JPH0629114A - Dust core and manufacture thereof - Google Patents

Abstract

PURPOSE:To eliminate strains to a satisfactory extent by raising heat treatment temperature and provide dust cores excellent in magnetic properties. CONSTITUTION:Since dust cores are formed by compression-molding magnetic powder together with resin mainly composed of borosiloxane resin, high temperature heat treatment is available. Furthermore, there is no strain produced by differential thermal expansion during cooling time, which makes it possible to eliminate residual stress to a satis factory extent so that the plastic deformation of the magnetic powder may be allowable. It is, therefore, possible to mold with a large compression force, thereby enhancing the space factor and hence attain enhanced magnetic properties in addition to stress removal effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust core used for an iron core of electric equipment such as rotating electric machines, transformers and reactors.

[0002]

2. Description of the Related Art Normally, a laminated iron core formed by punching and stacking electromagnetic steel sheets is used for the iron core of electric equipment.
Such a laminated iron core has extremely excellent magnetic characteristics when the magnetic flux flows in the in-plane direction of the electromagnetic steel sheet, but has a large eddy current generation with respect to the vertical magnetic flux component and has a low magnetic permeability. Therefore, in a three-dimensional iron core in which the flow of magnetic flux cannot be limited to a plane, a dust core obtained by hardening magnetic metal powder with a resin is used rather than using a laminated iron core.

[0003]

By the way, the main factors that influence the magnetic characteristics of a dust core are the proportion of magnetic powder in the total volume and the characteristics of magnetic powder. The dust core is a mixture of magnetic powder and resin, and the resin spreads the gap between the magnetic powders to obstruct the flow of magnetic flux. Therefore, in order to create a dust core with excellent magnetic properties, it is necessary to reduce the amount of resin, increase the pressure applied during manufacturing to reduce voids, and maximize the space factor of magnetic powder. Is. However, when the applied pressure is increased, the magnetic powder undergoes plastic deformation, resulting in residual stress. Since this residual stress deteriorates the magnetic properties, it needs to be removed.

However, the heat treatment for removing the residual stress in the magnetic powder causes deterioration of the resin, so that the temperature cannot be raised to the required temperature, and therefore the characteristics of the conventional dust core are not obtained. Is lower than that of a laminated iron core such as an electromagnetic steel plate, and thus is not used in a wide range, and there is a problem that the application is limited.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a dust core having excellent magnetic characteristics by increasing the heat treatment temperature to sufficiently remove strain.

[0006]

In order to achieve the above object, claim 1 of the present invention is a powder magnetic core obtained by compression molding magnetic metal powder together with a resin containing a borosiloxane resin as a main component. Item 2 is a powder magnetic core in which magnetic metal powder having an insulating coating on its surface is compression-molded together with a resin containing a borosiloxane resin as a main component, and Claim 3 is further provided with or without an insulating coating. The method is characterized in that the magnetic metal powder is compression-molded together with a resin containing a borosiloxane resin as a main component, and then strain relief heat treatment is performed at a temperature of 550 ° C. or higher.

[0007]

In order to improve the magnetic characteristics of the dust core by heat treatment, it is not enough to use a resin having excellent heat resistance. This is because the difference in the coefficient of thermal expansion during cooling causes stress in the magnetic powder, which reduces the magnetic properties. That is, it is necessary to select a resin that has excellent heat resistance and does not cause stress in the magnetic powder during cooling.

According to the present invention, by selecting a borosiloxane resin as the heat resistant resin, it is possible to obtain a dust core having excellent magnetic characteristics. That is, the dust core using the borosiloxane resin can be heat-treated at a high temperature, and does not cause strain due to the difference in thermal expansion during cooling, so that sufficient residual stress can be removed. If the stress can be further removed, plastic deformation of the magnetic powder is allowed.
It is also possible to apply a larger compressive force than before, and as a result, the space factor is improved, which is effective for improving the magnetic properties in addition to the stress relief effect.

[0009]

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

Pure iron powder having a particle size of 150 mesh pass is 98.
0% by mass, 1.5% by mass of borosiloxane resin, and 0.5% by mass of inorganic filler were kneaded by adding a solvent, filled in a mold, and compression-molded at a pressure of 900 MPa at 300 ° C.
It was cured by heating for 1 hour. Further, this powder magnetic core was subjected to strain relief annealing in N ₂ while changing the temperature between 500 ° C and 650 ° C.

In the present embodiment, the space factor is improved by increasing the compression force at the time of molding by about 50%, and the residual stress is removed by the heat treatment at a high temperature, so that the powder compact having excellent magnetic properties is obtained. Magnetic core becomes possible.

Table 1 shows the magnetic characteristics of the powder magnetic core of this example measured at the maximum magnetizing force Hm = 800 A / m. Further, as a comparative example, the characteristics of the dust core using the conventional epoxy resin are also shown.

[0013]

[Table 1]

When the heat treatment temperature is low, the magnetic properties are lower than those of the conventional materials, but at 550 ° C. or higher, the magnetic flux density is high and the coercive force is low, showing excellent magnetic properties.

When the powder magnetic core is used for high frequencies, it is necessary to make the electrical insulation between the particles of the magnetic powder more complete. For that purpose, the surface of the particles of the magnetic powder is coated with a phosphate coating in advance, and the magnetic powder after the surface treatment is compression-molded with a borosiloxane resin to obtain a dust core having excellent high frequency characteristics. You can Of course, instead of phosphate, chromate or another heat resistant insulating coating may be used.

[0016]

As described above, according to the present invention,
It is possible to provide a dust core having heat resistance, a high space factor, and excellent magnetic characteristics, and a high-frequency dust core having a low iron loss.

Claims (3)

[Claims] 1. A powder magnetic core, characterized in that magnetic metal powder is compression molded together with a resin containing a borosiloxane resin as a main component. 2. The dust core according to claim 1, wherein magnetic metal powder having an insulative coating applied on its surface is provided. 3. A pressure characterized by performing heat treatment for strain relief at a temperature of 550 ° C. or higher after compression-molding a magnetic metal powder with or without an insulating coating together with a resin containing a borosiloxane resin as a main component. A method for manufacturing a powder magnetic core.