Hot-worked magnet that has excellent cutting accuracy

Abstract

[Problem] To provide a hot-worked magnet with less chipping. [Solution] Provided is a hot-worked magnet that contains an aggregate of a plurality of magnetic powders, wherein: the magnet comprises a first surface that extends in the radial direction, a second surface that extends in the axial direction, and a ridge line that is formed by the intersection of the first surface and the second surface; and the surface roughness of the ridge line is within the range of 32–150 um. The hot-worked magnet exhibits little chipping.

Description

Hot-worked magnets with excellent cutting precision

[0001] The present invention relates to a hot-worked magnet and an actuator equipped with a hot-worked magnet.

[0002] Electronic devices use actuators equipped with magnets. Patent document 1 describes a hot-worked magnet and a method for manufacturing the same, using a powder 4 obtained by crushing a band 3 with a crystal grain size of several tens of nanometers as a raw material.

[0003] Japanese Patent Publication No. 2016-96203

[0004] To stabilize the operation of microactuators, the magnets used in them are required to have a uniform magnetic flux. However, hot-worked magnets are hard and prone to chipping and cracking, and the magnetic flux weakens in the chipped or cracked areas. In the case of small magnets used in microactuators, the effects of chipping and cracking are significant, causing variations in magnetic flux and resulting in the problem of not being able to obtain a uniform magnetic flux. Therefore, hot-worked magnets are not suitable for precision machining and are not suitable for use as magnets in microactuators.

[0005] For example, when hot-worked magnets are used in a rotary motor, the presence of defects (areas with weak magnetic flux) can cause differences in the behavior of the hot-worked magnets relative to the coil, preventing smooth movement of the magnets. This can lead to unstable rotational torque of the magnets and, consequently, unstable motor torque. Similarly, when hot-worked magnets are used in a magnetic encoder, defects in the hot-worked magnets can cause variations in the magnetic flux of the magnetic track, potentially leading to malfunction of the magnetic sensor.

[0006] This invention was made in view of the above circumstances and aims to provide a hot-worked magnet with minimal chipping. Furthermore, this invention aims to provide an actuator equipped with a hot-worked magnet with minimal chipping.

[0007] One aspect of the present invention relates to a hot-worked magnet comprising an aggregate of multiple magnetic particles, wherein the magnet has a first surface extending in the radial direction, a second surface extending in the axial direction, and a ridge formed by the intersection of the first surface and the second surface, and the surface roughness of the ridge is in the range of 32 μm to 150 μm. Furthermore, the present invention relates to an actuator equipped with the hot-worked magnet.

[0008] Figure 1 is an explanatory diagram of the first embodiment, a schematic perspective view of the motor showing the hot-worked magnet and substrate within the frame. Figure 2 is an explanatory diagram of the first embodiment, a plan view of the motor showing the hot-worked magnet and substrate excluding the frame. Figure 3 is an explanatory diagram of the first embodiment, a conceptual diagram of the motor showing a cross-section in a plane including the motor rotation axis. Figure 4 is an explanatory diagram of the first embodiment, a perspective view of the aperture adjustment device. Figure 5 is an explanatory diagram of the first embodiment, an exploded perspective view of the aperture adjustment device. Figure 6 is an explanatory diagram of the first embodiment, showing a cross-section in a plane including the motor rotation axis of the aperture adjustment device shown in Figure 5. Figure 7 is an explanatory diagram of the first embodiment, showing a state in which the opening area of ​​the aperture formed by the blades of the aperture adjustment device has increased. Figure 8 is an explanatory diagram of the first embodiment, showing a state in which the opening area of ​​the aperture formed by the blades of the aperture adjustment device has decreased. Figure 9 is an explanatory diagram of the second embodiment, a schematic perspective view of the magnetic encoder. Figure 10 is an explanatory diagram of the second embodiment, a schematic perspective view of the magnetic encoder. Figures 11(a) and (b) are optical microscope images showing hot-worked magnets ((a): 400x magnification, (b): 20,000x magnification). Figure 12(a) is an optical microscope image (magnification 80x) showing hot-worked magnet 5 obtained in Comparative Example 1 of the present invention, and Figure 12(b) is an optical microscope image (magnification 80x) showing hot-worked magnet 1 obtained in Example 1 of the present invention.

[0009] Hot-worked magnets have high hardness, and during manufacturing, particularly during cutting, grinding, and polishing (hereinafter also referred to as "cutting and other processes"), the surface of the hot-worked magnet, especially the edges, is prone to chipping. Chips and cracks in hot-worked magnets are caused by cracks that form inside the magnet, which cause magnetic powder to flake off during manufacturing or cutting and other processes, resulting in chipping and cracking of the surface. In addition, cutting and other processes of hot-worked magnets expose internal cracks, leading to chipping and cracking. Chips and cracks are particularly prone to occurring on the edges. Chips and cracks in hot-worked magnets can be measured, for example, by arithmetic surface roughness (hereinafter referred to as "surface roughness").

[0010] The hot-worked magnet described in Patent Document 1 uses powder 4 obtained by crushing a band 3 with a crystal grain size of several tens of nanometers as a raw material. However, it does not disclose how to reduce the surface roughness of the manufactured hot-worked magnet in order to make the magnetic flux uniform even when processed by cutting or other methods to make it small (thin) shape. Furthermore, it does not disclose means for suppressing cracks inside the hot-worked magnet. As described above, the hot-worked magnet of the present invention has a surface roughness, particularly the surface roughness of the edges where defects are likely to occur, in the range of 32 μm to 150 μm, so that variations in magnetic flux can be suppressed. For this reason, even when used in a microactuator, the driving of the microactuator can be stabilized. The present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0011] [Hot-Worked Magnet] The hot-worked magnet of the present invention is a magnet comprising an aggregate of multiple magnetic powders, the magnet having a first surface extending in the radial direction, a second surface extending in the axial direction, and a ridge line formed by the intersection of the first surface and the second surface, the surface roughness of the ridge line being in the range of 32 μm to 150 μm. Since the surface roughness of the ridge line, which is the part of the hot-worked magnet most prone to chipping, is in the range of 32 μm to 150 μm, the hot-worked magnet of the present invention is free from chipping and cracking on the surface, and the hot-worked magnet of the present invention can have a uniform magnetic flux without variation. Furthermore, chipping and cracking of hot-worked magnets are often caused by the peeling of the magnet from the cracked portion, but since the hot-worked magnet of the present invention has fewer chips and cracks, it is thought that the occurrence of internal cracks is also suppressed. If cracks occur in a hot-worked magnet, the magnetic flux may decrease due to a reduction in the volume fraction of the main phase. However, since the hot-worked magnet of the present invention can also suppress internal cracks, it is considered that the hot-worked magnet of the present invention can have a uniform magnetic flux without variation. Furthermore, if the surface roughness of the ridge line is less than 32 μm, there will be no chipping or cracking of the hot-worked magnet. On the other hand, it is thought that the magnetic powder constituting the hot-worked magnet contains many fine particles, which may cause a decrease in the magnetic flux of the hot-worked magnet.

