JP2022175413A - Manufacturing method of rare-earth magnet - Google Patents

Abstract

To provide a manufacturing method of a rare-earth magnet, in which a magnetization direction is a radial shape, and which can manufacture the rare-earth magnet of which a front surface magnetic flux density is almost uniform.SOLUTION: A manufacturing method of a rare-earth magnet, contains an orientation step of applying a pulse magnetic field to a compact 10a in a molding 2 arranged between a first coil c1 and a second coil c2. In the orientation step, a direction of the pulse magnetic field generated in the first coil c1 is reverse to a direction of the pulse magnetic field generated in the second coil c2. A first region A1 is a region where a distance from a center axis line ax1 of the first coil c1 is larger than r1 (1/2 of an inner diameter) and is smaller than R1 (1/2 of an outer diameter). A second region A2 is a region where the distance from a center axis line ax2 of the second coil c2 is larger than r2 (1/2 of the inner diameter) and is smaller than R2 (1/2 of the outer diameter). In the orientation step, one part of a whole part of the compact 10a is arranged in at least any one of the first region A1 and the second region A2.SELECTED DRAWING: Figure 5

Description

One aspect of the present invention relates to a method for manufacturing a rare earth magnet.

Rare earth magnets are parts of motors or actuators, for example, hard disk drives, hybrid cars, electric cars, magnetic resonance imaging (MRI), smart phones, digital cameras, flat-panel TVs, scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners. , washing and drying machines, elevators and wind power generators. The size, shape and magnetization direction (magnetization direction) required for rare earth magnets differ according to these various uses. Therefore, in order to efficiently manufacture a wide variety of rare earth magnets, a molding method is desired that can easily change the size, shape and magnetization direction of the rare earth magnets.

For example, in the method for producing a rare earth magnet described in Patent Document 1 below, a ring-shaped molded body (cylindrical molded body) is formed by molding alloy powder in a magnetic field generated between a pair of facing coils. It has a molding process. In the molding process described in Patent Document 1 below, alloy powder is compressed by a cemented carbide mold that fits inside the inner peripheral surface of each coil. As the alloy powder is compressed, a radial magnetic field (a magnetic field in which magnetic lines of force radiate from the central axis of each coil) generated between the pair of coils is applied to the alloy powder in the mold. As a result, the axes of easy magnetization of the alloy powder forming the compact are oriented radially from the central axis of the compact (cylinder) toward the outer peripheral surface of the compact.

In the above-described conventional method for manufacturing a rare earth magnet, a magnetic field is applied to the metal powder while pressurizing the metal powder containing the rare earth element at a high pressure (for example, 50 MPa or more and 200 MPa or less). As a result, a compact is formed from the metal powder oriented along the magnetic field. Such a molding method is hereinafter referred to as a "high pressure magnetic field press method". According to the high-pressure magnetic field pressing method, it is possible to easily orient the metal powder and obtain a compact having a high residual magnetic flux density Br and excellent mechanical strength. A sintered body is obtained by sintering the molded body, and the sintered body is processed into a desired shape to complete a magnet product.

However, the high-pressure magnetic field pressing method requires a large-scale and complicated molding apparatus because it is necessary to apply high pressure to the metal powder in the magnetic field, and limits the size and shape of the mold for molding. Due to this limitation, the general shape of compacts obtained by high-pressure magnetic field pressing is limited to coarse blocks. Therefore, when manufacturing a wide variety of magnet products by the conventional method, after sintering a block-shaped molded body to obtain a sintered body, the sintered body is formed according to the size and shape required for the magnet product. need to be processed. In the processing of the sintered body, the sintered body is cut and polished, so scraps containing expensive rare earth elements are generated. As a result, the yield rate of magnet products decreases. In addition, in the high-pressure magnetic field pressing method, galling between the dies or galling between the mold and the compact easily damages the mold or the compact. For example, cracks may occur in a compact obtained by high-pressure magnetic field pressing. As described in Patent Document 1 below, when a mold dedicated to a molded body having a specific shape is manufactured from a metal such as cemented carbide, the manufacturing cost of the mold is high. It is difficult to change direction easily.

For the reasons described above, the conventional manufacturing method using a high-pressure magnetic field press method is not suitable for manufacturing a wide variety of magnet products or a small amount of magnet products. As a molding method that replaces the high-pressure magnetic field pressing method, Patent Document 2 below discloses a method of molding a metal powder containing a rare earth element at a low pressure (0.049 MPa or more and 20 MPa or less). The method for producing a rare earth magnet described in Patent Document 2 below includes a molding step of supplying a metal powder containing a rare earth element into a mold to form a compact, and applying a pulse magnetic field to the compact held in the mold. It includes an orientation step of applying voltage to orient the metal powder contained in the compact, and a sintering step of sintering the compact after the orientation step. At least two coils arranged to have the same central axis are used in the orienting process. The direction of the pulsed magnetic field generated in one coil is opposite to the direction of the pulsed magnetic field generated in the other coil. In the orientation step, the compact is placed at a position between the two coils where the lines of magnetic force of the pulse magnetic field converge along the central axis. In other words, in the orientation process described in Patent Document 2 below, the formed body is placed between the two coils so that the formed body overlaps the central axis of each coil. As a result, the axis of easy magnetization of the alloy powder forming the compact is oriented radially, and a rare earth magnet having a high surface magnetic flux density is obtained.

As in the molding method described in Patent Document 2 below, when metal powder is molded at low pressure, the mold is not required to be durable against high pressure, and a large-scale and complicated molding apparatus is not required. Therefore, when metal powder is compacted at low pressure, the material, size and shape of the mold are not limited, and it is relatively easy to manufacture a wide variety of rare earth magnets using molds having various sizes and shapes. can. In addition, the high-pressure magnetic field pressing method takes a long time to compact and orient the metal powder. do.

JP-A-2001-192705 JP 2019-197778 A

2. Description of the Related Art Rare earth magnets whose magnetization directions are radially oriented (radially oriented magnets) are frequently used in motors that are power sources for hybrid vehicles, electric vehicles, and the like. For example, a radially oriented magnet mounted on a motor is curved in an arc shape. Within the motor, the curved surfaces of the radially oriented magnets are substantially parallel to the outer circumference of the rotor. The magnetization direction of the radially oriented magnets is radial in a cross section substantially perpendicular to the rotation axis of the rotor. The longitudinal direction (non-curved direction) of the radially oriented magnets is substantially perpendicular to the magnetization direction and substantially parallel to the rotation axis of the rotor. In the prior art described above, the alloy powder is oriented by a radial magnetic field generated in a region where the distance from the central axis of each coil is 1/2 or less of the inner diameter (2×r) of each coil. As a result, the distribution of the surface magnetic flux density along the longitudinal direction of the radially oriented magnet manufactured by the above prior art becomes non-uniform. For example, the surface magnetic flux density at both ends in the longitudinal direction is significantly lower than the surface magnetic flux density at the central portion in the longitudinal direction. Due to the non-uniform distribution of the surface magnetic flux density along the length, the torque of the motor is reduced.

An object of one aspect of the present invention is to provide a rare earth magnet manufacturing method capable of manufacturing a rare earth magnet having a radial magnetization direction and a substantially uniform surface magnetic flux density.

A method for producing a rare earth magnet according to one aspect of the present invention includes a molding step of supplying a metal powder containing a rare earth element into a mold to form a compact, and applying a pulse magnetic field to the compact held in the mold. It includes an orientation step of applying voltage to orient the metal powder contained in the compact, and a sintering step of sintering the compact after the orientation step.
A first coil and a second coil are used in the orientation step. The direction of the pulsed magnetic field generated in the first coil is opposite to the direction of the pulsed magnetic field generated in the second coil.
The inner diameter of the first coil is denoted as 2×r1, the outer diameter of the first coil is denoted as 2×R1, and the first region is between the first coil and the second coil, the center of the first coil It is defined as a region whose distance from the axis is greater than r1 and less than R1.
The inner diameter of the second coil is denoted by 2×r2, the outer diameter of the second coil is denoted by 2×R2, and the second region is between the first coil and the second coil, the center of the second coil It is defined as a region whose distance from the axis is greater than r2 and less than R2.
In the orienting step, a part or the whole of the compact is placed in at least one of the first region and the second region.

In the orienting step, the first coil, the second coil, and the mold may be fixed by a fixing member, and part or all of the fixing member may be non-magnetic.

Part or all of the mold may be non-magnetic.

The non-magnetic material may be resin.

One or both of the first coil and the second coil may be air core coils.

The density of the compact may be adjusted to 3.0 g/cm ³ or more and 4.4 g/cm ³ or less before the orientation step.

A plurality of molds may be used in the orientation step, and the compact may be held within each mold.
In a state in which a plurality of molds are stacked along at least one of the central axis of the first coil and the central axis of the second coil, a pulsed magnetic field may be applied to all compacts at once.

A plurality of molds may be used in the orientation step, and the compact may be held within each mold.
In a state in which a plurality of molds are arranged along the circumferential direction of at least one of the first coil and the second coil, the pulse magnetic field may be applied collectively to all the compacts.

Part or all of the first region may overlap part or all of the second region, and the orienting step places part or all of the compact within the region where the first region and said second region overlap each other. you can

In the molding step, the first mold may be used as the mold.
The orientation step includes a first orientation step of applying a pulsed magnetic field to the molded body held in the first mold to orient the metal powder contained in the molded body, and a pulsed magnetic field again to the molded body that has undergone the first orientation step. and a second orientation step of applying to orient the metal powder contained in the compact.
In the second orientation step, a plurality of molded bodies that have undergone the first orientation step may be taken out from the first mold and held in one second mold. A plurality of compacts in the second mold may be stacked along at least one of the central axis of the first coil and the central axis of the second coil, and all the compacts stacked in the second mold may be stacked together. A pulsed magnetic field may then be applied.
In the sintering step, a plurality of stacked compacts may be sintered.

According to one aspect of the present invention, there is provided a rare earth magnet production method capable of producing a rare earth magnet having a radial magnetization direction and a substantially uniform surface magnetic flux density.

