JPH0935932A - Method for producing anisotropic magnet by dry molding method - Google Patents

Abstract

(57) Abstract: A magnet having high magnetic characteristics is manufactured by a dry molding method at a low cost with high productivity, and a magnet having a uniform plate thickness is manufactured. A magnet powder is molded in a magnetic field, Then, in the method of manufacturing an anisotropic magnet by firing, the molding is
The present invention is characterized in that the magnet powder is pressed without applying a magnetic field to form a preform having a density of 20 to 30% of the theoretical density, and then pressed in a magnetic field to form a form. In the initial stage of compression molding, a preform having a uniform density without applying a magnetic field is obtained. When a magnetic field is applied in this state, the density of the preform is relatively low, so that each magnet powder easily rotates and is oriented in the magnetic field direction. However, there is no degree of freedom to move each magnet powder, and there is no fear that the density of each part of the preform will be non-uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an anisotropic magnet such as a ferrite magnet or a rare earth magnet by a dry molding method.

[0002]

2. Description of the Related Art Generally, for anisotropic ferrite magnets, Ba ferrite powder or Sr ferrite powder having an average particle size of 0.2 to 1.5 μm is used. There are two manufacturing methods, a wet molding method and a dry molding method. In the wet molding method, a slurry in which ferrite powder is mixed with a liquid such as water is molded in a magnetic field. In the dry molding method, dried powder is molded in a magnetic field.

In the case of the wet molding method, a slurry-like raw material is put into a mold and molded while applying a magnetic field so that the particles are easily aligned in the magnetization direction. Since the raw material contains a liquid such as water, the powder easily moves and rotates, so that it is aligned with the easy axis of magnetization. However, since it is necessary to squeeze water or the like from the raw material after molding, the productivity is poor. In the case of the dry molding method, a dry powdery raw material is put into a mold and molded while applying a magnetic field so that the powder is easily aligned in the magnetization direction. Since the raw material is a dry powder, the rotation and movement of the powder are not so easy as the slurry, and the frictional resistance is large, so that it is extremely difficult to align the particles in the magnetization direction to the same extent as in the wet molding method. However, since it uses dry powder, it has good productivity.

Further, the pressing direction may be parallel to or perpendicular to the magnetic field direction. The orientation in the right-angled direction is less disrupted during the molding than in the parallel direction. However, in forming in the magnetic field in the perpendicular direction, when aligning the easy axis of magnetization in the thickness direction, compression molding is performed from the length direction.
Therefore, when a thin and long magnet having a thickness-length ratio (thickness / length) of 0.5 or less is manufactured, uneven density distribution occurs in the length direction, and it is difficult to obtain a high-performance magnet.

When the pressing direction is parallel to the magnetic field direction, when a thin magnet is manufactured, it tends to be thick at the center and thin at the ends. Therefore, it is necessary to polish the surface to a required plate thickness. Incidentally, JP-A-5-17
No. 5066 discloses a method of periodically varying the magnetic field strength during compression molding or molding while oscillating the magnetic pole portion. However, the above problems have not been solved.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnet having a magnetic powder with a high orientation, and a magnet having the same high magnetic properties as those of a wet molding method by a dry molding method with high productivity at a low cost. The purpose is to manufacture magnets of uniform thickness.

[0007]

As a result of research to achieve the above object, it was discovered that a high-performance magnet can be obtained by not applying a magnetic field at the initial stage of compression molding of magnet powder. Then, the density of the magnet powder compact when a magnetic field is applied, the strength of the magnetic field, the press speed, and the relationship between the density and orientation after molding, and the magnetic properties of the sintered magnet were studied in detail to complete the present invention. It is a thing.

The method for producing an anisotropic magnet by the dry molding method of the present invention is a method for producing an anisotropic magnet by forming magnet powder in a magnetic field and then firing the magnetic powder. In the forming, a magnetic field is applied. It is characterized in that the above-mentioned magnet powder is pressed without a preform having a density of 20 to 30% of the theoretical density, and then pressed in a magnetic field to obtain a preform.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Ferrite magnet powder such as Ba ferrite magnetic powder and Sr ferrite magnetic powder, and rare earth magnet powder such as SmCo magnetic powder and NdFeB magnet powder are used as magnet powder that can be used in the manufacturing method of the present invention. can do. The particle size of the magnet powder is not particularly limited, and the same particle size as the conventional one can be used. Further, the mold used for molding, the pressing device, the magnetic field applying device, and the like used in the conventional dry molding method can be used as they are.
Further, the sintered body of the magnet powder can be sintered by the same method as the conventional one.

