Rare earth magnet and method for manufacturing rare earth magnet

Abstract

To provide a rare earth magnet that can achieve both high magnetic properties and low eddy current loss, and a method for manufacturing the same.SOLUTION: A rare earth magnet 1 includes coated magnet powder 5 formed by forming a coating 4 made of an insulating material on the surface of flake-shaped rare earth magnet powder 2. The rare earth magnet powder 2 has an average dimension that is short in a first direction and long in a third direction perpendicular to the first direction on a surface perpendicular to a magnetization direction of the rare earth magnet 1. A method for manufacturing the rare earth magnet 1 includes a primary molding step and a secondary molding step. In the primary molding step, the coated magnet powder 5 is pressed in the first direction to obtain a primary rare earth magnet product 6. In the secondary molding step, the primary product 6 is pressed in a second direction intersecting the first direction to plastically deform it, thereby obtaining the rare earth magnet 1.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a rare earth magnet and a method for manufacturing a rare earth magnet. [Background technology]

[0002] In recent years, efforts to realize a low-carbon or carbon-free society have become more active, and research and development into electrification technologies is being conducted to reduce CO2 emissions and improve energy efficiency in vehicles. One method for improving energy efficiency is to improve the efficiency of the motor used as the power source. In recent years, rare earth magnets have been widely used to improve motor efficiency. Because rare earth magnets are metallic magnets, their electrical resistance is low, but when they are incorporated into motors, eddy current loss increases, which can reduce motor efficiency. Various proposals have been made with the aim of reducing eddy current loss.

[0003] Patent Document 1 discloses a rare earth magnet capable of reducing eddy current loss, which has rare earth magnet powder covered with a film-like coating layer containing rare earth oxide. The particles of the magnet powder coated with the rare earth oxide have binders containing rare earth oxide particles interposed between them. The rare earth magnet is produced by high-temperature pressure molding of a mixture of the rare earth magnet powder coated with the rare earth oxide and the rare earth oxide.

[0004] Patent Document 2 discloses a method for producing a rare earth magnet in which, for the purpose of achieving high electrical resistance, Nd-Fe-B based magnet powder is mixed with an oxide such as CaO, a nitride such as BN, or a fluoride such as CaF2, and this mixture is then subjected to hot plastic working to obtain an anisotropic magnetic material.

[0005] Patent Document 3 discloses a first method for producing rare earth magnets, which includes the steps of preparing an isotropically quenched powder such as Nd-Fe-B magnet powder, mixing the isotropically quenched powder with a predetermined compound that will form the insulating layer, cold-forming (pre-forming) the mixture, hot-forming (densifying) the cold-formed body, and hot plastic working (anisotropizing).The document describes that the magnets produced by this method are composed of Nd-Fe-B quenched powders with long sides of 100 to 400 μm and thicknesses of 20 to 40 μm, generally stacked with compound powders in between. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4784173 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-22905 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-27852 Summary of the Invention [Problem to be solved by the invention]

[0007] To prevent the magnetic properties of rare-earth magnets from deteriorating, it is better to mix a small amount of insulating compound into the magnet powder. However, because the magnet powder is flaky, the magnet powder generally forms a layered structure during the densification process of the mixture of the magnet powder and insulating compound. Therefore, when magnets are manufactured using conventional manufacturing methods, the magnet powder and insulating compound deform during the hot plastic working process, spreading in a direction perpendicular to the pressure direction (i.e., along the main surface of the magnet powder). Therefore, if the amount of insulating material is reduced, the insulating layer is broken during hot plastic working, and the magnet powder particles that were separated by the insulating layer become electrically connected. This increases the eddy current path (reducing the effect of disrupting the eddy current path), resulting in increased eddy current loss during motor operation.

[0008] In view of the above background, the present invention aims to provide a rare earth magnet that can achieve both high magnetic properties and low eddy current loss, and a method for manufacturing such a rare earth magnet, which will ultimately contribute to improving energy efficiency. [Means for solving the problem]

[0009] In order to solve the above problems, one aspect of the present invention is a rare earth magnet (1) comprising a coated magnet powder (5) in which a coating (4) made of an insulating material is formed on the surface of flake-shaped rare earth magnet powder (2), and the rare earth magnet powder has an average dimension in a plane perpendicular to the magnetization direction of the rare earth magnet that is short in a first direction and long in a third direction perpendicular to the first direction.

