JPH09330841A - Manufacture of surface-multipolar anisotropic ring magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a surface-multipolar anisotropic ring magnet having high circularity. SOLUTION: In a method for manufacturing a surface-multipolar ring magnet, the magnet is manufactured by sintering a molded product after the product is obtained in a magnetic field by providing six or more magnetic poles on the outer periphery of a molding space 2 of a molding die. The cross-sectional shape of the outer peripheral surface of the space 2 is formed in a polygon having vortexes at the positions corresponding to the magnetic poles. This method is specially effective to the manufacture of a surface-multipolar anisotropic ring magnet meeting an inequality, (D2 -D1 )/2<(πD2 /2P), where D1 , D2 , and P respectively represent the inside diameter, outside diameter, and number of magnetic poles of the magnet.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a surface multipolar anisotropic ring magnet by a sintering method.

[0002]

2. Description of the Related Art A rotor for a stepping motor or the like is provided with multipole anisotropy on its outer peripheral surface during molding and, after sintering, has a multipole surface magnetized to correspond to this anisotropy. A polar anisotropic ring magnet is used. In a surface multi-pole anisotropic ring magnet, magnet particles with magnetic anisotropy are arranged so as to connect adjacent magnetic poles on the outer peripheral surface in an arc shape. Compared with anisotropic ring magnets, it is advantageous in terms of magnetic properties and magnetization.

However, for example, in Nd-Fe-B type magnets, the shrinkage ratio at the time of sintering is greatly different between the direction of the easy axis of magnetization and the direction orthogonal thereto. When the shrinkage has a large anisotropy, a relatively large unevenness is generated on the outer peripheral surface of the magnet when the molded body having the surface multipolar anisotropy is sintered. When it is applied to a rotor of a motor, it is required that the circularity is good, and therefore it is necessary to grind the outer peripheral surface of the magnet. Therefore, the cost becomes high.
In addition, the irregularities on the outer peripheral surface of the magnet increase the impact during grinding, which is a major factor in causing cracks and internal cracks.

In the surface multi-pole anisotropic ring magnet, the magnetic flux connecting the adjacent magnetic poles is concentrated from the outer peripheral surface of the magnet to a certain depth. For example, Japanese Patent Laid-Open No. 64-27208 describes that when the radial thickness of the magnet is half the distance between adjacent magnetic poles, the surface magnetic flux density of the magnet is 98% or more of the maximum value. There is. When applied to a rotor, the lighter the ring-shaped magnet, the more preferable. Therefore, it is desired to reduce the radial thickness as much as possible within a range that does not impair the magnetic characteristics. However, if the radial thickness is reduced, cracks are likely to occur during the above-described outer peripheral surface grinding process, leading to a reduction in yield.

Incidentally, such a problem is caused by Nd-Fe-B.
Not only the system magnets but also ferrite sintered magnets having a large anisotropy of shrinkage.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface multipole anisotropic ring-shaped magnet having a high roundness at a low cost.

[0007]

This and other objects are achieved by any one of the following constitutions (1) and (2). (1) A method for producing a surface multipolar anisotropic ring magnet by forming 6 or more magnetic poles around the outer periphery of a molding space of a molding die, performing molding in a magnetic field, and then sintering. A method for producing a surface multi-pole anisotropic ring magnet, wherein the cross-sectional shape of the outer peripheral surface is a polygon whose apex is the position corresponding to the magnetic pole. (2) When the inner diameter is D ₁ , the outer diameter is D ₂ , and the number of magnetic poles is P, a surface multipolar anisotropic ring satisfying the formula I (D ₂ −D ₁ ) / 2 <(πD ₂ / 2P) The method for producing a surface multipolar anisotropic ring magnet according to (1) above, which is for producing a magnet.

