JP2012147629A - Method for manufacturing ring magnet, and rotor having ring magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To overcome a problem of a ring magnet attached to a rotor causing the larger vibration of the rotor because of the magnet having a density changing in a circumferential direction.SOLUTION: The method for manufacturing a ring magnet comprises the steps of: roughly pulverizing a rare earth alloy into rare earth magnetic coarse powder, followed by re-pulverizing the coarse powder into rare earth magnetic powder; using a sieve of mesh to selectively sort the resultant rare earth magnetic powder; adding resin to the sorted rare earth magnetic material powder to prepare mixed powder; preparing a compressed object by charging the mixed powder into a mold having an outer periphery mold for restricting an outer peripheral surface of the compressed object, and an inner periphery mold for restricting an inner peripheral surface of the compressed object, and performing the compression molding; preparing hardened object by hardening the compressed object in a high-temperature atmosphere; and rustproofing a surface of the hardened object.

Description

  The present invention relates to a method of manufacturing a ring magnet and a rotor provided with the ring magnet.

  Some hard disk drive devices (hereinafter referred to as “HDDs”) use a brushless motor to rotate a recording disk at high speed. As such a brushless motor, one having a ring magnet in its rotor is known (Reference Document 1). In addition, HDDs are mounted on so-called hard disk recorders and the like, and the opportunity to be used in a quiet room is increasing.

  HDDs used in a quiet room are required to reduce vibrations of the brushless motor rotor and be quieter than those installed in stationary electronic devices used in offices. Yes.

JP 2009-303417 A

A method of slowing down the rotation of the brushless motor can be considered in order to reduce the noise of the HDD. However, with this method, the waiting time for reading / writing data of the HDD becomes long, so that the usability may be deteriorated.
For this reason, a method of reducing the vibration of the rotor of the brushless motor by reducing the unbalance amount of the rotor of the brushless motor can be considered. The unbalance amount is the amount of deviation from the center of rotation of the center of gravity when the object is stationary or rotating. When a rotor with a large unbalance amount rotates, it is considered that vibration increases. The rotor of the brushless motor includes a hub engaged with the central hole of the recording disk, and a ring magnet fixed to the hub. When the unbalance amount of the ring magnet is large, the unbalance amount of the brushless motor rotor becomes large. That is, there is a problem of reducing the unbalance amount of the ring magnet in order to make the HDD quiet.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a ring magnet with a reduced unbalance amount and a brushless motor rotor with reduced vibration during rotation.

  In order to solve the above problems, an aspect of the present invention relates to a method of manufacturing a ring magnet. The method of manufacturing this ring magnet includes a step of re-grinding a rare earth magnetic coarse powder coarsely pulverized with a rare earth alloy to obtain a rare earth magnetic powder, and a step of selecting the re-grinded rare earth magnetic powder using a mesh sieve. Adding a resin to the selected rare earth magnetic powder to obtain a mixed powder; an outer peripheral mold for regulating the outer peripheral surface of the compressed body; and an inner circumference for regulating the inner peripheral surface of the compressed body. A step of obtaining a compressed body by filling in a mold having a mold and compression molding, a step of obtaining a cured body by curing the compressed body in a high-temperature atmosphere, and rust prevention on the surface of the cured body Applying a process.

  According to this aspect, the unbalance amount of the ring magnet can be reduced.

  Another aspect of the present invention relates to a rotor of a brushless motor. The rotor of this brushless motor includes a ring magnet and a hub fixed to the outer periphery of the ring magnet. Then, after the ring magnet is fixed to the hub, the unbalance amount is further inspected.

  According to this aspect, it is possible to reduce vibration during rotation of the rotor of the brushless motor by suppressing the influence of the unbalance amount of the ring magnet.

  Note that any combination of the above-described constituent elements, and those obtained by replacing the constituent elements and expressions of the present invention with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the rotor of the brushless motor which reduced the ring magnet which reduced the amount of unbalance, and the vibration at the time of rotation can be provided.

