JPH02272712A - Manufacture of rare earth anisotropic magnet - Google Patents

Abstract

PURPOSE:To prevent cracks in molding and to elevate magnetic anisotropy by extruding magnetic isotropic stuffed or hollow magnet material while giving compressing force to the free face which does not contact with an extrusion mold. CONSTITUTION:To manufacture a columnar stuffed magnet material 16, first magnet powder 16 is filled in the space formed by a die 10 and a lower punch 12. These molds are heated to 600-900 deg.C in advance. These whole are held in a sealed bath, and inside of the bath is exhausted or filled with inert gas so as to put it in oxidation preventive atmosphere. The magnetic power 16 is maintained in the mold for one to three minutes after charge, thus the temperature of the powder 16 rises to the specified temperature by the heat transmitted from the mold, and then an upper punch 14 is screwed down so as to compress the powder 16. Hereby, compressing molding material (columnar magnet material) 18 can be obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing rare earth magnets, and in detail, Nd
R -Fe -B system (R
relates to a method of manufacturing a permanent magnet (La-based rare earth element).

(Conventional technology and issues to be solved by IJ+)R
-Fe-B permanent magnets are produced by (a) melting the base alloy, casting it into a mold to form an ingot, pulverizing it into ultrafine powder, and molding this powder using a mold in a magnetic field. A sintered magnet that is compacted and sintered to make an anisotropic magnet;
There is an ultra-quenched magnet in which an isotropic magnetic material is obtained by hot pressing at 00°C, and then plastically deformed with an area reduction of 40% or more at a temperature of 900°C or less to make it anisotropic.

If these magnets with high magnetic properties can be applied to small motors, especially for OA and FA, they will help miniaturize the motors.

Although it is extremely useful for reducing weight, the reality is that it has not been fully applied to motors due to technical problems in practical application.

In order to apply the rare earth magnet to these motors, it is most desirable to use a thin sleep-shaped or ring-shaped magnet with magnetic anisotropy in the radial direction.

In the above sintered magnet, it is difficult to apply a radial magnetic field when compacting the powder in a magnetic field, so the degree of anisotropy is 50 to 60% lower than that of plate magnets, and the magnet performance is There is a problem that the value decreases.

On the other hand, the latter type of super-quenched magnet does not require forming in a magnetic field, and anisotropy is achieved by 'gJ deformation, so the anisotropy is minimized even in the sleep-shaped or ring-shaped magnets mentioned above. However, since this rare earth magnet material is extremely brittle, large mold cracks occur when the material is extruded into a sleeve or ring shape.

(Means for Solving the Problems) An object of the present invention is to prevent molding cracks when molding the ultra-quenched magnet into a sleep-shaped or ring-shaped cross-sectional shape, and to obtain a magnet with high magnetic anisotropy. The gist of this is that when extruding a magnetically isotropic solid or hollow magnet material to form it into an annular cross-section, there is no contact with the extrusion mold of the magnet material. The purpose is to apply compressive force to the free surface and perform extrusion molding.

Here, extrusion molding is desirably carried out under vacuum at a pressure lower than 1 Torr or under heating at 650 to 900°C under an inert gas atmosphere.

Furthermore, in the present invention, after forming an antioxidant coating on the surface of the magnet material, extrusion molding can be carried out under heating in the atmosphere.

In the R-Fe-B magnet of the present invention, R is a La-based rare earth element represented by Nd, and this magnet contains a small amount of Goo DyJ:+, Ga, or other substances for improving magnetic properties. Substances such as Ni, Zn, Pb, and AI for improving corrosion resistance, heat resistance, and processability can be included.

'In the manufacturing method of the present invention, a magnetically isotropic solid or hollow material is extruded and formed into a sleep-like or ring-like shape with a uniform cross section. The magnet material can be prepared by crushing a powder obtained by pulverizing an ultra-quenched ribbon in a vacuum or an inert gas atmosphere. In this case, it is possible to obtain a solid, hollow molded body having a theoretical density ratio of 99% or higher.

