JP3201782B2 - Manufacturing method of dust core - 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 a dust core used for a choke coil, a transformer, a magnetic head and the like.

[0002]

2. Description of the Related Art A dust core using a high permeability magnetic powder having a flake shape is compared with a dust core using a high permeability powder having a granular shape. Attention has been paid to the prediction that the magnetic permeability will increase due to the small demagnetizing field in the longitudinal direction of the powder. However, since the powder is in the form of flakes, the density of the compression-molded product does not increase, and the magnetic permeability is low, which has hindered its practical use.

That is, as shown in FIG. 2, in a magnetic core obtained by compacting a flake-like high-permeability magnetic powder without a magnetic field into a green compact (1), the flake-like magnetic powder has a flake surface in a compression direction. Since the green compact is formed in a state in which it is somewhat aligned in the plane perpendicular to (2), the magnetic permeability of the toroidal coil in the direction of the magnetic path is high, and the compact is made of low-density granular high magnetic permeability magnetic powder of the same specific gravity. The magnetic permeability is about twice as high as that of the magnetic core. However, since the density is not sufficiently increased, the high permeability 100
When compared with a dust core made of a granular high magnetic permeability magnetic powder, the magnetic permeability was inevitably low.

From this fact, as shown in FIG. 3, a method of compressing and forming a flake-like high magnetic permeability magnetic powder while applying a magnetic field (3) perpendicularly to the compression direction (2) to obtain a green compact (1) is known. it was thought. However, only one axis in the longitudinal direction of the magnetic powder was aligned with the direction of the magnetic field, and there was no change in the positional relationship between the flake surface and the compression direction of each powder, and the magnetic permeability was hardly improved.

[0005]

According to the present invention, as a result of various studies in view of the above, a method of manufacturing a dust core whose magnetic permeability is remarkably improved has been developed.

That is, according to the present invention, a high-permeability magnetic core is produced by compacting a high-permeability magnetic powder, or by subjecting the compact to sintering or hot isostatic pressing (HIP). In the method, using a flake-shaped high magnetic permeability magnetic powder having an aspect ratio of 2 or more, after insulating the surface of the magnetic powder, applying a magnetic field in a direction perpendicular to the compression direction, a mold filled with the powder, and While one or both of the magnetic fields are rotated or rocked, compacting is performed in the magnetic field.

[0007]

According to the present invention, as shown in FIG. 1, the magnetic field (3) is moved in a direction perpendicular to the compression direction (2) of the flake-shaped high magnetic permeability magnetic powder, that is, the magnetic field (3) is moved in the above-mentioned orthogonal plane. The flake-shaped high-permeability magnetic powder is compression-molded into a green compact (1) while rocking or rotating, or while the mold is rocked or rotated while the magnetic field (3) is fixed, so that the compaction direction is reduced. Thus, a molded body having the flake surfaces of these flake-like magnetic powders in a plane perpendicular to the plane is obtained, so that the magnetic permeability is remarkably improved. For example, a dust core obtained by adding an organic binder to Sendust's flake high magnetic permeability alloy powder and molding in a rotating magnetic field of the present invention can obtain a high magnetic permeability of 100 to 500.
Even if the number of windings is small, sufficient inductance can be obtained, copper loss is reduced, and frequency characteristics of magnetic permeability are improved, so that use at a high frequency is possible.

Further, an inorganic insulating film is applied to the flake-like powder, molded by the above-mentioned rotating magnetic field using an inorganic binder, and then subjected to sintering or hot isostatic pressing.
A high magnetic permeability core having a magnetic permeability of 2000 or more can be obtained. Since these magnetic cores have a higher magnetic flux density than ferrite, they can be downsized when used for magnetic cores such as high frequency transformers. Further, a magnetic core using the flake-shaped sendust alloy powder can be used not only for a transformer but also for a magnetic head, so that it also replaces ferrite in material.

In the present invention, the aspect ratio of the flake-shaped high-permeability magnetic powder is set to 2 or more. If the aspect ratio is less than 2, the effect of molding in a rotating magnetic field cannot be sufficiently obtained, and the demagnetizing field of the magnetic powder is large. Therefore, a high magnetic permeability core cannot be obtained.