[0010] This configuration is achieved because the rare earth magnet is pressurized in the magnetization direction by plastic processing, and the pressure direction of the plastic processing is not perpendicular to the main surfaces of the rare earth magnet powder before pressing. Therefore, according to this embodiment, the coating made of insulating material is prevented from extending significantly along the main surfaces of the rare earth magnet powder during plastic processing, and discontinuities in the coating are suppressed. This prevents an increase in eddy current loss. Alternatively, while preventing discontinuities in the coating, the amount of insulating material added is reduced, preventing a deterioration in the magnetic properties of the rare earth magnet.

[0011] In the above aspect, in a cut surface of the rare earth magnet along the magnetization direction, the average dimension of the rare earth magnet powder in a direction perpendicular to the magnetization direction may have two peaks in a cut angle range of 0° to 360° defined on the plane perpendicular to the magnetization direction.

[0012] The average dimensions of the rare earth magnetic powder are roughly the same on the cross section between the first direction and the third direction, but with this configuration, it can be confirmed from, for example, four cross sections with different cutting angles that the rare earth magnetic powder is aligned with its longitudinal direction on the surface perpendicular to the magnetization direction.

[0013] In the above aspect, the insulating material may be an alkali metal fluoride or an alkaline earth metal fluoride.

[0014] According to this aspect, the alkali metal fluoride or alkaline earth metal fluoride that constitutes the coating is prevented from reacting with the rare earth that constitutes the rare earth magnetic powder, thereby preventing a deterioration in the magnetic properties of the rare earth magnetic powder and the insulating properties of the coating.

[0015] In order to solve the above-mentioned problems, one aspect of the present invention is a method for manufacturing a rare earth magnet (1), which includes a step of adding an insulating material to flake-shaped rare earth magnet powder (2) so that a coating (4) is formed on the surface of the rare earth magnet powder, and obtaining coated magnet powder (5) on which the coating is formed (FIG. 1(B)); a primary molding step (FIG. 1(C)) of placing the coated magnet powder inside a mold (10) that can apply pressure in a first direction, and pressing the coated magnet powder in the first direction using the mold to obtain a primary molded rare earth magnet product (6); and a step of plastically deforming the primary molded product by pressing in a second direction that intersects the first direction, Unmagnetized state and a secondary molding step (FIG. 1(E)) to obtain the rare earth magnet.

[0016] According to this aspect, in the secondary molding process, the coated magnet powder of the primary molded product is stretched in a third direction perpendicular to the first and second directions, while being compressed in the second direction, so that the thickness of the coating on the main surface of the rare earth magnet powder (i.e., the thickness in the first direction) is less likely to become thin. This prevents the coating from being broken, which in turn prevents an increase in eddy current loss. This means that the amount of insulating material added to the rare earth magnet powder can be reduced, thereby preventing a decrease in the magnetic properties of the rare earth magnet caused by the addition of insulating material.

[0017] In the above aspect, the second direction may be a direction perpendicular to the first direction.

[0018] According to this aspect, the coating is effectively prevented from becoming thinner in the first direction, and therefore, an increase in eddy current loss is effectively prevented, and the amount of insulating material added can be further reduced.

[0019] In the above aspect, in the primary molding process, the coated magnet powder is pressurized while being constrained in a direction perpendicular to the first direction, and in the secondary molding process, the primary molded product is pressurized without being constrained in a direction perpendicular to the second direction.

[0020] According to this embodiment, the density and strength of the primary molded product can be increased by the primary molding process, and the coated magnet powder can be stretched in the third direction by the secondary molding process, making the crystal orientation anisotropic.

[0021] In the above aspect, the secondary forming step may be performed by hot plastic working, which plastically deforms the primary formed product while hot.

[0022] According to this aspect, the crystal grains rotate so that their axes of easy magnetization are aligned in the second direction, which is the pressure direction, effectively anisotropizing the crystal orientation. Furthermore, the rare earth magnet's structure becomes denser and internal defects are reduced, improving the strength and hardness of the rare earth magnet.

