeability μ and the relative green compact density of the dust core of Example 1 of the present invention and the conventional example at a frequency of 10 kHz.

[0018]

[Table 1]

As is apparent from Table 1, it can be seen that by using the powder according to Example 1, a powder magnetic core having a higher relative green compact density and a larger μ can be obtained than before. Furthermore, it can be seen that μ is further increased by molding while applying a magnetic field so that it is parallel to the magnetic path.

The powder according to Example 1 of the present invention has shape anisotropy, and the longitudinal direction of the powder is the easy axis of magnetization.
Therefore, to confirm that the powder is oriented,
It suffices if the manufactured powder magnetic core is cut along the magnetic path and the cross section is observed to find that the long axes of the powder are aligned in the magnetic path direction. Therefore, according to Example 1, the powder magnetic core manufactured by compression molding in a magnetic field was cut along the magnetic path, and its cross section was observed with an optical microscope. The longitudinal direction of the powder particles was found to be parallel to the magnetic path. It was confirmed that the powders were lined up and oriented along the magnetic path.

(Example 2) Fe-Si as a ferromagnetic powder
-Epoxy resin powder as a binder is mixed with Al-based alloy powder, and the mixture is inserted into a mold and compression-molded by changing the molding pressure in a magnetic field or no magnetic field.
Cured at a temperature of 00 ° C.

The ferromagnetic powder according to Example 1 of the present invention has a flat shape such that the ratio of the major axis length to the minor axis length is about 10, and is magnetically anisotropic. For comparison, as a ferromagnetic powder according to a conventional example, a powder having a ratio of major axis length to minor axis length of about 1 and having a magnetically isotropic shape was used for comparison. Using.

The direction of the magnetic field applied during compression molding should be parallel to the magnetic path, and the magnetic field strength should be 10 kOe.
And

Table 2 shows the magnetic permeability μ and the relative green compact density at a frequency of 10 kHz for the dust cores of Example 2 of the present invention and the conventional example.

[0025]

[Table 2]

As is clear from Table 2, the dust core according to Example 2 has a higher relative green compact density than the conventional one, and
It can be seen that μ is highly dependent on the molding pressure and has high performance.

The powder magnetic core produced by molding in a magnetic field according to Example 2 was cut along the magnetic path in the same manner as in Example 1, and its cross section was observed with an optical microscope to find powder particles. It was confirmed that the longitudinal direction of was parallel to the magnetic path, and the powder was oriented along the magnetic path.

(Example 3) Fe-Si as a ferromagnetic powder
-Epoxy resin powder as a binder is mixed with Al-based alloy powder, inserted into a mold, and compression-molded at a molding pressure of 10 ton / cm ² in a magnetic field having different magnetic field strengths.
Cured at a temperature of ~ 200 ° C.

The ferromagnetic powder according to the third embodiment of the present invention has a flat shape such that the ratio of the major axis length to the minor axis length is about 10, and is magnetically anisotropic. For comparison, as a ferromagnetic powder according to a conventional example, a powder having a ratio of major axis length to minor axis length of about 1 and having a magnetically isotropic shape was used for comparison. Using. The direction of the magnetic field applied during compression molding was set parallel to the magnetic path.

Table 3 shows the applied magnetic field dependence of the magnetic permeability μ of the powder magnetic core of Example 3 of the present invention and the conventional example at a frequency of 10 kHz.

[0031]

[Table 3]

As is clear from Table 3, the dust core according to Example 3 has a strong magnetic field dependency and is higher in performance than the conventional one. Further, the dust core produced according to Example 3 was cut along the magnetic path in the same manner as in Examples 1 and 2, and its cross section was observed with an optical microscope. It was confirmed that they were arranged in parallel and the powder was oriented along the magnetic path.

(Example 4) As the ferromagnetic powder, various Fe-Si-Al (ell) having different ratios of the major axis length and the minor axis length were used.
Epoxy resin powder as a binder was mixed with the system alloy powder, which was inserted into a mold, compression-molded in a magnetic field at a molding pressure of 10 ton / cm ² , and cured at a temperature of 100 to 200 ° C. The direction of the magnetic field applied during compression molding was parallel to the magnetic path, and the magnetic field strength was 10 kOe.

Table 4 shows a frequency of 10 kHz according to the fourth embodiment of the present invention.
The magnetic permeability μ and the relative green compact density are shown.

[0035]

[Table 4]

As is clear from Table 4, it is understood that a powder magnetic core having a large μ can be obtained by using the powder having a large ratio of the major axis length to the minor axis length. In addition, the powder magnetic core produced in Example 4 was cut along the magnetic path in the same manner as in Examples 1 to 3, and its cross section was observed with an optical microscope. The longitudinal direction of the powder particles was found to be the magnetic path. It was confirmed that they were arranged in parallel and the powder was oriented along the magnetic path.