[0010]

Embodiments of the present invention will be described below. (Example 1) F having a thickness of about 3 μm and an aspect ratio of about 30
e-9.6 wt% Si-5.4 wt% Al alloy, Fe-78 wt% N
i-permalloy, Fe-6.5 wt% Si alloy, pure iron, F
Each flake-like magnetic powder of e ₈₀ Si ₁₃ C ₇ amorphous alloy, and the 1 hour heating to the surface of the flaky magnetic powder in the air at 400 ° C. and oxidized insulated. Each of these powders is added to a 5 wt% powdered phenol (Phenol T manufactured by Dai Nippon Printing
D739), a rotating magnetic field of 1 revolution / second was applied (the method of the present invention), a magnetic field was not applied (the comparative method), and a fixed magnetic field of 5 kOe was applied (the comparative method). Pressure 3ton / cm ² , rolling speed 1
0mm / sec, mold temperature is room temperature, outer diameter 9.8mm x inner diameter 6.
The primary molded product of 2 mm x 6 mm thickness is compression molded, and further compression molded into a toroidal shape of 10 mm outer diameter x 6 mm inner diameter x 4 mm thickness at a pressure of 4 ton / cm ^{2 in} a mold at 150 ° C.
A magnetic core was prepared by curing at 120 ° C. for 3 hours. In the above and cases, the direction of the magnetic field was always perpendicular to the direction of powder compression.

With respect to these magnetic cores, the saturation magnetic flux density, the magnetic permeability and the iron loss when a magnetic field was applied up to 10 mT at 1 MHz were examined, and the results are shown in Table 1.

[0012]

[Table 1]

As is apparent from Table 1, although the magnetic properties are hardly improved by molding in a fixed magnetic field, the magnetic properties of the article molded in a rotating magnetic field of the present invention are significantly improved. According to such a magnetic core of the present invention, it can be used for a normal mode choke of a switching power supply having a switching frequency of 1 MHz.

Example 2 An Fe-9.6 wt% Si-5.4 wt% Al alloy having a thickness of about 3 μm and an aspect ratio of about 500,
Fe-78wt% Ni permalloy, Fe-6.5wt% Si
The flake magnetic powder of the alloy and pure iron was heated in the air at 400 ° C. for 1 hour to oxidize and insulate the surface of the flake magnetic powder. After mixing 2 wt% of water glass with each of these powders, a pressure of 3 ton / cm ² was applied in each of the case where a rotating magnetic field of 1 rotation / second was applied (the method of the present invention) and the case where no magnetic field was applied (the comparative method). , Rolling speed 10mm / sec,
The mold temperature is room temperature, and the primary molded product of outer diameter 9.8mm × inner diameter 6.2mm × thickness 6mm is compression-molded, and 150mm each.
℃ outer diameter 10 mm × inner diameter 6 mm × a pressure of 4 ton / cm ² in a mold
After compression molding into a toroidal shape having a thickness of 4 mm, it was annealed at 400 ° C. for 1 hour, and then subjected to hot isostatic pressing at 2000 ° C. for 3 hours at 700 ° C. to produce a magnetic core. In the case of the method of the present invention, the rotating magnetic field is always applied in a direction perpendicular to the compression direction.

For each of these magnetic cores, the saturation magnetic flux density and the magnetic permeability and iron loss when a magnetic field was applied up to 10 mT at 1 MHz were examined. The results are shown in Table 2.

[0016]

[Table 2]

As is clear from Table 2, the magnetic core of the present invention molded in a rotating magnetic field has a high magnetic permeability of 1500 or more at 1 MHz, so that it can be used for a 1 MHz switching power transformer core. is there. The magnetic core using the flake Fe-Al-Si alloy powder of the present invention can be used for a magnetic head used in a MHz frequency band such as a hard disk or a VTR head.

[0018]

As described above, according to the present invention, the magnetic properties of the dust core are remarkably improved, and a remarkable effect such as a high magnetic permeability can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a molding method in a rotating magnetic field according to the present invention.

FIG. 2 is an explanatory view showing conventional compression molding without a magnetic field.

FIG. 3 is an explanatory view showing a conventional molding method in a fixed magnetic field.

[Explanation of symbols]

 1 Green compact 2 Compression direction 3 Magnetic field direction

Claims (1)

(57) [Claims] 1. A high-permeability magnetic powder is compacted or sintered or hot isostatically pressed on said compact.
P) In a method of producing a high-permeability magnetic core by performing a treatment, a flake-shaped high-permeability magnetic powder having an aspect ratio of 2 or more is used, the surface of the magnetic powder is insulated, and then a direction perpendicular to the compression direction. A method for producing a dust core, comprising: applying a magnetic field to the mold, and compacting in the magnetic field while rotating or swinging one or both of the mold and the magnetic field filled with the powder.