JP2003088057A - Motor field magnet and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pole magnetizing annular magnet for a small motor field wherein superior magnetic characteristic and a smooth surface magnetic flux density waveform are obtained, and to provide a manufacturing method of the magnet. SOLUTION: In the motor field magnet, a plane magnet molded body has two main surfaces composed of magnetic powder and binder having flexibility. In the pole magnetizing annular magnet, the magnetic powder is orientated only on a first main surface in such a manner that at least two magnetic poles are generated in stripe shapes, and the plane magnet molded body is bent annularly in such a manner that the stripe-shaped magnetic poles are arranged at an equal interval on a side surface of an annulur ring. At least 40 vol.% of anisotropic rare earth magnetic powder whose remanent magnetic flux density is at least 10 kG is contained, a thickness of the plane magnet molded body is at most 2 mm, an outer diameter of the annular magnet is at most 50 mm, and at least four poles are installed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-performance permanent magnet for a small motor field.

[0002]

2. Description of the Related Art Since a permanent magnet field type motor requires a strong magnetic flux density when it becomes small, the magnetic flux density is high.
Rare earth bonded magnets, which have excellent moldability, are often used. In addition, motor permanent magnets are often used in an annular shape, but in the case of an annular shape, as shown in Fig. 1, it is anisotropic so that magnetic flux comes out from one side of the outer peripheral surface or inner peripheral surface and goes out to the same surface. A polar anisotropic magnet that is magnetized and magnetized has little leakage magnetic flux, and generally the highest magnetic flux density can be expected with the same size.

However, as the diameter of the motor becomes smaller, the diameter of the magnet becomes smaller, and it is difficult to dispose the magnet or coil for generating the polar anisotropic magnetic field, and it is hardly used industrially. For this reason, isotropic rare earth magnets or radial anisotropic rare earth magnets shown in FIG. 2 are mainly used for small-diameter ring-shaped magnets in the industry, but in either case, the high magnetic flux density of the rare earth magnetic powder is sufficient. I can't say I'm using it. Further, in isotropic magnets and radial anisotropic magnets, the magnetic flux density distribution is determined by the magnetizing yoke, so the magnetic flux density curve becomes a rectangular wave that changes rapidly near the magnetic pole boundary, and the magnet was used as a field element for the motor. In this case, there is a problem that the cogging torque becomes large.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems, and in rare earth magnets, by making them anisotropic, conventional isotropic rare earth magnets and radial anisotropic rare earth magnets are provided. Provided are a small-sized annular magnet for a motor field, which has a high magnetic flux density and a low cogging torque when used as a motor, and a manufacturing method thereof.

[0005]

Means for Solving the Problem The present inventors previously filed a patent application 2
In Japanese Patent Laid-Open No. 000-396393, there is disclosed a method in which a magnetic powder is once formed into a flat sheet shape while being extremely anisotropically oriented on one side and then deformed into an annular shape to obtain an annular polar anisotropic magnet. As a result of applying the method to anisotropic rare earth magnetic powder and further researching, the present invention has been accomplished.

That is, the motor field magnet of the present invention has at least two flat magnet moldings having only two main surfaces, each of which has a magnetic powder and a flexible binder. Of the magnetic powder are oriented so that the magnetic poles are generated in stripes, and the flat magnet molding is bent in an annular shape so that the magnetic poles in stripes are arranged at equal intervals on the side surface of the ring. In a ring magnet, the residual magnetic flux density is 1
An anisotropic rare earth magnetic powder of 0 kG or more is contained in an amount of 40% by volume or more, the thickness of the flat magnet molding is 2 mm or less, the outer diameter of the annular magnet is 50 mm or less, and 4 poles or more. And the coefficient b of the third or higher harmonic component obtained by expanding the surface magnetic flux density curve into a Fourier series represented by the following formula (I).
_{2k + 1} (k represents a natural number of 1 or more) and the coefficient b ₁ of the first-order component satisfy the following expression (II).

[0007]

[Equation 3] (F (θ) in the formula represents a surface magnetic flux density curve of the motor field magnet.)

