JP2007135346A - Yoke-integrated magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a high magnetic performance as a magnet is maintained as an isotropic magnet. <P>SOLUTION: A yoke-integrated magnet 1 is provided with the cylindrically molded magnet 3 and a yoke 2 integrally combined with the inner circumference of the magnet 3 by coinjection molding. A protrusion 21 is formed by circumferentially and circularly protruding a portion of the yoke 2 toward the magnet 3 in a plurality of positions at a regular interval. A magnetization region 31 is defined as a surface of the magnet 3 between the protrusion sections 21. Opposite magnetic poles are alternately formed in the magnetization regions 31. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a yoke-integrated magnet, and more particularly to a yoke-integrated magnet with improved magnetic performance.

Bonded magnets made by mixing magnetic powder and an appropriate resin material as a binder and then compressing, injecting or extruding them into a predetermined shape have a high degree of freedom in shape and can be easily manufactured as lightweight and compact. Therefore, it is widely used for spindle motors of HDDs (Hard Disk Drives). In this case, it is often the case that a ring-shaped yoke portion is joined and integrated with the peripheral surface of a bonded magnet formed in a ring shape, and delivered to a customer as a yoke-integrated magnet. Patent Document 1 shows an example of this type of yoke-integrated magnet.
JP-A-10-201154

  By the way, as a bonded magnet, an anisotropic magnet having high magnetic performance is attracting attention in place of a conventional isotropic magnet. Anisotropic magnets have a uniform magnetic moment in the metal structure, and in the case of ring-shaped bonded magnets, they are placed around the mold using a radial magnetic field forming device. The magnetic moment of the magnetic powder is oriented in the radial direction by the magnetic field excited by the electromagnetic coil. In this case, a ring-shaped bond magnet is required to be small in response to a request for miniaturization of the spindle motor, but a large current is supplied to the electromagnetic coil of the magnetic field forming device that is miniaturized according to the small bond magnet. Therefore, it is difficult to obtain an anisotropic small bonded magnet, and a yoke-integrated magnet that exhibits high magnetic performance while the magnet portion (bonded magnet) remains an isotropic magnet is desired. It was.

  The present invention has been made in view of such a demand, and an object of the present invention is to provide a yoke-integrated magnet that exhibits high magnetic performance while the magnet portion is an isotropic magnet.

  In order to achieve the above object, according to the first aspect of the present invention, in the yoke-integrated magnet (1) including the magnet portion (3) and the yoke portion (2) joined thereto, a part of the yoke portion (2) is formed. It protrudes toward a magnet part (3) in multiple places at intervals, and it is set as the protrusion part (21), and the surface of the magnet part (3) located between these protrusion parts (21) is a magnetization area | region (31). And

  In the first aspect of the present invention, since the protrusion is formed, the surface magnetic flux density distribution in each magnetic pole formed in the magnetized region does not form the protrusion even if the magnet is made an isotropic magnet. It becomes wider than the surface magnetic flux density distribution of the conventional yoke-integrated magnet, and the magnetic performance is improved.

  In the second aspect of the invention, the magnet part (3) is formed into a cylindrical shape, the yoke part (2) is joined to the inner or outer peripheral surface thereof, and the protruding parts (21) are formed at equal intervals in the circumferential direction. Then, magnetic poles having opposite polarities are alternately formed in the magnetized region (31) formed on the peripheral surface of the magnet portion (3) where the yoke portion (2) is not joined.

  In the second aspect of the present invention, the motor torque can be sufficiently increased by using the rotor of a spindle motor or the like.

  In this 3rd invention, the said protrusion part (21) is protruded in circular arc shape toward the said magnet part (3). In the third invention, the surface magnetic flux density distribution can be most effectively improved.

  In the fourth invention, the yoke part (2) is made of a resin molded body containing a soft magnetic material, and the magnet part (3) is made of a resin molded body containing a hard magnetic material, and the yoke part (2) and The magnet part (3) is joined and integrated by two-color molding. According to the fourth aspect of the invention, the yoke-integrated magnet can be efficiently manufactured.

