Rare earth magnet and method for manufacturing rare earth magnet

Abstract

The invention provides a rare earth magnet and a method of manufacturing the same. The rare earth magnet achieves high magnetic performance and low eddy current loss. A rare earth magnet includes coated magnet powder particles, each of which includes a sheet-like rare earth magnet powder particle and an insulating material coating disposed on the rare earth magnet powder particle. In a plane perpendicular to a magnetization direction of the rare earth magnet, an average size of the rare earth magnet powder particles in a first direction is shorter than an average size in a third direction perpendicular to the first direction. A manufacturing method thereof includes a first molding operation including applying pressure to coated magnet powder particles in a first direction to produce a first molded product, and a second molding operation including applying pressure to the first molded product in a second direction intersecting the first direction, thereby causing plastic deformation to produce a rare earth magnet.

Description

Technical Field

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

[0002] In recent years, efforts to achieve a low-carbon or decarbonized society have become more active, and for vehicles, research and development related to electrification technologies are also being carried out in order to reduce carbon dioxide emissions and improve energy efficiency. Methods for improving energy efficiency include improving the efficiency of motors used as power sources. Recently, rare earth magnets have been increasingly used to improve motor efficiency. Since rare earth magnets are metal magnets, they generally have a low resistance, which causes the problem that incorporating rare earth magnets into motors increases eddy current losses, which reduces the efficiency of the motors. Regarding how to reduce eddy current losses, various proposals have been made.

[0003] Patent Document 1 discloses a rare earth magnet capable of reducing eddy current losses, which has rare earth magnet powder particles, and each rare earth magnet powder particle is covered with a film-like coating containing a rare earth oxide. A binding portion containing rare earth oxide particles is interposed between the coated rare earth magnet powder particles. A method for producing a rare earth magnet includes: performing high-temperature and high-pressure forming of a mixture of a rare earth oxide and rare earth magnet powder particles coated with the rare earth oxide.

[0004] Patent Document 2 discloses a method for manufacturing a rare earth magnet, which includes: mixing Nd-Fe-B magnet powder with an oxide such as CaO and a nitride such as BN or a fluoride such as CaF2 for the purpose of high resistance; and processing the resulting mixture by thermoplastic molding to produce an anisotropic magnet.

[0005] Patent Document 3 discloses a first method for manufacturing a rare earth magnet, which includes: preparing isotropic rapidly-cooled powder particles such as Nd-Fe-B magnet powder particles; mixing the isotropic rapidly-cooled powder particles with a predetermined composite for forming an insulating layer; processing the mixture by cold molding to produce a cold-molded product (temporary molding); and processing the cold-molded product by hot molding (densification); and processing the resulting product by thermoplastic molding (imparting anisotropy) to produce a rare earth magnet, and discloses that: the magnet thus produced generally includes stacked Nd-Fe-B rapidly-cooled powder particles with a composite powder material therebetween, and each particle has a long side length of 100 μm to 400 μm and a thickness of 20 μm to 40 μm.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: JP4784173B

[0009] Patent Document 2: JP2003 - 022905A

[0010] Patent Document 3: JP2010 - 027852A SUMMARY OF THE INVENTION

[0011] TECHNICAL PROBLEM

[0012] In order to minimize the deterioration of the magnetic properties of a rare - earth magnet, it is desirable to reduce the amount of an insulating composite material to be mixed with magnet powder particles. However, since each of the magnet powder particles is flaky, the magnet powder particles are usually stacked in the step of densifying the mixture of the magnet powder particles and the insulating composite material. Therefore, when performing the method of manufacturing a magnet of the prior art, the thermoplastic molding (densifying) process causes the magnet powder particles and the insulating composite material to deform and spread in a direction perpendicular to the pressing direction (i.e., along the main surface of the magnet powder particles). This means that during the thermoplastic molding process, a reduced amount of the insulating composite material may cause fractures in the insulating layer, thereby forming an electrical connection between magnet powder particles that should be separated by the insulating layer. In this case, larger eddy - current paths (less effective in breaking the eddy - current paths) are formed in the produced magnet, which results in larger eddy - current losses during the operation of a motor using the magnet.

[0013] The present invention has been made in view of the above problems of the prior art, and the main object of the present invention is to provide a rare - earth magnet and a method for manufacturing a rare - earth magnet that achieve both high magnetic properties and low eddy - current losses.

