JPS6012713A - Manufacture of magnetic core - Google Patents

Abstract

PURPOSE:To partly remove metal magnetic powder, prevent drop of electrical resistivity of core and obtain best characteristic of core by placing a liquid dissolving metal magnetic powder in contact with the surface of dust core material having completed the cutting work of grinding work. CONSTITUTION:The Fe powder and Ni powder in average grain size and epoxy resin are mixed in the specified volume ratio, the mixed material is subjected to the specified heat treatment after it is molded through compression and thereby a cylindrical core material 2 is formed. This core material 2 is sent to the cutting work and thereby a plurality of slots 3 and a plurality of tooth 4 are formed alternately and radially. This core material 2 is immersed into the mixing solution of ferric chloride and hydrochloric acid, the rate surface is removed by about 30mum and thereby a core 5 for magnetic deflection is manufactured. Drop of electrical resistivity of core 5 is prevented by the contact with the mixed solution and the best characteristic of core material 2 can be obtained.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method of manufacturing a magnetic core by mixing and molding metal magnetic powder and an electrically insulating binder, and then machining the mixture. In particular, the present invention relates to a method of manufacturing a magnetic core that can prevent properties from deteriorating due to cutting or grinding after molding.

[Technical background of the invention and its problems]

Generally, in a conductive magnetic core, eddy current loss increases in proportion to the square of the operating frequency. Therefore, cores for high frequencies are used with high electrical resistivity in order to suppress eddy current loss.

Such cores include ferrite cores and dust cores. A ferrite core is obtained by mixing iron oxide powder and a divalent metal, followed by pressure molding and sintering, and is characterized by its extremely high resistivity. However, this ferrite core is hard and brittle, making machining difficult. This not only limits the shape of the core that can be produced, but also requires a sintering process, which makes it difficult to maintain high dimensional accuracy.

On the other hand, the dust core is made by binding metal magnetic powder with an electrically insulating binder such as epoxy resin, and the resistivity of the core is increased by the action of the insulator interposed between the magnetic powders. Since such a dust core has good machinability, high dimensional accuracy can be ensured by cutting or grinding after molding.

However, when such dust cores are cut or ground, particles of magnetic powder that is a conductor and insulating resin that exists between these particles are deformed on the machined surface, or so-called "paris" are formed in these particles. As a result, the magnetic powder particles may come into contact with each other, resulting in an extremely low resistivity of the core.

[Purpose of the invention]

The present invention has been made in view of these problems, and its purpose is to eliminate the influence of machining on the magnetic properties when machining a dust core material to produce a magnetic core of a desired shape. An object of the present invention is to provide a method for manufacturing a magnetic core that enables the following.

[Summary of the invention]

The present invention involves cutting or grinding a dust core material made of metal magnetic powder bound with an insulating binder to obtain a magnetic core of a desired shape, and then cutting or grinding a dust core material made of metal magnetic powder bound with an insulating binder to obtain a magnetic core of a desired shape. The feature is that the magnetic powder is brought into contact with a liquid that dissolves it.

〔Effect of the invention〕

According to the present invention, contact points between metal magnetic particles generated on a machined surface by cutting or grinding can be dissolved and separated using a dissolving solution. Therefore, a decrease in the resistivity of the core can be prevented, and a magnetic core with a desired shape that can maximize the characteristics of the dust core can be manufactured.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained based on examples.

Example 1 Fs-2% Si powder with an average particle size of 70 μm and an epoxy resin were mixed at a volume ratio of 84:16, and
After compression molding at a pressure of MPa, heat treatment was performed at 200° C. for 1 hour to obtain a cylindrical core material with an outer diameter of 65 W11 + an inner diameter of 45 m and a height of 455 m.

The entire surface of this core material is ground to create an outer diameter of 60.2mm.
tnm + inner diameter 49.8 tan, height 40.2m
The core I was then immersed in a phosphoric acid solution to obtain a core I which was dissolved by 100 μm from the ground surface as shown in FIG.

