JP2800249B2 - Manufacturing method of rare earth anisotropic magnet - Google Patents

Description

The present invention relates to a method for manufacturing a rare earth magnet, and more particularly, to a method for producing Nd.
The present invention relates to a method for producing an R-Fe-B-based (R is a La-based rare earth element) permanent magnet represented by a -Fe-B-based magnet.

(Problems to be Solved by the Related Art and the Invention) R-Fe-B-based permanent magnets include (a) a base material alloy melted and cast into a mold to form an ingot, which is pulverized to an extremely fine The powder is compacted and compacted using a metal mold in a magnetic field, and then sintered and anisotropically magnetized. The coarsely pulverized powder is heated to about 700 ° C
Hot-pressed to make isotropic magnetic material
There is a super-quenched magnet which is anisotropically subjected to plastic deformation processing at a temperature of 0 ° C. or less and a surface reduction rate of 40% or more.

These high magnetic property magnets, if applicable to small motors for OA and FA, are extremely useful in reducing the size and weight of motors. Therefore, the fact is that it is not sufficiently applied to motors.

In order to apply the rare-earth magnet to these motors, it is most preferable to use a thin-walled sleeve or ring-shaped magnet that is magnetically anisotropic in the radial direction.
It is difficult to apply a magnetic field in the radial direction when molding powder in a magnetic field, so the degree of anisotropy is 50-60% lower than that of a plate magnet, and the magnet performance is reduced. There is.

On the other hand, the latter super-quenched magnet does not require molding in a magnetic field and performs anisotropic deformation by plastic deformation. However, since this rare earth magnet material is extremely brittle, a large forming crack occurs when the material is formed into a sleeve shape or a ring shape by extrusion.

(Means for Solving the Problems) An object of the present invention is to provide a magnet having a high magnetic anisotropy in the above-mentioned super-quenched magnet, which is prevented from forming cracks when it is formed into a sleeve-like or ring-shaped annular cross section. The gist of the invention is that a magnetic or isotropic solid or hollow magnet material is extruded rearward or forward by using an extrusion mold including a punch and a die, so that the magnet material is annular in cross section. When the magnetic material is extruded and magnetic anisotropy is imparted, the free surface at the rear end or the free surface at the front end of the magnet material that moves rearward or forward as it is extruded is compressed forward or rearward by pressing means. Extrusion is performed while applying a force and moving the free surface backward or forward in a state where a compressive force is applied.

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

Further, in the present invention, after forming the antioxidant film on the surface of the magnet material, it can be extruded under heating in the air.

In the R-Fe-B-based magnet of the present invention, R is a La-based rare earth element represented by Nd, and a small amount of Co, D
y ₂ O ₃ , Ga and other substances for improving magnet properties, Ni, Zn, P
b, Al and other substances for improving corrosion resistance, heat resistance, and workability can be contained.

In the manufacturing method of the present invention, a magnetically isotropic solid or hollow material is extruded and formed into a ring shape such as a sleeve shape or a ring shape. Here, the magnet material can be prepared by compacting the powder obtained by grinding the ultra-quenched ribbon in a vacuum or an inert gas atmosphere. In this case, a solid or hollow shaped body having a theoretical density ratio of 99% or more can be obtained.

As the extrusion molding method, any of rear extrusion molding and front extrusion molding is possible. In these forming processes, the above-mentioned magnet material is brought into contact with the forming surface of a forming die such as a die and a punch, and is plastically deformed while being restrained by the forming surface. For example, in backward extrusion, a part of the flow direction of the material, that is, a part of the rear end face is a free surface, and in front extrusion, a part of the front end face is a free surface.

Therefore, in the present invention, a 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, as the pressing means, a means capable of moving the free surface of the material and pressing the same surface.

When the free surface of the material is extruded while being pressurized in this way, the conventional forming cracks can be effectively avoided, and a sleeve-shaped or ring-shaped annular rare earth anisotropic magnet having high magnetic properties. Is obtained.

(Example) Next, an example of the present invention will be described in detail with reference to the drawings.

First, FIGS. 2 and 3 show a method for obtaining an isotropic magnet 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 punch.

In order to manufacture the columnar solid magnet material 18 according to the present embodiment, first, the magnet powder 16 is filled into the gap formed by the die 10 and the lower punch 12. These molding dies are not shown
It is previously heated to 600 to 900 ° C, preferably 700 to 800 ° C. Further, the entirety of these is held in a closed tank, and the atmosphere in the tank is evacuated to a pressure lower than 1 Torr or filled with an inert gas such as an argon gas to provide an antioxidant atmosphere.

After filling the magnet powder 16, the magnet powder 16 is held in the mold for 1 to 3 minutes, and the temperature of the magnet powder 16 is increased by heat transfer from the mold. When the magnet powder 16 reaches a predetermined temperature, the upper punch 14 is pressed down to compress the magnet powder 16. The pressurizing pressure at this time is
It gives 0.5 to 2 ton / cm ² , preferably 1 to 1.5 ton / cm ² . As a result, a compacting material (columnar magnet material) 18 having a theoretical density ratio of 99% or more is obtained.

