Method for manufacturing multipolar magnet

Abstract

This method for manufacturing a multipolar magnet comprises: a first step for changing the distribution of a rare-earth-based material in a hot-worked magnet (10) that has a plurality of magnetic powders containing said rare-earth-based material; and a second step for magnetizing the hot-worked magnet (10) that has undergone the first step, and obtaining a multipolar magnet (20) comprising a plurality of magnetic pole portions. In the first step, it is preferable to increase the amount of the rare earth-based material interposed between the plurality of magnetic powders to change the distribution of the rare-earth-based material in the hot-worked magnet (10). In the first step, it is more preferable to heat the hot-worked magnet (10) at a predetermined temperature to change the distribution of the rare-earth-based material in the hot-worked magnet (10).

Description

Manufacturing method for multi-pole magnet

[0001] The present invention relates to a method for manufacturing a multi-pole magnet.

[0002] Patent Document 1 describes a method for manufacturing a permanent magnet rotor, which has a rotation axis at the center of an iron core and includes pre-magnetized magnets in the iron core, and which heats and then magnetizes the pre-magnetized magnets, wherein the pre-magnetized magnets are neodymium magnets made of fine crystal grains with an average crystal grain size of 0.1 to 3.5 μm, and the method includes a heating step of heating the permanent magnet rotor within a range of at least a specific temperature (Ta°C) at which complete magnetization is achieved and at most a specific temperature (Tb°C) at which irreversible demagnetization occurs, to obtain a post-heated permanent magnet, and a magnetization step of magnetizing the post-heated permanent magnet to a magnetization rate of 98% or more.

[0003] Japanese Patent Application Laid-Open No. 2021-083288

[0004] However, the magnetization method of Patent Document 1 does not allow for the production of a multi-pole magnet that is strongly magnetized at a narrow pitch.

[0005] Therefore, an object of the present invention is to provide a method for manufacturing a multi-pole magnet that can produce a multi-pole magnet that is strongly magnetized at a narrow pitch.

[0006] In order to solve the above-mentioned problems and achieve the objectives, one embodiment of the present invention provides a method for manufacturing a multi-pole magnet, comprising: a first step of changing the distribution of the rare earth-based material in a hot-processed magnet having a plurality of magnetic powders containing the rare earth-based material; and a second step of magnetizing the hot-processed magnet that has undergone the first step to obtain a multi-pole magnet having a plurality of magnetic pole portions.

[0007] According to a method for manufacturing a multi-pole magnet according to one aspect of the present invention, a multi-pole magnet that is strongly magnetized with a narrow pitch can be obtained.

[0008] FIG. 1 is a diagram for explaining the magnetization in the second step in the manufacturing method of a multi-pole magnet of embodiment 1. FIG. 2 is a diagram for explaining the multi-pole magnet obtained in the second step in the manufacturing method of a multi-pole magnet of embodiment 1. FIG. 3 is a diagram for explaining the magnetization in the second step in the manufacturing method of a multi-pole magnet of another embodiment. FIG. 4 is a diagram for explaining the magnetization in the second step in the manufacturing method of a multi-pole magnet of another embodiment. FIG. 5 is a diagram showing the measurement results of the surface magnetic flux for the multi-pole magnet obtained in example 1. FIG. 6 is a diagram showing the measurement results of the surface magnetic flux for the multi-pole magnet obtained in example 2.

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially the same.

[0010] <Embodiment 1> A method for manufacturing a multi-pole magnet of embodiment 1 includes a first step of changing the distribution of the rare earth-based material in a hot-processed magnet having a plurality of magnetic powders containing the rare earth-based material, and a second step of magnetizing the hot-processed magnet that has undergone the first step to obtain a multi-pole magnet having a plurality of magnetic pole portions.

[0011] [First Step] In the first step, a hot-processed magnet having a ring shape and an easy axis of magnetization aligned in the radial direction is used. The hot-processed magnet preferably has a radial thickness of 4 mm or less.

