JP2005283268A - Powder evaluation method, rare earth sintered magnet, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powder evaluation method for accurately evaluating powder to the occurrence of cracks and chips in a forming body for forming the powder. <P>SOLUTION: The powder evaluation method is used to evaluate pulverized powder. Tapping density is measured for a different number of tapping times, and the powder is evaluated on the basis of the ratio of the tapping density. When for example the tapping density if the tapping count is small is set to be tapping density A, and when the tapping density if the tapping count is large is set to be tapping density B, powder is evaluated by the tapping density A/tapping density B. The powder is rare earth alloy powder, for example, used for manufacturing a rare-earth sintered magnet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a powder evaluation method for accurately evaluating powder, and more particularly to a powder evaluation method as an evaluation index of the degree of occurrence of cracks, chips, etc. in a molded body of rare earth alloy powder. Furthermore, this invention relates to the rare earth sintered magnet which applied the said powder evaluation method, and its manufacturing method.

  Rare earth sintered magnets, for example, Nd-Fe-B based sintered magnets have advantages such as excellent magnetic properties, Nd as a main component is abundant in resources, and is relatively inexpensive. In recent years, the demand has been increasing.

  As a method for producing a rare earth sintered magnet, a powder metallurgy method is known and widely used because it can be produced at low cost. In the powder metallurgy method, first, a raw material alloy ingot is roughly pulverized and finely pulverized to obtain a rare earth alloy powder having a particle size of about several μm. The rare earth alloy powder thus obtained is magnetically oriented in a magnetic field, and press molding is performed with the magnetic field applied. After molding in a magnetic field, the compact is sintered in a vacuum or in an inert gas atmosphere and further subjected to an aging treatment.

When a rare earth sintered magnet is produced by the above-mentioned powder metallurgy method, a rare earth alloy magnet used as a final product is obtained by sintering a compact formed from a rare earth alloy powder. The selection is important for ensuring the quality of the sintered magnet. Thus, particle size, specific surface area (BET value), and the like have been studied as criteria for selecting rare earth alloy powders to be used (for example, see Patent Document 1 and Patent Document 2).
JP 2001-143950 A JP 11-251123 A

  By the way, when a rare earth sintered magnet is produced by the powder metallurgy method as described above, since the compact before sintering is a green compact, the strength is weak, and the compact tends to be cracked or chipped. And has a significant impact on yield. Such cracking and chipping of the molded body depends on the rare earth alloy powder used, and for example, the degree of occurrence of cracking or chipping in the molded body varies with each pulverization.

  Therefore, it is necessary to accurately evaluate the powder (rare earth alloy powder) to be used for the problem of cracking or chipping in the molded body of such a rare earth alloy powder. It is hard to say that a method has been established. For example, the evaluation based on the average particle diameter by the laser diffraction method or the evaluation based on the simple measurement of the specific surface area does not correlate with the occurrence of cracks and chips in the molded body, and is not suitable as an evaluation method.

  The present invention has been proposed in view of such conventional circumstances, and shows a good correlation with the occurrence of cracks and chips in a molded body obtained by molding a powder, and can accurately evaluate the powder. An object is to provide a powder evaluation method. Another object of the present invention is to establish a powder evaluation so as to suppress the occurrence of cracks and chips in a molded body and to produce a rare earth sintered magnet with a high yield.

  In order to achieve the above-mentioned object, the present inventors have made various studies over a long period of time. As a result, the tapping density was measured twice by changing the number of tappings, and by taking these ratios, the knowledge that a good correlation was obtained with respect to the degree of cracking and chipping of the molded body was obtained. . The present invention has been completed based on such findings. That is, the powder evaluation method of the present invention is a powder evaluation method for evaluating finely pulverized powder, wherein the tapping density is measured at different tapping times, and the powder is evaluated by the ratio of these tapping densities. It is characterized by.

  The use of tapping density for powder evaluation has been attempted in, for example, Japanese Patent Application Laid-Open No. 2003-332113. In the invention described in the above publication, in a composite magnetic sheet obtained by dispersing a soft magnetic powder in a rubber matrix and forming into a sheet, it is specified that a powder having a ratio of tapping density to true density within a predetermined range is used. ing. However, for example, in the case of rare earth alloy powder, it is not always possible to accurately evaluate the powder by measuring the tapping density once.

