JP2001307914A - Magnetic powder for dust core, dust core using it, and method for manufacturing dust core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide magnetic powder which can be used effectively for the manufacture of a dust core which causes little core loss in a high frequency domain of several kHz or higher and a method for manufacturing a dust core using the magnetic powder. SOLUTION: The magnetic powder is composed of 100 pts.wt. soft magnetic powder and 0.5-10 pts.wt. inorganic binder component coating the soft magnetic powder and the inorganic binder component is composed of 10-95 wt.% water glass and 5-90 wt.% insulating oxide powder. In the method for manufacturing the dust core, the dust core is manufactured by forming a molded body by compression-molding the magnetic powder and heat-treating the molded body at 700-1,000 deg.C. The obtained dust core has an electric resistivity of >=0.1 Ω.m and, in the dust core, the magnetic powder is recrystallized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder for a dust core, a dust core using the same, and a method for producing the dust core. The present invention relates to a magnetic powder for a dust core which is effective for producing a dust core having a low core loss, a dust core using the magnetic powder, and a method for producing the same.

[0002]

2. Description of the Related Art A smooth choke coil for DC output of a switching power supply, a noise filter for a normal mode on an AC input side, and a choke coil for an active filter in an inverter controller have a complicated shape even if the target component has a complicated shape. Because it can be manufactured with high yield,
Fe-Si-Al alloy powder represented by Sendust,
Fe-Si based alloy powder such as Fe-6.5% Si, and Fe represented by PC permalloy and PB permalloy
-A dust core manufactured using a soft magnetic powder such as a Ni-based alloy powder is actually used.

[0003] Such a dust core is generally manufactured as follows. That is, first, a soft magnetic powder having a predetermined particle size distribution as described above is prepared, and the soft magnetic powder is kneaded with an electrically insulating binder component represented by water glass and having a binding ability. Is coated with a binder component. Then, after filling the powder into a mold, the powder is compression-molded at a predetermined pressure to obtain a molded article having a desired shape, and the molded article is subjected to heat treatment (annealing) to release molding distortion accumulated during compression molding. It is manufactured by curing the binder component.

In recent years, the miniaturization of electric and electronic devices has been rapidly progressing, and with this, compact and high efficiency have been required for dust cores incorporated in these devices. Is required. In this case, in order to obtain a highly efficient powder magnetic core, it is indispensable to reduce the core loss of the powder magnetic core. The above-mentioned core loss is roughly classified into an eddy current loss and a hysteresis loss. The former eddy current loss can be reduced by securing insulation between the soft magnetic powders. Further, the latter hysteresis loss can be reduced by releasing the strain accumulated in the magnetic powder used or the molding strain accumulated during the compression molding.

In the above-described method for manufacturing a dust core, for example, water glass is used as a binder component in order to bind soft magnetic powders to each other and form an insulating film between the powders. The annealing treatment is performed in order to remove crystal distortion by coarsening crystal grains in the powder. In that case, it is effective to raise the temperature during annealing in order to sufficiently remove the molding distortion.

[0006] However, when water glass is used as a binder component, the following problems occur when annealing is performed at a high temperature. That is, if the temperature at the time of annealing becomes too high, the water glass thermally decomposes and foams, and the insulating film of the water glass formed between the soft magnetic powders is damaged, and the powders come into contact with each other. The insulation between them disappears. As a result, there is a problem that eddy current loss in a high frequency region of several kHz or more becomes large, so that core loss becomes large and core efficiency is reduced.

For this reason, when water glass is used as the binder component, the upper limit of the annealing temperature is 70%.
Usually, it is limited to about 0 ° C. However, when the temperature at the time of annealing is about 700 ° C., molding distortion cannot be sufficiently removed. In particular, in the case of a high-density powder magnetic core that is compression-molded at a high pressure, at the above-mentioned temperature, the molding distortion cannot be sufficiently removed, and it is difficult to reduce the hysteresis loss.

The magnetic powder, which is the starting material of the dust core, is usually produced by crushing an alloy ingot having a desired composition or applying an atomizing method to a molten alloy having a desired composition. However, according to the former method, since a large plastic strain at the time of pulverization remains in the produced magnetic powder, prior to the production of the dust core, the magnetic powder is once subjected to a heat treatment to remove the plastic distortion. Before use.

In the latter case, the produced magnetic powder (atomized powder) has extremely fine crystal grains, so that the coercive force in the powder state becomes large. The hysteresis loss of the dust core increases. Therefore, it is customary to use the atomized powder after subjecting the atomized powder to heat treatment to coarsen the crystal grains.