It is a top view which shows the hard disk drive device which mounts the rotor of a brushless motor provided with the ring magnet manufactured with the manufacturing method which concerns on embodiment of this invention. It is the sectional view on the AA line which shows the part which concerns on a brushless motor among FIG. It is process drawing which shows the method of manufacturing a ring magnet. Fig.4 (a) is explanatory drawing which shows the state which set the outer peripheral surface of the hardening body to the attachment member of the balancing machine with sectional drawing. FIG.4 (b) is explanatory drawing which shows the state which set the internal peripheral surface of the hardening body to the attachment member of the balancing machine in a cross section. FIGS. 5A and 5B are explanatory views showing a state in which the outer peripheral surface of the cured body is set on the mounting member of the balancing machine in an upper surface and a cross section. 6A to 6D are explanatory views showing a step of filling a mixed powder in a mold to obtain a compressed body in a cross section passing through the center of the mold. FIG. 7 is a top explanatory view showing a state of the mixed powder filled in the mold in FIG. FIGS. 8A and 8B are explanatory diagrams showing the distribution of the unbalance amount of the rotor including the ring magnet.

The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components and members shown in the drawings are denoted by the same reference numerals, and repeated descriptions are appropriately omitted. In addition, the dimensions of the members in each drawing are appropriately enlarged or reduced for easy understanding. Also, in the drawings, some of the members that are not important for describing the embodiment are omitted.
In the following description, as a whole, for the sake of convenience, the lower side in FIG. 2 is expressed as “lower” and the upper side is expressed as “upper”. A line passing through the center of the ring magnet in the vertical direction is expressed as a central axis, a direction along the central axis is expressed as an axial direction, and a direction orthogonal to the central axis is expressed as a radial direction. In addition, the rotor of the brushless motor may be simply expressed as a rotor.

  According to the study by the present inventors, the unbalance amount of the rotor of the brushless motor in which the noise of the HDD caused by the unbalance amount is a problem is usually 16 mgcm or more. In addition, if the rotor mounted on such an HDD is replaced with one having an unbalance amount of about 8 mgcm, noise is improved for most HDDs. Therefore, a rotor with an unbalance amount of 8 mgcm or less is considered to cause almost no noise problem due to the unbalance amount of the ring magnet, even if it is actually mounted on a HDD used in a quiet room. It is done.

  The unbalance amount can be measured by rotating in a state where the rotating body to be measured is set on the measurement mounting member of the balancing machine. As the balancing machine, for example, BM-6141 manufactured by Kokusai Keiki Co., Ltd. can be used. This is preferable in that the deviation amount and the deviation direction from the rotation center of the center of gravity of the rotating body to be measured can be detected as the unbalance amount.

As a result of examining the rotor of a brushless motor in which the HDD noise caused by the unbalance amount is a problem, the present inventors have obtained the following knowledge.
(1) The unbalance amount of the rotor in which the ring magnet is fixed to the inner periphery of the cup-shaped hub by bonding changes even if either the hub or the ring magnet is replaced. For example, in a rotor with an unbalance amount of about 16 mgcm, the unbalance amount of the hub is usually 2 mgcm or less. On the other hand, the unbalance amount of the ring magnet is usually about 16 mgcm. Therefore, the inventors have recognized that a ring magnet with a small unbalance amount may be fixed in order to reduce the unbalance amount of the rotor.
(2) As a factor of a large unbalance amount, it is considered that mass is unevenly distributed in the circumferential direction. As a cause of uneven distribution of mass, it is considered that the density is uneven in the circumferential direction and the cross-sectional area is uneven in the circumferential direction. For the ring magnet having an unbalance amount of about 16 mgcm, no significant non-uniformity in the circumferential direction of the cross-sectional area was observed. Therefore, the ring magnet is considered to have non-uniform density in the circumferential direction. That is, the inventors have recognized that in order to reduce the unbalance amount of the ring magnet, it is preferable to reduce the uneven density in the circumferential direction.

