JPH0628214B2 - Bonded magnet manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention provides a powder for a bonded magnet, in which a solenoid coil and a magnetic pole are installed in the vicinity of an opening of a molding space of a mold and extruded and granulated after a magnetizing process. The present invention relates to a method for producing a bonded magnet having high characteristics and uniformity by putting a powder into the molding space, rapidly and uniformly filling the powder into the molding space by applying an alternating magnetic field, and then performing compression molding.

[Prior Art] In the manufacture of a bonded magnet, in order to improve its magnet characteristics, a method of filling powder for a bonded magnet into a molding space of a mold and compression-molding with a press molding machine is usually adopted.

In this case, the filling of the powder for the bonded magnet into the die molding space is performed by utilizing gravity-falling naturally. In other words, a bottomless powder supply mechanism that slides on the upper surface of the die that forms the mold causes the powder to naturally drop from the opening of the molding space, and then slides the powder supply mechanism to remove excess powder. The filling operation is completed with.

If the opening area of the die molding space is considerably large, it can be filled by such a method. However, when the area or width of the opening is small, it is difficult to perform sufficient filling by simply sliding the powder supply mechanism along the upper surface of the mold, and the variation in the filling amount is large.

Therefore, a method of filling the mold by applying slight vibration, a method of forcibly pressing the powder by providing a forced filling blade, a push rod, or the like in the upper part of the molding space may be adopted.

[Problems to be Solved by the Invention] In order to manufacture a bond magnet with high performance and little variation in characteristics, it is necessary to fill the molding space with powder for a bond magnet uniformly at a high density and at a constant filling amount. Is important.

However, in the method of filling the mold by applying slight vibration, the filling amount is likely to change depending on the state and shape of the powder. Further, even if vibration is applied, the time required for filling is not shortened so much, and the variation in filling amount is large. Furthermore, the tightening of the bolts and the like of the device may become loose due to vibration, and frequent maintenance is required.

In the method of forcedly filling by rotating the blade or press-fitting the push rod, not only the time required for filling is very long, but also the automation of powder filling in the pressing step is difficult and the production efficiency is extremely poor. In addition, because the shape of the filled powder is locally different from the previous shape (before filling) because it is forcedly pushed by the blades and push rods, it is difficult to perform uniform quantitative filling, and there is a variation in weight during molding. Non-uniformity of density distribution occurs.

As a result, the bonded magnets manufactured by the conventional technique had low magnet characteristics and large variations. This drawback is particularly serious in the case of a peculiar shape such as a thin ring shape.

Further, in the case of producing an anisotropic bonded magnet in the prior art, it was difficult to sufficiently orient a unique shape such as a thin ring shape in a mold. It is desirable to use a magnetized powder for a bonded magnet, but the magnetized powder has poor fluidity, and it is even more difficult to uniformly fill the powder.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method capable of efficiently producing a thin ring-shaped anisotropic bonded magnet with high performance and less variation in characteristics.

[Means for Solving the Problems] In the present invention that can achieve the above objects, a solenoid coil is provided on the vicinity of the outer periphery of an opening of a thin ring-shaped molding space formed by a mold, and the central axis of the solenoid coil is the molding space. A device in which a magnetic pole having a circular cross-section is arranged in the center of the solenoid coil near the inner circumference of the opening of the molding space is used so as to be installed so as to coincide with the central axis. Then, a mixture of magnet powder and a resin binder (for example, epoxy resin) is magnetized in that state. Then, it is granulated by an extrusion granulation method to obtain a powder for a bonded magnet. The powder for bonded magnet is put into the solenoid coil, and an alternating current is supplied to fill the molding space. Then, it is compression-molded while applying a magnetic field to manufacture a thin ring-shaped anisotropic bonded magnet.

In the present invention, any magnet powder such as rare earth-based, ferrite-based, alnico-based, or neodymium-iron-boron-based magnet powder can be used.

[Operation] When an alternating current is supplied by installing a solenoid coil and a magnetic pole in the vicinity of the opening of the molding space of the mold in such a direction that the central axis substantially coincides with the depth direction of the molding space, an alternating magnetic field is generated. This alternating magnetic field changes in the depth direction of the molding space. The granulated powder that has been magnetized in such a situation reacts very actively to such changes in the magnetic field and is sucked into the molding space. Then, this powder is sequentially filled in the space. Moreover, since the remaining powder is also vibrating, it is quickly sucked into the molding space.

