JP2014049599A - CURVATURE CORRECTION METHOD OF NdFeB-BASED PLATE-LIKE MAGNET, AND MANUFACTURING METHOD OF NdFeB-BASED PLATE-LIKE MAGNET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a curvature correction method capable of correcting the out-of-plane curvature of an NdFeB-based plate-like magnet appropriately.SOLUTION: A three-point bending load is applied to an NdFeB-based plate-like magnet under a temperature range of 500-950°C, so that the maximum surface stress is within a range of 1-12 MPa. Since a load is applied in a direction for correcting curvature directly, application of an unnecessary load to the NdFeB-based plate-like magnet can be suppressed, and curvature can be corrected while preventing fracture.

Description

The present invention provides a method for correcting curvature in a plate-like NdFeB-based magnet, and a method for producing an NdFeB-based plate magnet including a step of performing the method for correcting curvature. Here, the “NdFeB magnet” is a magnet having Nd ₂ Fe ₁₄ B as a main phase, but is not limited to the one containing only Nd, Fe and B, and rare earth elements other than Nd, Co, Ni, It may contain other elements such as Cu and Al.

  NdFeB magnets have the feature that many magnetic properties such as residual magnetic flux density are much higher than conventional permanent magnets. Therefore, NdFeB magnets are used in various products such as motors for hybrid and electric vehicles, motors for electric assist type bicycles, industrial motors, voice coil motors such as hard disks, high-end speakers, headphones, and permanent magnet magnetic resonance diagnostic equipment. Is used.

  NdFeB magnets of various shapes are used according to the various applications described above. For example, rotors of large motors such as those for automobiles are often used in a state where a large number of plate-like NdFeB magnets (NdFeB magnets) are arranged. When attaching an NdFeB-based plate magnet to such a rotor, it is necessary to insert the NdFeB-based plate magnet into a predetermined slot, so that each NdFeB-based plate magnet is required to have high dimensional accuracy and shape accuracy.

  In NdFeB-based plate magnets, a major problem in dimensional accuracy and shape accuracy is the occurrence of curvature. The bending of the plate magnet includes a bending in a direction perpendicular to the plate surface (hereinafter referred to as “out-of-plane bending”) and a bending in the plate surface (in-plane bending). Among these, as the thickness of the plate-shaped magnet decreases, out-of-plane curvature becomes more prominent, and the adverse effect on attachment to a rotor or the like is great. Hereinafter, “out-of-plane bending” will be simply referred to as “curving” as appropriate. In order to avoid such a bending problem, it is possible to ensure dimensional accuracy and shape accuracy by preparing and grinding an NdFeB magnet larger than a predetermined size in advance, but the material is wasted. There is a problem of making it.

  In an NdFeB-based plate-like sintered magnet produced by a sintering method (see, for example, Patent Document 1), the non-uniformity of the packing density of the alloy powder before sintering, each part in heating during heating and subsequent cooling Due to the temperature difference (temperature rise / cooling temperature difference), etc., bending tends to occur. In particular, in the method described in Patent Document 1, the pressless method (for the purpose of improving the coercive force without reducing the residual magnetic flux density, the alloy powder filled in the cavity was oriented in a magnetic field without compression molding. Since the packing density of the alloy powder is likely to be non-uniform, bending is more likely to occur than the pressing method in which compression molding is performed. In addition, even in a NdFeB-based plate-like hot plastic working magnet manufactured by a hot plastic working method (see, for example, Patent Document 2), the temperature (temperature decrease rate) can be kept uniform during the cooling process after hot plastic working. Difficult and prone to bending.

With respect to such bending, NdFeB-based plate magnets are not targeted, but Patent Documents 3 and 4 describe methods for correcting the bending generated in long materials such as metal bars and plates. Has been.
Among these, Patent Document 3 discloses that a cemented carbide long material made of tungsten carbide is gripped at both ends with a chuck while being heated to 900 to 1450 ° C., and 500 to 5000 kgW / cm ² (49 to 490 MPa) in the longitudinal direction. It is described that a tensile load of 1 is applied. In addition, this document describes that the correction effect is further improved by applying the tensile load while applying a weight or a patch plate to the object to be corrected.
Patent Document 4 describes that a long material made of an Mn-Al magnet is corrected while being heated to 550 to 800 ° C. Specifically, when the long material is a bar material, the bar material is sandwiched between three rolls arranged so that the cross section is arranged in a triangle shape, and the length can be corrected by rotating the roller. Have been described. On the other hand, no specific correction method is described for the case of a plate material.