FIG. 1 is a perspective view of a molded body and a cross-sectional view of the molded body. FIG. 2 is an exploded perspective view of a mold (first mold) used in the molding process. FIG. 3 is a cross-sectional view including the first coil, the second coil, the first region, and the second region, and the cross section in FIG. 3 is substantially parallel to the central axes of the first coil and the second coil, respectively. , and center axes of the first coil and the second coil, respectively. FIG. 4 is a cross-sectional view including the first coil, the second coil, the first region and the second region, and FIG. 4 shows the distribution of magnetic lines of force of the pulse magnetic field formed by the first coil and the second coil. 4 is substantially parallel to the central axes of the first and second coils and includes the central axes of the first and second coils. FIG. 5 is a cross-sectional view including the first coil, the second coil, the first region, the second region, and the compact, and FIG. shows an orientation process using a radial pulsed magnetic field extending from the central axis of each of the first and second coils, and the cross section in FIG. are parallel and include the central axes of the first coil and the second coil, respectively. FIG. 6 corresponds to FIG. 5, and FIG. 6 is a cross-sectional view including the first region, the second region, and the compact, and FIG. The cross-section in FIG. 6 is substantially perpendicular to the central axis of each of the first and second coils. FIG. 7 is a cross-sectional view including the first coil, the second coil, the first region, the second region, and the compact, and FIG. shows the orientation process using a radial pulsed magnetic field converging towards the central axes of the first and second coils respectively, the cross section in FIG. substantially parallel to the axis and including central axes of each of the first coil and the second coil. FIG. 8 corresponds to FIG. 7, FIG. 8 is a cross-sectional view including the first region, the second region and the compact, and FIG. Fig. 8 illustrates an orientation process using a focused radial pulsed magnetic field, the cross-sections in Fig. 8 being substantially perpendicular to the central axes of the first and second coils respectively. FIG. 9 is a cross-sectional view including a first region, a second region, and a plurality of compacts, and FIG. 9 is an orientation using a radial pulsed magnetic field extending from the central axis of each of the first and second coils. 9 shows the process, and the cross section in FIG. 9 is substantially perpendicular to the central axis of each of the first coil and the second coil. FIG. 10 is a side view of a fixing member that fixes the first coil, the second coil, and the mold, and the side surface in FIG. 10 is substantially parallel to the central axes of the first coil and the second coil, respectively. FIG. 11 shows the upper surface of each member (the first fixing plate, the holder for the molded body, and the second fixing plate) constituting the fixing member shown in FIG. It is substantially perpendicular to the central axis of each of the first coil and the second coil. FIG. 12 is a cross-sectional view including a plurality of molds stacked along the central axes of the first coil and the second coil, and each compact held in each mold; In a state in which a plurality of molds are stacked along the central axes of the coil and the second coil, respectively, it shows an orientation step in which a pulse magnetic field is applied collectively to all compacts. substantially parallel to and including the central axes of the first and second coils; FIG. 13 is a cross-sectional view including a second mold and a plurality of compacts stacked within the second mold, and FIG. 13 is substantially parallel to the central axes of the first and second coils, respectively, and is aligned with the central axes of the first and second coils, respectively. including. FIG. 14 is a schematic diagram showing a method of measuring the surface magnetic flux density of a rare earth magnet along the arc direction (bending direction) of the rare earth magnet. FIG. 15 is a distribution diagram of the surface magnetic flux densities of the rare earth magnets of Examples 1 to 3, and the horizontal axis in FIG. 15 corresponds to the opening angle of the rare earth magnet (arc direction of the rare earth magnet). FIG. 16 is a distribution map of the surface magnetic flux density of the rare earth magnet of Example 1 and a distribution map of the surface magnetic flux density of the rare earth magnet of Example 1 obtained by simulation. corresponding to the opening angle of (arc direction of the rare earth magnet). 17 is a distribution map of the surface magnetic flux densities of the rare earth magnets of Example 1 and Comparative Example 1, and a distribution map of the surface magnetic flux densities of the rare earth magnet of Example 1 obtained by simulation. The horizontal axis corresponds to the longitudinal direction of the rare earth magnet. FIG. 18 is a distribution diagram of the surface magnetic flux densities of three types of rare earth magnets with different densities of compacts, and the horizontal axis in FIG. 18 corresponds to the opening angle of the rare earth magnet (arc direction of the rare earth magnet). .

Preferred embodiments of the present invention will be described below with reference to the drawings. In the drawings, similar components are provided with similar reference numerals. The present invention is not limited to the following embodiments. Although the molds are omitted from FIGS. 5-9 for convenience of explanation, each compact shown in FIGS. 5-9 is actually held in one mold.

(Preparation process of metal powder)
In the method for producing a rare earth magnet (sintered magnet) according to this embodiment, an alloy is first produced. The method of manufacturing the alloy may be, for example, strip casting. The alloy may be in the form of flakes or ingots. The alloy contains rare earth elements. Rare earth elements include one or more elements selected from the group consisting of Sc, Y and lanthanoids belonging to Group 3 of the long period periodic table. The lanthanoid may be at least one selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The raw material alloy is selected from the group consisting of B, N, Fe, Co, Cu, Ni, Mn, Al, Nb, Zr, Ti, W, Mo, V, Ga, Zn, Si and Bi, in addition to the rare earth elements. may contain at least one element that is The chemical composition of the alloy may be adjusted according to the chemical compositions of the main phase and grain boundary phase of the rare earth magnet to be finally obtained. In other words, starting materials containing the above elements may be weighed and blended according to the composition of the desired rare earth magnet to prepare the raw material for the alloy. Rare earth magnets can be, for example, neodymium magnets, samarium-iron-nitrogen magnets, samarium-cobalt magnets, or praseodymium magnets. _The main phase of the rare earth _magnet can be, for example, _Nd2Fe14B , _{Sm2Fe17N3 , SmCo5} , _Sm2Co17 , _{or PrCo5} . The grain boundary phase may be, for example, a phase (R-rich phase) having a higher rare earth element content than the main phase. Grain boundary phases may include B-rich phases, transition metal-rich phases, oxide phases or carbide phases.

Coarse powder of the alloy is obtained by coarsely pulverizing the alloy. In coarse pulverization, for example, the alloy may be pulverized by occluding hydrogen in grain boundaries (R-rich phase) of the alloy. For coarse grinding of the alloy, mechanical grinding methods such as disc mills, jaw crushers, Braun mills or stamp mills may be used. The particle size of the coarse powder obtained by coarse pulverization may be, for example, 10 μm or more and 100 μm or less.

Fine powder of the alloy is obtained by pulverizing the coarse powder. For fine pulverization, the alloy powder may be pulverized by a jet mill, ball mill, vibration mill, wet attritor, or the like. The particle size of the fine powder obtained by pulverization may be, for example, 0.5 μm or more and 5 μm or less. In the following, coarse powders or fine powders are sometimes referred to as alloy powders.

Organics may be added to the coarse powder. An organic substance may be added to the fine powder. That is, the organics may be mixed with the alloy powder either before or after pulverization. The organic matter functions, for example, as a lubricant. Addition of a lubricant to the alloy powder suppresses agglomeration of the alloy powder. Also, by adding a lubricant to the alloy powder, friction between the mold and the alloy powder is likely to be suppressed in the subsequent steps. As a result, the alloy powder is easily oriented in the orientation step, and scratches on the surface of the compact obtained from the alloy powder or the surface of the mold are easily suppressed. The organic substance may be, for example, at least one of a long-chain fatty acid and a long-chain fatty acid derivative. The long-chain fatty acid derivative may be at least one selected from the group consisting of long-chain fatty acid esters, long-chain fatty acid amides and long-chain fatty acid salts. For example, the organic substance may be at least one selected from the group consisting of ethylene glycol distearate, methyl stearate, octadecylamine acetate, octylamine, caprylic acid, lauric acid amide and oleic acid amide. The lubricant is not limited to the above composition. The lubricant may be a powdered organic substance. The lubricant may be a liquid organic substance. An organic solvent in which a powdery lubricant is dissolved may be added to the alloy powder.

(Molding process)
In the molding step, the metal powder (alloy powder) obtained by the above procedure is fed into a mold to form a compact. The size, shape and structure of the compact are not limited. The dimensions, shape and structure of the finally obtained rare earth magnet may be substantially the same as the dimensions, shape and structure of the compact. The size, shape and structure of the mold may vary depending on the size, shape and structure of the compact and are not limited. The molding process may be dry molding. The molding step may be wet molding in which a compact is formed from metal powder and an organic solvent.

As shown in FIG. 1, the compact 10 in this embodiment is an arc segment type compact (C-shaped compact). That is, the molded body 10 is a columnar body, and the cross section 10cs of the molded body 10 perpendicular to the longitudinal direction DL of the shaped body 10 (in other words, the end face of the column perpendicular to the height direction of the columnar body) is circular. It includes an arc-shaped long side LA and an arc-shaped short side SA, and the long side LA and the short side SA are substantially parallel to each other. A direction substantially parallel to the long side LA and the short side SA is denoted as an arc direction DA (curving direction). When the length of the long side LA is represented by LL and the radius of curvature of the long side LA is represented by LR, the opening angle θ1 (unit: °) of the long side LA is (360/2π)×(LL/LR ). When the length of the short side SA is expressed as SL and the radius of curvature of the short side SA is expressed as SR, the opening angle θ2 (unit: °) of the short side SA is (360/2π)×(SL/SR ). The opening angle θ1 of the long side LA may be substantially equal to the opening angle θ2 of the short side SA. When .theta.1 and .theta.2 are substantially equal to each other, .theta.1 and .theta.2 are each expressed as the opening angle .theta. The size relationship between the width W of the molded body 10 in the arc direction DA and the width h of the molded body 10 in the longitudinal direction DL (the height of the columnar body) is not limited. The shortest distance between the long side LA and the short side SA may be rephrased as the thickness T of the compact 10 .

As shown in FIG. 2, the mold 2 for forming the arc segment type compact 10 includes a lower mold 8, a cylindrical side mold 6 arranged on the lower mold 8, and the side mold 6 a mating punch (male); In FIG. 2, the punch (male type) is omitted. A space 6a corresponding to the shape and size of the molded body 10 penetrates the side mold 6 in the vertical direction. The side mold 6 may be rephrased as a side wall of the mold. The lower mold 8 may be plate-shaped. The position of the side mold 6 in the horizontal direction may be fixed by fitting the lower part of the side mold 6 into the protrusion formed on the surface of the lower mold 8 . In the molding process, the side mold 6 is placed on the lower mold 8 and the opening (hole) on the lower surface side of the side mold 6 is closed with the lower mold 8 . With such arrangement, the side mold 6 and the lower mold 8 constitute a die. The side mold 6 and the lower mold 8 may be rephrased as a cavity (female mold). The alloy powder is introduced into the die (space 6 a ) through the opening (hole) on the upper surface side of the side mold 6 . By inserting the punch into the die, the alloy powder in the die is compressed by the tip end face of the punch to form the compact 10 . After the molding 10 is formed, the upper opening of the side mold 6 is closed with the plate-like upper mold 4 . In the orientation step to be described later, the compact 10 is held in a mold 2 composed of an upper mold 4, a side mold 6 and a lower mold 8. As shown in FIG.

The shape of the compact is not limited to the arc segments described above. For example, the shape of the molded body may be an angular sector plate, a polygonal prism (a cube, a rectangular parallelepiped, or a rectangular plate, etc.), a cylinder, other columns, a cylinder (ring), or a sphere. . The cross-sectional shape of the molded body may be fan-shaped, polygonal, arcuate (a shape surrounded by circles and chords), circle or ring. The shape and structure of the mold are not limited to the shapes and structures described above, and may be changed according to the shape of the compact.

In the molding process, the pressure exerted by the mold 2 on the alloy powder may be adjusted to 0.049 MPa or more and 20 MPa or less (0.5 kgf/cm ² or more and 200 kgf/cm ² or less). The pressure may be, for example, the pressure exerted by the tip surface of the punch on the alloy powder. By forming the molded body 10 from the alloy powder at a pressure lower than that of the conventional high-pressure magnetic field pressing method, friction between the mold 2 and the molded body 10 is easily suppressed, and damage to the mold 2 or the molded body 10 (for example, the molded body 10 cracks) are easily suppressed. If the pressure is too high, the mold 2 is bent, making it difficult to secure the desired capacity of the die and to obtain the desired density of the compact 10 . If the pressure is too high, it is difficult to use a mold made of resin, which is inferior in durability (mechanical strength) to a mold, in the molding process. If the pressure is too high, cracks are likely to form in the compact 10 due to springback, leaving cracks in the rare earth magnet. Springback is a phenomenon in which the compact 10 formed by pressurizing the alloy powder expands as the pressure is released. In the conventional high-pressure magnetic field pressing method, it was necessary to perform molding and orientation of the alloy powder at the same time under high pressure. On the other hand, in the present embodiment, since it is not necessary to perform molding and orientation at the same time, the orientation process can be performed after the molding process. By separating the molding process and the orientation process, smaller and less expensive devices (eg, a press molding device and a magnetic field applying device) can be used for each step. By separating the molding process and the orientation process, it is easy to orient the alloy powder in the compact 10 in a desired direction in the orientation process. The molding step and the orientation step may be performed substantially simultaneously.