[0023] In the above aspect, the secondary forming step may be carried out at a temperature higher than the hot temperature of the primary forming step.

[0024] According to this embodiment, a liquid phase is more likely to occur at the grain boundaries, so that the crystal orientation can be more effectively anisotropic. Also, the rare earth magnet powder can be plastically deformed with a high upsetting ratio. [Effects of the Invention]

[0025] According to the above aspects, it is possible to provide a rare earth magnet that can achieve both high magnetic properties and low eddy current loss, and a method for manufacturing the rare earth magnet. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is an explanatory diagram of a method for manufacturing a rare earth magnet according to an embodiment; [Figure 2]SEM photo of the cross section of a rare earth magnet primary molding after primary molding [Figure 3] SEM images of cross sections along the magnetization direction of a rare earth magnet after secondary molding: (A) a cross section along the first direction, and (B) a cross section along the third direction. [Figure 4] Plan view of a rare earth magnet viewed from the magnetization direction [Figure 5] Graph showing the shape characteristics of rare earth magnet powder in rare earth magnets [Figure 6] 1 is an explanatory diagram of a method for manufacturing a rare earth magnet according to a comparative example; [Figure 7] SEM photograph of a cross section of a rare earth magnet after secondary molding in a comparative example DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0028] First, a method for manufacturing a rare earth magnet 1 according to an embodiment will be described. Figure 1 is an explanatory diagram of the method for manufacturing a rare earth magnet 1 according to an embodiment. As shown in Figure 1(A), first, rare earth magnet powder 2 is manufactured. Through this process, rare earth magnet powder 2 is obtained.

[0029] The raw material of the rare earth magnet powder 2 is not limited to this, but for example, a neodymium magnet (Nd-Fe-B magnet, more precisely NdFe 14 B) may be used. The method for obtaining the rare earth magnet powder 2 from the rare earth magnet raw material is, for example, the melt spinning method. The melt spinning method is a manufacturing method for producing fine flake-shaped (thin piece) magnetic powder for magnets containing Nd—Fe—B crystals by spraying an alloy molten at high temperature onto a cooled roll and rapidly cooling it.

[0030] The rare earth magnet powder 2 obtained in this process is an isotropic quenched powder with no uniform crystal orientation, and due to its flake shape, has two main surfaces 2a. In this specification, the main surfaces 2a are defined as the largest of a pair of flat surfaces facing in opposite directions. When viewed perpendicular to the main surfaces 2a, the rare earth magnet powder 2 has an aspect ratio of approximately 1 (e.g., 0.7 to 1.0). The aspect ratio is the ratio of the minor axis (minor axis) to the major axis (long axis diameter) of a particle, and is expressed as b / a, where a is the major axis and b is the minor axis. The major axis (major axis diameter) refers to the maximum Feret diameter, and the minor axis (minor axis diameter) refers to the minimum Feret diameter. The measurement method for the major and minor axes complies with the provisions of JIS Z8890:2017, "Evaluation of the Particle Properties of Powders."

[0031] Next, as shown in Figure 1(B), an insulating coating process is performed to form an insulating coating on the surface of the rare earth magnetic powder 2. In this process, an insulating substance is added to the rare earth magnetic powder 2 so that a coating 4 is formed on the surface of the rare earth magnetic powder 2, thereby obtaining a coated magnetic powder 5 on which the coating 4 is formed.

[0032] The insulating material is preferably, but not limited to, an alkali metal fluoride or an alkaline earth metal fluoride. In this embodiment, calcium fluoride (CaF2), which is an alkaline earth metal fluoride, is used as the insulating material. The insulating material is not limited to calcium fluoride, and may be an alkaline earth metal fluoride such as magnesium fluoride, barium fluoride, or strontium fluoride, or an alkali metal fluoride such as lithium fluoride. Alternatively, the insulating material may be a mixture of these.