As the above extrusion molding method, either backward extrusion molding or forward extrusion molding is possible. In these forming processes, the magnet material comes into contact with the forming surface of a mold such as a die or punch and is plastically deformed while being constrained by them. In extrusion molding, a part of the end face in the flow direction of the material, that is, on the rear side, becomes a free surface, and in forward extrusion molding, a part of the end face on the front side becomes a free surface.

Therefore, in the case of undeveloped January, compressive force is applied to these free surfaces using a predetermined pressurizing means, and the material is plastically deformed under such pressurizing conditions. Therefore, in the present invention, it is necessary to use a pressurizing means that can press the free surface of the material while moving it.

In this way, when the free surface of the material is extruded while being pressurized, the molding cracks that conventionally occur can be effectively avoided, and rare earth anisotropic magnets with an annular cross section of a sleeve shape or a ring shape with high magnetic properties can be produced. is obtained.

(Example) Next, embodiments of the present invention will be described in detail based on the drawings.

First, FIGS. 2 and 3 show a method for obtaining an isotropic magnetic material. 2 shows a method for obtaining a solid cylindrical magnet material, and FIG. 3 shows a method for obtaining a hollow cylindrical magnet material.

In FIG. 2, 10 is a die, 12 is a lower punch (knockout punch), and 14 is an upper bunch.

In order to manufacture the cylindrical solid magnet material 18 according to this example, the gap formed by the die 10 and the lower punch 12 is first filled with magnet powder 16 . Note that these molds are preheated to 600 to 900°C, preferably 700 to 800°C, by a method not shown.

The whole is kept in a closed tank, and the atmosphere inside the tank is kept in a vacuum with a pressure lower than 1 Torr, or it is filled with an inert gas such as argon gas to create an oxidation-preventing atmosphere.

After filling the magnet powder 16, it is held in the mold for 1 to 3 minutes, and the temperature of the magnet powder 16 is raised by heat transfer from the mold. When the magnet powder 16 reaches a predetermined temperature, the upper bunch 14 is then lowered to compress the magnet powder 16. The pressurizing pressure at this time is 0.5 to 2)-cm/cm, preferably 1 to 1
．． 5) Give -ton/cm2. This results in a theoretical density ratio of 9
A powder compacting material (cylindrical magnet material) 18 having a content of 9% or more is obtained.

In FIG. 3, in order to obtain a thick hollow cylindrical magnet material 20, the gap between the die 10 and the center core 22 is filled with magnet powder 16, and the cylindrical lower bunch 24 is filled with magnet powder 16.
The magnet powder 16 is compacted by the upper punch 26 and the upper punch 26 . After that, the lower bunch 24 is raised to form a cylindrical magnet material 20.
Remove from the mold.

It is also possible to mix 2% or less of a lubricant such as lithium stearate into the magnet powder 16 to improve lubrication with the mold during the above-mentioned molding.

Next, an example of a method for forming the cylindrical magnet material 18 obtained by the method shown in FIG.
This will be explained based on diagram J1. First, the material 18 is set in the space formed by the diene and the lower bunch 13. Note that these molds are preheated to 650 to 900°C, preferably 700 to 850°C, by a method not shown. In addition, the above-mentioned material 18, which is kept as a whole in a closed tank and the atmosphere inside the tank is kept under a vacuum with a pressure lower than 1 Torr, or is filled with powdered active gas such as argon gas to prevent oxidation, is prepared separately. It may be heated in advance by a method such as high frequency heating and then set in the mold, or it may be heated within the mold by heat transfer from the mold.

After heating the material 18 to a predetermined temperature, a cylindrical pressure mold 28
is rolled down to apply compressive force to the l: face 30 of the material 18.

The compression force at that time is 0.2 to 1 ton/Cl1 in terms of pressure.
12, preferably 0.4 to 0.6 tons/c112. Further, as a means for applying a downward force to the pressurizing die 28, a hydraulic cylinder or a pneumatic cylinder may be used. By using these cylinders, the upper surface 30 of the material 18 can be
The pressure mold 28 can be freely moved up and down in accordance with the change in position. That is, the material 18 can be plastically deformed while applying a constant compressive force to the free surface of the material 18.