[0012] Hot-worked magnets are obtained from magnetic powder containing rare earth materials. The magnetic powder is obtained, for example, by pulverizing a magnetically isotropic thin ribbon produced by a rapid cooling method. Examples of rare earth materials contained in the magnetic powder include praseodymium (Pr). Other rare earth materials besides praseodymium (Pr) include neodymium (Nd), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The rare earth elements other than Pr may be used singly or in combination of two or more.

[0013] Specifically, in order to obtain a multi-pole magnet with a narrow pitch and strong magnetization in the first embodiment, the magnetic powder is preferably an Nd—Fe (iron)—B (boron) magnetic powder containing Pr. Furthermore, in order to obtain a multi-pole magnet with a narrow pitch and strong magnetization in the first embodiment, the Nd—Fe—B magnetic powder preferably contains Co, with a portion of the Fe (usually less than 50 atomic %) being substituted with Co. The Nd—Fe—B magnetic powder may also contain other elements. Examples of such other elements include titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), copper (Cu), gallium (Ga), and oxygen (O). The other elements may be used singly or in combination of two or more.

[0014] The hot-worked magnet can be produced using the above magnetic powder, for example, by the method described in Heki, "Development of High-Performance Hot-Worked Nd—Fe—B Magnets," J. Jpn. Soc. Powder Metallurgy, 69 (2022) S3-S13 https: / / doi.org / org / 10.2497 / jjspm.69.S3. That is, the above magnetic powder is cold-formed at room temperature, and then hot-formed at approximately 800°C to produce a cylindrical compact with nearly true density. This compact is then subjected to hot plastic working at approximately 800°C. During the hot plastic working, the compact is extruded backward, resulting in a ring-shaped hot-worked magnet with anisotropy.

[0015] In the first step, the hot-worked magnet is heated, for example, from room temperature to a predetermined temperature (i.e., a temperature above the Curie temperature of the magnetic powder). Specifically, in the first step, the amount of rare earth material present between the magnetic powder particles is increased, thereby changing the distribution of the rare earth material in the hot-worked magnet. More specifically, the amount of Pr present between the magnetic powder particles is increased, thereby changing the distribution of the rare earth material in the hot-worked magnet. By performing this first step, a multi-pole magnet with a narrow pitch and strong magnetization is finally obtained. While Pr is used as an example of the rare earth material present between the magnetic powder particles, this is not limiting. Specifically, La, Ce, Pr, Nd, PrNd (didymium), or a mixture of these elements may also be used.

[0016] [Second Step] In the second step, the hot-processed magnet that has undergone the first step is magnetized in multiple poles in the radial direction to obtain a multi-pole magnet. Similar to the hot-processed magnet, the multi-pole magnet also has a ring shape and is provided with multiple magnetic poles in the circumferential direction. Specifically, the multiple magnetic poles include 20 or more magnetic poles.

[0017] Magnetization can be performed by UHM magnetization, such as that disclosed in JP 2021-093521 A. That is, the hot-worked magnet, which is the object to be magnetized, is heated to a temperature equal to or higher than the Curie temperature of the magnetic powder contained therein (for example, 250°C or higher and 500°C or lower), and a magnetizing magnetic field is continuously applied to the object to be magnetized by a permanent magnet, which is the field source, while the object is cooled to below the Curie temperature.

[0018] FIG. 1 is a diagram illustrating the magnetization step in the second step of the manufacturing method for a multi-pole magnet according to the first embodiment. FIG. 2 is a diagram illustrating the multi-pole magnet obtained in the second step of the manufacturing method for a multi-pole magnet according to the first embodiment. An outer jig 110 and an inner jig 120 are used to magnetize the hot-worked magnet 10. The outer jig 110 is made of a non-magnetic metal material and is cylindrical. The outer jig 110 has an insertion hole 112 into which the hot-worked magnet 10 is inserted. The permanent magnet 114 is embedded radially on the side of the insertion hole 112 of the outer jig 110 and is used to generate a magnetic field for the hot-worked magnet 10. The permanent magnet 114 is, for example, a rectangular SmCo magnet. When viewed from above and below, the permanent magnets 114 are formed in a concentric circle centered on the center of the outer jig 110, and a plurality of them (for example, 20 or more; in FIG. 1 , 28 permanent magnets are shown as an example) are arranged at equal intervals in the circumferential direction.

