JPH0793220B2 - Iron core manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an iron core, more specifically, it has excellent frequency characteristics of magnetic permeability and
The present invention relates to a method for manufacturing an iron core having a high magnetic flux density.

[0002]

2. Description of the Related Art Conventionally, a device for exchanging alternating current to a direct current, a device for converting direct current to an alternating current, a device for converting an alternating current of a certain frequency to an alternating current of a different frequency, and a device for converting a direct current to a direct current such as a so-called chopper. Such electric power converters or non-contact circuit breakers have electric circuit components such as semiconductor switching elements represented by thyristors or transistors, turn-on stress mitigating reactors connected thereto, and commutation. Reactors, energy storage reactors, matching transformers, etc. are used.

As an example of such a power conversion device, a first
The figure shows an electric circuit diagram of the device that converts direct current to alternating current. The power converter shown in FIG. 1 is composed of a semiconductor switching element 1, a turn-on stress mitigating reactor 2 and a matching transformer 3.

In these reactors and transformers, a current containing a high frequency component reaching from 100 KHz to over 500 KHz in some cases may flow due to semiconductor switching.

Conventionally, the following is used as the core of the reactor and the transformer. That is, (a) a laminated iron core prepared by laminating thin electromagnetic steel sheets or permalloy plates with interlayer insulation, (b) carbonyl iron fine powder, permalloy fine powder, etc. are combined using a resin such as phenol resin. Examples thereof include a so-called dust core that has been attached, or a so-called ferrite core that is produced by sintering (c) an oxide-based magnetic material.

Among these, the laminated iron core exhibits excellent electrical characteristics in the commercial frequency band, but in the high frequency band, the iron loss of the iron core is remarkable, and in particular, the eddy current loss is the square of the frequency. It has a property that the magnetizing force increases proportionally, and the magnetizing force is less likely to change due to the skin effect of the iron core material as it enters from the surface of the plate material forming the iron core to the inside. Therefore, in the high frequency band, the laminated iron core can be used only at a magnetic flux density much lower than the saturation magnetic flux density originally possessed by the iron core material itself, and the eddy current loss is extremely large. Have Further, the laminated core has a problem that the effective magnetic permeability at high frequencies is significantly lower than the effective magnetic permeability at commercial frequencies. When the laminated iron core having these problems is used for a reactor or a transformer connected to a semiconductor switching element in which a current having a high frequency component flows, the effective magnetic permeability and the magnetic flux density are compensated. Therefore, the iron core itself has to be made large in size, and accordingly, there is a problem that copper loss becomes large in combination with a low effective magnetic permeability.

On the other hand, a dust magnetic material called a dust core is used as an iron core material.
No. 235, etc., for details. However, such dust cores generally have fairly low magnetic flux density and permeability. Even in the dust core using the carbonyl iron powder having a relatively high magnetic flux density, the magnetic flux density at a magnetizing force of 10,000 A / m is slightly higher than 0.1 T, and the magnetic permeability is 1.25 × 10 5. ^-5 H / m. Therefore, in a reactor or transformer that uses a dust core as an iron core material, in order to compensate for the low magnetic flux density and low magnetic permeability, enlarging the iron core is unavoidable. There is a problem that the loss becomes large.

Further, the ferrite core used in a small electric device has a high specific resistance value and a relatively excellent high frequency characteristic. However, the ferrite core
A magnetic flux density of 0.4T at a magnetizing force of 10,000 A / m
It is as low as the operating temperature range of the iron core, -40 to 120
There is a problem in that the magnetic permeability and the value of the magnetic flux density at the same magnetizing force change by several tens of% at a temperature of ° C. Therefore, when the ferrite core is used as an iron core material such as a reactor or a transformer connected to a semiconductor switching element, the iron core needs to be large because the magnetic flux density is low. However, the ferrite core is
Since it is a sintered body, it is difficult to manufacture a large-sized iron core and it is not suitable as an iron core. Further, the ferrite core has a large copper loss due to its low magnetic flux density, and since the magnetic permeability and the magnetic flux density are greatly affected by temperature, its characteristic change is large when used in a reactor or a transformer. Furthermore, since it has a large magnetostriction as compared with an electromagnetic steel plate or the like, there is a problem that the noise emitted from the iron core becomes large.

[0009]

As described above, there has been a problem in the related art that excellent magnetic flux density, effective electric resistance and frequency characteristics of effective permeability cannot be obtained.

