JPH07297016A - Dust core - Google Patents

Abstract

(57) [Summary] [Object] To provide a powder magnetic core of Fe—Al—Si alloy powder having high magnetic permeability and high insulation. [Structure] A mixed powder in which a specific amount of a Ti-based oxide film forming agent is added to an alloy powder containing Fe-Al-Si as a main component and a silicate is added as a binder is compression-molded, and then the mixture is heated in a non-oxidizing atmosphere at 500 A dust core produced by heat treatment at ℃ to 1100 ℃.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Ferrite cores and dust cores are used as choke coils used at high frequencies. Of these, the ferrite core has a drawback that the saturation magnetic flux density is small. On the other hand, a dust core produced by molding iron (Fe) -silicon (Si) -aluminum (Al) alloy-based metal powder (hereinafter, Fe-Si-Al powder) is a soft magnetic ferrite. Compared with this, it has an advantage that the saturation magnetic flux density is remarkably large and the material cost is low.

There is a correlation between the magnetic permeability of a dust core produced by compression molding of this Fe-Si-Al powder and the filling rate of the metal powder. It is necessary to sufficiently increase the metal powder filling rate of the powder magnetic core. As a method for increasing the filling rate, increasing the compression molding pressure is convenient and is generally used. But,
On the other hand, when the metal powder is compression-molded, the soft magnetic properties are deteriorated due to compression strain, and when the metal powder is molded at a high pressure, this deterioration is remarkable and it is difficult to fully utilize the properties of the material. Become. For such deterioration of soft magnetic properties due to compression strain, a compression molded body (hereinafter referred to as a green compact)
It is effective to release the strain and recover the soft magnetic property by heat-treating. However, in the temperature range where the strain of metal powder can be released, most organic resins such as epoxy resin, phenol resin, vinyl chloride resin, etc. cannot be used as binders for green compacts, and inorganic binders cannot be used. Need to use. As an inorganic binder, silicate-based water glass is well known. However, compared with an organic binder such as an epoxy resin, this has poor wettability, resulting in a low filling rate of metal powder. I have a problem.

In recent years, with the downsizing of electronic devices, there has been an increasing demand for higher frequencies in dust cores, and a dust magnet in which an inner conductor and metal powder are integrally molded from a conventional wire-wound magnetic core. The core has come to be required. In such an integrally-molded powder magnetic core, high insulation between the internal conductor and the metal powder is required, but when the binder is an organic resin such as an epoxy resin, high insulation is likely to be obtained. As described above, since the heat treatment is impossible, the compression strain cannot be released, and it is difficult to obtain high magnetic permeability. On the other hand, when a silicate-based binder such as water glass is used, it is possible to increase the magnetic permeability by heat treatment, but it is difficult to obtain high insulation.

When the green compact is heat-treated in an oxidizing atmosphere for the purpose of improving the insulating property, a high insulating property can be obtained, but the magnetic permeability is increased due to the formation of an excessive oxide film. descend. On the other hand, when the heat treatment is performed in a non-oxidizing atmosphere, the magnetic permeability does not decrease, but the high insulating property cannot be obtained because the oxide film is not formed. It was difficult to realize at the same time.

[0006]

SUMMARY OF THE INVENTION The technical problem of the present invention is that the soft magnetic characteristics are not deteriorated even when the green compact density is increased by high pressure compression molding, the magnetic permeability is high, and the high insulating property between metal powders is high. Is to provide a dust core having sufficient strength.

[0007]

The present invention relates to Fe, Si,
After the Ti-based oxide film forming agent is mixed in the alloy powder containing Al as the main component in the range of X defined by the formula 1 in the range of 0.0001 to 0.02, water glass is mixed, and compression molding is performed. It is a dust core produced by heat-treating a compression-molded body at 500 ° C. to 1100 ° C. in a non-oxidizing atmosphere. By mixing a Ti-based oxide film forming agent with the alloy powder before molding in advance, high magnetic permeability can be obtained. so,
Moreover, a powder magnetic core having a high insulating property is realized.

Regarding the amount of the Ti-based oxide film forming agent mixed, X =
The reason why 0.0001 to 0.02 is set is that when X is less than 0.0001, no significant improvement in insulation property (withstand voltage) is observed. On the other hand, the reason why it is set to 0.02 or less is that the magnetic permeability of the dust core remarkably decreases when the mixing amount exceeds 0.02.

If the amount of water glass, which is a silicate binder, is less than 0.5 wt% of the alloy powder, sufficient green compact strength cannot be obtained. Since the magnetic permeability of the dust core decreases without improving the powder strength, it is desirable to use water glass in an amount of 0.5 wt% to 10 wt% with respect to the alloy powder. .

