JPH11329821A - Dust core and manufacturing method thereof - Google Patents

Abstract

(57) [Problem] To provide a dust core having high magnetic permeability, excellent high-frequency characteristics, and good core loss characteristics, and a method for producing the same. SOLUTION: An alloy powder containing Fe—Si—Al as a main component has an aspect ratio of 5 or more, a short axis diameter of the powder of 50 μm or less, and a long axis diameter of 20 μm to 100 μm.
A powder obtained by mixing powders each having a major axis diameter of 20 μm or less and 100 μm or more at a total weight ratio of 20% or less, and a powder obtained by mixing a binder and compression molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-performance dust core used for a choke coil or the like and a method for producing the same.

[0002]

2. Description of the Related Art 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 manufactured by molding a metal powder has an advantage of being superior in DC superimposition since it has a higher saturation magnetic flux density than soft magnetic ferrite.

However, since the dust core is made by mixing metal powder with an organic binder and compression-molding, it has the disadvantages of low magnetic permeability and poor frequency characteristics of magnetic permeability. Is high.

On the other hand, in response to the demand for miniaturization of electronic components accompanying the recent demand for miniaturization of electronic equipment, it is strongly desired to improve the magnetic properties of the dust core. As a specific example, while achieving the miniaturization of the dust core and the requirement that the inductance of the coil be the same, the improvement of the permeability of the dust core, the improvement of the frequency characteristics, and the improvement of the core loss are strong. Is desired.

[0005] In general, there are two methods for improving the magnetic permeability of a dust core, which are methods of increasing the magnetic permeability of the raw material itself and increasing the filling rate.

Conventionally, the method of improving magnetic permeability mainly focuses on improving the filling rate. Examples of the means include increasing the molding pressure, changing the binder conditions variously, and using two or more different shapes. , Mixing powders having different particle sizes, compositions, etc., have been studied.

[0007]

However, the improvement of the magnetic permeability of the dust core by the above-mentioned method has already been studied. For example, even if the molding pressure is increased, the life of the mold is reduced. For example, the situation was not negligible in terms of manufacturing costs. Therefore, significant improvement from the current characteristic level is difficult, and it has not been possible to cope with recent miniaturization of equipment.

[0008] Further, it is essential to reduce the core loss as well as to improve the magnetic permeability. However, the core loss of the conventional dust core is considered to depend on the method of producing the raw material and the like. Few cases have been reduced.

Accordingly, an object of the present invention is to provide a dust core having high magnetic permeability, excellent high-frequency characteristics, and good core loss characteristics, and a method for producing the same.

[0010]

Means for Solving the Problems The present inventors have studied to achieve the above object, and as a result, the raw material powder has an aspect ratio of 5 or more, the minor axis diameter of the powder is 50 μm or less, and the major axis diameter is 50 μm or less. By using a powder having a major axis diameter of 20 μm to 100 μm and a total of powders of 20 μm or less and 100 μm or more in a weight ratio of 20% or less, the magnetic permeability and core loss characteristics of the dust core are reduced. It was found that it was significantly improved.

That is, according to the present invention, an alloy powder containing Fe-Si-Al as a main component has an aspect ratio of 5 or more, a minor axis diameter of 50 μm or less, and a major axis diameter of 20 μm to 1 μm.
A powder having a major axis diameter of 20 μm or less and 100 μm
This is a dust core obtained by mixing a powder obtained by mixing the above powders at a total weight ratio of 20% or less and a binder, and compression molding.

Further, the present invention is the method for producing a dust core, wherein the step of compression-molding the powder mixed with the binder is carried out in a temperature range from room temperature to a curing temperature of the binder.

Further, the present invention is the above-mentioned method for producing a dust core, wherein the step of curing the binder is performed while maintaining the shape of the molded body.

The flattening of the raw material powder has a great effect on the improvement of the magnetic permeability of the dust core, but on the other hand, the anisotropy of the powder shape causes the magnetic properties to show anisotropy depending on the magnetization direction. The degree of powder orientation in the direction greatly affects the electromagnetic characteristics of the dust core.

Various methods for improving the degree of powder orientation are conceivable, for example, magnetic field orientation and the like. However, if the powder shape is not uniform, the powder orientation will be destroyed when the powder is compressed. The reason for the improvement in the magnetic properties is considered to be that the degree of powder orientation in the direction of the magnetic path was improved by adjusting the powder shape to a certain range.

Here, when the heat treatment of the powder is performed in the air,
An insulating layer is formed on the surface of the powder, and the frequency characteristics of magnetic permeability can be remarkably improved. In addition, by performing the heating in a state of being heated during molding, a magnetic core having a higher magnetic permeability can be obtained.
By hardening the binder while keeping the dimensions of the molded body constrained, a magnetic core with higher magnetic permeability can be obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Starting materials may be variously considered, such as pulverized powder from an ingot by melting method, atomized powder, and the like. However, if the concentration distribution of the composition is uniform, there is no limitation on the production method. The aspect ratio of the powder can be changed by grinding with an attritor or the like. The aspect ratio can be arbitrarily changed depending on the pulverization time, but the aspect ratio is set to 5 or more, the thickness of the powder is set to 50 μm or less, and the total of the powders having a major axis diameter of 20 μm or less and 100 μm or more is expressed in weight ratio. By using a powder having a content of 20% or less, a dust core excellent in magnetic permeability and core loss characteristics can be manufactured.