[0033] The method for forming the coating 4 on the surface of the rare earth magnet powder 2 is not limited to this, but may be performed by sputtering, for example. Alternatively, the coating 4 of alkali metal fluoride or alkaline earth metal fluoride may be formed on the surface of the rare earth magnet powder 2 by spraying a dispersion liquid in which alkali metal fluoride particles or alkaline earth metal fluoride particles are dispersed onto the rare earth magnet powder 2 and drying it.

[0034] 1(C), the coated magnet powder 5 is subjected to primary molding. In this process, the coated magnet powder 5 is placed inside a primary molding die 10 (hot press), and the coated magnet powder 5 is compressed and deformed in a first direction by the primary molding die 10, thereby obtaining a primary molded product 6 of a rare earth magnet 1 in which the coated magnet powder 5 is densified.

[0035] The primary molding die 10 has a cylindrical die body 11 having a cross-sectional shape that matches the shape of the primary molded product 6, and an upper die 12 and a lower die 13 that can apply a compressive force in a first direction to the object inside the die body 11. That is, in this process, pressure is applied to the primary molded product 6 while the coated magnet powder 5 is constrained in a direction perpendicular to the first direction. In this embodiment, the first direction is the up-down direction, but is not limited to this.

[0036] The primary molded product 6 is formed by hot press molding, in which the primary molding die 10 is heated to a predetermined temperature and a predetermined pressure is applied for a predetermined time. When compressed and deformed by pressure, the coated magnet powder 5 in the primary molding die 10 is oriented so that the main surfaces 2a of the rare earth magnet powder 2 face a first direction, and the particles are stacked on top of each other in a direction (first direction) perpendicular to the main surfaces 2a.

[0037] Figure 2 is an SEM photograph of a cross section of primary molded product 6 of rare earth magnet 1 after primary molding. As shown in Figure 2, in primary molded product 6 of rare earth magnet 1, rare earth magnet powder 2 is stacked in a direction (first direction) perpendicular to main surface 2a.

[0038] The primary molded product 6 is formed by hot compression processing in which the coated magnet powder 5 is compressed and deformed in a hot primary molding die 10 heated to a predetermined temperature. The primary molded product 6 is formed in a hot state with the die temperature set to 600°C to 700°C, preferably about 640°C.

[0039] After primary molding, the resulting primary molded article 6 is removed from the primary molding die 10 and rotated 90°, as shown in FIG. 1(D). The primary molded article 6 is rotated around a rotation axis on a horizontal plane, i.e., around an axis parallel to the main surface 2a of the rare earth magnet powder 2. The rotation angle of the primary molded article 6 is 90° in this embodiment, but is not limited to this. However, the rotation angle is preferably close to 90°, and more preferably 90° perpendicular to the first direction.

[0040] Thereafter, as shown in FIG. 1(E), secondary molding is performed on the primary molded product 6. In this process, the primary molded product 6 rotated at the angle shown in FIG. 1(D) is placed inside the secondary molding die 15. Next, the secondary molding die 15 applies pressure in a second direction that intersects with the first direction, which is the pressure direction of the primary molding (the lamination direction of the rare earth magnet powder 2), thereby plastically deforming the primary molded product 6. Unmagnetized state A rare earth magnet 1 (secondary formed product) is obtained.

[0041] The rotation process in Fig. 1(D) is performed because the pressure direction in the secondary molding in Fig. 1(E) is the same vertical direction as the pressure direction in the primary molding. Therefore, if the pressure direction in the secondary molding in Fig. 1(E) is a direction different from the first direction, such as a horizontal direction, the rotation process in Fig. 1(D) is not necessary.

[0042] The secondary molding die 15 is composed of an upper pressure die 16 and a lower pressure die 17 arranged opposite each other. The upper pressure die 16 and the lower pressure die 17 have upper pressure surfaces 16a and lower pressure surfaces 17a that fit the shape of the primary molded article 6 in order to pressurize the primary molded article 6 in the second direction (the up-down direction in this embodiment). Since the primary molded article 6 in this embodiment has a rectangular parallelepiped shape, the upper pressure die 16 and the lower pressure die 17 have upper pressure surfaces 16a and lower pressure surfaces 17a that are made up of a pair of opposing surfaces that extend horizontally and parallel to each other, and apply a compressive force to the primary molded article 6 in the up-down direction that is perpendicular to the first direction.

