JP7356003B2 - Method for manufacturing a mold for a polar anisotropic annular bonded magnet body - Google Patents

Description

The present invention relates to a method for manufacturing a mold for a polar anisotropic annular bonded magnet molded body.

When injection molding a bonded magnet composition to produce a polar anisotropic annular bonded magnet molded body, the molten bonded magnet composition is injected into a mold, and when it solidifies in the mold, the volume increases. Shrink. The degree of shrinkage changes depending on the content of the thermoplastic resin in the composition, which has a large shrinkage rate with respect to temperature. In addition, since the composition for a bonded magnet contains magnetic powder, the magnetic field causes anisotropy in contraction, causing distortion of the molded body, making it impossible to obtain a molded body in which the shape of the mold is directly transferred. Therefore, in order to obtain a perfectly circular molded product, an expert has to correct the mold after measuring how much the molded bonded magnet molded product is distorted.

On the other hand, Patent Document 1 discloses that in a magnetic field, an external force is applied to each of the magnetic compounds filled in a mold to increase the packing density of the magnetic compounds so that the indentation depth of the magnetic compounds is set at equal intervals. A method for manufacturing a long magnet molded body by compression molding is disclosed. However, this method is intended for long magnet moldings, and cannot be applied to a mold for a polar anisotropic annular bonded magnet molding.

Furthermore, Patent Document 2 discloses a method in which a test resin molded product is manufactured using a test mold for resin molding created by resin flow analysis, and the mold is manufactured based on the actual measured values of the dimensions. has been done. However, in this method, it is necessary to prepare a test mold in advance.

Japanese Patent Application Publication No. 2006-11312 Japanese Patent Application Publication No. 2006-142678

The present invention provides a mold for a polar anisotropic annular bonded magnet molded body that can produce a bonded magnet molded body with small distortion and high roundness without modifying the mold or creating a test mold, and the mold. The purpose is to provide a manufacturing method.

The present inventor has conducted various studies on molds for forming polar anisotropic annular bonded magnets, and has determined that the outer circumferential shape of the mold cavity can be defined from the contracted length of the formed object, the radius of the magnetic pole portion, and the number of magnetic poles of the formed object. discovered a mold for a bonded magnet molded body that can produce a molded body with high roundness without modifying the mold or preparing a test mold in advance, and completed the present invention.

That is, the present invention (1) calculates the following formula from the shrinkage rate α1 of the molded article in the direction perpendicular to the magnetic field, the contraction rate α2 in the parallel direction, and the wall thickness T of the polar anisotropic annular bonded magnet molded body to be manufactured:
Tc=T×(α1/100-α2/100)
A step of determining the shrinkage length Tc of the molded body by
(2) From the shrinkage rate α2 and the radius D of the polar anisotropic annular bonded magnet molded body to be produced, the following formula:
Dm=D/(1-α2/100)
a step of determining the radius Dm of the magnetic pole part of the mold cavity, and
(3) A mold for a polar anisotropic bonded annular magnet including the step of defining the outer peripheral shape of the mold cavity from Tc, Dm and the number of magnetic poles P of the polar anisotropic bonded bonded magnet to be produced. Regarding the manufacturing method.

According to the manufacturing method of the present invention, a mold for a polar anisotropic annular bonded magnet molded body that can obtain a bonded magnet molded product with high roundness without the need to modify the mold or create a test mold can be produced. can do.

FIG. 2 is a conceptual diagram showing the direction of contraction of a bonded magnet molded body in the presence of a magnetic field. It is a schematic diagram showing the magnetic pole part and the part between magnetic poles of a polar anisotropic annular bonded magnet molded object. FIG. 2 is a schematic diagram of a mold for a polar anisotropic annular bonded magnet molded body as viewed from the filling direction of a resin composition for a bonded magnet. FIG. 2 is a schematic diagram of a mold for a polar anisotropic annular bonded magnet molded body and a molded body molded within the mold as seen from the filling direction of a resin composition for a bonded magnet.

Embodiments of the present invention will be described in detail below. However, the embodiment shown below is an example for embodying the technical idea of the present invention, and the present invention is not limited to the following. Note that in this specification, the term "process" is used not only to refer to an independent process, but also to include a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved. included.