[0008]

In the present invention, the cross-sectional shape of the outer peripheral surface of the molding space of the molding die is a polygon whose apex is at the position corresponding to the magnetic pole, as shown in FIG. The molded body obtained by using such a mold, depending on the shape of the molding space,
The outer peripheral surface has a polygonal shape. When this molded body is sintered, the shrinkage rate in the radial direction becomes large near the apex of the polygon and becomes small near the center of the side of the polygon. As a result, after sintering, the shape of the magnet is almost a perfect circle, and it is not necessary to perform the grinding process, or even if the grinding process is required, only a small polishing allowance is required. Therefore, it is possible to reduce the manufacturing cost, and it is possible to prevent the occurrence of cracks during grinding, which is a problem when the radial thickness is small, and it is possible to reduce the cost by improving the yield.

In the polygonal shaped body, magnetic flux concentrates at the apex. This is because the sleeve 4 is made of a non-magnetic material and the sleeve thickness is smallest at the apex. Since the magnetic flux is concentrated in this way, compared to the conventional ring-shaped molded body, it is possible to achieve an oriented state in which the peak value of the surface magnetic flux density of the ring magnet is high even if the orientation magnetic field strength is the same.

Further, in the surface multi-pole anisotropic ring magnet having a small radial thickness, since the magnet powder is oriented in an arc shape over the entire radial direction, cracking due to anisotropy of shrinkage occurs during sintering. It's easy to do. Conventionally, this crack was more likely to occur as the orientation magnetic field strength increased. However, in the polygonal shaped body, since the magnetic flux concentrates at the apex as described above, a sufficiently high surface magnetic flux density (peak value) can be obtained even when the orientation magnetic field strength is lowered to prevent cracking. For this reason,
There are few cracks during sintering and the yield is improved. On the contrary, if the yield is equal to that of the conventional one, the strength of the orientation magnetic field can be increased, so that a higher surface magnetic flux density (peak value) can be obtained.

The sixth method of Japanese Patent Laid-Open No. 2-139907
In the figure, a mold in which the outer peripheral surface of the molding space is shaped like a petal is described in consideration of the reduction ratio in advance. However, as described in the same publication, it is difficult to manufacture such a mold having an irregular shape, so that the cost becomes high. Further, since the punch of the molding apparatus needs to have the same outer peripheral shape, the cost is significantly increased. Moreover, the more complicated the shape, the lower the precision of the mold, so that the powder is likely to cause galling during molding.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a specific configuration of the present invention will be described in detail.

In the present invention, magnet powder is molded in a magnetic field using a dry molding method or a wet molding method and then sintered to produce a surface multipolar anisotropic ring magnet.

<Magnet Powder> The composition of the magnet powder used in the present invention is not particularly limited, and various materials such as rare earth magnet powder and oxide magnet powder can be used. The present invention exerts a remarkable effect when magnet powders that are largely different in the easy axis direction and the direction orthogonal thereto are used.

As such rare earth magnet powder, R-
TB (R is at least one rare earth element including Y, T
Is Fe, or Fe and Co) based magnet powder.

In the R-T-B type magnet powder, R is usually 2
7-38 wt%, T 51-72 wt%, B 0.5-
It is preferable to contain 4.5% by weight. If the R content is too low, a phase rich in iron precipitates and high coercive force cannot be obtained, and if the R content is too high, high residual magnetic flux density cannot be obtained. If the B content is too small, a high coercive force cannot be obtained, and if the B content is too large, a high residual magnetic flux density cannot be obtained. The amount of Co in T is preferably 30% by weight or less. Further, in order to improve the coercive force, Al,
Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W,
Elements such as V, Zr, Ti and Mo may be added,
If the added amount exceeds 6% by weight, the residual magnetic flux density will decrease.

In addition to these elements, the magnet powder may contain unavoidable impurities or trace additives such as carbon and oxygen.

The magnet powder having such a composition has a main phase having a substantially tetragonal crystal structure. It usually contains a non-magnetic phase in a volume ratio of about 0.5 to 10%.

The method for producing the magnet powder is not particularly limited, but it is usually produced by casting a mother alloy ingot and crushing it, or by crushing the alloy powder obtained by the reduction diffusion method. The average particle size of the magnet powder is usually 1 to
It is about 10 μm.

Examples of the oxide magnet powder include magnetoplumbite type magnet powder such as Sr ferrite and Ba ferrite.