[0014] TECHNICAL SOLUTION

[0015] As a solution to the above - mentioned task to be accomplished, one aspect of the present invention provides a rare - earth magnet 1 including coated magnet powder particles 5, each of the coated magnet powder particles including a flaky rare - earth magnet powder particle 2 and an insulating material coating 4 on the surface of the rare - earth magnet powder particle 2, wherein the rare - earth magnet has a magnetization direction, and wherein, in a transverse plane perpendicular to the magnetization direction, the average size of the rare - earth magnet powder particles in a first direction is shorter than the average size in a third direction perpendicular to the first direction.

[0016] The rare earth magnet is produced by plastically forming the material by applying pressure in the magnetization direction; that is, before pressing, the material is pressed along a pressing direction that is not perpendicular to the main surface of the rare earth magnet powder particles. This configuration prevents the coating of the insulating composite material from significantly spreading along the main surface of the rare earth magnet powder particles during the plastic deformation process, thereby preventing the occurrence of fractures in the coating. This suppresses an increase in eddy current loss. In other words, this configuration allows for a reduction in the amount of the insulating composite material while preventing the occurrence of fractures in the coating, which minimizes the deterioration of the magnetic properties of the rare earth magnet.

[0017] Preferably, the above-mentioned rare earth magnet may also be configured such that in a cross-section of the rare earth magnet extending in the magnetization direction at a cutting angle defined in the transverse plane, the average size of the rare earth magnet powder particles in a direction perpendicular to the magnetization direction varies with the cutting angle of the cross-section, such that the average size has two peaks at cutting angles within a range of 0 degrees to 360 degrees.

[0018] In a cross-section extending between two cross-sections extending in the first direction and the third direction, the average size of the rare earth magnet powder particles is substantially the same. Therefore, in this configuration, in a plurality (e.g., four) of cross-sections in planes extending at different cutting angles defined in the transverse plane, it is possible to confirm that the rare earth magnet powder particles are arranged side by side in a plane perpendicular to the magnetization direction, such that the corresponding longitudinal directions of the rare earth magnet powder particles are aligned with each other.

[0019] Preferably, the above-mentioned rare earth magnet may also be configured such that the insulating material is an alkali metal fluoride or an alkaline earth metal fluoride.

[0020] This configuration minimizes the reaction between the coating formed of the alkali metal fluoride or alkaline earth metal fluoride and the rare earth in the material of the rare earth magnet powder particles. This prevents the deterioration of the magnetic properties of the rare earth magnet powder particles and the deterioration of the insulating properties of the coating.

[0021] As a solution to the above-mentioned task to be completed, another aspect of the present invention provides a method for manufacturing a rare earth magnet 1, the method comprising the steps of: adding an insulating material to magnetic powder particles to produce coated magnet powder particles 5, such that each of the coated magnet powder particles in the coated magnet powder particles includes flaky rare earth magnet powder particles and a coating of the insulating material on the surface of the rare earth magnet powder particles ( Figure 1(B)); performing a first forming operation, the first forming operation comprising the steps of: placing the coated magnet powder particles in a mold 10 configured to allow pressing in a first direction, and applying pressure to the coated magnet powder particles in the mold in the first direction, so that the coated magnet powder particles are compressed and deformed to produce a first formed product 6( Figure 1 (C)); and performing a second forming operation, the second forming operation comprising the steps of: applying pressure to the first formed product in a second direction intersecting the first direction, so that the first formed product is plastically deformed to produce the rare earth magnet( Figure 1 (E)).

[0022] In the second forming operation of this configuration, when compressed along the second direction, the coated magnet powder particles of the first formed product unfold along a third direction perpendicular to the first and second directions. This prevents the thickness of the coating on the main surface of the rare earth magnet powder particles (i.e., the thickness in the first direction) from being prone to thinning. This also prevents the occurrence of breaks in the coating, thereby suppressing an increase in eddy current loss. Therefore, this configuration allows a reduction in the amount of the insulating composite material, thereby minimizing the deterioration of the magnetic properties of the rare earth magnet caused by the addition of the insulating composite material.

[0023] Preferably, the above method can also be configured such that the second direction is perpendicular to the first direction.

[0024] This configuration effectively prevents the coating from becoming thinner in the first direction, thereby effectively suppressing an increase in eddy current loss. Therefore, this configuration allows a further reduction in the amount of the insulating composite material.

[0025] Preferably, the above method can also be configured such that the first forming operation comprises the steps of: pressing the coated magnet powder particles while restricting deformation of the coated magnet powder particles in a direction perpendicular to the first direction, and wherein the second forming operation comprises the steps of: pressing the first formed product without restricting deformation of the first formed product in a direction perpendicular to the second direction.