In the manufacturing method of the present invention, the magnetic field is not applied at the initial stage of molding, that is, until the density is 20 to 30% of the theoretical density. And the theoretical density of 20-30
%, A magnetic field is applied, and the magnet powder constituting the compact is pressed while being oriented in the magnetic field direction by the magnetic field to form a compact. The magnitude of the applied magnetic field is 15 kO
It is desirable to be e or more. This is because the magnet powder is easily oriented on the easy axis of magnetization. The obtained molded body should have a density of 50 to 60% of the theoretical density. If it is less than 50%, the density is difficult to increase even if it is sintered. On the other hand, if it exceeds 60%, it is difficult to obtain a high-performance magnet even if the orientation of the compact is excessively sintered.

When ferrite magnet powder is used as the magnet powder, 20 to 30% of the theoretical density is 1.0 to
Becomes 1.5 g / cm ³ or so, 50% to 60% of the theoretical density
Is 2.6 to 3.0 g / cm ³ . Further, it is preferable that the magnet powder is molded in a mold, and the strain rate of the compression molding under application of a magnetic field is 0.5 to 5.0 / sec. When the strain rate of compression molding is converted to the compression molding rate, it means that when the thickness of the molded body in the compression direction is 1 mm, it becomes 0.5 to 5.0 / sec.

In the present invention, in order to clarify the conditions of the initial compression molding in which a magnetic field is not applied and the compression molding in which a magnetic field is applied, those obtained by the initial compression molding are used as a preform and a magnetic field. The molded body obtained by acting the above was described as a molded body. In practice, if the initial molding conditions are determined,
Without taking out the preform from the mold, after the initial molding is completed, a predetermined magnetic field is applied to continuously advance the compression molding to obtain the molded body at a stretch. Note that, of course, after the initial molding, if necessary, the pre-molded body may be taken out, transferred to a different mold and subjected to compression molding by applying a magnetic field to obtain a molded body.

[0013]

When the magnet powder is compression-molded in the magnetic field, the density of the magnetic powder becomes higher toward the center. If you press in this state,
The density of the molded body becomes higher toward the center, and when this is sintered, the thickness becomes larger toward the center and becomes a drum shape. In the method of the present invention, no magnetic field is applied in the initial stage of compression molding. For this reason, the density of the preformed body is unlikely to be different between the central portion and the peripheral portion, and the preformed body has a uniform density. In this state, a magnetic field is applied to the preform. Since the density of this preform is relatively low at 20 to 30% of the theoretical density, each magnet powder constituting the preform can be easily rotated and each magnet powder can be easily oriented in the magnetic field direction. However, there is not enough freedom to move each magnet powder. Therefore, there is no fear that the magnetic powder will be concentrated in the central portion of the preform and the density of each portion will be non-uniform.

In this state, a magnetic field is applied and further pressure is applied to finally form a molded body. Since the magnetic powder is applied and pressed, the magnet powder is pressed while its orientation is regulated. Therefore, the orientation of each magnet powder is maintained and a compact having a high orientation is obtained. In this state, the powder is taken out of the mold, and each magnet powder is sintered and integrated while maintaining its high orientation. Therefore, a highly oriented magnet having a uniform density in each portion can be obtained. Moreover, since the molded body itself has a uniform density, it does not deform due to sintering. That is, a sintered body having a uniform thickness can be obtained. Therefore, the magnet obtained by the manufacturing method of the present invention can be assembled to parts without polishing to make the thickness uniform. For example, a rectangular magnet for a linear motor can be assembled as it is manufactured.

[0015]

The present invention will be described in more detail with reference to the following examples. Example 1 The first example of the present invention is a dry Sr ferrite magnetic powder (9.0% SrO, 88.0% F) having an average particle size of 1.3 μm.
e ₂ O ₃ , 0.9% Al ₂ O ₃ , 0.5% CaO, 0.
1% Cr ₂ O ₃ , 0.4% SiO ₂ , 0.3% MnO;
Volume%, the same applies hereinafter), 12 mm x 24 mm x
A 4.2 mm magnet was produced. The magnetic field press used was a withdrawal molding method, and the excitation was
Helmholtz coil type magnetizer (outer diameter 650 mm,
The inner diameter was 410 mm).