[0008]

[Equation 4]

The motor field magnet of the present invention is characterized in that the maximum value of the surface magnetic flux density is 1650 G or more. Further, the anisotropic rare earth magnetic powder is anisotropic Sm-Fe-
It is characterized by being an N-based magnetic powder.

The residual magnetic flux density of the anisotropic rare earth magnetic powder can be obtained by preparing a measurement sample in which the magnetic powder is anisotropically oriented in advance and measuring it with a vibrating sample magnetometer. The maximum value of the surface magnetic flux density curve and the surface magnetic flux density is measured by the following method. First, the measuring portion of the Gauss meter is applied to the side surface of the ring where the magnetic poles of the motor field magnet are generated, and the relationship between each rotation angle and the surface magnetic flux density is measured with the Gauss meter. A surface magnetic flux density curve is obtained by plotting the surface magnetic flux density by the rotation angle. In addition, the maximum value of the surface magnetic flux density on the surface magnetic flux density curve is obtained.

A point at which the surface magnetic flux density is 0 is defined as a boundary point between magnetic poles, and a surface magnetic flux density curve between two boundary points between adjacent magnetic poles is defined as a surface magnetic flux density curve obtained from a single magnetic pole. Next, the scale is changed so that the rotation angle (radian) of the surface magnetic flux density curve obtained from one magnetic pole is 0 to π, and the surface magnetic flux density curve obtained from a plurality of magnetic poles is defined as a periodic function f (θ). To do. It is expanded to the Fourier series represented by the following equation (I), and the coefficient b ₁ of the first-order component and the coefficient b _{2k + 1} of the harmonic component of the third or higher order (k is a natural number of 1 or higher) are calculated. The coefficients of the third order or more each harmonic component _{b 2k + 1} and the ratio of the coefficient _{b 1} of the first-order component which is a basic wave _{(b 2k +} 1 /
b ₁ ) is calculated.

[0012]

[Equation 5] (F (θ) in the formula represents a surface magnetic flux density curve of the motor field magnet.)

The method of manufacturing a magnet for a motor field according to the present invention further comprises a step of forming a flat magnet molded body having two main surfaces composed of anisotropic rare earth magnetic powder and a binder having flexibility.
Of orienting the magnetic powder so that at least two or more magnetic poles are generated in stripes only on the main surface of the plate, and the flat magnet molding is performed so that the stripes of magnetic poles are arranged at equal intervals on the side surface of the ring. In a method for manufacturing a poled annular magnet having a step of bending a body in an annular shape, the residual magnetic flux density is 10 kG.
The anisotropic rare earth magnetic powder described above is mixed with 40% by volume or more and a flexible binder, and then magnetic field molding is performed to polar anisotropy so that only the first main surface has magnetic poles of 4 poles or more. Thickness is 2m
It is characterized in that a flat magnet molding having two main surfaces of m or less is formed, and the flat magnet molding is bent in an annular shape to form a pole magnetized annular magnet having an outer diameter of 50 mm or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The anisotropic rare earth magnetic powder according to the present invention must be hard anisotropic rare earth magnetic powder. An isotropic magnetic powder cannot be made extremely anisotropic, and magnetic powders other than rare earth-based magnetic powders do not exhibit as high magnetization as hard rare earth magnetic powders, so that it is not possible to obtain a high surface magnetic flux density due to polar anisotropy. The anisotropic rare earth magnetic powder has magnetic properties such that the residual magnetic flux density is less than 10 kG or the anisotropic rare earth magnetic powder content is less than 40% by volume. It is not possible to obtain a higher surface magnetic flux density than an anisotropic rare earth magnet. Therefore, the magnetic characteristic of anisotropic rare earth magnetic powder is that the residual magnetic flux density is 1
The effectiveness of the present invention cannot be exhibited unless it is 0 kG or more and the anisotropic rare earth magnetic powder is 40% by volume or more.

