JPH07161523A - Rare earth permanent magnet and its production - Google Patents

Abstract

PURPOSE:To obtain an ideal sinusoidal surface flux density waveform without requiring strict management of magnetizing field in an AC servo motor or a DC brushless motor. CONSTITUTION:The rare earth permanent magnet is an arcuate magnet principally comprising R(at least one kind of rare earth element including Y), Fe, and B and exhibiting radial anisotropy highest in the peripheral center and decreasing continuously toward the end part. The magnet is produced by pressing a powder principally comprising R, Fe, and B at 700-1000 deg.C in a nonoxidative atmosphere to produce a columnar isotropic compact body having circular or elliptical cross-section and the extruding the compact body into arcuate shape at 700-1000 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth-Fe-B system permanent magnet, particularly an arcuate permanent magnet having radial anisotropy, and a method for producing the same.

[0002]

2. Description of the Related Art Typical permanent magnets currently in use are alnico type cast magnets, ferrite magnets and rare earth-transition metal type magnets. In particular, rare earth (R) -F
The e-B system permanent magnet has been extensively researched and developed as a permanent magnet having an extremely high coercive force and energy product. The manufacturing method includes the following.

(1) Sintering method (Japanese Unexamined Patent Publication No. 59-46008) (2) Quenching / warm working method (Japanese Unexamined Patent Publication No. 60-100402) (3) Casting / hot working method (Japanese Unexamined Patent Publication No. No. 62-276803) Recently, an AC servomotor using an R-Fe-B magnet and a D
The field of high-performance motors such as C brushless motors is drawing attention. Conventionally, an R-Fe-B system arc magnet manufactured by the sintering method (1) is used for such a motor.
A magnet was used which was magnetized to have multiple poles and laminated to a rotor. When such a magnet is used, there is a problem that the surface magnetic flux density waveform of the magnet is trapezoidal and the cogging torque is large. In order to avoid this, various measures have been taken to make the magnetic flux density waveform closer to a sine waveform by changing the curvatures of the outer circumference and the inner circumference.

The production of R-Fe-B system radial anisotropic ring-shaped magnets has also been attempted by the above methods (1) to (3). The sintering method (1) uses a repulsive magnetic field to orient the magnetic field in the radial direction and then sinters it.
In (2), the quenched ribbon is hot-pressed and then mechanically oriented by forward and backward extrusion. In the casting / hot working method of (3), a cast alloy is hot-rolled to form an anisotropic magnet material in the plate thickness direction into a circular arc shape by bending,
The arc-shaped segments obtained are fused to form a ring. The magnets produced by these three manufacturing methods have uniform radial anisotropy, and various multipole magnetized patterns can be obtained by controlling the magnetizing magnetic field.

On the contrary, there have been disclosed some methods of using an arcuate or ring-shaped magnet whose anisotropic state is not uniform according to the characteristics of various motors. Japanese Unexamined Patent Publication (Kokai) No. 5-6813 discloses that the magnetic characteristics in the radial direction of an arc-shaped warm formed magnet are high at the end portion and gradually decrease toward the central portion. 2-
Japanese Patent No. 276210 discloses a ring-shaped magnet whose anisotropy is different between the inner circumference side and the outer circumference side, and a manufacturing method thereof.

[0006]

However, each of the manufacturing methods has problems that there are considerable restrictions on the shape of the magnet and that the manufacturing cost is high. In particular, the sintering method and the rapid cooling / warm working method have a problem that a product having a length longer than the diameter of the ring cannot be manufactured and the mechanical strength is low.

Further, the R-Fe-B system magnet produced by the method (1) or (3) is called a creation type, and the initial magnetization curve has a steep rise. on the other hand,
The warm formed magnet exhibits a complicated S-shaped initial magnetization curve in which the creation and pinning are combined, and it is difficult to control the magnetization by the magnetizing magnetic field in both of them. Therefore, there is a problem that a dedicated magnetizing coil is required, and a complicated one needs a magnetic field analysis by the finite element method for its design. In addition, a magnet magnetized in multiple poles by such a method has a large variation in the vicinity of the boundary between the poles and is easily demagnetized due to a temperature rise or a demagnetizing field, which causes a problem that the surface magnetic flux density waveform is distorted.

