JPH04309207A - Manufacture of bonded magnet - Google Patents

Abstract

PURPOSE:To increase surface magnetic flux density, by combining in a cylinder type a plurality of preliminarily molded bodies made of mixture of anisotropic magnetic powder and resin, and performing compression molding and curing. CONSTITUTION:Mixture of anisotropic magnetic powder and resin, e.g. thermosetting epoxy resin is pressed into a cylindrical shape under a first pressure in the direction 4 perpendicular to the magnetic field applying direction 3. Thereafter preliminarily molded bodies 2 are formed by dividing the cylinder into a plurality of segments by planes in the radial directions. A plurality of the molded bodies 2 are combined in a cylinder shape and compression-molded in the direction indicated by arrow 7 under a second pressure higher than the first pressure. Curing process is performed, and then coating process may be performed according to demand. Thereby a cylinder radial orientated type anisotropic bonded magnet having large surface magnetic flux density, i.e., high characteristics can be manufactured.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing compression molded anisotropic bonded magnets.

0002

[Prior Art] In recent years, magnetic powder and binder resin are mixed, a molded body is produced by compression molding or injection molding, and then, as the case may be, post-processing such as hardening treatment or painting treatment is performed to produce a so-called permanent magnet. Bonded magnets have been developed and put into practical use. Compared to sintered magnets manufactured using the sintering method, these bonded magnets have a greater degree of freedom in shape as they can be manufactured into thin-walled cylindrical shapes, flat shapes, etc., and have the advantage of being almost never likely to crack. Demand has been rapidly increasing in recent years. Among these, cylindrical or disk-shaped magnets for motors are in particular demand because they take advantage of the advantages of bonded magnets. On the other hand, due to the demand for higher properties, rare earth alloys are increasingly being used as raw material magnetic powders. Furthermore, in the case of anisotropic magnetic powder, since rare earth magnetic powder generally has a high coercive force, a large orienting magnetic field is required during molding.

0003

[Problem to be solved by the invention] However, when compression molding a cylindrical radially oriented anisotropic bonded magnet used for a motor, an orienting magnetic field is applied from the inside of the cylinder to the outside of the cylinder in the radial direction of the cylinder. At that time, the magnetic flux enters the inside of the cylinder from the upper and lower surfaces (bottom surface), and
It will come out from the side of the cylinder (or vice versa)
. Therefore, as the height of the cylinder becomes higher with respect to the inner diameter of the cylinder, the area of the side surface of the cylinder becomes larger than the area of the upper and lower surfaces of the cylinder, and the magnetic flux that enters the inside of the cylinder from the upper and lower surfaces of the cylinder is The magnetic flux is dispersed on the side of the cylinder (the magnetic flux density becomes lower) and exits to the outside of the cylinder. This fact means that
This causes the problem that the orientation magnetic field cannot be increased during compression molding. As a result, since the characteristics of the magnetic powder cannot be fully utilized, a problem arises in that only bonded magnets with a low degree of orientation of the anisotropic powder, that is, with low characteristics can be produced.

Therefore, the technical problem of the present invention is that even when the orienting magnetic field cannot be made sufficiently large due to the shape of the radially oriented anisotropic bonded magnet during compression molding,
The purpose of this method is to provide a method for manufacturing compression-molded anisotropic bonded magnets with high characteristics by establishing a manufacturing process that can produce molded bodies with a high degree of orientation.

[0005]

