JPH0211006B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a cylindrical oxide (ferrite magnet) having radial magnetic anisotropy, and particularly to a method for manufacturing a cylindrical magnet having radial anisotropy. Generally, ferrite magnets are obtained by molding and sintering ferrite particle powder. These ferrite particles have a magnetoplumbite-type hexagonal crystal structure represented by the chemical formula MOnFe ₂ O ₃ , and the C axis thereof is the magnetic easy axis. In the above formula, M is one or more of Ba, Sr, and Pb, and n is 5.0 to 6.3. Therefore, the conditions for improving the characteristics of this ferrite magnet are: (1) Increasing the density of the sintered body (2) Making the crystal closer to monomagnetic so as not to deteriorate the coercive force Hc (3) Aligning the magnetic easy axes in the same direction is essential. Note that magnets whose C axes are not aligned are called isotropic magnets, and magnets whose C axes are aligned are called anisotropic magnets. Anisotropic magnets have a residual magnetic flux density (Br) that is twice that of isotropic magnets.
It is known that the maximum energy product (B _H )max is more than three times as large as that of B H . In order to align the C-axes, generally a magnetic field is applied when ferrite powder is molded, and the C-axes are aligned in the direction of the magnetic field. By the way, cylindrical magnets are used as rotor magnets for micro motors and small generators.
Since this cylindrical magnet uses magnetic force in the radial direction, having anisotropy in the radial direction as shown in FIG. 1 improves the performance of this magnet. For this reason, various forming methods have been attempted to align the C-axes in the radial direction, but in magnets obtained by the press sintering process, increasing the degree of orientation in the radial direction causes cracks during the cooling process of sintering. . Therefore, the degree of orientation must be significantly lowered, and the magnetic properties can only be improved by at most 20% of the isotropy. In order to solve this contradictory phenomenon, the inventors of the present invention filed Patent Application No. 184370 (Japanese Unexamined Patent Publication No. 1983-72704).
In this specification, we proposed a molding method in which the powder is filled into the cavity of a mold and at least 16 or more magnetic poles are used to create anisotropy in the radial direction. Furthermore, in 1982
In Patent Application No. 109004 (Japanese Unexamined Patent Publication No. 1820-1982), the outer or inner circumferential portion is multipolar anisotropic, the opposite side is isotropic, and has an integral concentric structure. As a result, we were able to invent a cylindrical magnet with transparent radial anisotropy and magnetic properties that do not cause cracks. However, this ferrite magnet has a residual magnetic flux density of Br during sintering.
Increasing the density in order to increase the density causes crystal growth and reduces the coercive force H _C , which is a contradictory property. During manufacturing, the holding force H _C
It was found that the density of the sintered body needs to be 4.78 g/cm ³ or less in order to deteriorate _{the I} H _C 30000e. However, the theoretical density of this ferrite magnet (assuming the number of holes is 0) is 5.14 g/cm ³ , and increasing the density will improve (B _H )max. As a result of further research into this cylindrical permanent magnet having an isotropic part and an anisotropic part, the inventors of the present application found that
When the cavity of a mold with magnetic poles arranged on the outer or inner periphery of the cylindrical cavity is filled with the final product at 100%, 30% of the ferrite particles with a small average particle size are used.
The fine particles are magnetically oriented and adsorbed by the magnetic poles, and then the remaining amount is filled so that the ferrite powder with a large average particle size is mainly filled in the areas where the powder is not magnetically adsorbed. By filling, compression molding, and sintering, we succeeded in manufacturing a cylindrical permanent magnet with high density, an isotropic part and an anisotropic part. In general, magnetoplumbite-type ferrite powder with a hexagonal crystal structure has a uniaxial particle diameter of approximately 1 μm, and it is common for those skilled in the art to grind it to 1 μm or less in order to increase the degree of orientation during magnetic field orientation. It is. On the other hand, particles with a particle size exceeding 1 μm are not easily oriented in a magnetic field and their properties deteriorate. In the present invention, in order to intentionally create oriented regions and non-oriented regions inside the core, particles with a diameter of 1 μm or less that are easily oriented are arranged near the magnetic poles, and particles of 1 μm or more that are difficult to be oriented are arranged in other parts. It is characterized by the arrangement of The present invention therefore relates to a molding method for obtaining a cylindrical permanent magnet with multipole magnetic orientation in the radial direction, and its gist is to form hexagonal oxide magnetic powder with an average particle diameter of 1.0 μm Prepare the following first slurry and a second slurry exceeding 1.0 μm separately, and inject the first slurry into a filling mold equipped with a plurality of magnetic poles around the periphery that exert magnetic force in the radial direction. The method of manufacturing a radially anisotropic cylindrical permanent magnet is characterized in that the magnet is magnetically oriented and then filled with the second slurry, compression molded, and sintered. The cylindrical permanent magnet according to the present invention has a density of 4.98 g/cm ³ or more, and its product characteristics are the same in shape.
The properties were improved by more than 5% compared to the conventional one, which weighed about 4.77g/cm ³ . That is, ferrite particles having an average particle diameter of 1.0 μm or less, preferably 0.9 μm or less, are oriented by magnetic poles arranged on the outer or inner periphery of the mold, and form an anisotropic portion. Ferrite particles filled after this with an average particle diameter of more than 1.0 μm, preferably 1.1 μm or more, are coarse in particle size and are not easily oriented and form an isotropic part. Example 1 A 16-pole rare earth permanent magnet was placed on the outer periphery of a mold having a cavity with an outer diameter of 28φ and an inner diameter of 16φ, and the calcined Sr-ferrite was crushed to 0.7μm to 1.56μm and several types of A slurry was prepared, and the slurry was filled into the mold and compression molded, and then the degree of orientation of the portion of the molded product that came into contact with the magnetic pole of the mold was measured. The results are shown in FIG. At this time, the magnetic field when 5 mm away from the magnetic pole was 680G. When the ferrite particles exceed 1.1 μm, the particle orientation (X-ray orientation degree F) becomes smaller than 470, and it is understood that in the present invention, it is difficult to magnetically orient the slurry of 1.1 μm or more that is filled later. As a result, it is found that it is better to fill the magnetically oriented portion with thin particles and fill the isotropic region with coarse particles. Example 2 A magnetized rare earth magnet with a width of 4.4 mm was attached to the outer circumference of a mold having a cavity with an outer diameter of 28 φ and an inner diameter of 16 φ.
16 pieces were placed on the circumference, spaced apart from each other. This cavity is filled with 0%, 25%, 50%, 75%, and 100% Sr-ferrite slurry with an average particle size of 0.78 μm, respectively.
Each slurry with an average particle size of 1.3 μm after orientation
After filling and compressing 100%, 75%, 50%, 25%, and 0%, each molded body was sintered at 1440°C, 1180°C, and 1220°C for 90 minutes. Table 1 shows the sintered body density and _I H _C at this time, and the magnetic flux Bo in the open magnetic path after magnetization.