<Molding Step> In the molding step, either a dry molding method or a wet molding method may be used. Normally, the dry molding method is used for rare earth magnet powder.

FIG. 1 shows a cross-sectional view of a structural example of a molding die used in the present invention. FIG. 1 is a cross-sectional view of the ring-shaped molding space 2 taken along a plane including the radial direction. The mold shown in the drawing has a mold frame 3 whose inner peripheral surface has a circular cross-sectional shape,
The sleeve 4 is embedded, and the sectional shape of the inner peripheral surface of the sleeve 4 is polygonal (regular dodecagon in the illustrated example). The mold 3 is made of a magnetic material, and the sleeve 4 is made of a non-magnetic material. A cylindrical core rod 5 is provided inside the sleeve 4, the inner peripheral surface of the sleeve 4 constitutes the outer peripheral surface of the molding space 2, and the outer peripheral surface of the core rod 5 constitutes the inner peripheral surface of the molding space 2. There is.

A groove 31 is provided in the mold 3, and between two adjacent grooves, there is a polygonal vertex forming the inner peripheral surface of the sleeve. The coil 6 is provided in the groove 31, and by these coils, an arc-shaped magnetic flux exists in the molding space, with the vicinity of the apex of the polygon serving as a magnetic pole.

The number of magnetic poles, that is, the number of angles of the polygon is 6.
Or more, preferably 8 or more. If the number of magnetic poles is too small, the outer peripheral surface of the magnet remains polygonal even if anisotropic contraction occurs due to sintering, and the effect of the present invention cannot be realized.

The materials of the mold, sleeve, core rod, etc. are
It may be the same as the conventional one and is not particularly limited.

When the rare earth magnet powder is molded by the dry molding method, the molding conditions are preferably as follows.

In applying the magnetic field, the pulse magnetic field is applied to the green compact at least twice when the relative density of the green compact of the magnet powder is within the range of 25 to 55%, preferably 30 to 45%. It is preferable to have a configuration. In this specification, the relative density is a percentage of a value obtained by dividing the measured density by the theoretical density. The measured density is calculated from the weight of the magnet powder filled in the molding space of the molding device and the internal volume of the molding space. The strength of the pulsed magnetic field is preferably 0.5 kOe or more,
More preferably, it should be 1 kOe or more, and the strength of all pulsed magnetic fields should be within this range. If the intensity of the pulse magnetic field is less than the above range, the orientation of the magnet powder tends to be insufficient. Although there is no particular upper limit to the strength of the pulsed magnetic field, it is usually set to 25 kOe or less because the size of the magnetic field generator becomes large, and even if the strength exceeds 25 kOe, the degree of orientation is hardly improved.

The duration of the pulsed magnetic field is typically 10 μs
It is preferably about 0.5 sec. If the duration is less than the above range, the orientation tends to be insufficient, and if it exceeds the above range, the heat generation of the magnetic field applying coil tends to be too large. In this specification, the duration is the time from the start to the end of the magnetic field application. The interval for applying the pulse magnetic field is not particularly limited.

Further, the pulse magnetic field may be applied at least twice while increasing the density of the green compact, or the pulse magnetic field may be applied at least twice while keeping the density of the green compact substantially constant. . The molding pressure may be constant from the start to the end of compacting, may be gradually increased or decreased, and may be irregularly changed. The molding pressure is not particularly limited, but if the molding pressure is too low, the strength of the molded body will be insufficient and handling problems will occur, so it is usually preferable to set it to about 0.5 to ³ ton / cm ² .

The magnetic field may be applied even when the relative density of the green compact is outside the above range. That is, a pulse magnetic field, a steady magnetic field, an intermittent magnetic field, etc. may be applied before and / or after applying the pulse magnetic field in the density range.

Further, even if the pulse magnetic field is applied at least once before the pressurization, the characteristics of about 90% or more of those obtained when the pulse magnetic field is applied at least twice during the pressurization can be obtained. However, it is most preferable to combine the two, that is, to apply the pulse magnetic field at least once before the pressurization and to apply the pulse magnetic field at least twice during the pressurization.

