JPH065642B2 - R-TM-B system radial anisotropic permanent magnet and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to rare earth / transition metal / boron (hereinafter referred to as “R-TM-
It is abbreviated as "B". ) System radial anisotropic permanent magnet and a method for manufacturing the same, and more particularly to a magnetic anisotropy permanent magnet having good circularity and circularity and good squareness Hk of demagnetization curve.

[Conventional technology]

In stepping motors, linear actuators, magnetic couplings, etc., so-called radial anisotropic cylindrical permanent magnets whose magnetization anisotropic directions are radial are often used. This is because the magnetic flux density on the surface can be made higher than that of the conventional isotropic permanent magnet. Therefore, the radial anisotropic permanent magnet is greatly demanded as one that can meet the needs of the above-mentioned electronic devices that are light, thin, short and small.

By the way, the conventional radial anisotropic permanent magnet has been manufactured by a method of molding permanent magnet powder in a magnetic field. This method is well known for rare earth cobalt magnets, and an improved method has been proposed for the R-TM-B system permanent magnet as a new material, which is based on the same principle (JP-A-61-161).
154118, JP-A-61-284907, JP-A-62-117305).

When the radial anisotropic permanent magnet is used as a rotor or a stator in the above-mentioned electronic equipment, the circularity of the inner diameter of the cylinder, the straightness of the cylinder, etc. are accompanied by the tendency of the gap size to decrease due to miniaturization. There is also a strong demand for improvement in dimensional accuracy, and under the present circumstances, roundness of 0.1 mm or less and straightness of 0.05 mm or less were required.

[Problems to be solved by the invention]

However, as far as the conventional magnetic field molding method is used, cracks are likely to occur during sintering, and it is the current situation that sintering must be performed with a low degree of orientation (JP-A-62-117305). Issue). This is because the radial orientation causes not only magnetic anisotropy but also mechanical anisotropy to cause non-uniformity in shrinkage during sintering. Therefore, in the above publication, the degree of orientation is limited to 70 to 98%. In fact, according to the additional test conducted by the present inventor, in the large-sized ring anisotropic permanent magnet, the cracking failure during sintering was severe unless the orientation degree was lowered to about 70%. In addition, the magnetic properties, particularly the squareness in the demagnetization curve, are poor, and as a result, (BH) max is not able to fully bring out the original potential of the material.

In addition, an internal grinding step is required after sintering to secure the roundness of the inner diameter of the cylinder when incorporated as a product, which is a factor of cost increase. As for the straightness of the cylinder, there was a problem of yield reduction due to warpage during sintering.

[Means for solving problems]

Therefore, the present invention provides an R-TM-B type radial anisotropic permanent magnet having an inner diameter circularity of 0.1 mm or less and a squareness Hk of 10 or less.
R-TM-B system radial anisotropic anisotropic magnet characterized by having a value of KOe or more and R-TM-B system radial anisotropically characterized by sintering in a constrained state, especially a cylinder inserted in the inner diameter Method for producing a magnetic permanent magnet.

The present inventors have found that sintering a compact in a restrained state induces the effect of improving the circularity of the inner diameter of the radial anisotropic permanent magnet and improving the squareness of the demagnetization curve. Is.

In the present invention, the circularity of the inner diameter is defined by the deformation amount of the inner diameter (the maximum value of the swing width with respect to the perfect circle). The squareness Hk is
This is a guideline for the square shape of the second quadrant (demagnetization curve) of the hysteresis curve of the permanent magnet, and is defined by the value of the magnetizing force H when the magnetic flux density B becomes 90% of the residual magnetic flux density Br.
The larger the value of Hk, the better the squareness and the larger (BH) max. In the present invention, it is not clear why the squareness Hk is improved in the R-TM-B type radial anisotropic permanent magnet sintered in a restrained state, but the tetragonal intermetallic compound Nd ₂ Fe is used.
_{In the} R-TM-B alloy consisting of ₁₄ B, unlike the case of the R-Co alloy (hexagonal system), the stress field generated by the constraint, particularly the contribution of shear stress is effective in expressing good magnetic properties. It is supposed to be. Therefore, the effect of the present invention is not limited to the constraint that the cylinder is inserted into the inner diameter surface of the cylinder.

Incidentally, the sintering used in the present invention is not only ordinary sintering in which powder metallurgical particles and bonds between particles occur, but also one in which plastic working is added in a high temperature state also referred to as firing (Japanese Patent Application Laid-Open No. S60-12065). 60
-100402 publication)). In short, it suffices that it is heated in a restrained state.