Examples of the anisotropic rare earth magnetic powder include anisotropic Sm-Fe-N magnetic powder, anisotropic Sm-Co magnetic powder, anisotropic Nd-Fe-B magnetic powder, and these. A magnetic powder of a system in which a part of the constituent elements is replaced with another element, or an anisotropic rare earth magnetic powder of a system in which two or more types of magnetic powders are mixed, and the like, which is selected according to each application and use condition. Should do. In addition, the anisotropic rare earth magnetic powder is 40
It is also possible to mix other magnetic powder such as ferrite as long as the content is at least volume%.

In the present invention, anisotropic Sm-Fe-N magnetic powder is preferably used as the anisotropic rare earth magnetic powder. The anisotropic Sm-Fe-N magnetic powder has a coercive force development mechanism of a nucleation type and a particle size of 2 to 3 μm.
Used as a single domain particle size of m. Therefore, it is excellent in moldability. In addition, the anisotropic Sm-Fe-N-based magnetic powder produced by a production method in which the particle size characteristics of the raw material powder, the production conditions and the like are accurately controlled and which is not premised on crushing does not contain fine particles or coarse particles, It is almost spherical. Therefore, it is excellent in magnetic field orientation and can be preferably used for a polar anisotropic magnet molding having a complicated orientation pattern as in the present invention.

In order to form a flexible magnet by using the above-mentioned magnetic powder, a binder having flexibility at room temperature is necessary, and a so-called rubber or elastomer corresponds to the binder. As some examples, synthetic rubbers include styrene-butadiene rubber, nitrile rubber, butadiene rubber, silicone rubber, butyl rubber, urethane rubber, and fluororubber, and thermoplastic resins include polyethylene, polypropylene, polybutene, and chlorinated rubber. Polyolefin resin such as polyethylene and polystyrene, vinyl resin such as vinyl chloride and polyvinyl acetate, styrene resin, polyester, polyamide, polyurethane, ethylene vinyl acetate copolymer and the like can be used.

Even for the binders other than the above, the binder itself is flexible at room temperature and can retain the deformable flexibility without breaking even after being mixed and molded with the magnetic powder. Therefore, it should be selected according to the molding method, application and use conditions. Again 2
Copolymers, polymer alloys, and mixtures of one or more resins can also be used if necessary.

Next, the anisotropic rare earth magnetic powder and the binder are mixed. At this time, additives such as a lubricant, a plasticizer and an antioxidant are also mixed for the purpose of improving moldability and stability. What should be done should be done as needed within the range in which the effectiveness of the present invention is not lost.

The molding method in the present invention is preferably extrusion molding or injection molding. In the case of extrusion molding, the orientation magnetic field generating magnets or coils for making the poles anisotropic are arranged in the die by the required number of magnetic poles. Depending on the type of magnetic powder used and the fluidity of the binder, it should be set so as to give a sufficient magnetic field for anisotropic formation. Since the molding shape is a flat sheet shape, the magnets or coils can be easily arranged, the die shape is simple, and the cost of the die and the accessory parts can be reduced. The mixture of the magnetic powder and the binder may be extruded into a die and molded as it is while kneading the mixture with a kneader, or it may be extruded again after once kneading into a granular pellet.

In the case of injection molding, magnetic powder, binder and additives are mixed in advance and then kneaded by a kneading machine to form granular pellets. After that, injection molding is performed, but it is necessary to arrange orientation magnetic field generating magnets or coils for polar anisotropy in the mold by the required number of magnetic poles. The magnet or coil should be set so as to give a sufficient magnetic field for anisotropic formation depending on the type of magnetic powder used and the fluidity of the binder. Since the molding shape is a flat sheet, it is easy to arrange magnets or coils, the shape of the mold is simple, and if the sheet size and the number of magnetic poles are large, the size can be cut according to the intended specifications. There is also an advantage that it can be used as a mold common to a plurality of different types of ring shapes, and the cost of the mold and accessory parts can be reduced.

The thickness of the flat magnet molding to be molded is 2 m.
When the thickness exceeds m, the flexibility becomes low and the outer diameter is 50
It becomes impossible to form a ring shape of mm or less. Therefore, the thickness of the flat magnet molded body to be molded needs to be 2 mm or less.