[0026] In this configuration, the first forming operation allows an increase in the density and strength of the first formed product, and the second forming operation allows the coated magnet powder particles to unfold in the third direction, which makes the crystal orientation anisotropic.

[0027] Preferably, the above method can also be configured such that the second forming operation is performed by using a thermoplastic forming process, which causes the first formed product to plastically deform at a high temperature.

[0028] In this configuration, the grains rotate to allow their respective easy magnetization axes to point in the second direction (the pressing direction). In other words, the easy magnetization axes are aligned with each other, effectively making the crystal orientation anisotropic. Furthermore, this configuration allows the structure of the rare earth magnet to become denser, reducing internal defects, thereby improving the strength and hardness of the rare earth magnet.

[0029] Preferably, the above method may also be configured such that the second molding operation is performed at a temperature higher than the temperature at which the first molding operation is performed.

[0030] In this configuration, a liquid phase is more likely to form at grain boundaries, which allows the crystal orientation to be effectively made anisotropic.This configuration also allows the rare earth magnet powder particles to be plastically deformed at a high compaction rate (partial reduction in upset height).

[0031] Beneficial effects

[0032] As described above, the present invention may be embodied as a rare earth magnet and a method of manufacturing the rare earth magnet, which achieve high magnetic performance and low eddy current loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is an explanatory diagram showing a method of manufacturing a rare earth magnet according to an embodiment of the present invention, and includes Figure 1 (A) to Figure 1 (E);

[0034] Figure 2 shows an SEM image of a cross section of a first molded product of a rare earth magnet after a first molding operation;

[0035] Figure 3A and Figure 3B An image of a cross section taken along the magnetization direction of the rare earth magnet after the second forming operation is shown, wherein Figure 3A shows an SEM image of a cross section taken along a first direction, and Figure 3B An SEM image of a cross section taken along the third direction is shown.

[0036] Figure 4 is a plan view of a rare earth magnet viewed from the magnetization direction;

[0037] Figure 5 is a graphical representation showing shape features of rare earth magnet powder particles in a rare earth magnet;

[0038] Figure 6 is an explanatory diagram showing a method of manufacturing a rare earth magnet according to a comparative example, and includes Figure 6(A) and Figure 6 (B); and

[0039] Figure 7 is an SEM image of a cross section of a rare earth magnet according to a comparative example after the second molding operation.

[0040] Reference Signs List

[0041] 1: Rare earth magnets

[0042] 2: Rare earth magnet powder particles

[0043] 2a: Main surface

[0044] 4: Coating

[0045] 5: Coating magnet powder particles

[0046] 6: First molded product

[0047] 10: First mold

[0048] 15: Second mold DETAILED DESCRIPTION

[0049] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0050] First, a method for manufacturing the rare earth magnet 1 according to the embodiment of the present invention will be described below. Figure 1 : is an explanatory diagram showing a method for manufacturing a rare earth magnet according to an embodiment of the present invention. Figure 1 As shown in (A) of FIG. 1 , the first process is a step of producing rare earth magnet powder particles 2. This process produces rare earth magnet powder particles 2 to be used.

[0051] Examples of the material of the rare earth magnet powder particles 2 include, but are not limited to, neodymium magnets (Nd-Fe-B magnets, or more precisely, Nd2Fe 14 B) An example of a method for producing rare earth magnet powder particles 2 from raw materials for rare earth magnets is melt spinning. This melt spinning method involves spraying a high-temperature molten alloy onto a cooling roll for rapid cooling, thereby producing fine magnet powder particles for magnets in the form of flakes (sheets) containing Nd—Fe—B crystals.

[0052] The rare earth magnet powder particles 2 produced in this process are isotropic rapidly cooled powder particles with non-aligned crystal directions, and each of these particles is flaky and thus has a major surface 2a. The term "major surface 2a" is defined herein as each pair of the largest opposing flat surfaces. When viewed from a direction perpendicular to the major surface 2a, each of the rare earth magnet powder particles 2 has an aspect ratio of about 1 (e.g., 0.7 to 1.0). The term "aspect ratio" refers to the ratio of the short diameter (minor axis diameter) to the long diameter (major axis diameter) of an object and is expressed as b / a, where "a" is the long diameter and "b" is the short diameter. The term "major axis (major axis diameter)" refers to the maximum Feret diameter, and the term "minor axis (minor axis diameter)" refers to the minimum Feret diameter. The method for measuring the major and minor axes complies with the provisions of JIS Z 8890:2017 "Particle Characteristics of Particle Systems".