The method for manufacturing a mold for a polar anisotropic annular bonded magnet molded body of this embodiment is as follows:
(1) From the shrinkage rate α1 of the molded product in the direction perpendicular to the magnetic field, the shrinkage rate α2 in the parallel direction, and the wall thickness T of the polar anisotropic annular bonded magnet molded body to be manufactured, the following formula:
Tc=T×(α1/100-α2/100)
A step of determining the shrinkage length Tc of the molded body by
(2) From the shrinkage rate α2 and the radius D of the polar anisotropic annular bonded magnet molded body to be produced, the following formula:
Dm=D/(1-α2/100)
a step of determining the radius Dm of the magnetic pole part of the mold cavity, and
(3) It is characterized by including the step of defining the outer peripheral shape of the mold cavity from Tc, Dm, and the number P of magnetic poles of the polar anisotropic annular bonded magnet molded body to be produced.

FIG. 1 shows a conceptual diagram of contraction in the direction of the magnetic field. In the absence of a magnetic field, it contracts equally in both the vertical and horizontal directions, but in the presence of a magnetic field, the contraction due to the magnetic field is large in the direction perpendicular to the magnetic field, and small in the direction parallel to the magnetic field. For example, when molding a 10 x 10 mm compact as shown in Figure 1, if the shrinkage rate in the direction parallel to the magnetic field is 0.3% and the shrinkage rate in the direction perpendicular to the magnetic field is 0.9%, then If a mold is made with dimensions of 10/(1-0.003) = 10.03 mm and dimensions perpendicular to the magnetic field of 10/(1-0.009) = 10.09 mm, the A perfect square shaped body can be formed using a mold.

By the way, in the case of an annular bonded magnet molded body, there are complicated factors, unlike a square molded body. FIG. 2 shows a top view of a polar anisotropic annular bonded magnet molded body having a diameter of 2D, an inner diameter of 2I, a wall thickness of T (=DI), and a number of magnetic poles of 8. Here, the arrow in FIG. 2 represents the direction of the magnetic field. Such a molded body is injection molded using a mold equipped with orientation magnets as shown in FIG. In the magnetic pole part where magnetic poles such as N and S poles exist, the contraction due to the magnetic field is small, and in the part between the magnetic poles where no magnetic pole exists, the contraction due to the magnetic field is large. Therefore, in this example, there are eight parts where the shrinkage is large and eight parts where the shrinkage is small. Taking into account the contraction caused by these magnetic fields, the outer peripheral shape of the mold cavity, that is, the partition wall 4 in FIG. In this case, if the shape of the inner surface that is in contact with the bonded magnet composition during molding is specified, a mold that can mold a bonded magnet molded body with high roundness can be produced. Moreover, FIG. 4 shows a state in which the bonded magnet composition injected into the mold is filled.

Regarding the shape of the polar anisotropic annular bonded magnet molded body, the outer radius D is not particularly limited, but it is 10 mm or more and 80 mm or less, from the viewpoint of ease of filling the bonded magnet composition into a mold during injection molding due to the fluidity of the bonded magnet composition. is preferable, and more preferably 20 mm or more and 50 mm or less. Further, the inner radius I of the molded body is determined by the outer radius D and the wall thickness T.

The wall thickness T of the molded body is not particularly limited, but it is preferably 2 mm or more and 10 mm or less, and more preferably 4 mm or more and 8 mm or less, because it is easy to obtain a bonded magnet that satisfies the orientation, residual magnetic flux density, and sinusoidal magnetic flux density. . Note that the wall thickness T is preferably 1/2 or more of the length of the magnetic pole pitch (distance between magnetic poles). When the wall thickness T is 1/2 or more of the magnetic pole pitch length, the geometric semicircle of the lines of magnetic force is contained within the bonded magnet, so it is possible to suppress a decrease in magnetic force due to interruption of the magnetic path.

The height in the direction perpendicular to the thickness direction of the molded body is not particularly limited, but from the viewpoint of ease of filling the bonded magnet composition into a mold during injection molding due to the fluidity of the bonded magnet composition, it is preferably 5 mm or more and 30 mm or less, and 10 mm or more. More preferably, the distance is 20 mm or less.

