JP2001196216A - Dust core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dust core of low loss which has high saturation magnetic flux density. SOLUTION: Amorphous soft magnetic alloy powder A and fine powder B of soft magnetic metal which are different in grain diameter is stirred and mixed in a condition that the mode of grain size distribution of the powder A is at least five times that of the powder B and the volume percentage of the powder B to the total sum of volumes of the powder A and powder B is at least 3 vol.% and at most 50 vol.%. After that, binder and lubricant are added, and pressure molding is performed by using a metal mold having a specified shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an inductance element such as a choke coil and a transformer mounted on an electric circuit.

[0002]

2. Description of the Related Art Currently, ferrite is mainly used as a magnetic core material for inductance elements such as transformers and choke coils. Ferrite has excellent moldability and workability, and is inexpensive.
This is a highly versatile magnetic material that can be used up to high frequencies and has features such as low loss and high magnetic permeability.

On the other hand, as a soft magnetic material other than ferrite, there is a dust core using a metal soft magnetic material powder such as an Fe-Al-Si alloy, permalloy, or pure iron powder. In the case of inductors that are used by adjusting the magnetic permeability μi from several tens to one hundred and several tens, such as a smoothing choke coil and a PFC (power factor improvement) choke coil for harmonic countermeasures, a dust core is used instead of ferrite. The cases where are used are increasing. This powder magnetic core has a feature that the saturation magnetic flux density is higher than that of the ferrite, so that the magnetic core can be miniaturized and the stability of temperature characteristics of magnetic permeability is excellent. However, the magnetic core loss is larger than that of ferrite, and it has not been widely adopted for applications in which heat generation due to the magnetic core loss is a problem.

[0004] Recently, as means for solving the above-mentioned problems, development of powder magnetic cores made of powders of amorphous alloys with small magnetic core loss, ultra-microcrystalline alloys on which nanoscale microcrystals are precipitated, and the like has been actively pursued. The magnetic core loss of the powder is as low as or less than ferrite, and is suitable as a powder for a dust core.

[0005]

However, the strength of amorphous or microcrystalline metal is remarkably higher than that of a conventionally used coarse crystalline soft magnetic metal, and the powder is broken during pressure molding. Tends to be difficult. Conventional materials, such as pure iron and permalloy, are easily plastically deformed, and Fe-Al-Si alloys are brittle.Each powder is deformed or broken at the time of pressure molding. As a result, the density of the magnetic core is increased and the density is increased. It is relatively easy to convert. In contrast, amorphous alloys,
Powders made of ultra-microcrystalline alloys and the like are difficult to deform and break at room temperature, so it is difficult to densify them under the same pressure as conventional materials, and it is difficult to adopt a room-temperature dry molding method that is cost-effective. Was. For this reason, conventional molding examples using these powders are mainly examples of molding at a high temperature at which the powder is easily deformed by hot pressing or the like, and a method of providing a magnetic core excellent in characteristics at low cost and in large quantities. Was not established.

[0006] Dust cores using metal powders, including conventional materials, are generally mass-produced by dry molding at room temperature.
Like the ferrite, the powder is put into a mold and molded under pressure, and then heat-treated. However, unlike ferrite which is densified by a sintering reaction, the main purpose of heat treatment of a dust core is to remove distortion due to pressure molding, and heat treatment hardly densifies. The reason is that, when the metal powder is sintered at an increased heat treatment temperature, the insulation between the metal powders is broken, and the eddy current loss at a high frequency increases, which is not suitable as a high-frequency magnetic material. Therefore, in the dust core, it is necessary to densify only by pressure molding and to achieve a predetermined density. For this reason, the molding pressure is several hundred MPa to 2000 MPa, which is several times higher than that of ferrite molding, and the durability of the mold is increased. Due to the problem, there was a problem that a magnetic core having a complicated shape could not be molded.

An object of the present invention is to provide a dust core having a high saturation magnetic flux density and a low loss by reducing the magnetic core loss in the dust core, reducing the high molding pressure which is the above problem. Is what you do.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a dust core obtained by mixing powder A composed of an amorphous soft magnetic alloy and fine powder B of a soft magnetic alloy, and pressing the mixture. A dust core in which the mode of the particle size distribution is at least 5 times that of powder B and the volume percentage of powder B with respect to the total volume of powder A and powder B is 3% or more and 50% or less. .

The present invention also provides a powder magnetic core obtained by mixing powder A comprising a microcrystalline soft magnetic alloy for precipitating nanoscale microcrystals and fine powder B of a soft magnetic alloy and pressing the mixture. Powder magnetic core whose mode of particle size distribution is 5 times or more of that of powder B and whose volume percentage of powder B to the total volume of powder A and powder B is 3% or more and 50% or less. is there.