In FIG. 3, to obtain a thick hollow cylindrical magnet material 20, a gap between the die 10 and the center core 22 is filled with the magnet powder 16, and a cylindrical lower punch 24 and an upper punch 24 are formed. 26, the magnet powder 16 is compacted. Then lower punch
24 is raised to take out the cylindrical magnet material 20 from the mold.

It is also possible to mix a lubricant such as lithium stearate of 2% or less in the magnet powder 16 to improve the lubrication with the mold at the time of the molding.

Next, an example of a method of forming the cylindrical magnet material 18 obtained by the method of FIG. 2 into a sleeve shape by backward extrusion will be described with reference to FIG. First, punch the material 18 with the die 11 and the lower punch.
Set in the space formed by 13. These molds are previously heated to 650 to 900 ° C, preferably 700 to 850 ° C by a method not shown. Further, the whole is held in a closed tank, and the atmosphere in the tank is evacuated to a pressure lower than 1 Torr or filled with a powdered active gas such as argon gas to prevent oxidation.

The material 18 may be heated in advance by a method such as high-frequency heating and then set in the mold, or may be heated in the mold by heat transfer from the mold.

After the temperature of the material 18 is raised to a predetermined temperature, a compressive force is applied to the upper surface 30 of the material 18 by pressing down a cylindrical pressing mold 28 as a pressing means. The compression force at that time is 0.2 to 1 ton / c in pressure
m ² , preferably 0.4 to 0.6 ton / cm ² . Also pressurized
It is preferable to use a hydraulic cylinder, a pneumatic cylinder, or the like as the means for applying the rolling force to 28. By using these cylinders, the pressing mold 28 can be freely moved up and down in accordance with a change in the position of the upper surface 30 of the material 18. That is, material 18
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 material 18 is formed into a sleeve-shaped molded product 34. The pushing force is 2 to 5 tons / cm ² , preferably 2.5 to
3.5 tons / cm ² .

As described above, by applying a constant pressure to the upper surface 30 during extrusion molding, it is possible to prevent the occurrence of molding cracks on the inner surface 38 or the outer surface 40 of the sleeve-shaped molded product 34.

After the completion of the extrusion, the lower punch 13 is raised to knock out the sleeve-shaped molded product 34 from the mold, and the bottom 42 is separately cut and removed.

The above is an example of the case where the magnet material 18 is formed in an anti-oxidation atmosphere. However, by forming an anti-oxidation coating on the surface of the magnet material 18 in advance, these shaping can be performed in the atmosphere. The antioxidant film may be plated with an oxidation-resistant metal such as nickel, or may be an air-tight material such as water glass and dried after coating.

In the present invention, in addition to the above-mentioned backward extrusion, a forward extrusion molding method can also be used. In this case, the sleeve-like molded product 34 can be molded without generating molding cracks.
An example of molding by this front extrusion will be described with reference to FIG.

In FIG. 4, reference numeral 44 denotes a pressurizing type which is slidably fitted to the lower punch 15, in which a cylindrical magnet material 18 is set in a space formed by the die 11 and the lower punch 15, and At 44, a predetermined compressive force is applied to the lower surface of the material 18. In this state, the extrusion punch 32 is lowered to form the material 18 into a sleeve-shaped molded product 46. At this time, as the material 18 is deformed, the pressing die 44 is moved backward in the forward extrusion direction by the extrusion punch 32, that is, in the downward direction in FIG. This can prevent the inner and outer peripheral surfaces of the sleeve-shaped molded product 46 from cracking.

By the way, in forming such a sleeve-shaped molded product 46, in order to generate a sufficient magnetic anisotropy in the radial direction, the extrusion reduction area is required to be 40 to 80%, preferably 55 to 65%. 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 area may become too large.

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

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

Although the case of backward extrusion has been described above, the cylindrical material 20 can be formed into a similar sleeve shape by forward extrusion.

Experimental Example 1 A 20 μm-thick ribbon obtained by ultra-quench cooling a magnetic alloy having a composition of Ni ₁₃ Fe _82.7 B _4.3 was pulverized to obtain a flake-like powder having a size of about 200 μm.

Using a mold of the type shown in Fig. 2, pressurize and compact under argon gas atmosphere at 700 ° C and under a pressure of 1 ton / cm ² to obtain a cylindrical material 30 mm in diameter and 19 mm in height. I got 18.
The theoretical density ratio of this material 18 was 99.6%.