  Therefore, in the present invention, the tapping density is measured at different tapping times, and the powder is evaluated by the ratio of these tapping densities. As for the mechanism of obtaining a good correlation between the degree of cracking and chipping of the molded body by changing the tapping frequency in this way and taking the tapping density, the details are unknown, but by the measurement, The state of the powder is accurately grasped, and powder evaluation suitable as an evaluation method for cracks and chips of the molded body is realized.

  The rare earth sintered magnet of the present invention and the method for producing the same realize the improvement of the yield by applying the powder evaluation method. That is, the rare earth sintered magnet of the present invention is characterized in that a molded body formed by using the rare earth alloy powder evaluated by the powder evaluation method is sintered. In addition, the method for producing a rare earth sintered magnet of the present invention comprises forming a rare earth alloy powder and then sintering the compact to produce a rare earth sintered magnet. The rare earth alloy powder is measured and evaluated by the ratio of these tapping densities.

  According to the powder evaluation method of the present invention, it is possible to provide a powder evaluation method that shows a good correlation with the occurrence of cracking and chipping in a molded body obtained by molding a powder and can accurately evaluate the powder. Is possible. In addition, according to the present invention, by establishing powder evaluation, it is possible to suppress the occurrence of cracks and chips in the molded body and to produce rare earth sintered magnets with high yield.

  Hereinafter, the powder evaluation method to which the present invention is applied, the rare earth sintered magnet and the manufacturing method thereof will be described in detail.

  The powder evaluation method of the present invention is an evaluation method for cracks and chips when a powder is formed into a molded body. This is an evaluation method that serves as a reference for determining what kind of powder should be used in order to suppress cracking and chipping in a molded body.

  The powder evaluation method of the present invention basically uses a tapping density. The tapping density is a bulk density that is reached when the powder is filled only by the action of gravity by a tapping operation, and is measured using, for example, a container shown in FIG. This container is composed of a tapping density measuring container 1 and an auxiliary container 2 that is mounted on the tapping density measuring container 1 and expands the internal volume. At the time of measurement, as shown in FIG. 1B, with the auxiliary container 2 attached, the powder 3 exceeding the internal volume of the tapping density measuring container 1 is naturally filled and a tapping operation is performed. As the number of tapping increases, the volume gradually decreases and the density of the powder in the tapping density measuring container 1 increases. After performing the tapping operation for a predetermined number of times, as shown in FIG. 1C, the auxiliary container 2 is removed, and the powder that overflows and rises from the tapping density measuring container 1 is removed by so-called grinding, and its weight is measured. By subtracting the previously measured weight of the tapping density measuring container 1 and dividing the obtained value by the internal volume of the tapping density measuring container 1, the tapping density can be obtained.

  However, in the present invention, the powder is not evaluated by one tapping density measurement, but the tapping density is measured by different tapping times, and the powder is evaluated by the ratio of these tapping densities. Specifically, when the tapping density is measured twice with different tapping times, the tapping density when the tapping frequency is small is tapping density A, and the tapping density when the tapping frequency is large is tapping density B. The powder is evaluated by (tapping density A / tapping density B).

  The number of tappings for measuring the tapping density A and the number of tappings for measuring the tapping density B may be different from each other, but each has an optimum tapping number. In tapping, as the number of tapping increases, the tapping density gradually increases. When the number of tapping is increased to some extent, it is saturated and the tapping density does not increase so much. In the present invention, it is preferable to take a ratio between the tapping density in the region where the tapping density gradually increases and the tapping density in the saturated region. Specifically, when the density when saturated is 1, the tapping density A is set to 0.85 to 0.92, preferably 0.88 to 0.92, and the tapping density B is set. Let be the density at saturation. Note that the saturation may be confirmed by, for example, the fact that the tapping density does not change even if the difference in the number of tappings is 300 times. As an example of the number of tappings satisfying such a condition, the number of tappings at the tapping density A is 15 to 120 times, for example, 60 times, and the number of tappings at the tapping density B is 600 times or more, for example, 1200 times. Note that the optimum value of the number of times of tapping differs depending on the powder to be evaluated, and may be set as appropriate from the viewpoint of the density. Further, the tapping condition can be arbitrarily set. For example, the tapping may be 1 cm / second.

  The ratio of the tapping density as described above is measured to determine whether or not the powder is suitable for molding. At this time, for example, the correlation between the ratio of the tapping density measured in advance and the strength of the compact, or The defect occurrence rate (for example, the occurrence rate of cracks) is taken, and the suitability is determined based on this correlation data. In the determination, in addition to the ratio of the tapping density, for example, an average particle diameter (D50) measured by a laser diffraction method or the like can be used in combination to perform a more accurate determination.