[0010] However, such heat treatment of the starting material is not industrially preferable because it leads to an increase in manufacturing cost due to an increase in the number of manufacturing steps of the dust core.

[0011]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the production of a conventional dust core, and is designed to ensure sufficient insulation between magnetic powders even when annealed at a high temperature. By using the magnetic powder for the dust core and the magnetic powder, a dust core having a small core loss even in a high frequency range of several kHz is obtained, and further, annealing at a high temperature causes coarsening of crystal grains in the magnetic powder. It is an object of the present invention to provide a method for manufacturing a dust core, which eliminates the need to perform a heat treatment on the magnetic powder performed prior to the manufacture of the dust core.

[0012]

In order to achieve the above object, in the present invention, 100 parts by weight of a soft magnetic powder and 0.5 to 10 parts by weight of an inorganic binder component coating the soft magnetic powder are used. The inorganic binder component comprises 10 to 95% by weight of water glass and 5 to 90% by weight of insulating oxide powder.
And a magnetic powder for a dust core.

[0013] In particular, the soft magnetic powder is made of Fe-Si
-Al-based alloy powder, Fe-Si-based alloy powder, and Fe
At least one selected from the group consisting of -Ni alloy powder, the insulating oxide powder, SiO ₂ powder, Al ₂ O ₃ powder, CaO powder, MgO powder, TiO ₂ powder, Fe ₂ O ₃
The present invention provides a magnetic powder for a dust core, which is at least one selected from the group consisting of powder, K ₂ O powder, and Na ₂ O ₃ powder.

Further, in the present invention, any one of the above magnetic powders is formed and then annealed to have an electrical resistivity of 0.1 Ω · m or more, and the magnetic powder has a recrystallized structure. And a dust core having a core loss of 3000 kW / m ³ or less. Further, in the present invention, there is provided a method for producing a dust core, which comprises subjecting any of the above magnetic powders to compression molding to obtain a molded body, and then subjecting the molded body to a heat treatment at a temperature of 700 to 1000 ° C. Provided.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the magnetic powder for a dust core of the present invention will be described. The magnetic powder comprises a soft magnetic powder,
It is composed of an inorganic binder component described below covering the surface. As the soft magnetic powder to be used, any soft magnetic powder that has been conventionally used for the production of a dust core may be used, but the purpose is to produce a dust core to be used in a high frequency region of several kHz or more. In the case, for example, Fe-9.5%
Fe-Si such as Si-5.5% Al (Sendust)
-Al-based alloy powder; Fe- such as Fe-6.5% Si
Si-based alloy powder; F such as Fe-80% Ni (PC permalloy) and Fe-47% Ni (PB permalloy)
It is preferably an e-Ni-based alloy powder. These may be used alone or in combination of two or more.

These soft magnetic powders may be pulverized powder of an ingot of a predetermined alloy or atomized powder. Further, the particle size of these powders is not particularly limited, but is usually under 100 mesh (Tyler sieve).
May be used. The inorganic binder component covering the surface of the soft magnetic powder is composed of water glass and heat-resistant insulating oxide powder. Therefore, the inorganic binder component is not only electrically insulating as a whole, but also has a higher heat resistance than the case where the water glass is used alone.

Examples of the insulating oxide powder include SiO ₂ powder, Al ₂ O ₃ powder, CaO powder, and MgO powder.
Powder, TiO ₂ powder, Fe ₂ O ₃ powder, K ₂ O powder, Na ₂
One or more types such as O ₃ powder can be mentioned as preferred examples. Also, natural minerals containing each of the above-mentioned metal oxides as components, such as kaolin, refractory clay, pottery stone,
Powders of halloysite, sericite, bentonite, laurite, clay, and the like can also be used.

In preparing the magnetic powder of the present invention, the soft magnetic powder and the above-mentioned inorganic binder component may be kneaded using, for example, a mixer. During the kneading process, the surface of the soft magnetic powder is covered with an electrically insulating inorganic binder component. In the kneading mode at this time, the soft magnetic powder, the water glass, and the insulating oxide powder may be simultaneously kneaded, or the water glass and the insulating oxide powder are mixed in advance to form an inorganic binder component,
This may be kneaded with the soft magnetic powder, or the soft magnetic powder and the insulating oxide powder may be mixed in advance, water glass may be added to the mixed powder, and the whole may be kneaded.