The density of the molded body 10 that has undergone the molding process (the molded body 10 before the orientation process) is 3.0 g/cm ³ or more and 4.4 g/cm ³ or less, preferably 3.2 g/cm ³ or more and 4.2 g/cm ³ or more. Below, more preferably, it may be adjusted to 3.4 g/cm ³ or more and 4.0 g/cm ³ or less. The density of the molded body 10 may be adjusted, for example, by the pressure exerted by the mold 2 on the molded body 10 during the molding process. The density of the compact 10 may be adjusted, for example, by the mass of the alloy powder supplied into the mold 2. When the density of the compact 10 before the orientation process is within the above range, the magnetic flux density on the surface of the finally obtained rare earth magnet tends to increase. The lower the density of the molded body 10 before the orientation step, the easier it is for the alloy powder forming the molded body 10 to rotate freely and to be oriented along the magnetic field. As a result, the surface magnetic flux density of the rare earth magnet tends to increase. If the density of the molded body 10 before the orientation process is too low, the mechanical strength of the molded body 10 is insufficient, and the friction between the molded body 10 and the mold 2 in the subsequent process causes the alloy located on the surface of the molded body 10 Orientation of the powder is disturbed. As a result, the surface magnetic flux density of the rare earth magnet tends to decrease. Also, if the density of the molded body 10 before the orientation process is too low, the mechanical strength of the molded body 10 is insufficient, and the rare earth magnet tends to crack. If the density of the compact 10 before the orientation step is too high, deformation of the rare earth magnet is likely to be suppressed, but the alloy powder that constitutes the compact 10 is difficult to rotate freely and is difficult to orient along the magnetic field. As a result, the surface magnetic flux density of the rare earth magnet tends to decrease.

(Orientation process)
As shown in FIG. 3 and the like, the orientation step uses a first coil c1 and a second coil c2 that generate a pulse magnetic field. In the orientation step, the mold 2 is arranged between the first coil c1 and the second coil c2, and a pulsed magnetic field is applied to the compact 10 held in the mold 2. As shown in FIG. As a result, the alloy powder contained in the compact 10 is oriented along the pulse magnetic field.

The inner diameter of the first coil c1 is expressed as 2×r1. The outer diameter of the first coil c1 is expressed as 2×R1. The central axis ax1 of the first coil c1 may be defined as a straight line that includes the center of a circle that matches the inner circumference of the first coil c1 and that is parallel to the inner circumference of the first coil c1. The central axis ax1 of the first coil c1 may be defined as a straight line that includes the center of a circle that matches the outer circumference of the first coil c1 and that is parallel to the outer circumference of the first coil c1. The first area A1 is defined as an area where the distance from the central axis line ax1 of the first coil c1 is greater than r1 and less than R1 between the first coil c1 and the second coil c2.

The inner diameter of the second coil c2 is expressed as 2×r2. The outer diameter of the second coil c2 is expressed as 2×R2. The center axis ax2 of the second coil c2 may be defined as a straight line that includes the center of a circle that matches the inner circumference of the second coil c2 and that is parallel to the inner circumference of the second coil c2. The center axis ax2 of the second coil c2 may be defined as a straight line that includes the center of a circle that matches the outer circumference of the second coil c2 and that is parallel to the outer circumference of the second coil c2. The second area A2 is defined as an area where the distance from the central axis line ax2 of the second coil c2 is larger than r2 and smaller than R2 between the first coil c1 and the second coil c2.

One or both of the central axis ax1 of the first coil c1 and the central axis ax2 of the second coil c2 is denoted as "central axis ax". As shown in FIGS. 3 to 13, the central axis ax1 of the first coil c1 may substantially coincide with the central axis ax2 of the second coil c2. The central axis ax1 of the first coil c1 does not have to coincide with the central axis ax2 of the second coil c2. For example, the central axis ax1 of the first coil c1 may be substantially parallel to the central axis ax2 of the second coil c2. The central axis ax1 of the first coil c1 may be inclined with respect to the central axis ax2 of the second coil c2. The central axis ax1 of the first coil c1 may intersect the central axis ax2 of the second coil c2.

The first coil c1 and the second coil c2 may be the same coil. The first coil c1 and the second coil c2 may be different coils. For example, the inner diameter (2×r1) of the first coil c1 may be equal to the inner diameter (2×r2) of the second coil c2. The inner diameter of the first coil c1 may differ from the inner diameter of the second coil c2. The outer diameter (2×R1) of the first coil c1 may be equal to the outer diameter (2×R2) of the second coil c2. The outer diameter of the first coil c1 may differ from the outer diameter of the second coil c2. The width t1 of the first coil c1 in the direction parallel to the central axis ax1 of the first coil c1 may be equal to the width t2 of the second coil c2 in the direction parallel to the central axis ax2 of the second coil c2. The width t1 of the first coil c1 may differ from the width t2 of the second coil c2.

In the orientation step, a pulsed magnetic field generated in the first coil c1 and a pulsed magnetic field generated in the second coil c2 are applied to the compact 10. FIG. The pulsed magnetic field generated in the first coil c1 is denoted as "first pulsed magnetic field". The pulsed magnetic field generated in the second coil c2 is denoted as "second pulsed magnetic field". The orienting step can be rephrased as a step of orienting the alloy powder in the compact along a pulsed magnetic field synthesized from the first pulsed magnetic field and the second pulsed magnetic field. In the following, the magnetic field synthesized from the first pulsed magnetic field and the second pulsed magnetic field is referred to as the "synthetic pulsed magnetic field". The number of times the synthetic pulse magnetic field is applied to the compact 10 may be one or more times.

In the orientation step, a first pulsed magnetic field and a second pulsed magnetic field are generated simultaneously. The direction of the first pulsed magnetic field is opposite to the direction of the second pulsed magnetic field. For example, on the central axis ax, the direction of the first pulse magnetic field is opposite to the direction of the second pulse magnetic field. In other words, the direction of the first pulsed magnetic field inside the first coil c1 is opposite to the direction of the second pulsed magnetic field inside the second coil c2.

For example, when each of the first coil c1 and the second coil c2 is regarded as a magnet, the north pole of the first coil c1 and the north pole of the second coil c2 may face each other. When the N pole of the first coil c1 and the N pole of the second coil c2 face each other, the resultant pulsed magnetic field is denoted as "N Pole Facing Magnetic field". The S pole of the first coil c1 and the S pole of the second coil c2 may face each other. When the S pole of the first coil c1 and the S pole of the second coil c2 face each other, the synthesized pulsed magnetic field is denoted as "S Pole Facing Magnetic field". Based on the direction of the current I1 in the first coil c1 and the direction of the current I2 in the second coil c2, the north pole opposing magnetic field or the south pole opposing magnetic field may be freely synthesized.

The dimensions of the first coil c1 are substantially equal to the dimensions of the second coil c2, the central axis ax1 of the first coil c1 substantially coincides with the central axis ax2 of the second coil c2, and the N of the first coil c1 on the central axis ax When the pole faces the north pole of the second coil c2 and the intensity of the first pulse magnetic field is substantially equal to the intensity of the second pulse magnetic field, the synthesized pulse magnetic field (north pole facing magnetic field) shown in FIG. 4 is synthesized. The curves in FIG. 4 are magnetic field lines of the resultant pulsed magnetic field. The tangent to the magnetic field lines of the resultant pulsed magnetic field at any position is the direction of the resultant pulsed magnetic field at the arbitrary position.

The dimensions of the first coil c1 are substantially equal to the dimensions of the second coil c2, the central axis ax1 of the first coil c1 substantially coincides with the central axis ax2 of the second coil c2, and the S When the pole faces the S pole of the second coil c2 and the intensity of the first pulse magnetic field is substantially equal to the intensity of the second pulse magnetic field, the magnetic force lines of the S pole facing magnetic field are the magnetic force lines of the N pole facing magnetic field in FIG. are distributed in the same manner as However, the direction of the magnetic field at each point on the magnetic force line of the S pole opposing magnetic field is opposite to the magnetic field direction at each point on the magnetic force line of the N pole opposing magnetic field.

In the orientation step, part or all of the molded body 10 is arranged in at least one of the first area A1 and the second area A2. At least one of the first area A1 and the second area A2 is denoted as "radial magnetic field area A". As shown in FIG. 4, the distribution of magnetic field lines in the radial magnetic field region A differs from the magnetic field line distribution in the region where the compact is placed in the prior art orientation process. The region where the molded body is arranged in the orientation process of the prior art is the region where the distance from the central axis ax is r1 or less or r2 or less between the first coil c1 and the second coil c2. In the portion of the compact 10 located within the radial magnetic field region A, the axis of easy magnetization of the alloy powder forming the compact 10 is radially oriented. As a result, the magnetization direction of the rare earth magnet obtained by sintering the compact 10 is radial. Furthermore, in the orientation process, the distribution of the surface magnetic flux density of the molded body 10 along the direction substantially parallel to the central axis ax (for example, the longitudinal direction DL of the molded body 10) becomes substantially uniform. As a result, the distribution of the surface magnetic flux density of the rare earth magnet along the same direction (longitudinal direction DL) also becomes substantially uniform. Since the magnetization direction of the rare earth magnet tends to be radial and the surface magnetic flux density distribution of the rare earth magnet along the longitudinal direction DL tends to be substantially uniform, the entire compact 10 is arranged within the radial magnetic field region A. is preferred. For the same reason, part or all of the first region A1 preferably overlaps part or all of the second region A2, and part or all of the molded body 10 is such that the first region A1 and the second region A2 overlap each other. It is preferably located within the region. That is, the radial magnetic field area A is preferably an area where the first area A1 and the second area A2 overlap each other. For example, the radial magnetic field area A shown in FIGS. 3 to 13 is an area where the entire first area A1 overlaps the entire second area A2.

The details of the orientation process are described below with reference to the respective drawings. In FIGS. 5 to 9, 12 and 13, the direction of the magnetic force line H overlapping the compact (10a, 10b, 10c or 10d) is the magnetization of each metal crystal grain (each alloy particle) at a position overlapping the magnetic force line H in the compact. The orientation direction of the easy axis is indicated. In other words, the direction of the magnetic lines of force H that overlap the compact indicates the direction of the magnetic moment of each magnetic domain that overlaps the magnetic lines of force H in the compact. The direction of the magnetic lines of force H overlapping the compact is substantially the same as the magnetization direction of the rare earth magnet obtained by sintering the compact.