Next, the extrusion punch 32 is pressed down to perform backward extrusion,
The raw material 18 is molded into a sleeve-shaped molded product 34. This extrusion force is 2 to 5 tons/cm2. with punch surface pressure. It is preferably 2.5 to 3.5)-n/c+s.

In this manner, by applying a constant pressure to the E surface 30 during extrusion, the inner surface 38 or the outer surface 401 of the sleeve-shaped molded product 34 is heated. : Can prevent molding cracks from occurring.

After the extrusion molding is completed, the lower bunch 13 is raised to knock out the sleeve-shaped molded product 34 from the mold, and the bottom part 42 is separately removed.
Cut and remove.

The above is an example of molding the magnet material 18 in an oxidation-preventing atmosphere.
These moldings can also be carried out in the atmosphere by providing the following conditions. As this anti-oxidation coating,
It may be plated with an oxidation-resistant metal such as nickel, or it may be coated with an airtight material such as water glass and then dried to form a coating.

In the present invention, a forward extrusion molding method may be used in addition to the above-mentioned backward extrusion, and even in this case, the sleeve-shaped molded product 34 can be molded without causing molding cracks.

An example of molding by this forward extrusion will be explained based on FIG. 4.

In FIG. 4, reference numeral 44 denotes a pressure mold that is slidably fitted into the lower bunch 15. A cylindrical magnet material 18 is set in the space formed by the die 11 and the lower punch 15, and this pressure mold At 44, a predetermined compressive force is applied to the lower surface of the material 18. In this state, lower the upper bunch 32 and press the material 1.
8 is molded into a sleeve-shaped molded product 46. At this time, the pressing mold 44 is moved backward in the forward extrusion direction by the upper bunch 32, that is, downward in the figure, as the material 18 is deformed, and a constant compressive force is continued to be applied to the material 18. This can prevent the occurrence of cracks on the inner and outer circumferential surfaces of the sleeve-shaped molded product 46.

By the way, in order to produce sufficient magnetic anisotropy in the radial direction in molding the sleeve-shaped molded product 46, the extrusion area reduction rate should be 40 to 80%, preferably 55 to 65%.
is necessary. Therefore, in order to obtain a thin sleeve,
If a circular material 18 as shown in FIGS. 1 and 4 is used as the magnet material, the extrusion reduction rate may become too large.

Therefore, in such a case, extrusion molding is performed using a thick cylindrical material 20 obtained by the method shown in FIG. That is, the third
A thick cylindrical material 20 is obtained by the method shown in the figure, and this is set in the space formed by the tie 11 and the lower punch 17 as shown in FIG.
Apply a constant compressive force to 0.

Next, the extrusion punch 32 is pressed down to extrude the material 20 backward into a sleeve shape. At this time, since compressive force is constantly applied to the upper surface 30 by the pressurizing die 28, the occurrence of cracks in the molded product is prevented.

The cylindrical material 20 described above using backward extrusion can also be formed into a similar sleeve shape by forward extrusion.

[Experimental Example 1] Ni+3Fe'a2. A ribbon having a thickness of 20 L obtained by ultra-quenching a magnetic alloy having a composition of tB 4.2 was crushed to obtain a flake-like powder with a size of about 20 (ML).

Using a mold of the type shown in Figure 2, this was heated at 700°C9 at a pressure of 1 ton/c+i in an argon gas atmosphere.
"Diameter: 3011I11.Height: 19"
A cylindrical material 18 of m11 was obtained. The theoretical density ratio of this material 18 was 99.6%.

This material 18 is molded into a pressure mold 28 using a mold shown in FIG.
While applying compressive stress of various magnitudes to the free surface, the sleeve-shaped molded product 34 was obtained by extruding it backward using the tie 11 and punches 13 and 32, and the depth of the molding crack that occurred on the inner surface 38 and The relationship with the compressive stress applied to the upper surface 30 was investigated. The results are shown in Figure 6. In this case, the sleeve-shaped molded product 34 had an outer diameter of 30 mm, an inner diameter of 23 mm, and an extrusion area reduction rate of 59%. Also, the heating molding temperature is 750°
C, and these were treated in an argon gas atmosphere.

As is clear from the figure, when compressive stress is applied, the depth of the shear cracks that occur becomes significantly smaller.