  The ring magnet manufactured by the method according to the embodiment and the rotor of the brushless motor including the ring magnet are preferably used by being mounted on a rotating device such as a disk drive device, particularly an HDD.

  FIG. 1 is a top view showing an HDD equipped with a brushless motor. The rotor of the brushless motor includes a ring magnet manufactured by the method according to the embodiment. FIG. 1 shows a state in which the top cover is removed in order to show the inner configuration of the HDD 1. The HDD 1 includes a base 4, a brushless motor 2, and a magnetic recording disk 8. The brushless motor 2 includes a rotor 6. The magnetic recording disk 8 is placed on the rotor 6 and rotates as the rotor 6 rotates. The rotor 6 is rotatably attached to the base 4 via a bearing unit (not shown in FIG. 1).

  FIG. 2 is a cross-sectional view taken along line AA showing a portion related to the brushless motor 2 in FIG. The brushless motor 2 includes a stator 3 and a rotor 6. The stator 3 includes a laminated core 40 and a coil 42. The laminated core 40 has an annular portion and nine salient poles extending outward in the radial direction therefrom. A coil 42 is wound around the salient pole. The inner periphery of the annular portion of the laminated core 40 is bonded and fixed to the protruding portion of the base 4. The bearing unit includes a cylindrical sleeve 25 and a bottomed cup-shaped housing 24. The housing 24 is bonded and fixed to a through hole 4 c provided in the base 4. The sleeve 25 is bonded and fixed to the housing 24.

  The rotor 6 includes a hub 28, a ring magnet 32, and a shaft 26. The hub 28 is made of a steel material such as SUS430F having soft magnetism. The hub 28 is formed by, for example, pressing or cutting a steel plate. The hub 28 is formed in a predetermined shape having a substantially cup shape. The magnetic recording disk 8 is placed on the disk placement surface of the hub 28. The shaft 26 is fixed to a hole 28c provided in the center of the hub 28 in a state where both press-fitting and adhesion are used. The shaft 26 is rotatably supported by the sleeve 25.

  The ring magnet 32 is made of iron and neodymium as main components and includes a rare earth material. The ring magnet 32 is inspected for an unbalance amount. For example, if the measured unbalance amount exceeds a predetermined maximum value, it may be excluded as a defective product. The inspection object may be extracted and inspected for each production lot. The surface of the ring magnet 32 is subjected to rust prevention treatment. The ring magnet 32 may be subjected to rust prevention treatment on the surface after the unbalance amount is inspected. It is possible to prevent waste of the rust prevention treatment by eliminating it as a defective product after the rust prevention treatment. The ring magnet 32 is bonded and fixed to the cylindrical inner peripheral surface 28 f of the substantially cup-shaped hub 28. The rotor 6 is further inspected for an unbalance amount after the ring magnet 32 is fixed to the hub 28. For example, if the measured unbalance amount exceeds a predetermined maximum value, it may be excluded as a defective product. Further, the rotor 6 may be processed so as to reduce the unbalance amount. A rotor with a large unbalance amount is prevented from being incorporated in the HDD.

  The ring magnet 32 is provided with 12 driving magnetic poles in the circumferential direction. The ring magnet 32 faces the salient poles of the laminated core 40 in the radial direction. When a three-phase substantially sinusoidal drive current flows through the coil 42, a field magnetic pole is generated along the outer peripheral surface of the salient pole. The ring magnet 32 generates a rotational driving force by the action of the field magnetic pole and the driving magnetic pole. As a result, the ring magnet 32 rotates the hub 28 and the magnetic recording disk 8.