Therefore, the iron loss value per unit weight at this core IO magnetic flux density of 0.3T is calculated from 50Hz, 400Hz and 2
I tried measuring each frequency of kHz. For comparison, measurements were also taken before and after machining (before dissolution treatment). The results were as shown in the table. In addition, in the table, the iron loss value before machining is assumed to be 1, and the values are expressed as a ratio to this value.

Table As is clear from this table, the iron loss increases significantly as the frequency increases after machining, but when the process of immersing it in a solution after machining is performed, the iron loss decreases significantly, and before machining It is almost the same. This is because the contact areas between the metal magnetic powder particles produced on the machined surface by machining were dissolved and separated by the dissolving solution. Therefore, the effectiveness of the present invention is understood.

Example 2 Fe-45%Ni powder with an average particle size of 53 μm and an epoxy resin were mixed at a weight ratio of 76:24.
After compression molding at a pressure of 0 MPa, heat treatment was performed at 200°C for 1 hour to obtain an outer diameter of 100 ta as shown in Figure 2.
A disk-shaped core material 2 with a height of nt 50 m was obtained. After cutting this core material 2, the results are shown in Figures 3 (-) and (h).
As shown in the figure, a plurality of slots 3 and a plurality of teeth 4 were formed in a shape that was alternately arranged radially. This core was further immersed in a mixed solution of ferric chloride and hydrochloric acid, and the surface was coated for about 30 minutes.
By removing μm, a core 5 for electromagnetic polarization was obtained.

Then, a coil is wound around this core 5, and the frequency of 15 kHz is
When the core 5 was excited to a constant magnetic flux density by applying a sawtooth alternating current signal, the temperature of the core 5 increased by 30° C. relative to the ambient temperature and became stable. For comparison, after the cutting process,
When excitation was performed under the same conditions as described above before the mixed solution immersion step, the core temperature reached 85° C. relative to the ambient temperature.

As described above, it was confirmed from the comparison of the temperature rise of the core that the magnetic core manufactured by employing the present invention has extremely low iron loss.

Example 3 Iron powder with an average particle size of 53 μm and polyamide resin were mixed at a volume ratio of 4:1, compression molded at a pressure of 600 MPa, and then heat treated at 200° C. for 30 minutes to obtain the above example. A disk-shaped core material 2 having the same shape as 2 was obtained. This core material 2 was cut into the shape shown in FIGS. 3(a) and 3(b) in the same manner as described above. Further, this core was immersed in a mixed solution of ferric chloride and hydrochloric acid, and about 30 μm of the surface was removed to obtain a core for electromagnetic polarization.

In this manufacturing process, magnetization was carried out under the same conditions as in Example 2 after the cutting process, before the immersion process in the mixed solution, and after the immersion process. is 60℃ compared to before the soaking process.
It was confirmed that the core of this example also had extremely low iron loss.

Note that the present invention is not limited to Examples 1 to 3 above, and for example, Fe-M alloy, Fe-81
-At alloy, pe-Co alloy, etc. may be used, and resins such as polyimide, polycarbonate, and polyester may be used as the binder. In other words, the present invention can be made in various liquid forms without departing from the gist thereof.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the appearance of the core obtained in the first embodiment of the present invention, and FIG. 2 is a perspective view showing the core material at an intermediate step in the second and third embodiments of the present invention. , Figure 3 (-
) is a front view of the core obtained in the same example, FIG. 3(b)
FIG. 2 is a cross-sectional view taken along the line A-A in FIG. ! , 5... Core, 2... Material, 3... Slot,
4... Teeth. Applicant's representative Patent attorney Takehiko Suzue No. 10 No. 3 ￥ 7 Diagram (b)

Claims (1)

[Claims] After a core material is formed by mixing and molding a metal magnetic powder and an electrically insulating binder, the core material is subjected to cutting or grinding to produce a magnetic core of a desired shape. A method for manufacturing a magnetic core, characterized in that a part of the metal magnetic powder is removed by contacting the cut or ground surface with a liquid that dissolves the metal magnetic powder.