When the temperature range of the heat treatment of the dust core in the non-oxidizing atmosphere is less than 500 ° C., the magnetic permeability is not significantly improved as compared with the dust core not subjected to the heat treatment.
If the temperature exceeds ℃, the insulating property of the dust core will be significantly reduced.

[0011]

When a Ti-based oxide film forming agent is mixed with Fe-Si-Al powder, an oxide film is formed on the surface of the alloy powder,
The wettability with respect to water glass is improved. Therefore, this Fe
When water glass is mixed with a mixed powder of —Si—Al powder and a Ti-based oxide film forming agent and compression molding is performed, a green compact having a high density can be obtained. By subjecting this green compact to a heat treatment in an appropriate temperature range in a non-oxidizing atmosphere, the compression strain is released,
It is possible to obtain a dust core having high magnetic permeability. At this time,
Although water glass is thermally decomposed, the silicon compound which is the main component in water glass remains. Since the residual substance after the heat treatment containing this silicon compound as a main component basically has a strong bonding force, by using water glass capable of holding an appropriate residual amount of the silicon compound after the heat treatment, Sufficient strength can be secured.

[0012]

EXAMPLES Examples of the present invention will be described below.

(Example 1) 10 wt% S in a vacuum melting furnace
An i-5 wt% Al-bal.Fe alloy ingot was prepared, crushed using a jaw crusher and a disc mill, and classified to 100 μm or less to obtain a crushed ingot alloy powder.

Next, titanium isopropoxide, which is a titanium-based oxide film forming agent, is added to the alloy powder by X defined by the formula 1.
However, X = 0.00005, 0.00007, 0.0001
0, 0.0005, 0.0002, 0.0003, 0.0
005, 0.0010, 0.0015, 0.002, 0.0
03, 0.005, 0.010, 0.015, 0.02,
The mixture was mixed so as to be 0.03, 0.05, 0.06, 0.08, 0.1.

Next, water glass as a binder is mixed with the alloy powder having the oxide film formed thereon in an amount of 0.5 wt%, 5.0 wt% and 10.0 wt% of the weight of the alloy powder, and the molding pressure is 5
A ring-shaped green compact having a ton / cm ² outer diameter of 20 mm, an inner diameter of 10 mm and a height of 5 mm was produced.

At the same time, alloy powders produced under the same conditions were
With a molding pressure of 5 ton / cm ² , a square having a side of 10 mm and a thickness of 5 mm was formed into a plate shape to prepare a withstand voltage measurement sample.

Next, these green compacts are heat-treated at 800 ° C. for 2 hours in an Ar atmosphere (in a non-oxidizing atmosphere), and then,
Wind around the ring-shaped powder compact sample (compact powder core),
Using a YHP impedance analyzer 4194A, μ of the dust core at a frequency of 100 kHz was measured.

Further, silver paste was applied to the upper and lower end surfaces of the plate-shaped green compact sample, and the interplane AC withstanding voltage of the green compact was measured using an AC withstand voltage measuring instrument manufactured by Kikusui Denshi. The result is shown in FIG. FIG. 1 is a characteristic diagram showing the relationship between the mixing amount of the Ti-based oxide film forming agent added to the alloy powder and the characteristics of the obtained dust core using the addition amount of water glass as a parameter. 1A shows the magnetic permeability of the dust core at a frequency of 100 kHz, and FIG. 1B shows the inter-plane AC withstand voltage.

From FIG. 1 (a), regardless of the mixing amount of water glass, the mixing ratio X of titanium isopropoxide is 0.000.
When it exceeds 1, μ is sharply improved. Furthermore, as the mixing ratio of titanium isopropoxide increases, the amount of mixing becomes 0.1.
It can be seen that μ increases to 003, but when it exceeds 0.005, μ decreases. When the amount of titanium isopropoxide mixed is in the range of 0.005 to 0.02, μ of the powder magnetic core has started to decrease, but it is higher than that of the powder magnetic core not mixed with titanium isopropoxide. Is maintained.

The surface withstand AC withstand voltage of the green compact is shown in FIG.
As shown in (b), when the mixing ratio X of titanium isopropoxide exceeds 0.0001, regardless of the mixing amount of water glass, the titanium oxide rapidly improves. Further, as the mixing amount of titanium isopropoxide increases, the withstand voltage of the green compact is improved. Therefore, from the behavior of both μ and withstand voltage, X is 0.0
It is useful in the range of 001 to 0.02.

Example 2 Titanium isopropoxide was added to the ingot crushed alloy powder prepared in Example 1 at X = 0.0.
Water glass was mixed with the alloy powder mixed so as to be No. 02 in an amount of 5% based on the weight of the alloy powder, and a green compact was produced in the same manner as in Example 1.