The final relative density of the green compact, that is, the relative density of the molded body is usually about 50 to 60%.

<Sintering Step> The ring-shaped molded product having the polygonal outer peripheral surface obtained as described above is sintered and magnetized.

There are no particular restrictions on various conditions during sintering, but in the case of a rare earth magnet, for example, 0.5 at 1000 to 1200 ° C.
It is preferable to sinter for about 12 hours, particularly for about 1 to 5 hours, and then quench. In this case, the sintering atmosphere is preferably vacuum or a non-oxidizing gas atmosphere such as Ar gas.

The present invention is particularly suitable for manufacturing a ring magnet having a small radial thickness as described above. Such a ring magnet has an inner diameter of D ₁ , an outer diameter of D ₂ , and a magnetic pole number of P.
Then, the formula I (D ₂ −D ₁ ) / 2 <(πD ₂ / 2P) is satisfied, and in particular, the formula II (D ₂ −D ₁ ) /2≦0.9 (πD ₂ / 2P) ) Is satisfied. In such a ring magnet, since the magnetic powder is magnetically oriented over the entire radial direction,
Although cracks are likely to occur due to anisotropic shrinkage during sintering, the present invention can suppress the occurrence of cracks. Further, a magnet having a small radial thickness is likely to be cracked during grinding for smoothing the outer peripheral surface, but in the present invention, grinding is unnecessary, or a slight polishing allowance is required. Since there is no impact during grinding due to grinding, such cracks are less likely to occur.

[0036]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

<Example 1> The composition is 30 Nd-3Dy-1.
B-bal. Fe (wt%) alloy ingot,
It was made by casting. The alloy ingot was roughly crushed to-# 32 with a jaw crusher and a brown mill, and then finely crushed with a jet mill to obtain a magnetic powder having an average particle diameter of 4 µm.

This magnet powder was put into a molding die having the shape shown in FIG. 1 to perform dry magnetic field molding. The core rod of the mold had a diameter of 18.8 mm, the inner peripheral surface of the sleeve had a regular dodecagonal cross section, and the distance between the opposite apexes of the inner peripheral surface of the sleeve was 25 mm. The magnetic field was applied four times while the density of the green compact of the magnet powder was 25 to 55% of the true density. The molding pressure was 1.5 t / cm ² . The obtained molded body was sintered in vacuum at 1100 ° C. for 2 hours, then rapidly cooled, and then A
Aging treatment was performed at 600 ° C. for 1 hour in an atmosphere of r.
With this ring magnet, there is almost no cracking during sintering,
The yield in the sintering process was 99%.

The obtained magnet has an average outer diameter of 20 mm and an inner diameter of 1
It was a ring shape of 5 mm, and the difference between the maximum outer diameter and the minimum outer diameter was 0.1 mm. The maximum outer peripheral surface of this magnet is 0.2
mm was ground and smoothed to obtain the final product. The yield in grinding (no cracking or chipping) was 98%. It should be noted that the total number of production is 1000. When the surface magnetic flux density of the product was measured, the peak value at the magnetic pole was 62.
It was 00 G, and the half width of the peak was 19 °.

<Comparative Example 1-1> With the shape shown in FIG. 2 (the inner peripheral surface of the sleeve 4 has a circular cross section), the outer diameter of the molding space is 25.
A ring magnet was produced in the same manner as in Example 1 except that a molding die having a diameter of 1 mm and an inner diameter of 18.8 mm was used, and the current passed through the coil when a magnetic field was applied was 1.8 times that of Example 1. . With this ring magnet, cracking occurred during sintering, and the yield in the sintering process was 89%. This ring magnet had concave portions near the magnetic poles on the outer peripheral surface and convex portions between the magnetic poles, and the difference between the maximum outer diameter and the minimum outer diameter was 0.5 mm. The outer peripheral surface of this magnet was ground and smoothed so as to have the same diameter as in Example 1 to obtain a final product. Yield in grinding is 75
%Met. When the surface magnetic flux density of the product was measured, the peak value at the magnetic pole was 6000 G and the half width of the peak was 21 °.

