Patent Grant
10232538
The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2015-085889, filed Apr. 20, 2015. The contents of this application are incorporated herein by reference in their entirety.
Technical Field
The present disclosure relates to a bond magnet and a method for manufacturing a bond magnet.
Discussion of the Background
Japanese Unexamined Patent Application Publication No. 5-3115 and Japanese Patent No. 3152659 describe a method in which a magnet is divided into small pieces to be subjected to saturated magnetization by a magnetizing apparatus and then are arranged to be formed into a multipolar magnet.
According to one aspect of the present invention, a method for manufacturing a bond magnet includes providing a bond magnet composition including a magnetic material and a resin, extruding the bond magnet composition in one direction to produce a molded body while orienting the magnetic material in the one direction, magnetizing the molded body in the one direction using an axial magnetization to produce a magnetized molded body, and laminating the magnetized molded body to produce a laminated molded body including first magnetized molded layers and second magnetized molded layers. The first magnetized molded layers and the second magnetized molded layers are alternately laminated. A first magnetization direction of each of the first magnetized molded layers is opposite to a second magnetization direction of each of the second magnetized molded layers.
According to another aspect of the present invention, a bond magnet includes a plurality of magnet pieces which is magnetized by axial magnetization and which is laminated such that N-poles and S-poles of the plurality of magnet pieces are alternately arranged. The plurality of magnet pieces include an anisotropic Sm—Fe—N-based magnetic material and a resin. A distance λ between an N-pole among the N-poles and an S-pole adjacent to the N-pole among the S-poles is equal to or more than 0.1 mm and equal to or less than 1.0 mm.
According to further aspect of the present invention, a method for manufacturing a bond magnet includes providing a bond magnet composition including a magnetic material and a resin, extruding the bond magnet composition in one direction to produce a molded body, orienting the magnetic material in the one direction, magnetizing the molded body in the one direction using an axial magnetization to produce a magnetized molded body, and laminating the magnetized molded body to produce a laminated molded body including a first magnetized molded layer and a second magnetized molded layer adjacent to the first magnetized molded layer such that a first magnetization direction of the first magnetized molded layer is opposite to a second magnetization direction of the second magnetized molded layer.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.
Hereinafter, embodiments will be described appropriately with reference to drawings. However, the following methods for manufacturing bond magnets and the bond magnets are described to embody the technological thought of the present disclosure and thus unless specific description is made, the present disclosure is not limited to the following. Further, what is described in an embodiment and an example is also applicable to other embodiments and examples.
The size or positional relationship of members illustrated in each drawing may be exaggerated in order to make the description clear. The direction “x” is also called the “lateral” direction, the direction “y” is also called the “longitudinal” direction, and the direction “z” is also called the “vertical” direction or the “height (thickness)” direction.
As described above, a multipolar magnet with high magnetic properties can be manufactured with high productivity not by applying multipolar magnetization after molding the bond magnet in the final shape but by having a magnetizing process for magnetizing by the axial magnetization in the same direction as the extrusion direction, between the extrusion molding process and the laminating process.
Hereinafter, each process will be described.
Preparation Process
The preparation process is a process of preparing a bond magnet composition including a magnetic material and a resin. An anisotropic magnetic material can be used as the magnetic material.
The bond magnet composition can be acquired, for example, by mixing a magnetic material and a resin, heating and kneading the acquired mixture and then cutting into pieces having an appropriate size after cooling. The blending ratio of a magnetic material to a resin depends on the type of the resin but the ratio of the magnetic material to the entire bond magnet composition is preferably 45 to 65 vol %. Other than the magnetic material and the resin, antioxidants, lubricants or others can be further mixed. The bond magnet composition may be a lump like a pellet or be in a starch-syrup state at room temperature.
Examples of an anisotropic magnetic material include an Sm—Co based magnetic material, Nd—Fe—B based magnetic material, Sm—Fe—N based magnetic material, and others. The magnetic material is preferably in a powder state. A ferrite based magnetic material has weaker magnetic force than a rare-earth based magnetic material. Since a smaller size of the molded body may cause a shortage of magnetic force, a rare-earth magnetic powder such as an Sm—Co-based powder, Nd—Fe—B-based powder, or Sm—Fe—N-based powder is used in the present embodiment. This is because a magnetization direction of a rare-earth anisotropic magnetic powder is aligned in the same direction very easily by being subjected to a magnetic field applied during the orientation, and consequently exhibits strong magnetic force of the bond magnet.