First, a mold having a cavity shape of 13.6 mm × 27.6 mm and a depth of 17 mm was used, and 5.6 g of the magnetic powder was supplied to the cavity of the mold. The punch is hard chrome plated SKD11
Using a punch manufactured by K.K., compression was performed at a strain rate of compression molding of 1 / second to various densities without applying a magnetic field to obtain preforms shown in Table 1.

[0017]

[Table 1]

Next, 18 kOe was applied to each of the obtained preforms.
A magnetic field of (1) was applied and pressure was applied again while aligning, and pressure was applied until the density of the molded body reached 2.8 g / cm ³ to mold the molded body. After that, each of the obtained molded bodies is 800 ° C. in the atmosphere.
The temperature was raised at a heating rate of / hr and then sintered at 1235 ° C. for 1 hour. In this way, each magnet shown in Table 1 was manufactured.

The density of each of the obtained preforms and the degree of orientation of the formed compact, and the density of each of the obtained magnets,
The differences in magnetic properties, degree of orientation and magnet thickness were measured. These measured values are summarized in Table 1. The difference in the thickness of the magnet indicates the difference in the thickness between the central portion and the peripheral portion of the magnet. The degree of orientation of the molded body and the degree of orientation of the magnet were determined from the ratio between the residual magnetic flux density and the saturation magnetization by measuring the respective magnetization curves. As the saturation magnetization, the value of magnetization at 20 kOe was used.

In the case of a molded body, in order to prevent the shape from breaking during measurement, the molded body is immersed in a melted paraffin having a melting point of 45 ° C. to allow the paraffin to penetrate into the pores of the molded body, and then cooled. Then, the paraffin was solidified and the molded body was solidified and used as a sample for magnetization measurement. From these results, the density of the preform is 1.0 to 1.5 g / cm.
³ (ratio to theoretical density = 20 to 30%),
The most desirable magnetic characteristics were obtained, and the difference in thickness between the central portion and the end of the magnet was small.

The density of the preform is 1.0 g / cm.^ThreeLess than
In the case of, the magnetic powder is applied to the center of the compact by applying a magnetic field.
Thought that the difference in plate thickness became 0.2 mm or more
I have. The density of the preform is 1.66 g / cm.
^Three(32% of theoretical density) is distributed by applying a magnetic field.
The magnetic properties are desired because the amount of magnetic powder that is not suitable is increased.
It is expected that nothing was obtained. Therefore, magnetic powder
To move (orient) to the easy axis of magnetization without moving
The density of the green body is 1.0 to 1.5 g / cm^ThreeTo be
Was revealed. Example 2 Dry Sr ferrite magnetic powder having an average particle size of 13 μm
(9.3% SrO, 88.0% Fe_TwoO_Three, 0.3% r
Al_TwoO_Three, 0.4% CaO, 0.6% Cr_TwoO _Three,
0.4% SiO_Two, 0.3% MnO;% by volume)
A 12 mm × 24 mm × 4.2 mm magnet was manufactured. for
The magnetic field press machine that was used was a withdrawal molding method.
The excitation is a Helmholtz coil type magnetizer (outer diameter
650 mm, inner diameter 410 mm).

Using the same mold as used in Example 1,
The magnetic powder (5.6 g) was supplied to the cavity and pressed by a punch without a magnetic field to form a preform having a density of 1.24 g / cm ³ . Then, while applying a magnetic field of 18 kOe to orient, the strain rate of compression molding is 0.5,
Density 2.8g / c at 1, 2.5, 5 and 12.5 / sec
It was compressed to m ³ to form a molded body. After heating these at a heating rate of 800 ° C./hr in the atmosphere,
For 1 hour. This produced each magnet shown in Table 2.

The magnetic characteristics of the obtained magnet were investigated and summarized in Table 2.