  The above-mentioned powder evaluation method can be applied to the evaluation of all powders used for molding and sintering, and is particularly suitable for application to the production of rare earth sintered magnets, for example. Hereinafter, a method for producing a rare earth sintered magnet will be described.

  First, the rare earth sintered magnet to be manufactured is mainly composed of rare earth elements, transition metal elements and boron. What is necessary is just to select a magnet composition arbitrarily according to the objective.

  For example, R-T-B (R is a concept including one or more rare earth elements, where the rare earth element includes Y. T is one or two of transition metal elements essential for Fe or Fe and Co. In order to obtain a rare earth sintered magnet having excellent magnetic properties, the rare earth element R is 20 to 20 in the magnet composition after sintering. It is preferable that the composition be such that 40% by weight, boron B is 0.5 to 4.5% by weight, and the balance is the transition metal element T. Here, R is one or more selected from rare earth elements, that is, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu. Especially, since Nd is abundant in resources and relatively inexpensive, the main component is preferably Nd. Further, the inclusion of Dy is effective in improving the coercive force Hcj because it increases the anisotropic magnetic field.

  Alternatively, the additive element M can be added to form an R-T-B-M rare earth sintered magnet. In this case, examples of the additive element M include Al, Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W, V, Zr, Ti, Mo, Bi, and Ga. A seed | species or 2 or more types can be selected and added. The addition amount of these additional elements M is preferably 3% by weight or less in consideration of magnetic characteristics such as residual magnetic flux density. If the amount of additive element M added is too large, the magnetic properties may be deteriorated.

  Of course, it is needless to say that the present invention is not limited to these compositions, and can be applied to all known compositions as rare earth sintered magnets.

  Powder metallurgy is employed to produce the rare earth sintered magnet described above. The manufacturing process by the powder metallurgy manufacturing method basically includes an alloying process, a coarse pulverization process, a fine pulverization process, a magnetic field forming process, a sintering / aging process, a processing process, and a surface treatment process. The In order to prevent oxidation, most of the steps after sintering are performed in a vacuum or in an inert gas atmosphere (in a nitrogen atmosphere, an Ar atmosphere, etc.).

  In the alloying step, a raw material metal or alloy is blended in accordance with the magnet composition, melted in a vacuum or an inert gas, for example, Ar atmosphere, and cast into an alloy. As a casting method, a strip casting method (continuous casting method) in which molten high-temperature liquid metal is supplied onto a rotating roll and an alloy thin plate is continuously cast is preferable from the viewpoint of productivity and the like. It is not limited to that. As the raw material metal (alloy), pure rare earth elements, rare earth alloys, pure iron, ferroboron, and alloys thereof can be used. A solution treatment may be performed as necessary for the purpose of eliminating solidification segregation. As a condition for the solution treatment, for example, it is held in a 700 to 1500 ° C. region for 1 hour or more under vacuum or Ar atmosphere.

  A single alloy having an almost final magnet composition may be used as the alloy, or a plurality of types of alloys having different compositions may be mixed so that the final magnet composition is obtained. Mixing may be performed in any process of alloy, raw material coarse powder, and raw material fine powder.

  In the coarse pulverization step, the previously cast raw alloy thin plate, ingot, or the like is pulverized until the particle size is about several hundred μm. As the pulverizing means, a stamp mill, a jaw crusher, a brown mill, or the like can be used. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after occlusion of hydrogen.

  The coarse pulverization step can be constituted by a plurality of steps in which a plurality of pulverization means are combined. For example, the coarse pulverization step can be made into two steps, a hydrogen pulverization step and a mechanical coarse pulverization step. The hydrogen pulverization step is a step in which hydrogen is occluded in the cast raw material alloy and pulverized in a self-destructive manner utilizing the fact that the hydrogen occlusion amount varies depending on the phase. Thereby, it can grind | pulverize to the magnitude | size about particle size several mm. The mechanical coarse pulverization step is a step of pulverizing using a mechanical method such as a brown mill as described above. The raw alloy powder pulverized to a size of about several millimeters by the hydrogen pulverization step is used. Then, pulverize until the particle size is about several hundred μm. When performing the hydrogen pulverization step, the mechanical coarse pulverization step may be omitted.