JP 2006-019521 A Japanese Patent Laid-Open No. 11-329810 JP-A-62-214826 JP 09-291348 A

  In the method described in Patent Document 3, since a tensile load is applied in the direction of the chord (relative to the arc of curvature) of the long material, the long material is pulled by a component force in the chord direction that does not directly contribute to correction of the curvature. If such an unnecessary load is applied to the NdFeB-based plate magnet that is more brittle than the cemented carbide, the NdFeB-based plate magnet may be broken. In addition, the method described in Patent Document 4 is intended only for a workpiece substantially made of a rod, and cannot correct the curvature of the plate magnet.

  The problem to be solved by the present invention is a method for correcting curvature that can properly correct the out-of-plane curvature of an NdFeB-based plate magnet, and a method for producing an NdFeB-based plate magnet that includes a step of performing this method of correcting curvature. Is to provide.

  In order to solve the above problems, the NdFeB-based plate magnet curving correction method according to the present invention provides an out-of-plane curvature of the NdFeB-based plate magnet, and the NdFeB-based plate magnet is within a range of 500 to 950 ° C. It is characterized by correcting by applying a three-point bending load such that the maximum surface stress is in the range of 1 to 12 MPa at a temperature of

  Unlike the method described in Patent Document 3, the NdFeB-based plate magnet bending correction method according to the present invention applies a three-point bending load to the NdFeB-based plate magnet in a direction that directly corrects the bending. Therefore, it can suppress that unnecessary load is applied to the NdFeB-based plate magnet, and the NdFeB-based plate magnet can be prevented from breaking.

  If the maximum surface stress is less than 1 MPa, the curvature can hardly be corrected. On the other hand, if the maximum surface stress exceeds 12 MPa, the NdFeB-based plate magnet may be broken. Therefore, in the method according to the present invention, the value of the maximum surface stress is set in the range of 1 to 12 MPa.

The maximum surface stress σ is the length L, width W and thickness t of the NdFeB-based plate magnet, and the load F applied to the surface of the NdFeB-based plate magnet at the middle point in the longitudinal direction and the width direction, The following formula (1)
σ = 3FL / (2wt ² )… (1)
It is represented by When applying an actual three-point bending load, this equation (1) is transformed (2)
F = 2wt ² σ / (3L)… (2)
The load F obtained by substituting the value of σ within the range of 1 to 12 MPa may be applied.

  If the temperature at which the curvature is corrected is less than 500 ° C., sufficient plasticity cannot be imparted to the NdFeB-based plate magnet, and the NdFeB-based plate magnet may be broken. On the other hand, the upper limit of the temperature is preferably higher in the range lower than the melting point in terms of imparting sufficient plasticity, but when the temperature exceeds 950 ° C, the crystal grains in the NdFeB-based plate magnet become coarse. This causes the NdFeB-based plate magnet to become brittle or to reduce the coercive force. Therefore, in the method according to the present invention, the temperature at which the NdFeB-based plate magnet is straightened is set within the range of 500 to 950 ° C. Further, in order to surely prevent the NdFeB-based plate magnet from being seized onto a member such as a weight used when the load F is applied, the upper limit of the temperature is preferably less than 900 ° C.

  The NdFeB-based plate magnet correction method according to the present invention is typically an NdFeB-based plate-like sintered magnet manufactured by a sintering method or an NdFeB-based plate-like hot manufactured by a hot plastic working method. It can be suitably used for correcting the curvature of a plastic working magnet.

  In the present invention, after the correction, it is desirable to perform an aging treatment at a temperature at which the NdFeB-based plate magnet is in a range of 450 to 550 ° C. This aging treatment can reduce crystal defects in the NdFeB-based plate magnet, particularly in the crystal grains near the grain boundary, thereby increasing the coercive force.