[0024]

[Table 2]

It can be seen from Table 2 that the magnetic properties are most desirable when the compression rate during compression in the magnetic field is 0.5 to 5 / sec. It should be noted that even if the strain rate of compression molding is slower than 0.5 / sec, it has desirable magnetic properties, but it is not economical in terms of productivity. Example 3 Dry Sr ferrite magnetic powder having an average particle size of 1.4 μm (9.0% SrO, 88.0% Fe ₂ O ₃ , 0.9% r
Al ₂ O ₃ , 0.5% CaO, 0.1% Cr ₂ O ₃ ,
0.4% SiO ₂ , 0.3% MnO; volume%) was used.

In order to obtain 18 magnets each having a size of 12 mm × 24 mm × 4.2 mm, a mold having 18 cavities having a depth of 17 mm and lengths and widths of 13.6 mm and 27.6 mm was used. The magnetic powder of 5.6 g was inserted into each cavity of the mold. A Helmholtz coil with an outer diameter of 650 mm and an inner diameter of 410 m was used to generate the magnetic field. Then, a magnetic field pressing machine of a withdrawal molding system was used. The punch used was hard chrome plated SKD11.

Molding was performed by applying a magnetic field of 18 kOe and then applying a magnetic field of 18 kOe after applying a magnetic field of 1.2 g / cm ³ at a strain rate of 1 / sec for compression molding.
Was compressed at a strain rate of 1 / sec in compression molding to obtain a molded body having a density of 2.8 g / cm ³ . The obtained molded body was heated in the air at a heating rate of 800 ° C./hr and then sintered at 1235 ° C. for 1 hour to manufacture a magnet.

The orientation of the 18 compacts before sintering was 78 to 80%. The magnetic characteristic values of the manufactured magnet are as follows: maximum energy product 3.3 to 3.5 MGOe, residual magnetic flux density 3.7 to 3.8 kG, true coercive force 3.6 kO.
e and a coercive force of 3.3 to 3.4 kOe, and the difference in thickness between the central portion and the end was 0.1 mm or less.

[0029]

In the manufacturing method of the present invention, since the density of the molded body obtained by compression molding is uniform, even if the heating up to the sintering temperature or the cooling after sintering is accelerated, there is little cracking during the sintering. . Further, since the magnets that can be manufactured have a uniform plate thickness, they can be assembled to parts without post-processing, especially polishing. Furthermore, according to the manufacturing method of the present invention, a magnet having stable magnetic properties can be obtained economically with high productivity.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Honda Aichi Prefecture, Nagakute Town, Aichi Prefecture, Nagata 1 No. 41 Yokomichi Yokoshiro Central Research Institute Co., Ltd. (72) Inventor Masashi Okada Ichiriyama Town, Kariya City, Aichi Prefecture 100 Kanayama Toyota Auto Body Co., Ltd. (72) Inventor Hiroki Kuroki 100 Kanayama, Ichiriyama-cho, Kariya City, Aichi Prefecture Toyota Body Co., Ltd. (72) Hiroshi Shinoda 100 Kanayama, Ichiriyama-cho, Kariya City, Aichi Prefecture Toyo Inside Tatai Co., Ltd.

Claims (6)

[Claims] 1. A method for producing an anisotropic magnet by molding magnet powder in a magnetic field and then firing the magnet powder, wherein the molding is performed by pressurizing the magnet powder without applying a magnetic field to a theoretical density of 20 to 20%. A method for producing an anisotropic magnet by a dry molding method, which comprises forming a preform having a density of 30% and then applying pressure in a magnetic field to form a compact. 2. The method for producing an anisotropic magnet by the dry molding method according to claim 1, wherein the magnet powder is a rare earth magnet powder. 3. The method for producing an anisotropic magnet by the dry molding method according to claim 1, wherein the magnitude of the magnetic field when the molded body is pressed in the magnetic field is 15 kOe or more. 4. The method for producing an anisotropic magnet by the dry molding method according to claim 1, wherein the compact obtained by pressurizing in the magnetic field has a density of 50 to 60% of the theoretical density. 5. The magnet powder is a ferrite magnet powder,
20 to 30% of theoretical density is 1.0 to 1.5 g / c
m ³ and the density of 50-60% of the theoretical density is 2.6-
The method for producing an anisotropic magnet by the dry molding method according to claim 4, wherein the amount is 3.0 g / cm ³ . 6. The molding is carried out in a mold, and the strain rate of compression molding under application of a magnetic field is 0.5 to 5.0 / sec.
A method for producing an anisotropic magnet by the dry molding method described.