[0012] The magnetic powder is not particularly limited, but magnetic powder of rare earth magnets, as described later, is preferred. An example of rare earth magnet magnetic powder is magnetic powder of R-Fe-B magnets. The R-Fe-B (boron) magnet that constitutes the powder of the R-Fe-B magnet is R ２ Fe １４ Phase B (for example, R ２ Fe １４It contains a type B compound phase as the main phase. In addition, R-Fe-B magnets usually further contain an R-rich phase, etc. R represents a rare earth element containing Nd. That is, R contains Nd as an essential component. Examples of rare earth elements include neodymium (Nd) and praseodymium (Pr), as well as 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). Along with Nd, one other rare earth element may be used, or two or more may be used in combination. At least Nd is required to be used as R. Fe may be partially substituted with Co. If a portion of the Fe is substituted with Co, it is preferable that the Fe content is 50 atomic% or more, when the total amount of Fe and Co is set to 100 atomic%.

[0013] R-Fe-B magnets may contain other elements. Examples of other elements include titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W). These other elements may be used individually or in combination of two or more. In R-Fe-B magnets, R is preferably present in an amount of 12 atomic% to 16 atomic%. B is preferably present in an amount of 6 atomic% to 8 atomic%. When other elements are included, the total amount of these other elements is preferably more than 0 atomic% and 3 atomic% or less. The remainder here is the sum of Fe and any other elements that are inevitably included.

[0014] For example, as an R-Fe-B magnet, Nd ２ Fe １４ We will explain using an Nd-Fe-B magnet, which employs an Nd-Fe-B alloy with B as the main phase, as an example.

[0015] The shape of hot-worked magnets is not particularly limited and can include ring-shaped, round, plate-shaped, arc-shaped (segment-shaped), semi-circular, fan-shaped, prism-shaped, cylindrical, and conical shapes.

[0016] In this specification, the axial direction of a hot-worked magnet refers to the direction of pressure applied during the hot plastic deformation process described later, and the radial direction of a hot-worked magnet refers to the direction perpendicular to the axial direction. The first radially extending surface refers to a surface parallel to the surface that is pressed during the hot plastic deformation process described later, for example, the top surface or the bottom surface. The second axially extending surface refers to a surface perpendicular to the first radially extending surface. However, in the case of a conical or hollow conical hot-worked magnet, it refers to a surface that extends approximately in the axial direction, i.e., the outer circumferential surface or the inner circumferential surface. Here, the hot plastic deformation process is a concept that includes anisotropy and densification of the magnet.

[0017] Furthermore, in a hot-worked magnet, when it has a ridge extending in the magnetization direction (first ridge) and a ridge extending in another direction (second ridge), it is preferable that the dimension of the first ridge is shorter than the dimension of the second ridge. The surface roughness of both the first and second ridges is preferably in the range of greater than 0 μm and 150 μm or less. In a magnet used in a microactuator with one side magnetized to multiple poles, a magnet in which the dimension of the first ridge is shorter than the dimension of the second ridge is easier to magnetize, and since it is possible to make the hot-worked magnet thinner, it becomes possible to miniaturize the microactuator.

[0018] The surface roughness of the ridge of the obtained hot-worked magnet is the arithmetic mean roughness calculated by measuring the ridge from a direction that is at an equal angle from the first face extending in the radial direction and the second face extending in the axial direction (for example, in the case of a rectangular parallelepiped, the direction that is 135 degrees from the first face and the second face) using a surface roughness meter (SURFCOM 1800G / 2800G manufactured by Tokyo Seimitsu Co., Ltd.). Since the surface roughness of the ridge of the hot-worked magnet of the present invention is in the range of 32 μm to 150 μm, the magnetic flux of the magnetized hot-worked magnet has little variation and is uniform.

[0019] The particle size distribution of the magnetic powder in the hot-worked magnet is preferably in the range of 32 μm to 150 μm, more preferably in the range of 32 μm to 125 μm, and even more preferably in the range of 32 μm to 75 μm. One of the causes of cracks between magnetic powder particles is the voids between the magnetic powder particles that occur during the manufacture of the fired magnet body, which will be described later. This is due to the voids between the magnetic powder particles that fill the first mold, which will be described later. In addition, during the hot plastic deformation of the fired magnetic body, which will be described later, grain boundary sliding and crystal growth occur in the crystal grains in the magnetic powder, causing the crystals to align in the direction of pressure (direction in which magnetization is easily possible), and the magnetic powder to flatten. At this time, the voids between the magnetic powder particles that occurred in the fired magnet body due to the pressure and crystal growth during hot plastic deformation are filled, and cracks are reduced. However, if coarse particles are present, grain boundary sliding is less likely to occur, voids between the magnetic powder particles remain, and cracks remain. On the other hand, in the case of fine particles, the gaps between magnetic particles can be filled and cracks can be reduced, but the increase in the surface area of ​​the magnetic particles leads to increased oxidation on the surface of the magnetic particles, resulting in a decrease in the electrostatic properties of the hot-worked magnet. Because the particle size distribution of the magnetic particles in the hot-worked magnet is within this range, meaning that there is little variation in the particle size and no coarse or fine particles (particles with a particle size smaller than the above range) are included, the gaps between the magnetic powders can be reduced, making it less likely for gaps (cracks) to occur between the magnetic particles during the hot-pressing process. Furthermore, the gaps in the magnetic particles of the fired magnet body can be filled during hot plastic working, reducing cracks without decreasing the electrostatic properties. Therefore, peeling of magnetic particle clumps is less likely to occur during processing processes such as cutting of the hot-worked magnet. In addition, even if the magnetic particles on the surface peel off during processing processes such as cutting, the surface roughness of the edges is expected to be in the range of 32 μm to 150 μm.

[0020] The average particle size of the magnetic powder in hot-worked magnets is preferably in the range of 60 μm to 110 μm, and more preferably in the range of 60 μm to 100 μm. Because the average particle size of the magnetic powder in hot-worked magnets is within this range, i.e., because it does not contain coarse particles (particles with a particle size larger than the above numerical range), the voids between the magnetic powders can be reduced, making it less likely for voids (cracks) to occur between the magnetic powders during the hot-pressing process, and the voids in the magnetic powder of the fired magnet body can be filled during hot plastic working, further reducing cracks. As a result, peeling of the magnetic powder is less likely to occur during processing processes such as cutting of hot-worked magnets. Furthermore, even if the magnetic powder on the surface peels off during processing processes such as cutting, the surface roughness of the ridges is expected to be in the range of 32 μm to 150 μm. In addition, because it does not contain fine particles that are easily oxidized, a decrease in electrostatic properties is less likely to occur.

[0021] The particle size distribution and average particle size of the magnetic powder in hot-worked magnets are calculated from crystal images obtained by microscopic observation using an optical microscope (Hitachi Technologies F-2000 series). When measuring the particle size of the magnetic powder, microscopic observation is performed at a magnification of 200x or 400x, and when measuring the crystal grain size, it is performed at a magnification of 20,000x. The particle size is measured for n = 100 to 200 samples, and the particle size distribution and average particle size are calculated. In this specification, the particle size of flattened magnetic powder refers to the longest width.