In the case of performing the aging treatment, after the correction, before the aging treatment, the NdFeB-based plate magnet is maintained at a temperature within a range of 750 to 850 ° C., and then subjected to aging pre-heat treatment for rapid cooling. It is desirable to do. The technical significance of this aging pre-heat treatment is as follows.
For NdFeB magnets, the reason is not clear, but when it is slowly cooled within the temperature range of 600 to 750 ° C, the coercive force decreases (therefore, the aging treatment is 450 to 550 ° C, which is lower than this temperature range). It is known that the coercive force is recovered by heating the magnet whose coercive force is lowered to 750 ° C. or more and then rapidly cooling the magnet. However, during the correction, since a load is applied to the NdFeB plate magnet, it is difficult to rapidly cool the temperature from 500 to 950 ° C. during correction to room temperature after the correction is completed. , Even within the temperature range of 600-750 ° C., it must be gradually cooled. Therefore, after the correction, that is, after this slow cooling, the adverse effect of slow cooling can be eliminated by heating to 750 to 850 ° C. and then rapidly cooling.

  Needless to say, the method of correcting the curvature of the NdFeB-based plate magnet according to the present invention can be performed as one step (curving correction step) when manufacturing the NdFeB-based plate magnet.

  According to the present invention, the out-of-plane curvature can be appropriately corrected without breaking the NdFeB-based plate magnet.

The schematic side view which shows the definition of the curvature amount in a NdFeB type plate-shaped sintered magnet. The schematic longitudinal cross-sectional view which shows the Example of the curvature correction method of the NdFeB type plate-shaped magnet which concerns on this invention. FIG. 3 is a schematic side view showing a state in which a three-point bending load is applied to the NdFeB-based plate magnet in the NdFeB-based plate magnet bending correction method according to the present invention. 6 is a graph showing a history of temperature change given to an NdFeB-based plate magnet in Example 3.

  An embodiment of a method for correcting curvature of an NdFeB-based plate magnet according to the present invention will be described with reference to FIGS. In this embodiment, an example of correcting the curvature of the NdFeB-based plate-like sintered magnet is shown.

First, a method for producing an NdFeB-based plate-like sintered magnet that is a target for correcting curvature will be described.
First, a thin piece of NdFeB alloy as a raw material was produced by strip casting. The flakes were coarsely pulverized using a hydrogen storage method and then finely pulverized using a jet mill to obtain an alloy powder of an NdFeB alloy having an average particle size of several μm. The alloy powder was filled in a rectangular parallelepiped container, and magnetically oriented by applying a magnetic field of 4.5 T (Tesla) without applying pressure for forming (shaping). After this magnetic orientation treatment, the alloy powder was heated to 990 ° C. while being filled in a container, and then rapidly cooled to room temperature to obtain a sintered body. Then, by processing this sintered body so that the length L was 55.7 mm, the width W was 14.0 mm, and the thickness t was 2.9 mm, a large number of NdFeB-based plate-like sintered magnets to be corrected were obtained. .

In each of the NdFeB-based plate-like sintered magnets 10 to be corrected, an arc-shaped curve was generated such that the center was displaced in the thickness direction rather than both ends in the longitudinal direction (see FIG. 1). Hereinafter, the magnitude δ of the displacement is referred to as “bending amount”. The amount of curvature δ is determined from the difference H _max between the highest position of the upper surface 101 and the lowest position of the lower surface 102 when the convexly curved surface is the upper surface 101 and the concavely curved surface is the lower surface 102. It is defined by a value (δ = H _max −t _avg ) obtained by subtracting the average thickness t _avg of the sintered magnet 10. The value of δ was different for each NdFeB-based plate-like sintered magnet 10 and was δ = 0.43 to 0.55 mm.

In Example 1, a plurality of experiments for straightening the NdFeB-based plate-like sintered magnet 10 were performed, and the temperature during correction was common (800 ° C.), and the maximum surface stress σ was changed. A specific method is as follows.
As shown in FIG. 2, the NdFeB-based plate-like sintered magnet 10 was placed on the table 12 in the heating furnace 11 with the convexly curved surface facing upward. A load F was applied to the NdFeB-based plate-like sintered magnet 10 by placing a weight 13 on the upper surface of the NdFeB-type plate-like sintered magnet 10 in the center in the longitudinal direction. As a result, as shown in FIG. 3, a three-point bending load is applied to the NdFeB-based plate-like sintered magnet 10 with both ends as fulcrums 151 and the center in the longitudinal direction as a force point 152. Here, the magnitude of the load F was different for each sample. In this state, the NdFeB-based plate-like sintered magnet 10 was heated to 800 ° C. in vacuum and maintained for 1 hour. Thereafter, the temperature of the NdFeB-based plate-like sintered magnet 10 was gradually cooled to room temperature. The temperature of the NdFeB-based plate-like sintered magnet 10 was measured using a thermocouple (not shown) disposed in the vicinity of the NdFeB-based plate-like sintered magnet 10.