(Embodiment 5) As a ferromagnetic powder, an Fe-Si-Al alloy powder having a flat and magnetically anisotropic shape with a major axis to minor axis ratio of 10 was used. Epoxy resin powder is mixed as a binder, inserted into a mold, and the E-type magnetic core is compression molded at a molding pressure of 10 ton / cm ² in a magnetic field and no magnetic field, at a temperature of 100 to 200 ° C. Cured.

FIG. 1 shows the magnetic field application direction during molding. In the figure, (a) the magnetic field is applied so that the direction of application during compression molding in a magnetic field is along the direction of the magnetic flux of the magnetic circuit of the dust core to be formed (Example 5), (b) dust This is performed for a magnetic core (comparative example 1) molded so that the magnetic flux direction of the magnetic circuit is partly the same as the magnetic field.
On the other hand, (c) shows no magnetic field (Comparative Example 2). The molding pressure is applied in the direction perpendicular to the paper surface in the figure.

Table 5 shows a frequency of 10 kHz according to the fifth embodiment of the present invention.
The magnetic permeability μ and the relative green compact density are shown. together,
The measured values under the same conditions of those molded in a non-magnetic field are also shown. The numbers in Table 5 correspond to the numbers in FIG.

[0040]

[Table 5]

As is clear from Table 5, when the magnetic field is applied along the magnetic flux of the magnetic circuit of the E-type dust core, the magnetic permeability μ and the relative green compact density increase.

The powder magnetic core produced by compression molding in a magnetic field according to Example 5 was cut along the magnetic path in the same manner as in Examples 1 to 4, and its cross section was observed with an optical microscope. It was confirmed that the longitudinal direction of the powder particles was parallel to the magnetic path, and the powder was oriented along the magnetic path.

(Embodiment 6) As a ferromagnetic powder, a Fe-Si-Al alloy having a flat and magnetically anisotropic shape having a ratio of the major axis length to the minor axis length of 10 is obtained. Epoxy resin powder as a binder is mixed with the powder, and it is inserted into a mold and the molding pressure is 10 tons / cm in a magnetic field and no magnetic field.
^2. Compress the toroidal dust core with ² to 100 ~ 20
Cured at a temperature of 0 ° C.

FIG. 2 shows the application direction of the magnetic field during molding. As shown in the figure, when the toroidal dust core 5 was molded, a pulse current was applied to induce a magnetic field along the direction of the magnetic flux of the magnetic circuit of the dust core 5. The average magnetic path length of this dust core was 2 cm, and the current I passing through the central portion was a pulse current of about 10000A. The magnetic field H passing through the magnetic circuit is about 6 kOe.

Table 6 shows the magnetic permeability μ and the relative compact density of the toroidal type dust core of Example 6 of the present invention at a frequency of 10 kHz. In addition, the measured values (Comparative Example 3) under the same conditions of those molded in a non-magnetic field are also shown. The numbers in Table 6 correspond to the numbers in FIG.

[0046]

[Table 6]

Regarding the alloy system used in the examples of the present invention, only the Fe-Si-Al (ell) system has been described, but the same effect can be expected with other alloy systems. Also,
In the examples of the present invention, only the epoxy-based resin is shown as the binder, but it is clear that the same effect can be obtained even if other kinds of thermosetting resins are used. In addition, although some molding methods have been described in the examples,
It is clear that the same effect can be obtained by using other molding methods.

[0048]

As described above, according to the present invention, a magnetically anisotropic shape, specifically, a flat shape or a needle shape in which the ratio of the major axis length to the minor axis length is greater than 1. By using powder and orienting it so that it is parallel to the magnetic path, one with a higher μ than the conventional dust core can be obtained. Further, in order to orient the powder so as to be parallel to the magnetic path, a magnetic field may be applied parallel to the magnetic path, and a dust core having higher performance than the conventional one can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing a magnetic field application direction when molding an E-shaped dust core.

FIG. 2 is a diagram showing a current applied when molding a toroidal dust core and a magnetic field induced by the current.

[Explanation of symbols]

 1,2,3 E type dust core 5 Toroidal type dust core

Claims (4)

[Claims] 1. A powder compact containing ferromagnetic powder having magnetic anisotropy, wherein the easy axis of magnetization of the ferromagnetic powder is oriented along the magnetic flux of a magnetic circuit. Dust core. 2. When a ferromagnetic powder having magnetic anisotropy is formed by applying a forming pressure in a magnetic field, a magnetic field is applied along the direction of the magnetic flux of the magnetic circuit, thereby A method for manufacturing a dust core, which comprises orienting an axis of easy magnetization. 3. The method for manufacturing a powder magnetic core according to claim 2, wherein the molding is performed so that a load direction of the molding pressure and a magnetic field applying direction are orthogonal to each other. .. 4. The method for manufacturing a dust core according to claim 2 or 3, wherein the dust core has a toroidal shape, and at the time of molding, an electric conductor is provided at the center to conduct electricity. A method for manufacturing a dust core, comprising applying a magnetic field to the green compact.