The present invention solves the above problems and provides an iron core having excellent frequency characteristics of magnetic permeability and high magnetic flux density as a method of manufacturing an iron core used for a reactor or a transformer connected to a semiconductor element. It is to provide a manufacturing method of.

[0011]

The iron core manufacturing method of the present invention comprises mixing magnetic powder, a binder resin, and an inorganic compound powder, and then molding the mixture. That is, in the iron core manufacturing method of the present invention, when the average particle size is 10 to 100 μm, the average particle size is D μm, and the specific electrical resistivity is ρ μΩ-cm, D and ρ are shown only by numerical values and ρ / D ² Electrically insulative binder resin and electrical insulation having a total volume of 1.5 to 40% with either or both of iron powder and iron alloy magnetic powder satisfying the relationship of ≧ 4 × 10 ⁻³ It is characterized in that it is molded after mixing with a powder of a hydrophilic inorganic compound.

The iron powder or iron alloy magnetic powder used in the present invention is
Its specific electrical resistivity is 10 μΩ-cm to several tens of μΩ at most
Since it is about −cm, in order to obtain sufficient iron core material characteristics even at an alternating current including a high frequency that causes a skin effect, these powders must be made into fine particles so as to sufficiently contribute to magnetization from the particle surface to the inside of the particle. Therefore, the average particle size is required to be 100 μm or less. However, when the average particle diameter is extremely small, less than 10 μm, the density of the obtained iron core does not increase at a molding pressure of 10000 MPa or less that is usually applied in the molding step of the iron core described below, and as a result, the magnetic flux density It causes the inconvenience of deterioration. After all, in the present invention,
The average particle size of the iron powder or the iron alloy magnetic powder is set in the range of 10 to 100 μm.

The average particle size (Dμm) of these powders
As for the relationship between the electric resistivity and its specific electrical resistivity (ρμΩ-cm), D and ρ are shown only by numerical values, and ρ / D ² ≧ 4 ×
It is necessary to satisfy the relationship of 10 ⁻³ .

The iron powder or iron alloy magnetic powder used in the present invention may be any one as long as it satisfies the above-mentioned specifications. For example, pure iron powder or Fe represented by Fe-3Si.
-Si alloy powder, Fe-Al alloy powder, Fe-Si-Al alloy powder, Fe-Ni alloy powder, and Fe-Co alloy powder can be mentioned, and the powder by each of these or an appropriate combination thereof can be mentioned.

The electrically insulating binder resin used in the present invention coats the surface of the iron powder or iron alloy magnetic powder described above to make the powders electrically insulated from each other and has a sufficient effect on the AC magnetization of the entire iron core. At the same time as giving an electric resistance value, it also functions as a binder for binding these powders. Examples of such a binder resin include various resins such as epoxy resin, polyamide resin, polyimide resin, and polyester resin, or resins formed by appropriately combining these.

The powder of the electrically insulating inorganic compound used in the present invention reduces the frictional resistance between the iron powder or the iron alloy magnetic powder during the molding of the iron core to increase the molding density of the iron core, and at the same time, to improve the conductivity. By interposing between the iron powder or the iron alloy magnetic powder, which is the body, it also has the function of increasing the effective electrical resistance value for the alternating-current magnetization of the entire iron core. Examples of such an inorganic compound include calcium carbonate, silica, magnesia, alumina, various types of glass, and the like, or an appropriate combination thereof. However, it goes without saying that these inorganic compounds must be those which do not react with the iron powder, the iron alloy magnetic powder, and the binder resin described above.

The average particle size of the inorganic compound powder is 1/5 or less (20 μm or less) of the average particle size of the iron powder or the iron alloy magnetic powder in view of the dispersibility and the characteristics of the iron core material. Limited.

In the iron core obtained by the present invention, the total amount of the binder resin and the powder of the inorganic compound is set within the range of 1.5 to 40% compared with the total volume. When the volume ratio is less than 1.5%, the molding density of the iron core does not increase and the effective electric resistance value decreases, and when it exceeds 40%, the increasing tendency of the effective electric resistance value reaches a saturated state. Has a lower molding density and a lower saturation magnetic flux density, resulting in a magnetizing force of 10
The magnetic flux density at 000 A / m is about ferrite.

As for the volume ratio of the binder resin and the inorganic compound powder to each other, the ratio of the former to the latter is 98 to 20.
vol%: 2 to 80 vol%, preferably 95 to 30v
ol%: 5 to 70 vol%.