[0043] In the secondary molding, pressure is applied to the primary molded product 6 without restraining the primary molded product 6 in a direction perpendicular to the second direction. Therefore, through the secondary molding, the primary molded product 6 is compressed in the vertical direction, which is the pressure direction of the secondary molding, and plastically deforms so as to be stretched in the horizontal direction perpendicular to the vertical direction. Specifically, the thickness (dimension in the first direction) of the rare earth magnet powder 2 in the rare earth magnet 1 is thicker than the thickness of the rare earth magnet powder 2 in the primary molded product 6. When viewed from the first direction, the aspect ratio of the rare earth magnet powder 2 in the rare earth magnet 1 is smaller than the aspect ratio of the rare earth magnet powder 2 in the primary molded product 6. The aspect ratio of the rare earth magnet powder 2 in the rare earth magnet 1 is preferably smaller than 1, for example, approximately 0.15 to 0.5.

[0044] By hot plastic working, the rare earth magnet powder 2 of the primary molded product 6 exhibits magnetic anisotropy (uniaxial anisotropy) in which the c-axis direction (direction of easy magnetization) of the crystal grains is aligned parallel to the pressure direction. (Secondary molded product) is magnetized in the direction in which this magnetic anisotropy is manifested.

[0045] In this way, during secondary molding, the primary molded product 6 is pressurized in a second direction intersecting the first direction, causing plastic deformation. As a result, the rare earth magnetic powder 2 and the coating 4 around it are stretched in directions perpendicular to the second direction, i.e., in the first and third directions. In other words, the coating 4 between adjacent rare earth magnetic powder particles 2 in the first direction is stretched in the third direction, thinning it, but is not stretched in the second direction. This prevents the coating 4 from becoming too thin in the first direction, thereby suppressing an increase in eddy current loss. This effect will be described in more detail later.

[0046] Furthermore, the secondary forming is performed by hot compression processing, in which the primary molded product 6 is compressed and deformed in a hot state with the secondary molding die 15 heated to a predetermined temperature; more specifically, by hot plastic processing, in which the primary molded product 6 is plastically deformed in a hot state at a temperature higher than that in the primary molding process. The temperature of the secondary molding die 15 for secondary forming is preferably a temperature at which some of the crystal grains of the rare earth magnet powder 2 change into a liquid phase, for example, about 850°C. This allows the rare earth magnet powder 2 to be plastically deformed with a high upsetting ratio. In this embodiment, during secondary forming, the primary molded product 6 of the rare earth magnet 1 is plastically processed with an upsetting ratio of about 70%.

[0047] FIG. 3 shows the magnetization direction of the rare earth magnet 1 after secondary molding. (Second direction) A cross section along (A) the first direction In line with cross section (Cross section seen in the third direction) , (B) Third direction In line with cross section (Cross section viewed in the first direction) 3(A) and 3(B). The third direction is a direction perpendicular to the first and second directions. In the rare earth magnet 1, the minor axis of the rare earth magnet powder 2 in the first direction shown in FIG. 3(A) is shorter than the major axis in the third direction shown in FIG. 3(B). The aspect ratio of the rare earth magnet powder 2 in this embodiment is approximately 0.2. As shown in FIG. 3(A), the average minor axis of the rare earth magnet powder 2 is approximately the same as the average dimension of the rare earth magnet powder 2 in the first direction (the dimension in the thickness direction of the rare earth magnet powder 2).

[0048] By plastically deforming the coated magnet powder 5 into this shape and stretching it in the third direction, the coating 4 is stretched in the third direction and compressed in the second direction. In other words, the coating 4, made of an insulating material, is prevented from stretching significantly along the main surface 2a of the rare earth magnet powder 2 during plastic processing, and discontinuities in the coating 4 are suppressed. This prevents an increase in eddy current loss. Alternatively, by suppressing discontinuities in the coating 4 while reducing the amount of insulating material added, it is possible to prevent a deterioration in the magnetic properties of the rare earth magnet 1.