Since this filling is performed by a magnetic attraction force that is much larger than the force due to natural fall, etc., even if the opening area of the molding space of the mold is small or the width of the opening is extremely narrow, it takes a very short time. Is done smoothly. Moreover, unlike the conventional forced filling using blades or the like, the powder for bonded magnets is filled almost uniformly without breaking.

In the present invention, since the filling into the molding space is performed by the magnetic attraction force, the magnetized granulated powder can be efficiently and uniformly filled, which is particularly advantageous for the production of anisotropic bonded magnets.

In order to obtain a magnetized granulated powder, first a mixture of magnet powder and resin binder is magnetized and then granulated by an extrusion granulation method. A uniform granulated powder is obtained.

[Embodiment] First, an apparatus suitable for carrying out the method of the present invention will be described. A part of an apparatus for producing a cylindrical or ring-shaped bonded magnet is shown in FIG.

This device vertically slides in a die 10 having a circular hole in the center, a lower rod 12 arranged with a gap in the center thereof, and a cylindrical gap between the die 10 and the lower rod 12. And a lower cylindrical punch 14 which is freely movable.
The cylindrical space formed by these three members constitutes the molding space 18. The molding space 18 is filled with bonded magnet powder, and a cylindrical upper punch (not shown) is inserted from above and pressurized to perform compression molding. The mold structure of such a press molding machine is basically the same as the conventional case.

In the present invention, the solenoid coil 20 and the magnetic pole 22 are coaxially arranged near the opening of the molding space 18 of the mold. The solenoid coil 20 has a molding space 18 in the central axis direction.
The direction is almost the same as the depth direction of. Here, the solenoid coil 20 has an inner diameter slightly larger than the outer diameter of the molding space 18, and a magnetic pole 22 having a diameter equal to or smaller than the diameter is provided on the lower rod 12 in the center. A hopper 23 is provided above the solenoid coil 20.
To provide.

In this embodiment, the die 10 and the lower rod 12 are made of a magnetic material, and the lower punch 14 (also the upper punch) is made of a non-magnetic material.

The hopper 23 is used to supply the powder for the bonded magnet. As described above, the solenoid coil 20 and the magnetic pole 22 are installed in the vicinity of the opening of the molding space 18 of the mold, and the powder 24 for the bond magnet is placed above the molding space 18. Under this condition, an alternating current is supplied to the solenoid coil 20. The frequency of the alternating current used is not particularly limited, but may be a normal commercial frequency. By passing an alternating current through the solenoid coil 20, alternating magnetic force lines are generated as shown by a broken line in FIG.
An alternating magnetic field is formed in the inside of the unit 8. The shape of the lines of magnetic force changes depending on the material (magnetic material or non-magnetic material) of the mold constituent member, but for convenience sake, the approximate path is shown. Due to this AC magnetic field, the powder 24 for the bonded magnet, which is piled up in the upper part of the molding space 18, is magnetically attracted to the inside thereof and reacts to the AC magnetic field to repeat complicated vibrations, and even if the gap is very narrow. It will be filled in a short time.

Therefore, after that, the filling operation is completed by removing the excess powder for the bonded magnet by a sliding method or the like, and then the upper punch is lowered and pressed to perform compression molding.

Magnetic pole 22 located at the center of solenoid coil 20
Has a function of concentrating an AC magnetic field in the molding space 18,
As a result, the bond magnet powder 24 can be effectively sucked into the molding space 18 even with a weak current.

Next, the result of manufacturing the bonded magnet according to the method of the present invention will be described.

Samarium cobalt (Sm ₂
Co ₁₇ ) -based alloy with a jet mill has an average particle size of 3 μm
The powder was pulverized, and the powder was molded in a magnetic field, then sintered and aged to obtain a raw material.

This raw material sintered body was crushed by a jaw crusher and sieved to obtain a powder having a particle size of 120 μm or less. This permanent magnet powder was treated with a coupling agent and then mixed with an epoxy resin. This mixture was magnetized in a magnetic field of 20 kOe and granulated by an extrusion granulator to obtain granulated powder having a particle size of 400 to 800 μm.

