JP2006019322A - Magnetic circuit incorporating rare-earth permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic circuit wherein the breakage of an adhesive layer due to a difference in coefficient of thermal expansion between a magnet and a yoke can be prevented. <P>SOLUTION: The magnetic circuit has incorporated an R-Fe-B (R: element selected from rare-earth elements including Sc and Y) rare-earth permanent magnet and a yoke, and it is provided with a metallic material between the permanent magnet and the yoke. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic circuit incorporating an R—Fe—B (R represents an element selected from rare earth elements including Sc and Y) series rare earth permanent magnets.

  In recent years, powerful permanent magnets typified by Nd-Fe-B rare earth magnets have been developed and used in head drive devices for hard disk drives, which are computer components, and in MRI, which is a medical diagnostic device. The above fields of use are expanding. These are rarely used as a single permanent magnet, and are used in a form (magnetic circuit) in which the permanent magnet is incorporated in what is called a yoke.

The Nd—Fe—B rare earth permanent magnet is an intermetallic compound and is a so-called ceramic produced by a powder metallurgy method. Therefore, it becomes a hard and brittle material, and it is impossible to machine a screw hole, and the actual situation is that fixing to the yoke relies on adhesion. Therefore, in order to fix the permanent magnet, it is essential to use an adhesive, and the magnetic circuit is manufactured by being bonded to the yoke.
On the other hand, Nd-Fe-B rare earth magnets have different magnet distortion depending on the temperature. By simply attaching a yoke to the Nd-Fe-B rare earth magnet with an adhesive, the difference between the materials of the magnet and the yoke The stress is applied to the adhesive, the adhesive is destroyed, and the magnet is peeled off from the yoke.
The above problem is considered to be caused by the expansion and contraction of the Nd-Fe-B rare earth magnet depending on the magnetization direction.
The present invention intends to provide a magnetic circuit that uses the expanding and contracting rare earth magnet to prevent the breakage of the adhesive while using the rare earth magnet, the adhesive, and the yoke member that have been conventionally used.

The present invention has been found as a result of extensive studies of the above problems.
The inventors of the present invention have found that the destruction of the adhesive layer can be prevented by interposing a metal member between the yoke material to which the magnet is bonded.
Accordingly, the present invention provides a magnetic circuit incorporating an R—Fe—B (R represents an element selected from rare earth elements including Sc and Y) series rare earth permanent magnets and a yoke, Provided is a magnetic circuit including a metal material between a yoke and a yoke.

According to the present invention, even if the yoke material expands due to a temperature rise, the portion bonded to the magnet is a metal material, and the stress acting on the adhesive layer can be reduced. It becomes possible to maintain magnet peeling and dimensional stability.
According to the present invention, it is possible to manufacture a magnetic circuit that prevents adhesion failure between a magnet and a yoke.

The R—Fe—B rare earth magnet used in the present invention is usually 5 to 40% by mass of R (wherein R represents one or more elements selected from rare earth elements including Sc and Y). .), 50 to 90 mass% Fe, and 0.2 to 8 mass% B.
In order to improve the magnetic properties, preferably C, Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Sn, Hf, Ta and W Often, one or more elements selected from a group consisting of such as are added. These preferable addition amounts are 30% by mass or less in the case of Co and 8% by mass or less in the case of other elements with respect to the total mass of R, Fe and B.

The present invention is characterized in that a rare earth magnet is fixed to the yoke by interposing a metal material. The reason is that, in the case of a metal material, since the rare earth magnet is also an intermetallic compound, it is easy to obtain an adhesive that firmly adheres to both. For example, in the case of a resin material, an adhesive that firmly adheres to both a resin and a metal is rare. Further, since the metal material is easy to machine, it can be easily fixed to the yoke by performing screw hole machining or the like. Ceramic materials are often difficult to machine, and metal materials are also superior in this respect.
The metal material interposed between the rare earth magnet and the yoke material is not particularly limited as long as it is a metal that relieves stress of the adhesive, but a metal material made of a magnetic material and a nonmagnetic material may be used. Among them, an alloy called invar is preferable, but invar made of a magnetic material is preferable for the purpose of a magnetic circuit.
Specific examples of the invar include Fe—Ni, Fe—Ni—Co, Ni—Mo—Fe, Cr—Fe—Mn, and Mn—Ge. For example, an alloy composed of Fe: 64.6% by mass and Ni: 35.4% by mass, a super invar composed of Fe: 64.2% by mass, Ni: 31.0% by mass and Co: 4.8% by mass, Magnetic materials include Fe: 5.5% by mass, Cr: 94.0% by mass and Ge: 0.5% by mass, Fe: 5.0% by mass, Mn: 75.0% by mass, and Ge: An alloy composed of 20.0% by mass is exemplified.
Further, in order to prevent the stress from being applied to the adhesive, the difference in thermal expansion coefficient from the magnet is 10 × 10 ⁻⁶ or less, preferably, the magnet has a non-magnetization direction and a negative thermal expansion coefficient. It is desirable to select a metal material that is −3 × 10 ⁻⁶ or more and 8 × 10 ⁻⁶ (1 / K) or less. If a metal material with an excessively high coefficient of thermal expansion is used, the adhesive layer may be destroyed by heat, causing the magnet to peel off or causing stress strain between the yoke and the magnet, which may reduce the function as a magnetic circuit. is there.
Further, the stress is further relaxed by making the shape of the invar preferably the same as either the magnet size or the yoke size, or the size between the magnet and the yoke.