[0049] The particle shape of the rare earth magnet powder 2 in a plane perpendicular to the magnetization direction of the rare earth magnet 1 will be described in detail. FIG. 4 is an explanatory diagram for explaining the particle shape of the rare earth magnet powder 2, and is a plan view of the rare earth magnet 1 viewed from the magnetization direction. During secondary molding, the rare earth magnet powder 2 is pressed from a second direction intersecting the first direction, so that on the plane perpendicular to the magnetization direction (plan view of FIG. 4 ), the rare earth magnet powder 2 is aligned along a predetermined direction so that its longitudinal axis is aligned in a third direction perpendicular to the first direction. However, it is difficult to identify the first and third directions from the rare earth magnet 1. Therefore, as shown in FIG. 4 , the rare earth magnet 1 viewed from the magnetization direction is cut at various angles, and the average dimension value of the rare earth magnet powder 2 in the direction perpendicular to the magnetization direction is calculated from the cut surfaces. This allows the shape characteristics of the rare earth magnet powder 2 in the rare earth magnet 1 to be understood.

[0050] figure 4 In the figure, the cutting lines are drawn so as to pass through a single point on the rare earth magnet 1, but the actual cutting lines may be set at positions separated from each other. In the illustrated example, the cutting lines are set at 45° intervals. The AA cutting line and the -E cutting line are simply viewed from different angles (they have symmetrical shapes), and the dimensions and shape of the rare earth magnet powder 2 are the same. teeth It is essentially the same.

[0051] FIG. 5 is a graph showing the shape characteristics of the rare earth magnet powder 2 in the rare earth magnet 1, illustrating the correlation between the cutting angle and the average dimension of the rare earth magnet powder 2. The horizontal axis represents the cutting angle, and the vertical axis represents the average dimension in the direction perpendicular to the magnetization direction of the rare earth magnet powder 2. This average dimension corresponds to the average aspect ratio of the rare earth magnet powder 2.

[0052] Because the rare earth magnetic powder 2 is oriented with its longitudinal axis aligned in the third direction, the average dimension of the rare earth magnetic powder 2 in the direction perpendicular to the magnetization direction has two peaks in the cutting angle range of 0° to 360° defined on a plane perpendicular to the magnetization direction, as shown in Figure 5. In this example, the CC cross section in Figure 3 is the longitudinal direction of the rare earth magnetic powder 2, i.e., the plane along the third direction. The AA cross section is the lateral direction of the rare earth magnetic powder 2, i.e., the plane along the first direction.

[0053] The average dimensions of the rare earth magnetic powder 2 are roughly the same in the BB cross section and the DD cross section, which are located between the third direction and the first direction. In this example, from the four cut surfaces cut at different angles, it can be confirmed that the rare earth magnetic powder 2 is aligned with its longitudinal direction aligned in the plane perpendicular to the magnetization direction.

[0054] Next, a method for manufacturing the rare earth magnet 101 according to a comparative example will be described, followed by a description of the effects of the rare earth magnet 101 according to the embodiment and the method for manufacturing the same.

[0055] FIG. 6 is an explanatory diagram of a method for manufacturing a rare earth magnet 101 according to a comparative example, showing steps corresponding to those shown in FIGS. 1(C) to 1(E). In the comparative example, the processes shown in FIGS. 1(A) and 1(B) are also carried out in advance. As shown in FIG. 6(A), in the comparative example, primary molding of coated magnet powder 5 is also carried out. In this step, the same process as that described in FIG. 1(C) is carried out.

[0056] 6(B), secondary molding is then performed on the primary molded article 6 removed from the primary molding die 10. In this process, the primary molded article 6 is placed inside the secondary molding die 15 so that the second direction, which is the pressure direction of the secondary molding die 15, coincides with the first direction, which is the pressure direction of the primary molding die 10. Then, pressure is applied to the primary molded article 6 in the same direction as the pressure direction of the primary molding, causing plastic deformation of the primary molded article 6, thereby obtaining a rare earth magnet 101 according to the comparative example.

[0057] Similar to the above embodiment, the secondary forming is performed by hot plastic processing, which plastically deforms the primary formed product 6 in a hot state, using a secondary forming die 15. In the comparative example, the direction in which the secondary forming die 15 applies pressure to the primary formed product 6 is different from that in the above embodiment.