5 and 6 show magnetic lines of force H of the N pole facing magnetic field. FIG. 5 is a cross section substantially parallel to and including the central axis line ax. FIG. 6 is a cross section substantially perpendicular to the central axis line ax. As shown in FIG. 6, the magnetic force lines H of the N-pole opposing magnetic field in the radial magnetic field region A spread radially from the central axis line ax. The cross section of each molded body 10a and molded body 10b shown in FIG. 5 is substantially parallel to the central axis ax and the longitudinal direction DL of each molded body, and substantially perpendicular to the arc direction DA of each molded body. The cross section of each molded body 10a and molded body 10b shown in FIG. 6 is substantially perpendicular to the central axis ax and the longitudinal direction DL of each molded body, and substantially parallel to the arc direction DA of each molded body.

As shown in FIGS. 5 and 6, the entire molded body 10a and the entire molded body 10a are arranged within the radial magnetic field region A. FIG.

As shown in FIG. 6, the arc-shaped short side of the molded body 10a (concave surface of the molded body 10a) and the arc-shaped long side of the molded body 10a (convex surface of the molded body 10a) are each connected to the first coil c1 and the second coil c2 are arranged substantially parallel to the outer peripheral surface and the inner peripheral surface of each. In other words, the curvature of the arc-shaped short side (concave surface) of the molded body 10a and the arc-shaped long side (convex surface) of the molded body 10a are the same as the outer and inner peripheral surfaces of the coils c1 and c2, respectively. Each curvature may be adjusted to approximately the same value.
The arc-shaped short side (concave surface) of the molded body 10a faces the central axis line ax. Since the radial magnetic lines of force H overlapping the compact 10a in the radial magnetic field region A go from the short side (concave surface) of the compact 10a to the long side (convex surface) of the compact 10a, the magnetization of each metal crystal grain in the compact 10a The easy axis is radially oriented, the short side (concave surface) of the compact 10a is the south pole, and the long side (convex surface) of the compact 10a is the north pole.
In a cross section perpendicular to the central axis ax, the intensity of the combined pulsed magnetic field on the concentric circle centered on the central axis ax is substantially equal, and the arc-shaped short side of the compact 10a and the arc-shaped long side of the compact 10a are substantially equal in intensity. are arranged substantially parallel to the outer and inner peripheral surfaces of the coil c1 and the coil c2, respectively, so that the distribution of the surface magnetic flux density of the molded body 10a along the arc-shaped short side of the molded body 10a is substantially The distribution of the surface magnetic flux density of the molded body 10a along the arc-shaped long side of the molded body 10a also becomes substantially uniform. That is, the surface magnetic flux density of the compact 10 becomes substantially uniform along the arc direction DA shown in FIG.
As shown in FIGS. 4 and 5, in the radial magnetic field region A, the intervals between the lines of magnetic force H in the direction substantially parallel to the central axis line ax are substantially uniform. The longitudinal direction of the molded body 10a is substantially parallel to the central axis line ax. Therefore, the distribution of the surface magnetic flux density of the compact 10a along the direction substantially parallel to the center axis ax becomes substantially uniform. That is, the surface magnetic flux density of the compact 10 becomes substantially uniform along the longitudinal direction DL shown in FIG. For example, the distribution of the surface magnetic flux density measured along the longitudinal direction DL on the convex surface (the surface including the long side LA on the arc) of the compact 10a is substantially uniform. The distribution of the surface magnetic flux density measured along the longitudinal direction DL on the concave surface (the surface including the short side SA on the arc) of the compact 10a is also substantially uniform.

As shown in FIG. 6, the arc-shaped long side (convex surface) of the molded body 10b faces the central axis line ax. Since the radial magnetic lines of force H overlapping the compact 10b in the radial magnetic field region A are directed from the long side (convex surface) of the compact 10b to the short side (concave surface) of the compact 10b, the magnetization of each metal crystal grain in the compact 10b The easy axis is radially oriented, the long side (convex surface) of the compact 10b is the south pole, and the short side (concave surface) of the compact 10b is the north pole.
As shown in FIGS. 4 and 5, in the radial magnetic field region A, the intervals between the lines of magnetic force H in the direction substantially parallel to the central axis line ax are substantially uniform. The longitudinal direction of the molded body 10b is substantially parallel to the central axis line ax. Therefore, the distribution of the surface magnetic flux density of the compact 10b along the direction substantially parallel to the center axis ax becomes substantially uniform.

7 and 8 show magnetic lines of force H of the S pole opposing magnetic field. FIG. 7 is a cross section substantially parallel to and including the central axis line ax. FIG. 8 is a cross section substantially perpendicular to the central axis line ax. As shown in FIG. 8, the magnetic force lines H of the S pole opposing magnetic field in the radial magnetic field region A are radial and converge toward the central axis line ax. The cross section of each molded body 10c and molded body 10d shown in FIG. 7 is substantially parallel to the central axis ax and the longitudinal direction DL of each molded body, and substantially perpendicular to the arc direction DA of each molded body. The cross section of each molded body 10c and molded body 10d shown in FIG. 8 is substantially perpendicular to the central axis ax and the longitudinal direction DL of each molded body, and substantially parallel to the arc direction DA of each molded body.

As shown in FIGS. 7 and 8, the entire compact 10c and the entire compact 10d are placed within the radial magnetic field region A. As shown in FIGS.

As shown in FIG. 8, the arc-shaped short side of the molded body 10c (concave surface of the molded body 10c) and the arc-shaped long side of the molded body 10c (convex surface of the molded body 10c) are the coil c1 and the coil c1, respectively. c2 are arranged substantially parallel to the outer peripheral surface and the inner peripheral surface of each c2. In other words, the curvature of the arc-shaped short side (concave surface) of the molded body 10c and the curvature of the arc-shaped long side (convex surface) of the molded body 10c are equal to the outer and inner peripheral surfaces of the coils c1 and c2, respectively. Each curvature may be adjusted to approximately the same value.
The arc-shaped short side (concave surface) of the molded body 10c faces the central axis line ax. Since the radial magnetic lines of force H overlapping the compact 10c in the radial magnetic field region A are directed from the long side (convex surface) of the compact 10c to the short side (concave surface) of the compact 10c, the magnetization of each metal crystal grain in the compact 10c The easy axis is radially oriented, the long side (convex surface) of the compact 10c is the south pole, and the short side (concave surface) of the compact 10c is the north pole.
For the same reason as for the molded body 10a, the distribution of the surface magnetic flux density of the molded body 10c along the arc-shaped short sides of the molded body 10c becomes substantially uniform, and the molded body 10c along the arc-shaped long sides The distribution of the surface magnetic flux density of 10c also becomes substantially uniform.
As shown in FIGS. 4 and 7, in the radial magnetic field region A, the intervals between the lines of magnetic force H in the direction substantially parallel to the central axis line ax are substantially uniform. Alternatively, the longitudinal direction of the molded body 10c is substantially parallel to the central axis line ax. Therefore, the surface magnetic flux density of the compact 10c along the direction substantially parallel to the central axis line ax becomes substantially uniform.

As shown in FIG. 8, the arc-shaped long side (convex surface) of the compact 10d faces the central axis line ax. Radial magnetic lines of force H superimposed on the compact 10d in the radial magnetic field region A go from the short side (concave surface) of the compact 10d to the long side (convex surface) of the compact 10d. The easy axis is radially oriented, the short side (concave surface) of the compact 10d is the south pole, and the long side (convex surface) of the compact 10d is the north pole.
As shown in FIGS. 4 and 7, in the radial magnetic field region A, the intervals between the lines of magnetic force H in the direction substantially parallel to the central axis line ax are substantially uniform. Alternatively, the longitudinal direction of the molded body 10d is substantially parallel to the central axis line ax. Therefore, the surface magnetic flux density of the compact 10d becomes substantially uniform along the direction substantially parallel to the central axis line ax.

The rare earth magnet obtained by sintering the molded body that has undergone the above orientation step includes a cross section in which the magnetization direction is radial (radial magnetization plane), and the surface of the rare earth magnet along a direction substantially perpendicular to the radial magnetization plane The magnetic flux density distribution is substantially uniform. A radially magnetized surface is, for example, a cross section of each of the compacts 10a, 10b, 10c and 10d shown in FIGS. According to the above orientation step, regardless of the shape of the molded body, a rare earth magnet including a radial magnetization surface and having a substantially uniform surface magnetic flux density distribution along a direction substantially perpendicular to the radial magnetization surface can be manufactured. can be done.

As shown in FIGS. 6 and 8, the direction of the composite pulse magnetic field (lines of magnetic force H) in the radial magnetic field region A, the orientation of the compact 10 with respect to the direction of the composite pulse magnetic field (lines of magnetic force H), and the direction in the radial magnetic field region A By changing the position of the compact 10, the alloy powder can be radially oriented in the compact 10 at desired locations and directions.

As shown in FIG. 4, in the region between the central axis ax and the radial magnetic field region A, the intervals between the magnetic lines of force H in the direction substantially parallel to the central axis ax are uneven. In other words, in the region where the distance from the central axis ax is r1 or less or r2 or less, the intervals between the magnetic lines of force H in the direction substantially parallel to the central axis ax are uneven. Therefore, when a synthetic pulse magnetic field is applied to the compact 10 in the region between the central axis ax and the radial magnetic field region A, the surface magnetic flux density of the compact 10 is non-uniform along the direction substantially parallel to the central axis ax. , and the surface magnetic flux density of the rare earth magnet also becomes non-uniform along the direction substantially perpendicular to the radial magnetization plane.

When the direction of the first pulse magnetic field and the direction of the second pulse magnetic field are the same, a homogeneous pulse magnetic field (with uniform direction and intensity A pulsed magnetic field) is formed, and radial magnetic lines of force H are less likely to occur in either the first area A1 or the second area A2. As a result, it is difficult to orient the alloy powder in the compact 10 radially, and it is difficult to manufacture a rare earth magnet whose magnetization direction is radial.

If a pulsed magnetic field is applied to the molded body 10 using only one of the first coil c1 and the second coil c2, radial lines of magnetic force H are generated in a direction substantially perpendicular to the central axis ax. The intervals between the magnetic lines of force H in substantially parallel directions are non-uniform. Therefore, the surface magnetic flux density of the compact 10 becomes non-uniform along the direction substantially parallel to the central axis ax, and the surface magnetic flux density of the rare earth magnet also becomes non-uniform along the direction substantially perpendicular to the radial magnetization plane.

The volume of the radial magnetic field region A in which part or the whole of the compact 10 is arranged is the inner diameter and outer diameter of the first coil c1, the inner diameter and outer diameter of the second coil c2, and the first coil c1 and the second coil c2. It can be freely increased or decreased by changing the dimension such as the distance d. Therefore, it is possible to freely adjust the volume of the radial magnetic field region A according to the size and shape of the compact, and freely adjust the orientation direction of the alloy magnets in the compact according to the size and shape of the compact. can do. Therefore, it is possible to efficiently manufacture a wide variety of rare earth magnets having different sizes, shapes and magnetization directions. On the other hand, as in the prior art, when the molded body is arranged in a region inside the inner peripheral surface of at least one of the pair of coils, the dimension, shape and orientation of the molded body are restricted, and a wide variety of types of coils are available. Efficient production of rare earth magnets is difficult.

