JP2000021664A - Production of dust core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To orient powder in the magnetic circuit direction of a core by mixing flat soft magnetic metal powder with binder, extrusion molding the mixture to produce a thin flat molding, laminating the thin moldings such that the orientation of powder is in parallel with the magnetic circuit direction of a dust core and then compression molding the laminate. SOLUTION: Molding material is fed, under thermally fused state, into the heated cylinder of an extruder and then extruded from a die by means of a screw located in the cylinder to produce a molding. The molding material is produced by admixing flat powder with a binder being fluidized thermally. The moldings are laminated such that the orientation of flat powder is aligned with the magnetic circuit direction of the core and then subjected to thermal compression molding. Preferably, the flat powder has aspect ratio (diameter/ thickness) of 10-40 and actual diameter of 10-80 μm in order to ensure high magnetic characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust core,
In particular, the present invention relates to a method for manufacturing a high-performance dust core that is optimal for a choke coil or the like.

[0002]

2. Description of the Related Art Soft magnetic ferrite cores and dust cores are used as choke coils used at high frequencies. Among them, the ferrite core has a disadvantage that the saturation magnetic flux density is small. On the other hand, a dust core produced by molding a soft magnetic metal powder has an advantage that it has an excellent DC superimposition characteristic because it has a significantly higher saturation magnetic flux density than a ferrite core. . However, since the dust core is made by mixing metal powder with an organic binder and compression molding, the magnetic permeability is low,
Further, it has a disadvantage that the high-frequency characteristics of the magnetic permeability are poor.

[0003] In addition, in response to the demand for miniaturization of electronic parts accompanying the recent demand for miniaturization of electronic equipment, it is strongly desired to improve the magnetic characteristics of the dust core. This is because it is required that the inductance of the coil be equivalent while achieving the miniaturization of the dust core.
For that purpose, it is essential to improve the magnetic permeability of the dust core and the frequency characteristics.

Methods for improving the magnetic permeability of a dust core are roughly classified into the following two points. Increase the filling rate of metal powder. The long axis direction of the flattened metal powder is oriented in the direction of the magnetic path of the dust core to reduce the demagnetizing coefficient.

In the method (1), the cross-sectional area of the powder in the direction of the magnetic path is reduced, and an improvement in frequency characteristics due to a reduction in eddy current loss can be expected.

As means for increasing the pressure, for example, increasing the molding pressure, changing the conditions of the binder variously, and blending two or more powders having different shapes, particle sizes, compositions, and the like have been studied. However, the improvement of the magnetic permeability of the dust core by those methods has already been thoroughly studied. For example, even if the method of increasing the molding pressure is used, the mold cost is increased, and the manufacturing cost cannot be ignored. In the situation.

[0007] As for the method described above, the conventional production method in which a binder is added to metal powder and compression molding is performed has the following two problems.

A) When the compression direction of the dust core is ring-shaped or the like and the compression direction is perpendicular to the magnetic path of the magnetic core, orientation of the flattened powder in the direction of the magnetic path can be expected to some extent. Orientation becomes insufficient due to disturbance of the orientation due to the resistance of the raw material powder to the wall surface of the mold.

B) In response to recent demands for downsizing, cost reduction, and high performance of electronic equipment, it is necessary to simultaneously reduce the mounting area, winding cost, and leakage magnetic flux of the dust core. The shape of the magnetic core is required to be a pot type or an EE type. In order to obtain these shapes by compression molding, orientation is impossible because there are places where the compression direction is not perpendicular to the magnetic path of the magnetic core.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high magnetic permeability, high frequency characteristics, and a high degree of shape freedom by sufficiently orienting the flattened powder in the direction of the magnetic path of the magnetic core. Another object of the present invention is to provide a method for manufacturing a dust core which can be easily manufactured.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies on a molding method for sufficiently orienting the flattened powder in the direction of the magnetic path of the magnetic core. The present invention has been accomplished by applying known extrusion molding.

That is, according to the present invention, a thin plate-like compact obtained by mixing a binder with a flat soft magnetic metal powder and extruding the powder is formed so that the magnetic path direction of the dust core and the orientation direction of the powder are parallel. This is a method for manufacturing a dust core which is laminated and compression molded.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In extrusion molding, a molding raw material in a heat-melted state is supplied into a heated cylinder of an extruder, and then extruded from a die by a screw located in the cylinder to form a molded body. Things.

The raw material for molding is prepared by mixing a binder having fluidity by applying heat to the flat powder. Therefore, when this molding material is extruded from the die during the extrusion molding process, the molding material is formed by the shearing force due to the extrusion and the fluidity of the molding material.
The flat powder is strongly oriented in the long axis direction in the direction of the flow path in the mold so that the flow resistance is minimized. Furthermore, by laminating the obtained molded body such that the orientation direction of the flat powder and the magnetic path direction of the magnetic core match, even in the case of a core having a complicated shape, the flat powder is oriented in the magnetic path direction of the magnetic core. Sufficient orientation can be achieved.