The present invention also provides a dust core in which the soft magnetic alloy fine powder B is an amorphous alloy or an ultra-microcrystalline alloy that precipitates nanoscale microcrystals.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention achieves a significant improvement in molding density by mixing a fine powder B with a coarse powder A. This is because (1) fine particles (fine powder B) fill the voids between the coarse particles (coarse powder A) to improve the particle space factor in the required magnetic core shape, and (2) pressurization. This is presumed to be due to the fact that the fine particles can move relatively freely at the time of molding (at the time of molding), which facilitates rearrangement of the coarse particles. That is, even if the powder material is hard to be deformed and broken by pressure, such as amorphous soft magnetic alloy powder and ultra-microcrystalline soft magnetic alloy powder, the powder magnetic core is formed by a room temperature dry molding method which is excellent in mass productivity. be able to. Moreover, the inventor's diligent studies have revealed that the mode of the particle size distribution of the coarse powder A is at least five times that of the fine powder B, and that the volume percentage of the powder B with respect to the total volume of the coarse powder A and the fine powder B is By setting the content to 3% or more and 50% or less, it is possible to obtain a dust core having excellent magnetic properties, which are features of an amorphous soft magnetic alloy and a microcrystalline soft magnetic alloy.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described below.
As the powder A, an amorphous powder prepared by adding Fe as a main component, adding B, Si, or the like in a complex manner, melting the mixture, and then rapidly cooling it by a water atomizing method was used. Fe-Al-Si as powder B
Water atomized fine powder of the alloy composition was used. The powder A was not heat-treated after atomization, and the powder B was annealed in hydrogen at 550 ° C. 1 and 2 show the particle size distributions of powders A and B, respectively.
Shown in The particle size distribution is measured by a laser scattering method. The mode of the particle size of the powder A is in the rank of 44 to 62 μm, and the central value 53 μm is the mode of the powder A. (Hereinafter, the mode of particle size of each powder was calculated by this method). The mode of the particle size of the powder B is 6.7 μm. The mode ratio between powder A and powder B is 7.9.

After a predetermined amount of powders A and B were placed in a mortar and mixed with stirring, a polyimide varnish was added as a binder, and the mixture was further stirred and granulated through a 60 mesh sieve. The amount of the binder was determined so that the solid content of the varnish after the solvent was dried was 1.0 part by weight based on 100 parts of the powder. Further, 0.3 part of zinc stearate was added and mixed as a lubricant to 100 parts of the granulated powder.

Approximately 3.0 g of the above granulated powder is weighed with an outer diameter of 13.4
mm, 7.7 mm inside diameter in a toroidal mold,
Pressure molding was performed at a molding pressure of 5 × 10 ⁸ to 15 × 10 ⁸ Pa. The height of the molded dust core is about 5 mm. After heat treating the dust core in a nitrogen atmosphere at 470 ° C. for 60 minutes, the dimensions and weight were measured to calculate the density and the space factor. Next, place the dust core in a plastic case and wind it.
The magnetic permeability μi at 100 kHz was measured with an R meter. In addition, 100 KH by B-H analyzer
The core loss Pc at 100 mT was measured. Furthermore, the sum of the saturation magnetic flux densities of the respective magnetic materials and the volume percentage multiplied by the volume percentage was defined as the composite saturation magnetic flux density, and the product obtained by multiplying this by the space factor was regarded as the composite saturation magnetic flux density Bs of the obtained magnetic core.

Table 1 shows that the molding pressure of Example 1 was 15 × 10 ^8.
The data of the sample prototyped in Pa is shown. As a conventional material for comparison, an Mn-Zn based ferrite core adjusted to have a magnetic permeability μi of about 70 by inserting a gap, Fe-A
The data of the dust core (formed at 20 × 10 ⁸ Pa) using the l-Si alloy powder is also shown. When measuring the ferrite core, a litz wire bundled with a copper wire was wound in order to reduce eddy current loss due to the leakage magnetic flux generated from the gap crossing the copper wire.

In this embodiment, since the molding density can be increased,
Both μi and Bs have higher values than Comparative Example 1-8 in which fine powder is not added. Since the loss of the amorphous alloy itself is low, the loss is lower than that of the dust core of the related art, and shows excellent magnetic characteristic values as a whole.

[0017]

[Table 1]

FIG. 3 shows the relationship between the density at three points of the sample and the molding pressure in the first embodiment. Comparative Example 1-8 (Powder A: 1
Example 1-3 (powder A: 90%, powder B: 10%) and 1-4 (powder A: 80%, powder B: 20)
%), The density greatly increased under the same molding pressure.

