Magnetic body, rotary apparatus, and method for manufacturing magnetic body

Abstract

Provided is a magnetic body excellent in magnetic force characteristics, a rotary apparatus including the magnetic body, and a method for manufacturing the magnetic body.　A magnet (10) includes a plurality of magnetic particles, has a cylindrical shape extending in an axial direction, and is provided with an end surface (11) facing the axial direction. The end surface (11) is provided with an inner layer (12) and an outer layer (13) in a radial direction. The outer layer (13) and the inner layer (12) are provided with a plurality of magnetic poles (19) in a circumferential direction. The relative density of the magnetic particles exceeds 95%. The inner layer (12) and the outer layer (13) are separated from each other in the radial direction by a boundary (14) defining the inner layer (12) and the outer layer (13).

Description

Magnetic body, rotating device, and method for manufacturing magnetic body

[0001] The present invention relates to a magnetic body, a rotating device, and a method for manufacturing a magnetic body.

[0002] As the magnetic body, a rare earth magnet using a rare earth element is known (for example, see Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2016-081942

[0004] In order to meet the need for higher performance of rotating devices such as motors, it is required to improve magnetic force characteristics such as the surface magnetic flux density of the magnetic body.

[0005] Therefore, an example of an object of the present invention is to provide a magnetic body having excellent magnetic force characteristics, a rotating device including the magnetic body, and a method for manufacturing the magnetic body.

[0006] (1): The magnetic body of the present invention includes a plurality of magnetic particles, is cylindrical and extends in the axial direction, has an end face facing the axial direction, the end face includes an inner layer and an outer layer in the radial direction, the outer layer and the inner layer include a plurality of magnetic poles in the circumferential direction, the relative density of the magnetic particles exceeds 95%, and in the radial direction, the inner layer and the outer layer are separated with a boundary defining the inner layer and the outer layer as a boundary.

[0007] (2): In the magnetic body of (1), the inner peripheral edge of the end face may be rounder than the outer peripheral edge of the end face.

[0008] (3): In the magnetic body of (1), the outer peripheral edge of the end face may be rounder than the inner peripheral edge of the end face.

[0009] (4): In any of the magnetic bodies of (1) to (3), the residual magnetic flux density of the end face in the axial direction may be larger than the residual magnetic flux density of the outer surface in the radial direction.

[0010] (5): In any of the magnetic bodies of (1) to (4), the plurality of magnetic particles may have a portion oriented in a direction intersecting the axial direction.

[0011] (6): In any of the magnetic materials described in (1) to (5), the inner layer and the outer layer may be formed by plastic deformation.

[0012] (7): The rotating device of the present invention comprises a rotor having any of the magnetic materials (1) to (6) and a stator facing the rotor.

[0013] (8) The present invention provides a method for manufacturing a magnetic material, comprising the steps of: sintering a plurality of magnetic particles to form a sintered body; and plastically deforming the sintered body to form a plastic body, wherein in the step of forming the plastic body, an inner layer of plastic material and an outer layer of plastic material are formed on the end face of the plastic body facing in the axial direction.

[0014] (9) In the method for manufacturing the magnetic material of (8), the step of forming the plastic body may include a step of heating at a temperature equal to or higher than the liquid phase formation temperature of the magnetic particles.

[0015] (10): In the method for manufacturing a magnetic material according to (9), the temperature may be 650°C or higher.

[0016] (11): The magnetic material of the present invention is a magnetic material comprising a plurality of magnetic particles, wherein the magnetic material is a cylinder extending in the axial direction, the cylinder has an outer circumferential surface and an inner circumferential surface, the outer circumferential surface or the inner circumferential surface has a plurality of magnetic poles arranged in the circumferential direction, the relative density of the magnetic particles exceeds 95%, the outer circumferential surface or the inner circumferential surface has a region in the radial direction where the distance from the outer circumferential surface to the inner circumferential surface is short, and the region with a long distance is between the plurality of magnetic poles formed in the region with a short distance.

[0017] (12): In the magnetic material of (11), there may be a boundary in the circumferential direction between the region with a short distance and the region with a long distance.

[0018] (13): In the magnetic material of (11) or (12), the region with a shorter distance may be more anisotropic than the region with a longer distance.

[0019] (14): In any of the magnetic materials from (11) to (13), the plurality of magnetic particles may have portions oriented in directions intersecting the axial direction.

[0020] (15): In any of the magnetic materials from (11) to (14), the region with the short distance may be formed by plastic deformation.

[0021] (16): The rotating device of the present invention comprises a rotor having any of the magnetic materials (11) to (15), and a stator facing the rotor.

[0022] (17): The present invention provides a method for manufacturing a magnetic material, comprising the steps of: sintering a plurality of magnetic particles to form a sintered body; and plastically deforming the sintered body to form a plastic body, wherein the method also includes the step of forming a region on the radially oriented outer or inner surface of the plastic body in which the distance from the outer surface to the inner surface is short and a region in which the distance is long, and magnetizing the plastic body such that the region with the short distance becomes the pole.

[0023] (18): In the method for manufacturing a magnetic material according to (17), the step of forming the plastic body may include a step of heating at a temperature equal to or higher than the liquid phase formation temperature of the magnetic particles.

[0024] (19): In the method for manufacturing the magnetic material of (18), the temperature may be 650°C or higher.

[0025] Figure 2 is a schematic cross-sectional view showing a part of an example of a rotating device equipped with a magnetic material according to the first embodiment. Figure 3 is a schematic perspective view showing the magnetic material according to the first embodiment. Figure 4 is a cross-sectional view along the axial direction of the magnetic material shown in Figure 2. Figure 5 is a diagram for explaining the magnetization of the magnetic material shown in Figure 2. Figure 5 is a flowchart for explaining the manufacturing method of the magnetic material. Figure 5 is a diagram for explaining the second step. Figure 5 is a diagram for explaining the initial stage of the third step. Figure 5 is a diagram for explaining the final stage of the third step. Figure 5 is a cross-sectional view along the axial direction of the magnetic material according to the second embodiment. Figure 5 is a diagram for explaining the initial stage of the third step in the manufacturing method of the magnetic material according to the second embodiment. Figure 6 is a diagram for explaining the final stage of the third step in the manufacturing method of the magnetic material according to the second embodiment. Figure 7 is a schematic view showing the magnetic material according to the third embodiment with a line of sight in the axial direction. Figure 8 is a cross-sectional view along the axial direction for explaining the initial stage of the third step in the manufacturing method of the magnetic material according to the third embodiment. Figure 9 is a cross-sectional view along the axial direction for explaining the third step in the manufacturing method of the magnetic material according to the third embodiment. Figure 10 is a schematic view showing the magnetic material according to the fourth embodiment with a line of sight in the axial direction. Figure 10 is a cross-sectional view along the axial direction for explaining the initial stage of the third step in the manufacturing method of the magnetic material according to the fourth embodiment. This is a radial cross-sectional view illustrating the third step in the manufacturing method of a magnetic material according to the fourth embodiment. This is a diagram based on a photograph of the first plastic body according to the embodiment. This is a diagram obtained by removing the dashed lines indicating the boundary from the photograph in Figure 19. This is a diagram based on a photograph of the second plastic body according to the embodiment. This is a diagram obtained by removing the dashed lines indicating the boundary from the photograph in Figure 20. This is a graph illustrating the surface magnetic flux density (magnetic properties) of the magnetic material according to the embodiment. This is a graph illustrating the magnetostatic properties of the magnetic material according to the embodiment in the magnetization direction. This is a graph illustrating the magnetostatic properties of the magnetic material according to the embodiment in the perpendicular direction.

[0026] The following examples illustrate embodiments for carrying out the magnetic material, rotating device, and method for manufacturing the magnetic material according to the present invention, with reference to the accompanying drawings. The embodiments illustrated below are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved from the following embodiments without departing from its spirit. In addition, in the accompanying drawings, the dimensions of each component may be exaggerated or reduced, or hatching may be omitted, in order to facilitate understanding.

[0027] (First Embodiment) Figure 1 is a schematic cross-sectional view showing a part of an example of a rotating device equipped with a magnetic material according to the first embodiment. More specifically, Figure 1 is a cross-sectional view showing a part of a motor 1, which is an example of a motor as a rotating device.

[0028] As shown in Figure 1, the motor 1 comprises a housing 2 (motor case), a shaft 3, a bearing Be, a stator 4, and a rotor 8. Hereinafter, the direction in which the shaft 3 extends will be referred to as the "axial direction." The direction that intersects the central axis of the shaft 3 and is perpendicular to the axial direction will be referred to as the "radial direction." In the radial direction, the side closer to the central axis of the shaft 3 may be referred to as the "inside," and the side further from the central axis of the shaft 3 may be referred to as the "outside." In addition, the circumferential direction of a circle centered on the central axis of the shaft 3 may be referred to as the "circumferential direction."

[0029] The housing 2 is a cylindrical (in this embodiment, cylindrical) member extending in the axial direction, and may be made of a magnetic material such as iron. The radial center of the housing 2 may coincide with the central axis of the shaft 3. Bearings Be are arranged on both sides of the housing 2 in the axial direction. The shaft 3 is rotatably supported by the bearings Be relative to the housing 2 and the stator 4.