[0022] Furthermore, it is preferable that the average grain size of the hot-worked magnet is in the range of 0.05 μm to 1.0 μm, more preferably in the range of 0.1 μm to 1.0 μm, and even more preferably in the range of 0.3 μm to 0.6 μm. When the average grain size is within the above range, the hot-worked magnet has high hardness in the axial direction. If the average grain size is smaller than 0.05 μm, there is a concern that it will become amorphous and anisotropy will not be achieved. On the other hand, if the average grain size is larger than 1.0 μm, there is a concern that the magnetic properties will deteriorate. Also, if the average grain size is larger than 1.0 μm, there is a concern that the effects of deterioration due to cutting and other processing during the manufacture of the hot-worked magnet will be greater. Furthermore, in the hot-worked magnet described later, when the average grain size is within the above range (i.e., relatively small), deterioration due to cutting and other processing during manufacture is suppressed to the vicinity of the surface. In contrast, when the average grain size is larger than the above range, there is a concern that deterioration will reach deeper through the grain boundaries and the magnetic properties will deteriorate.

[0023] <Method for manufacturing hot-worked magnets> Hot-worked magnets can be manufactured by the following steps: 1) preparing magnet powder; 2) filling a first mold with magnet powder, setting it in a sintering apparatus, and sintering it to obtain a sintered magnet body; and 3) setting the sintered magnet body in a second mold, setting it in a sintering apparatus, and performing hot plastic deformation to obtain a hot-worked magnet.

[0024] [Step 1] The magnet powder used in the step of preparing the magnet powder includes the rare earth magnet powder mentioned above. For example, as an R-Fe-B magnet, Nd ２ Fe １４ We will explain using an Nd-Fe-B magnet, which employs an Nd-Fe-B alloy with B as the main phase, as an example.

[0025] Nd-Fe-B magnet powder is manufactured, for example, by an ultra-rapid cooling method (melt-spun method). Specifically, an Nd-Fe-B alloy is melted by high-frequency induction heating under reduced pressure or in an argon atmosphere. Next, the molten alloy is sprayed onto a copper rotating roll and ultra-rapidly cooled (rapid cooling) to produce ribbon-shaped thin strips. Next, these thin strips are pulverized. For example, it is preferable to break the thin strips into pieces of several millimeters to several tens of millimeters and then pulverize them using a pulverizer or the like. These thin strips are then pulverized to obtain pulverized powder.

[0026] After crushing ribbon-shaped thin strips to obtain crushed powder, the crushed powder is classified using a sieve with a predetermined mesh size, and then heat-treated to obtain magnetic powder. At this stage, the magnetic powder is magnetically isotropic because the easy magnetization axes of each crystal grain are not aligned in one direction. The obtained magnetic powder is classified using a sieve with a predetermined mesh size to obtain magnetic powder with a particle size in the range of 32 μm to 150 μm, preferably 32 μm to 125 μm. Because the magnetic powder is within the above range, when filling the first mold described below with the magnetic powder, the particle size is uniform and the gaps between particles are small, so the sintered magnetic body obtained by hot pressing is less prone to cracking.

[0027] In addition, instead of actually manufacturing the magnetic powder, pre-manufactured magnetic powder can be used as a substitute. For example, anisotropic magnetic powders such as MQA grade and MQU grade of MagneQuench® manufactured by MagneQuench Co., Ltd., and MAGFINE® manufactured by Aichi Steel Ltd. are suitable. Examples of MQA grade MagneQuench® include MQP-14-12 (product name), MQP-8-5 (product name), MQP-10-8.5HD (product name), MQP-11-8 (product name), MQP12-8HD (product name), MQA37-16 (product name), and MQP-A (product name). Examples of MAGFINE® include MF15P (product name) and MF18P (product name).

[0028] [Step 2] Next, a first mold is prepared. The first mold can be appropriately selected from the shape of the hot-worked magnet to be manufactured (a shape that can be set in the second mold described below). For example, the first mold for obtaining a ring-shaped hot-worked magnet consists of a hollow cylindrical die, hollow cylindrical upper and lower punches inserted inside the die, and a cylindrical core positioned inside the upper and lower punches. The die, upper punch, lower punch, and core are made of a conductive material (e.g., graphite, cemented carbide, etc.). For example, the first mold for obtaining a plate-shaped hot-worked magnet consists of a hollow die and upper and lower punches inserted inside the die. The die, upper punch, and lower punch are made of a conductive material (e.g., graphite, cemented carbide, etc.). Shapes such as round, plate, arc (segment), semi-circular, fan, prismatic, cylindrical, and conical can also be manufactured in the same way as plate-shaped hot-worked magnets.

[0029] Next, the first mold is filled with rare earth magnet powder (Nd-Fe-B type magnet powder), set in a sintering apparatus (SPS apparatus: discharge plasma sintering apparatus) and sintered, and the sintered magnet body (hot-pressed magnet body) is removed from the first mold.

[0030] The magnet powder filled in the cavity of the first mold is pressurized by the upper and lower punches due to the pressure applied between the upper and lower electrodes. Furthermore, an electric current flows from the upper electrode to the upper punch, which then flows through the die, core, and magnet powder, and through the lower punch to the lower electrode. This generates Joule heat and a discharge plasma within the magnet powder, thereby heating the powder. The magnet powder is heated to a temperature of 600°C to 700°C while being pressurized, for example, at 30 to 50 MPa; this process is called hot pressing. Sintering is preferably carried out under reduced pressure in an inert gas atmosphere such as argon and nitrogen.

[0031] After heating, the current is cut off and the device is cooled. After cooling to a predetermined temperature, the first mold is removed from the sintering apparatus. Specifically, a ring-shaped sintered magnet body formed by the sintering of magnet powder is removed from the first mold. In this state, the ring-shaped sintered magnet body has, for example, a relative density of approximately 90%, the orientation of the easy magnetization axes of its crystal grains is random, and it is magnetically isotropic.

[0032] [Step 3] Next, prepare the second mold. The preparation of the second mold may be carried out in parallel with the preparation of the first mold, or it may be carried out before the preparation of the first mold. Set the sintered magnet body made in the hot pressing process described above into the second mold, and set the second mold into the sintering apparatus to perform hot plastic deformation. The second mold can be appropriately selected depending on the shape of the hot-worked magnet to be manufactured.

[0033] In the sintering apparatus, an upper electrode is positioned at the upper end of the punch, and a lower electrode is positioned at the lower end of the die. The upper and lower electrodes are made of a conductive material (e.g., graphite, cemented carbide, etc.). The sintering apparatus includes a power supply device and a control device that apply a predetermined voltage between the upper and lower electrodes and supply a predetermined current. The sintering apparatus may be the same as the sintering apparatus used in the hot pressing process described above, or it may be a separate apparatus.

[0034] The sintered magnet body, positioned between the die and punch of the second mold, is pressurized by the die and punch. It is also heated by discharge plasma and Joule heat generated by the flow of current through the path upper electrode → punch → sintered magnet body → die → lower electrode. Hot plastic deformation begins with the application of pressure at 30-100 MPa, followed by heating, and is pressurized while heating to, for example, a range of 600°C to 700°C. During heating, ON-OFF DC pulse current is applied to the sintered magnet body. During hot plastic deformation, it is desirable to adjust the pressure so that the processing speed does not increase, preferably so that the processing speed remains constant. Hot plastic deformation is preferably performed under reduced pressure and in an inert gas atmosphere such as nitrogen or argon. Hot plastic deformation is preferably performed while monitoring the displacement, from the start of displacement until completion. Here, the displacement is typically monitored by the displacement amount of a pressure-controlled servo motor.