The average particle diameter of the magnetic powder to be used is preferably smaller than 20%, more preferably smaller than 15%, and still more preferably smaller than 10% of the thickness of the molded body subjected to the extrusion molding described below. When the particle diameter is too large, the extrusion moldability may degrade and the molding of the sheet magnet itself becomes difficult. The Sm—Fe—N based magnetic powder is preferable because its average particle diameter is approximately 3 μm and approximately spherical and thus its extrusion moldability is excellent. In the present description, the value of the average particle diameter is based on the air permeability method or Fisher-SubSieve-Sizers-No. (F.S.S.S.No.).
The above-described magnetic material can be used as one kind alone and also as a mixture of two or more kinds. A surface treatment (for example, an oxidation resistance treatment or a coupling treatment) may be performed, as needed.
Examples of the resin to be used includes, but is not particularly limited to, thermoplastic resins such as polypropylene, polyethylene, polyvinyl chloride, polyester, polyamide, polycarbonate, polyphenylene sulfide, and acrylic resins, thermoplastic elastomers such as ester-based and polyamide-based elastomers, and thermosetting resins such as epoxy resins, phenolic resins, unsaturated polyester resins, urea resins, melamine resins, polyimide resins, allyl resins, and silicone resins. It is preferable to add an antioxidant, a metal deactivator, and a lubricant during the mixing with the magnetic material in order to reduce degradation of the binder due to a thermal history during the kneading or the molding.
Extruding Process
The extruding process is a process of extruding the bond magnet composition in one direction (e.g., direction x) by the extrusion molding while orienting the magnetic material in one direction (e.g., direction x). The extruding process is performed by using an extrusion molding apparatus. An extrusion molding apparatus 200 illustrated in
The screw section 10 conveys the bond magnet composition to the mold section 20 by a screw 30. The bond magnet composition prepared in the preparation process is supplied into a cylinder 50 from a hopper 40. The cylinder 50 is provided outside periphery of the screw 30, and if the need arises, the cylinder 50 may be heated to be in a state suitable for easily conveying the bond magnet composition.
The bond magnet composition conveyed into the mold section 20 is molded into a shape corresponding to the cavity of the mold. The cavity whose dimension in the direction y is longer than the dimension in the direction z can produce a sheet-shaped molded body whose plane direction is the direction x-y (hereinafter, the sheet-shaped molded body formed through the extrusion process is also called “sheet magnet 300”). As
The orienting magnet 60 is built in the mold section 20. When the molten bond magnet composition is cooled into a solid, the magnetic powder is orientated at the same time. The orientation method may be an electromagnet method or may be a permanent magnet method. That is, the orienting magnet 60 may be an electromagnet or may be a permanent magnet. The magnetic material used for the permanent magnet is preferably a material whose residual magnetic flux density Br is 1 T or more, and for example, an Nd—Fe—B sintered magnet can be used.
According to the example illustrated in
Here, the relationship between the orientation rate and the thickness (direction z) of the sheet-shaped molded body subjected to the extrusion molding according to the present embodiment is described.
As illustrated in
On the other hand, in the extrusion molding according to the present embodiment, the orientation rate increases as the thickness goes toward the thin sheet-thickness region. In particular, in the region of 1 mm or less, an orientation rate of 85% which is higher than that of the injection molding by 20% is exhibited.
Further, in order to confirm the detailed orientation state of the molded body related to the extrusion molding, a sheet magnet is molded by use of a similar material to that in the case in
In the region where the thickness is 0.5 mm or less, it is found that almost no difference of the orientation rate between the outermost surface and the central part exists. It is considered that an area of the outermost surface having a high orientation rate is dominant in the region where the thickness is 0.5 mm or less. Even in the extrusion molding similarly to the injection molding, it is considered that the flowability of the bond magnet composition reduces near the wall but a high orientation rate is achieved because a certain shearing occurs near the cavity wall continuously and compulsorily at the time of discharge of the bond magnet composition in the extrusion molding, and a magnetic powder becomes capable of moving around freely near the wall even in the thin sheet-thickness region where originally the achievement of orientation is difficult.
As described above, a molded body with a high orientation rate can be obtained by molding a sheet-shaped molded body through the extrusion molding. Further, it is possible to obtain a molded body orientated in one direction, which facilitates alignment of the magnetization direction with the orientation direction in the magnetization conducted in the next magnetizing process, and the properties of the anisotropic magnetic powder can be sufficiently brought out.