[Step (1)]
In step (1), from the shrinkage rate α1 of the molded article in the direction perpendicular to the magnetic field, the contraction rate α2 in the parallel direction, and the wall thickness T (=DI) of the polar anisotropic annular bonded magnet molded body to be manufactured, The following formula:
Tc=T×(α1/100-α2/100)
The shrinkage length Tc of the molded body is determined by: The contraction length Tc represents the difference in contraction between the magnetic pole part and the part between the magnetic poles. The contraction rate α1 (%) in the direction perpendicular to the magnetic field and the contraction rate α2 (%) in the parallel direction to the magnetic field used in the calculation are calculated by applying the composition for bonded magnet molded body in the mold while applying the magnetic field applied during actual molding. Determined from the dimensions of the molded product obtained by molding at similar injection molding temperatures and the mold dimensions. The resin composition used may be substantially the same as the bonded magnet molding composition actually molded using the mold. Substantially the same means that the same matrix resin and the same magnetic material are used and the magnetic material is contained in the same amount. Since the amount of optional components is small and does not have a large effect on the shrinkage rate, it is not necessary to include the same components in the same amount. The shape of the molded article used to measure the shrinkage rate is not particularly limited as long as the shrinkage rate in the directions perpendicular and parallel to the orienting magnetic field can be measured, and examples thereof include prismatic, cylindrical, spherical, and annular shapes. There is no problem as long as the applied magnetic field strength is comparable to the magnetic field strength applied during actual molding using the mold.

[Step (2)]
In step (2), the following formula is calculated from the shrinkage rate α2 and the radius D of the polar anisotropic annular bonded magnet molded body to be manufactured:
Dm=D/(1-α2/100)
Find the radius Dm of the magnetic pole part of the mold cavity.

[Step (3)]
In step (3), the outer peripheral shape of the mold cavity is defined from Tc, Dm, and the number P of magnetic poles of the polar anisotropic annular bonded magnet molded body to be produced. Here, in the case of a mold as shown in FIG. 3, the outer peripheral shape of the mold cavity refers to the peripheral shape of the inner surface of the partition wall 4 that comes into contact with the composition during injection molding.

The method of defining the outer peripheral shape of the mold cavity is not particularly limited, and examples thereof include a method of defining it using polar coordinates (r, θ), a method of defining it using orthogonal coordinates (x, y), and the like.

When defined by polar coordinates (r, θ), the radius r from the center of the mold cavity to the outer periphery is calculated using the following formula:
r=(Dm+β×Tc/2)+(β×Tc/2) sin(Pθ)
(However, β is a correction coefficient, and 0.7≦β≦1.0.)
It is expressed as Here, Dm corresponds to the radius of the magnetic pole portion, and (Dm+β×Tc/2) corresponds to the radius of the portion between the magnetic poles. By adding a variable radius (β×Tc/2) sin (Pθ) that periodically varies depending on the number of magnetic poles P to the radius between the magnetic poles (Dm+β×Tc/2), the outer peripheral shape is defined by polar coordinates.

β is 0.7 or more and 1.0 or less, preferably 0.9 or more. When β is 1.0, this corresponds to the case where contraction with respect to the magnetic field is completely taken into account. The tolerance of a general molded product is ±0.05 mm, which is even stricter, and if half of this is taken as the tolerance, there is no problem if β is 0.7 or more. The number of magnetic poles P is not particularly limited as long as it is an integer of 2 or more, but is preferably 2 or more and 12 or less from the viewpoint of the orientation of the bonded magnet.

When the outer peripheral shape of the mold cavity is defined by orthogonal coordinates (x, y), the orthogonal coordinates (x, y) of the outer peripheral part, with the center of the mold cavity as the origin, are determined by the following formula:
x={(Dm+β×Tc/2)+(β×Tc/2) sin(Pθ)}×cosθ
y={(Dm+β×Tc/2)+(β×Tc/2)sin(Pθ)}×sinθ
(However, β is a correction coefficient, 0.7≦β≦1.0, and 0≦θ≦2π.)
It is expressed as β is 0.7 or more and 1.0 or less, preferably 0.9 or more. The details of β are as described above.