The above-mentioned iron powder, iron alloy magnetic powder or a mixed powder of both of them, the binder resin and the inorganic compound powder are sufficiently kneaded in a predetermined amount, for example, with a mixer, and the obtained kneaded product is obtained. It is filled in a mold and compression-molded. At this time,
The molding pressure applied may be usually 10,000 MPa or less. The obtained molded product is used as an iron core as it is, but if necessary, it may be heat-treated at a temperature of about 30 to 300 ° C. to cure the binder resin.

[0021]

【Example】

Examples 1 to 6 Various magnetic powders having different average particle diameters, inorganic compound powders and binder resins were mixed in the proportions (volume%) shown in Table 1, and they were sufficiently kneaded. The obtained kneaded product was filled in an iron core molding die and pressure-molded under various pressures to obtain a molded body having a predetermined shape. This molded body was heat-treated to cure the binder resin to obtain an iron core.

For these iron cores, the density and the magnetizing force are 1000
The magnetic flux density at 0 A / m was measured, and the effective electric resistance value was calculated from the eddy current loss of the iron core with respect to the AC magnetization.

The above results are collectively shown in Table 1.

[0024]

[Table 1] Further, when the changes in the magnetic permeability and the magnetic flux density at temperatures of -40 to 120 ° C were measured for the iron cores of Examples 1 to 4, respectively, the change rates were all less than 10%.

Further, for the iron core of Example 3 and the iron core made of a conventional dust core, a DC magnetization curve showing the change in magnetic flux density under each magnetic force was determined and shown in FIG.
It was confirmed that the iron core (curve A) of the present invention has a higher magnetic flux density than the conventional one (curve B). Examples 7 to 10 84 vol% of iron powder or iron alloy magnetic powder having different specific electrical resistivity (ρ) and average particle size (D), and average particle size 1 μ
1 vol% of alumina powder of m or less, 15 v of epoxy resin
ol% was kneaded and the kneaded product was molded at a pressure of 600 MPa, and the obtained molded body was subjected to heat treatment at 200 ° C. for 1 hour to obtain an iron core.

For these iron cores, 1 kHz to 500 kHz
The effective magnetic permeability of Hz was measured, and the ratio based on the effective magnetic permeability of 1 kHz was obtained. The results are shown in Table 2 as a relationship with ρ / D ² .

[0027]

[Table 2] Example 11 40 vol% Fe-3Al powder having an average particle size of 63 μm, 10 vol% Fe-Ni powder having an average particle size of 53 μm or less, Fe powder having an average particle size of 44 μm or less, glass powder 0.8 vol% having an average particle size of 8 μm, polyamide Resin 14.2vol%
After kneading and kneading the kneaded product under a pressure of 800 MPa, the molded body was subjected to heat treatment at 100 ° C. for 1 hour to obtain an iron core. The practical resistivity of this iron core was 350 mΩ-cm or more.

In the above examples, similar results were obtained even when a polyimide resin or a polycarbonate resin was used in place of the epoxy resin and other inorganic compounds such as magnesium were used.

[0029]

As is clear from the above description, according to the present invention, the magnetic core has a much higher magnetic flux density than the conventional ferrite core core and the dust core core, and has a high effective electric resistance value. , 1 to 5 compared to the laminated core
It is possible to provide a method for manufacturing an iron core with a small change in effective magnetic permeability in the frequency band of 00 kHz.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an electric circuit diagram of a device for converting direct current into alternating current.

FIG. 2 is a diagram showing a DC magnetization curve in an iron core of the present invention (Example 3) and a conventional dust core.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor switching element 2 ... Reactor for mitigating turn-on stress 3 ... Transformer for matching 4 ... Load for alternating current 5 ... DC power supply A ... DC magnetization curve of iron core of the present invention B ... Linear magnetization curve of conventional dust core

Claims (1)

[Claims] 1. When the average particle diameter is 10 to 100 μm, the average particle diameter is D μm, and the specific electrical resistivity is ρ μΩ-cm,
D and ρ are shown only by numerical values, and either or both of iron powder and iron alloy magnetic powder satisfying the relationship of ρ / D ² ≧ 4 × 10 ⁻³ , and the total amount is 1.5 to A method for producing an iron core, comprising mixing 40% of an electrically insulating binder resin and an electrically insulating inorganic compound powder having an average particle size of 20 μm or less, and then molding.