Generally, when the sleeve-shaped molded product 34 is used as a magnet, its inner and outer surfaces are ground, and shallow molding cracks are removed at that time, so the crack depth is 0.5 mm or less. If it is shallow, preferably 0.2 mm or less, it will not pose a practical problem.

Next, after cutting and removing the bottom part of this sleeve-shaped molded product 34, it is magnetized in the radial direction, and its maximum magnetic energy (
) in the radial direction was set to 1111, 34 MGOe
I got it.

[Experimental Example 2] Using the same flaky powder as above, it was heated for 75 minutes in an argon gas atmosphere using a mold of the type shown in Figure 3.
Pressed into powder under the conditions of 0°C and pressure of 1.3 tons/cII+2, resulting in an outer diameter of 30 ma+, an inner diameter of 15 mm, and a height of 20 mm.
A cylindrical material 20 was obtained. Theoretical density ratio of this material 20 is 9
It was 9.3%.

The entire surface of this material 20 was plated with nickel to a thickness of 50 lumens to form an anti-corrosion coating.

The material 20 coated with this oxidation-resistant coating is heated to 800°C in the atmosphere with a high-frequency heating device, and the mold shown in Fig. 5 is heated to 700°C in advance and extruded backward in the air. I did it. In this case, the outer diameter of the sleeve-shaped molded product 48 was 30 mm, and the inner diameter was changed to vary the area reduction rate from 30 to 80%. Additionally, the pressure applied to the upper surface 30 of the material 20 is 0.
．． Experiments were conducted both with 8 tons/c [l' and without pressurization. The pressure of the extrusion punch 32 was 3 tons/C12.

FIG. 7 shows the depth of molding cracks that occurred on the inner surface of the sleeve-shaped molded product during this extrusion molding.

From this figure, it can be seen that when compressive stress is applied to the top surface 30, crack prevention 1
It turns out that it has a remarkable effect on h.

Furthermore, after cutting and removing the bottom of the ssort-shaped molded product 48 and grinding the outer and inner surfaces, it was magnetized in the radial direction and the maximum magnetic energy product in the radial direction was measured. The results are shown in FIG. Ta.

According to this figure, extremely high properties are obtained with an area reduction rate of 40% or more and exceeding 30 MGOe.

Although the embodiments of the present invention have been described in detail above, the present invention can be practiced with various modifications based on the knowledge of those skilled in the art without departing from the spirit thereof.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a method of manufacturing an anisotropic earth magnet according to an embodiment of the present invention, and FIGS. 52 and 3 are explanatory diagrams of a method of molding a magnet material, respectively. 4 and 5 are explanatory diagrams of other embodiments of the present invention, and FIG. 6 is a diagram showing the relationship between compressive stress and crack depth obtained as a result of an experiment conducted according to the method of FIG. 1. It is. Figure 7 and S+'A are diagrams showing the relationship between extrusion area reduction rate and crack depth obtained as a result of experiments conducted in reverse to the method shown in Figure 5, respectively, and extrusion area reduction rate and maximum magnetic flux. FIG. 3 is a diagram showing a relationship with an energy product. 10.1 Tie 13.15, 17.32 Punch 18.20: Material 28.45: Pressure mold 34. 46, 48: Molded product Figure 2 Figure C Figure Compressive stress (tons 7'cm2) Fig. Extruded window area ratio ('/, ) Fig. Extruded window area ratio ('/, )

Claims (3)

[Claims] (1) When extruding a magnetically isotropic solid or hollow magnet material to form it into an annular cross-section, compressive force is applied to the free surface of the magnet material that does not come into contact with the extrusion mold. A method for producing an anisotropic rare earth magnet, which is characterized by extrusion molding. (2) The rare earth anisotropic magnet according to claim (1), wherein the extrusion molding is performed under vacuum at a pressure lower than 1 Torr or under heating at 650 to 900°C in an inert gas atmosphere. Production method. (3) After forming an antioxidant coating on the surface of the magnet material,
A claim characterized in that extrusion molding is carried out under heating in the atmosphere (
The method for manufacturing a rare earth anisotropic magnet according to 1) or (2).