  After the coarse pulverization step is completed, a pulverization aid is usually added to the coarsely pulverized raw material alloy powder. As the grinding aid, for example, a fatty acid compound or the like can be used. In particular, by using a fatty acid amide as the grinding aid, a rare earth sintered magnet having good magnetic properties can be obtained. The addition amount of the grinding aid is preferably 0.03 to 0.4% by weight. When the grinding aid is added within this range, the amount of residual carbon after sintering can be reduced, which is effective in improving the magnetic properties of the rare earth sintered magnet.

  After the coarse pulverization step, a fine pulverization step is performed. This fine pulverization step is performed using, for example, a jet mill. The conditions for fine pulverization may be appropriately set according to the airflow pulverizer to be used, and the raw material alloy powder is finely pulverized until the average particle size becomes about 1 to 10 μm, for example, 3 to 6 μm. A jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, accelerates powder particles by this high-speed gas flow, and collides powder particles with each other. Or, it is a method of crushing by generating a collision with a target or a container wall. Jet mills are generally classified into jet mills that use fluidized beds, jet mills that use vortex flow, jet mills that use impingement plates, and the like.

  After the pulverization step, the raw material alloy fine powder (rare earth alloy powder) is formed in the magnetic field in the magnetic field forming step. Specifically, the raw material alloy fine powder obtained in the fine pulverization step is filled in a mold in which an electromagnet is arranged, and is molded in a magnetic field in a state where crystal axes are oriented by applying a magnetic field. Forming in the magnetic field may be either longitudinal magnetic field shaping or transverse magnetic field shaping. The forming in the magnetic field may be performed at a pressure of about 130 to 160 MPa in a magnetic field of 800 to 1500 kA / m, for example.

  In the present invention, when forming the rare earth alloy powder in a magnetic field, the rare earth alloy powder to be used is evaluated by the above-described powder evaluation method, and its suitability is determined. That is, for the rare earth alloy powder obtained by the fine pulverization step, the tapping density is measured at different tapping times, and the ratio of these tapping densities is measured. Compare the measurement results with the correlation diagram between the tapping density and the compact strength, or the correlation diagram between the tapping density and the defect occurrence rate (the occurrence rate of cracks and cracks). If it is expected, use it as it is. If the tapping density ratio is high and cracking or chipping is expected when formed into a molded body, it can be reused by mixing it with other pulverized powder to the extent that it has little effect, or returning to the alloying process. Then, it is reused through the grinding process again.

  Next, in the sintering / aging process, sintering and aging treatment are performed. That is, after forming the raw material alloy fine powder in a magnetic field, the compact is sintered in a vacuum or an inert gas atmosphere. The sintering temperature needs to be adjusted according to various conditions such as composition, pulverization method, difference in particle size and particle size distribution, etc. For example, sintering may be performed at 1000 to 1150 ° C. for about 5 hours, and rapid cooling after sintering. Is preferred. After sintering, the obtained sintered body is preferably subjected to aging treatment. This aging treatment is an important step in controlling the coercive force Hcj of the obtained rare earth sintered magnet. For example, the aging treatment is performed in an inert gas atmosphere or in a vacuum. As the aging treatment, a two-stage aging treatment is preferable, and in the first aging treatment step, the temperature is maintained at a temperature of about 800 ° C. for 1 to 3 hours. Next, a first quenching step is provided for quenching to room temperature to 200 ° C. In the second stage aging treatment step, the temperature is maintained at about 550 ° C. for 1 to 3 hours. Next, a second quenching step for quenching to room temperature is provided. Since the coercive force Hcj is greatly increased by heat treatment at around 600 ° C., when aging treatment is performed in a single stage, it is preferable to perform aging treatment at around 600 ° C.

  After the sintering / aging step, a processing step and a surface treatment step are performed. The processing step is a step of mechanically forming into a desired shape. A surface treatment process is a process performed in order to suppress the oxidation of the obtained rare earth sintered magnet, for example, forms a plating film and a resin film on the surface of a rare earth sintered magnet.

  According to the above manufacturing process, the rare earth alloy powder (raw material alloy fine powder) used for the green body before sintering is evaluated by the powder evaluation method of the present invention, and there is little generation of cracks and chips when the green body is formed. Therefore, it is possible to minimize a decrease in yield due to cracking or chipping. Moreover, since the rare earth alloy powder determined to be defective can be determined and reused before sintering, the raw material cost can be reduced.

  Next, specific examples of the present invention will be described based on experimental results.