[0035] The crystal grains of hot-worked magnets produced by hot plastic deformation have a flattened shape, and the easy magnetization axis of the crystal grains is oriented perpendicular to the flattened plane of the crystal grains. Crystal grains produced during the ultra-rapid cooling method are isotropic, but hot plastic deformation causes the crystal grains to grow into a flattened shape, and the flattened plane of the particles aligns in the direction of mechanical pressure. In other words, the easy magnetization axis aligns with the direction of pressure (the direction of the short axis of the crystal grain). Therefore, the easy magnetization axis of the crystal grains within the magnet aligns in the thickness direction of the hot-worked magnet (a sintered magnet body is transformed into a hot-worked magnet by hot plastic deformation).

[0036] After heating, the sintering apparatus is cooled by cutting off the current. After cooling to a predetermined temperature, the second mold is removed from the sintering apparatus, and the hot-worked magnet obtained by hot plastic deformation from the sintered magnet body is removed from the second mold.

[0037] Hot-worked magnets obtained by hot plastic deformation exhibit magnetic anisotropy; for example, their relative density is approximately equal to their true density, resulting in high magnetic properties. The fabricated hot-worked magnets, for instance, have an average grain size within the above range, and their Curie point is in the range of 250°C to 400°C.

[0038] [Cutting and other processing steps] The hot-worked magnet obtained by hot plastic processing can be processed by cutting or the like into a predetermined shape as needed. For example, a hot-worked magnet that has been hot plastically processed into a desired shape such as a ring shape is ground on a surface grinder so as to have a desired thickness. Specifically, grinding is performed such that the thickness direction coincides with the pressing direction during the production of the hot-worked magnet, that is, the easy magnetization axis direction. In other words, processing such as cutting is performed only in the short axis direction (i.e., the easy magnetization axis direction) of the columnar grains having a flat shape in the hot-worked magnet. Grinding is performed, for example, using a rotating grindstone made of a diamond grindstone or the like.

[0039] For example, the hot-worked magnet (ring-shaped magnet after cutting and other processing) obtained as described above has a structure of a main phase containing an R ２ Fe １４ B compound. Specifically, the average crystal grain size of the main phase is within the above range. Also, in this hot-worked magnet, the easy magnetization axis is oriented in the short axis direction of the columnar grains of the main phase.

[0040] The surface roughness of the ridge line of the obtained hot-worked magnet is measured using a SURFCOM1800G / 2000G (manufactured by Tokyo Seimitsu Co., Ltd.). Although it is preferable to measure the entire surface of the hot-worked magnet for the surface roughness, in this specification, since the ridge portion of the hot-worked magnet is most likely to chip or crack, the ridge line having the highest surface roughness is measured and taken as the surface roughness. Since the surface roughness of the ridge line of the hot-worked magnet of the present invention is in the range of 32 μm or more and 150 μm or less, the magnetic flux of the obtained hot-worked magnet has little variation and is uniform. Note that in this specification, when the magnetic flux is uniform, it means that when used in a micro actuator, there is little variation to the extent that smooth movement of the hot-worked magnet can be realized and stable behavior is exhibited.

[0041] The magnetic powder particle size distribution of the obtained hot-worked magnet is preferably in the range of 32 μm or more and 150 μm or less, more preferably in the ranges of 32 μm or more and 125 μm or less, and 32 μm or more and 75 μm or less. When the magnetic powder particle size distribution of the hot-worked magnet is within this range, cracks are less likely to occur during hot plastic processing, and magnetic powder peeling is less likely to occur in processing steps such as cutting. Therefore, the surface roughness of the ridge line is considered to be in the range of 32 μm or more and 150 μm or less.

[0042] The average particle size of the magnetic powder of the obtained hot-worked magnet is preferably in the range of, for example, 60 μm or more and 110 μm or less, and more preferably in the range of 60 μm or more and 100 μm or less. When the average particle size of the magnetic powder of the hot-worked magnet is within this range, cracks are less likely to occur during the hot plastic working of the hot-worked magnet, and magnetic powder peeling is less likely to occur in machining processes such as cutting. Therefore, the surface roughness of the ridge line is considered to be in the range of 32 μm or more and 150 μm or less.

[0043] The magnetic powder particle size distribution and average particle size of the hot-worked magnet can be measured from a plurality of images obtained by microscopic observation using the above-described optical microscope (Hitachi Technologies F-2000 series). As an example, optical microscope photographs of a hot-worked magnet produced using magnet powder in the range of 45 μm or more and 355 μm or less are shown in FIGS. 11(a) (20,000 times) and (b) (1,000,000 times).

[0044] As the magnetization means of the hot-worked magnet, known means can be used. For example, for the magnetization of a ring-shaped hot-worked magnet, UHM magnetization as disclosed in Japanese Patent Application Laid-Open No. 2021-093521 is preferably used. That is, it can be carried out by heating the magnetizable object (for example, a hot-worked magnet, that is, a hot-worked magnet after machining such as cutting) to a temperature above the Curie point of its magnetic powder and continuously applying a magnetization magnetic field to the magnetizable object by a permanent magnet, which is a magnetic field source, while cooling it to a temperature below the Curie point. In this way, a ring-shaped hot-worked magnet magnetized with a pitch of a predetermined magnetic pole in the circumferential direction can be obtained.

[0045] Before magnetization, the obtained hot-worked magnet can be subjected to a known rust prevention treatment to prevent oxidation of its surface. The rust prevention treatment is not particularly limited, but for example, treatments such as nickel plating or composite plating of nickel plating and copper plating can be carried out.

[0046] <Actuator> The hot-worked magnet of the present invention can have various shapes by selecting the first and second molds and processing such as cutting, and can be used in existing actuators. Hereinafter, with reference to the attached drawings, embodiments of an aperture adjustment device and a magnetic encoder will be described as examples of actuators according to the present invention, but the present invention is not limited to the embodiments described below.

[0047] (First Embodiment) First, the first embodiment will be described with reference to the attached figures. In the first embodiment, with reference to Figure 1, the motor 1 comprises a hot-worked magnet 3, a substrate 4 having a coil 31 which is provided opposite the hot-worked magnet 3 in the direction A along the rotation axis L of the motor 1 (the "up and down direction" in Figure 3, hereinafter referred to as "rotation axis direction A"), and a magnetic fluid, for example, a magnetic fluid 5 (for convenience, shown as an annular member) provided between the hot-worked magnet 3 and the coil 31 of the substrate 4.

[0048] Referring to Figure 1, the magnetic fluid 5 supports the surface of the hot-worked magnet 3 and the coil 31 of the substrate 4 so that they can rotate relative to each other. In the first embodiment, the magnetic fluid 5 supports the surface of the hot-worked magnet 3 so that it can rotate relative to the coil 31 (fixed) of the substrate 4. The motor 1 is of the axial gap type, with a magnetic gap formed between the hot-worked magnet 3 and the coil 31 via the magnetic fluid 5.