[Means for Solving the Problems] The present inventors have discovered that even in a radially oriented anisotropic compression molded bonded magnet having a cylindrical shape and a length larger than the inner diameter of the cylinder, a high powder content is required. As a result of examining various molding methods to find a molding method with a high degree of orientation, we found that during compression molding in a magnetic field, the factor that greatly influences the degree of powder orientation is the strength of the magnetic field at low pressure (approximately 2 tons/cm2 or less). We found that the strength of the magnetic field does not significantly affect the degree of orientation after the density has increased to a certain degree, and we found that this is an advantageous method for applying an orienting magnetic field at a low pressure stage during compression molding. The present invention was achieved by combining molding methods that emphasize densification and molding at a high pressure stage. That is, according to the present invention, a mixture of anisotropic magnetic powder and resin is preformed by applying a first pressure in a direction crossing the direction of applying a magnetic field, and the cylinder is divided into a plurality of parts by a plane in the radial direction. The production of a bonded magnet is characterized by forming a preformed body having a shape, combining a plurality of the preformed bodies into a cylindrical shape, compression molding them at a second pressure higher than the first pressure, and subjecting them to a hardening treatment. method is obtained. In the present invention, the curing process refers to a process of curing a resin, and refers to curing processes such as curing of a reaction-curable resin, cooling curing after heating of a thermoplastic resin, and heat curing of a thermosetting resin. Further, in the present invention, after the curing treatment, post-treatment such as painting treatment may be performed as necessary.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. The ribbon produced by the liquid quenching method is hot-formed and then subjected to hot upsetting, and the resulting compact is crushed to have a composition of 30% Nd by weight.
, 1% Pr, 66% Fe, 3% Co, and 1% B were produced. The maximum particle size of the anisotropic magnetic powder at this time was 420 μm, and the average particle size was 165 μm. Next, this anisotropic magnetic powder and thermosetting epoxy resin are mixed, and this mixture is inserted into the hole 1a of the mold 1 as shown in FIG. 1(a). A preformed body 2 having a shape that is a part of a cylinder having an outer diameter of 22 mm, an inner diameter of 19 mm, and a height of 15 mm as shown in b) and having an angle of 44° from the central axis is placed in the radial direction of the cylinder as shown by the white arrow 3. A magnetic field of 20 kOe is applied in the direction shown in FIG.
It was produced by preforming under pressure at m 2 . Thereafter, as shown in FIG. 1(c), the eight preforms are combined into a cylindrical shape and inserted into the cylindrical hole 6a of the mold 6.
This hole 6 is parallel to the central axis of the cylinder (arrow 7).
6 tons/cm2 with punch 8 having a shape corresponding to a
The final cylindrical molded body 10 shown in FIG. 1(d) was obtained by compression molding at a pressure of . Subsequently, this molded body 10 was subjected to a thermosetting treatment, and the inner periphery of this molded body was magnetized with eight poles to form a radially oriented multipolar bonded magnet. The characteristics of the obtained multipolar bonded magnet were evaluated by measuring the surface magnetic flux density in response to the angle (center angular displacement). The evaluation results are shown in Figure 2. In addition, the characteristics of bonded magnets manufactured using conventional methods are also listed. As shown in FIG. 2, the bonded magnet produced by the anisotropic bonded magnet production method according to the embodiment of the present invention has a higher surface magnetic flux due to the higher orientation of the anisotropic powder than the conventional one. It has become possible to manufacture a cylindrical radially aligned anisotropic bonded magnet with high density, that is, high characteristics.

[0007]

[Effects of the Invention] As is clear from the above explanation, the present invention has made it possible to manufacture anisotropic bonded magnets with extremely high characteristics.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a method for manufacturing a bonded magnet according to an example of the present invention. (a) is a perspective view showing a method for manufacturing a preform according to an example of the present invention. (b) is a perspective view showing a preformed body obtained by the method of (a). (c) is a perspective view showing a method for manufacturing a compression molded body. (d) is a perspective view showing a compression molded product obtained by the method of (c).

FIG. 2 is a diagram showing the characteristics of a bonded magnet according to an embodiment of the present invention, and a conventional example is also shown for comparison.

[Explanation of symbols]

1 Mold 1a Hole 2 Preformed body 3 Orienting magnetic field application direction 4 Compression direction 5 Punch 6 Mold 6a Cylindrical hole 7 Arrow indicating compression direction 8 Punch 10 Molded object

Claims (1)

[Claims] [Claim 1] A mixture of anisotropic magnetic powder and resin,
Preforming is performed by applying pressure with a first pressure in a direction crossing the direction of applying the magnetic field to form a preformed body having a shape in which a cylinder is divided into multiple parts by a plane in the radial direction, and the preformed bodies are combined into a plurality of cylindrical shapes. A method for manufacturing a bonded magnet, characterized in that compression molding is performed at a second pressure that is higher than the first pressure, and a hardening treatment is performed.