[0058] Fig. 7 is an SEM photograph of a cross section of a rare earth magnet 101 after secondary molding according to a comparative example. As shown in Fig. 7, in the rare earth magnet 101 obtained by this manufacturing method, the rare earth magnet powder 2 is thinner in the first direction than in the state after primary molding shown in Fig. 2, and has been plastically deformed so as to extend in directions (second and third directions) perpendicular to the first direction. and 1 direction In line with Although only the cross section is shown, the rare earth magnet powder 2 is disk-shaped and is aligned in the second direction perpendicular to the third direction in FIG. and 1 direction Surface along The aspect ratio of the rare earth magnet powder 2 in the rare earth magnet 101 is the same as the aspect ratio of the primary molded product 6, and is 0.7 to 1.0.

[0059] Thus, in the comparative example, the rare earth magnetic powder 2 is stretched in a direction perpendicular to the first direction in both the primary molding and secondary molding. That is, in both processes, the coating 4 made of an insulating material is stretched in the second and third directions along the main surfaces 2a of the rare earth magnetic powder 2 between adjacent rare earth magnetic powder particles 2 in the first direction. As a result, the coating 4 of the rare earth magnetic powder 2 is easily interrupted, and the rare earth magnetic powder particles 2 that were separated by the coating 4 are electrically connected at the interrupted portions of the coating 4. This increases the volume of the rare earth magnetic powder 2, thereby increasing eddy current loss that occurs when the motor is operating.

[0060] In contrast, in the rare earth magnet 1 according to the embodiment, as shown in Figure 3, the coated magnet powder 5 has an average dimension that is short in the first direction and long in the third direction on a plane perpendicular to the second direction, which is the magnetization direction of the rare earth magnet 1. In other words, the pressure direction of the plastic processing by secondary molding is not perpendicular to the main surface 2a of the rare earth magnet powder 2 before pressing. Therefore, as described above, the coating 4 made of an insulating material is prevented from extending significantly along the main surface 2a of the rare earth magnet powder 2 during plastic processing, and discontinuities in the coating 4 are suppressed.

[0061] As described above, the insulating material is an alkaline earth metal fluoride. This prevents the alkali metal fluoride that makes up the coating 4 from reacting with the rare earth that makes up the rare earth magnetic powder 2. This prevents a deterioration in the magnetic properties of the rare earth magnetic powder 2 and the insulating properties of the coating 4. The same effect can be achieved even if the insulating material is an alkali metal fluoride.

[0062] In addition, in the manufacturing method of the rare earth magnet 1 according to the embodiment, as shown in FIGS. 1(D) and 1(E), the rare earth magnet 1 is obtained by plastically deforming the primary molded product 6 by pressurizing it in a second direction intersecting the first direction during secondary molding. In this way, during the secondary molding process shown in FIG. 1(E), the coated magnet powder 5 of the primary molded product 6 is stretched in the third direction while compressed in the second direction, making it difficult for the thickness of the coating 4 along the main surface 2a of the rare earth magnet powder 2 (i.e., the thickness in the first direction) to become thin. This prevents discontinuities in the coating 4, thereby suppressing increases in eddy current loss. This also reduces the amount of insulating material added to the rare earth magnet powder 2, thereby preventing a decrease in the magnetic properties of the rare earth magnet 1 due to the addition of insulating material.

[0063] The second direction is a direction perpendicular to the first direction. This effectively prevents the coating 4 from becoming thinner in the first direction, thereby effectively preventing an increase in eddy current loss. This allows for a further reduction in the amount of insulating material added.

[0064] 1(C), the coated magnet powder 5 is compressed while being constrained in a direction perpendicular to the first direction, and in the secondary molding process, the primary molded product 6 is compressed without being constrained in a direction perpendicular to the second direction. Therefore, the primary molding process can increase the density and strength of the primary molded product 6, and the secondary molding process can stretch the coated magnet powder 5 in a third direction, making the crystal orientation anisotropic.