[0053] Next, as shown in (B) of Figure 1 an insulation coating operation is performed to form an insulation coating on the surface of the rare earth magnet powder particles 2. This operation involves adding an insulating material to the rare earth magnet powder particles 2 such that a coating 4 is formed on the surface of each rare earth magnet powder particle 2, thereby producing coated magnet powder particles 5 having the coating 4 formed thereon.

[0054] Examples of preferred insulating materials include, but are not limited to, alkali metal fluorides or alkaline earth metal fluorides. In the present embodiment, calcium fluoride (CaF2) as an alkaline earth metal fluoride is used as the insulating material, but the insulating material is not limited to calcium fluoride. In some cases, the insulating material may be an alkaline earth metal fluoride (e.g., magnesium fluoride, barium fluoride, or strontium fluoride), an alkali metal fluoride (e.g., lithium fluoride), or a combination thereof (i.e., a mixture).

[0055] Examples of methods for forming the coating 4 on the surface of each of the rare earth magnet powder particles 2 include, but are not limited to, sputtering. Another example of a method for forming the coating may be a method including the following steps: fluid dispersion spraying of alkali metal fluoride particles or alkaline earth metal fluoride particles onto the rare earth magnet powder particles 2, and then drying the coated rare earth magnet powder particles 2, thereby forming an alkali metal fluoride or alkaline earth metal fluoride coating 4 on the surface of each of the rare earth magnet powder particles 2.

[0056] Then, as shown in Figure 1As shown in (C) of, a first molding operation for forming (shaping) the coated magnet powder particles 5 is performed. This operation includes: placing the coated magnet powder particles 5 in a first mold 10 (hot press), and applying pressure to the coated magnet powder particles 5 along a first direction with the first mold 10, so that the coated magnet powder particles 5 are compressed and deformed to produce a first molded product 6 of the rare earth magnet 1 in which the coated magnet powder particles 5 have been densified.

[0057] The first mold 10 includes a cylindrical mold body 11 having a cross-sectional shape conforming to the shape of the first molded product 6, and an upper mold 12 and a lower mold 13 that can apply a compressive force to an object in the mold body 11 along the first direction. Therefore, the first molding operation includes: applying pressure to the coated magnet powder particles 5 while restricting the deformation of the coated magnet powder particles 5 in a direction perpendicular to the first direction, thereby forming the first molded product 6. In the present embodiment, the first direction is the vertical direction, but it is not limited thereto.

[0058] The first molding operation includes: processing the coated magnet powder particles 5 into the first molded product 6 by hot press molding, wherein the first mold 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 particles 5 in the first mold 10 are oriented such that the main surface 2a of each of the rare earth magnet powder particles 2 faces the first direction, resulting in the coated magnet powder particles 5 being stacked on top of each other in a direction perpendicular to the main surface 2a (i.e., the first direction).

[0059] Figure 2 An SEM image of a cross-section of the first molded product 6 of the rare earth magnet 1 after the first molding operation is shown. As Figure 2 shown, the first molded product 6 of the rare earth magnet 1 includes rare earth magnet powder particles 2 stacked along a direction perpendicular to the main surface 2a (i.e., the first direction).

[0060] The first molding operation for forming the first molded product 6 is performed by using a hot press process, wherein the coated magnet powder particles 5 are compressed and deformed at a high temperature, and the first mold 10 is heated to a predetermined temperature. Preferably, the predetermined temperature is a temperature within the range of about 600 °C to about 700 °C, preferably 640 °C.

[0061] After the first molding operation, a rotating operation is performed, wherein, as Figure 1As shown in (D), the obtained first molded product 6 is removed from the first mold 10 and rotated 90 degrees. The rotation of the first molded product 6 is performed in a horizontal plane about the rotation axis, that is, about an axis parallel to the main surface 2a of each of the rare earth magnet powder particles 2. In this embodiment, the rotation angle of the first molded product 6 is 90 degrees. Although this angle is not limited to 90 degrees, the rotation angle is preferably close to 90 degrees, and more preferably, 90 degrees perpendicular to the first direction.

[0062] Then, if Figure 1 As shown in (E), a second molding operation for molding the first molded product 6 is performed. This operation includes: rotating the first molded product 6 to the position shown in FIG. Figure 1 After the angle shown in (D) is reached, the first molded product 6 is placed in the second mold 15, and pressure is applied to the first molded product using the second mold 15 along a second direction intersecting the first direction, which is the pressing direction in the first molding operation (i.e., the stacking direction of the rare earth magnet powder particles 2), thereby plastically deforming the first molded product 6 to produce a rare earth magnet 1 (i.e., the second molded product).