[0030] The stator 4 includes a stator core 5, an insulator 6, and a plurality of coils 7. The stator core 5 may be constructed, for example, by laminating a plurality of electromagnetic steel sheets (a plurality of magnetic materials) in the axial direction, or by applying pressure to magnetic iron powder to solidify it, or by being made of amorphous material. The stator core 5 is fixed to the inner circumferential surface of the housing 2. The insulator 6 covers the stator core 5 such that the inner circumferential surface of the stator core 5 is exposed from the insulator 6, and is fixed to the stator core 5. The plurality of coils 7 are arranged at predetermined intervals in the circumferential direction and are wound around the stator core 5 via the insulator 6. This insulates the plurality of coils 7 from the stator core 5. The plurality of coils 7 may be electrically connected to a circuit board (not shown) provided in the housing 2.

[0031] The rotor 8 is positioned radially inward relative to the stator 4. Thus, although an inner rotor type motor is shown in Figure 1, the motor, being a rotating device, may also be an outer rotor type motor. The rotor 8 comprises a rotor yoke 9 and a magnet 10 (permanent magnet) as a magnetic material. The rotor yoke 9 may be made of a magnetic material and has a cylindrical shape with a bottom. The rotor yoke 9 is fixed to the shaft 3. Therefore, the rotor yoke 9 rotates together with the shaft 3 around the central axis of the shaft 3. The magnet 10 (magnetic material) has a cylindrical shape (cylindrical in this embodiment) and is fixed to the outer circumferential surface of the rotor yoke 9. The outer circumferential surface of the magnet 10 faces the inner circumferential surface of the stator core 5 radially, with an air gap between them. Therefore, when current is supplied to the multiple coils 7, a magnetic interaction occurs between the stator core 5 and the magnet 10, causing the shaft 3 and rotor 8 to rotate.

[0032] As will be described later, the magnet 10 has excellent magnetic properties. Therefore, the motor 1 equipped with the magnet 10 can exhibit high performance in terms of output, torque, and efficiency. The magnet 10 as a magnetic material will be described in detail below.

[0033] The magnet 10 contains multiple magnetic particles and is also called a bulk magnet or binderless magnet. Figure 2 is a schematic perspective view of the magnet 10 (magnetic material). Figure 3 is a cross-sectional view of the magnet 10 (magnetic material) along the axial direction.

[0034] As shown in Figures 2 and 3, the magnet 10 comprises an outer circumferential surface 15, an inner circumferential surface 16, and two end faces 11 in the axial direction (facing in the axial direction). The two end faces 11 are one end face 11A and the other end face 11B in the axial direction. Here, one side in the axial direction becomes the upper side in the vertical direction in the manufacturing method of the magnetic material (magnet) described later, and the other side in the axial direction becomes the lower side in the vertical direction in the manufacturing method of the magnetic material (magnet) described later. Hereinafter, one side in the axial direction may be referred to as "upper," and the end face 11A on that side may be referred to as "upper end face 11A." Also, the other side in the axial direction may be referred to as "lower," and the end face 11B on the other side may be referred to as "lower end face 11B." The upper end surface 11A connects the upper end of the outer circumferential surface 15 and the upper end of the inner circumferential surface 16 in the radial direction, and the lower end surface 11B connects the lower end of the outer circumferential surface 15 and the lower end of the inner circumferential surface 16 in the radial direction.

[0035] Focusing on the upper end surface 11A, the first connection portion 18 where the inner circumferential surface 16 and the upper end surface 11A connect forms a substantially 90° angle, whereas the second connection portion 17 where the outer circumferential surface 15 and the upper end surface 11A connect does not form an angle and is rounded. In other words, the second connection portion 17 (the outer edge of the upper end surface 11A) is rounder than the first connection portion 18 (the inner edge of the upper end surface 11A).

[0036] As shown in Figure 2, the end face 11 comprises an inner layer 12 (hereinafter sometimes referred to as "inner layer 12") and an outer layer 13 (hereinafter sometimes referred to as "outer layer 13") in the radial direction. Specifically, the inner layer 12 and the outer layer 13 are separated at the end face 11 by a boundary 14 that defines the inner layer 12 and the outer layer 13 in the radial direction. When viewed with a line of sight in the axial direction, the boundary 14 can be seen as a linear ring that is generally concentric with the outer circumferential surface 15 and the inner circumferential surface 16.

[0037] Figure 4 is a diagram illustrating the magnetization of the magnet 10. As shown in Figure 4, the magnet 10 has multiple magnetic poles 19 in the circumferential direction. The multiple magnetic poles 19 are formed continuously in the circumferential direction of the magnet 10. Focusing on a pair of adjacent magnetic poles 19, 19 in the circumferential direction, on one side of the magnetic pole 19, the inner portion is magnetized to one pole p1 of N and S, and the outer portion is magnetized to the other pole p2 of N and S. On the other side of the magnetic pole 19, the inner portion is magnetized to the other pole p2, and the outer portion is magnetized to one pole p1. Therefore, the inner layer 12 and outer layer 13 of the end face 11 have multiple magnetic poles 19.

[0038] Next, we will explain how to manufacture the magnet 10 (magnetic material).

[0039] Figure 5 is a flowchart illustrating the manufacturing method Ps for the magnet 10 (magnetic material). As shown in Figure 5, the manufacturing method Ps for the magnetic material comprises a first step St1, a second step St2, a third step St3, and a fourth step St4.

[0040] Step 1, St1, is a compounding process in which a compound is produced by mixing rare-earth iron-based magnetic powder, which is a magnetic particle, with a binder.

[0041] The rare earth iron-based magnet powder preferably contains at least Nd as a rare earth element, for example, Nd-Fe-B magnet powder. Nd-Fe-B magnet powder usually further contains a rare earth-rich phase (Nd-rich phase), etc. Nd-Fe-B magnet powder may be used alone or in combination of two or more types. The rare earth iron-based magnet powder may also contain rare earth elements other than Nd. Examples of rare earth elements other than Nd include praseodymium (Pr), 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). Furthermore, in Nd-Fe-B magnetic powder, Fe may be partially (usually less than 50 atomic percent) substituted with Co. Nd-Fe-B magnetic powder may also contain other elements. Examples of other elements include titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), copper (Cu), and gallium (Ga). These other elements may be used individually or in combination of two or more.

[0042] By mixing a binder with magnetic particles to create a compound, it becomes easier to increase the density of the magnetic powder and mold it into a desired shape (for example, a thin-walled cylindrical shape with a thickness of 1 mm to several mm). The binder is not particularly limited as long as it exhibits this effect, but polystyrene is particularly preferred as the binder. This is because rare earth magnetic powders tend to oxidize relatively easily, while polystyrene does not contain oxygen, thus suppressing the oxidation of the rare earth magnetic powder.

[0043] In the first step St1, first, a binder is dissolved in an organic solvent to prepare a resin solution. Here, the organic solvent is not particularly limited as long as it can dissolve the binder and evaporates during drying. For example, methyl ethyl ketone may be used as the organic solvent. Next, the resin solution in which the binder is dissolved and rare earth iron-based magnet powder (magnetic particles) are kneaded. Then, the kneaded product obtained by kneading is dried to evaporate the organic solvent, and then pulverized. The pulverized product obtained by pulverization is classified to obtain a compound. In this compound, the relative density (or volume %) of the magnetic particles may be about 80%.

[0044] After the first step St1, a second step St2 is performed. The second step St2 is a step of sintering a plurality of magnetic particles contained in the compound to form a sintered body. FIG. 6 is a diagram for explaining the second step St2.

[0045] As shown in FIG. 6, in the second step St2, a mold 50 is prepared. The mold 50 includes a lower punch 51, a core 52, an upper punch 53, and a die 54. The lower punch 51, the upper punch 53, the die 54, and the core 52 may be formed of a conductive material (for example, graphite, cemented carbide, etc.). In FIG. 6, the lower diagram shows a cross section along the axial direction of the mold 50, and the upper diagram shows a cross section of the mold 50 along the line A - A (that is, along the radial direction).

[0046] The lower punch 51 includes a pedestal portion 51A which is the bottom of the mold 50, and a cylindrical tubular portion 51B extending vertically upward from the pedestal portion 51A. The core 52 has a cylindrical shape. The outer diameter of the core 52 and the inner diameter of the tubular portion 51B are substantially equal. The lower portion of the core 52 is fitted into the space inside the tubular portion 51B, and the upper portion of the core 52 protrudes upward from the tubular portion 51B. The die 54 has a cylindrical shape. The inner diameter of the die 54 and the outer diameter of the tubular portion 51B are substantially equal. The lower portion of the inner peripheral surface of the die 54 contacts the upper portion of the outer peripheral surface of the tubular portion 51B. In the mold 50, the upper portion of the tubular portion 51B fits into the lower portion of the cylindrical gap 55 formed between the outer peripheral surface of the core 52 and the inner peripheral surface of the die 54, whereby the die 54 is supported. The width W1 of the gap 55 is substantially equal to the radial distance from the outer peripheral surface of the core 52 to the inner peripheral surface of the die 54.