[0049] Referring to Figures 1 and 2, the hot-worked magnet 3 is a hot-worked magnet formed in a ring shape as described above. The hot-worked magnet 3 has multiple magnetic poles. Specifically, the magnetic poles are formed at a predetermined pitch in the circumferential direction C of the hot-worked magnet 3. The hot-worked magnet 3 has alternating north poles and south poles along the circumferential direction C. From the viewpoint of magnetic flux density, the pitch of the multiple magnetic poles is preferably 2.0 mm or less. Here, the pitch of the magnetic poles is the length in the circumferential direction of the hot-worked magnet 3. Also, from the viewpoint of magnetic flux density, the number of poles is preferably 16 or more.

[0050] The hot-worked magnet 3 includes a rare-earth magnet, and the surface roughness of the ridge line 12 formed by the intersection of a surface extending in the radial direction R and a surface extending in the axial direction A of the hot-worked magnet 3 is preferably in the range of 32 μm to 150 μm. Because the surface roughness of the ridge line 12 is in the range of 32 μm to 150 μm, the hot-worked magnet 3 can rotate smoothly due to electromagnetic interaction with the coil 31, and the rotational torque perpendicular to the axial direction is stable.

[0051] The hot-worked magnet 3 preferably has a magnetic powder particle size distribution in the range of 32 μm to 150 μm. Furthermore, it is preferable that the average magnetic powder particle size is in the range of 60 μm to 110 μm, and more preferably in the range of 60 μm to 100 μm. By having a magnetic powder particle size distribution in the above range, cracks are less likely to occur during hot plastic deformation of the hot-worked magnet 3, chipping of the surface and edges 12 due to processing steps such as cutting can be suppressed, and the surface roughness of the surface and edges 12 of the hot-worked magnet 3 can be made 150 μm or less.

[0052] Furthermore, the hot-worked magnet 3 includes a rare-earth magnet, and the average grain size of the rare-earth magnet is preferably in the range of 0.05 μm to 1.0 μm, more preferably in the range of 0.1 μm to 1.0 μm, and even more preferably in the range of 0.3 μm to 0.6 μm. When the average grain size is within the above range, the crystal structure is fine, and therefore the hot-worked magnet 3 has high hardness. If the average grain size is smaller than 0.05 μm, it becomes amorphous, and there is a concern that the anisotropic property will not be exhibited. On the other hand, if the average grain size is larger than 1.0 μm, there is a concern that the magnetic properties will deteriorate. Also, if the average grain size is larger than 1.0 μm, there is a concern that the effects of deterioration due to processing such as cutting during the manufacture of the hot-worked magnet 3 will be greater. Furthermore, in the hot-worked magnet described later, when the average grain size is within the above range (i.e., relatively small), deterioration due to processing such as cutting during manufacture is suppressed to the vicinity of the surface. In contrast, if the average grain size is larger than the range mentioned above, there is a concern that degradation may reach deeper through the grain boundaries, leading to a decrease in magnetic properties.

[0053] The hot-worked magnet 3 has a thickness H (see Figure 3) of 1.0 mm or less (excluding 0 mm or less). The hot-worked magnet 3 has a mass of 0.1 g or less (excluding 0 g or less).

[0054] Here, the magnetic material used in the hot-worked magnet 3 can be either anisotropic or isotropic magnetic powder. When prioritizing magnetic properties, anisotropic magnetic powders such as MQA grade of MagneQuench® manufactured by MagneQuench Co., Ltd. or MAGFINE® manufactured by Aichi Steel Ltd. are suitable. On the other hand, for applications where the rotational speed of the motor 1 is 100 rpm or more, isotropic magnetic powders such as MQU grade and MQP grade of MagneQuench® manufactured by MagneQuench Co., Ltd. are suitable. This is because, as the rotational speed of the motor 1 increases, a reverse current is generated in the coil 31 that cancels out the current that is originally applied, which reduces the efficiency of the motor 1. Therefore, when the rotational speed of the motor 1 is 100 rpm or more, it is preferable to use isotropic magnetic powder that reduces the back electromotive force.

[0055] Referring to Figure 1, a magnetic fluid, such as a magnetic fluid 5, is magnetically held on the surface of the hot-worked magnet 3, that is, the surface 19 facing the coil 31 (hereinafter referred to as the "coil-facing surface 19") (see Figure 3). In other words, the surface of the hot-worked magnet 3 is oriented toward the substrate 4 having the coil 31. The coil-facing surface 19 corresponds to the surface of the hot-worked magnet 3. The magnetic fluid 5 is a magnetic colloidal solution containing, for example, ferromagnetic ultrafine particles such as magnetite and composite ferrite, a surfactant, and a base liquid such as water and oil. The ferromagnetic ultrafine particles are on the nano-order (in the range of 1 nm to 999 nm). Note that the magnetic fluid 5 is not always magnetized, and includes particles that are magnetized by the magnetic force of the hot-worked magnet 3.

[0056] Referring to Figures 1 and 2, the substrate 4 is, for example, a circuit board such as a flexible printed circuit board. The substrate 4 has a substrate body 21 made of an insulating plate, and a circuit portion 23 formed on the surface 22 of the substrate body 21 facing the hot-worked magnet 3 (hereinafter referred to as the "hot-worked magnet facing surface 22"). The circuit portion 23 has a coil 31, a plurality (four in this embodiment) of lands 35A to 35D, and a plurality (four in this embodiment) of connection portions 36A to 36D.

[0057] The coil 31 has a first coil group 33 and a second coil group 34, which are a plurality of coils extending in a constant pattern in the circumferential direction on the substrate body 21. One end of the first coil group 33 is connected to the land 35A via a connecting part 36A, and the other end is connected to the land 35B via a connecting part 36B. On the other hand, one end of the second coil group 34 is connected to the land 35C via a connecting part 36C, and the other end is connected to the land 35D via a connecting part 36D. The coil 31 is arranged such that the first coil group 33 is positioned further outward than the second coil group 34 in the radial direction R (hereinafter referred to as "radial direction R") of a circle centered on the rotation axis L.

[0058] Thus, the coil 31 is constructed such that the first coil group 33 and the second coil group 34 do not intersect; in other words, the first coil group 33 and the second coil group 34 are electrically insulated from each other. The width of the coil 31 (first coil group 33 and second coil group 34) along the radial R is greater than the width of the hot-worked magnet 3 along the radial R. This prevents the hot-worked magnet 3 from shifting radially during the operation of the motor 1, thereby ensuring the stability of the motor 1's operation.

[0059] Then, when an AC voltage is applied between land 35A and land 35B by the AC power supply 40 (see Figure 7), S poles are formed on the parts of the coil 31 that are opposite the S poles of the hot-worked magnet 3, and N poles are formed on the parts of the coil 31 that are opposite the N poles of the hot-worked magnet 3. As a result, the repulsive force of the magnetic poles causes the hot-worked magnet 3 to rotate in one direction around the rotation axis L, and the magnetic poles of the hot-worked magnet 3 and the magnetic poles of the parts of the coil 31 become opposite, forming a magnetic circuit between the hot-worked magnet 3 and the coil 31.