The distribution of the magnetic lines of force H in the synthesized pulse magnetic field as shown in FIGS. 4 to 8 can be easily reproduced by simulation using a computer. Changing control factors such as the dimensions of the first coil c1 and the second coil c2, the relative placement of the first coil c1 and the second coil c2, the current I1 in the first coil c1, and the current I2 in the second coil c2. , the distribution of the magnetic lines of force H in the synthesized pulse magnetic field may be freely controlled. The relative arrangement of the first coil c1 and the second coil c2 is, for example, the distance between the central axis ax1 of the first coil c1 and the central axis ax2 of the second coil c2, the distance between the central axis ax1 of the first coil c1 and the second coil c2. It may be the angle formed by the central axis ax2 of the coil c2, the distance d between the first coil c1 and the second coil c2, and the like. Even if the dimensions of the first coil c1 are different from the dimensions of the second coil c2, the distribution of the lines of magnetic force H as shown in FIGS. It is possible. Even if the central axis ax1 of the first coil c1 does not coincide with the central axis ax2 of the second coil c2, the distribution of the lines of magnetic force H as shown in FIGS. It is possible to synthesize within A.

A plurality of molds may be used in the orientation step, and the compact may be held within each mold. In a state in which a plurality of molds are arranged along at least one of the circumferential directions of the first coil and the second coil, the pulse magnetic field may be applied collectively to all the compacts in the mold. For example, as shown in FIG. 9, the short sides and long sides of each of the plurality of molded bodies 10a are substantially parallel to the outer and inner peripheral surfaces of the first coil c1 and the second coil c2. A plurality of molds 2 may be arranged. Since the synthesized pulse magnetic field can have rotational symmetry with the central axis line ax as the axis of rotation, the alloy powders in the plurality of compacts 10a arranged along the circumferential direction of each coil are similarly and simultaneously oriented. be able to. As a result, the productivity of rare earth magnets is improved.

As shown in FIG. 12, in a state in which a plurality of molds 2 are stacked along the central axis line ax in the radial magnetic field region A, a pulse magnetic field is applied to all compacts 10a in the mold 2 at once. good too. As a result, the productivity of rare earth magnets is improved. The cross section of the molded body 10a shown in FIG. 12 is substantially parallel to the central axis ax and the longitudinal direction DL of the molded body 10a, and substantially perpendicular to the arc direction DA of the molded body 10a.

In the molding process, the mold 2 may be used as the first mold. The orientation step includes a first orientation step of applying a synthetic pulse magnetic field to the molded body 10a held in the first mold (mold 2) to orient the alloy powder contained in the molded body 10a, and a first orientation step. A second orientation step may be included in which the composite pulse magnetic field is applied again to the formed body 10a that has undergone the process to orient the alloy powder contained in the formed body 10a. As shown in FIG. 13, in the second orientation step, a plurality of molded bodies 10a that have undergone the first orientation step may be taken out from the first mold and held in one second mold 2a. The cross section of the molded body 10a shown in FIG. 13 is substantially parallel to the central axis ax and the longitudinal direction DL of the molded body 10a, and substantially perpendicular to the arc direction DA of the molded body 10a. A plurality of compacts 10a in the second mold 2a may be stacked along the central axis ax, and a synthetic pulse magnetic field may be applied collectively to all the compacts 10a stacked in the second mold 2a. In the sintering step, the stacked compacts 10a may be sintered. If the second orientation step is not performed and the plurality of compacts 10a that have undergone the first orientation step are stacked and sintered, the plurality of compacts 10a will be difficult to sinter with each other, and the rare earth magnet will be difficult to sinter. It is difficult to have sufficient strength. On the other hand, when the second orientation step is performed, the plurality of stacked compacts 10a are easily sintered together, and a long rare earth magnet having high mechanical strength can be manufactured. The distribution of the magnetic lines of force H in the synthesized pulsed magnetic field in the second orientation step may be substantially the same as the distribution of the magnetic lines of force H in the synthesized pulsed magnetic field in the first orientation step. In the second orientation step, a plurality of second molds 2a may be used, and a plurality of compacts 10a may be held within each of the second molds 2a. In a state in which a plurality of second molds 2a are arranged along at least one of the circumferential directions of the first coil c1 and the second coil c2, a pulse magnetic field is collectively applied to all the compacts 10a in the second mold 2a. may be applied. As a result, the productivity of rare earth magnets is improved.

One or both of the first coil c1 and the second coil c2 may be air-core coils. The air-core coil has a high withstand power, a small inductance, and a core loss (iron loss) caused by a high-frequency current is difficult to occur in the air-core coil. Therefore, when one or both of the first coil c1 and the second coil c2 are air-core coils, it is easy to use a high-frequency power source as the power source for the synthetic pulse magnetic field. In order to achieve a high intensity of the synthesized pulsed magnetic field without using an air-core coil, a large-sized magnetic field orienting device is required, which increases the production cost of rare earth magnets. However, the ferromagnetic material of at least one of the magnetic core (iron core) and the magnetizing yoke may be arranged inside or at the end of at least one of the first coil c1 and the second coil c2. A ferromagnetic material may be arranged between the first coil c1 and the second coil c2. However, if a ferromagnetic material other than the compact exists in the vicinity of the first coil c1 and the second coil c2, the distribution of the magnetic lines of force H of the composite pulse magnetic field may be disturbed or the strength of the composite pulse magnetic field may decrease. There is

The intensity of the first pulse magnetic field may be controlled based on at least one of the inner diameter (2×r1) of the first coil c1 and the current I1 in the first coil c1. As r1 decreases, the intensity of the first pulse magnetic field increases, and as the current I1 increases, the intensity of the first pulse magnetic field increases.
The intensity of the second pulse magnetic field may be controlled based on at least one of the inner diameter (2×r2) of the second coil c2 and the current I2 in the second coil c2. As r2 decreases, the intensity of the second pulse magnetic field increases, and as the current I2 increases, the intensity of the second pulse magnetic field increases.
The intensity of the first pulsed magnetic field may be the same as the intensity of the second pulsed magnetic field. When the intensity of the first pulsed magnetic field is the same as the intensity of the second pulsed magnetic field, the magnetic field lines of the resultant pulsed magnetic field are likely to have symmetry as shown in FIG. The intensity of the first pulsed magnetic field may be different than the intensity of the second pulsed magnetic field.

The resultant pulsed magnetic field may be an alternating magnetic field. That is, the synthetic pulse magnetic field may be a magnetic field that repeats changes in strength and direction with the passage of time, and the above-described N pole opposing magnetic field and S pole opposing magnetic field may be generated alternately. The resultant pulsed magnetic field may be a decaying alternating magnetic field. In other words, the resultant pulsed magnetic field may decay over time while repeatedly reversing. The maximum intensity (amplitude) of the pulse wave (first pulse wave PW1) of the composite pulse magnetic field first applied to the compact 10 is the pulse of the composite pulse magnetic field applied to the compact 10 following the first pulse wave PW1. It may be greater than the maximum intensity of the wave (second pulse wave PW2). The direction of the second pulse wave PW2 may be opposite to the direction of the first pulse wave PW1. The application of the first pulse wave PW1 may orient the alloy powder forming the compact 10, and the application of the second pulse wave PW2 may demagnetize the compact 10. FIG. A method of generating an alternating magnetic field may be an AC method or a DC inversion method.

The intensity of the composite pulse magnetic field in the radial magnetic field region A may be, for example, 796 kA/m or more and 7958 kA/m or less (10 kOe or more and 100 kOe or less), or 2387 kA/m or more and 4775 kA/m or less (30 kOe or more and 60 kOe or less). When the intensity of the composite pulse magnetic field is 796 kA/m or more, the degree of orientation of the alloy powder tends to be sufficiently improved. The higher the degree of orientation of the alloy powder, the higher the magnetic flux density on the surface of the obtained rare earth magnet. When the strength of the composite pulse magnetic field exceeds 7958 kA/m, it becomes difficult to improve the degree of orientation of the alloy powder even if the strength of the composite pulse magnetic field is increased. Also, if the strength of the composite pulse magnetic field exceeds 7958 kA/m, a large magnetic field generator is required, increasing the cost of the orientation process. The strength of the composite pulse magnetic field in the radial magnetic field region A is not necessarily limited to the above range.

The duration of the composite pulsed magnetic field may be, for example, 10 μs or more and 0.5 seconds or less. The duration of the synthetic pulsed magnetic field is the time from the start of application of the synthetic pulsed magnetic field to the compact 10 to the end of the application. When the duration of the synthetic pulse magnetic field is 10 μs or more, the degree of orientation of the alloy powder tends to be sufficiently increased. The longer the duration of the composite pulse magnetic field, the greater the amount of heat generated in the first coil c1 and the second coil c2 that generate the composite pulse magnetic field, which tends to waste power. The half period of the first pulse wave PW1 that is first applied to the molded body 10 as the composite pulse magnetic field may be, for example, 0.01 milliseconds or more and 100 milliseconds or less, preferably 1 millisecond or more and 30 milliseconds or less. . When the half period of the first pulse wave PW1 is within the above range, the rotation of the individual alloy powders easily follows the application of the composite pulse magnetic field, and the alloy powders are easily oriented. As a result, the magnetic properties (for example, surface magnetic flux density) of the finally obtained rare earth magnet are likely to be improved. Regardless of whether an alloy powder with high fluidity or an alloy powder with low fluidity is used, the shorter the half period of the first pulse wave PW1, the better the degree of orientation of the alloy powder and the surface of the rare earth magnet. magnetic flux density tends to increase.

The synthetic pulse magnetic field has a higher magnetic field strength than the static magnetic field frequently used in the conventional high-pressure magnetic field pressing method, and is applied to the compact 10 in a short period of time. Therefore, by the orientation process using the synthetic pulse magnetic field, the molded body 10 with a high degree of orientation can be obtained in a short time compared to the case of using a static magnetic field, and as a result, a rare earth magnet with a high magnetic flux density on the surface can be manufactured. . However, if a composite pulsed magnetic field is applied to the molded body 10 held in a mold made of an electric conductor (for example, metal), the magnetic field acting on the mold will be less than when a static magnetic field is applied. Since the strength changes abruptly in a short period of time, eddy currents tend to flow in the mold due to electromagnetic induction, and a reverse magnetic field is likely to occur.

The mold 2 may move due to the impact associated with the application of the composite pulsed magnetic field. The movement of the mold 2 disturbs the orientation of the alloy powder in the compact 10 . Further, the movement of the mold 2 creates a gap in the mold 2, through which the alloy powder leaks. Therefore, in order to suppress movement of the mold 2, the mold 2 arranged within the radial magnetic field region A may be fixed with a fixing member. That is, in the orientation step, the first coil c1, the second coil c2, and the mold 2 may be fixed by the fixing member.

For example, as shown in FIGS. 10 and 11, the fixation member 30 includes a first fixation plate 32, a retainer 34, a second fixation plate 36 and four connecting members 38. As shown in FIG. Each of the first fixation plate 32, retainer 34, and second fixation plate 36 may be square or rectangular. The four connecting members 38 pass through connecting holes formed at the four corners of the first fixing plate 32, the holder 34, and the second fixing plate 36, respectively. As shown in FIG. 11, the holder 34 includes a first member 34a having a recess, a plate-like second member 34b, and a third member 34c (bolt, screw, or the like). The mold 2 containing the molded body 10 fits into the recess of the first member 34a. The mold 2 is fixed to the holder 34 by sandwiching the mold 2 between the first member 34a and the second member 34b and fixing the second member 34b to the first member 34a with the third member 34c. The first fixing plate 32, the first coil c1, the holder 34, the second coil c2, and the second fixing plate 36 are stacked in this order. By fixing the first fixing plate 32, the holder 34, and the second fixing plate 36 to each other by the connecting member 38, the first coil c1, the second coil c2, and the mold 2 are fixed. The shape and structure of the fixing member 30 are not limited.