[Table] As can be seen from this table, when the slurry using 1.3 μm powder exceeds 75%, _I H _C increases, but the anisotropic part decreases and Bo decreases. But 1.3μm25%~75%
In this case, even if the sintered density is increased, _{the I} H _C shows more than 3000,
The magnetic flux Bo in the open magnetic path improved as the sintered density increased. Although the present invention has been described above with reference to the above-mentioned embodiments, when the powder has a single particle size and is oriented in multiple poles in the radial direction, Bo and the holding force _I H _C are contradictory, which is particularly preferable as a rotor for a micromotor. It was nothing. The present invention aims to solve the above-mentioned drawbacks by magnetically attracting and orienting thin particles to multi-pole magnetic poles during magnetic field forming, and then filling coarse particles in areas that do not significantly affect the magnetic properties. A magnetically almost isotropic region is formed. By doing this, it was possible to control the magnetic properties to desired values, such as the coercive force _I H _C and the magnetic flux Bo in the open magnetic path. Furthermore, in the case of only magnetically oriented regions (i.e., orientation of thin particles), cracks occur due to the difference in thermal expansion coefficient depending on the direction of magnetic orientation, but in the present invention, since regions without magnetically oriented are formed, these cracks are completely eliminated. Summer.

[Brief explanation of drawings]

FIG. 1 is a plan view of a cylindrical magnet having anisotropy in the longitudinal direction, and FIG. 2 shows an orientation degree curve with respect to the pulverized particle size, which shows the experimental results of the inventor of the present application.

Claims (1)

[Claims] 1 Hexagonal oxide magnetic particles with an average particle diameter of
The first slurry is less than 1.0 μm and the second slurry is more than 1.0 μm.
The first slurry is prepared separately, and the first slurry is injected into a filling mold having a plurality of magnetic poles around the periphery that exert a magnetic force in the radial direction for magnetic orientation. A method for manufacturing a radially anisotropic cylindrical permanent magnet, characterized by filling the magnet with compression molding and sintering. 2 The average particle size of the first slurry is 0.9 μm or less,
The method for manufacturing a radially anisotropic cylindrical permanent magnet according to claim 1, wherein the second slurry has a thickness of 1.1 μm.