Moreover, the mold for the polar anisotropic annular bonded magnet molded body of this embodiment is
The polar coordinates (r, θ) of the outer circumference of the cavity are expressed by the following formula, with the center of the mold cavity as the origin:
r=(Dm+β×Tc/2)+(β×Tc/2) sin(Pθ)
(In the formula, the shrinkage rate of the molded product in the direction perpendicular to the magnetic field is α1, the shrinkage rate in the parallel direction is α2, the wall thickness of the polar anisotropic annular bonded magnet molded body to be produced is T, the number of magnetic poles is P, the polar anisotropic The radius of the annular bonded magnet molded body is D, the shrinkage length Tc of the resulting molded body is T×(α1/100-α2/100), and the radius Dm of the magnetic pole part of the mold cavity is D/(1-α2). /100), β is a correction coefficient, and 0.7≦β≦1.0.)
It is characterized by being defined by. The formulas, variables, constants, etc. are as described above.

Moreover, the mold for the polar anisotropic annular bonded magnet molded body of this embodiment is
The orthogonal coordinates (x, y) of the outer circumference of the cavity are determined by the following formula, with the center of the mold cavity as the origin:
x={(Dm+β×Tc/2)+(β×Tc/2) sin(Pθ)}×cosθ
y={(Dm+β×Tc/2)+(β×Tc/2)sin(Pθ)}×sinθ
(In the formula, the shrinkage rate of the molded product in the direction perpendicular to the magnetic field is α1, the shrinkage rate in the parallel direction is α2, the wall thickness of the polar anisotropic annular bonded magnet molded body to be produced is T, the number of magnetic poles is P, the polar anisotropic The radius of the annular bonded magnet molded body is D, the shrinkage length Tc of the resulting molded body is T×(α1/100-α2/100), and the radius Dm of the magnetic pole part of the mold cavity is D/(1-α2). /100), β is a correction coefficient, 0.7≦β≦1.0, and 0≦θ≦2π.)
It is characterized by being defined by. The formulas, variables, constants, etc. are as described above.

FIG. 3 shows a schematic diagram of the mold for a polar anisotropic annular bonded magnet molded body of the present embodiment as viewed from the filling direction of the bonded magnet resin composition. The mold has a structure in which an orienting magnet 2 and a partition wall 4 whose outer circumferential shape is defined by the method described above are installed in a cavity surrounded by a metal steel material 3 made of magnetic steel. A composition for a bonded magnet is injected into a cavity 1 formed by a metal steel material 3 and a partition wall 4 in the center to give a shape.

It is preferable that the metal steel material 3 is made of magnetic steel material. Examples of magnetic steel materials include pre-hardened steel, hardened steel, and carbon steel. On the other hand, the partition wall 4 is preferably made of non-magnetic steel. Examples of non-magnetic steel materials include aluminum alloys, stainless steel, and aging treated steel. The orientation magnet 2 is preferably made of a magnetic material. Examples of the magnetic material include NdFeB sintered magnets and SmCo sintered magnets, and NdFeB sintered magnets are preferred from the viewpoint of the strength of the orienting magnetic field.

Furthermore, the method for manufacturing a polar anisotropic annular bonded magnet molded body of the present embodiment includes a step of injection molding a composition for a bonded magnet using the mold for the polar anisotropic annular bonded magnet molded body. It is characterized by

The bonded magnet composition used includes a thermoplastic resin and magnetic powder.

The magnetic powder used in this embodiment is not particularly limited, but SmFeN-based, NdFeB-based, and SmCo-based rare earth magnetic powders can be used. As the rare earth magnetic powder, it is more preferable to use SmFeN-based magnetic powder because it has higher heat resistance than NdFeB-based magnetic powder, and because it does not use rare metals compared to SmCo-based magnetic powder. The SmFeN-based magnetic powder is a nitride consisting of the rare earth metal Sm, iron Fe, and nitrogen N, which has a Th ₂ Zn ₁₇ type crystal structure and whose general formula is Sm _x Fe _100-xy N _y . . Here, the x value of the atomic % of rare earth metal Sm is in the range of 8.1 to 10%, the y of the atomic % of N is in the range of 13.5 to 13.9 (atomic %), and the remainder is mainly It is considered to be Fe. Furthermore, in addition to SmFeN-based magnetic powder, NdFeB-based, SmCo-based rare earth magnetic powder, or ferrite-based magnetic powder can be used in combination.

SmFeN magnetic powder can be produced, for example, by the method disclosed in Japanese Patent No. 3,698,538. As a result, SmFeN magnetic powder having an average particle size of 2 μm to 5 μm and a standard deviation of 1.5 μm or less can be suitably used.