Magnetizing Process
The magnetizing process is a process of applying the axial magnetization to the molded body subjected to the extrusion molding in one direction (direction x). As described above, since the orientation of the magnetic material in the sheet-shaped molded body is the in-plane direction (direction x), simple magnetization can be applied in the travelling direction in the extrusion molding (direction x). Hence, an air-core coil with a strong magnetizing magnetic field can be used as a magnetizer 70 illustrated in
In the present embodiment, in other words, magnetization can be performed by using simple axial magnetization, not by using a multipolar magnetizing yoke made in combination with a soft magnetic material and a coil, or the like to apply multipolar magnetization after the final shape of the bond magnet is formed. Due to this, a magnetization defect caused from the limitation of magnetizing magnetic field that occurs because of multipolar magnetization can be avoided.
Laminating Process
The laminating process is a process of laminating magnetized molded body such that the magnetization direction is alternately oriented in opposite directions. Specifically, as illustrated in
An adhesive may be used or may not be used to a space between the molded body, namely lamination surfaces. When an adhesive is used, since the distance between the neighboring magnetic poles increases by the thickness of the adhesive, the thicknesses of the molded body and the adhesive are determined in consideration of the magnetic pole pitch of the bond magnet that is finally desirable. When the thickness of the adhesive is zero, namely, when no adhesive is used, the thickness of the sheet-shaped molded body becomes the distance between the laminated magnetic N and S poles (magnetic pole pitch of the multipolar magnet).
In the laminating process, a long sheet may be folded to be laminated as described above in consideration of the productivity, or separated sheets cut in a specific length may be stacked alternately for making the lamination. In the case where sheets previously cut are used for the lamination, the cutting process described later can be omitted.
Cutting Process
The cutting process is a process of acquiring a multipolar bond magnet having N-poles and S-poles disposed alternately on its end surface after the laminated molded body is cut out perpendicularly to the lamination direction. A multipolar bond magnet 100 can be obtained after the folded sheet magnet is cut out into the part enclosed by the lines in
Bond Magnet 100
Here, the orientation rate of the magnetic material of each magnet piece is preferably 85% or more. The magnetization rate of each magnet piece is preferably 95% or more. The lamination of such magnet pieces can achieve an extremely high surface magnetic flux density despite a multipolar magnet with a small pitch of 0.1 mm to 1.0 mm (inclusive) between the magnetic poles.
According to the method illustrated in
First, 60 vol % of an anisotropic Sm—Fe—N-based magnetic powder having an average particle diameter of 2.8 μm subjected to a surface treatment with ethyl silicate and an amino-based coupling agent and 40 vol % of nylon 12 are weighed out, and after mixing these materials sufficiently with a mixer, the mixture is kneaded at 220° C. with a biaxial kneading machine. Pellets each having a length of approximately 3 mm are obtained after cooling. By use of these pellets as a bond magnet composition, a sheet-shaped molded body is acquired by the extrusion molding.
In the extrusion molding process, the material is formed in the mold into a sheet-shaped piece having a width (direction y) of 10 mm and a thickness (direction z) of 0.1 mm and is oriented such that the direction of the easily magnetizable axis of the Sm—Fe—N-based magnetic powder is aligned parallel to the in-plane direction (direction x) by using the orientation magnetic field of the orienting magnet as shown in
The oriented sheet magnet is subjected to the axial magnetization successively in the same direction as the orientation direction (direction x) by use of an air-core coil as a magnetizer 70 as illustrated in
The orientation rate of sheet magnet of the bond magnet, the magnetization rate of the sheet magnet and the surface magnetic flux density at a position λ/2 away from the bond magnet obtained in Example 1 are shown in Table 1.
Multipolar bond magnets are acquired similarly to Example 1 except that the thicknesses of the sheet magnets are 0.3 mm, 0.5 mm and 1.0 mm respectively. The orientation rate of sheet magnet of the bond magnet, the magnetization rate of the sheet magnet and the surface magnetic flux density at a position λ/2 away from the bond magnet obtained in each example are shown in Table 1.
For a bond magnet composition, 60 vol % of an anisotropic Nd—Fe—B-based magnetic powder having an average particle diameter of 100 μm subjected to a surface treatment with methyl silicate and an amino-based coupling agent and 40 vol % of nylon 12 are weighed out, and after mixing these materials sufficiently with a mixer, the mixture is kneaded at 220° C. with a biaxial kneading machine. Pellets each having a length of approximately 3 mm are obtained after cooling. By use of these pellets as a bond magnet composition, a multipolar bond magnet is obtained similarly to Example 1 except that the thickness of the sheet magnet is 1.0 mm. The orientation rate of sheet magnet of the bond magnet, the magnetization rate of the sheet magnet and the surface magnetic flux density at a position λ/2 away from the bond magnet are shown in Table 1.