[0047] The upper punch 53 includes a base 53A having a cylindrical shape, and a cylindrical tubular portion 53B extending vertically downward from the base 53A. The inner diameter of the tubular portion 53B is substantially equal to the outer diameter of the core 52, and the radial width of the tubular portion 53B may be substantially equal to the width W1 of the gap 55 or slightly smaller than the width W1. Therefore, the tubular portion 53B of the upper punch 53 can slide along the axial direction (vertical direction) within the gap 55, whereby the height (vertical (axial) length) of the gap 55 between the lower end surface of the tubular portion 53B and the upper end surface of the tubular portion 51B can be adjusted.

[0048] In the second step St2, the compound C produced in the first step St1 is enclosed in the gap 55 between the outer peripheral surface of the tubular portion 51B, the inner peripheral surface of the die 54, and the upper end surface of the tubular portion 51B, and the tubular portion 53B of the upper punch 53 is inserted into the gap 55 and slid downward, thereby filling the gap 55 with the compound C.

[0049] Next, the mold 50 is placed in the sintering apparatus and the compound C is sintered. The sintering apparatus may be a discharge plasma sintering apparatus (SPS). In this sintering process, the compound C is heated to 600 to 700°C while being pressurized, for example, at 30 to 50 MPa (hot press). Through this sintering process, the binder contained in the compound C is substantially removed, and a sintered body is formed. This sintered body has a cylindrical shape. The thickness of the sintered body is substantially equal to the width W1 of the gap 55. After the sintering process is completed, the mold 50 is removed from the sintering apparatus and the sintered body is removed from the mold 50.

[0050] In sintered bodies produced by the sintering process, the binder is eliminated as described above, so the relative density (or volume %) of magnetic particles in the sintered body exceeds 95%. In other words, the porosity in the sintered body is 5% or less. Thus, the sintered body is formed of high-density magnetic particles and is densified. In a densified sintered body, multiple magnetic particles are randomly oriented. Because such a sintered body is formed of densified oriented components (magnetic particles), it is possible to create a magnetic material with excellent magnetic properties by magnetizing the sintered body.

[0051] The third step, St3, is performed after the second step, St2. The third step, St3, is a process in which the sintered body produced in the second step, St2, is plastically deformed to form a plastic body. Figure 7 is a diagram illustrating the initial stage of the third step, St3. Figure 8 is a diagram illustrating the final stage of the third step, St3.

[0052] As shown in Figures 7 and 8, in the third step St3, a mold 60 is prepared. The mold 60 includes a lower punch 61, a core 62, an upper punch 63, and a die 64. The lower punch 61, upper punch 63, die 64, and core 62 may be made of a conductive material (e.g., graphite, cemented carbide, etc.). In Figures 7 and 8, the lower figure shows a cross-section of the mold 60 along the axial direction, and the upper figure shows a cross-section of the mold 60 along the line A-A (i.e., along the radial direction).

[0053] The lower punch 61, core 62, upper punch 63, and die 64 have a configuration that is generally similar to that of the lower punch 51, upper punch 53, die 54, and core 52 of the mold 50. The lower punch 61 includes a base portion 61A and a cylindrical portion 61B. The upper punch 63 includes a base 63A and a cylindrical portion 63B. The mold 60 differs from the mold 50 in that the width W2 of the cylindrical gap 65 formed between the outer circumferential surface of the core 62 and the inner circumferential surface 64A of the die 64 is greater than the width W1 of the mold 50. Furthermore, the mold 60 differs from the mold 50 in that the outer diameter of the core 62 is substantially equal to the inner diameter of the sintered body S produced in the second step St2, the inner diameter of the die 64 is larger than the inner diameter of the die 54, and the thickness of the cylindrical portions 61B and 63B is substantially equal to the width W2.

[0054] In the third step St3, the first step is the placement step. In this placement step, as shown in Figure 7, the sintered body S is inserted into the gap 65 and the lower end surface Sa of the sintered body S is brought into contact with the upper end surface of the cylindrical portion 61B. Here, since the inner diameter of the sintered body S and the outer diameter of the core 62 are substantially equal, the inner circumferential surface Sc of the sintered body S is in contact with the outer circumferential surface of the core 62. Next, the cylindrical portion 63B of the upper punch 63 is inserted into the gap 65 and the lower end surface of the cylindrical portion 63B is brought into contact with the upper end surface Sb of the sintered body S. In this way, the sintered body S is placed in the gap 65 of the mold 60. At this time, a radial gap 65A is formed between the outer circumferential surface Sd of the sintered body S and the inner circumferential surface 64A of the die 64. The radial length of the gap 65A is substantially equal to the difference between the width W2 and the width W1.

[0055] Next, a hot plastic deformation process is performed. In this hot plastic deformation process, first, the mold 60 in which the sintered body S is placed is placed in the sintering apparatus described above. Then, as shown in Figure 8, the sintered body S is pressed in the axial direction by sliding the upper punch 63 downward, while the sintered body S is heated by the discharge plasma and Joule heat of the sintering apparatus. The pressure applied in the hot plastic deformation process may be 30 to 100 MPa. The heating temperature in the hot plastic deformation process is above the liquid phase formation temperature of the magnetic particles, for example, 650°C or higher. In other words, the hot plastic deformation process includes a step of heating at a temperature above the liquid phase formation temperature of the magnetic particles.

[0056] During this hot plastic deformation process, the sintered body S melts and undergoes plastic deformation. The sintered body S is compressed axially (vertically) while expanding radially outward, and the gap 65A is largely filled by the plastically deformed sintered body S. Here, the outer portion Pe of the upper end of the plastically deformed sintered body S (i.e., the portion in contact with the inner circumferential surface 64A of the die 64) does not form corners due to the influence of gravity and surface tension, and instead has a rounded shape. Furthermore, the magnetic particles in the inner portion of the sintered body S, which was originally a solid sintered body S, tend to orient themselves axially (in the direction of pressure) due to being pressed axially. On the other hand, the magnetic particles in the outer portion of the plastically deformed sintered body S, which is formed by the flow of magnetic particles toward the die 64, tend to orient themselves radially. In other words, multiple magnetic particles have portions that are oriented in directions that intersect axially.

[0057] Then, by stopping the operation of the sintering apparatus and cooling to a predetermined temperature, the plastically deformed sintered body S solidifies, and a cylindrical plastic body P formed by hot plastic working (plastic deformation) is created. After removing the mold 60 from the sintering apparatus, the plastic body P is removed from the mold 60.

[0058] After the third step St3, the fourth step St4 is performed. In this fourth step St4, the plastic body P is magnetized radially, for example by pulse magnetization. As a result, multiple magnetic poles 19 are formed in the circumferential direction, and the magnet 10 (magnetic material) shown in Figures 2 and 4 is manufactured.

[0059] In the plastic body P, as described above, the magnetic particles in the inner part, which was originally the sintered body S, tend to be oriented in the axial direction, while the magnetic particles in the melted and radially outward-spreading part tend to be oriented in the radial direction. For example, for this reason, the end face 11 of the magnetic body (magnet 10) is divided into an inner layer 12 and an outer layer 13, separated by a boundary 14 that radially defines the inner layer 12, which roughly corresponds to the part that was originally the sintered body S, and the outer layer 13, which melted and spread radially. In other words, the inner layer 12 and the outer layer 13 of the magnet 10 are formed by plastic deformation. Furthermore, the hot plastic deformation process that forms the plastic body P creates a radially-oriented end face of the plastic body P (end face 11 of the magnet 10) with an inner layer of the plastic body P (inner layer 12) and an outer layer of the plastic body P (outer layer 13). Furthermore, the aforementioned outer portion Pe is formed by the hot plastic deformation process, and this portion Pe becomes the second connection portion 17 of the magnet 10.

[0060] As described above, the magnet 10 (magnetic material) contains multiple magnetic particles, is cylindrical in shape extending in the axial direction, and has an end face 11 facing in the axial direction. The end face 11 has an inner layer (inner layer 12) and an outer layer (outer layer 13) in the radial direction, and the outer layer 13 and inner layer 12 have multiple magnetic poles 19 in the circumferential direction, and the relative density of magnetic particles exceeds 95%. In the magnet 10, the inner layer 12 and the outer layer 13 are separated by a boundary 14 that defines the inner layer 12 and the outer layer 13 in the radial direction.

[0061] In this magnet 10 (magnetic material), the magnetic particles are densely packed so that the relative density of the magnetic particles exceeds 95%, thus exhibiting excellent magnetic properties such as excellent surface magnetic flux density. Furthermore, the inner layer 12 and the outer layer 13 are separated by a boundary 14. In other words, the magnet 10 is manufactured by plastically deforming a densified sintered body S. Therefore, the magnet 10 has anisotropy compared to the sintered body S and exhibits even better magnetic properties.

[0062] (Second Embodiment) Next, a magnetic material (magnet) according to the second embodiment will be described. In this embodiment, the differences from the first embodiment will be described, and other components will be denoted by the same reference numerals as in the first embodiment, and will not be described unless specifically required.