A part or the whole of the fixing member 30 may be a non-magnetic material because the distribution of the magnetic lines of force H of the synthesized pulse magnetic field is hardly disturbed and the alloy powder in the compact 10 is easily orientated radially. A non-magnetic material may be translated as a material that is neither paramagnetic nor ferromagnetic. For example, the non-magnetic material may be at least one substance selected from the group consisting of resin, stainless steel, aluminum, molybdenum, tungsten, carbonaceous materials, and ceramics. For example, the non-magnetic material forming part or the whole of the fixing member 30 may be resin. However, part or the whole of the fixing member 30 may be a magnetic material (at least one kind of metal selected from the group consisting of Fe, Co and Ni, etc.). For example, the entire holder 34 may be made of resin, and each of the first fixing plate 32 and the second fixing plate 36 may be made of iron.

Part or all of mold 2 may be the non-magnetic material described above. When part or all of the mold 2 is made of a non-magnetic material, the distribution of the magnetic lines of force H of the composite pulse magnetic field is less likely to be disturbed, and the alloy powder in the molded body 10 is easily orientated radially. If part or all of the mold 2 is made of a non-magnetic material, the vibration of the mold 2 due to the magnetism of the mold 2 itself is likely to be suppressed in the orientation process, and the compact 10 held in the mold 2 may be damaged. is easily suppressed. For example, the nonmagnetic material forming part or all of the mold 2 may be resin. All of the lower mold 8, the side mold 6, and the upper mold 4 may be non-magnetic. Of the lower mold 8, side mold 6, and upper mold 4, only the side mold 6 may be non-magnetic. Of the lower mold 8, side mold 6, and upper mold 4, only the lower mold 8 may be non-magnetic. Of the lower mold 8, the side mold 6, and the upper mold 4, only the upper mold 4 may be non-magnetic. Among the lower mold 8, the side mold 6, and the upper mold 4, the side mold 6 and the upper mold 4 may be non-magnetic, and the lower mold 8 may be a substance other than non-magnetic. Of the lower mold 8, the side mold 6, and the upper mold 4, the lower mold 8 and the side mold 6 may be non-magnetic, and the upper mold 4 may be made of a material other than a non-magnetic material. Of the lower mold 8, side mold 6, and upper mold 4, the lower mold 8 and upper mold 4 may be non-magnetic, and the side mold 6 may be other than non-magnetic. Part or all of the mold 2 may be the magnetic material described above.

Part or all of the mold 2 may be made of resin. When part or all of the mold 2 is made of resin, when applying a synthetic pulse magnetic field to the compact 10 placed in the mold 2, it is difficult for an eddy current to flow in the mold 2, and a reverse magnetic field is also generated. hard to do By suppressing the reverse magnetic field, the orientation direction of the alloy powder is suppressed from being disturbed by the reverse magnetic field. As a result, it is possible to easily manufacture a rare earth magnet that includes a cross section in which the magnetization direction is radial (radial magnetization plane) and that has a substantially uniform surface magnetic flux density distribution along a direction substantially perpendicular to the radial magnetization plane. . Also, by suppressing the reverse magnetic field, the phenomenon that the alloy powder forming the compact 10 is attracted to the surface of the mold 2 by the reverse magnetic field is suppressed. As a result, the compact 10 tends to have a uniform density, and cracks are less likely to occur in the sintered body (rare earth magnet) in the sintering process. Furthermore, since part or all of the mold 2 is made of resin, the temperature rise of the mold 2 due to eddy current loss is suppressed in the orientation process, and an impact (magnetic force) acts instantaneously on the mold 2 itself. hard. As a result, the mold 2 is less likely to wear out. As described above, the mold 2 made of resin is preferable to a mold because the effects of the present invention can be easily obtained, but the effects of the present invention can be obtained even when using a mold.

If a synthetic pulse magnetic field is applied to the compact 10 held in the mold, the saturation magnetic flux density of the metal (for example, iron) that makes up the mold is limited. The strength of the magnetic field acting effectively is lower than the strength of the resultant pulsed magnetic field outside the mold. However, when the mold 2 is made of resin, a strong synthetic pulse magnetic field is likely to be applied to the compact 10 inside the mold 2 without being shielded by the mold 2 .

The resin contained in at least one of the fixing member 30 and the mold 2 may be an insulating resin. By using the fixing member 30 and the mold 2 made of an insulating resin, eddy currents and reverse magnetic fields are easily suppressed in the orientation process, and the fixing member 30 and the mold 2 are less likely to receive instantaneous impacts. For the same reason, the resistivity of the resin contained in at least one of the fixing member 30 and the mold 2 is, for example, 1 Ω·m or more and 1×10 ²⁰ Ω·m or less, preferably 1×10 ⁹ Ω·m or more. It may be ×10 ¹⁶ Ω·m or less.

The resin contained in at least one of the fixing member 30 and the mold 2 is, for example, acrylic resin, polyethylene (high-density polyethylene, etc.), polyethylene terephthalate, polybutylene terephthalate, polychlorotrifluoroethylene, polytetrafluoroethylene, ethyl cellulose, polypropylene. , polybutene, polystyrene, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, atactic polypropylene, polymethacrylic Methyl acid, methacrylic acid copolymer, polycarbonate, polyetheretherketone, polyetherimide, polyacetal, modified polyphenylene oxide, polyphenylene sulfide, polyamide (polyamide 6, polyamide 46, polyamide 66, polyamide 6.66), polyimide, polyarylate , polyvinyl alcohol, epoxy resin, phenol resin, polyester resin, unsaturated polyester resin, liquid crystal polymer, paraffin wax and silicon resin. A mold 2 composed of a conductive plastic with a higher resistivity than metal and graphite may be used. As a result, charging of the mold 2 is suppressed, and adhesion of the alloy powder to the mold 2 due to charging of the mold 2 is suppressed.

The larger the contact area between the molded body 10 and the portion where the eddy current flows in the mold 2, the more likely cracks in the sintered body and the deterioration of magnetic properties due to the eddy current occur. In this embodiment, of the lower mold 8, the side mold 6, and the upper mold 4, the contact area between the side mold 6 and the molded body 10 is the contact area between the lower mold 8 and the upper mold 4, and the molded body 10. wider than Therefore, out of the lower mold 8, the side mold 6 and the upper mold 4, at least the side mold 6 may be made of resin. By forming the side mold 6, which has a large area in contact with the compact 10, from a resin, the occurrence of eddy currents and reverse magnetic fields in the side mold 6 is effectively suppressed, and the orientation direction of the alloy powder is less likely to be disturbed by the reverse magnetic field. .

The position of the portion of the mold 2 that is made of resin is not limited. Depending on the size and shape of the mold 2 or the direction of the synthesized pulse magnetic field, the portion of the mold 2 that needs to suppress eddy currents may be made of resin. For example, an eddy current and a reverse magnetic field are likely to occur in a portion of the mold 2 that forms a circuit that circulates in the direction of the composite pulse magnetic field that orients the alloy powder. Therefore, in the mold 2, if the side mold 6, which is a portion that forms a circuit that circulates in the direction of the composite pulse magnetic field that orients the alloy powder, is made of resin, the eddy current and the reverse magnetic field are likely to be suppressed. .

When part of the mold 2 is made of resin, the parts of the mold 2 other than the resin are, for example, iron, silicon steel, stainless steel, permalloy, aluminum, molybdenum, tungsten, carbonaceous materials, ceramics, and silicon resin. may be formed from at least one selected from the group consisting of A portion of the mold 2 other than the resin may be made of an alloy (for example, an aluminum alloy).

If the lower die 8, the side die 6, and the punch are all made of metal, metal scraps are separated from the surface of the side die 6 or the punch due to friction between the side die 6 and the punch during the forming process. , may be mixed into the compact 10 . Metal scraps (for example, aluminum or aluminum alloy) mixed in the compact 10 may impair the magnetic properties of the finally obtained rare earth magnet. In contrast, when the mold 2 is partially or wholly made of resin, wear debris (resin) of the mold 2 affects the magnetic properties of the rare earth magnet more than when the mold 2 is made of only metal. impact is suppressed. For example, of the side mold 6 and the punch that rub against each other in the molding process, if one side (for example, the side mold 6) is made of resin and the other (for example, the punch) is made of metal, the friction between the side mold 6 and the punch causes , instead of metal scraps, resin scraps having a lower hardness than metal are likely to be generated. Resin scraps are less likely to impair the magnetic properties of rare earth magnets than metal scraps. For example, only the side mold 6 may be made of resin, and the lower mold 8, punch and upper mold 4 may be made of metal (eg, aluminum or aluminum alloy).

Since the shrinkage rate of a neodymium magnet during the sintering process is anisotropic, it is difficult to accurately predict the shape (especially complicated shape) of the neodymium magnet (sintered compact) after shrinkage. Therefore, for the net shape, trial and error is required to adjust the dimensions and shape of the mold 2, and as the material of the mold 2, a resin that is easy to cut is suitable. In other words, the mold 2 made of resin is suitable for efficiently manufacturing a wide variety of rare earth magnets for various uses. Conventional molds are difficult to process and expensive, so they are not suitable for manufacturing a wide variety of rare earth magnets for various uses.

When repeating the molding process and the orientation process using the same mold 2, the inside of the mold 2 may be cleaned after each molding and orientation. For example, the inside of the mold 2 may be cleaned by attracting excess alloy powder remaining inside the mold 2 with a magnetic field. By cleaning the inside of the mold 2 after each molding and orientation, the accuracy of weighing the alloy powder molded in the mold 2 is improved, and variations in the density and dimensions of the resulting compact 10 are suppressed. As a result, variations in the density, dimensions and magnetic properties of the finally obtained rare earth magnet are suppressed. If the mold 2 is made of ferromagnetic metal (such as iron), the mold 2 itself is attracted by the magnetic field when cleaning the inside of the mold 2, making it difficult to clean the mold 2. However, if the mold 2 is made of a non-ferromagnetic resin, the inside of the mold 2 can be easily cleaned because the mold 2 itself is not attracted by the magnetic field. If the mold 2 is made of a ferromagnetic metal (for example, iron), the mold 2 itself is magnetized in the orientation process, and the alloy powder adheres to the mold 2. Therefore, the orientation direction of the alloy powder is disturbed, and the mechanical strength of the molded body 10 is impaired. However, by using the mold 2 made of resin, the magnetization of the mold 2 itself is suppressed.

While supplying the alloy powder into the mold 2, the mass of the alloy powder compacted in the mold 2 may be measured together with the mass of the mold 2. When simultaneously measuring the mass of the alloy powder compacted in the mold 2 and the mass of the mold 2, the heavier the mass of the mold 2, the lower the accuracy of the weighing, and the accuracy of measuring the mass of the alloy powder itself. also decreases. However, by using the mold 2 made of resin, which is lighter than the conventional metal, the mass of the alloy powder and the mass of the mold 2 itself can be measured with high accuracy.