Next, a method for manufacturing the ring magnet 32 will be described with reference to FIG.
In FIG. 3, reference numeral 301 denotes a step of manufacturing a thin ribbon 301a of a rare earth alloy. In step 301, a raw material 300a such as iron or neodymium is received. A rare earth alloy is produced from the raw material 300a. The manufactured rare earth alloy is melted and sprayed onto the surface of a metal roll rotating at a high speed to be rapidly cooled to manufacture a thin ribbon 301a. For example, the rare earth alloy may include 28 wt% neodymium, 0.9 wt% boron, 5.0 wt% cobalt, and the balance iron. For example, the metal roll may be made of copper. The metal roll may be rotated at a peripheral speed of 25 m / sec. Ribbon 301a may be manufactured to a thickness of about 30 μm.

  In FIG. 3, reference numeral 302 denotes a step of manufacturing the annealed body 302a by annealing the rare-earth alloy ribbon 301a. For example, the ribbon 301a may be annealed at 550 ° C. for 10 minutes.

  In FIG. 3, reference numeral 303 denotes a step of coarsely pulverizing the annealed body 302a to produce the rare earth magnetic coarse powder 303a. If the size of the rare earth magnetic coarse powder 303a is too small, it may ignite during storage or transportation. In response to this, for example, the annealed body 302a may be pulverized into a rare earth magnetic coarse powder 303a having a size of about 200 μm. The possibility of ignition is reduced.

  In FIG. 3, reference numeral 304 denotes a step of re-grinding the coarsely pulverized rare earth magnetic coarse powder 303a to obtain the rare earth magnetic powder 304a. If the size of the rare earth magnetic powder 304a is too large, the difference in density in the circumferential direction of the ring magnet 32 may become large. Correspondingly, for example, the rare earth magnetic coarse powder 303a may be pulverized into a rare earth magnetic powder 304a having a size of about 100 μm. This is preferable in that uneven density in the circumferential direction of the ring magnet 32 can be suppressed.

  In FIG. 3, reference numeral 305 denotes a step of obtaining the sorted powder 305a by sorting the re-ground rare earth magnetic powder 304a using a mesh sieve 305b. When sorting with a coarse mesh sieve having too few meshes, the sorted powder 305a contains large-sized rare earth magnetic powder. In this case, the density difference in the circumferential direction of the ring magnet 32 may increase. If the screen is sorted with a fine mesh screen having too many meshes, the time required for the sorting becomes longer, and the workability is lowered. Correspondingly, for example, the screen may be selected using a mesh sieve having a mesh number of 120 to 160 per 25.4 mm. This is preferable in that the density non-uniformity in the circumferential direction of the ring magnet 32 can be further suppressed and the time required for selection can be suppressed.

  In FIG. 3, reference numeral 306 denotes a step of adding a resin to the sorted rare earth magnetic sorted powder 305a to obtain a mixed powder 306a. For example, 2% by weight of a thermosetting epoxy resin may be added and mixed as a binder.

  In FIG. 3, reference numeral 307 denotes a step of obtaining the compressed body 307a by filling the mold 307b with the mixed powder 306a and compressing it. 6A to 6D are explanatory views showing step 307 in a cross section passing through the center of the mold 307b. In the present embodiment, the mold 307b includes an outer peripheral mold 307c that regulates the outer peripheral surface of the compression body 307a and an inner peripheral mold 307d that regulates the inner peripheral surface of the compression body 307a. That is, an annular space is formed between the outer peripheral mold 307c and the inner peripheral mold 307d. First, a predetermined amount of the mixed powder 306a is placed on the upper surface of the mold 307b. The mixed powder 306a is pushed by a brush 307e that slides in the direction of the arrow 51 in FIG. 6A (FIG. 6A). The pressed mixed powder 306a is filled between the outer peripheral mold 307c and the inner peripheral mold 307d (FIG. 6B). Next, the mixed powder 306a is pressurized and compressed by the upper mold 307f (FIG. 6C). By removing the upper mold 307f, a compressed body 307a is obtained (FIG. 6D).