<Comparative Example 1-2> A ring magnet was produced in the same manner as in Comparative Example 1 except that the current passed through the coil when a magnetic field was applied was the same as that in Example 1. As a result, cracking occurred during sintering. The yield in the sintering process was 98%. This ring magnet has concave portions near the magnetic poles on the outer peripheral surface and convex portions between the magnetic poles, and the difference between the maximum and minimum outer diameters is 0.
4 mm. The outer peripheral surface of this magnet was ground and smoothed so as to have the same diameter as in Example 1 to obtain a final product. The yield in grinding was 80%. When the surface magnetic flux density of the product was measured, the peak value at the magnetic pole was 5300 G and the half width of the peak was 21 °.

<Embodiment 2> A molding die in which the inner peripheral surface of the sleeve has a decagonal cross section, the distance between the opposite vertices of the inner peripheral surface of the sleeve is 17.5 mm, and the diameter of the core rod is 12.5 mm. Was used to produce a surface 10-pole anisotropic ring magnet. The manufacturing conditions other than the molding die were the same as in Example 1.

The obtained ring magnet showed almost no cracks during sintering, and the yield in the sintering process was 99%. This ring magnet has an average outer diameter of 14 mm and an inner diameter of 10
mm, the difference between the maximum and minimum outside diameter is 0.08
It was mm. The outer peripheral surface of this magnet was ground to a maximum of 0.2 mm and smoothed to obtain the final product. Yield in grinding is 9
8%. When the surface magnetic flux density of the product was measured,
The peak value at the magnetic pole was 5600 G, and the full width at half maximum of the peak was 23 °.

<Comparative Example 2> The same procedure as in Example 2 was carried out except that a molding die having an inner peripheral surface of a sleeve having a circular cross section was used, and the current passed through the coil when a magnetic field was applied was 1.5 times. A surface 10-pole anisotropic ring magnet was produced. The inner diameter of the sleeve was 17.5 mm. With this ring magnet, cracking occurred during sintering, and the yield in the sintering process was 93%. This ring magnet had a concave portion near the magnetic poles on the outer peripheral surface and a convex portion between the magnetic poles, and the difference between the maximum outer diameter and the minimum outer diameter was 0.4 mm. The outer peripheral surface of this magnet is used in the second embodiment.
The finished product was ground and smoothed so as to have the same diameter as. The yield in grinding was 78%. When the surface magnetic flux density of the product was measured, the peak value at the magnetic pole was 52.
It was 00 G, and the half width of the peak was 25 °.

From the above results, the effect of the present invention is clear. That is, in Examples 1 and 2, the peak value of the surface magnetic flux density is high, and the yield is extremely high. On the other hand, in Comparative Example 1-2 using the conventional mold, the peak value of the surface magnetic flux density is extremely low and the yield is also low. Further, in Comparative Examples 1-1 and 2 in which the orientation magnetic field strength was higher than those in Examples, the yield was remarkably low, and the peak value of the surface magnetic flux density was lower than those in Examples 1 and 2.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a configuration example of a molding die used in the present invention.

FIG. 2 is a cross-sectional view of a configuration example of a conventional molding die.

[Explanation of symbols]

 2 Molding space 3 Formwork 31 Groove 4 Sleeve 5 Core rod 6 Coil

Claims (2)

[Claims] 1. A method for producing a surface multipolar anisotropic ring magnet, which comprises forming 6 or more magnetic poles around the outer periphery of a molding space of a molding die, performing molding in a magnetic field, and then sintering. A method for producing a surface multi-pole anisotropic ring magnet, wherein the cross-sectional shape of the outer peripheral surface of the molding space is a polygon whose apex is a position corresponding to the magnetic pole. _2. A surface multipolar anisotropic that satisfies the formula I (D ₂ −D ₁ ) / 2 <(πD ₂ / 2P), where D _{1 is} the inner diameter, D _{2 is} the outer diameter, and P is the number of magnetic poles. A method for producing a surface multi-pole anisotropic ring magnet according to claim 1, which produces a flexible ring magnet.