  In addition, the code | symbol in the said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

  As described above, the yoke-integrated magnet of the present invention can exhibit high magnetic performance while the magnet portion is an isotropic magnet.

(First embodiment)
FIG. 1 shows a front view of a yoke-integrated magnet, and FIG. 2 shows a longitudinal sectional view taken along line II-II in FIG. In each figure, a yoke-integrated magnet (hereinafter simply referred to as a magnet) 1 is a cylindrical body, and an inner peripheral side is a yoke part 2 and an outer peripheral side is a magnet part 3. In this embodiment, the yoke part 2 and the magnet part 3 are integrally joined to each other by two-color integral molding. In this molding, first, one of the yoke part material or the magnet part material is injection molded by a two-color molding machine, and after cooling in the mold, the other yoke part material or magnet part material is injected, and the yoke part 2 and the magnet part 3 are injected. Are integrally joined. The magnet 1 manufactured in this way is used while the magnet portion 3 remains an isotropic magnet without being processed by the magnetic field forming apparatus.

(Composition of yoke part material)
As the soft magnetic material constituting the yoke part material, powder (iron powder) containing iron as a main component is used. The average particle size is preferably in the range of 10 μm to 200 μm. If it exceeds 200 μm, it is not smoothly injected into the cavity of the molding die, and if it is less than 10 μm, the surface area of the iron powder becomes excessive and is oxidized by molding at a high temperature, and the characteristics deteriorate. The shape of the iron powder may be a sphere formed by a gas atomization method or an irregular shape such as electrolytic iron powder. As the resin material, a thermoplastic resin is used. For example, nylon 12, nylon 6, PPS, EEA, EVA, polypropylene, polyethylene, PVC, CPVC, and the like can be used, but the material is not limited thereto. The mixing ratio of the iron powder and the thermoplastic resin is preferably 40 vol% to 80 vol% in terms of the volume content of the iron powder. If it is lower than 40 vol%, the saturation magnetic flux density Br cannot be sufficiently obtained among the intended magnetic characteristics. On the other hand, when it exceeds 80 vol%, since the mixing ratio of the resin is low, it is difficult to flow during injection molding, and a good molded product cannot be obtained.

  In addition, in order to improve the bonding force between the iron powder and the thermoplastic resin material, a coupling treatment may be performed on the surface of the iron powder. Coupling agents used include silane-based γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, etc., titanate-based tetraisopropyl titanate, tetraisobutyl orthotitanate, etc., aluminum-based acetoalkoxyaluminum diisopropylate, zirconium Zirconium tributoxy systemate and the like can be used, but are not limited thereto.

(Composition of magnet part material)
As the hard magnetic material constituting the magnet part material, an alloy-based powder (magnetic powder) mainly composed of Nd—Fe—B can be used. In addition to the Nd—Fe—B system, ferrite, SmCo5, Sm2Co17, and the like can be used. The average particle size of the magnetic powder is preferably in the range of 10 μm to 200 μm. If it exceeds 200 μm, it is not smoothly injected into the cavity of the molding die. On the other hand, if it is less than 10 μm, the surface area of the magnetic powder becomes excessive, and the magnetic performance deteriorates at high temperature use. As the resin material, a thermoplastic resin is used, and nylon 12, nylon 6, PPS, EEA, EVA, polypropylene, polyethylene, PVC, CPVC, and the like can be used, but are not limited thereto. The mixing ratio of the magnetic powder and the thermoplastic resin is preferably 40 vol% to 80 vol% in terms of the volume content of the magnetic powder. If it is lower than 40 vol%, the desired magnetic force cannot be obtained. When it exceeds 80 vol%, since the mixing ratio of the resin is low, it is difficult to flow during injection molding, and a good molded product cannot be obtained.