  In FIG. 3, reference numeral 308 denotes a step of curing the compression body 307a in a high temperature atmosphere to obtain a cured body 308a. For example, the compression body 307a may be subjected to a curing process at 170 ° C. for 1 hour in an argon atmosphere.

  In FIG. 3, reference numeral 309 denotes a step of inspecting the unbalance amount of the cured body 308a. For example, in the step of inspecting, if the measured unbalance amount exceeds a predetermined maximum value, it may be excluded as a defective product. In addition, a sampling inspection may be performed for each production lot. When the unbalance amount measured for the extracted cured body 308a exceeds a predetermined maximum value, a product belonging to the production lot may be excluded as a defective product. This is preferable in that the inspection time is shortened. Inspecting the cured body 308a before the rust prevention treatment is preferable in that waste of the rust prevention treatment for defective products can be prevented.

  The hardened body 308a is formed aiming at a predetermined cylindrical shape, but inevitably has some deformation. The cured body 308a having such a deformation has a concern that the measured unbalance amount varies depending on the state of being set on the attachment member 111 of the balancing machine 110. In response to this concern, the unbalance amount may be inspected with the outer peripheral surface of the cured body 308a set on the mounting member 111. For the rotor 6 to which the outer peripheral surface of the ring magnet 32 is fixed, it becomes easier to reduce the unbalance amount. The same applies to the ring magnet 32 having a rust-proof surface. 4A and 4B are explanatory views schematically showing a state in which the cured body 308a is set on the mounting member 111 of the balancing machine 110 in a cross section. 4A shows a state in which the outer peripheral surface of the cured body 308a is set on the mounting member 111, and FIG. 4B shows a state in which the inner peripheral surface is set.

  The cured body 308a is considered to have non-uniform density in the circumferential direction along with the above-described deformation. For this reason, there is a concern that the unbalance amount of the rotor 6 varies depending on the circumferential position where the ring magnet 32 is fixed to the hub 28. In response to this concern, the unbalance amount inspection may be performed by the following method. First, the first unbalance amount is measured in a state where the outer peripheral surface of the cured body 308a is set on the measurement attachment member 111 at the first circumferential position. Next, the second unbalance amount is measured in a state where the outer peripheral surface of the cured body 308a is set on the measurement attachment member 111 at a second circumferential position different from the first circumferential position. Then, an inspection is performed based on the measured first unbalance amount and the measured second unbalance amount. This is preferable in that the accuracy of the inspection of the unbalance amount of the cured body 308a is improved. The same applies to the ring magnet 32 having a rust-proof surface.

  This will be specifically described with reference to FIGS. FIGS. 5A and 5B are explanatory views showing a state in which the outer peripheral surface of the cured body 308a is set on the mounting member 111 of the balancing machine, as viewed from above, and a cross section. 5A and 5B, the mark M is displayed on the mounting member 111 as a mark, and the mark m is displayed on the cured body 308a. FIG. 5A shows a state in which the cured body 308a is set on the attachment member 111 so that the mark M and the mark m coincide with each other. In this state, the first unbalance amount is measured. FIG. 5B shows a state in which the cured body 308a is set on the attachment member 111 so that the mark M and the mark m are positioned on the opposite sides with the rotation axis interposed therebetween. In this state, the second unbalance amount is measured.

  For example, in the step of inspecting, a value obtained as a result of a predetermined calculation using the first unbalance amount and the second unbalance amount as parameters may be excluded as a defective product. As an example of such calculation, one that calculates the sum, average value, and maximum value of the first unbalance amount and the second unbalance amount can be considered. Alternatively, the unbalance amount may be calculated as a vector composed of the displacement amount and the displacement direction of the center of gravity. Note that the angle between the first circumferential position and the second circumferential position is not limited to 180 degrees, and may be another angle. For example, it may be 90 degrees.

