JPH1174140A - Manufacture of dust core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dust core having high permeability and a high-frequency characteristic by extrusion-molding flaky soft magnetic metal powder into a plate-like shape. SOLUTION: Flaky powder having lengths of 40 μm and an average thickness of 2 μm, and aspect ratio of about 20 is obtained by crushing an Fe-Si-Al alloy ingot with a disk mill and grinding the crushed pieces in a ball mill for 50 hours. Then, a raw molding material is obtained by mixing a silicone resin and stearic acid with the flaky powder at a mixing ratio of 93:6:6 in wt.% and kneading the mixture for 30 seconds with a pressure kneader and the raw material is pelletized. Then, the pelletized raw material is extrusion-molded into platy bodies having thicknesses of 0.50, 1.4, 7, 10, and 13 mm by means of an extrusion-molding machine by using a mold, which has a width of 20 mm and a variable width at a molding temperature of 200 deg.C. Thereafter, a dust core is obtained by punching each obtained molded body into a toroidal shape of 15 mm ϕ×10 mm and heat-treating the punched body at 700 deg.C for two hours. Therefore, the permeability and high-frequency characteristics of the dust core can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a dust core used 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 low. On the other hand, a dust core made 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. I have. However, since the dust core is prepared by mixing a metal powder with an organic binder or the like and compression-molding the powder magnetic core, it has a drawback of low magnetic permeability and poor high-frequency characteristics of the magnetic permeability.

[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 that the magnetic properties of the dust core be improved. this is,
This is because it is required that the inductance of the coil be equivalent while achieving the miniaturization of the dust core, and for that purpose, it is essential to improve the permeability of the dust core and the frequency characteristics. is there.

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 improvement in frequency characteristics due to reduction of eddy current loss can be expected.

As means for increasing the pressure, for example, increasing the molding pressure, changing the conditions of the binder in various ways, 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 these methods has already been thoroughly studied. I cannot do it.

[0007] In the conventional manufacturing method in which a binder is added to metal powder and compression molding is performed, the shape of the dust core is such that the compression direction such as a ring shape is perpendicular to the magnetic path of the magnetic core. In the case of the direction, the orientation of the flat powder in the direction of the magnetic path can be expected to some extent, but the orientation becomes insufficient due to the disorder of the orientation due to the resistance of the raw material powder for molding to the wall surface of the mold. There are problems such as.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a powder magnetic core having high magnetic permeability and excellent high-frequency characteristics by sufficiently orienting the flat powder in the direction of the magnetic path of the magnetic core. It is to provide a manufacturing method.

[0009]

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

That is, the present invention is a method for producing a dust core formed by extruding a flat soft magnetic metal powder into a plate shape.

The present invention also provides a method for producing a dust core, wherein the dust core is formed to a thickness of 10 mm or less.

The present invention also relates to a method for manufacturing a dust core in which the obtained compact is laminated to a thickness of 10 mm or less.

In extrusion molding, a molding raw material in a heated and molten state is supplied into a heated cylinder of an extrusion molding machine, and then extruded from a die by a screw located in the cylinder.

The raw material for molding is prepared by mixing a flat powder with a binder having fluidity by applying heat. Therefore, when this molding material is extruded from the die during the extrusion molding process, the flow force in the mold is set so that the flow resistance is minimized by the shearing force due to the extrusion and the fluidity of the molding material. The flat powder is strongly oriented in the major axis direction. Therefore, by molding using a mold in which the direction of the magnetic path of the magnetic core and the direction of the flow path in the mold coincide, the flat powder can be sufficiently oriented in the direction of the magnetic path of the magnetic core. Become.

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 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 vibration 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, 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 10 to 40.
８０80 μm is desirable for obtaining preferable high magnetic properties.

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

In the present invention, the thickness of the molded product obtained by extrusion molding is set to 10 mm or less.
When a molded body having a thickness exceeding the above range is used, the shearing force at the time of molding becomes small, and no remarkable improvement in the magnetic permeability is recognized as compared with the magnetic permeability of the dust core in the conventional method.

The required thickness of the dust core is 10 m.
If the diameter exceeds m, a dust core having higher characteristics than a dust core manufactured by a conventional method can be obtained by laminating thin sheets extruded to a size of 10 mm or less.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION A binder is mixed with a flat soft magnetic metal powder and extruded so that the extrusion direction of a molding material is the direction of the magnetic path of a magnetic core, or obtained by extrusion. The thin plate-shaped compacts are laminated to obtain a compact of a dust core.

[0022]

EXAMPLE An ingot powder of an Fe--Si--Al alloy was pulverized by a disk mill, and the obtained powder was pulverized by a ball mill for 50 hours. The average length in the longitudinal direction was 40 μm, the average thickness was 2 μm, and the aspect ratio was about 20. Was obtained.

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 form a raw material for molding and pelletized.

Next, the pelletized product was molded with an extrusion molding machine at a molding temperature of 200 ° C., a width of 20 mm, and a thickness variable to a thickness of 0.5 mm.
A plate-shaped molded body of 1, 4, 7, 10, 13 mm was obtained.

The obtained compact was punched into a toroidal shape of φ15 mm × 10 mm and heat-treated at 700 ° C. × 2 hr to obtain a dust core. Similarly, the thickness is 5.5.
Two rings having a thickness of 10 mm were prepared and laminated by hot pressing so as to have a thickness of 10 mm, and then heat-treated in the same manner to obtain a dust core.

As a comparative example, a raw material powder for molding was used in a mold of φ15 mm × 10 mm with a thickness of 0.5 mm.
It was compression-molded to 5, 5, 4, 7, 10, and 13 mm to obtain a dust core, and similarly heat-treated. The powder was prepared so that the filling rate of the powder was about 75% in all samples.

Next, these rings are wound, and YHP
The magnetic permeability at a frequency of 100 kHz was measured by using an impedance analyzer 4149A manufactured by Toshiba Corporation. Table 1 shows the results.

[0028]

From Table 1, it can be seen that the magnetic permeability of the dust core whose sample thickness is 10 mm or less shows a higher value than the magnetic permeability of the dust core according to the conventional method. Further, it can be seen that the dust core having a thickness of 10 mm produced by laminating the rings according to the present invention has a higher magnetic permeability than the dust core having a thickness of 10 mm according to the conventional method.

FIG. 1 shows the frequency characteristics of the magnetic permeability of a dust core having a thickness of 0.5 mm. FIG. 1 shows that the magnetic permeability of the dust core in the method of the present invention shows a constant value up to a higher frequency.

[0031]

As described above, according to the present invention,
It is possible to provide a method for manufacturing a dust core having higher magnetic permeability and excellent frequency characteristics than before.

[Brief description of the drawings]

FIG. 1 is a diagram showing frequency characteristics of magnetic permeability of a dust core when the thickness of a sample is 0.5 mm.

[Explanation of symbols]

 1 present invention method 2 conventional method

Claims (3)

[Claims] 1. A method for producing a dust core, wherein a flat soft magnetic metal powder is formed into a plate by extrusion. 2. The method for manufacturing a dust core according to claim 1, wherein the method comprises forming the dust core to a thickness of 10 mm or less. 3. The method of manufacturing a dust core according to claim 1, wherein the obtained molded body is laminated to a thickness of 10 mm or less.