[0063] Figure 9 is a cross-sectional view of the magnet 210 according to the second embodiment, along the axial direction. As shown in Figure 9, the magnet 210 differs from the magnet 10 in that the shape of its upper end surface 211A is different from the shape of the upper end surface 11A of the magnet 10, but is otherwise common to the magnet 10. The upper end surface 211A of the magnet 210 connects the upper end of the outer circumferential surface 15 and the upper end of the inner circumferential surface 16 in the radial direction. On the upper end surface 211A, the second connecting portion 217 where the outer circumferential surface 15 and the upper end surface 211A are angular, whereas the first connecting portion 218 where the inner circumferential surface 16 and the upper end surface 211A are not angular and are rounded. That is, the first connecting portion 218 (the inner edge of the upper end surface 211A) is rounder than the second connecting portion 217 (the outer edge of the upper end surface 211A).

[0064] In the manufacturing method Ps for the magnet 210 (magnetic material), the first step St1, the second step St2, and the fourth step St4 are the same as in the manufacturing method Ps for the magnet 10, and only the third step St3 differs from the manufacturing method Ps for the magnet 10. The third step St3 according to the second embodiment will be described below.

[0065] Figure 10 is a diagram illustrating the initial stage of the third step St3 according to the second embodiment. Figure 11 is a diagram illustrating the final stage of the third step St3 according to the second embodiment.

[0066] As shown in Figures 10 and 11, in the third step St3, a mold 260 is prepared. The mold 260 includes a lower punch 261, a core 262, an upper punch 263, and a die 264. The lower punch 261, upper punch 263, die 264, and core 262 may be made of a conductive material (e.g., graphite, cemented carbide, etc.). In Figures 10 and 11, the lower figure shows a cross-section of the mold 260 along the axial direction, and the upper figure shows a cross-section of the mold 260 along the line A-A (i.e., along the radial direction).

[0067] The lower punch 261 includes a base portion 261A, which is the bottom of the die 260, and a cylindrical tube portion 261B extending vertically upward from the base portion 261A. The upper punch 263 includes a base 263A and a cylindrical tube portion 263B extending vertically downward from the base 263A. The core 262 has a cylindrical shape. The outer diameter of the core 262 is substantially equal to the inner diameters of the tube portions 261B and 263B. The lower portion of the core 262 is fitted into the space inside the tube portion 261B, and the upper portion of the core 262 protrudes upward from the tube portion 261B. The die 264 has a cylindrical shape. The inner diameter of the die 264 is substantially equal to the outer diameters of the tube portions 261B and 263B. The lower portion of the inner circumferential surface 264A of the die 264 is in contact with the upper portion of the outer circumferential surface of the cylindrical portion 261B. In the mold 260, the die 264 is supported by the upper portion of the cylindrical portion 262B fitting into the lower portion of the cylindrical gap 265 formed between the outer circumferential surface 262A of the core 262 and the inner circumferential surface 264A of the die 264.

[0068] The width W2 of the gap 265 is substantially equal to the radial distance from the outer circumferential surface 262A of the core 262 to the inner circumferential surface 264A of the die 264, and is greater than the width W1 of the sintered body S produced in the second step St2. Also, the inner diameter of the die 264 is substantially equal to the outer diameter of the sintered body S, and the outer diameter of the core 262 is smaller than the inner diameter of the sintered body S.

[0069] The radial width of the cylindrical portion 263B of the upper punch 263 may be substantially equal to or slightly smaller than the width W2 of the gap 265. Therefore, the cylindrical portion 263B can slide along the axial direction (vertical direction) within the gap 265, thereby adjusting the height (vertical length) of the gap 265 between the lower end surface of the cylindrical portion 263B and the upper end surface of the cylindrical portion 261B.

[0070] In the third step St3, the first step is the placement step. In this placement step, as shown in Figure 10, the sintered body S is inserted into the gap 265, and the lower end surface Sa of the sintered body S is brought into contact with the upper end surface of the cylindrical portion 261B. Here, since the outer diameter of the sintered body S and the inner diameter of the die 264 are substantially equal, the outer peripheral surface Sd of the sintered body S is in contact with the inner peripheral surface 264A of the die 264. Next, the cylindrical portion 263B of the upper punch 263 is inserted into the gap 265, and the lower end surface of the cylindrical portion 263B is brought into contact with the upper end surface Sb of the sintered body S. In this way, the sintered body S is placed in the gap 265 of the mold 260. At this time, a radial gap 265A is formed between the inner peripheral surface Sc of the sintered body S and the outer peripheral surface 262A of the core 262. The radial length of the gap 265A is substantially equal to the difference between the width W2 and the width W1.

[0071] Next, a hot plastic deformation process is performed. In this hot plastic deformation process, first, the mold 260 in which the sintered body S is placed is placed in the sintering apparatus described above. Then, as shown in Figure 11, the sintered body S is pressed in the axial direction by sliding the upper punch 263 downward, while the sintered body S is heated by the discharge plasma and Joule heat of the sintering apparatus. The pressure applied in the hot plastic deformation process may be 30 to 100 MPa. The heating temperature in the hot plastic deformation process is above the liquid phase formation temperature of the magnetic particles, for example, 650°C or higher.

[0072] During this hot plastic deformation process, the sintered body S melts and undergoes plastic deformation. The sintered body S is compressed axially (vertically) while expanding radially inward, and the gap 265A is largely filled by the plastically deformed sintered body S. Here, the inner portion Pf of the upper end of the plastically deformed sintered body S (i.e., the portion in contact with the outer surface 262A of the core 262) is not given corners due to the influence of gravity and surface tension, and has a rounded shape. Furthermore, during the hot plastic deformation process, the magnetic particles in the outer portion of the plastically deformed sintered body S, which was originally a solid sintered body S, tend to orient themselves axially due to being pressed in the axial direction. On the other hand, the magnetic particles in the inner portion of the plastically deformed sintered body S, which is formed by the flow of magnetic particles toward the core 262, tend to orient themselves radially (in a direction intersecting the axial direction). In other words, multiple magnetic particles have portions that are oriented in a direction intersecting the axial direction.

[0073] Then, by stopping the operation of the sintering apparatus and cooling to a predetermined temperature, the plastically deformed sintered body S solidifies, and a cylindrical plastic body P formed by hot plastic working (plastic deformation) is created. After removing the mold 260 from the sintering apparatus, the plastic body P is removed from the mold 60.

[0074] The magnet 210 (magnetic material) manufactured in this manner contains multiple magnetic particles, is cylindrical in shape extending in the axial direction, and has an end face 11 facing in the axial direction. The end face 11 has an inner layer (inner layer 12) and an outer layer (outer layer 13) in the radial direction, and the outer layer 13 and inner layer 12 have multiple magnetic poles 19 in the circumferential direction, with a relative density of magnetic particles exceeding 95%. In the magnet 210, the inner layer 12 and the outer layer 13 are separated by a boundary 14 that defines them in the radial direction. Therefore, the magnet 210 produces the same effect as the magnet 10.

[0075] (Third Embodiment) Next, a magnetic material (magnet) according to the third embodiment will be described. In this embodiment, the differences from the embodiments described above will be explained, and other components will be denoted by the same reference numerals as in the embodiments described above, and will not be described unless specifically required.

[0076] Figure 12 is a schematic diagram showing a magnet 310 (magnetic material) according to the third embodiment, viewed from the axial direction. The magnet 310 contains a plurality of magnetic particles and is also called a bulk magnet or binderless magnet. The plurality of magnetic particles are the same as the magnetic particles of the magnet 10 according to the first embodiment, and the relative density of magnetic particles in the magnet 310 exceeds 95%.

[0077] As shown in Figure 12, the magnet 310 is cylindrical, specifically having a cylindrical shape that extends in the axial direction. The cylindrical magnet 310 includes end faces 311 on one and the other side in the axial direction, an outer circumferential surface 315, and an inner circumferential surface 316. When viewed with a line of sight in the axial direction, the outer circumferential surface 315 has a substantially circular outline. On the other hand, the inner circumferential surface 316 has an overall circular outline, but has an uneven shape along the circumferential direction.

[0078] For example, the magnet 310 may be fixed to the outer circumferential surface of the rotor yoke 9 (see Figure 1) to constitute an inner rotor type motor, or the magnet 310 may be fixed to the inner circumferential surface of another rotor yoke to constitute an outer rotor type motor.

[0079] When the magnet 310 is viewed with a line of sight in the axial direction, the magnet 310 has a shape in which a first region 311A ​​with a thin thickness (length in the radial direction) and a second region 311B with a thicker thickness are alternately arranged along the circumferential direction. The first region 311A ​​is a region where the radial distance (thickness T1) from the outer circumferential surface 315 to the inner circumferential surface 316 is small, and the second region 311B is a region where the thickness T2 from the outer circumferential surface 315 to the inner circumferential surface 316 is greater than the thickness T1. In other words, the inner circumferential surface 316 has a shape in which recesses 316A that form the inner circumferential surface of the first region 311A ​​(the radially outer surface of the inner circumferential surface 316) and protrusions 316B that form the inner circumferential surface of the second region 311B (the radially inner surface of the inner circumferential surface 316) are alternately arranged along the circumferential direction. In other words, when viewed with a line of sight in the axial direction, the inner circumferential surface 316 has a region in the radial direction where the distance from the outer circumferential surface 315 to the inner circumferential surface 316 is short (recess 316A) and a region where the distance is long (protrusion 316B).