[0063] need Figure 1 The rotation operation shown in (D) is because Figure 1 The pressing direction of the second forming operation shown in (E) is the same vertical direction as the pressing direction of the first forming operation. Therefore, in some cases, when the pressing direction of the second forming operation is different from the pressing direction of the first forming operation, for example, when the pressing direction of the second forming operation is horizontal, it is not necessary to Figure 1 The rotation operation shown in (D).

[0064] The second mold 15 includes an upper mold 16 and a lower mold 17 that face each other. The upper mold 16 and the lower mold 17 have upper and lower pressure surfaces 16a and 17a that conform to the shape of the first molded product 6 and are capable of applying pressure to the first molded product 6 in a second direction (a vertical direction in this embodiment). Since the first molded product 6 has a rectangular shape in this embodiment, the upper mold 16 and the lower mold 17 have upper and lower pressure surfaces 16a and 17a that are a pair of horizontal surfaces that face each other and are parallel to each other and are configured to apply a compressive force to the first molded product 6 in a vertical direction perpendicular to the first direction.

[0065] The second forming operation includes pressing the first formed product 6 without restricting the deformation of the first formed product 6 in a direction perpendicular to the second direction. Thus, in the second forming operation, the first formed product 6 is plastically deformed by compressing the first formed product 6 in the vertical direction, which is the pressing direction of the second forming operation, while allowing the first formed product 6 to deform in the horizontal direction perpendicular to the vertical direction. Specifically, for each of the rare earth magnet powder particles 2 in the rare earth magnet 1, the thickness (dimension in the first direction) becomes thicker than when it existed in the first formed product 6 before the second forming operation. The aspect ratio of each of the rare earth magnet powder particles 2 in the rare earth magnet 1 as observed from the first direction becomes smaller than when it existed in the first formed product 6 before the second forming operation. Preferably, the aspect ratio of each of the rare earth magnet powder particles 2 in the rare earth magnet 1 is less than 1, for example, 0.15 to 0.5.

[0066] In the thermoplastic forming process, the rare earth magnet powder particles 2 of the first formed product 6 generate magnetic anisotropy (uniaxial anisotropy), in which the c-axis direction (easy magnetization direction) of the crystal grains is oriented parallel to the pressing direction. The rare earth magnet powder particles 2 of the rare earth magnet 1 are magnetized along the direction of this magnetic anisotropy.

[0067] In this way, in the second forming operation, the first formed product 6 is pressed and plastically deformed along a second direction intersecting the first direction. This causes the rare earth magnet powder particles 2 and the coating 4 around the particles to spread in a direction perpendicular to the second direction (i.e., the first direction and the third direction). In other words, the coating 4 between the rare earth magnet powder particles 2 adjacent to each other in the first direction becomes thinner by spreading in the third direction and not spreading in the second direction. This prevents the coating 4 from becoming too thin in the first direction, which reduces the increase in eddy current loss. Details of this effect will be discussed later.

[0068] The second forming operation is carried out by using a hot compression process, in which the second mold 15 is heated to a predetermined temperature to compress and deform the first formed product 6. More specifically, by using a thermoplastic forming process, in which the first formed product 6 is plastically deformed at a temperature higher than that in the first forming operation. Preferably, the temperature of the second mold 15 in the second forming operation is the temperature at which some of the crystal grains of the rare earth magnet powder particles 2 undergo a phase change to the liquid phase, for example, about 850 degrees. This process allows the rare earth magnet powder particles 2 to plastically deform at a high compaction rate. In this embodiment, the first formed product 6 of the rare earth magnet 1 is plastically processed at a compaction rate of about 70% in the second forming operation.

[0069] Figure 3A and Figure 3B Shows an image of a cross-section taken along the magnetization direction of the rare earth magnet 1 after the second forming operation. Figure 3A shows a SEM image of a cross-section taken along a first direction, and Figure 3B shows a SEM image of a cross-section taken along a third direction. The third direction is a direction perpendicular to the first direction and the second direction. Each of the rare earth magnet powder particles 2 in the rare earth magnet 1 generally has a short diameter and a long diameter in the Figure 3A and Figure 3B first direction and the third direction shown in. In the present embodiment, the aspect ratio of each of the rare earth magnet powder particles 2 is about 0.2. As shown in Figure 3A , the average value of the short diameter of the rare earth magnet powder particles 2 is substantially the same as the average value of the size of the rare earth magnet powder particles 2 in the first direction (the size in the thickness direction).