The formed flat magnet molding is cut according to the size of the target ring and then rolled into an annular magnet. In the case of magnetizing the inner surface, an annular or cylindrical container is prepared, and an annular magnet can be formed by bending and inserting the container so that the anisotropic magnetic pole is located inside. The container may be magnetic or non-magnetic. If necessary, the magnet can be fixed with an appropriate adhesive or pressure sensitive adhesive.

In the case of magnetizing the outer surface, an annular, cylindrical or columnar core rod is prepared, and the outer side of the core rod is wound so that the anisotropic magnetic pole is on the outer side to form an annular, cylindrical or columnar magnet. can do. The material of the core rod may be magnetic or non-magnetic. Further, it is necessary to fix it to the core rod with an appropriate adhesive or pressure sensitive adhesive.

Regarding the magnetization of the magnet, it may be magnetized in the state of a flat sheet and then ring-shaped, or it may be demagnetized once and then ring-shaped and then magnetized.

In the case of a ring-shaped magnet having an outer diameter of more than 50 mm, it is technically possible, but the superiority of the present invention is lost because it is easy to form anisotropy into a ring from the beginning by the conventional technique. Be seen. Therefore, the present invention is limited to a ring-shaped motor field magnet having an outer diameter of the magnet portion of 50 mm or less.

The same can be applied to the case of an annular magnet having two magnetic poles, but it can be easily manufactured by a conventional method and the present invention is not superior. Therefore, the present invention is limited to a multi-pole motor field magnet having four or more magnetic poles.

By the method disclosed above, a ring-shaped permanent magnet having a surface magnetic flux density of 1650 G or more can be obtained and can be used as a field element such as a rotor or a stator of a permanent magnet field type motor.

Further, according to the present invention, since the distribution of the surface magnetic flux is determined when the magnetic field is shaped and oriented in polar anisotropy, a smooth curve close to a sine curve is obtained after magnetization, as shown in FIG. Found in. That is, the cogging torque of the motor can be reduced by obtaining the surface magnetic flux density curve in which the coefficient of the third-order or higher harmonic component is 0.25 times or less the coefficient of the first-order component in the direction along the circumference of the magnetized surface. Can be made smaller.

[0030]

EXAMPLES Examples of the present invention will be described below.
The present invention is not limited to the specific examples. Example 1 The anisotropic rare earth magnetic powder used in the example is S
It is an Sm-Fe-N-based magnetic powder having m ₂ Fe ₁₇ N ₃ as a main phase, and has a residual magnetic flux density of 10.5 kG. The magnetic characteristics of this magnetic powder are the vibrating sample magnetometer (VSM).
The orientation magnetic field is 10 kOe and the magnetizing magnetic field is 2
The true density of the magnetic powder was 0 kOe and 7.66 g / cm ³ . 42% by volume of this Sm-Fe-N magnetic powder,
Using 58% by volume of polybutylene terephthalate (PBT) elastomer to which a lubricant and an antioxidant were added, they were mixed and kneaded according to a conventional method to obtain a compound. This compound was injection molded into a flat sheet shape in a polar anisotropic magnetic field in which a permanent magnet was arranged on one side of the cavity. The dimension after molding was 100 mm in length, 10 mm in width, and 1.5 mm in thickness, and the anisotropic magnetic poles were arranged at intervals of 16 mm between magnetic poles in the longitudinal direction.

The obtained flat sheet-shaped molded product is 64 m in length.
It was cut at a position of m, width of 5 mm, and four magnetic poles. Further, a magnetic pole of 4 poles was magnetized with a magnetic field of 20 kOe to obtain a flat sheet flexible magnet. This magnet has an inner diameter of 22m
While the magnetic poles were directed inward, they were rolled into the inner surface of the annular resin container of m to produce an inner magnetized annular magnet.
The maximum value was 1732 G as a result of measuring the surface magnetic flux density of the inner surface of the obtained annular magnet along the inner circumference with a Gauss meter.