At this time, the amount used as the inorganic binder component is set to 0.5 to 10 parts by weight based on 100 parts by weight of the soft magnetic powder. If the amount used is less than 0.5 parts by weight, the surface of the soft magnetic powder cannot be completely covered, resulting in an uncoated portion, or the thickness of the coating layer is reduced, so that the thickness of the coating layer is reduced during compression molding described below. This is because phenomena such as damage of the coating layer occur, and as a result, sufficient insulation between the magnetic powders cannot be secured. On the other hand, if the amount is more than 10 parts by weight, defects such as cracks will frequently occur in the compact during compression molding described below.

The composition of the inorganic binder component is water glass 10
９５95% by weight, and insulating oxide powder 5５〜90% by weight. When the content of water glass is less than 10% by weight (the content of insulating oxide powder is more than 90% by weight), the binding property between the magnetic powders is reduced and the strength of the manufactured dust core is reduced. Is more than 95% by weight (when the amount of the insulating oxide powder is less than 5% by weight), when the total amount of the inorganic binder component exceeds 6 parts by weight, the water glass foams in an annealing process described later, As a result, defects such as cracks occur in the dust core, and when the total amount of the inorganic binder component is 6 parts by weight or less, the amount of the insulating oxide powder is reduced. Can not be secured.

In the present invention, a dust core is manufactured as follows by using the above magnetic powder. First, the magnetic powder of the present invention is filled in a mold. At this time, it is preferable to mix an appropriate amount of a lubricant such as zinc stearate from the viewpoint of improving moldability. Then, it is compression molded to obtain a molded article having a desired shape. The molding pressure at this time is not particularly limited, but is 1000MP in terms of increasing the bulk density of the molded body and increasing its strength.
It is preferable to set it to a or more.

The resulting compact is then annealed to produce the desired dust core. Annealing is performed in an inert atmosphere such as Ar, for example, at a temperature of 700 to 1000 ° C.
Is set to In the present invention, by setting the temperature at the time of annealing to the high temperature as described above, for example, even if the soft magnetic powder of the starting material is a pulverized powder and is not subjected to heat treatment, Not only the plastic strain at the time, but also the molding strain at the time of compression molding is reliably removed, and at the same time, recrystallization proceeds. Even if the soft magnetic powder is an atomized powder, the above-mentioned molding distortion is surely removed, and the fine crystal grains have a coarse recrystallized structure.

Here, if the temperature during annealing is lower than 700 ° C., the above-mentioned effects are not sufficiently exhibited, and the hysteresis loss of the obtained dust core increases and the overall core loss increases. Further, if the temperature at the time of annealing is higher than 1000 ° C., the insulating layer covering the surface of the soft magnetic powder is broken by foaming of the water glass of the inorganic binder component.
The eddy current loss of the obtained dust core increases and the overall core loss increases.

In the thus manufactured powder magnetic core of the present invention, the insulating property between the soft magnetic powders is secured by the interposition of the inorganic binder component, so that the eddy current loss is small and the powder magnetic core is annealed at a high temperature. Therefore, the molding distortion at the time of compression molding is surely removed, and at the same time, the powder magnetic core has a small hysteresis loss due to a coarse recrystallized structure and a small core loss as a whole.

More specifically, it has an insulating property with an electric resistivity of 0.1 Ω · m or more, and has a high frequency range of 100 kHz, 0.1 mm.
The core loss at a magnetic flux density of 1T is 3000 kW / m ³ or less.

[0026]

EXAMPLES Examples 1 to 7 and Comparative Examples 1 to 6 (1) Production of Magnetic Powder A soft magnetic powder of Sendust was produced by a gas atomizing method. On the other hand, water glass and refractory clay powder were mixed at the ratio (% by weight) shown in Table 1 to prepare an inorganic binder component.

Next, the above sendust powder (100
The inorganic binder component was kneaded at the indicated ratio (parts by weight) with respect to 100 parts by weight (under the mesh). After drying the kneaded material, the mixture was classified with a 100 mesh Tyler sieve, and various powders below the 100 mesh were collected. (2) Manufacture of a dust core 0.5% by weight of zinc stearate was added to each of the above powders based on 100 parts by weight of the powder, and the mixture was filled in a mold and then compression molded at room temperature at a molding pressure of 1300 MPa. Into a ring-shaped molded body having an outer diameter of 28 mm, an inner diameter of 20 mm, and a height of 5 mm.

Then, each of the compacts is filled with Ar at a temperature of 900 ° C.
Annealing was performed for one hour in an atmosphere to produce a dust core.
In this process, the presence or absence of cracks in the compact and the presence or absence of cracks during annealing were observed. The results are shown in Table 1. (3) Characteristics of the dust core Each powder core has a frequency of 100 kHz and a magnetic flux density of 0.1 T.
Was measured with an AC B-H analyzer, and the electrical resistivity was measured with an LCR meter.