  In FIG. 3, 310 indicates a step of obtaining the ring magnet 32 by subjecting the surface of the cured body 308a to rust prevention treatment. For example, electrodeposition coating or spray coating may be applied to the surface of the cured body 308a. This is preferable in that the oxidation of the ring magnet 32 can be suppressed and the change in characteristics over time can be reduced.

  FIG. 7 is an explanatory view showing the state of the mixed powder 306a filled in the mold 307b in FIG. The mixed powder 306a is filled between the outer peripheral mold 307c and the inner peripheral mold 307d by being pushed by the brush 307e sliding leftward. For this reason, it is considered that the density on the 306aa side in the relatively pressed direction is high and the density on the opposite 306ab side is low. That is, there is a concern that the unbalance amount increases due to nonuniformity in the circumferential direction of the filled mixed powder 306a. In response to this concern, step 311 may be included in which the relative positions of the outer peripheral mold 307c and the inner peripheral mold 307d are changed according to the inspected unbalance amount 309a.

  In FIG. 3, 311 indicates a step of changing the relative positions of the outer peripheral mold 307c and the inner peripheral mold 307d in step 307 based on the unbalance amount 309a inspected in step 309. That is, by changing the relative positions of the outer peripheral mold 307c and the inner peripheral mold 307d in accordance with the inspected unbalance amount 309a, the unbalance amount of the cured body 308a to be manufactured thereafter is reduced.

  An example of step 311 will be described. First, a mark is displayed on the cured body 308a. For example, the mark m is displayed on the 306aa side of the cured body 308a. The mark m may be formed by attaching an ink-like material. Further, the mark m may be formed as unevenness by the mold 307b. Next, in step 309, a deviation amount and a deviation direction of the center of gravity of the cured body 308a from the rotation center are detected. Correction information 311a is obtained according to the displacement amount and the displacement direction. The relative positions of the outer peripheral mold 307c and the inner peripheral mold 307d are changed according to the correction information 311a.

  When the displacement amount is larger than a predetermined value and the displacement direction is on the mark m side, the inner peripheral mold 307d is moved to the left side in FIG. As a result, the width of the mold 307b on the mark m side becomes narrow, and the mass on the mark m side of the cured body 308a to be manufactured thereafter becomes small. As a result, the center of gravity of the cured body 308a approaches the center of rotation. That is, the unbalance amount of the cured body 308a is reduced. Further, when the displacement amount is larger than a predetermined value and the displacement direction is on the side opposite to the mark m, the inner peripheral mold 307d is moved to the right side in FIG. As a result, the center of gravity of the cured body 308a manufactured thereafter approaches the center of rotation, and the unbalance amount is reduced. When the deviation amount is smaller than a predetermined value, the relative positions of the outer peripheral mold 307c and the inner peripheral mold 307d are not changed. Note that the relationship among the inspected unbalance amount 309a and the correction amount of the relative position of the outer peripheral mold 307c and the inner peripheral mold 307d can be determined by experiments.

  Step 311 can be executed for each manufacturing cycle of the cured body 308a. Moreover, you may make it perform every predetermined time. Further, it may be executed every predetermined number of manufacturing cycles or every manufacturing lot.

  The optimum relative positions of the outer peripheral mold 307c and the inner peripheral mold 307d vary depending on manufacturing conditions such as the temperature and humidity of the manufacturing environment, the temperature and wear of the mold 307b, the manufacturing lot of the mixed powder 306a, and the like. Even when the manufacturing conditions change, it is possible to manufacture a ring magnet that suppresses an increase in the unbalance amount by correcting the relative position according to the inspected unbalance amount 309a.

  FIG. 8B shows an unbalance amount distribution of a rotor including a ring magnet manufactured by the method according to the comparative example. Steps 305 and 311 were not included, and in step 305, selection was performed with a mesh sieve having 80 meshes per 25.4 mm. The average value of the unbalance amount of the 20 rotors 6 was 7 mgcm, and the maximum value was 10 mgcm. When the upper limit 81 is 8 mgcm, the defect rate is considered to be about 10%.

