JPH056813A - Circular magnet having characteristic distribution and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a circular magnet which has a high radial magnetic characteristic that has a magnetic anisotropy gradually increasing from the center towards an edge by making the most use of a warm-worked magnet and by improving the processing method. CONSTITUTION:An Nd13.8FebalCo7.5B6Ga1.25 alloy is manufactured by arc melting. This alloy is injected onto a single roll which rotates at the speed of 20m/sec. in an Ar atmosphere to make an unfixed form flake. Then, the obtained flake is roughly smashed into a green compact of 500mum or smaller and the green compact is compressed by hot pressing. After that, the green compact is subjected to warm plastic forming at 750 deg.C between an upper and a lower punch having a certain curvature to form a circular magnet. The radius of curvature of the lower punch is fixed, 65mm, while that of the upper punch is variable, 69, 65, or 61. The shape of the compact is so adjusted that the final expansion angle of the circular magnet may be fixed, 55 deg.C, and the maximum height of the center of the magnet may be uniform, 10mm. By this method, a circular magnet having an improved magnetic characteristic can be manufactured stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent magnet substantially composed of a rare earth element, a transition metal, and boron, and relates to an improvement of a warm-worked magnet which imparts magnetic anisotropy by warm working and has an arc shape. The present invention relates to an arc-shaped magnet whose maximum energy product in the radial direction gradually increases from the central portion to the end portion, and a manufacturing method thereof.

[0002]

2. Description of the Related Art RTB-based magnets, which are essentially composed of rare earths, transition metals, and boron, have been attracting attention because they are inexpensive and have high magnetic properties. However, this magnet is
-34242 and the sintered magnet disclosed in JP-A-60-10
It is roughly classified into the ultra-quenching magnet described in JP-A No. 0402. Regardless of which manufacturing method is used, it is necessary to mold into a desired shape, and it is difficult to intentionally control arbitrary magnetic characteristics in this molding process. For example, when trying to obtain magnetic anisotropy in a sintered magnet, a step of molding in a magnetic field is essential, and the shape is restricted by the molding direction and the orientation magnetic field direction. Although it is possible to control the magnetic characteristics in the magnet by controlling the orientation magnetic field strength, it is technically difficult and it is not a method that makes full use of the potential of this system magnet. Therefore, most arc-shaped magnets have a straight orientation. On the other hand, in the case of ultra-quenched magnets, molten metal of RTB-based alloy is solidified by the ultra-quenching method to obtain thin strips or flakes, crushed, hot-pressed, and then subjected to warm plastic working to impart magnetic anisotropy. These are permanent magnets (hereinafter referred to as "warm-worked magnets"), and the ribbons and flakes obtained by the ultra-quenching method further have innumerable fine crystal grains inside. Therefore, although the thin strip or thin piece obtained by the ultra-quenching method has an irregular shape with a thickness of about 30 μm and a side length of 500 μm or less, the crystal grains contained therein are 1 to 90 μm smaller than that of the sintered magnet. It is as fine as 0.02 to 1.0 μm, and it is possible to obtain essentially excellent magnetic characteristics close to the critical dimension of 0.3 μm of the single magnetic domain of the magnet of this system. In warm-working magnets, close correlation between plastic flow and magnetic alignment in the direction perpendicular to it is important. In other words, when producing a warm-worked magnet having a required shape, it is possible to improve the orientation by allowing plastic flow to be carried out efficiently and sufficiently over the entire workpiece, which in turn makes it possible to produce a magnet with high magnetic properties. Become.