[0060] Meanwhile, an AC voltage with a phase difference of 90 degrees from the AC voltage applied between land 35A and land 35B is applied between land 35C and land 35D by the AC power supply 40 (see Figure 7). As a result, the magnetic poles of the hot-worked magnet 3 and the magnetic poles of each part of the coil 31 become the same, and the repulsive force of the magnetic poles causes the hot-worked magnet 3 to rotate in one direction around the rotation axis L, so that the magnetic poles of the hot-worked magnet 3 and the magnetic poles of each part of the coil 31 become opposite, and a magnetic circuit is formed by the hot-worked magnet 3 and the coil 31.

[0061] Furthermore, the aspect ratio of motor 1, that is, the ratio of the thickness of motor 1 to the outer diameter (thickness of motor 1 / outer diameter of motor 1), is in the range of 0.05 or more and 0.2 or less. In addition, the rotational torque of motor 1 is 20 μN or more when the drive current is 300 mA, and is greater than the static friction force or kinetic friction force generated between the coil-facing surface 19 of the hot-worked magnet 3 (see Figure 3) and the hot-worked magnet-facing surface 42 of coil 31 (see Figure 3).

[0062] Then, referring to Figure 1, the magnetic fluid 5 held by the hot-worked magnet is in contact with the coils 31 (first coil group 33 and second coil group 34) of the substrate 4, and an axial gap type device is constructed in which the coils 31 of the substrate 4, the magnetic fluid 5, and the hot-worked magnet are arranged in that order in the axial direction.

[0063] In small (thin) hot-worked magnets, variations in magnetic flux due to chipping or cracking are more likely to occur. When conventional magnets are used, the magnetic flux in the chipped part of the magnet weakens, resulting in a weaker electromagnetic interaction (attraction and repulsion) with the coil. In other words, during rotation of the magnet, the attractive (repulsive) force in the chipped part of the magnet weakens, while the attractive (repulsive) force in the part that is point-symmetric with respect to the rotation of the magnet becomes relatively stronger relative to the chipped part. As a result, the magnet cannot maintain a state perpendicular to the axis of rotation, which may lead to unstable rotational torque. In contrast, in the first embodiment, a magnet 3 with a surface roughness of 150 μm or less on the edge 12 is used, so variations in magnetic flux of the magnet 3 are suppressed and the rotational torque is stabilized, thus stabilizing the torque of the motor 1.

[0064] Next, an embodiment of driving a plurality (six blades 54, 54 in this embodiment) incorporated into an aperture adjustment device 50 of a camera mounted on a smartphone or the like using the motor 1 described above will be explained based on Figures 3 to 8. Referring to Figures 3 to 5, the aperture adjustment device 50 has a motor housing 52, a hot-worked magnet 3 (including magnetic fluid 5) of the motor 1, a substrate 4 of the motor 1, a rotating body 53, and a plurality (six blades in this embodiment) of blades 54, 54. The rotating body 53 and the blades 54, 54 correspond to weights. Referring to Figures 5 and 6, the motor housing 52 has a base 57 and a cover 58. The motor housing 52 has an internal space 60 defined by the base 57, the cover 58, and the substrate body 21 of the motor 1. The hot-worked magnet 3, the rotating body 53, and the plurality of blades 54, 54 are housed in the internal space 60. The magnetic fluid is placed between the hot-worked magnet 3 and the substrate 4, and contributes to reducing the rotational resistance of the hot-worked magnet 3.

[0065] Referring to Figure 5, the base 57 is formed in a rectangular shape as viewed from the direction of rotation axis A. The base 57 has a hole (hereinafter referred to as "axis hole 64") that penetrates in the direction of rotation axis A, a small-diameter recess 65 formed on the opening periphery of the axis hole 64 on one side of rotation axis A (the "upper side" in Figure 4), a large-diameter recess 66 formed on the opening periphery of the small-diameter recess 65 on one side of rotation axis A, and a notch 67 formed to surround the lands 35A to 35D on the substrate body 21. The opening periphery of the axis hole 64, the small-diameter recess 65, and the large-diameter recess 66 on one side of rotation axis A is formed in a circular shape coaxial with respect to the rotation axis L (see Figure 4). The substrate 4 of the motor 1 is fixed to the base 57 of the motor housing 52.

[0066] Referring to Figures 5 and 6, the hot-worked magnet 3 and the rotating body 53 (described later) are rotatably housed in the shaft hole 64 of the base 57. The outer circumferential surfaces of the hot-worked magnet 3 and the rotating body 53 are rotatably supported on the inner circumferential surface of the shaft hole 64. The inner circumferential surface of the shaft hole 64, i.e., the base 57, corresponds to the component. A coating made of, for example, a fluororesin coating may be formed on the outer circumferential surface of the hot-worked magnet 3. This makes it possible to reduce the rotational resistance of the hot-worked magnet 3 from the motor housing 52 when the motor 1 is rotating, and to stabilize the rotational torque of the motor 1. The base 57 has a plurality of (six in this embodiment) pins 69, 69 formed on the bottom surface (reference numerals omitted) of the small-diameter recess 65. The plurality of pins 69, 69 are arranged at equal intervals (60-degree intervals in this embodiment) on a circle (circumferential direction) centered on the rotation axis L (see Figure 4).

[0067] The rotating body 53 is composed of a ring-shaped plate member having the same outer and inner diameters as the hot-worked magnet 3. The rotating body 53 is fixed coaxially to the hot-worked magnet 3 by adhesive or the like on the rotating body mounting surface 20 of the hot-worked magnet 3 (the surface opposite to the coil-facing surface 19 in the rotation axis direction A). The rotating body 53 has a plurality of pins 73, 73 formed on the surface 72 (hereinafter referred to as the "wing-facing surface 72") opposite to the surface facing the hot-worked magnet 3 (joint surface) in the rotation axis direction A. The plurality of pins 73, 73 are arranged at equal intervals (60-degree intervals in this embodiment) on a single circle (circumferential direction) centered on the rotation axis L (see Figure 4).

[0068] The cover 58 is composed of a ring-shaped plate. The cover 58 has a surface (hereinafter referred to as the "double-sided width portion 75") that is formed to match the shape of the base 57 and is aligned radially in the direction of the rotation axis A. The cover 58 has a plurality of (six in the first embodiment) pin holes 77, 77 arranged at equal intervals (60-degree intervals in the first embodiment) on a circle (circumferential direction) centered on the rotation axis L (see Figure 4). See also Figure 4, corresponding pins 69, 69 provided on the base 57 are fitted into the pin holes 77, 77. The cover 58 has a plurality of (six in the present embodiment) elongated holes 79, 79 arranged at equal intervals (60-degree intervals in the present embodiment) on a circle centered on the rotation axis L (see Figure 4) and extending along the circle. See also Figure 4. The corresponding pins 73, 73 provided on the rotating body 53 are fitted into the elongated holes 79, 79.