[0070] As the coated magnet powder particles 5 are plastically deformed into this shape and spread along the third direction, the coating 4 spreads along the third direction and is compressed along the second direction. In other words, during the plastic molding process, the coating 4 of the insulating material is prevented from spreading significantly along the main surface 2a of the rare earth magnet powder particles 2, which prevents breakage from occurring in the coating. This suppresses an increase in eddy current loss. In other words, the above process allows a reduction in the amount of the insulating material while preventing breakage from occurring in the coating 4, which minimizes deterioration of the magnetic properties of the rare earth magnet.

[0071] The particle shape of the rare earth magnet powder particles 2 in a plane perpendicular to the magnetization direction of the rare earth magnet 1 will be described in detail. Figure 4 is an explanatory diagram showing the particle shape of the rare earth magnet powder particles 2 and is also a plan view of the rare earth magnet 1 observed from the magnetization direction. In the second molding operation, pressure is applied to the rare earth magnet powder particles 2 in a second direction intersecting the first direction, causing the rare earth magnet powder particles 2 to exist side by side in a plane perpendicular to the magnetization direction (where the observed Figure 4 plan view), such that the corresponding longitudinal directions of the rare earth magnet powder particles are aligned with each other. However, it is difficult to directly identify the first direction and the third direction from the outside of the rare earth magnet 1. Therefore, the following operations are performed, as shown in Figure 4 , the rare earth magnet 1 is cut along a cutting line at various defined angles as observed from the magnetization direction, and the average size of the rare earth magnet powder particles 2 in a direction perpendicular to the magnetization direction is determined in each of the cross-sections, so that the shape characteristics of the rare earth magnet powder particles in the rare earth magnet can be identified.

[0072] In Figure 4In the example shown, all the cutting lines are determined to pass through a single point on the rare earth magnet 1. However, in other cases, the cutting lines can be determined at positions far apart from each other. In the shown example, the cutting lines are at 45-degree intervals. The A-A cutting line and the E-E cutting line are substantially the same in terms of the size and shape of the rare earth magnet powder particles 2, where the only difference is the observation direction (the shape is symmetric in the left-right direction).

[0073] Figure 5 is a graphical representation showing the shape characteristics of the rare earth magnet powder particles 2 in the rare earth magnet 1, which indicates the correlation between the cutting angle and the average size of the rare earth magnet powder particles 2. The horizontal axis represents the cutting angle, and the vertical axis represents the average size of the rare earth magnet powder particles 2 in the direction perpendicular to the magnetization direction. The value of this average size corresponds to the value of the average aspect ratio of the rare earth magnet powder particles 2.

[0074] As Figure 5 shown, since the rare earth magnet powder particles 2 are oriented with their long axes aligned with each other in the third direction, the average size of the rare earth magnet powder particles 2 in the direction perpendicular to the magnetization direction has two peaks at cutting angles within the range of 0 degrees to 360 degrees in the defined transverse plane (i.e., the plane perpendicular to the magnetization direction). In this example, Figure 4 the C-C cross-section in

[0075] is in a plane parallel to the long axis of the rare earth magnet powder particles 2 (i.e., along the third direction). The A-A cross-section is in a plane parallel to the short axis of the rare earth magnet powder particles 2 (i.e., along the first direction).

[0076] Next, a method for manufacturing the rare earth magnet 101 of the comparative example will be described first, and then the effects achieved by the rare earth magnet 101 according to the embodiments of the present invention and its manufacturing method will be described.

[0077] Figure 6 is an explanatory diagram showing a method for manufacturing the rare earth magnet 101 according to the comparative example, showing the processing operations corresponding to the processing operations shown in Figure 1 the (A) of Figure 1 and [[ID=2 the (B) of Figure 6As shown in (A) thereof, in the comparative example, the first molding operation was also performed on the coated magnet powder particles 5. In this process, the same operations as those of the present invention described in reference to Figure 1 of (C) were performed.

[0078] Subsequently, as shown in (B) of Figure 6 , a second molding operation was performed on the first molded product 6 transferred from the first mold 10. In this process, the first molded product 6 was placed in the second mold 15 such that the second direction as the pressing direction was the same as the first direction as the pressing direction for the first mold 10. Then, the second molding operation involved pressing the first molded product 6 along the same direction as the pressing direction of the first molding operation, thereby plastically deforming the first molded product 6 to produce the rare earth magnet 101.