[0003]

R by the above-mentioned rapid quenching method
In the -T-B warm working magnet, a special process of giving the magnetic anisotropy by warm working without using an orientation magnetic field is taken, and the magnetic anisotropy is parallel to the pressing direction. Therefore, it has been limited to a simple shape such as a flat plate-shaped magnet or one in which the C-axis direction is uniformly oriented by extrusion processing. However, when designing a magnetic circuit as an application using permanent magnets, for example, it is more efficient for the magnetic circuit to have a distribution in which the magnetic characteristics in the easy axis direction of the magnet alone gradually increase from the central portion to the end portion. There are many cases. Specifically, an arc-shaped magnet used in a voice coil actuator (hereinafter referred to as VCM) is used by incorporating it into a soft magnetic yoke, and at that time, the magnetic flux strength generated between the gaps is an efficient circuit. A high and uniform magnetic field is desired. However, even if a magnet having uniform magnetic characteristics is set in the yoke,
The magnetic flux distribution tends to decrease at the end of the groove, and an ideal uniform magnetic field cannot be obtained. Therefore, a measure is taken to intentionally make a notch in the center of the magnet to reduce the amount of magnetic flux and then to smooth the gap magnetic field incorporated in the yoke. or,
In the arc-shaped magnet used as the stator of the rotating machine, the magnetic characteristics in the radial direction gradually increase from the center to the end of the arc, compared with the case where a permanent magnet magnetized uniformly in the radial direction of the arc is used. It is more effective to use the one with less gogging torque. Therefore, by utilizing the characteristics of the warm-worked magnet and improving the processing method, it is possible to obtain an arc-shaped magnet that has high magnetic properties in the radial direction and that has a high degree of magnetic anisotropy from the central part to the end part. To aim.

[0004]

The present invention uses an RTB-based quenched thin piece containing a rare earth element R containing yttrium and a transition metal T as a main component and boron B as a raw material, and this raw material is warm worked. The average particle size having magnetic anisotropy is 0.
In the arc-shaped warm-worked magnet of 02 to 1.0 μm, the maximum energy product in the radial direction is high at the end portion and has a characteristic distribution that gradually decreases toward the center portion. Furthermore, the present invention uses 500
By intentionally changing the curvature of the upper and lower punches in the method of processing a warm-worked magnet, in which the upper and lower punches are subjected to plasticizing to give magnetic anisotropy after being pressed and densified at a temperature of ℃ to 900 ℃ The present invention relates to a method of manufacturing an arc-shaped magnet, characterized by performing plastic working with different working rates in the pressing direction at the end portion and the central portion of the arc-shaped magnet. According to the conventional method, the curvature of the upper and lower punches is a simple design in which the value is added to the radius of curvature of the lower punch in consideration of the thickness of the arc-shaped magnet which is the final shape. However, the pressing force applied for anisotropy is a component force in the vertical and parallel directions to the upper and lower punch surfaces, and the arc-shaped magnet with a larger divergence angle from the center of curvature has a stress acting perpendicular to the radial direction. The magnetic anisotropy increases and magnetic anisotropy is hard to be imparted. Therefore, the curvature of the upper and lower punches is slightly changed as compared with the usual design, so that a substantially strong component force in the anisotropy direction is applied at the ends of the arc-shaped magnet. That is, the die used during warm working is designed to satisfy either or both of the following conditions. For the curvature of the upper punch, Rupper ≤ Rl
ower + t (1), the curvature of the lower punch is R
It is represented by the equation (2) where lower ≧ Rdens. Ruppe here
r is the radius of curvature of the machined surface of the upper punch, Rlower is the radius of curvature of the machined surface of the lower punch, t is the thickness of the arc-shaped magnet (arbitrary constant value), and Rdens. is the radius of consolidation of the lower punch. . By changing the curvatures of the upper and lower punches based on the above design, it is possible to manufacture an arc-shaped magnet in which the degree of magnetic anisotropy is intentionally controlled. Further, in the process of performing the warm working by the above method, the working may be divided into a plurality of times in order to suppress the generation of cracks in the outer peripheral portion, and the outer circumference may be restrained at each working rate. Further, in order to suppress the bulging phenomenon that occurs during warm working, the compact may be preformed into any shape. Further, a method of slowing the plastic deformation speed to the extent that the magnetic properties such as coercive force are not deteriorated may be adopted.