[0069] Multiple blades 54, 54 are provided between the cover 58 and the rotating body 53. In this embodiment, as described above, "six" blades 54, 54 are provided. Multiple blades 54, 54 are arranged to surround (alongside the shaft hole 64) formed in the base 57 of the motor housing 52. An opening 85 is formed inside the multiple blades 54, 54. Multiple blades 54, 54 are formed to be the same shape. Referring to Figure 7, a pin hole 82 is formed on one side (the "clockwise side" in Figure 7) of the shaft hole 64 (see Figure 5) in the circumferential direction (hereinafter referred to as "circumferential direction C"). A corresponding pin 69 provided in the base 57 is fitted into the pin hole 82. On the other side of the pin hole 82 in the circumferential direction C (the "counterclockwise side" in Figure 7), an arc-shaped elongated hole 84 is formed on the blade 54. A corresponding pin 73, provided on the rotating body 53, is fitted into the elongated hole 84. The total weight of the multiple blades 54, 54 (weights) is heavier than the weight of the hot-worked magnet 3.

[0070] Then, from the state shown in Figure 8, when an AC voltage with a 90-degree phase shift is applied to the first coil group 33 and the second coil group 34 of the motor 1 by the AC power supply 40, the hot-worked magnet 3 and the rotating body 53 rotate together around the rotation axis L in the counterclockwise direction as shown in Figure 8. As a result, the pin 73 of the rotating body 53 moves within the corresponding elongated hole 84 of the blade 54 from one side in the circumferential direction to the other side. Consequently, the multiple blades 54, 54 rotate clockwise as shown in Figure 8 around the pins 69, 69 of the base 57, and as shown in Figure 7, the opening area of ​​the opening 85 formed by the multiple blades 54, 54 increases. Light can pass through this opening.

[0071] On the other hand, from the state shown in Figure 7, when an AC voltage with a 90-degree phase difference is applied by the AC power supply 40 to the first coil group 33 and the second coil group 34 of the motor 1, such that the hot-worked magnet 3 and the rotating body 53 rotate together clockwise around the rotation axis L, the pins 73 of the rotating body 53 move within the corresponding elongated holes 84 of the blades 54 from one side in the circumferential direction to the other side. As a result, the multiple blades 54, 54 rotate counterclockwise around the pins 69, 69 of the base 57 in the direction shown in Figure 7, and as shown in Figure 8, the aperture area of ​​the opening 85 formed by the multiple blades 54, 54 decreases. In this way, the aperture adjustment device 50 adjusts the amount of light incident on the camera lens unit (not shown) by making the aperture area of ​​the opening 85 formed by the multiple blades 54, 54 variable.

[0072] Furthermore, according to the first embodiment, since the motor 1 is of the axial gap type and can be miniaturized along the rotation axis direction A, the aperture adjustment device 50 into which the motor 1 is incorporated can be miniaturized.

[0073] Furthermore, according to the first embodiment, by using a hot-worked magnet 3 in which the surface roughness of the ridge line 12 is in the range of 32 μm to 150 μm, it is possible to stabilize the rotational torque of the hot-worked magnet, and consequently, it becomes possible to smoothly vary the opening area of ​​the opening 85 formed by the multiple blades 54, 54 of the aperture adjustment device 50 into which the motor 1 is incorporated.

[0074] Furthermore, in the first embodiment, the hot-worked magnet 3 and the rotating body 53 are rotatably housed in a shaft hole 64 formed in the base 57 of the motor housing 52, so that when the motor 1 is not rotating, displacement of the hot-worked magnet 3 relative to the coil 31 can be suppressed.

[0075] (Second Embodiment) Next, a second embodiment will be described with reference to Figure 9. In the second embodiment, with reference to Figure 2, the magnetic encoder 101 has two magnetic tracks, a main track 102 and a sub-track 103, and the main track 2 and the sub-track 3 are arranged concentrically on the outer and inner circumferences, respectively, with an unmagnetized region 4 (which is smaller than the surface magnetic flux value of the main track and the sub-track, and this value includes zero) in between.

[0076] As shown in Figure 2, the main track 102 and the sub-track 103 are magnetized such that their north poles and south poles are arranged alternately next to each other. The sensor module 105, which is equipped with magnetic sensors 106A and 106B for detecting the magnetic fields of the main track 102 and the sub-track 103, is positioned on some of the magnetic poles of the main track 2 and the sub-track 3, as shown in Figure 2.

[0077] The main track 102 and the sub-track 103 are hot-worked magnets containing the rare-earth magnets described above, and it is preferable that the surface roughness of the edges of the hot-worked magnets is in the range of 32 μm to 150 μm.

[0078] The main track 102 and the sub-track 103 preferably have a magnetic particle size distribution in the range of 32 μm to 150 μm. Alternatively, the average magnetic particle size is preferably in the range of 60 μm to 110 μm. By having the magnetic particle size distribution or average magnetic particle size within the above range, cracks are less likely to occur during hot plastic deformation of the main track 102 and the sub-track 103, chipping of the surface and edges due to processing steps such as cutting can be suppressed, and the surface roughness of the surface and edges of the main track 102 and the sub-track 103 can be set to the range of 32 μm to 150 μm.

[0079] Hot-worked magnets can be used by hot-plasticly deforming the rare earth elements described above into a predetermined shape, then processing them by cutting or other means, and finally magnetizing them. Before magnetization, surface treatment can also be performed as described above. The main track 102 and the sub-track 103 are magnetized with multiple magnetic pole pairs (N poles and S poles) at equal pitches in the circumferential direction, and the number of magnetic poles on the main track 102 and the sub-track 103 are different from each other. For example, if the main track 102 is magnetized with n pole pairs, the sub-track 102 will be magnetized with (n-1) pole pairs.

[0080] The magnetic pole pitch is determined by the magnetic pole width of the magnetic track formed on the magnetic encoder 101. If the magnetic pole width of the magnetic sensors 106A and 106B that detect the magnetic track of the magnetic encoder 101 is limited, the magnetic pole pitch of the magnetic track formed on the magnetic encoder 101 will be the same width as the magnetic pole width of the magnetic sensors 6A and 6B. For example, if the magnetic pole width of magnetic sensor 106A is limited to 1.28 mm (or 1.5 mm), the main track 2 of the magnetic encoder 1 will be magnetized to 1.28 mm (or 1.5 mm), as shown in Figure 9.

[0081] When the magnetic encoder 101 is rotated around a concentric center, a phase shift occurs between magnetic sensors 106A and 106B because the number of magnetic poles of the main track 102 and the sub-track 103 are different. By detecting this phase shift and calculating the absolute angle of the magnetic encoder 101, the rotational position of the device on which the magnetic encoder 101 is installed can be detected.

[0082] The hot-worked magnet of the present invention is suitable for use as a main track and sub-track for a magnetic encoder because the dimension of the first ridge line extending in the magnetization direction is shorter than the dimension of the second ridge line extending in other directions. However, small (thin) hot-worked magnets are prone to variations in magnetic flux due to chipping or cracking. When conventional magnets are applied to a magnetic encoder, the magnetic flux in the chipped part of the magnet weakens, making it impossible to accurately detect the phase difference between the main track and the sub-track between magnetic sensor 106A and magnetic sensor 106B, which may prevent accurate detection of the rotational position of the device on which the magnetic encoder is installed. In contrast, in the second embodiment, the main track 102 and the sub-track 103 are made of hot-worked magnets with a surface roughness of 150 μm or less on the ridge line 107, so that the phase difference between the main track and the sub-track can be accurately detected between magnetic sensor 106A and magnetic sensor 106B, and the rotational position of the device on which the magnetic encoder is installed can be detected with high angular accuracy.