[0008]

DISCLOSURE OF THE INVENTION The present invention is applicable to a radial anisotropic magnet having a wider range of shapes than ever before, and in order to obtain an ideal magnetizing pattern, a radial anisotropic anisotropic magnet is used. The degree of anisotropy is changed in the circumferential direction rather than the sex.

Specifically, an arc magnet having R (where R is at least one of rare earth elements including Y), Fe and B as basic raw material components, and having the highest radial anisotropic shape in the central portion in the circumferential direction. And a rare earth permanent magnet characterized by continuously decreasing anisotropy toward the end, and a method for producing such a magnet, wherein R (where R is a rare earth element containing Y) is used. Powder containing at least one of Fe, B and Fe, B as a raw material basic component in a non-oxidizing atmosphere.
It is pressed at a temperature of 0 to 1000 ° C. to form a cylindrical isotropic consolidated body having a circular or elliptical cross section, and 700 to 100
It is an extrusion molding in an arc shape at a temperature of 0 ° C.

The R-Fe-B type powder is obtained by a method of crushing an ingot, a liquid quenching method, a mechanical alloying method, a gas atomizing method or the like. It is made compact by compressing it and then anisotropically made by applying plastic deformation. Examples of the method of consolidation include hot pressing, HIP, extrusion and pack rolling. The temperature may be in the range of 700 to 1000 ° C, but is preferably 700 to 800 ° C in order to prevent coarsening of the particle size.
The temperature of the extrusion molding may be in the range of 700 to 1000 ° C., but 700 to 800 when the powder obtained by the liquid quenching method or the mechanical alloying method is used in view of the balance between the coarsening of the particle size and the orientation. ℃, 9 when using powder obtained by crushing ingot or gas atomizing method
The temperature is preferably 00 to 1000 ° C. As described above, in the method of making anisotropic by plastic deformation, Cu, Ga, Ag, Au, P
By adding d, Al, etc., the grain size becomes finer, the structure becomes uniform, and the coercive force and the maximum energy product are improved.

When a cylindrical compact is extruded to form an arc-shaped magnet having a width substantially equal to the diameter of the circle, the plastic strain in the radial direction is the largest and anisotropic in this direction. However, this strain amount is not constant along the circumferential direction. Since the amount of compressive strain is largest in the radial direction at the central portion and the degree of anisotropy is large, the residual magnetic flux density in the same direction is also high. The amount of strain decreases continuously as it approaches the edge in the circumferential direction, and almost in-plane anisotropy occurs near the edge.

Therefore, since the residual magnetic flux density in the radial direction of the arc-shaped magnet thus obtained changes gently along the circumferential direction, the magnetic flux density is almost sinusoidal without strictly controlling the magnetizing magnetic field. The waveform is obtained. Also,
The boundary between the poles is also extremely stable, unlikely to be affected by temperature changes in the motor and demagnetizing fields.

Further, since it is produced by extrusion, it can be used for a long magnet and the production efficiency is high. A circular arc shape corresponding to the extruded cross section can also be applied over a wide range, and it can be manufactured in a flat plate shape or one having different outer and inner curvatures. Furthermore, by making the cross-sectional shape of the extruded billet oval rather than circular, the amount of strain can be adjusted and a desired surface magnetic flux density waveform can be obtained.

Next, examples of the present invention will be described.

[0015]

Example 1 An alloy having a composition of Pr ₁₆ Fe _77.4 B _5.1 Cu _1.5 was melted in an argon atmosphere using an induction heating furnace, and an average powder particle size of 10 was obtained by a gas atomizing method.
A powder of 0 μm was obtained. This powder is made of low carbon steel φ32mm
The mixture was placed in a columnar capsule (1), degassed, sealed, and consolidated by hot pressing at 700 ° C. Then heat to 950 ° C,
Extrusion molding was performed in an arc shape having an outer diameter of 60 mm, a thickness of 5 mm, and a central angle of 60 degrees. The extruded magnet thus obtained was heat-treated in argon gas at 1000 ° C. for 20 hours and 500 ° C. for 2 hours, and then the capsule was removed by grinding to give a length of 4
The desired arcuate magnet was obtained by cutting to 0 mm.