The experimental results of Example 1 are shown in Table 1. In Table 1, instead of the load F, the weight W of the weight 13 (unit: kgW) is shown, but by multiplying this W by the gravitational acceleration g (9.8 m / s ² ), the load F (unit: N) Is required. Table 1 also shows the value of the maximum surface stress σ obtained by the equation (1). In Example 1, the experiment was performed within a range where σ was 1.4 (sample 3) to 11.1 (sample 7) MPa. For comparison, experiments were also performed when no load F was applied (σ = 0) (Sample 1), when σ was less than 1 MPa (Sample 2), and when σ exceeded 12 MPa (Sample 8). It was.

As a result of this experiment, the sample 1 which is a comparative example in which the load F is not applied is not corrected at all, and the correction effect is smaller in the sample 2 in which σ is less than 1 MPa than in this example. Moreover, in the sample 8 which is a comparative example in which σ exceeds 12 MPa, the sample was broken by an operation for correction. On the other hand, in the samples 3 to 7 of the present example, the curvature amount δ _A after the correction was as small as 19 to 65% of the curvature amount δ _B before the correction, and the effect of correcting the curvature could be confirmed. In this example, the sample did not break.

In Example 2, a plurality of experiments for correcting the curvature of the NdFeB-based plate-like sintered magnet 10 were performed, the value of the maximum surface stress σ was common (8.3 MPa, load F was 1.2 kgW), and the correction temperature was changed. The specific experimental method is the same as that in Example 1 except for the correction temperature and the value of the maximum surface stress σ. Therefore, in this experiment, after maintaining a predetermined correction temperature for 1 hour, the temperature is gradually cooled to room temperature. The experimental results are shown in Table 2.

As a result of this experiment, when the correction temperature was 450 ° C. (sample 9, comparative example), the curvature could hardly be corrected. This is considered to be due to the fact that the NdFeB-based plate-like sintered magnet 10 does not have sufficient plasticity when the temperature is 450 ° C. On the other hand, when the correction temperature is in the range of 500 to 950 ° C. (samples 10 to 15, this example), the bending amount δ _A after the correction processing is 12 to 63% of the bending amount δ _B before correction. The value was small, and the effect of correcting curvature was confirmed. In this example, the sample did not break.

  As described above, in Example 2, the inside of the heating furnace 11 is gradually cooled after maintaining a predetermined correction temperature for 1 hour during correction. During this slow cooling, the temperature of the NdFeB-based plate-like sintered magnet 10 slowly passes through the range of 600 to 750 ° C., so that the NdFeB-based plate-like sintered magnet 10 has magnetic properties, particularly coercive force. The problem of degradation occurs. Therefore, in Example 3, as shown schematically in FIG. 4, samples 9 to 15 subjected to the operation of Example 2 were subjected to two stages of heat treatment: pre-aging heat treatment and aging treatment.

  In the aging preliminary heat treatment, the NdFeB-based plate-like sintered magnet 10 is heated to 800 ° C. and maintained for 1 hour in a heating furnace 11 whose inside is evacuated, and then a normal temperature inert gas is introduced into the heating furnace 11. Rapid cooling was performed. In the aging treatment, each sample after the aging preliminary heat treatment is once brought to room temperature, and then the NdFeB-based plate-like sintered magnet 10 is heated to 520 ° C. in the heating furnace 11 whose inside is evacuated and maintained for 1 hour, Rapid cooling was performed by introducing an inert gas into the heating furnace 11. For comparison, the same two-stage heat treatment was performed on the NdFeB-based plate-like sintered magnet 10 that was not subjected to the curvature correction operation (Sample 0).

The coercive force of Samples 9 to 15 and Sample 0 was measured before the two-stage heat treatment (after the operation of Example 2 in Samples 9 to 15) and after the two-stage heat treatment, respectively. Hereinafter, the coercive force before the aging preliminary heat treatment is “H _cJ-B ”, and the coercive force after the aging treatment is “H _cJ-A ”. The measurement results of these coercive _forces H _cJ-B and H _cJ-A are shown in Table 3.