[0019] The inner jig 120 is made of a non-magnetic metal material and is formed in a cylindrical shape. The permanent magnets 124 are, for example, rectangular SmCo magnets, and are embedded radially on the outer periphery of the inner jig 120 to generate a magnetic field for the hot-worked magnet 10. When viewed from above and below, the permanent magnets 124 are formed concentrically around the center of the inner jig 120, and multiple permanent magnets 124 (for example, 20 or more, 28 in FIG. 1 as an example) are arranged at equal intervals in the circumferential direction.

[0020] During magnetization, the hot-processed magnet 10 that has undergone the first step is sandwiched between an outer jig 110 and an inner jig 120. Specifically, for the hot-processed magnet 10 that has been heated to or above the Curie temperature of the magnetic powder in the first step, the outer jig 110 is placed on the outer periphery of the hot-processed magnet 10, and the inner jig 120 is placed on the inner periphery. Then, application of a magnetizing magnetic field by the permanent magnets 114, 124, which serve as field sources, begins. The permanent magnets 114, 124 of the outer jig 110 and the inner jig 120 are arranged so that the magnetizing magnetic field is applied in the direction indicated by the arrow in FIG. 1 . In other words, adjacent permanent magnets 114, 124 are arranged so that the magnetizing magnetic field is applied in opposite directions. In this state, while the hot-processed magnet 10 is cooled to below the Curie temperature (for example, room temperature), a magnetizing magnetic field is continuously applied by the permanent magnets 114, 124, which serve as field sources, to magnetize the hot-processed magnet 10. As a result, a multi-pole magnet 20 is obtained as the magnetized hot-processed magnet 10. In FIG. 2, the multi-pole magnet 20 has 28 magnetic pole portions in the circumferential direction. In this way, in embodiment 1, the second process is performed on the hot-processed magnet that has undergone the first process, and therefore a multi-pole magnet that is strongly magnetized with a narrow pitch is obtained.

[0021] <Embodiment 2> In Embodiment 1, the second step is performed after the first step. In contrast, in Embodiment 2, the first and second steps may be performed simultaneously. Specifically, the hot-worked magnet 10 is placed between the outer jig 110 and the inner jig 120, and the application of a magnetizing magnetic field by the permanent magnets 114, 124, which serve as field sources, begins. Next, the hot-worked magnet is heated, for example, from room temperature until it reaches a predetermined temperature (i.e., a temperature equal to or higher than the Curie temperature of the magnetic powder). Next, while the hot-worked magnet 10 is cooled to below the Curie temperature (e.g., room temperature), the magnetizing magnetic field is continuously applied by the permanent magnets 114, 124, which serve as field sources, to magnetize the hot-worked magnet 10. In this case, a multi-polar magnet 20 is obtained as the magnetized hot-worked magnet 10.

[0022] <Other Embodiments> In the first and second embodiments, the number of permanent magnets 114 on the outer periphery jig 110 is the same as the number of permanent magnets 124 on the inner periphery jig 120. However, the number of permanent magnets 114 on the outer periphery jig 110 may be different from the number of permanent magnets 124 on the inner periphery jig 120. In other words, the manufacturing method of a multi-pole magnet according to the embodiments may be used to manufacture a multi-pole magnet 20 in which the number of magnetic pole portions on the inner periphery is different from the number of magnetic pole portions on the outer periphery.

[0023] 3 and 4 are diagrams illustrating the magnetization step in the second step in the manufacturing method of a multi-pole magnet according to other embodiments. In embodiments 1 and 2, an outer jig 110 and an inner jig 120 are used in the second step. However, it is also possible to use only the outer jig 110 as shown in FIG. 3, or only the inner jig 120 as shown in FIG. 4. In these cases, too, a magnetizing magnetic field is applied in the direction shown by the arrows in FIGS. 3 and 4, and a multi-pole magnet is obtained in the same way as in embodiments 1 and 2.

[0024] The multi-pole magnet obtained by the above-described embodiment is suitable for use in servo motors, low-frequency generators, magnetic gears, and the like.

[0025] The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples.