The raw material powder used in the present invention is obtained by crushing an R-TM-B-based casting alloy (see, for example, JP-A-59-46008).
However, even if it is by ultra-quenching (for example, JP-A-59-64)
No. 739), or a material obtained by super-quenching is consolidated by hot pressing or the like to cause a plastic flow and magnetic anisotropy is imparted (see Japanese Patent Laid-Open No. 60-100402). Anything is fine.

It is also possible to emphasize the stress-induced anisotropy according to the invention by adding some additional stress during sintering.

Hereinafter, the present invention will be specifically described based on Examples.

〔Example〕

(Example 1) A magnet alloy having a composition of Nd _0.9 Dy _0.1 (FebalB _0.08 Nb _0.015 ) _5.7 was prepared by arc melting, cast in a water-cooled copper mold, coarsely crushed with a stamp mill to pass 35 mesh, and then pole-milled. Were pulverized for 3 hours to obtain an average particle size of 5 μm. The powder was filled in a mold having an outer diameter of 28.5 x an inner diameter of 20.7 x a length of 25 (mm), and was molded by a lateral magnetic field of 2230 (G) (the magnetic field applying direction was perpendicular to the molding direction). A 25 ton mechanical press was used as the molding machine. Molding pressure is 0.7ton / cm ² , magnetic field strength is 10.7
It is 00 (Oe).

Here, 13 types of cylinders having a diameter (d) of 17.78 to 19.80 (mm) were inserted after molding, and as a comparative example, hollow cylinders in which no cylinders were inserted were prepared.

The obtained molded body was sintered at 1050 ° C. for 2 hours with the cylinder inserted. Sintered body at 900 ℃ for 2 hours and 600
A two-step heat treatment was performed at ℃ × 1 hour.

The inner diameter D of the sintered product without inserting the cylinder was 17.6 mm, and the relationship between the ratio d / D of the diameter of the inserted cylinder d and the magnetic characteristics of the obtained permanent magnet is shown in FIG. Here, the symbol M // indicates the magnetic characteristic in the direction parallel to the anisotropic direction, and the symbol M⊥ indicates the magnetic characteristic in the direction perpendicular to the anisotropic direction.

From Fig. 1, squareness H in the range of diameter d / D from 1.055 to 1.125
It can be seen that k becomes 10 K _Oe or more. Also, (BH) max has improved to over 17MGOe and Hk is 11.6K at d / D = 1.08.
Oe and (BH) max are 18.6MGOe and 7.8 (KOe), 16.6 (MGOe) and 1.48 times in Hk, respectively, when sintered without any conventional constraint.
An increase of 1.12 times in (H) max is a surprising effect.

Also, as shown in Table 1, the circularity of the inner diameter is 0.095 (m
m), but could be reduced to about 0.06 (mm). The number of samples is 10 for each diameter ratio, and the average value is shown.

From Table 1, when a cylinder is inserted into the inner diameter and restrained,
It can be seen that when the preferable ranges of Hk and (BH) max are set, the circularity of the inner diameter slightly deteriorates, but the circularity is still superior to that obtained by the conventional sintering method.

The orientation degree of the product obtained by the present invention is about 94%.
No cracks were found.

(Example 2) In the same manner as in Example 1, the squareness Hk value and the presence or absence of cracks when only the degree of orientation was changed were confirmed. In this case,
The diameter ratio of the inserted cylinder was selected to be 1.08. From this result, it can be seen that in the present invention, a radial anisotropic permanent magnet having good squareness (10 KOe or more) can be obtained without sufficient cracking in a state of high orientation.

[Advantages of the Invention] According to the present invention, it is possible to mass-produce radial anisotropic permanent magnets having a high magnetic energy product, which has an unexpected effect of improving squareness, and it is possible to produce a circular cylinder with a perfect inner diameter. A good product can be obtained without grinding the inner surface.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the ratio of the inserted cylinder diameter d to the cylinder inner diameter D of the radial anisotropic permanent magnet in one embodiment of the present invention, the squareness Hk to d / D, and the maximum magnetic energy product (BH) max. Is.

Claims (4)

[Claims] 1. A composition of rare earth (R), transition metal (TM), boron (B)
In a cylindrical radial anisotropic permanent magnet consisting of, the inner diameter roundness is 0.085 mm or less, and the squareness Hk is 10K.
An R-TM-B system radial anisotropic permanent magnet characterized by being Oe or more. 2. R-characterized by sintering in a restrained state
Method for manufacturing TM-B type radial anisotropic permanent magnet. 3. The R according to claim 2, wherein the restraint is performed with a cylinder inserted in the inner diameter.
A method for manufacturing a TM-B type radial anisotropic permanent magnet. 4. The R-TM according to claim 3, wherein a ratio d / D of the cylindrical diameter d and the cylindrical inner diameter D is 1.01 to 1.125. -A method for producing a B-based radial anisotropic permanent magnet.