First, sample 10 (and comparative sample 9 having a correction temperature of 450 ° C.) having a correction temperature of 500 ° C. passed through a temperature range of 600 ° C. to 750 ° C. during slow cooling after heating during correction. Therefore, a high coercive force H _{cJ-B of} about _{18 kOe} is obtained even before the aging preliminary heat treatment, which is the same as that of the sample 0 not subjected to the correction treatment. For sample 11 as well, the coercive force H _cJ-B before aging pre-heat treatment was as high as 17.9 _kOe because it hardly passed the temperature range in the slow cooling after heating during correction.

On the other hand, in samples 12 to 15 having a correction temperature of 700 to 950 ° C., the coercive force H _cJ-B before the aging preliminary heat treatment is 14.2 to 16.3 kOe, which is lower than that of the sample 0 that has not been subjected to the correction treatment. ing. This is considered to be due to passing through a temperature range of 600 to 750 ° C. during slow cooling after heating during correction. In these samples 12 to 15, the aging _preheat treatment with rapid cooling from 800 ° C. and the aging treatment were performed, so that the coercive force H _cJ-A after the aging treatment was the same as that of the sample 0 not subjected to the straightening treatment 18.0. Can be increased to ~ 18.6kOe.

The present invention is not limited to the above embodiments.
For example, in the above embodiment, the method of correcting the curvature of the NdFeB-based plate-like sintered magnet has been described. However, the method according to the present invention can also be used to correct the curvature of the NdFeB-based plate-like hot plastic working magnet. The NdFeB-based plate-like hot plastic working magnet can be produced by the method described in Patent Document 2, for example.

  In the above embodiment, a three-point bending load is applied to the NdFeB-based plate-like sintered magnet 10 using the weight 13, but heat resistance during operation (within a temperature range of 500 to 950 ° C.) is ensured. If possible, a three-point bending load may be applied using a press machine or the like other than the weight 13.

  In any of the above-described embodiments, the time for maintaining the correction temperature is 1 hour, but this maintenance time is not particularly limited. Even if the maintenance time is slight (nearly zero), a certain degree of correction effect can be obtained, and if it is 1 minute or longer, it can be corrected sufficiently. In addition, the maintenance time has no particular upper limit in terms of correction of curvature, but if it is too long, there arises a problem that the coercive force is lowered or the productivity is lowered. Therefore, the maintenance time is desirably 500 minutes or less.

  Further, in Example 3 described above, the temperature maintenance time during the aging preliminary heat treatment and the aging treatment is 1 hour, but these times are not particularly limited. Even if these maintenance times are small, there is an effect to improve the coercive force to some extent, but taking into account the sufficient coercive force improvement effect and production efficiency, the maintenance time at the aging preliminary heat treatment is 30 to 120 minutes The maintenance time during the aging treatment is preferably 60 to 500 minutes.

DESCRIPTION OF SYMBOLS 10 ... NdFeB type plate (sintered) magnet 101 ... Upper surface 102 of NdFeB type plate (sintered) magnet ... Lower surface 11 of NdFeB type plate (sintered) magnet 11 ... Heating furnace 12 ... Stand 13 ... Weight 151 ... Support point 152 ... Strength

Claims (5)

  The out-of-plane curvature of the NdFeB-based plate magnet is subjected to a three-point bending load such that the maximum surface stress is within the range of 1-12 MPa at a temperature where the NdFeB-based plate magnet is in the range of 500-950 ° C. A method for correcting the curvature of a NdFeB-based plate magnet, characterized by correcting by giving.   The method of correcting curvature of an NdFeB-based plate magnet according to claim 1, wherein the NdFeB-based plate magnet is a sintered magnet.   3. The method of correcting curvature of an NdFeB-based plate magnet according to claim 1 or 2, wherein after the correction, the aging treatment is performed at a temperature at which the NdFeB-based plate magnet is in a range of 450 to 550 ° C.   The aging pre-heat treatment is performed after the correction and before the aging treatment, wherein the NdFeB-based plate magnet is held at a temperature within a range of 750 to 850 ° C and then rapidly cooled. The method for correcting curvature of the described NdFeB-based plate magnet.   A method for producing a NdFeB-based plate magnet, comprising the step of correcting the curvature of the NdFeB-based plate magnet according to claim 1.

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