JPH01228107A - Dust core - Google Patents

Abstract

PURPOSE:To contrive improvement in filling adaptability into a metal mold, and to make it possible to obtain a high density molded body even in a low molding pressure by a method wherein, after the mixture of the ferromagnetic powder of grain diameter of 50mum or less and binder resin has been granulated in the granulation diameter of 0.2-0.5mm in advance, the mixture is filled in the metal mold and molded by applying pressure. CONSTITUTION:After the mixture of the ferromagnetic powder of grain diameter of 50mum or less and binder resin has been granulated into the grain diameter of 200-500mum, the mixture is filled into a mold and the title dust core is formed by molding. When the dust core is formed using the ferromagnetic powder of grain diameter of 50mum, after the mixture has been granulated into the grain diameter of 200-500mum in advance, the fluidity of the mixture can be improved by molding, and the filling adaptability into the mold can be improved. As a result, the pressure powder magnetic core having high molded body density and improved strength and magnetic characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a powder magnetic core used for magnetic cores of electrical equipment such as motors and transformers, permanent magnet materials, and the like.

(Prior art) Examples of using powder magnetic cores as the magnetic cores of electrical equipment such as motors and transformers are known. A powder magnetic core is well known, which is formed by bonding powder using a binder resin made of thermosetting resin such as epoxy resin, and then molding it into a predetermined shape (for example, Japanese Patent Publication No. 47-225
No. 14, JP 50-14207, JP 49-41
No. 97, etc.).

Conventionally, this type of powder magnetic core is made by filling a mold with a mixture of ferromagnetic powder such as iron, iron alloy, or ferrite, and a binder resin made of thermosetting resin such as epoxy resin, and compression molding. After forming a molded body, the molded body is taken out from the mold and cured by heating in a thermostatic oven or the like.

By the way, in this type of powder magnetic core, in order to prevent eddy current loss and improve powder properties, ferromagnetic powder with a relatively small particle size is used as the ferromagnetic powder that carries the magnetic properties. was.

(Problem to be Solved by the Invention) However, when the front diameter of the ferromagnetic powder used is small, the fluidity of the mixture (compound) of the ferromagnetic powder and binder resin deteriorates, causing it to flow into the mold. There was a problem in that flecks such as poor pouring and inclusion of air bubbles were likely to occur, resulting in poor filling properties into the mold.

For this reason, when powder magnetic cores according to the prior art are formed using ferromagnetic powder with a small particle size, many voids are likely to be formed in the compact after compression molding, resulting in a decrease in the density of the compact. Therefore, there was a problem that the mechanical strength and magnetic properties of the dust core deteriorated.

The present invention has been made in view of the above circumstances, and even when formed using ferromagnetic powder with a small particle size as a material, the porosity in the compact can be kept low and the density of the compact can be reduced. The object of the present invention is to provide a powder magnetic core with high strength and improved magnetic properties.

(Means for Solving the Problems) In order to achieve the above object, the powder magnetic core according to the present invention has the following features:
It is characterized in that a mixture of ferromagnetic powder with a particle size of 50 μm or less and a binder resin is granulated to a particle size of 200 μm to 500 μm, then filled into a mold and molded.

(Function) When forming a powder magnetic core using ferromagnetic powder with a particle size of 50 μm or less, the mixture is granulated in advance to a granulation size of 200 μm to 500 μm and then molded. Improves fluidity and improves mold filling.

(Example) Hereinafter, the present invention will be explained in detail based on the illustrated example.

FIG. 1 is a process diagram showing an example of the manufacturing process of a powder magnetic core according to the present invention, and in this example, the ferromagnetic powder is
An example using μm reduced iron powder and a thermosetting epoxy resin as the binder resin is shown, and the blending ratio is 3% by weight of the epoxy resin and the balance is the reduced iron powder.

Hereinafter, the manufacturing process of the powder magnetic core will be explained along with FIG.

In the figure, first, reduced iron powder and epoxy resin, which were weighed at their respective compounding ratios, were stirred for about 1 hour using a stirrer or the like.
Mix (S2).

Next, a mixture (compound) of reduced iron powder and epoxy resin is poured into a mold for forming a plate, and a compression pressure of 1 to
Pressure molding is performed using n/a&, and the compound is temporarily molded into a block shape as shown in FIG. 3 (1) (S3).

Next, the compound 1 temporarily formed into a block shape is pulverized for about 30 minutes using, for example, a hammer mill 2 or a stamp mill as shown in FIG. 3(n) to granulate a powdery compound. (S4).

The compound that has been crushed and granulated into powder is shown in Figure 3 (n
Sifting (classification) using a classification net 4 etc. as shown in [)
The compound powder with a particle size of 0.5 mm+(500 μm) or more is removed, and the compound powder 5 with a particle size of 0.5 mm or less is selected (S5).

Incidentally, as a method for granulating the compound, a well-known dish spinning method, extrusion method, etc. may be used.