Here, the reason why the particle size of the powder is specified is as follows. If the aspect ratio is less than 5, the magnetic permeability of the dust core is not sufficient, and if the short axis diameter of the powder exceeds 50 μm, This is because the core loss characteristics of the dust core are substantially reduced, and the major axis diameter is 20 μm or less and 100 μm or less.
If the total of the above powders exceeds 20% by weight, the degree of powder orientation in the dust core is remarkably reduced, so that the magnetic permeability of the dust core and the core loss increase. .

Here, a magnetic core having a higher magnetic permeability can be obtained by performing the powder molding at a temperature not lower than room temperature and not higher than the curing temperature of the binder. This is presumably because the fluidity of the binder was improved with an increase in the temperature, so that the friction between the alloy powders during molding was reduced, which had a favorable effect on the filling of the powder and the orientation of the powder. The reason why the molding temperature is specified is that the fluidity of the binder improves at room temperature or higher, and when the curing temperature is exceeded, curing of the binder starts and the fluidity decreases.

The magnetic permeability can also be improved by curing the binder of the molded body while keeping the dimensions of the molded body constrained. This is because molded bodies made of high aspect ratio powder have large springback,
This is because it is very effective to improve the filling rate when the binder is hardened after molding while keeping the dimensions at the time of molding.

[0021]

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

(Example 1) BalFe-10 wt% Si-5 wt% Al alloy powder produced by the atomizing method was used as a raw material, and the powder was flattened using a ball mill. In this example, a powder having an aspect ratio of 10 was produced. Next, using a 20 μm and a 100 μm sieve, this powder was used to prepare a 20 μm to 100 μm powder. Next, this powder was heat-treated at 700 ° C. in the air for 2 hours. Further, 3 wt% of a silicone resin was mixed with the powder, and molded at 5 (ton / cm ² ) at room temperature using a mold having an outer diameter of 20 mm and an inner diameter of 10 mm to obtain a toroidal dust core.

Next, these dust cores are subjected to a heat treatment at 170 ° C. for 2 hours in the air to cure the binder.
Heat treatment was performed at 700 ° C. for 2 hours in the air. Next, winding was performed on these magnetic cores, the inductance at 100 kHz was measured using a YHP impedance analyzer 4194A, and the magnetic permeability was determined by calculation. Also,
The applied magnetic field is 1000
G, the core loss characteristics of the dust core were measured under the conditions of a measurement frequency of 100 kHz.

Further, as a comparative example, an unclassified powder produced in exactly the same steps as in the above example was heat-treated at 700 ° C. in the air until the powder was flattened, and molded in exactly the same steps as in the above example. The properties of the magnetic core obtained by the heat treatment were measured. Table 1 shows the results.

(Table 1)

Table 1 shows that the magnetic core according to the present invention has improved magnetic permeability and core loss characteristics as compared with the comparative example.

(Example 2) 20 to 1 produced in Example 1
15, 20, 25, 30, and 100 μm powder in weight ratio
The powder having a size of 20 μm or less and the powder having a size of 100 μm or more generated by the powder classification process of Example 1 at a ratio of 40% were respectively 1:
After mixing at a ratio of 1, a magnetic core was prepared in exactly the same manner as in Example 1, and after winding, the magnetic permeability and core loss were measured in exactly the same manner as in Example 1. Table 2 shows the results.

(Table 2)

From Table 2, it is found that powder having a particle size of 20 μm or less and 100 μm
It can be seen that when the powder of m or more exceeds 20%, the magnetic permeability and the core loss characteristics are rapidly deteriorated. This is presumably because the degree of powder orientation in the direction of the magnetic path is significantly reduced as the particle size distribution of the powder becomes wider. In other words, when the powder content is 20% or less, not only does the permeability increase when the degree of orientation of the powder is high, but also high magnetization can be obtained in a low magnetic field.
It is presumed that the core loss characteristics were also significantly improved.

In the above embodiment, the heat treatment of the powder was performed at 700 ° C. in the air. However, the heat treatment can be performed in a temperature range of 300 ° C. to 1000 ° C. and in an atmosphere containing oxygen. Effects can be obtained.

[0031]

As described above, according to the present invention,
By using raw material powder with uniform aspect ratio,
A dust core having a high magnetic permeability and a low core loss can be easily manufactured. Further, by molding at a temperature not lower than room temperature and not higher than the curing temperature of the binder, a dust core having more excellent magnetic properties can be obtained. Further, by hardening the binder while keeping the dimensions of the magnetic core constrained, it becomes possible to manufacture a dust core having more excellent magnetic properties.

Claims (3)

[Claims] An alloy powder containing Fe—Si—Al as a main component has an aspect ratio of 5 or more, a powder having a minor axis diameter of 50 μm or less, and a major axis diameter of 20 μm to 100 μm.
A dust core obtained by mixing a powder obtained by mixing powders having a major axis diameter of 20 μm or less and 100 μm or more at a total weight ratio of 20% or less, a binder, and compression molding. 2. The method for producing a dust core according to claim 1, wherein the step of compression-molding the powder mixed with the binder is performed at a temperature range from room temperature to a curing temperature of the binder. . 3. The method according to claim 2, wherein the step of curing the binder is performed while maintaining the shape of the molded body.