[0080] When viewed with a line of sight in the axial direction, the first region 311A ​​and the second region 311B can each be seen as being in a substantially arc shape, and in the circumferential direction, a boundary 314 extending roughly along the radial direction can be seen between the first region 311A ​​and the second region 311B.

[0081] In magnet 310, the first region 311A ​​(the region where the distance from the outer surface 315 to the inner surface 316 is short) is more anisotropic than the second region 311B (the region where the distance from the outer surface 315 to the inner surface 316 is long). In magnet 310, magnetic poles 319 are formed in the first region 311A. That is, in magnet 310, there is a region with a long radial distance (second region 311B) between the multiple magnetic poles 319 formed in the region with a short radial distance (first region 311A). Magnetic poles are not formed in this second region 311B, but they may be formed.

[0082] Focusing on a pair of adjacent magnetic poles 319, 319 in the circumferential direction, on one magnetic pole 319, the inner portion is magnetized to one pole p1 of N and S, and the outer portion is magnetized to the other pole p2 of N and S. On the other magnetic pole 319, the inner portion is magnetized to the other pole p2, and the outer portion is magnetized to one pole p1.

[0083] Next, we will explain the manufacturing method Ps for the magnet 310 (magnetic material).

[0084] The manufacturing method Ps for magnet 310 includes a first step St1, a second step St2, a third step St3, and a fourth step St4, similar to the manufacturing method Ps for magnet 10. The first step St1 and the second step St2 of the manufacturing method Ps for magnet 310 are the same as the first step St1 and the second step St2 of the manufacturing method Ps for magnet 10. Therefore, the third step St3 and the fourth step St4 will be described below.

[0085] Figure 13 is an axial cross-sectional view illustrating the initial stage of the third step St3 in the third embodiment. Figure 14 is a radial cross-sectional view illustrating the third step St3 in the third embodiment.

[0086] As shown in Figures 13 and 14, in the third step St3, a mold 360 is prepared. The mold 360 includes a lower punch 361 (sizing core), a regulating ring 362, an upper punch 363, and a die 364. The lower punch 361, upper punch 363, die 364, and regulating ring 362 may be made of a conductive material (e.g., graphite, cemented carbide, etc.).

[0087] The lower punch 361 is slidably mounted on a base 365. The lower punch 361 includes a plurality (four in this embodiment) of punch pieces 361A. In this embodiment, each of the plurality of punch pieces 361A has the same shape and dimensions. Each of the plurality of punch pieces 361A has an arc shape when viewed in the axial direction and a right trapezoid shape when viewed in cross-section along the axial direction. Specifically, the punch piece 361A includes an upper end surface 361Aa, a lower end surface 361Ab, an outer peripheral surface 361Ac, an inner peripheral surface 361Ad, and a pair of side surfaces 361Ae, 361Ae.

[0088] The upper end surface 361Aa is the upper end surface in the axial direction (vertical direction) and has an arc shape when viewed with a line of sight in the axial direction. The lower end surface 361Ab is the lower end surface in the axial direction (vertical direction) and has an arc shape that is radially longer than the upper end surface 361Aa when viewed with a line of sight in the axial direction. The lower end surface 361Ab is in contact with the upper surface of the base 365. The pair of side surfaces 361Ae, 361Ae are both end surfaces in the circumferential direction of the punch piece 361A and extend radially when viewed with a line of sight in the axial direction.

[0089] The outer circumferential surface 361Ac is the radially outer surface and has an arc shape such that, when viewed with a line of sight in the axial direction, the outer circumferential surfaces 361Ac of each of the four punch pieces 361A form part of the same circle. Furthermore, in a cross-sectional view along the axial direction, the outer circumferential surface 361Ac extends in the axial direction (vertical direction) and is perpendicularly connected to the upper end surface 361Aa and the lower end surface 361Ab.

[0090] The inner circumferential surface 361Ad is the radially inward surface and has an arc shape such that, when viewed axially, the inner circumferential surfaces 361Ad of each of the four punch pieces 361A form part of the same circle. When viewed axially, the length of the inner circumferential surface 361Ad is shorter than the length of the outer circumferential surface 361Ac. Furthermore, in a cross-sectional view along the axial direction, the inner circumferential surface 361Ad is inclined to protrude inward towards the bottom, and connects to the upper end surface 361Aa at an obtuse angle and to the lower end surface 361Ab at an acute angle.

[0091] Multiple (four in this embodiment) punch pieces 361A are arranged on a base 365 with spacing in the circumferential direction (approximately equal spacing in this embodiment). Inside the inner circumferential surfaces 361Ad of the multiple punch pieces 361A, a first space 361H1 is formed which can be viewed as approximately circular when viewed with a line of sight in the axial direction. In addition, between adjacent punch pieces 361A, 361A in the circumferential direction, a second space 361H2 is formed which can be viewed as approximately arc-shaped when viewed with a line of sight in the axial direction.

[0092] The die 364 has a cylindrical shape and is positioned on the base 365. The die 364 is located outside the lower punch 361 and surrounds the lower punch 361. A cylindrical gap 366 is formed radially between the inner surface of the die 364 and the outer surface of the lower punch 361 (each outer surface 361Ac of the multiple punch pieces 361A). The radial length of this gap 366 is substantially equal to the thickness of the sintered body S formed in the second step St2.

[0093] The regulating ring 362 has a cylindrical shape and is mounted on the inner circumferential surface of the die 364 so as to be axially slidable. The inner diameter of the regulating ring 362 is larger than the outer diameter of the lower punch 361. Therefore, a gap 367 is formed radially between the inner circumferential surface of the regulating ring 362 and the outer circumferential surface 361Ac of the punch piece 361A. The upper portion of the regulating ring 362 protrudes above the upper end of the die 364.

[0094] The upper punch 363 includes a first part 363A, a second part 363B, and a third part 363C.

[0095] The first part 363A has a cylindrical shape coaxial with the lower punch 361. The lower surface 363Aa of the first part 363A faces the upper surface 362A of the regulating ring 362 in the axial direction. The second part 363B has a cylindrical shape with a smaller outer diameter than the first part 363A. The second part 363B is connected to the lower surface 363Aa of the first part 363A and is arranged coaxially with the first part 363A. The second part 363B is slidably mounted on the inner circumferential surface of the regulating ring 362 in the axial direction.

[0096] The third portion 363C has a frustoconical shape, with the outer diameter becoming smaller towards the lower portion. The third portion 363C is connected to the lower surface of the second portion 363B and is arranged coaxially with the first portion 363A and the second portion 363B. The third portion 363C can enter the first space 361H1 of the lower punch 361. The inclination angle of the outer circumferential surface 363Ca of the third portion 363C is approximately equal to the inclination angle of the inner circumferential surface 361A of the punch piece 361A. The portion of the outer circumferential surface 363Ca of the third portion 363C that is in the first space 361H1 is in contact with the inner circumferential surface 361A of the punch piece 361A. The outer circumferential surface 363Ca of the third portion 363C can slide against the inner circumferential surface 361A of the punch piece 361A.

[0097] The mold 360 is configured such that each punch piece 361A is pressed radially as the third portion 363C slides downward. More specifically, the mold 360 is configured such that as the third portion 363C moves downward, the multiple punch pieces 361A move radially outward.

[0098] In the third step St3, the first step is the placement step. In this placement step, as shown in Figure 13, the sintered body S produced in the second step St2 is inserted into the gap 366, and the lower end surface Sa of the sintered body S is brought into contact with the upper surface of the base 365. Next, the outer circumferential surface of the regulating ring 362 is brought into contact with the inner circumferential surface of the die 364, and the regulating ring 362 is inserted inside the die 364. By sliding the regulating ring 362 downwards, the lower surface of the regulating ring 362 is brought into contact with the upper end surface Sb of the sintered body S. Next, the lower part of the outer circumferential surface of the second part 363B of the upper punch 363 is brought into contact with the inner circumferential surface of the regulating ring 362. As a result, the lower part of the second part 363B and the third part 363C of the upper punch 363 are placed inside the regulating ring 362. In this state, the lower part of the outer circumferential surface 363Ca of the third part 363C is in contact with the upper part of the inner circumferential surface 361Ad of each punch piece 361A. In this way, a mold 360 in which the sintered body S is placed is formed. In this state, the inner circumferential surface Sc of the sintered body S is located inside the inner circumferential surface of the regulating ring 362 and is in contact with the outer circumferential surface 361Ac of the punch piece 361A.