The above results are collectively shown in Table 1.

[0030]

[Table 1]

As is clear from Table 1, the annealing temperature is 90
At 0 ° C., 75% by weight of water glass and refractory clay powder 2
5% by weight of an inorganic binder component is a soft magnetic powder 100
If the amount is less than 0.5 part by weight, the electric resistivity is decreased and the core loss is increased, and the amount is less than 10 parts by weight.
If the amount is more than the weight part, cracks occur more frequently during molding and annealing.

Examples 1, 5 to 7, Comparative Examples 3 and 4
In each case, the inorganic binder component is the same as 4 parts by weight, but when the refractory clay powder in this inorganic binder component is less than 5% by weight (Comparative Example 4), the core loss is large and the core loss is more than 90% by weight ( In the case of Comparative Example 3), occurrence of cracks and the like is observed. For this reason, the inorganic binder component used is 10 to 95% by weight of water glass and 5 to 90% by weight of the refractory clay powder, and the inorganic binder component is 0.5 to 1% by weight based on 100 parts by weight of the sendust powder.
It can be seen that the magnetic powder should be produced using 0 parts by weight.

Examples 8 to 12 and Comparative Examples 7 to 10 When manufacturing a dust core using the magnetic powder of Example 1 in Table 1, the annealing temperature was changed as shown in Table 2. The characteristics of the obtained dust core were measured in the same manner as in Examples 1 to 7. The results are shown in Table 2.

[0034]

[Table 2]

As is apparent from Table 2, the core loss of the obtained dust core increases when the annealing temperature is lower than 700 ° C., although the powder of Example 1 is used as the magnetic powder. If the temperature is higher than 1000 ° C., core loss increases and cracks are observed. From this, it is understood that the temperature during annealing should be set in the range of 700 to 1000 ° C.

Examples 13 to 23 and Comparative Examples 11 to 20 As a soft magnetic powder, a mixed powder consisting of 30% by weight of sendust powder under 100 mesh and 70% by weight of a gas atomized powder of Fe-6.5% Si was used. Except for
Magnetic powder was produced in the same manner as in Examples 1 to 7. Using these magnetic powders, ring-shaped compacts were manufactured in the same manner as in Examples 1 to 7, and each compact was annealed at the temperature shown in Table 3 to obtain a dust core.

Table 3 shows the characteristics of each dust core.

[0038]

[Table 3]

[0039]

As is apparent from the above description, since the magnetic powder of the present invention is made of a soft magnetic powder coated with a heat-resistant and electrically insulating inorganic binder component, it is not necessary to mold the magnetic powder in the production of a dust core. The body can be annealed at a high temperature of 700-1000C. Therefore, in the obtained dust core, insulation between the soft magnetic powders is secured, and at the same time, molding distortion during compression molding is removed, and the magnetic powder after the heat treatment has a coarse recrystallized structure. In addition, the core loss in the high frequency region is small.

Claims (6)

[Claims] 1. A soft magnetic powder comprising 100 parts by weight of a soft magnetic powder and 0.5 to 10 parts by weight of an inorganic binder component coating the soft magnetic powder, wherein the inorganic binder component is water glass 10 to 9 parts by weight.
A magnetic powder for a dust core, comprising 5% by weight and 5 to 90% by weight of an insulating oxide powder. 2. The powder compact according to claim 1, wherein the soft magnetic powder is at least one selected from the group consisting of Fe—Si—Al alloy powder, Fe—Si alloy powder, and Fe—Ni alloy powder. Magnetic powder for magnetic core. 3. The method according to claim 1, wherein the insulating oxide powder is SiO ₂ powder,
_{3. The method according to} claim 1, wherein the powder is at least one selected from the group consisting of Al ₂ O ₃ powder, CaO powder, MgO powder, TiO ₂ powder, Fe ₂ O ₃ powder, K ₂ O powder, and Na ₂ O ₃ powder.
Magnetic powder for dust core. 4. The magnetic powder according to claim 1, which is molded and then annealed, and has an electrical resistivity of 0.1Ω.
M, and wherein the magnetic powder has a recrystallized structure. 5. The dust core according to claim 4, wherein the core loss is 3000 kW / m ³ or less. 6. A dust core, wherein the magnetic powder according to any one of claims 1 to 3 is compression-molded into a compact, and the compact is subjected to a heat treatment at a temperature of 700 to 1000 ° C. Manufacturing method.