[0026] [Examples] [Example 1] In the first step, a hot-worked magnet having a ring shape and an easy axis of magnetization aligned in the radial direction was used. The hot-worked magnet had a radial thickness of 4 mm or less. The hot-worked magnet was obtained from magnetic powder containing a rare earth material. That is, the magnetic powder was an Nd—Fe (iron)—B (boron) magnetic powder containing Pr. Furthermore, a portion of the Fe (usually less than 50 atomic %) was substituted with Co, and the hot-worked magnet contained Co. The hot-worked magnet was produced using the above magnetic powder, as described in Heki, "Development of High-Performance Hot-Worked Nd—Fe—B Magnets," J. Jpn. Soc. Powder Powder Metallurgy, 69 (2022) S3-S13 https: / / doi.org / 10.2497 / jjspm.69. The magnet was produced by the method described in S3. That is, it was a hot-processed magnet obtained by the following method. The magnetic powder was cold-formed at room temperature, and then hot-formed at about 800°C to produce a cylindrical compact with nearly true density. This compact was then subjected to hot plastic working at about 800°C. During the hot plastic working, the magnet was extruded backward, resulting in a ring-shaped hot-processed magnet with anisotropy.

[0027] In the first step, the hot-processed magnet was heated from room temperature to a temperature (400°C) above the Curie temperature (370°C) of the magnetic powder. The second step was started while maintaining this heated state. That is, as shown in FIG. 1 , for the hot-processed magnet 10 heated to 400°C in the first step, an outer jig 110 was placed on the outer periphery of the hot-processed magnet 10, and an inner jig 120 was placed on the inner periphery. Then, application of a magnetizing magnetic field by permanent magnets 114, 124, which serve as field sources, was started. In this state, while the hot-processed magnet 10 was cooled to room temperature, a magnetizing magnetic field was continuously applied by the permanent magnets 114, 124, which serve as field sources, to magnetize the hot-processed magnet 10. However, in Example 1, unlike FIG. 1 , the permanent magnets 114 were formed concentrically around the center of the outer jig 110 when viewed from above and below, and 24 permanent magnets 114 were arranged at equal intervals circumferentially. Furthermore, when viewed from above and below, the permanent magnets 124 were formed concentrically around the center of the inner jig 120, with 24 permanent magnets arranged at equal intervals in the circumferential direction. In this way, a multi-pole magnet 20 was obtained as the hot-worked magnet 10 after magnetization. The multi-pole magnet 20 had 24 magnetic pole portions in the circumferential direction.

[0028] [Example 2] In the first step, a hot-processed magnet having a ring shape and an easy axis of magnetization aligned in the radial direction was used. The hot-processed magnet had a radial thickness of 4 mm or less. The hot-processed magnet was the same as that used in Example 1.

[0029] In the first step, the hot-processed magnet was heated from room temperature to a temperature (400°C) above the Curie temperature (370°C) of the magnetic powder. The second step was started while maintaining this heated state. That is, as shown in FIG. 1 , for the hot-processed magnet 10 heated to 400°C in the first step, an outer jig 110 was placed on the outer periphery of the hot-processed magnet 10, and an inner jig 120 was placed on the inner periphery. Then, application of a magnetizing magnetic field by permanent magnets 114, 124, which serve as field sources, was started. In this state, while the hot-processed magnet 10 was cooled to room temperature, a magnetizing magnetic field was continuously applied by the permanent magnets 114, 124, which serve as field sources, to magnetize the hot-processed magnet 10. However, in Example 2, unlike FIG. 1 , the permanent magnets 114 were formed in concentric circles around the center of the outer jig 110 when viewed from above, and 100 of them were arranged at equal intervals circumferentially. Furthermore, when viewed from above and below, the permanent magnets 124 were formed concentrically around the center of the inner jig 120, with 100 of them arranged at equal intervals in the circumferential direction. In this way, a multi-pole magnet 20 was obtained as the hot-worked magnet 10 after magnetization. The multi-pole magnet 20 had 100 magnetic pole portions in the circumferential direction.