<Examination of tapping frequency>
First, an auxiliary container was attached to a tapping density measuring container having an internal volume of 25 cm ³ , and 100 g of pulverized rare earth alloy powder was naturally filled to a bulk density. Tapping was performed at 1 cm / sec using a product name ABD powder evaluation apparatus manufactured by Tsutsui Rikagakuki Co., Ltd., and the number of tapping was measured 5 times from 0 to 1200 times. FIG. 2 shows numerical values obtained by dividing the density at each tapping frequency by the density at 1200 tapping times. Samples A and B seem to be saturated at 1200 times because there is almost no difference in density between 900 and 1200 tapping. Further, it was recognized that the density difference between the sample A and the sample B was increased in a region where the number of tappings was small. On the other hand, FIG. 3 shows the variation R [= (maximum−minimum) / average × 100] of the measurement values (number of measurement samples n = 10). As the number of tapping increases, the measurement value variation R decreases.

<Example>
Based on the examination results, the rare earth alloy powder was evaluated as follows.
The composition of the raw material alloy is as follows: Nd 24.5 wt%, Pr 6.0 wt%, Dy 1.8 wt%, Co 0.5 wt%, Al 0.2 wt%, Cu 0.07 wt%, B 1.0 wt%, the balance Fe. The raw material metal or alloy was blended so as to have the above composition, and the raw material alloy thin plate was melted and cast by a strip casting method.

  The obtained raw material alloy thin plate is hydrogen pulverized and then mechanically coarsely pulverized by a brown mill to obtain raw material alloy coarse powder. Fatty acid amide 0.1% by weight was added to the raw material alloy coarse powder as a grinding aid. Next, the mixture was finely pulverized in a high-pressure nitrogen gas atmosphere using an airflow pulverizer (jet mill) to obtain an average particle diameter D50 = 4.1 μm to obtain a rare earth alloy powder.

  Eighteen lots of rare earth alloy powder samples obtained for each pulverization step were extracted and the tapping density was measured. The method for measuring the tapping density is as follows.

First, an auxiliary container was attached to a tapping density measuring container having an internal volume of 25 cm ³ , and 100 g of pulverized rare earth alloy powder was naturally filled to a bulk density. Tapping was performed at 1 cm / sec using an ABD powder evaluation apparatus manufactured by Tsutsui Riken Kikai Co., Ltd. The tapping density A was measured at 60 tapping times, and the tapping density B was measured at 1200 tapping times. In calculating the tapping density, the auxiliary container was removed, the obtained powder layer was ground into the container, and the weight was determined. The respective tapping densities (tapping densities A and B) were calculated by subtracting the weight of the container measured in advance and dividing by the volume of the tapping density measuring container.

  A tapping density ratio P (= tapping density A / tapping density B) was calculated and evaluated. The evaluation items are the strength of the compact and the occurrence rate of cracks.

Measurement of molded body strength Each of the obtained powders was molded in a magnetic field to obtain a molded body having a predetermined shape. In molding in a magnetic field, the powder was molded at a molding pressure of 147 MPa in a magnetic field of 1200 kA / m. The magnetic field direction is a direction perpendicular to the pressing direction.

  The molded body strength was measured in accordance with Japanese Industrial Standard JIS R 1601. That is, as shown in FIG. 4, the molded body 11 is placed on the two round bar-shaped supports 12, 13, and the round bar-shaped support 14 is arranged at the center position on the molded body 11. A load was applied. The chip size of the molded body 11 was 20 mm × 18 mm × 6 mm. The direction in which the bending pressure is applied is the pressing direction.

Measurement of occurrence rate of cracks and chips Each of the obtained powders was molded in a magnetic field to obtain a molded body having a predetermined shape. In molding in a magnetic field, the powder was molded at a molding pressure of 147 MPa in a magnetic field of 1200 kA / m. The magnetic field direction is a direction perpendicular to the pressing direction. The shape of the molded body was 70 mm × 40 mm × 5 mm. After the obtained molded body was sintered at 1030 ° C. for 4 hours, the appearance was checked visually for the presence or absence of cracks, and the occurrence rate of cracks was determined (number of samples n = 100).

  FIG. 5 shows the relationship between the ratio P of the tapping density and the strength of the compact (marked with ● in the figure). A good correlation was found between the tapping density ratio P and the strength of the compact. FIG. 6 shows the relationship between the tapping density ratio P and the crack chip rate. Specific data is shown in Table 1. The ratio P of the tapping density showed a good correlation with the occurrence rate of cracks and chips.