Although acquisition of a multipolar bond magnet was attempted similarly to Example 5 except that the thickness of the sheet magnet was 0.5 mm, any molded body could not be discharged from the end of the mold during the extrusion molding and the sheet magnet could not be molded.
After 65 vol % of an anisotropic ferrite magnetic powder and 35 vol % of nylon 12 are weighed out and mixed sufficiently with a mixer, the mixture is kneaded at 220° C. with a biaxial kneading machine. Pellets each having a length of approximately 3 mm are acquired after cooling. Next, a molded body having a total length (direction x) of 20 mm, a width (direction y) of 10 mm and a height (direction z) of 5 mm is acquired with the injection molding machine while being oriented sufficiently in the axial direction. Then, multipolar magnetization is applied to the surface having a size of 20 mm×10 mm at 0.5 mm intervals. The intensity of the magnetizing magnetic field is 15 kOe. The surface magnetic flux density of the obtained bond magnet is shown in Table 1. Since the piece is not formed of a lamination structure but formed of an integrally molded body, a sheet magnet is not formed; however the magnetic pole pitch is shown in parentheses as a reference value. Similarly, instead of the orientation rate of the sheet magnet, the orientation rate of the integrally molded body is shown in parentheses as a reference value.
A commercially available isotropic compressed magnet having a total length (direction x) of 20 mm, a width (direction y) of 10 mm and a height (direction z) of 5 mm is prepared and multipolar magnetization is applied to the surface having a size of 20 mm×10 mm at 1.2 mm intervals. The intensity of the magnetizing magnetic field is 15 kOe. The surface magnetic flux density of the obtained bond magnet is shown in Table 1. Since the piece is not formed of a lamination structure but formed of an integrally molded body, a sheet magnet is not formed; however the magnetic pole pitch is shown in parentheses as a reference value.
As is clear from Table 1, by the manufacturing of a sheet magnet through the extrusion molding by use of an anisotropic Sm—Fe—N-based magnetic powder having an average particle diameter of 2.8 μm, a sheet magnet having a high orientation rate in the thin sheet-thickness region of 1.0 mm or less can be acquired. By laminating this sheet magnet to form a multipolar bond magnet, a multipolar magnet having both of a high orientation rate and a high magnetization rate in a region of a magnetic pole pitch of 1 mm or less can be acquired, which was conventionally difficult for anisotropic rare-earth magnets.
When an approximation curve obtained by connecting the plotted points of Examples 1 to 5 in
B(gauss)>1520λ−20 (1)
(In the expression, B denotes a surface magnetic flux density B (gauss) at a position λ/2 away from the bond magnet.)
The method for manufacturing a bond magnet according to the present embodiment has a preparation process a bond magnet composition including a magnetic material and a resin, an extruding process the bond magnet composition in one direction by the extrusion molding while orienting the magnetic material in the direction, a magnetizing process to magnetize the molded body subjected to the extrusion molding in the direction by the axial magnetization, and a laminating process to laminate the molded body magnetized in the magnetizing process so as to be oriented the magnetization direction alternately in opposite directions.
Further, a bond magnet according to another embodiment is a bond magnet which includes an anisotropic Sm—Fe—N-based magnetic material and a resin and in which N-poles and S-poles of a plurality of magnet pieces magnetized by the axial magnetization are laminated alternately and the distance between the N-pole and the S-pole is 0.1mm to 1.0 mm (inclusive).
According to an embodiment of the present invention, a method capable of manufacturing a multipolar magnet having strong magnetic properties with high productivity can be provided. According to another embodiment, a multipolar magnet that is an anisotropic bond magnet, has strong magnetic properties, and a small magnetic pole pitch can be provided.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-085889 | Apr 2015 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5682670 | Bell et al. | Nov 1997 | A |
| Number | Date | Country |
|---|---|---|
| 05-003115 | Jan 1993 | JP |
| 07-509348 | Oct 1995 | JP |
| 2005-050988 | Feb 2005 | JP |
| 2006-329749 | Dec 2006 | JP |
| 2013-105964 | May 2013 | JP |
| Entry |
|---|
| Japanese Office Action for corresponding JP Application No. 2015-085889, dated Mar. 27, 2018 (w/ machine translation). |
| Number | Date | Country | |
|---|---|---|---|
| 20160303788 A1 | Oct 2016 | US |