The material can be oriented in the direction of the magnetic path by directly compression molding while heating the molding material, but the effect is insufficient. A higher degree of orientation can be obtained by laminating the laminated thin plates and performing compression molding while heating.

As the soft magnetic metal powder used in the present invention, it is preferable to use a powder composed of iron-based soft magnetic metal particles. Fe-based soft magnetic metals include Fe, Fe-
Si-Al, Fe-Ni, Fe-Co, Fe-Si, F
It is selected according to the required magnetic characteristics by e-P, Fe-Mo-Ni, or the like.

The flat soft magnetic metal powder is prepared by coarsely pulverizing an ingot of a required composition with a disk mill or the like, and then pulverizing with a pulverizer using a pulverizing medium such as a ball mill having a rolling action and a shearing action. It is obtained by doing.
Instead of the coarse grinding method using the ingot grinding method described above,
It is also possible to use a gas atomizing method, a water atomizing method, a rotating disk method, or the like.

Aspect ratio (diameter / thickness) of flat powder
Is preferably about 10 to 40, and the actual diameter is 1
0 to 80 μm is desirable for obtaining high magnetic properties.

The binder used in the present invention includes:
It is possible to use various organic polymers and silicone resins that can be extruded, and various types are selected according to the required characteristics of the magnetic core.

[0020]

The present invention will be described below with reference to examples.

First, Fe-Si-Al is melted by vacuum melting.
An alloy ingot was obtained. Next, this was roughly pulverized with a disk mill to obtain a powder having a size of 100 μm or less. This powder was pulverized by a wet ball mill for 50 hours to obtain a flat powder having an average diameter of 40 μm and an average thickness of 2 μm, that is, an aspect ratio of 20. The average diameter and average thickness of the powder were determined by averaging 100 powders in an electron micrograph.

The obtained flat powder was kneaded with a silicone resin and stearic acid in a weight ratio of 93: 6: 1 by a pressure kneader for 30 minutes to obtain pellets as a raw material for molding.

Next, a plate-shaped molded product having a width of 20 mm and a thickness of 2 mm was obtained from the pellets at a molding temperature of 200 ° C. by an extruder.

[0024] As shown in FIG.
Are stacked, and molds 2, 3, 12, and
13, after compression molding at 200 ° C.,
Heat treatment was performed at 00 ° C. for 2 hours to obtain a dust core of the present invention. The arrow in FIG. 1 indicates the orientation direction of the flat powder.

As a comparative example, the above-prepared raw material for molding was compression-molded at 200 ° C. by a compression-molding die having the same shape as that shown in FIG.
For 2 hours to obtain a conventional dust core having the same shape as the present invention.

Next, a 50-turn winding was applied to the dust core, and the impedance was measured at 1 kHz to 40 MHz using an impedance analyzer.
The frequency characteristic of the magnetic permeability of Hz was measured. The dimensions of the magnetic core used for the measurement were such that the length of the bottom (magnetic joint) was 30 mm,
The thickness of the bottom is 5 mm, and the length of the magnetic leg (the length from the bottom surface to the joint surface) is 20 mm.

Table 1 shows the values of the magnetic permeability at 100 kHz of the product of the present invention and the conventional product.

[0028]

From Table 1, it can be seen that the product of the present invention has a higher magnetic permeability than the conventional product in each of the shapes a and b.

FIG. 2 shows the frequency characteristic of the magnetic permeability of the shape a. FIG. 2 shows that the magnetic permeability of the dust core obtained by the method of the present invention shows a constant value up to higher frequencies.

[0031]

According to the present invention, it is possible to provide a method of manufacturing a dust core which has a higher magnetic permeability, higher frequency characteristics, a higher degree of freedom in shape, and can be more easily manufactured than conventional methods. It is possible. Therefore, the present invention is extremely effective industrially.

[Brief description of the drawings]

FIG. 1 is a view showing a dust core of shapes a and b obtained in an example and a molding method.

FIG. 2 is a diagram showing frequency characteristics of magnetic permeability of a dust core having a shape a obtained in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molded object 2, 3, 12, 13 Die 4 Dust core of shape a 14 Dust core of shape b

Claims (1)

[Claims] 1. A flat soft magnetic metal powder mixed with a binder, and a thin plate-like compact obtained by extrusion molding is laminated so that the direction of the magnetic path of the dust core and the orientation direction of the powder are parallel. And manufacturing the powder magnetic core by compression molding.