[0065] The secondary forming process shown in Figure 1(E) is carried out by hot plastic processing, which plastically deforms the primary formed product 6 while hot. As a result, the crystal grains rotate and become aligned so that their axes of easy magnetization are oriented in the second direction, which is the direction of pressure application, effectively anisotropizing the crystal orientation. Furthermore, the rare earth magnet 1 has a denser structure and fewer internal defects, improving the strength and hardness of the rare earth magnet 1.

[0066] Furthermore, the secondary compaction process is performed at a higher temperature than the hot-press temperature of the primary compaction process. This facilitates the formation of a liquid phase at the grain boundaries, enabling more effective anisotropy of the crystal orientation. Furthermore, the rare earth magnet powder 2 can be plastically deformed with a high upsetting ratio.

[0067] While the specific embodiments have been described above, the present invention is not limited to these embodiments and modifications, and can be implemented in a wide variety of ways. For example, in the above embodiment, the primary molded product 6 is rotated 90° in FIG. 1(D) because the rare earth magnet 1 has a rectangular parallelepiped shape. However, as noted above, the rotation angle is not limited to this. For example, if the primary molded product 6 is octagonal when viewed horizontally, the rotation angle may be 90° or 45°. Furthermore, if the primary molded product 6 is hexagonal when viewed horizontally, the rotation angle may be 22.5°, 45°, 67.5°, or 90°. If the primary molded product 6 is circular when viewed horizontally, the rotation angle may be any angle greater than 0° and less than 180°. Furthermore, the specific configuration, arrangement, quantity, and materials of each component and part may be modified as appropriate without departing from the spirit and scope of the present invention. Furthermore, some or all of the configurations of the above embodiments may be combined with each other. On the other hand, not all of the components shown in the above embodiment are necessarily required, and they can be selected as appropriate. [Explanation of symbols]

[0068] 1: Rare earth magnet 2: Rare earth magnet powder 2a: Main surface 4:Coating 5: Coated magnet powder 6: Primary molded product 10: Primary molding die 15: Secondary molding mold

Claims

1. A rare earth magnet, The magnet powder comprises a coated magnet powder in which a coating made of an insulating material is formed on the surface of flake-shaped rare earth magnet powder, The rare earth magnet, wherein the rare earth magnet powder has an average dimension that is short in a first direction and long in a third direction perpendicular to the first direction in a plane perpendicular to the magnetization direction of the rare earth magnet.

2. 2. The rare earth magnet according to claim 1, wherein, in a cut surface of the rare earth magnet taken along the magnetization direction, the average dimension of the rare earth magnet powder in a direction perpendicular to the magnetization direction has two peaks in a cut angle range of 0° to 360° defined on a plane perpendicular to the magnetization direction.

3. 3. The rare earth magnet according to claim 1, wherein the insulating material is an alkali metal fluoride or an alkaline earth metal fluoride.

4. A method for producing a rare earth magnet, comprising: a step of adding an insulating material to the rare earth magnet powder so that a coating is formed on the surface of the flake-shaped rare earth magnet powder, thereby obtaining a coated magnet powder having the coating formed thereon; a primary molding step of placing the coated magnet powder inside a mold capable of applying pressure in a first direction, compressing and deforming the coated magnet powder by applying pressure in the first direction using the mold, and obtaining a primary molded rare earth magnet product; a secondary molding step of pressurizing the primary molded product in a second direction intersecting the first direction to plastically deform the product, thereby obtaining the rare earth magnet in an unmagnetized state.

5. The method for manufacturing a rare earth magnet according to claim 4 , wherein the second direction is a direction perpendicular to the first direction.

6. In the primary compacting step, the coated magnet powder is compressed in a state where the coated magnet powder is constrained in a direction perpendicular to the first direction, The method for producing a rare earth magnet according to claim 5 , wherein in the secondary forming step, the primary molded product is pressurized without being constrained in a direction perpendicular to the second direction.

7. The method for producing a rare earth magnet according to claim 4, wherein the secondary forming step is performed by hot plastic working, which plastically deforms the primary molded product while hot.

8. The method for producing a rare earth magnet according to claim 4 , wherein the secondary forming step is carried out at a temperature higher than the hot temperature of the primary forming step.

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