The alloy powder may be oriented with a synthetic pulsed magnetic field while the alloy powder in the mold 2 is pressed. That is, the compact 10 in the mold 2 may be compressed also in the orientation process. The pressure exerted by the mold 2 on the compact 10 may be adjusted to 0.049 MPa or more and 20 MPa or less for the reasons described above.

The density of the molded body 10 that has undergone the molding step and the orientation step is 3.0 g/cm ³ or more and 4.4 g/cm ³ or less, preferably 3.2 g/cm ³ or more and 4.2 g/cm ³ or less, more preferably 3. .4 g/cm ³ or more and 4.0 g/cm ³ or less. The density of the molded body 10 may be adjusted, for example, by the pressure exerted on the molded body 10 by the mold 2 . The density of the compact 10 may be adjusted, for example, by the mass of the alloy powder supplied into the mold 2.

Part or all of the mold 2 may be separated from the compact 10 before the sintering step or the heating step described below.

(Heating process)
In the heating step following the separation step, the compact may be heated at a temperature lower than the sintering temperature. For example, in the heating step, the molded body 10 may be heated to adjust the temperature of the molded body 10 to 200° C. or higher and 450° C. or lower. For example, in the heating step, the molded body 10 may be heated by irradiating the molded body 10 with infrared rays. In the forming process, the pressure applied to the alloy powder is lower than that of the conventional high-pressure magnetic field pressing method, so that the alloy powder is hard to be compacted and the compact 10 to be obtained is likely to crumble. However, the heating process increases the mechanical strength of the molded body 10 and suppresses breakage of the molded body 10 during the manufacturing process. However, the heating step is not essential.

The mechanism by which the shape retention of the molded article 10 is improved by adjusting the temperature of the molded article 10 to 200° C. or higher and 450° C. or lower is not clear. For example, an organic substance (e.g., lubricant) added to the alloy powder may be decomposed into carbon by heating at 200° C. or higher, and the alloy powder (alloy particles) may bind together through carbon. There is As a result, the shape retention of the molded body 10 may be improved. If the temperature of the molded body 10 exceeds 450° C. in the heating process, there is a possibility that carbides of the metals forming the alloy powder are generated or the alloy powders (alloy particles) are directly sintered. On the other hand, when the temperature of the molded body 10 is adjusted to 200° C. or higher and 450° C. or lower, metal carbides are not necessarily formed, and alloy particles are not necessarily directly sintered.

(Sintering process)
In the sintering step, the compact 10 that has undergone the orientation step is heated and sintered. After the orientation step, the sintering step may be performed without the above heating step. After the orientation step, the sintering step may be performed through the heating step described above.

In the sintering step, the molded body 10 separated from part or all of the mold 2 may be heated for the following reasons. Preferably, the compact 10 completely separated from the mold 2 may be heated in the sintering step. However, in the sintering step, the compact 10 may be heated together with the mold 2 .

If, in the sintering step, the molded body 10 is not separated from the resin mold 2 and both the molded body 10 and the mold 2 are heated, the resin constituting the mold 2 decomposes and the carbon component derived from the resin is released. is mixed in the compact 10. Even if the mold made of resin is burnt out in the course of the sintering process, it is difficult to sufficiently prevent the carbon component generated along with the burnout from being mixed into the compact 10 . As a result, the carbon component remains in the sintered body (rare earth magnet), and the carbon component impairs the magnetic properties (eg, coercive force) of the rare earth magnet. On the other hand, when the molded body 10 separated from the mold 2 is heated, the carbon component derived from the resin is less likely to be mixed into the molded body 10, and the magnetic properties (eg, coercive force) of the rare earth magnet are less likely to be impaired by the carbon component.

If the molded body 10 and part or all of the mold 2 are heated together in the sintering step, the molded body 10 may be heated due to the difference in coefficient of thermal expansion between the molded body 10 and the mold 2. stress is likely to act on the molded body 10, and the molded body 10 may be deformed or damaged. Furthermore, in the sintering step, when the compact 10 and the mold 2 are all heated together, the volume and heat capacity of the entire object to be heated are large. As a result, the number of compacts 10 to be heated at one time is limited, the time required for the sintering process is lengthened, energy is wasted, and the productivity of rare earth magnets is reduced. On the other hand, when heating the compact 10 separated from the mold 2, the volume and heat capacity of the entire object to be heated are smaller than when the compact 10 and the entire mold 2 are heated together. As a result, it is easy to raise the temperature of a large number of compacts 10 all at once, and the time and energy required for the sintering process can be easily suppressed, thereby improving the productivity of rare earth magnets.

The sintering temperature may be, for example, 900° C. or higher and 1200° C. or lower. The sintering time may be, for example, 0.1 hours or more and 100 hours or less. The sintering process may be repeated. In the sintering step, the compact 10 may be heated in inert gas or vacuum. The inert gas may be a noble gas such as argon.

Aging treatment of the sintered body may be performed. Aging may be performed in inert gas or vacuum. The aging treatment may consist of multistage heat treatments at different temperatures.

The sintered body may be cut or ground. A protective layer may be formed on the surface of the sintered body. The protective layer may be, for example, a resin layer or an inorganic layer (eg, metal layer or oxide layer). A method for forming the protective layer may be, for example, a plating method, a coating method, a vapor deposition polymerization method, a vapor phase method, or a chemical conversion treatment method.

(Magnetizing process)
In the magnetizing step, the sintered body is magnetized within the radial magnetic field region. In the magnetization step, a composite pulse magnetic field generated by the first coil c1 and the second coil c2 used in the orientation step may be applied to the sintered body. The synthetic pulse magnetic field (distribution of the lines of magnetic force) applied to the sintered compact in the magnetization step may be substantially the same as the synthetic pulse magnetic field applied to the compact 10 in the orientation step. The position and orientation of the sintered body in the radial magnetic field region in the magnetization step may be substantially the same as the position and orientation of the compact 10 in the radial magnetic field region in the orientation step. The number of times the synthetic pulse magnetic field (pulse wave) is applied to the sintered body may be one or more times. Also in the magnetization step, the position of the sintered body may be fixed by a jig or the like. The synthetic pulsed magnetic field applied to the sintered body in the magnetization step may be a synthetic pulsed magnetic field by a DC magnetic field. As long as the distribution of the magnetization direction of the sintered body (rare earth magnet) magnetized by the magnetization process as described above is substantially the same as the orientation direction of the alloy powder in the compact 10 that has undergone the orientation process, the magnetization process The composite pulsed magnetic field applied to the sintered body in may differ from the composite pulsed magnetic field applied to the compact 10 in the orientation step.

A rare earth magnet (sintered magnet) is manufactured by the above method. The shape of the rare earth magnet may be substantially the same as the shape of the compact.

The invention is not necessarily limited to the embodiments described above. Various modifications of the present invention are possible without departing from the gist of the present invention, and these modifications are also included in the present invention.

The present invention is explained in detail by the following examples and comparative examples. The invention is not limited by the following examples.

(Example 1)
An alloy in flakes containing 29% by weight Nd, 1% by weight Dy, 1% by weight B and the balance Fe was produced by strip casting. The alloy was coarsely pulverized by a hydrogen absorption method to obtain a coarse powder. Oleamide (lubricant) was added to the coarse powder. Subsequently, the coarse powder was pulverized by a jet mill in an inert gas to obtain a fine powder (alloy powder containing rare earth elements). The content of oleic acid amide in the fine powder was 0.1% by mass. The particle size (D50) of the fine powder was adjusted to 4 µm.

In the molding step, the compact was formed by compressing the fine powder filled in the mold with the mold. As a mold, a mold 2 having the shape and structure shown in FIG. 2 was used. The punch, upper mold 4, side mold 6 and lower mold 8 used in the molding process were made of insulating plastic (non-magnetic material).

As the molded body, an arc segment type molded body 10 (C-shaped molded body) shown in FIG. 1 was formed. The thickness T of the molded body 10 was 5 mm. The width h of the compact 10 in the longitudinal direction DL was 20 mm. The width W of the compact 10 in the arc direction DA was 50 mm. The area of the cross section 10cs of the compact 10 in the direction perpendicular to the longitudinal direction DL was about 2.5 cm ² . The opening angle θ of the molded body 10 was 60°. In the molding process, the density of the molded body 10 was adjusted to 3.6 g/cm ³ (3.6 g/cc).

A first coil c1 and a second coil c2 were used in the orientation step. Both the first coil c1 and the second coil c2 were air-core coils. The dimensions and shapes of the first coil c1 and the second coil c2 were the same. Both the inner diameter (2×r1) of the first coil c1 and the inner diameter (2×r2) of the second coil c2 were 56 mm. That is, both r1 and r2 were 28 mm. Both the outer diameter (2×R1) of the first coil c1 and the outer diameter (2×R2) of the second coil c2 were 132 mm. That is, both R1 and R2 were 66 mm. The width t1 of the first coil c1 in the direction parallel to the central axis ax1 of the first coil c1 was 20 mm. The width t2 of the second coil c2 in the direction parallel to the center axis ax2 of the second coil c2 was also 20 mm.

As shown in FIGS. 10 and 11, the first coil c1, the second coil c2, and the mold 2 (the mold 2 holding the compact 10) were fixed by the fixing member 30. As shown in FIGS. It was fixed by the fixing member 30 . Both the first fixing plate 32 and the second fixing plate 36 constituting the fixing member 30 were made of iron. The entire holder 34 (the holder 34 to which the mold 2 is fixed) constituting the fixing member 30 was made of insulating engineering plastic (non-magnetic material). The dimensions of each of the first fixing plate 32, the holder 34 and the second fixing plate 36 shown in FIG. 11 were 180 mm long×180 mm wide.

The positions and orientations of the first coil c1, the second coil c2, and the compact 10 fixed by the fixing member 30 are the same as those of the first coil c1, the second coil c2, and the compact 10a shown in FIGS. Their positions and orientations were substantially the same. That is, the central axis ax1 of the first coil c1 substantially coincided with the central axis ax2 of the second coil c2. The entire first area A1 overlapped the entire second area A2. That is, the radial magnetic field region A was a region in which the entire first region A1 overlapped with the entire second region A2. The entire compact 10 was placed within the radial magnetic field region A. The arc direction DA of the compact 10 was substantially parallel to the inner and outer peripheral surfaces of the first coil c1 and the second coil c2, respectively. The longitudinal direction DL of the compact 10 was substantially parallel to the central axis line ax. A distance d between the first coil c1 and the second coil c2 in a direction substantially parallel to the central axis line ax was 31 mm. That is, the interval between the first coil c1 and the second coil c2 was 31 mm. The distance between the first coil c1 and the compact 10 in the direction substantially parallel to the central axis line ax was equal to the distance between the second coil c2 and the compact 10 in the same direction. The compact 10 was placed in the center of the radial magnetic field region A in a direction substantially perpendicular to the central axis line ax. The distance between the central axis line ax and the center of the compact 10 was 46 mm. The center of the molded body 10 can be rephrased as an arc dividing the thickness T of the molded body 10 equally. The radius of curvature of the arc that equally divides the thickness T of the compact 10 was 75.8 mm.

The orientation step was performed with the first coil c1, the second coil c2, the mold 2, and the compact 10 arranged as described above. In the orientation step, an N-pole opposing magnetic field (pulse magnetic field) generated by the first coil c1 and the second coil c2 was applied to the compact 10 inside the mold 2 . The voltage applied to each coil was 2500V. The strength of the pulse magnetic field in the radial magnetic field region A was controlled within a range of 3.23T or more and 3.84T or less.