A second embodiment according to the present invention will be described below. As the powder A, the same amorphous powder as in the first embodiment is used. As powder B, Fe, Cu, Nb, B, and Si were added in combination to produce an amorphous alloy powder by a water atomization method, and the powder was heat-treated at 550 ° C. to precipitate fine crystals of about 10 nm. Use the fine powder obtained by classification. The mode of the particle size of the powder B is 6.7 μm. The mode ratio of powders A and B is 7.9.

The experimental procedure, the amounts of binder and lubricant added, the dimensions of the molded magnetic core, the measuring method, and the like are the same as in the first embodiment. The heat treatment conditions for the magnetic core are the same as in the first embodiment.
70 ° C. × 60 minutes.

Table 2 shows that the molding pressure of Example 2 was 15 × 10 ⁸
The data of the sample prototyped in Pa is shown. The core loss of the microcrystalline soft magnetic alloy used as powder B in this example is a lower value than the amorphous soft magnetic alloy used for powder A,
As a result, in this embodiment, a low core loss value comparable to ferrite is obtained.

[0022]

[Table 2]

A third embodiment according to the present invention will be described below. As the powder A, use is made of an amorphous alloy powder prepared by a water atomization method in which Cu, Nb, B, and Si are added to Fe in a complex manner. As the powder B, a fine powder obtained by classifying powder obtained by the same composition and the same method is used. The mode of particle size of powder A is 37.5 μm, and the mode of particle size of powder B is 6.7 μm. The mode ratio of powders A and B is 5.6.

The experimental procedure, the amounts of binder and lubricant added, the dimensions of the molded magnetic core, the measuring method, and the like are the same as in the first embodiment. The heat treatment condition of the molded magnetic core is 550 ° C. × 30 in a nitrogen atmosphere.
By this heat treatment, fine crystals having a diameter of about 10 nm are precipitated on the powders A and B.

Table 3 shows that the molding pressure of Example 3 was 15 × 10 ^8.
The data of the sample prototyped in Pa is shown. In this embodiment,
A core loss value even lower than that of the second embodiment is obtained.

[0026]

[Table 3]

A further comparative example of the third embodiment according to the present invention will be described below. As the powder A, the powder of the third example was classified and only fine powder having a size of 31 μm or less was selected and used. The mode of the particle size is 26.5 μm. The same powder as in the third example was used as the powder B. The particle size mode ratio between powder A and powder B is 4.0. Experimental procedures, conditions, and the like are the same as in the third embodiment. If the particle size mode ratio is less than 5, the effect of improving the space factor will be small, and optimum magnetic characteristics cannot be obtained.

[0028]

[Table 4]

[0029]

According to the dust core of the present invention, a powder made of an amorphous soft magnetic alloy or a microcrystalline soft magnetic alloy, which has been conventionally difficult to mold and is relatively expensive, is formed by a normal room temperature dry molding method. Thus, a dust core having high saturation magnetic flux density, high magnetic permeability, and low loss, which are the material characteristics of the soft magnetic metal powder, can be provided at low cost. In addition, since the soft magnetic metal powder has significantly different particle diameters to improve moldability, shapes other than a ring shape can be produced, and the range of application can be expanded.

[Brief description of the drawings]

FIG. 1 is a particle size distribution diagram of a soft magnetic powder A used in a first embodiment of the present invention.

FIG. 2 is a particle size distribution diagram of a soft magnetic powder B used in a first embodiment of the present invention.

FIG. 3 is a graph showing a relationship between density and molding pressure according to the first embodiment of the present invention.

Claims (4)

[Claims] 1. A powder magnetic core obtained by mixing powder A made of an amorphous soft magnetic alloy and fine powder B of a soft magnetic alloy and molding the mixture under pressure, the mode of the particle size distribution of the powder A is A powder magnetic core, wherein the volume percentage of the powder B is 3% or more and 50% or less with respect to the total volume of the powder A and the powder B, which is at least 5 times that of B. 2. A particle size distribution of powder A in a dust core obtained by mixing powder A made of a microcrystalline soft magnetic alloy for precipitating nanoscale microcrystals and soft magnetic alloy fine powder B and pressing and molding. Wherein the mode value of the powder B is at least 5 times that of the powder B, and the volume percentage of the powder B with respect to the total volume of the powder A and the powder B is 3% or more and 50% or less. core. 3. The dust core according to claim 1, wherein the soft magnetic alloy fine powder B is an amorphous alloy. 4. The dust core according to claim 1, wherein the soft magnetic alloy fine powder B is a microcrystalline alloy that precipitates nanoscale microcrystals.