Example 2 A flat sheet-like molded product was produced in the same manner as in Example 1. Next, the flat sheet-shaped molded product was cut at a position having a length of 65 mm and a width of 6 mm and having 4 magnetic poles. Then, a magnetic pole was wound around the outer surface of a cylindrical resin core rod having an outer diameter of 19 mm, and the magnetic pole was wound outward and fixed with an adhesive. Four magnetic poles were magnetized with a magnetizing magnetic field of 20 kOe to produce an outer magnetized annular magnet. The maximum value was 1719 G as a result of measuring the surface magnetic flux density of the outer surface of the obtained annular magnet along the outer circumference with a Gauss meter.

[Example 3] A flat sheet-like molded product was produced in the same manner as in Example 1. Next, the flat sheet-shaped molded product was cut at a position having a length of 96 mm and a width of 10 mm and having 6 magnetic poles. Further, a 6-pole magnetic pole was magnetized with a magnetizing magnetic field of 20 kOe to obtain a flat sheet flexible magnet. This magnet was rolled into the inner surface of an annular resin container having an inner diameter of 32 mm, with the magnetic poles facing inward, to produce an inner magnetized annular magnet. As a result of measuring the surface magnetic flux density of the inner surface of the obtained annular magnet along the inner circumference with a Gauss meter, the maximum value was 172
It was 8G.

3 to 6 are schematic views of the flat sheet-shaped molded product before cutting, the flat sheet-shaped molded product after cutting, and the annular magnet obtained in Examples 1 to 3. 3 to 6 are schematic views, and the thickness of the molded body is shown thicker than the actual size ratio.

Comparative Example 1 Example 1 based on the prior art
An isotropic toroidal magnet having the same size as was produced. Nd ₂ F
Using isotropic magnetic powder produced by pulverizing a quenched ribbon isotropic Nd-Fe-B system to the e _{14 B} as a main phase. The magnetic properties of the magnetic powder were measured by a vibrating sample magnetometer (VSM) in the same manner as in Example 1 except that the true density was 7.60 g / cm ³ and the residual magnetic flux density was 8.8 kG. It was 42% by volume of this isotropic rare earth magnetic powder and 58% by volume of an epoxy resin were mixed and compression molded according to the conventional technique. The shape of the molded body is an annular shape having an outer diameter of 22 mm, a thickness of 1.5 mm and a height of 5 mm. Four magnetic poles were magnetized on the inner peripheral surface of this molded body with a magnetizing magnetic field of 20 kOe to obtain an annular magnet. As a result of measuring the surface magnetic flux density of the inner surface of the obtained annular magnet with a Gauss meter along the inner circumference, the maximum value is 1067G.
Met.

[Comparative Example 2] A radial anisotropic annular magnet having the same dimensions as in Example 1 was produced by using the conventional technique. 42% by volume of anisotropic Sm—Fe—N magnetic powder used in Example 1
And 58% by volume of a polyamide resin containing a lubricant and an antioxidant were mixed, kneaded and injection-molded in a magnetic field by a conventional technique. The compact had a ring shape having an outer diameter of 22 mm, a thickness of 1.5 mm and a height of 5 mm, and magnetic powder was radially and anisotropically oriented from the inner peripheral surface to the outer peripheral surface. Four magnetic poles were magnetized on the inner peripheral surface of this molded body with a magnetizing magnetic field of 20 kOe to obtain an annular magnet. The maximum value was 1314 G as a result of measuring the surface magnetic flux density of the inner surface of the obtained annular magnet along the inner circumference with a Gauss meter.

The surface magnetic flux density in Example 1 is higher than the surface magnetic flux density obtained by the magnets of the same size prepared in Comparative Examples 1 and 2 by using the conventional technique, which shows the effectiveness of the present invention. Further, the measured values of the surface magnetic flux density in the circumferential direction of the magnets of Example 1 and Comparative Example 2 are graphed in FIGS. Each curve was numerically Fourier expanded to calculate the coefficient of a harmonic having a period of 3, 5, 7, 9 times the fundamental wave that coincides with the magnetic pole. Example 1 is shown in formula (III), and Comparative example 2 is shown in formula (IV).