In the sintering step following the orientation step, the molded body 10 removed from the mold 2 was sintered in a vacuum atmosphere. The molded body 10 was sintered in a state in which the molded body 10 was placed on a flat surface so that the longitudinal direction DL of the molded body 10 was in the vertical direction. The sintering temperature (maximum temperature) was adjusted to 1080°C. Sintering time was adjusted to 4 hours. An aging treatment was performed following the sintering process. In the aging treatment, the sintered body was heated at 900° C. (maximum temperature) for 1 hour. Subsequently, the sintered body was heated at 500° C. (maximum temperature) for 1 hour.

After grinding the entire surface of the sintered body obtained by the sintering process, a magnetizing process was carried out. In the magnetization process, an N-pole opposing magnetic field (pulse magnetic field) was applied to the sintered body in the same manner as the molded body 10 in the orientation process.

A rare earth magnet of Example 1 was produced through the above steps. The shape of the rare earth magnet was substantially the same as the shape of the compact 10 before the sintering process.

(Examples 2 and 3)
In the orientation step of Example 2, the entire compact 10 was placed within the radial magnetic field region A. FIG. However, the distance between the center of the compact 10 and the central axis ax in the orientation process of Example 2 was shorter than the distance between the center of the compact 10 and the central axis ax in the orientation process of Example 1. The molded body 10 in the orientation step of Example 2 corresponds to the molded body 10 of Example 1 moved parallel to the central axis ax by 10 mm.

In the orientation step of Example 3, the entire compact 10 was placed within the radial magnetic field region A. FIG. However, the distance between the center of the compact 10 and the central axis ax in the orientation process of Example 3 was longer than the distance between the center of the compact 10 and the central axis ax in the orientation process of Example 1. The molded body 10 in the orientation step of Example 3 corresponds to the molded body 10 of Example 1 moved in parallel by 5 mm toward the outer peripheral surfaces of the first coil c1 and the second coil c2.

Rare earth magnets of Examples 2 and 3 were produced in the same manner as in Example 1, except for the position of the compact 10 within the radial magnetic field region A.

(Comparative example 1)
The entire compact 10 in the orientation step of Comparative Example 1 was arranged between the central axis line ax and the radial magnetic field region A. That is, in the orientation step of Comparative Example 1, the N-pole opposing magnetic field (pulse magnetic field) was applied to the compact 10 arranged outside the radial magnetic field region A. FIG. The position of the molded body 10 of Comparative Example 1 in the direction parallel to the central axis line ax was substantially the same as the position of the molded body 10 of Example 1 in the same direction.

A rare earth magnet of Comparative Example 1 was produced in the same manner as in Example 1 except for the position of the compact 10 in the orientation step.

[Measurement of surface magnetic flux density along arc direction of rare earth magnet]
The surface magnetic flux densities of the rare earth magnets of Examples 1 to 3 were measured by the following method.

A jig 40 and a Hall element 42 shown in FIG. 14 were used to measure the surface magnetic flux density. In FIG. 14, for convenience of explanation, the reference numeral of the rare earth magnet is written as 10a like the compact. The jig 40 was a cylinder that freely rotated about the rotation axis axr. The rare earth magnet (10a) is mounted on the jig (40) so that the arc-shaped short side of the rare earth magnet (10a) (the side corresponding to the short side SA of the compact (10) in FIG. 1) is in contact with the surface of the jig (40). fixed to the surface. That is, the rare earth magnet ( 10 a ) was fixed to the surface of the jig 40 so that the concave surface of the rare earth magnet ( 10 a ) was in contact with the surface of the jig 40 . The position of the Hall element 42 was fixed so that the center of the rare earth magnet (10a) in the longitudinal direction DL was located directly below the Hall element 42. The distance between the Hall element 42 and the surface (convex surface) of the rare earth magnet (10a) was maintained at 0.5 mm. By continuously measuring the surface magnetic flux density of the rare earth magnet (10a) with the Hall element 42 while the jig 40 was rotated, the distribution of the surface magnetic flux density along the arc direction DA was obtained. That is, the entire surface (convex surface) of the rare earth magnet (10a) was scanned by the Hall element 42 along the arc direction DA.

The distribution of the surface magnetic flux densities of Examples 1 to 3 along the arc direction DA is shown in FIG. In FIG. 16, the surface magnetic flux density distribution of Example 1 reproduced by computer simulation is compared with the measured surface magnetic flux density distribution of Example 1. FIG. The horizontal axis of each of FIGS. 15 and 16 corresponds to the opening angle θ of the rare earth magnet (10a). The origin (0°) of the horizontal axis in each of FIGS. 15 and 16 indicates the center of the surface (convex surface) of the rare earth magnet (10a) in the arc direction DA. FIG. 15 shows that although the surface magnetic flux density at both ends of the rare earth magnet (10a) in the arc direction DA is slightly high, the surface magnetic flux density distribution along the arc direction DA in each of Examples 1 to 3 is substantially uniform. It is shown that. FIG. 15 shows the tendency of the surface magnetic flux density to increase as the distance between the center axis of each coil and the compact decreases. FIG. 16 shows that the measured surface magnetic flux density distribution approximately agrees with the simulation results.

[Measurement of surface magnetic flux density along the longitudinal direction of rare earth magnet]
The surface magnetic flux densities of the rare earth magnets of Example 1 and Comparative Example 1 were measured in the following directions.

The position of the Hall element 42 was fixed so that the center of the rare earth magnet (10a) in the arc direction DA was positioned directly below the Hall element 42. The distance between the Hall element 42 and the surface (convex surface) of the rare earth magnet (10a) was maintained at 0.5 mm. The surface magnetic flux density distribution of the rare earth magnet (10a) along the longitudinal direction DL is obtained by continuously measuring the surface magnetic flux density of the rare earth magnet (10a) with the Hall element 42 while moving the rare earth magnet (10a) in parallel along the longitudinal direction DL. was gotten. That is, the surface (convex surface) of the rare earth magnet (10a) was scanned by the Hall element 42 along the longitudinal direction DL.

FIG. 17 shows the distribution of the surface magnetic flux densities of Example 1 and Comparative Example 1 along the longitudinal direction DL. FIG. 17 also shows the distribution of the surface magnetic flux density of Example 1 reproduced by simulation using a computer. The horizontal axis of FIG. 17 corresponds to the longitudinal direction DL of the rare earth magnet (10a). 8 mm on the horizontal axis of FIG. 17 indicates the center of the surface (convex surface) of the rare earth magnet (10a) in the longitudinal direction DL. As shown in FIG. 17, the distribution of the surface magnetic flux density along the longitudinal direction DL of Example 1 was substantially uniform. The measured surface magnetic flux density distribution of Example 1 substantially agreed with the simulation results. In Comparative Example 1, the surface magnetic flux density at both ends of the rare earth magnet (10a) in the longitudinal direction DL was significantly lower than the surface magnetic flux density at the center of the rare earth magnet (10a) in the same direction.

(Examples 4 and 5)
In the orientation step of Example 4, the density of the compact 10 was adjusted to 3.55 g/cm ³ (3.55 g/cc). In the orientation step of Example 5, the density of the compact 10 was adjusted to 3.50 g/cm ³ (3.50 g/cc). Rare earth magnets of Examples 4 and 5 were produced in the same manner as in Example 1 except for the density of the compact 10 . In the same manner as in Example 1, the surface magnetic flux density distributions of Examples 4 and 5 along the arc direction DA were measured. The surface magnetic flux density distributions of Examples 4 and 5 are shown in FIG. 18 together with the distribution of Example 1 and its simulation results.

For example, according to the method of manufacturing a rare earth magnet according to one aspect of the present invention, a rare earth magnet suitable for the rotor of an SPM motor or the rotor of an IPM motor can be manufactured.
used for

c1... first coil, c2... second coil, ax1... central axis of first coil, ax2... central axis of second coil, A1... first area, A2... second area, 2... type (first type) , 2a... Second mold, 10, 10a, 10b, 10c, 10d... Molded body.

Claims (10)

A molding step of supplying a metal powder containing a rare earth element into a mold to form a compact;
an orienting step of applying a pulse magnetic field to the compact held in the mold to orient the metal powder contained in the compact;
a sintering step of sintering the compact after the orientation step;
with
In the orientation step, a first coil and a second coil are used,
the direction of the pulsed magnetic field generated in the first coil is opposite to the direction of the pulsed magnetic field generated in the second coil;
The inner diameter of the first coil is expressed as 2 × r1,
The outer diameter of the first coil is expressed as 2 × R1,
A first region is defined as a region between the first coil and the second coil, the distance from the central axis of the first coil is greater than r1 and less than R1,
The inner diameter of the second coil is expressed as 2 × r2,
The outer diameter of the second coil is expressed as 2 × R2,
A second region is defined as a region between the first coil and the second coil, the distance from the central axis of the second coil is greater than r2 and less than R2,
In the orienting step, a part or the whole of the compact is arranged in at least one of the first region and the second region.
A method for producing a rare earth magnet. In the orienting step, the first coil, the second coil, and the mold are fixed by a fixing member;
A part or the whole of the fixing member is a non-magnetic material,
A method for producing a rare earth magnet according to claim 1. A part or the whole of the mold is non-magnetic,
3. A method for producing a rare earth magnet according to claim 1 or 2. wherein the non-magnetic material is a resin;
4. A method for producing a rare earth magnet according to claim 2 or 3. One or both of the first coil and the second coil are air-core coils,
A method for producing a rare earth magnet according to any one of claims 1 to 4. Before the orientation step, the density of the molded body is adjusted to 3.0 g/cm ³ or more and 4.4 g/cm ³ or less.
A method for producing a rare earth magnet according to any one of claims 1 to 5. In the orientation step, a plurality of the molds are used,
holding said molded body in each said mold;
In a state in which a plurality of the molds are stacked along at least one of the central axis of the first coil and the central axis of the second coil, the pulse magnetic field is applied collectively to all the compacts. to be
A method for producing a rare earth magnet according to any one of claims 1 to 6. In the orientation step, a plurality of the molds are used,
holding said molded body in each said mold;
The pulse magnetic field is collectively applied to all the compacts in a state in which a plurality of the molds are arranged along the circumferential direction of at least one of the first coil and the second coil,
A method for producing a rare earth magnet according to any one of claims 1 to 7. Part or all of the first region overlaps part or all of the second region,
In the orienting step, a part or the whole of the compact is arranged in a region where the first region and the second region overlap each other.
A method for producing a rare earth magnet according to any one of claims 1 to 8. In the molding step, a first mold is used as the mold,
The orientation step includes
a first orientation step of applying a pulse magnetic field to the compact held in the first mold to orient the metal powder contained in the compact;
a second orientation step of applying the pulse magnetic field again to the compact that has undergone the first orientation step to orient the metal powder contained in the compact;
including
In the second orientation step, the plurality of molded bodies that have undergone the first orientation step are taken out from the first mold and held in one second mold, and the plurality of molded bodies in the second mold are aligned with the The pulse magnetic field is collectively applied to all the compacts stacked along at least one of the central axis of the first coil and the central axis of the second coil and stacked in the second mold. is,
In the sintering step, the plurality of stacked compacts are sintered.
A method for producing a rare earth magnet according to any one of claims 1 to 9.

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