The granulated powder was filled in a mold forming space by an apparatus as shown in FIG. 1, and was placed in a radial orientation magnetic field of 10 kOe,
A ring-shaped bonded magnet having radial anisotropy was manufactured by molding at a pressure of 3 ton / cm ² .

The shape of the molding space of the mold is 18 mm in outer diameter and 16 mm in inner diameter.
φ, height 16 mm. The alternating magnetic field applied at the time of filling the granulated powder is 50 e or more and the frequency is 10 Hz or more. The weight of the powder to be filled is 1.5 g on average.

Thereafter, curing treatment was performed at 120 ° C. for 1 hour, and 24-pole magnetization was performed at 20 to 30 kOe using a pulse magnetizer.

For comparison, the same powder for bonded magnet was used and manufactured by the conventional method. Filling in the conventional method is a natural dropping method in which powder is put into a slide type filling jig and dropped and filled in the molding space by reciprocating on a die,
This is a combination of forced press fitting with a push rod. Others are the same as the method of this embodiment.

Table 1 shows various properties of the obtained bonded magnet.

As can be seen from Table 1, the method of the present invention has improved density and surface magnetic flux as compared with the prior art, has less variation in surface magnetic flux, and can significantly shorten the filling time.

The permanent magnet powder used in the present invention may be any of ferrite-based, alnico-based, neodymium-iron-boron-based, etc. other than the samarium-cobalt-based magnet powder. The effect of the molding space is particularly remarkable when the shape of the molding space is a thin-walled cylindrical shape or a thin-walled plate shape, but it can be applied to any other shape.

[Advantages of the Invention] As described above, according to the present invention, in the vicinity of the opening of the molding space of the mold, the solenoid coil and the magnetic pole are installed in the direction in which the central axis direction substantially coincides with the depth direction of the molding space, and the bond is magnetized. The powder for magnets is put in the coil, and an alternating magnetic field is applied to fill the molding space for compression molding. Therefore, a magnetic attraction force acts on the powder for bonded magnets to open the molding space. Even if the area is small or the opening is extremely narrow, the magnetic attraction force allows the powder for the bonded magnet to be rapidly filled in the molding space. Moreover, since the powder for the bonded magnet is filled by the magnetic attraction force instead of forcing it mechanically, the shape of the original powder is maintained as it is, the density distribution is uniform, and the weight of the compact is constant. Variation is reduced.

In particular, when manufacturing a thin ring-shaped anisotropic bonded magnet, it is possible to rapidly and uniformly fill the magnetized powder for bonded magnets, so that the particles can be sufficiently oriented in the mold.
Further, in the present invention, since the mixture of the permanent magnet powder and the resin binder is magnetized and then extruded and granulated, it is possible to obtain a granulated powder having a uniform particle size and characteristics, which leads to an increase in the filling amount and uniformity. Be done. As a result, the characteristics of the bonded magnet are improved.

Furthermore, since the present invention only installs the solenoid coil on the upper part of the mold, it can be applied to any existing molding machine.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a main part of a molding apparatus used in the method of the present invention and an alternating magnetic force line. 10 ... Die, 12 ... Lower rod, 14 ... Lower punch, 18 ... Molding space, 20 ... Solenoid coil, 2
2 ... Magnetic pole, 24 ... Powder for bonded magnet.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location B29L 31:34 (72) Inventor Kazuo Matsui 5 36-11 Shinbashi, Minato-ku, Tokyo Fuji Electric Chemical Incorporated (56) Reference JP-A-51-47295 (JP, A) JP-A-61-26205 (JP, A) JP-A-51-20593 (JP, A)

Claims (1)

[Claims] 1. A solenoid coil is installed in the vicinity of the outer periphery of an opening of a thin-walled ring-shaped molding space formed by a mold so that its central axis coincides with the central axis of the molding space, and the center of the solenoid coil is formed. Using a device in which a magnetic pole with a circular cross-section is placed in, the powder for bonded magnets granulated by the extrusion granulation method after the magnetizing treatment is put into the solenoid coil, and an alternating current is supplied to the molding space. A method for producing a bonded magnet, which comprises filling and compressing by applying a magnetic field to obtain a thin ring-shaped anisotropic magnet.