On the other hand, NdFeB-based magnetic powder can be manufactured, for example, by the HDDR method described in Japanese Patent No. 3565513. The NdFeB magnetic powder having an average particle size of 40 to 200 μm and a maximum energy product of 34 to 42 MGOe (270 to 335 kJ/m ³ ) can be suitably used. Further, Sm--Co magnetic powder can be manufactured, for example, according to Japanese Patent No. 3505261, and the above-mentioned magnetic powder can have an average particle size of 10 to 30 μm.

The thermoplastic resin is not particularly limited, and examples thereof include polypropylene, polyethylene, polyvinyl chloride, polyester, polyamide, polycarbonate, polyphenylene sulfide, and acrylic resin. Among these, polyamide, particularly polyamide 12, is preferred. Polyamide 12 has a relatively low melting point, low water absorption, and is a crystalline resin, so it has good moldability. It is also possible to use a mixture of these as appropriate.

The blending amount of the thermoplastic resin is not particularly limited, but is preferably 3 parts by mass or more and 20 parts by mass or less, more preferably 5 parts by mass or more and 15 parts by mass or less, based on 100 parts by mass of the magnetic powder. If it exceeds 20 parts by mass, the magnetic force will be low, and if it is less than 3 parts by mass, fluidity during injection molding will tend to be insufficient.

A thermoplastic elastomer and an antioxidant can also be blended into the bonded magnet composition.

Examples of the thermoplastic elastomer include polystyrene, polyolefin, polyester, polyurethane, and polyamide. By including a thermoplastic elastomer, initial strength can be improved without impairing fluidity. Further, these may be mixed and used as appropriate. Among these, polyamide-based thermoplastic elastomers are preferred because they have excellent chemical resistance.

Examples of the antioxidant include phosphorus antioxidants and phenolic antioxidants. By including the phosphorous antioxidant, even when the composite member is exposed to high temperatures, changes in strength over time can be reduced. Examples of phosphorous antioxidants include tris(2,4-di-tert-butylphenyl) phosphite and the like.

The injection molding conditions and the like are not particularly limited, and the conditions used when injection molding a normal bonded magnet composition can be applied as they are.

Examples will be described below. Note that unless otherwise specified, "%" is based on mass.

Production Example Production of a composition for bonded magnets 7.74% by mass of 12 nylon resin powder and 0.3% by mass of phenolic antioxidant powder were added to 91.96% by mass of samarium iron nitrogen magnetic powder (average particle size 3 μm). After mixing with a mixer, the mixed powder was put into a twin-screw kneader and kneaded at 210°C to obtain a kneaded product. After cooling the obtained kneaded product, it was cut into appropriate sizes to obtain a bonded magnet composition.

Example In a mold for producing a molded article with a diameter of 10 mm x 7 mm, injection molding was carried out at 250° C. while applying a magnetic field of 716 kA/m, and the shrinkage rate of the composition was measured. The contraction rate α2 in the direction parallel to the magnetic field was 0.3%, and the contraction rate α1 in the direction perpendicular to the magnetic field was 1.0%.

In order to produce a polar anisotropic annular bonded magnet molded body with a diameter 2D of 50 mm, an inner diameter 2I of 40 mm, a wall thickness T of 5 mm, a height perpendicular to the wall thickness direction of 10 mm, and a number of magnetic poles P of 8, the shrinkage rate was Using α1 and α2, calculate the radius r from the center of the mold cavity to the outer periphery using polar coordinates (r, θ) using the following formula:
r=(Dm+β×Tc/2)+(β×Tc/2) sin(Pθ)
(However, β was set to 1.0.)
A partition wall having the inner circumferential shape determined by the following was fabricated. Tc was 0.035 mm, and Dm was 25.075 mm.

The prepared partition walls and eight orientation magnets were placed in a mold to produce a mold for a polar anisotropic annular bonded magnet molded body. Using the bonded magnet composition produced in the production example, injection molding was performed at a molding temperature of 250°C and a mold temperature of 90°C to produce 10 molded bodies. The roundness of the 10 obtained molded bodies was measured using a measuring microscope (manufactured by Mitutoyo Co., Ltd., model number MF-A1010). The roundness was 10 μm, and a polar anisotropic annular bonded magnet molded body with high roundness could be produced.