[0099] Next, in the third step St3, a hot plastic deformation process is performed. In this hot plastic deformation process, first, the mold 360 in which the sintered body S is placed is placed in the sintering apparatus. Then, as shown in Figure 15, the upper punch 363 is slid downward to bring the lower surface 363Aa of the upper punch 363 into contact with the upper surface 362A of the regulating ring 362, and then the upper punch 363 is slid further downward. At this time, the sintered body S is heated by the discharge plasma and Joule heat of the sintering apparatus. The pressure in the hot plastic deformation process may be 30 to 100 MPa. The heating temperature in the hot plastic deformation process is above the liquid phase formation temperature of the magnetic particles, for example, 650°C or higher. As a result, the sintered body S is pressed downward, and as shown in Figure 14, the portion of the inner circumferential surface Sc of the sintered body S that is in contact with the outer circumferential surface 361Ac of each punch piece 361A is pressed outward by the radial movement of each punch piece 361A outward. In this hot plastic deformation process, the sintered body S melts and undergoes plastic deformation. Then, by stopping the operation of the sintering apparatus and cooling to a predetermined temperature, the plastically deformed sintered body S solidifies, and a cylindrical plastic body P formed by hot plastic working (plastic deformation) is created.

[0100] In this way, the portion of the plastically deformed sintered body S that is in contact with the outer circumferential surface 361Ac of each punch piece 361A is pressed in two directions, axial and radial, and becomes a first region 311A ​​(see Figure 12) which is a region with a thin radial length (thickness). On the other hand, the portion that is not in contact with the outer circumferential surface 361Ac of each punch piece 361A (i.e., the portion facing the second space 361H2) is pressed in one direction, axial, and becomes a second region 311B (see Figure 12) which is thicker. Since the first region 311A ​​is a portion that has been pressed in two directions, it is anisotropic compared to the second region 311B, which is a portion that has been pressed in one direction. For example, it is thought that the multiple magnetic particles in the first region 311A ​​have more portions that are oriented radially intersecting the axial direction compared to the multiple magnetic particles in the second region 311B. And it is thought that the difference in orientation between the first region 311A ​​and the second region 311B is represented as the boundary 314 shown in Figure 12.

[0101] After removing the mold 360 from the sintering apparatus, the plastic body P is removed from the mold 360. Thus, the third step St3 is completed.

[0102] The third step St3 of the third embodiment is a step of forming a first region 311A ​​on the radially oriented inner circumferential surface of the plastic body P, where the distance from the outer circumferential surface to the inner circumferential surface is short in the radial direction, and a second region 311B where the distance is long.

[0103] After the third step St3, the fourth step St4 is performed. In this fourth step St4, the plastic body P is magnetized radially, for example by pulse magnetization. More specifically, in the fourth step St4 in this embodiment, pulse magnetization is performed on the first region 311A ​​of the plastic body P, for example, to magnetize the first region 311A ​​and form a magnetic pole 319. In this way, the magnet 310 shown in Figure 12 is manufactured. The fourth step St4 of the third embodiment is a step in which the first region 311A, which is a region with a short distance, becomes a magnetic pole 319.

[0104] As described above, the magnet 310 is a magnetic material containing a plurality of magnetic particles, and the magnetic material is a cylinder extending in the axial direction, and the cylinder has an outer circumferential surface 315 and an inner circumferential surface 316, the inner circumferential surface 316 has a plurality of magnetic poles 319 arranged in the circumferential direction, the relative density of magnetic particles exceeds 95%, and the inner circumferential surface 316 has a region in the radial direction where the distance from the outer circumferential surface 315 to the inner circumferential surface 316 is short (first region 311A) and a region where the distance is long (second region 311B), and the second region 311B is located between the plurality of magnetic poles 319 formed in the first region 311A.

[0105] As described above, the first region 311A ​​is an anisotropic region compared to the second region 311B due to plastic deformation in the radial direction. In the magnet 310, the magnetic particles are densely packed, and the magnetic poles 319 are formed in the more anisotropic first region 311A. For this reason, the magnet 310 exhibits excellent magnetic properties, such as excellent surface magnetic flux density.

[0106] (Fourth Embodiment) Next, a magnetic material (magnet) according to the fourth embodiment will be described. In this embodiment, the differences from the embodiments described above will be explained, and other components will be denoted by the same reference numerals as in the embodiments described above, and will not be described unless specifically required.

[0107] Figure 16 is a schematic diagram showing the magnet 410 (magnetic material) according to the fourth embodiment, viewed from the axial direction. The magnet 410 contains a plurality of magnetic particles and is also called a bulk magnet or binderless magnet. The plurality of magnetic particles are the same as the magnetic particles of the magnet 10 according to the first embodiment, and the relative density of magnetic particles in the magnet 410 exceeds 95%.

[0108] As shown in Figure 16, the magnet 410 is cylindrical, specifically having a cylindrical shape that extends in the axial direction. The cylindrical magnet 410 includes end faces 411 on one and the other side in the axial direction, an outer circumferential surface 415, and an inner circumferential surface 416. When viewed with a line of sight in the axial direction, the inner circumferential surface 416 has a substantially circular outline. On the other hand, the outer circumferential surface 415 has an overall circular outline, but has an uneven shape along the circumferential direction.

[0109] For example, the magnet 410 may be fixed to the outer circumferential surface of the rotor yoke 9 (see Figure 1) to constitute an inner rotor type motor, or the magnet 410 may be fixed to the inner circumferential surface of another rotor yoke to constitute an outer rotor type motor.

[0110] When the magnet 410 is viewed with a line of sight in the axial direction, the magnet 410 has a shape in which a first region 411A with a thin thickness (length in the radial direction) and a second region 411B with a thicker thickness are alternately arranged along the circumferential direction. The first region 411A is a region where the radial distance (thickness T1) from the inner circumferential surface 416 to the outer circumferential surface 415 is small, and the second region 411B is a region where the thickness T2 from the inner circumferential surface 416 to the outer circumferential surface 415 is greater than the thickness T1. In other words, the outer circumferential surface 415 has a shape in which recesses 415A that form the outer circumferential surface of the first region 411A (the radially inward surface of the outer circumferential surface 415) and protrusions 415B that form the outer circumferential surface of the second region 411B (the radially outward surface of the outer circumferential surface 415) are alternately arranged along the circumferential direction. When viewed with a line of sight in the axial direction, the outer peripheral surface 415 has a region in the radial direction where the distance from the inner peripheral surface 416 to the outer peripheral surface 415 is short (recess 415A) and a region where the distance is long (protrusion 415B).

[0111] When viewed with a line of sight in the axial direction, the first region 411A and the second region 411B can be seen as being in a substantially arc shape, and in the circumferential direction, a boundary 414 extending roughly along the radial direction can be seen between the first region 411A and the second region 411B.

[0112] In magnet 410, the first region 411A (the region where the distance from the inner circumferential surface 416 to the outer circumferential surface 415 is short) is more anisotropic than the second region 411B (the region where the distance from the inner circumferential surface 416 to the outer circumferential surface 415 is long). In magnet 410, magnetic poles 419 are formed in the first region 411A. That is, in magnet 410, there is a region with a longer radial distance (second region 411B) between the multiple magnetic poles 419 formed in the region with a short radial distance (first region 411A). Magnetic poles are not formed in this second region 411B, but they may be formed.

[0113] Focusing on a pair of adjacent magnetic poles 419, 419 in the circumferential direction, on one magnetic pole 419, the inner portion is magnetized to one pole p1 of N and S, and the outer portion is magnetized to the other pole p2 of N and S. On the other magnetic pole 419, the inner portion is magnetized to the other pole p2, and the outer portion is magnetized to one pole p1.

[0114] Next, we will explain the manufacturing method Ps for the magnet 410 (magnetic material).

[0115] The manufacturing method Ps for magnet 410 includes a first step St1, a second step St2, a third step St3, and a fourth step St4, similar to the manufacturing method Ps for magnet 10. The first step St1 and the second step St2 of the manufacturing method Ps for magnet 410 are the same as the first step St1 and the second step St2 of the manufacturing method Ps for magnet 10. Therefore, the third step St3 and the fourth step St4 will be described below.

[0116] Figure 17 is an axial cross-sectional view illustrating the initial stage of the third step St3 in the fourth embodiment. Figure 18 is a radial cross-sectional view illustrating the third step St3 in the fourth embodiment.

[0117] As shown in Figures 17 and 18, in the third step St3, a mold 460 is prepared. The mold 460 includes a lower punch 461 (sizing die), a regulating ring 462, an upper punch 463, and a core 469. The lower punch 461, upper punch 463, regulating ring 462, and core 469 may be made of a conductive material (e.g., graphite, cemented carbide, etc.).

[0118] The lower punch 461 is slidably mounted on a base 465. The lower punch 461 includes a plurality (four in this embodiment) of punch pieces 461A. In this embodiment, each of the plurality of punch pieces 461A has the same shape and dimensions. Each of the plurality of punch pieces 461A has an arc shape when viewed in the axial direction and a right trapezoid shape when viewed in cross-section along the axial direction. The punch piece 461A includes an upper end surface 461Aa, a lower end surface 461Ab, an outer peripheral surface 461Ac, an inner peripheral surface 461Ad, and a pair of side surfaces 461Ae, 461Ae.