Using a molding die shown in FIG. 1 and applying various sizes of compressive stress to the free surface of the material 18 with a pressing die 28,
A sleeve-like molded product 34 was obtained by extruding backward with the die 11 and the punches 13 and 32, and the relationship between the depth of the molding crack generated on the inner surface 38 and the compressive stress applied to the upper surface 30 was examined. Result 6
It is shown in the figure. In this case, the outer diameter of the sleeve-shaped molded product 34 was 30 mm, the inner diameter was 23 mm, and the extrusion reduction area was 59%. The heat molding temperature was 750 ° C., and these were processed in an argon gas atmosphere.

As is clear from the figure, the depth of cracks generated when compressive stress is applied becomes extremely small.

In general, when the above-mentioned sleeve-shaped molded product 34 is used as a magnet, its inner and outer surfaces are ground and, at that time, formed cracks having a shallow depth are removed, so the crack depth is 0.5 mm or less. However, if the depth is preferably as small as 0.2 mm or less, it will not be a practical obstacle.

Next, after cutting and removing the bottom of the sleeve-shaped molded product 34, it was magnetized in the radial direction, and its maximum magnetic energy (in the radial direction) was measured. As a result, 34MGOe was obtained.

[Experimental Example 2] The same flaky powder as above was used, and this was used in an argon gas atmosphere using a molding die of the type shown in FIG.
Compressed under pressure of 1.3 tons / cm ^{2 under} the conditions of
A cylindrical material 20 having a diameter of 0 mm, an inner diameter of 15 mm, and a height of 20 mm was obtained. The theoretical density ratio of this material 20 was 99.3%.

The entire surface of the material 20 was nickel-plated with a thickness of 50 μm to form an oxidation-resistant film.

The material 20 provided with the oxidation-resistant coating was heated to 800 ° C. by a high-frequency heating device in the air, and the mold shown in FIG.
While being heated to ℃, backward extrusion was performed in the air. In this case, the outer diameter of the sleeve-shaped molded product 48 is 30 mm,
By changing the inner diameter, the area reduction rate was changed to 30 to 80%. In addition, experiments were conducted both when a pressure of 0.8 ton / cm ² was applied to the upper surface 30 of the material 20 and when no pressure was applied. The pressure of the extrusion punch 32 was 3 tons / cm ² .

FIG. 7 shows the depth of molding cracks generated on the inner surface of the sleeve-shaped molded product in this extrusion molding.

From this figure, it can be seen that applying a compressive stress to the upper surface 30 is extremely effective in preventing cracking.

FIG. 8 shows the result of measuring the maximum magnetic energy product in the radial direction after cutting the bottom of the sleeve-shaped molded product 48 to remove the bottom and grinding the outer and inner surfaces, and magnetizing the outer surface and the inner surface in the radial direction. Was.

According to this figure, remarkably high characteristics are obtained at a surface reduction rate of 40% or more and over 30 MGOe.

Although the embodiments of the present invention have been described in detail, the present invention can be implemented in variously modified modes based on the knowledge of those skilled in the art without departing from the gist thereof.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a method of manufacturing a rare earth anisotropic magnet according to one embodiment of the present invention, and FIGS. 2 and 3 are explanatory views of a method of forming a magnet material, respectively. 4 and 5 are explanatory views of another embodiment of the present invention, and FIG. 6 is a view showing the relationship between compressive stress and crack depth obtained as a result of an experiment conducted according to the method of FIG. It is. FIG. 7 and FIG.
FIG. 3 is a diagram showing the relationship between the extrusion reduction area and the crack depth obtained as a result of an experiment conducted in accordance with the method shown in the figure, and the diagram showing the relationship between the extrusion reduction area and the maximum magnetic energy product. 10,11: Die 13,15,17,32: Punch 18,20: Material 28,45: Pressure type 34,46,48: Molded product

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiya Kinami 18 Chita Ryo, Minamikamochi, Kagiya-cho, Tokai City, Aichi Prefecture (56) References JP-A-1-169910 (JP, A) JP-A-58-206105 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01F 41/02 B22F 3/00, 3/20 C22C 33/02

Claims (3)

(57) [Claims] 1. A magnetic or isotropic solid or hollow magnet material is extruded rearward or forward by using an extrusion mold including a punch and a die, thereby extruding the magnet material into an annular cross section and magnetically extruding the magnetic material. When imparting anisotropy, compressive force is applied to the free surface at the rear end or the free surface at the front end of the magnet material that moves rearward or forward as it is extruded by pressing means forward or rearward, and A method for producing a rare-earth anisotropic magnet, wherein extrusion molding is performed while moving the surface backward or forward while applying a compressive force. 2. The rare-earth anisotropic material according to claim 1, wherein said extrusion molding is carried out under vacuum at a pressure lower than 1 Torr or in an inert gas atmosphere under heating at 650 to 900 ° C. Manufacturing method of magnet. 3. The production of a rare earth anisotropic magnet according to claim 1, wherein after forming an antioxidant film on the surface of the magnet material, the magnet is extruded under heating in the air. Method.