[0079] The similarity between the comparative example and the above-described embodiment of the present invention is that the second molding operation was performed by using a thermoplastic molding process, in which the first molded product 6 was plastically deformed at a high temperature using the second mold 15. The difference between the comparative example and the present invention is that the pressing direction of the first molded product 6 with respect to the second mold 15 is different from the above-described embodiment of the present invention.

[0080] Figure 7 is a SEM image of the cross section of the rare earth magnet 101 according to the comparative example after the second molding operation. As shown in Figure 7 , the rare earth magnet 101 produced by this manufacturing method has been plastically deformed such that the rare earth magnet powder particles 2 are thinner in the first direction than after the first molding operation as shown in Figure 2 and are expanded in the directions perpendicular to the first direction (the second direction and the third direction). Figure 7 Only the cross section in the third direction is shown, in which each of the rare earth magnet powder particles 2 is disc-shaped, and the same shape can also be seen in the cross section in the second direction perpendicular to the third direction in Figure 7 . The aspect ratio of each of the rare earth magnet powder particles 2 in the rare earth magnet 101 is the same as that of each of the rare earth magnet powder particles 2 in the first molded product 6, which is 0.7 to 1.0.

[0081] In the comparative example, the rare earth magnet powder particles 2 are deformed and expanded in a direction perpendicular to the first direction in both the first molding operation and the second molding operation. In other words, in the two molding operations, the coating 4 made of an insulating material expands in the second direction and the third direction along the main surface 2a between the rare earth magnet powder particles 2 adjacent to each other in the first direction. Therefore, breakage may occur in the coating 4 between the rare earth magnet powder particles 2, resulting in electrical connection of adjacent rare earth magnet powder particles 2 that should be separated by the coating 4 at the breakage point in the coating 4. This means that the substantial volume of each of the rare earth magnet powder particles 2 increases, leading to greater eddy current losses during the operation of a motor using the magnet.

[0082] In contrast, as Figure 3A and Figure 3B shown, the rare earth magnet 1 of the embodiment of the present invention is configured such that the coated magnet powder particles 5 in a plane perpendicular to the second direction (the magnetization direction of the rare earth magnet 1) have a short average size in the first direction and a long average size in the third direction. In other words, before the application of pressure, the pressing direction of the plastic molding process in the second molding operation is not perpendicular to the main surface 2a of the rare earth magnet powder particles 2. As a result, as described above, during the plastic molding process, the coating 4 made of an insulating material is prevented from expanding significantly along the main surface 2a of the rare earth magnet powder particles 2, which prevents the occurrence of breakage in the coating 4.

[0083] As described above, the insulating material is an alkaline earth metal fluoride. This feature suppresses the reaction of the alkaline earth metal fluoride with the rare earths that are the materials of the coating 4 and the rare earth magnet powder particles 2, respectively. This feature prevents deterioration of the magnetic properties of the rare earth magnet powder particles 2 and deterioration of the insulating properties of the coating 4. The same effect can be achieved when an alkaline earth metal fluoride is used as the insulating material.

[0084] In the method for manufacturing the rare earth magnet 1, as Figure 1 (D) of Figure 1 and Figure 1 (E) of

[0085] shown, the second molding operation involves applying pressure in a second direction intersecting the first direction, thereby plastically deforming the first molded product 6 to produce a rare earth magnet. In the second molding operation shown in Figure 1 (E) of

[0085] , when compressed along the second direction, the coated magnet powder particles 5 of the first molded product 6 expand along the third direction, which prevents the thickness (i.e., the thickness along the first direction) of the coating 4 along the main surface 2a of the rare earth magnet powder particles 2 from becoming thinner easily. This also prevents breakage from occurring in the coating 4, thereby suppressing an increase in eddy current losses. Therefore, this configuration allows a reduction in the amount of the insulating material, thereby minimizing deterioration of the magnetic properties of the rare earth magnet 1 due to the addition of the insulating material.The second direction is perpendicular to the first direction. This feature effectively prevents the coating from becoming thinner in the first direction, thereby effectively suppressing the increase in eddy current loss. Therefore, this feature allows for a further reduction in the amount of insulating composite material.

[0086] In some cases, Figure 1 the first forming operation shown in (C) of includes: pressing the coated magnet powder particles 5 while restricting the deformation of the coated magnet powder particles 5 in a direction perpendicular to the first direction, and the second forming operation includes: pressing the first formed product 6 without restricting the deformation of the first formed product 6 in a direction perpendicular to the first direction. As a result, the first forming operation allows an increase in the density and strength of the first formed product 6, and the second forming operation allows the coated magnet powder particles 5 to expand in the third direction, which makes the crystal orientation anisotropic.