Next, these green compacts were treated in an Ar atmosphere (in a non-oxidizing atmosphere) at 300 ° C., 400 ° C., 500 ° C., 6 ° C.
00 ℃, 700 ℃, 800 ℃, 900 ℃, 1000 ℃,
Heat treatment was performed for 2 hours at each temperature of 1050 ° C., 1100 ° C., and 1200 ° C. to obtain a measurement sample.

Next, the ring-shaped powder compact sample (powder magnetic core) after the heat treatment was wound, and Y was wound in the same manner as in Example 1.
Using an impedance analyzer 4194A manufactured by HP, μ of the dust core at a frequency of 100 kHz was measured.
Further, a silver paste was applied to the upper and lower end surfaces of the plate-shaped green compact sample, and the interplane AC withstanding voltage of the green compact was measured using an AC withstand voltage measuring device manufactured by Kikusui Electronics. The result is shown in FIG. FIG. 2 is a characteristic diagram showing the relationship between the heat treatment temperature and the characteristics of the green compact as a parameter with or without the addition of titanium isopropoxide, and FIG. 2 (a) shows the magnetic permeability of the green core. Two
(B) has shown surface alternating current withstand voltage.

As shown in FIG. 2A, the heat-treated product is
It can be seen that when the heat treatment temperature of the powder compact exceeds 400 ° C., μ of the powder magnetic core is rapidly improved regardless of the addition of titanium isopropoxide. Further, as the heat treatment temperature increases, μ linearly increases up to the heat treatment temperature of the green compact of up to 1000 ° C.
It can be seen that when the temperature exceeds ° C, μ decreases.
Further, although the μ of the powder magnetic core has decreased in the range of 1000 ° C. to 1200 ° C. for the heat treatment of the powder compact, the μ is kept higher than that of the powder magnetic core before the heat treatment. Further, when the heat treatment temperature of the powder compact is 1200 ° C. or lower, when compared at the same heat treatment temperature, the powder core mixed with titanium isopropoxide is better than the powder core not mixed with the oxide film forming agent. μ is high.

The inter-plane AC withstand voltage of the powder compact sample is shown in FIG.
As shown in (b), there is a tendency corresponding to increase and decrease of μ, and in the heat treatment temperature range of 500 ° C to 1100 ° C,
It has a higher withstand voltage than a dust core without heat treatment. Also, 12
Up to 00 ° C., the powder magnetic core in which titanium isopropoxide is always mixed has a higher withstand voltage than the powder compact in which titanium isopropoxide is not mixed. Therefore, from the behavior of both μ and withstand voltage, the heat treatment temperature is useful in the range of 500 ° C. to 1100 ° C.

The results of Examples 1 and 2 are as follows.
A Ti-based oxide film forming agent was added to the alloy powder at an amount of 0.0001-0.
03, mixed with water glass as a silicate-based binder and compression-molded, and then heat-treating the compression-molded green compact at 500 ° C to 1100 ° C in a non-oxidizing atmosphere,
This shows that it is possible to obtain a dust core with high magnetic permeability and high withstand voltage.

[0027]

The alloy powder surface is oxidized with a titanium oxide film forming agent to form an oxide film, which is compression molded using silicate as a binder, and the green compact after compression molding is subjected to a non-oxidizing atmosphere. By heat-treating in it, a powder magnetic core with high magnetic permeability and high withstand voltage was obtained.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the mixing amount of a Ti-based oxide film forming agent and the characteristics of a powder compact in Example 1, and FIG. 1A shows the magnetic permeability of a powder magnetic core at a frequency of 100 kHz. The figure and FIG.1 (b) are figures which show surface alternating current withstand voltage.

FIG. 2 is a characteristic diagram showing the relationship between the heat treatment temperature of the green compact and the properties of the green compact in Example 2, FIG. 2 (a) shows the magnetic permeability of the green core, and FIG. Indicates the face-to-face AC withstand voltage.

[Explanation of symbols]

a dust core mixed with 0.5 wt% water glass (○) b dust core mixed with 5 wt% water glass (△) c dust core mixed with 10 wt% water glass (□) d titanium isopropoxide Powder core not mixed (○) e Powder core mixed with titanium isopropoxide at X = 0.002 (●)

Claims (1)

[Claims] 1. In a dust core comprising an alloy powder containing iron, silicon and aluminum as main components, and a binder for binding them together, the titanium-based oxide film forming agent is defined by the formula 1, where X is 0. Included in the range of 0.0001 to 0.02, and further
A powder magnet, characterized in that a compression molded body containing 0.5 wt% to 10 wt% of silicate as the binder with respect to the weight of the alloy powder is heat-treated in the range of 500 ° C to 1100 ° C in a non-oxidizing atmosphere. core. [Equation 1]