Next, a large number of 3 mm square cube samples were cut out from this arc-shaped magnet along the circumferential direction, and the residual magnetic flux densities in the radial direction (r), circumferential direction (θ) and extrusion direction (z) were measured by VSM. did. Figure 1 shows the measurement results.
Shown in.

As is clear from FIG. 1, the residual magnetic flux density in the radial direction is highest at the center in the circumferential direction and becomes lower toward the end, and magnetic characteristics corresponding to the strain amount are obtained. The residual magnetic flux density in the circumferential direction shows a tendency opposite to that in the radial direction. Such changes are caused by differences in the degree of anisotropy due to the difference in strain amount. The central part clearly shows uniaxial anisotropy in the radial direction, but the end parts are perpendicular to the extrusion axis direction. It can be seen that the surface has anisotropy.

Example 2 An alloy having a composition of Nd ₁₀ Pr ₆ Fe _77.8 B _5.2 Ga _1.0 was melted using an induction heating furnace in an argon atmosphere, and a powder having an average particle diameter of 100 μm was obtained by a gas atomizing method. . This powder is made of low carbon steel φ
Place in a 32 mm cylindrical capsule, degas and seal to 70
It was consolidated by hot pressing at 0 ° C. Next, it was heated to 950 ° C. and extruded into an arc shape having an outer diameter of φ60 mm, a thickness of 5 mm and a central angle of 60 °. After heat-treating the obtained extruded magnet in argon gas at 1000 ° C. for 20 hours,
The capsule was removed by grinding and cut into a length of 40 mm to obtain the desired arc-shaped magnet.
Each of these arc-shaped magnets in the air-core coil in the plate thickness direction (1
Pole) and then bonded to the rotor. Also,
For comparison, Nd-Fe-obtained by a conventional sintering method was used for comparison.
An arcuate magnet having the same shape was cut out from the block of the B system magnet, and a rotor was manufactured by the same method. The anisotropic direction was made to coincide with the plate thickness direction at the center of the arc. FIG. 2 shows the results of measuring the circumferential magnetic flux density distribution of these two rotors.

Although the surface magnetic flux density of the conventional sintered magnet is trapezoidal, a waveform close to a sine wave is obtained when the method of the present invention is used. An ideal surface magnetic flux density waveform can be obtained without using such a dedicated magnetizing coil, whereby the cogging torque of the motor is significantly reduced.

[0020]

As described above, the rare earth permanent magnet of the present invention has a substantially sinusoidal surface without strictly controlling the magnetizing magnetic field by changing the degree of anisotropy in the circumferential direction of the arc-shaped magnet. A magnetic flux density waveform is obtained. by this,
The cogging torque of the motor is reduced, and the stability against temperature and demagnetizing field is improved.

Also, since it is made by extrusion,
It can be used for long magnets and the manufacturing cost is low. A wide range of arc shapes can be accommodated.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the circumferential position of an arc-shaped magnet and the residual magnetic flux density in three directions obtained in Example 1 of the present invention.

FIG. 2 is a diagram showing the relationship between the circumferential position and the surface magnetic flux density of a rotor using the magnet according to the conventional method and the magnet according to the present invention in Example 2 of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01F 1/08 41/02 G 8123-5E (72) Inventor Koji Akioka 3 Yamato, Suwa City, Nagano Prefecture No. 3-5 Seiko Epson Corporation

Claims (2)

[Claims] 1. An arc-shaped magnet containing R (wherein R is at least one of rare earth elements including Y), Fe and B as basic raw materials and having the highest radial anisotropy in the central portion in the circumferential direction. However, the rare earth permanent magnet is characterized in that the anisotropy continuously decreases toward the edges. 2. A cross section obtained by pressurizing a powder containing R (where R is at least one of rare earth elements including Y), Fe, and B as raw material basic components at a temperature of 700 to 1000 ° C. in a non-oxidizing atmosphere. A process for producing a rare earth permanent magnet, which comprises forming a circular columnar or elliptical columnar isotropic compact and then extruding it into an arc at a temperature of 700 to 1000 ° C.