According to the method for manufacturing a mold for a polar anisotropic annular bonded magnet molded body of the present invention, a mold for a polar anisotropic annular bonded magnet molded body that can produce a bonded magnet molded body with high roundness is produced. Since it can be manufactured, there is no need to modify the mold or create a test mold, so it has very high industrial value.

1: Cavity 2: Orienting magnet 3: Metal steel material (magnetic steel material)
4: Partition wall (non-magnetic steel)
5: Bonded magnet molded body

Claims (6)

(1) From the shrinkage rate α1 of the molded product in the direction perpendicular to the magnetic field, the shrinkage rate α2 in the parallel direction, and the wall thickness T of the polar anisotropic annular bonded magnet molded body to be manufactured, the following formula:
Tc=T×(α1/100-α2/100)
A step of determining the shrinkage length Tc of the molded body by
(2) From the shrinkage rate α2 and the radius D of the polar anisotropic annular bonded magnet molded body to be produced, the following formula:
Dm=D/(1-α2/100)
a step of determining the radius Dm of the magnetic pole part of the mold cavity, and
(3) A mold for a polar anisotropic bonded annular magnet including the step of defining the outer peripheral shape of the mold cavity from Tc, Dm and the number of magnetic poles P of the polar anisotropic bonded bonded magnet to be produced. Production method. In step (3), with the center of the mold cavity as the origin, the following formula:
r=(Dm+β×Tc/2)+(β×Tc/2) sin(Pθ)
(However, β is a correction coefficient, and 0.7≦β≦1.0.)
2. The method for manufacturing a mold for a polar anisotropic annular bonded magnet molded body according to claim 1, wherein the outer circumferential shape of the mold cavity is defined by the polar coordinates (r, θ) of the outer circumferential portion of the cavity. In step (3), with the center of the mold cavity as the origin, the following formula:
x={(Dm+β×Tc/2)+(β×Tc/2) sin(Pθ)}×cosθ
y={(Dm+β×Tc/2)+(β×Tc/2)sin(Pθ)}×sinθ
(However, β is a correction coefficient, 0.7≦β≦1.0, and 0≦θ≦2π.)
2. The method for manufacturing a mold for a polar anisotropic annular bonded magnet molded body according to claim 1, wherein the outer circumferential shape of the mold cavity is defined by the orthogonal coordinates (x, y) of the outer circumferential portion of the cavity. The polar coordinates (r, θ) of the outer circumference of the cavity are expressed by the following formula, with the center of the mold cavity as the origin:
r=(Dm+β×Tc/2)+(β×Tc/2) sin(Pθ)
(In the formula, the shrinkage rate of the molded product in the direction perpendicular to the magnetic field is α1, the shrinkage rate in the parallel direction is α2, the wall thickness of the polar anisotropic annular bonded magnet to be produced is T, the number of magnetic poles is P, the polar anisotropic annular bonded magnet is The radius of the bonded magnet molded body is D, the shrinkage length Tc of the resulting molded body is T x (α1/100-α2/100), and the radius Dm of the magnetic pole part of the mold cavity is D/(1-α2/100). ), β is a correction coefficient, and 0.7≦β≦1.0.)
A mold for a polar anisotropic annular bonded magnet body defined by: The orthogonal coordinates (x, y) of the outer circumference of the cavity are determined by the following formula, with the center of the mold cavity as the origin:
x={(Dm+β×Tc/2)+(β×Tc/2) sin(Pθ)}×cosθ
y={(Dm+β×Tc/2)+(β×Tc/2)sin(Pθ)}×sinθ
(In the formula, the shrinkage rate of the molded product in the direction perpendicular to the magnetic field is α1, the shrinkage rate in the parallel direction is α2, the wall thickness of the polar anisotropic annular bonded magnet to be produced is T, the number of magnetic poles is P, the polar anisotropic annular bonded magnet is The radius of the bonded magnet molded body is D, the shrinkage length Tc of the resulting molded body is T x (α1/100-α2/100), and the radius Dm of the magnetic pole part of the mold cavity is D/(1-α2/100). ), β is a correction coefficient, 0.7≦β≦1.0, and 0≦θ≦2π.)
A mold for a polar anisotropic annular bonded magnet body defined by: A method for producing a polar anisotropic annular bonded magnet molded body, comprising the step of injection molding a composition for a bonded magnet using the mold for a polar anisotropic annular bonded magnet molded body according to claim 4 or 5.

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