  FIG. 8A shows the distribution of the unbalance amount of the rotor 6 provided with the ring magnet 32 manufactured by the method according to an example of the present embodiment. Step 305 includes Step 304 and Step 311. In Step 305, selection was performed using a mesh sieve having a mesh size of 120 per 25.4 mm. Other conditions were the same as those in the comparative example. The average value of the unbalance amount of the 20 rotors 6 was 3 mgcm, and the maximum value was 4 mgcm. When the upper limit 81 is 8 mgcm, the defect rate can be reduced to 1% or less.

  The method for manufacturing the ring magnet according to the embodiment and the configuration and operation of the rotor including the ring magnet have been described above. It is to be understood by those skilled in the art that these embodiments are exemplifications, and that various modifications can be made to combinations of the respective components, and such modifications are within the scope of the present invention. Alternatively, the embodiments can be combined.

  2 brushless motor, 3 stator, 4 base, 6 rotor, 8 magnetic recording disk, 25 sleeve, 26 shaft, 27 housing, 28 hub, 28c hole, 28f inner peripheral surface, 32 ring magnet, 40 laminated core, 42 coil, 111 Attachment member, 301a Ribbon, 302a Annealed body, 303a Rare earth magnetic coarse powder, 304a Rare earth magnetic powder, 305a Sorted powder, 306a Mixed powder, 307a Compressed body, 307b Mold, 308a Hardened body, 309a Inspected unbalance amount.

Claims (8)

Re-pulverizing the rare earth magnetic coarse powder in which the rare earth alloy is coarsely pulverized to obtain the rare earth magnetic powder;
Screening the re-ground rare earth magnetic powder using a mesh sieve;
Adding a resin to the rare earth magnetic powder after selection to obtain a mixed powder;
The compressed powder is filled by compressing and molding the mixed powder into a mold having an outer peripheral mold that regulates the outer peripheral surface of the compressed body and an inner peripheral mold that regulates the inner peripheral surface of the compressed body. Obtaining step;
Curing the compressed body in a high temperature atmosphere to obtain a cured body;
Applying a rust preventive treatment to the surface of the cured body, and a method of manufacturing a ring magnet.   The method of manufacturing a ring magnet according to claim 1, further comprising a step of inspecting an unbalance amount using the cured body or the ring magnet as an object to be inspected.   3. The ring magnet according to claim 2, wherein after the unbalanced amount is inspected using the cured body or the ring magnet as an object to be inspected, the surface of the cured body is subjected to a rust prevention treatment. Method.   The inspection of the unbalance amount is characterized in that the unbalance amount is measured in a state where the outer peripheral surface of the object to be inspected is set on a measurement mounting member, and the inspection is performed based on the measured unbalance amount. A method for manufacturing the ring magnet according to claim 2. The inspection of the unbalance amount is performed by measuring the first unbalance amount in a state where the outer peripheral surface of the object to be inspected is set on the measurement mounting member at the first circumferential position, and the outer peripheral surface of the object to be inspected is measured. Measuring the second unbalance amount in a state of being set on the mounting member for measurement at a second circumferential position different from the first circumferential position;
5. The ring magnet according to claim 2, wherein an inspection is performed based on the measured first unbalance amount and the measured second unbalance amount. 6. Method.   The ring magnet according to any one of claims 2 to 5, further comprising a step of changing a relative position between the outer peripheral mold and the inner peripheral mold in accordance with the inspected unbalance amount. How to manufacture.   7. The sorting step according to claim 1, wherein the rare earth magnetic powder after re-grinding is sorted using a mesh sieve having a mesh size of 120 to 160 in the range of 25.4 mm. A method for manufacturing the ring magnet according to claim 1.   A ring magnet manufactured by the method according to any one of claims 1 to 7, and a hub fixed to an outer periphery of the ring magnet, and after fixing the ring magnet to the hub, A rotor of a brushless motor, wherein the balance amount is inspected.

Images