  In addition, in order to increase the bonding force between the magnetic powder and the thermoplastic resin material, a coupling treatment may be performed on the surface of the magnetic powder. Coupling agents used include silane-based γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, titanate-based tetraisopropyl titanate, tetraisobutyl orthotitanate, etc., aluminum-based acetoalkoxyaluminum diisopropylate, zirconium Zirconium tributoxy systemate and the like can be used, but are not limited thereto.

  In the present embodiment, projecting portions 21 projecting toward the magnet portion 3 are formed on the outer periphery of the yoke portion 2 in contact with the inner periphery of the magnet portion 3 at twelve locations at equal intervals in the circumferential direction. Then, each of the magnetized regions 31 formed in the circumferential direction on the outer periphery of the magnet unit 3 with the protruding portions 21 serving as boundary regions has 12 magnetic poles of N and S poles having opposite polarities alternately in the circumferential direction. Is formed. An example of the shape of the protrusion 21 is a semicircular shape as shown in FIG. 1, and the details thereof are shown in FIG. 3, examples of the inner diameter R1 of the yoke part 2, the outer diameter of the yoke part 2 (the inner diameter of the magnet part 3) R2, the outer diameter R3 of the magnet part 3, and the radius R4 of the protruding part 21 are 5.75 mm and 6.5, respectively. 75 mm, 8.05 mm, and 0.65 mm.

  FIG. 4 compares the surface magnetic flux density distribution (line X) of the magnet of the present invention in which such protrusions 21 are formed with the surface magnetic flux density distribution (line Y) of a conventional magnet in which the protrusions 21 are not formed. Therefore, in the magnet 1 of the present invention, the magnetic flux density distribution in each magnetic pole is sufficiently wider than that of the conventional one, and the magnetic performance is improved, and the motor torque is sufficiently increased when used in a spindle motor or the like. be able to.

(Other embodiments)
The shape of the protrusion 21 does not have to be semicircular, and may be, for example, a rectangular protrusion 22 as shown in FIG. 5 or a triangular protrusion 23 as shown in FIG. Moreover, in the said embodiment, it is good also considering the magnet part 3 as an inner peripheral side and the yoke part 2 as an outer peripheral side. Furthermore, the magnet 1 does not necessarily need to be integrally joined by two-color molding. A method of inserting a metal yoke body (part) into a mold as an insert material and injection molding the magnet part, or a metal yoke A method of fitting a separate bonded magnet to the body can be employed.

It is a front view of the yoke integrated magnet which shows one Embodiment of this invention. It is a longitudinal cross-sectional view of the yoke integrated magnet along the II-II line of FIG. It is a principal part enlarged front view of a yoke integrated magnet. It is a distribution curve of the surface magnetic flux density of a yoke integrated magnet. It is a principal part enlarged front view of the yoke integrated magnet which shows other embodiment of this invention. It is a principal part enlarged front view of the yoke integrated magnet which shows other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Yoke integral magnet, 2 ... Yoke part, 21 ... Projection part, 3 ... Magnet part, 31 ... Magnetization area | region.

Claims (4)

In a yoke-integrated magnet including a magnet part and a yoke part joined thereto, a part of the yoke part is projected toward the magnet part at a plurality of positions at intervals to form a projecting part between the projecting parts. A yoke-integrated magnet characterized in that the surface of the magnet portion located in the region is a magnetized region. The magnet part is formed into a cylindrical shape, the yoke part is joined to the inner peripheral surface or the outer peripheral surface, the protruding parts are formed at equal intervals in the circumferential direction, and the yoke part of the magnet part is joined. The yoke-integrated magnet according to claim 1, wherein magnetic poles having opposite polarities are alternately formed in the magnetized region formed on a peripheral surface that is not formed. The yoke-integrated magnet according to claim 1 or 2, wherein the protruding portion protrudes in an arc shape toward the magnet portion. The yoke part is made of a resin molded body containing a soft magnetic material, and the magnet part is made of a resin molded body containing a hard magnetic material, and the yoke part and the magnet part are joined and integrated by two-color molding. The yoke-integrated magnet according to any one of 1 to 3.

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