[0005]

[Example] [Example 1] Nd _13.8 Fe _bal Co _7.5 B ₆ G
An alloy having a composition of a _1.25 was prepared by arc melting. This alloy was injected onto a single roll rotating at 20 m / sec in an Ar atmosphere to produce an irregular flaky flakes. The obtained flakes were coarsely pulverized to a size of 500 μm or less to obtain a green compact, which was then consolidated by hot pressing. Next, this green compact is
Warm plastic working was performed between upper and lower punches having an arbitrary curvature at 50 ° C. to obtain arc-shaped magnets. Lower punch curvature radius is R = 65
mm is constant and the radius of curvature of the upper punch is R = 69,6
There are four types, 5, 61. The final spreading angle of the arc-shaped magnet is constant at 55 °, and the maximum height of the magnet center is 1 in each case.
The shape of the compact was adjusted so that it was equal at 0 mm.
Cut the processed sample into 5 ° intervals from the end of the magnet 3.2
A mm-square sample for magnetic property evaluation was used. As a comparative material, a sintered magnet molded and sintered in a straight alignment magnetic field and a radial alignment magnetic field was similarly cut out. Radial magnetic properties of these samples were measured by VSM. The outline of the experiment is shown in FIG. 1 and the magnetic characteristic measurement result is shown in FIG. As a result, the sintered magnet due to the straight orientation magnetic field is accompanied by a marked decrease in the maximum energy product from the central portion toward the end portions. For sintered magnets with radial orientation and samples with upper punch radius of curvature R = 75 mm, the trends are similar but much improved. The magnetic properties at the end of the arc-shaped magnet increased as the radius of curvature of the upper punch decreased. [Embodiment 2] Of the arc-shaped magnets prepared in Embodiment 1, four kinds of straight-oriented and radial-oriented sintered magnets and four kinds of warm-working magnets produced with upper punch curvature radii R = 75 mm and 65 mm are yawed. The magnetic field between the gaps incorporated in the magnet was investigated. FIG. 3 shows changes in the surface magnetic flux when a simple iron yoke was manufactured, and after incorporating each magnet, the probe was moved from θ = 0 ° to 55 °. As a result, in the comparative material, the rising of the magnetic flux is slow at the end of the magnet, and the area of the uniform magnetic field is narrow. On the other hand, the radius of curvature of the upper punch R =
The 65 mm magnet had a quick rising and smoothed magnetic field distribution.

[0006]

According to the present invention, it is possible to stably manufacture an arc-shaped magnet having improved magnetic characteristics from the central portion to the end portion in the radial direction.

[Brief description of drawings]

FIG. 1 is a diagram showing an arc-shaped magnet molding apparatus according to the present invention.

FIG. 2 is a diagram showing changes in the maximum energy product in the radial direction of each arc-shaped magnet at each measurement angle.

FIG. 3 is a diagram showing a result of examining a gap magnetic flux density when an arc-shaped magnet is incorporated in a yoke.

[Explanation of symbols]

1 end 2 Central part

Claims (2)

[Claims] 1. A warm-worked magnet containing a transition metal T as a main component, a rare earth element R containing yttrium and boron B, and having an arc-shaped magnetic anisotropy with an average particle diameter of 0.02 to 1.0 μm. And the maximum energy in the radial direction −
An arc-shaped magnet having a characteristic distribution in which the product is high at the end and gradually decreases toward the center. 2. An R-T-B containing a transition metal T as a main component and a rare earth element R containing yttrium and boron B.
A raw material is an RTB-based quenched thin piece obtained by quenching and solidifying a molten alloy of a system alloy. This raw material is pressed at a temperature of 500 ° C to 900 ° C to be densified, and then subjected to plastic working by upper and lower punches. In the warm working magnet processing method that imparts magnetic anisotropy, the plastic working with different working rates in the pressing direction at the end and center of the arc-shaped magnet is performed by intentionally changing the curvature of the upper and lower punches. And a method of manufacturing an arc-shaped magnet having an arc-shaped characteristic distribution.