In addition, as a method for classifying compound powder having a particle size of 0.5 mm or less, there is a method using a wet granulator as shown in FIG. 4. In the method using this wet granulator, the compound powder 7 formed in the same manner as described above is placed on the table 8.
The compound powder 11 having a particle size of 0.5 n+m or less is classified by passing it through a sorter 10 such as a strainer screen.

Next, the compound powder with a particle size of 0.5 mm or less selected in the classification process is filled into a mold, and then approximately 2 tons/a
A compact is formed by compression molding at a compression pressure of J (S6
). Then, the formed molded body is placed in a constant temperature bath or the like for about 15 minutes.
Hardened by heat treatment for about 1 hour at a temperature of 0°C (
S7), the molded body after heating and hardening is naturally cooled to form a powder magnetic core (S8).

Now, when the compact density was measured for the powder magnetic core according to the present invention formed through the granulation process as described above and the powder magnetic core formed without going through the conventional granulation process, the following results were obtained. Got the results.

As is clear from the above measurement results, the powder magnetic core according to the present invention is formed by mixing ferromagnetic powder with a binder resin, pre-forming, pulverizing and granulating the pre-formed compound, and then molding. The result was that the density of the molded body was higher in the case of .

In addition, in order to obtain the same density as the granulated molded product without the granulation process, the compression pressure during molding was required to be 3 ton/Ci (for the granulated product, the molding pressure was 2 ton/Cl). ).

This is because when ferromagnetic powder with small particle size is used as a magnetic material, the fluidity of the compound of this ferromagnetic powder and binder resin is poor, and for this reason, the compound is not directly filled into the mold as in the conventional technology. If this happens, the mold will not be filled sufficiently, the packing density will decrease, and voids will likely occur.

For this reason, if the granulation process is not performed, the density of the molded product will not be high enough when the compression pressure is low, and the density of the molded product will not be high. In order to achieve this, it is necessary to increase the compression pressure during molding.

In contrast, in the present invention, the compound is granulated to a particle size with good fluidity and then filled into a mold, so the filling properties are improved, the packing density is significantly improved, and the generation of voids is suppressed. . Therefore, even if the pressure during molding is low, the density of the molded product can be increased.

Therefore, the powder magnetic core according to the present invention can easily increase the compact density compared to conventional products, and can improve mechanical strength. Furthermore, since the density of the compact is high, it is possible to improve the magnetic properties, such as increasing the saturation magnetic flux density.

Note that the granulation diameter of the compound of ferromagnetic powder and binder resin is best when it is 0.2 mm to O.Smm, and the effect becomes weaker if it is larger or smaller.

As can be seen in the graph shown in Figure 2, which shows the relationship between granulation size and molding pressure (compression pressure to obtain a molded product with the same density), this is because when the granulation size of the compound is 0.2 mm or less, This is because when the thickness is 0.5 mm or more, the molding pressure becomes large.

In other words, if the granulation diameter of the compound is 0.2 mm or less, the fluidity of the powder will be poor, and the filling properties will be poor, similar to when the compound is molded without granulation, and the molding pressure will be high. In addition, when the granulation diameter of the compound is 0.5 mm or more, the fluidity is good, but voids are likely to form between the granulated powder, and to eliminate the second void, it is necessary to deform the granulated powder during molding. This is because the pressure needed to deform is necessary.

Therefore, in order to keep the compression pressure low during mold molding and obtain sufficient molding density, the granulation size of the compound must be 0.2
It is defined within the range of mm to 0.5 mm.

By specifying in this way, the compression pressure during molding can be lowered.

Note that if the compression pressure during molding is lowered, the damage to the mold will be reduced, it will be possible to take a large number of molded bodies with one mold, and productivity will be improved.

(Effects of the Invention) As described above based on the examples, according to the present invention, when forming a dust core using ferromagnetic powder with a particle size of 50 μm or less, ferromagnetic powder and binder resin By granulating the mixture in advance to a granulation diameter of 0.2 mm to 0.5 mm, and then filling it into a mold and pressurizing it, the filling performance into the mold is greatly improved. Even at relatively low molding pressure,
A high-density molded body can be obtained.

Therefore, according to the present invention, it is possible to easily provide a powder magnetic core that has a high compact density and improved mechanical strength and magnetic properties.

Furthermore, according to the present invention, when creating a compact with the same density as a conventional powder magnetic core, the molding pressure during molding can be lowered, so a large number of compacts can be produced from one mold. This also improves productivity.

[Brief explanation of the drawing]

Fig. 1 is a process diagram showing an example of the manufacturing process of a dust core according to the present invention, and Fig. 2 shows the relationship between the granulation diameter of the compound and the compacting pressure required to obtain a compact with the same density. The graph shown in FIG. 3 is an explanatory diagram of a granulation method showing one example of the granulation method, and FIG. 4 is an explanatory diagram showing another example of the granulation method. 1... Mixture, 2... Hammer mill for granulation,
5.11...Granulated powder. ／・−ゝ１、＼

Claims (1)

[Claims] A dust core characterized in that a mixture of ferromagnetic powder with a particle size of 50 μm or less and a binder resin is granulated to a particle size of 200 μm to 500 μm, then filled into a mold and molded.