[0119] The upper end face 461Aa is the upper end face in the axial direction (vertical direction) and has an arc shape when viewed with a line of sight in the axial direction. The lower end face 461Ab is the lower end face in the axial direction (vertical direction) and has an arc shape that is radially longer than the upper end face 461Aa when viewed with a line of sight in the axial direction. The lower end face 461Ab is in contact with the upper surface of the base 365. The pair of side faces 461Ae, 461Ae are both end faces in the circumferential direction of the punch piece 461A and extend radially when viewed with a line of sight in the axial direction.

[0120] The outer circumferential surface 461Ac is the radially outer surface and has an arc shape such that, when viewed axially, the outer circumferential surfaces 461Ac of each of the four punch pieces 461A form part of the same circle. Furthermore, in a cross-sectional view along the axial direction, the outer circumferential surface 461Ac is inclined to protrude outward towards the bottom, and connects to the upper end surface 461Aa at an obtuse angle and to the lower end surface 461Ab at an acute angle.

[0121] The inner circumferential surface 461Ad is the radially inward surface and has an arc shape such that, when viewed with a line of sight in the axial direction, the inner circumferential surfaces 461Ad of each of the four punch pieces 461A are part of the same circle. When viewed with a line of sight in the axial direction, the length of the inner circumferential surface 461Ad is shorter than the length of the outer circumferential surface 461Ac. Furthermore, in a cross-sectional view along the axial direction, the inner circumferential surface 461Ad extends in the axial direction (vertical direction) and is perpendicularly connected to the upper end surface 461Aa and the lower end surface 461Ab.

[0122] Multiple (four in this embodiment) punch pieces 461A are arranged on a base 465 with spacing in the circumferential direction (approximately equal spacing in this embodiment). Between adjacent punch pieces 461A, 461A in the circumferential direction, a space 461H is formed that can be seen as approximately arc-shaped when viewed with a line of sight in the axial direction.

[0123] The core 469 has a cylindrical shape and is positioned on the base 465 coaxially with the lower punch 461. The core 469 is positioned inside the lower punch 461 (inside the inner circumferential surface 461Ad of each punch piece 461A). When viewed axially, an annular gap 466 is formed between the core 469 and the inner circumferential surface 461Ad of each punch piece 461A. The radial length (width WL) of this gap 466 is substantially equal to the thickness of the sintered body S produced in the second step St2.

[0124] The regulating ring 462 has a cylindrical shape and is mounted on the outer circumferential surface of the core 469 so as to be axially slidable. The outer diameter of the regulating ring 462 is smaller than the inner diameter of the lower punch 461. Therefore, a gap 467 is formed radially between the outer circumferential surface of the regulating ring 462 and the inner circumferential surface 461Ad of the punch piece 461A. The upper portion of the regulating ring 462 protrudes above the upper end of the core 469.

[0125] The upper punch 463 includes a first part 463A, a second part 463B, and a third part 463C.

[0126] The first portion 463A has a cylindrical shape coaxial with the core 469. The lower surface 463Aa of the first portion 463A faces the upper surface 462A of the regulating ring 462 in the axial direction. The second portion 463B has a cylindrical shape with an outer diameter approximately equal to that of the first portion 463A. The second portion 463B is connected to the lower surface 463Aa of the first portion 463A and is arranged coaxially with the first portion 463A. The second portion 463B is slidably mounted on the outer circumferential surface of the regulating ring 462 in the axial direction.

[0127] The third portion 463C has a cylindrical shape with an outer diameter approximately equal to the outer diameter of the second portion 463B. The third portion 463C is connected to the lower surface of the second portion 463B and is arranged coaxially with the first portion 463A and the second portion 463B. The inner circumferential surface 463Ca of the third portion 463C is an inclined surface that slopes inward as it goes upward. The inclination angle of the inner circumferential surface 463Ca of the third portion 463C is approximately equal to the inclination angle of the outer circumferential surface 461Ac of the punch piece 461A. The inner circumferential surface 463Ca of the third portion 463C can slide against the outer circumferential surface 461Ac of the punch piece 461A.

[0128] The mold 460 is configured such that each punch piece 461A is pressed radially as the third portion 463C slides downward. More specifically, the mold 460 is configured such that as the third portion 463C moves downward, the multiple punch pieces 461A move radially inward.

[0129] In the third step St3, the first step is the placement step. In this placement step, as shown in Figure 17, the sintered body S produced in the second step St2 is inserted into the gap 466, and the lower end surface Sa of the sintered body S is brought into contact with the upper surface of the base 465. Next, the inner circumferential surface of the regulating ring 462 is brought into contact with the outer circumferential surface of the core 469, and the regulating ring 362 is slid downward, so that the lower surface of the regulating ring 462 is brought into contact with the upper end surface Sb of the sintered body S. Next, the lower part of the inner circumferential surface of the second portion 463B of the upper punch 463 is brought into contact with the outer circumferential surface of the regulating ring 462. In this state, the lower part of the inner circumferential surface 463Ca of the third portion 363C of the upper punch 463 is in contact with the upper part of the outer circumferential surface 461Ac of each punch piece 461A. In this way, the mold 460 in which the sintered body S is placed is constructed. In this state, the outer circumferential surface Sd of the sintered body S is located outside the outer circumferential surface of the regulating ring 462 and is in contact with the inner circumferential surface 461Ad of the punch piece 461A.

[0130] Next, in the third step St3, a hot plastic deformation process is performed. In this hot plastic deformation process, first, the mold 460 in which the sintered body S is placed is placed in the sintering apparatus. Then, as shown in Figure 17, the upper punch 463 is slid downward to bring the lower surface 463Aa of the upper punch 463 into contact with the upper surface 462A of the regulating ring 462, and then the upper punch 463 is slid further downward. At this time, the sintered body S is heated by the discharge plasma and Joule heat of the sintering apparatus. The pressure in the hot plastic deformation process may be 30 to 100 MPa. The heating temperature in the hot plastic deformation process is above the liquid phase formation temperature of the magnetic particles, for example, 650°C or higher. As a result, the sintered body S is pressed downward, and as shown in Figure 18, the portion of the outer peripheral surface Sd of the sintered body S that is in contact with the inner peripheral surface 461Ad of each punch piece 461A is pressed inward by the radial movement of each punch piece 461A inward. In this hot plastic deformation process, the sintered body S melts and undergoes plastic deformation. Then, by stopping the operation of the sintering apparatus and cooling to a predetermined temperature, the plastically deformed sintered body S solidifies, and a cylindrical plastic body P formed by hot plastic working (plastic deformation) is created.

[0131] In this way, the portion of the plastically deformed sintered body S that is in contact with the inner circumferential surface 461A of each punch piece 461A is pressed in two directions, axial and radial, and becomes a first region 411A (see Figure 16), which is a region with a thin radial length (thickness). On the other hand, the portion that is not in contact with the inner circumferential surface 461A of each punch piece 461A (i.e., the portion facing the space 461H) is pressed in one direction, axial, and becomes a second region 411B (see Figure 16), which is thicker. Since the first region 411A is a portion that has been pressed in two directions, it is anisotropic compared to the second region 411B, which is a portion that has been pressed in one direction. For example, it is thought that the multiple magnetic particles in the first region 411A have more portions that are oriented radially intersecting the axial direction compared to the multiple magnetic particles in the second region 411B. And it is thought that the difference in orientation between the first region 411A and the second region 411B is represented as the boundary 414 shown in Figure 16.

[0132] After removing the mold 460 from the sintering apparatus, the plastic body P is removed from the mold 460. Thus, the third step St3 is completed.

[0133] The third step St3 of the fourth embodiment is a step of forming a first region 411A on the radially oriented outer surface of the plastic body P, where the distance from the outer surface to the inner surface is short in the radial direction, and a second region 411B where the distance is long.

[0134] After the third step St3, the fourth step St4 is performed. In this fourth step St4, the plastic body P is magnetized radially, for example by pulse magnetization. More specifically, in the fourth step St4 in this embodiment, pulse magnetization is performed on the first region 411A of the plastic body P, for example, to magnetize the first region 411A and form a magnetic pole 419. In this way, the magnet 410 shown in Figure 16 is manufactured. The fourth step St4 of the fourth embodiment is a step in which the first region 411A, which is a region with a short distance, becomes a magnetic pole 419.

[0135] As described above, the magnet 410 is a magnetic material containing a plurality of magnetic particles, and the magnetic material is a cylinder extending in the axial direction, and the cylinder has an outer circumferential surface 415 and an inner circumferential surface 416, the outer circumferential surface 415 has a plurality of magnetic poles 419 arranged in the circumferential direction, the relative density of magnetic particles exceeds 95%, and the outer circumferential surface 415 has a region in the radial direction where the distance from the inner circumferential surface 416 to the outer circumferential surface 415 is short (first region 411A) and a region where the distance is long (second region 411B), and the second region 411B is located between the plurality of magnetic poles 419 formed in the first region 411A.

[0136] As described above, the first region 411A is an anisotropic region compared to the second region 411B due to plastic deformation in the radial direction. In the magnet 410, the magnetic particles are densely packed, and the magnetic poles 419 are formed in the more anisotropic first region 411A. For this reason, the magnet 310 exhibits excellent magnetic properties, such as excellent surface magnetic flux density.