[0038]

[Equation 6]

[0039]

[Equation 7]

Since the magnet has four magnetic poles, θ = 2
X α (α represents an angle in the ring and is 0 to 360 °). As can be seen from FIGS. 7 and 8, in Comparative Example 2 according to the prior art, a rectangular wave in which the magnetic flux density changes abruptly and the cogging torque becomes large when the field element of the motor is used. In No. 1, the curve is smooth and the cogging torque is small. When this is evaluated by the coefficient of the harmonic component of the third or higher order, it is 3 in the formula (IV) of Comparative Example 2.
While the following coefficients are as high as 0.30, all of the expressions (III) in Example 1 are 0.25 or less, which is a characteristic of the present invention.

[0041]

As described above, according to the present invention, it is possible to obtain a magnet for a motor field, which has a small diameter and a high surface magnetic flux density, which could not be industrially used conventionally. At the same time, according to the present invention, it is possible to inexpensively manufacture a plurality of magnets having different magnetizing surfaces, outer diameters, and magnetic pole numbers by using the same mold or die. Moreover, the obtained motor field magnet can reduce the cogging torque.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an anisotropic direction of a polar anisotropic magnet.

FIG. 2 is a schematic diagram showing an anisotropic direction of a radial anisotropic magnet.

FIG. 3 is a schematic view showing a flat sheet-shaped molded product obtained in Examples 1 to 3 before cutting.

FIG. 4 is a schematic view showing a flat sheet-shaped molded product (a) and an annular magnet (b) after cutting obtained in Example 1.

FIG. 5 is a schematic view showing a flat sheet-shaped molded product (a) and an annular magnet (b) after cutting obtained in Example 2.

FIG. 6 is a schematic view showing a flat sheet-shaped molded product (a) and an annular magnet (b) after cutting obtained in Example 3.

FIG. 7 is a diagram showing a surface magnetic flux density curve of the magnet molding obtained in Example 1.

FIG. 8 is a diagram showing a surface magnetic flux density curve of a magnet molded body obtained in Comparative Example 2.

Claims (5)

[Claims] 1. A flat magnet molding having two main surfaces composed of a magnetic powder and a flexible binder so that at least two magnetic poles are formed in stripes only on the first main surface. In the pole magnetized annular magnet obtained by orienting the magnetic powder in a circular shape and bending the flat magnet molded body in an annular shape so that the striped magnetic poles are arranged at equal intervals on the side surface of the ring, the residual magnetic flux density is 10 kG. 4 of the above anisotropic rare earth magnetic powder
A motor containing 0% by volume or more, the thickness of the flat magnet molded body being 2 mm or less, the outer diameter of the annular magnet being 50 mm or less, and having 4 or more magnetic poles. Field magnet. 2. A coefficient b _{2k + 1} of a harmonic component of a third order or higher obtained by expanding a surface magnetic flux density curve into a Fourier series represented by the following formula (I) (k represents a natural number of 1 or higher).
And the coefficient b ₁ of the first-order component satisfies the following formula (II): The magnet for motor field according to claim 1, wherein [Equation 1] (F (θ) in the equation represents the surface magnetic flux density curve of the motor field magnet.) 3. The magnet for motor field according to claim 1, wherein the maximum value of the surface magnetic flux density is 1650 G or more. 4. The anisotropic rare earth magnetic powder is anisotropic Sm-F.
The motor field magnet according to any one of claims 1 to 3, wherein the magnet is an e-N magnetic powder. 5. A flat magnet molding having two principal surfaces composed of anisotropic rare earth magnetic powder and a flexible binder, wherein at least two magnetic poles are striped only on the first principal surface. To orient the magnetic powder so that
In a method of manufacturing a pole-magnetized annular magnet, which comprises a step of bending the flat magnet molded body in an annular shape so that the striped magnetic poles are arranged at equal intervals on the side surface of the ring, a residual magnetic flux density of 10 kG or more is different. The anisotropic rare-earth magnetic powder is mixed with 40% by volume or more and a flexible binder, and then magnetically molded into polar anisotropy to have a magnetic pole of 4 poles or more only on the first main surface and a thickness. Is a flat magnet molding having two main surfaces of 2 mm or less, and the flat magnet molding is bent into an annular shape to have an outer diameter of 50 m.
The method for producing a motor field magnet according to any one of claims 1 to 4, wherein the pole magnetized annular magnet is m or less.