In the present invention, when the metal material is fixed to the magnet, it is preferable to use an adhesive, and the metal material portion can be fixed to the yoke by either screwing or bonding. When fixed with an adhesive, thermal stress and strain stress acting on the adhesive layer between the magnet and the metal material part and between the metal material part and the yoke can be reduced through the metal material part, and the coefficient of thermal expansion is further reduced. By taking into account, the stress can be further reduced and the peelability can be improved.
It is desirable that the thickness of the metal material portion be approximately the same as the length of the screw or the diameter of the screw for fixing to the yoke. The size of the screw diameter depends on the strength required to fix the metal material bonded to the magnet, but is preferably about 5 to 10 mm, and about 20 mm for larger ones. Further, when screwing to the yoke, the metal material is preferably subjected to processing such as screw holes in advance. When fastening with screws, the yoke and the end of the metal material are drilled and fixed.

  According to the present invention, a magnetic circuit is formed by fixing a structure in which a magnet and a metal material are bonded to a yoke. It is desirable to use an Invar alloy among metal materials in order to prevent peeling and distortion of the magnetic circuit.

The adhesive interposed between the magnet and the metal material is not particularly limited and may be any heat-resistant adhesive. Specifically, epoxy resin, silicone resin, acrylic resin, polyimide resin, polyester resin, polyamide Resins, polyvinyl alcohols and the like can be mentioned, and not only an adhesive but also a film-like adhesive film may be used.
The adhesive may be applied to either a metal material or a magnet, and if necessary, it can be heated and pressurized, semi-cured and cured, and the facing material can be bonded to produce a magnetic circuit. .

  The yoke material used in the present application is a generally used material such as iron (low carbon steel, SUS, etc.), aluminum, etc., and a material that can be easily processed, such as screwing, may be selected. The surface for the yoke material may be subjected to a surface treatment such as plating.

  The magnetic circuit of the present application is a device in which a magnet is incorporated, but applications such as magnetic circuits for magnetic head manufacturing processes, MRI, insertion light sources, and semiconductor manufacturing devices are widely used.

A dipole ring type magnetic circuit incorporating a trapezoidal segment magnet (Nd—Fe—B magnet) shaped as shown in FIG. 1 was manufactured. This is because the magnets constituting the ring have the same trapezoidal shape, but use a plurality of types of magnets 1 with different magnetization directions, and are assembled to the aluminum yoke 3 of the frame. It is a magnetic circuit that is susceptible to
As an example, a plate of a metal material to be bonded to a magnet (thermal expansion coefficient 7.8 × 10 ^{−6 in} the magnetization direction, thermal expansion coefficient −1.5 × 10 ⁻⁶ in the non-magnetization direction, trapezoidal height 50 mm) 2 using a Cr—Fe—Mn material (Fe 5.5, Cr 94.0, Mn 0.5, thermal expansion coefficient 1.0 × 10 ⁻⁶ , thickness 6 mm) was prepared. Two-part room-temperature curing epoxy adhesive is used to bond the magnet and the metal material plate, and aluminum (thermal expansion coefficient 22 × 10 ⁻⁶ ) is used for the outer yoke frame, with screw holes provided on the plate. A magnet was fixed to the yoke frame. As a comparative example, as shown in FIG. 2, the magnet 11 was directly bonded to the yoke frame 13 without using a metal plate.

In a magnet having a magnetization direction parallel to the adhesion surface including the magnetization direction, a thermal expansion coefficient of 7.8 × 10 ⁻⁶ of the magnetization direction is added to the thermal expansion coefficient of the magnet as a cosine component of an angle formed by the adhesion surface and the magnetization direction. Become. On the other hand, when the magnet has a magnetization direction perpendicular to the bonding surface, the coefficient of thermal expansion of the bonding surface of the magnet is −1.5 × 10 ^{−6 in the} non-magnetization direction. In the comparative example in which the magnet is directly bonded to the aluminum yoke, the magnet has a magnetization direction perpendicular to the bonding surface, and the magnet has a negative thermal expansion relative to the positive thermal expansion of the aluminum. Stress was generated and adhesion peeling occurred. However, in a magnetic circuit in which a metal material (Cr-Fe-Mn) is inserted between a magnet and a yoke, the thermal expansion coefficient of the metal material is almost zero, so the stress is small and the adhesion peels off. There was no problem with not occurring.

It is FIG. 1A which shows the dipole ring type | mold magnetic circuit incorporating the trapezoidal segment magnet (Nd-Fe-B type magnet), and FIG. 1B which shows the AA cross section in the said figure. It is FIG. 2A which shows the magnetic circuit which adhere | attached the magnet directly on the yoke frame, without using a metal plate, and FIG. 2B which shows the BB cross section in the said figure.

Explanation of symbols

1 Magnet 2 Plate 3 Yoke 11 Magnet 13 Yoke

Claims (3)

  R-Fe-B (R represents an element selected from rare earth elements including Sc and Y) A magnetic circuit incorporating a rare earth permanent magnet and a yoke, and a metal between the permanent magnet and the yoke A magnetic circuit comprising a material.   The magnetic circuit according to claim 1, wherein the metal material is Invar.   The magnetic circuit according to claim 1, further comprising an adhesive between the permanent magnet and the metal material.

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