[0137] (Examples) The present invention will be described in more detail below based on examples, but these examples are just one example of the present invention and the present invention is not limited to these examples.

[0138] First, compound C was produced in the first step St1. Next, compound C was sintered in the second step St2 to produce a first sintered body S in which magnetic particles were densely packed. Specifically, in the second step St2, a first sintered body S was produced with an outer diameter (diameter of the outer surface of the sintered body S in Figure 7) of 14.0 mm, an inner diameter (diameter of the inner surface of the sintered body S in Figure 7) of 12.0 mm, and a height (axial length of the sintered body S in Figure 7) of 15.9 mm. Next, the first sintered body S was plastically deformed in the third step St3 of the first embodiment to produce a first plastic body P1 shown in Figures 19 and 19A. Figure 19 is a diagram based on a photograph of the first plastic body P1, with a dashed line added to the part corresponding to the boundary 14 to clearly indicate the boundary 14 described above. Figure 19A is a diagram from Figure 19 with the dashed line indicating the boundary 14 removed.

[0139] In the third step St3 of the first embodiment, a first plastic body P1 was fabricated with an outer diameter (diameter of the outer circumferential surface 15 of the magnetic body in Figure 2) of 16.2 mm, an inner diameter (diameter of the inner circumferential surface 16 of the magnetic body in Figure 2) of 12.0 mm, and a height (axial length of the magnetic body in Figure 2) of 7.0 mm. As shown by the dashed line in Figure 19, it was found that a boundary 14 defining the inner layer (inner layer 12) and the outer layer (outer layer 13) could be seen at the end face 11 of the first plastic body P1. In the photographs of Figure 19 and Figure 19A, the inner layer 12 appears relatively white and the outer layer 13 appears relatively black, separated by the boundary 14. Then, in the fourth step St4 of the first embodiment, the first plastic body P1 was magnetized to fabricate the magnet 10 (magnetic body according to the embodiment) shown in Figure 4.

[0140] Furthermore, in the second step St2, a second sintered body S with an outer diameter of 15.0 mm, an inner diameter of 12.0 mm, and a height of 10.0 mm was produced. Next, in the third step St3 of the first embodiment, the second sintered body S was plastically deformed to produce a second plastic body P2 as shown in Figures 20 and 20A. Figure 20 is a diagram based on a photograph of the second plastic body P2, with a dashed line added to the part corresponding to the boundary 14 to clearly indicate the boundary 14 described above. Figure 20A is a diagram from Figure 20 with the dashed line indicating the boundary 14 removed.

[0141] In the third step St3 of the first embodiment, a second plastic body P2 with an outer diameter of 16.2 mm, an inner diameter of 12.0 mm, and a height of 6.8 mm was fabricated. As shown by the dashed line in Figure 20, it was found that a boundary 14 defining the inner layer (inner layer 12) and the outer layer (outer layer 13) could be seen at the end face 11 of the second plastic body P2. In the photographs of Figure 20 and Figure 20A, the inner layer 12 appears relatively white and the outer layer 13 appears relatively black, separated by the boundary 14. Then, in the fourth step St4 of the first embodiment, the second plastic body P2 was magnetized to fabricate the magnet 10 (magnetic material according to the embodiment) shown in Figure 4.

[0142] On the other hand, as a comparative example, a sintered body S having an outer diameter of 16.2 mm, an inner diameter of 12.0 mm, and a height of 7.0 mm was produced by the first step St1 and second step St2 of the first embodiment, and then this sintered body S was magnetized by the fourth step St4 of the first embodiment to produce a magnetic material according to the comparative example.

[0143] The magnetization characteristics (surface magnetic flux density (mT)) of the magnetic material according to the example and the magnetic material according to the comparative example were measured. The results are shown in Figure 21. As shown in Figure 21, it was found that the surface magnetic flux density of the magnetic material according to the example was approximately 28% higher than that of the magnetic material according to the comparative example.

[0144] Next, the magnetostatic properties (residual magnetic flux density (mT)) of the magnetic material according to the embodiment were measured. Figure 22 is a graph illustrating the magnetostatic properties of the magnetic material according to the embodiment in the magnetization direction. In other words, Figure 22 shows a J-H curve representing the residual magnetic flux density in the radial direction of the magnetic material according to the embodiment. On the other hand, Figure 23 is a graph illustrating the magnetostatic properties of the magnetic material according to the embodiment in the perpendicular direction. In other words, Figure 23 shows a J-H curve representing the residual magnetic flux density in the axial direction of the magnetic material according to the embodiment. As shown in Figures 22 and 23, it was found that in the magnetic material according to the embodiment, the residual magnetic flux density of the end face 11 in the axial direction (residual magnetic flux density in the axial direction) was greater than the residual magnetic flux density of the outer surface (outer peripheral surface 15) in the radial direction (residual magnetic flux density in the radial direction).

[0145] Although the present invention has been described above with reference to the above embodiments and examples, the present invention is not limited thereto. Those skilled in the art can appropriately modify the magnetic material, rotating device, and method for manufacturing the magnetic material according to the present invention in accordance with conventionally known knowledge. Such modifications, insofar as they still possess the configuration of the present invention, are of course included within the scope of the present invention.

[0146] 1...Motor (rotating machine), 4...Stator, 8...Rotor, 11, 11A, 11B, 311, 411...End face, 311A, 411A...First region (short distance region), 311B, 411B...Second region (long distance region), 12...Inner layer (inner layer), 13...Outer layer (outer layer), 14, 314, 414...Boundary, 19, 319, 419...Magnetic pole

Claims

1. A magnetic material comprising a plurality of magnetic particles, having a cylindrical shape extending in the axial direction, having an end face facing the axial direction, the end face comprising an inner layer and an outer layer in the radial direction, the outer layer and the inner layer comprising a plurality of magnetic poles in the circumferential direction, the relative density of the magnetic particles exceeding 95%, and the inner layer and the outer layer being separated by a boundary defining the inner layer and the outer layer in the radial direction.

2. The magnetic material according to claim 1, wherein the inner circumferential edge of the end face is rounder than the outer circumferential edge of the end face.

3. The magnetic material according to claim 1, wherein the outer edge of the end face is rounder than the inner edge of the end face.

4. The magnetic material according to claim 1, wherein the residual magnetic flux density of the end face in the axial direction is greater than that of the outer face in the radial direction.

5. The magnetic material according to claim 1, wherein the plurality of magnetic particles have portions oriented in directions intersecting the axial direction.

6. The magnetic material according to claim 1, wherein the inner layer and the outer layer are formed by plastic deformation.

7. A rotating device comprising a rotor having a magnetic material as described in any one of claims 1 to 6, and a stator facing the rotor.

8. A method for manufacturing a magnetic material, comprising the steps of: sintering a plurality of magnetic particles to form a sintered body; and plastically deforming the sintered body to form a plastic body, wherein in the step of forming the plastic body, an inner layer of plastic body and an outer layer of plastic body are formed on the end face of the plastic body facing in the axial direction.

9. The method for producing a magnetic material according to claim 8, wherein the step of forming the plastic body includes a step of heating at a temperature equal to or higher than the liquid phase formation temperature of the magnetic particles.

10. The method for manufacturing a magnetic material according to claim 9, wherein the temperature is 650°C or higher.

11. A magnetic material comprising a plurality of magnetic particles, wherein the magnetic material is a cylinder extending in the axial direction, the cylinder has an outer circumferential surface and an inner circumferential surface, the outer circumferential surface or the inner circumferential surface has a plurality of magnetic poles arranged in the circumferential direction, the relative density of the magnetic particles exceeds 95%, the outer circumferential surface or the inner circumferential surface has, in the radial direction, a region where the distance from the outer circumferential surface to the inner circumferential surface is short and a region where the distance is long, and the region where the distance is long lies between the plurality of magnetic poles formed in the region where the distance is short.

12. The magnetic material according to claim 11, wherein in the circumferential direction, there is a boundary between the region with a short distance and the region with a long distance.

13. The magnetic material according to claim 11 or 12, wherein the region with a shorter distance is more anisotropic than the region with a longer distance.

14. The magnetic material according to claim 11 or 12, wherein the plurality of magnetic particles have portions oriented in directions intersecting the axial direction.

15. The magnetic material according to claim 11 or 12, wherein the region with a short distance is formed by plastic deformation.

16. A rotating device comprising a rotor having a magnetic material according to any one of claims 11 to 15, and a stator facing the rotor.

17. A method for manufacturing a magnetic material, comprising the steps of: sintering a plurality of magnetic particles to form a sintered body; and plastically deforming the sintered body to form a plastic body, wherein the plastic body has a region where the distance from the outer surface to the inner surface is short and a region where the distance is long in the radial direction, and magnetizes the plastic body such that the region where the distance is short becomes the pole.

18. The method for producing a magnetic material according to claim 17, wherein the step of forming the plastic body includes a step of heating at a temperature equal to or higher than the liquid phase formation temperature of the magnetic particles.

19. The method for manufacturing a magnetic material according to claim 18, wherein the temperature is 650°C or higher.

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