[0087] In some cases, Figure 1 the second forming operation shown in (E) of is performed by using a thermoplastic forming process, which results in plastic deformation of the first formed product 6 at a high temperature. As a result, the crystal grains rotate to allow the corresponding easy magnetization axes to point in the second direction, which is the pressing direction; that is, to allow the corresponding easy magnetization axes to align with each other, which allows the crystal orientation to be effectively made anisotropic. In addition, this feature allows the structure of the rare earth magnet 1 to become dense, reducing internal defects, thereby improving the strength and hardness of the rare earth magnet 1.

[0088] In some cases, the second forming operation is performed at a temperature higher than the temperature at which the first forming operation is performed. As a result, a liquid phase is more likely to form at the grain boundaries, which allows the crystal orientation to be effectively made anisotropic. This feature also allows the rare earth magnet powder particles 2 to plastically deform at a high compaction rate.

[0089] Some embodiments of the present invention have been described. However, the present invention is not limited to these specific embodiments and can be implemented through various modifications. For example, in the above embodiments, since the rare earth magnet 1 has a rectangular prism shape, as Figure 1As shown in (D), the first molded product 6 is rotated 90 degrees. However, as mentioned above, the rotation angle is not limited to this angle. For example, when the first molded product 6 presents an octagonal shape as viewed horizontally, the rotation angle may be 90 degrees or 45 degrees. When the first molded product 6 presents a 16-sided polygonal shape as viewed horizontally, the rotation angle may be any one of 22.5 degrees, 45 degrees, 67.5 degrees or 90 degrees. When the first molded product 6 presents a circular shape as viewed horizontally, the rotation angle may be any angle between 0 degrees and 180 degrees. Generally, without departing from the scope of the present invention, various changes and modifications may be made to the features of the embodiment, such as the specific configuration, position, quantity and material of each component or element in the embodiment. In the above-mentioned embodiment, not all elements included therein are required. Therefore, various modifications may be made to the embodiment as appropriate, including eliminating some elements.

Claims

1. A rare earth magnet comprising coated magnet powder particles, each of the coated magnet powder particles comprising a flaky rare earth magnet powder particle and a coating of an insulating material on a surface of the rare earth magnet powder particle, in, The rare earth magnet has a magnetization direction, and In the embodiment, in a transverse plane perpendicular to the magnetization direction, an average size of the rare earth magnet powder particles in a first direction is shorter than an average size in a third direction perpendicular to the first direction.

2. The rare earth magnet according to claim 1, wherein In a cross section of the rare earth magnet extending in the magnetization direction at a cutting angle defined in the transverse plane, the average size of the rare earth magnet powder particles in a direction perpendicular to the magnetization direction varies with the cutting angle of the cross section, so that the average size has two peaks at cutting angles in the range of 0 degrees to 360 degrees.

3. The rare earth magnet according to claim 1 or 2, wherein The insulating material is an alkali metal fluoride or an alkaline earth metal fluoride.

4. A method for manufacturing a rare earth magnet, comprising the following steps: adding an insulating material to magnetic powder particles to produce coated magnet powder particles, so that each of the coated magnet powder particles includes a flaky rare earth magnet powder particle and a coating of the insulating material on a surface of the rare earth magnet powder particle; performing a first molding operation, the first molding operation comprising the steps of placing the coated magnet powder particles in a mold configured to allow pressurization in a first direction, and applying pressure in the first direction to the coated magnet powder particles in the mold, thereby compressively deforming the coated magnet powder particles to produce a first molded product; and A second molding operation is performed, the second molding operation including applying pressure to the first molded product in a second direction intersecting the first direction, thereby plastically deforming the first molded product to produce the rare earth magnet.

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

6. The method for manufacturing a rare earth magnet according to claim 5, wherein: The first molding operation includes the steps of: pressing the coated magnet powder particles while restricting deformation of the coated magnet powder particles in a direction perpendicular to the first direction, and Wherein, the second molding operation includes the following steps: pressing the first molded product without restricting deformation of the first molded product in a direction perpendicular to the second direction.

7. The method for manufacturing a rare earth magnet according to claim 4, wherein: The second molding operation is performed by using a thermoplastic molding process that causes the first molded product to be plastically deformed at a high temperature.

8. The method for manufacturing a rare earth magnet according to claim 4, wherein: The second molding operation is performed at a higher temperature than the temperature at which the first molding operation is performed.

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