[0030] [Distribution of Rare Earth Material] In the first step, we confirmed that the distribution of rare earth material in a hot-worked magnet containing multiple magnetic powders containing rare earth material changed. In Example 1, the amount of rare earth material interposed between multiple magnetic powders was examined for the hot-worked magnet before the first step (before heating) and after the first step (after heating). First, the hot-worked magnet before the first step (before heating) was divided in half axially. Elemental analysis was performed on the divided cross section using an electron probe microanalyzer (EPMA). Specifically, analysis was performed on the gaps between magnetic particles on the inner periphery (near the inner periphery) and at the center (a portion equidistant from the inner and outer peripheries of the divided hot-worked magnet). Next, similar to the above, the hot-worked magnet after the first step (after heating) was divided axially. Elemental analysis was performed on the divided cross section using an electron probe microanalyzer (EPMA). Specifically, analysis was performed on the gaps between magnetic particles on the inner periphery (near the inner periphery) and at the center (the portion equidistant from the inner and outer peripheries of the divided hot-processed magnet). Table 1 shows the detected elements and their amounts (wt%). The amounts of each element are the average values ​​measured at 10 locations between magnetic particles.

[0031]

[0032] It was confirmed that the amount of Pr present between the magnetic powder particles increased due to the heating in the first step, both on the inner circumferential side and in the central portion.

[0033] [Surface magnetic flux] The surface magnetic flux (Flux (mT)) was measured for the multi-pole magnet obtained in Example 1 and the multi-pole magnet obtained in Example 2. Specifically, an ultra-fine probe (manufactured by DMT Corporation) was used to carry out the evaluation with a Hall element size of 50 μm and a magnet-element distance of 0.14 mm. Figure 5 shows the results of measuring the surface magnetic flux for the multi-pole magnet obtained in Example 1. Figure 6 shows the results of measuring the surface magnetic flux for the multi-pole magnet obtained in Example 2. It was confirmed that the multi-pole magnets obtained in Examples 1 and 2 were strongly magnetized with a narrow pitch.

[0034] ​10 hot-worked magnet, 110 outer circumferential jig, 112 insertion hole, 114 permanent magnet, 120 inner circumferential jig, 124 permanent magnet, 20 multi-pole magnet

Claims

1. A method for manufacturing a multi-pole magnet, comprising: a first step of changing the distribution of rare earth-based material in a hot-processed magnet having a plurality of magnetic powders containing the rare earth-based material; and a second step of magnetizing the hot-processed magnet that has undergone the first step to obtain a multi-pole magnet having a plurality of magnetic pole portions.

2. The method for manufacturing a multi-pole magnet according to claim 1, wherein in the first step, the amount of rare earth material present between the plurality of magnetic powder particles is increased to change the distribution of the rare earth material in the hot-worked magnet.

3. A method for manufacturing a multi-pole magnet according to claim 1 or 2, wherein in the first step, the hot-worked magnet is heated at a predetermined temperature to change the distribution of the rare earth material in the hot-worked magnet.

4. The method for manufacturing a multi-pole magnet according to claim 3, wherein in the first step, the hot-worked magnet is heated to a temperature equal to or higher than the Curie temperature of the magnetic powder as the predetermined temperature, thereby changing the distribution of the rare earth material in the hot-worked magnet.

5. A method for manufacturing a multi-pole magnet as described in claim 4, wherein in the first step, the distribution of the rare earth material in the hot-processed magnet is changed, the hot-processed magnet having a ring shape and an easy axis of magnetization oriented in the radial direction, and in the second step, the hot-processed magnet that has undergone the first step is magnetized in multiple poles in the radial direction, thereby obtaining a multi-pole magnet having 20 or more magnetic pole portions as the multiple magnetic pole portions in the circumferential direction.

6. The method for manufacturing a multi-pole magnet according to claim 5, wherein in the first step, the distribution of the rare earth material in the hot-worked magnet having a radial thickness of 4 mm or less is changed.

7. A method for manufacturing a multi-pole magnet as set forth in claim 2, wherein in the first step, the amount of one or more of Pr, La, Ce, Nd, and PrNd is increased as the rare earth material present between the plurality of magnetic powder particles, thereby changing the distribution of the rare earth material in the hot-worked magnet.

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