[0083] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0084] In the examples, the Nd-Fe-B magnet powder used as the hot-worked magnet is Magnequench® MQU (manufactured by Magnequench, Nd 14.5 Fe Bal B6 (Nd content: 14.5 at%, B content: 6 at%, remainder being Fe) was used.

[0085] Example 1 Nd-Fe-B magnet powder was classified using 32 μm mesh and 150 μm mesh sieves to obtain magnet powder 1 with a particle size in the range of 32 μm to 150 μm. The obtained magnet powder was filled into a first mold and hot-pressed at a temperature of 600°C to 700°C and a pressure of 30 to 50 MPa to obtain a prismatic (30 mm × 40 mm × 10 mm) sintered magnet body 1. As described above, the obtained sintered magnet body 1 was set in a second mold and hot-plastic processed at a temperature of 600°C to 700°C and a pressure of 30 to 100 MPa for 1 to 30 minutes. The obtained hot-processed magnet was cut and surface-polished to obtain a thin plate-shaped (50 mm × 60 mm × 4 mm) hot-processed magnet 1.

[0086] Example 2 A hot-worked magnet 2 was obtained in the same manner as in Example 1, except that magnet powder 2 obtained by classifying Nd-Fe-B magnet powder using sieves of 32 μm mesh and 125 μm mesh was used.

[0087] Example 3 A hot-worked magnet 3 was obtained in the same manner as in Example 1, except that magnet powder 3 obtained by classifying Nd-Fe-B magnet powder using sieves of 32 μm mesh and 75 μm mesh was used.

[0088] Comparative Example 1 A hot-worked magnet 4 was obtained in the same manner as in Example 1, except that magnet powder 4 obtained by classifying Nd-Fe-B magnet powder using a 32 μm mesh sieve was used.

[0089] Comparative Example 2 A hot-worked magnet 5 was obtained in the same manner as in Example 1, except that magnet powder 5 obtained by classifying Nd-Fe-B magnet powder using a 355 μm mesh sieve was used.

[0090] The obtained hot-worked magnets 1 to 5 were observed using an optical microscope, and the magnetic particle size distribution and average particle size were calculated. The calculated magnetic particle size distribution and average particle size are shown in Table 1. Furthermore, an optical microscope image (80x magnification) of the cross-section of hot-worked magnet 1 is shown in Figure 12(b), and an optical microscope image (80x magnification) of the cross-section of hot-worked magnet 5 is shown in Figure 12(a). Note that the black area at the top of the screen in Figures 12(a) and (b) is the tape portion used to fix the hot-worked magnets.

[0091] The surface roughness of the obtained hot-worked magnet 1 was measured using a SURFCOM 1800G / 2800G (manufactured by Tokyo Seimitsu Co., Ltd.) at the intersection of the surface in contact with the upper punch (the first surface extending radially) and the surface extending in the direction of pressure (the second surface extending axially). The surface roughness of the surface-worked magnets 2 to 5 was evaluated in the same manner. A: Surface roughness is in the range of 32 μm or more and 150 μm or less. N: Surface roughness is less than 32 μm or greater than 150 μm.

[0092]

[0093] The hot-worked magnets of Examples 1 to 3, in which the magnetic powder particle size distribution falls within the range of 32 μm to 150 μm, showed that the surface roughness of the edges was between 32 μm and 150 μm, demonstrating that hot-worked magnets with fewer chips and irregularities can be obtained.

[0094] In contrast, it was shown that hot-worked magnets 5 with a magnetic particle size distribution of 355 μm or less and an average magnetic particle size of 300 μm have a surface roughness exceeding 150 μm, resulting in hot-worked magnets with chips and uneven surfaces.

[0095] Furthermore, optical microscope images confirmed that the hot-worked magnet of the present invention consists of magnetic powder formed from anisotropic crystal grains.

[0096] Furthermore, when a magnetic field of 5T is applied to the hot-worked magnets 1 to 5 to magnetize them, the hot-worked magnets 1 to 3 can obtain superior electrostatic properties compared to the hot-worked magnets 4 and 5.

[0097] Furthermore, comparing Figures 12(a) and (b), it can be seen that in the cross-sectional photograph of the hot-worked magnet 1 of the present invention (Figure 12(b)), there are almost no cracks inside the magnet, whereas in the cross-sectional photograph of the hot-worked magnet 5 (Figure 12(a)), a long crack has formed in the left-right direction of the photograph. From this, it can be seen that the hot-worked magnet of the present invention does not experience peeling of magnetic powder during processing such as cutting, and the surface roughness is in the range of 32 μm to 150 μm.

[0098] From the above, the hot-worked magnet of the present invention can be used as a small hot-worked magnet for actuators by magnetizing it. In the embodiments described above, the actuator was described as a motor 1 and a magnetic encoder 101, but the embodiments described above can be applied as actuators to linear drive devices, rotating devices, magnetophoresis devices, and the like.

[0099] 1 Motor (actuator), 2 Hot-worked magnet, 4 Substrate (component, base), 10 Inner circumference end (end), 11 Outer circumference end (end), 12 Magnetic pole portion (part), 15 Housing (component), 16 Inner cylindrical wall portion (wall), 17 Outer cylindrical wall portion (wall), 19 Coil opposing surface (surface), 31 Coil, 33 First coil group, 34 Second coil group, 53 Rotating body (weight), 54 Blade (weight), 57 Base (component), 101 Magnetic encoder, 102 Main track, 103 Sub-track, 104 Unmagnetized area, 105 Sensor module, 6A, 6B Magnetic sensor

Claims

1. A hot-worked magnet comprising an aggregate of multiple magnetic particles, wherein the magnet has a first surface extending in the radial direction, a second surface extending in the axial direction, and a ridge formed by the intersection of the first surface and the second surface, and the surface roughness of the ridge is in the range of 32 μm to 150 μm.

2. The hot-worked magnet according to claim 1, wherein the particle size distribution of the magnetic powder is in the range of 32 μm to 125 μm.

3. The hot-worked magnet according to claim 1, wherein the average particle size of the magnetic powder is in the range of 60 μm or more and 110 μm or less.

4. The hot-worked magnet according to claim 1, wherein the average particle size of the magnetic powder is in the range of 60 μm or more and 100 μm or less.

5. The hot-worked magnet according to claim 1, wherein the ridge line comprises a first ridge line extending in the magnetization direction and a second ridge line extending in another direction, and the dimension of the first ridge line is shorter than the dimension of the second ridge line.

6. The hot-worked magnet according to claim 5, wherein the surface roughness of the first ridge and the second ridge are both in the range of greater than 0 μm and less than or equal to 150 μm.

7. An actuator comprising a hot-worked magnet according to any one of claims 1 to 6, and a coil facing the hot-worked magnet.

Images