  Next, the same evaluation was performed by changing the number of tapping. Specifically, the tapping density A was measured at 300 tapping times, and the tapping density B was measured at 1200 tapping times. Thereafter, a sample similar to the example was prepared, and the strength of the compact and the occurrence rate of cracks were determined.

  FIG. 5 shows the relationship between the tapping density ratio P and the strength of the molded body in this case (□ in the figure). Similarly, FIG. 6 shows the relationship between the tapping density ratio P and the cracking occurrence rate (□ in the figure). When the ratio P between the tapping density at 300 times and the tapping density at 1200 times was taken, it was found that the variation was large and that there was no good correlation between the strength of the compact and the occurrence rate of cracks.

<Comparative Example 1>
The tapping density was measured as in the previous example. However, the measured tapping density is only once 1200 times. The measuring method of the tapping density was the same as in the previous example. First, an auxiliary container was attached to a tapping density measuring container having an internal volume of 25 cm ³ , and 100 g of the pulverized rare earth alloy powder was naturally filled to a bulk density. Tapping was performed at 1 cm / second using an ABD powder evaluation apparatus manufactured by Tsutsui Corporation. The tapping density at 1200 times of tapping was measured. In calculating the tapping density, the auxiliary container was removed, the obtained powder layer was ground into the container, and the weight was determined. The tapping density was calculated by subtracting the previously measured container weight and dividing by the volume of the tapping density measuring container.

  Thereafter, a sample similar to the example was prepared, and the strength of the molded body and the occurrence rate of cracks and chips were determined. FIG. 7 shows the relationship between the tapping density and the compact strength, and FIG. 8 shows the relationship between the tapping density and the occurrence rate of cracks. Specific data is shown in Table 1. In the measurement of the tapping density only once, there is no good correlation between the strength of the compact and the occurrence rate of cracks.

<Comparative example 2>
Furthermore, in this comparative example, the bulk density was calculated. The bulk density was obtained by naturally filling a rare earth alloy powder sieved in a container having an internal volume of 25 cm ³ , grinding the powder layer, and determining its weight. The bulk density was calculated by subtracting the previously measured weight of the container and dividing by the volume of the container.

  A density ratio P (= bulk density / tapping density) was calculated and evaluated. Thereafter, a sample similar to the example was prepared, and the strength of the molded body and the occurrence rate of cracks and chips were determined. FIG. 5 shows the relationship between the bulk density / tapping density ratio P and the strength of the molded body (Δ mark in the figure). FIG. 6 shows the relationship between the tapping density ratio P and the cracking occurrence rate (Δ in the figure). In the ratio P between the bulk density and the tapping density, the variation is large, and a good correlation is not found between the strength of the molded body and the occurrence rate of cracks.

  As is clear from the results of the above examples and comparative examples, the defect occurrence rate can be determined by measuring the tapping density at different tapping times and measuring the ratio of these tapping densities. Therefore, the defect occurrence rate can be determined before the firing step, and the rare earth permanent magnet can be manufactured with a high yield.

It is a figure explaining the measurement of a tapping density, (a) is a schematic perspective view which shows the state which attached the auxiliary container to the tapping density measurement container, (b) is a schematic sectional drawing which shows the filling state of powder, (c) FIG. 3 is a schematic cross-sectional view showing a state of powder cutting. Indicates the value obtained by dividing the density at each tapping frequency by the density at 1200 tapping times. It is a figure which shows the dispersion | variation R of the measured value in each tapping frequency. It is a schematic perspective view explaining the measuring method of bending strength. It is a figure which shows the ratio of the tapping density of rare earth alloy powder, and the relationship between the ratio of a bulk density and a tapping density, and a molded object strength. It is a figure which shows the ratio of the tapping density of rare earth alloy powder, and the relationship between the ratio of the bulk density and the tapping density and the occurrence rate of cracks. It is a figure which shows the relationship between a tapping density and a molded object intensity | strength at the time of measuring a tapping density only about the frequency | count of one tapping. It is a figure which shows the relationship between a tapping density at the time of measuring a tapping density only about the frequency | count of one tapping, and a cracking chip generation rate.

Explanation of symbols

1 Tapping density measuring container, 2 auxiliary container, 3 powder

Claims (13)

  A powder evaluation method for evaluating finely pulverized powder, wherein a tapping density is measured at different tapping times, and the powder is evaluated by a ratio of these tapping densities.   The powder is evaluated by tapping density A / tapping density B, where tapping density A when the tapping frequency is small is tapping density A and tapping density when the tapping frequency is large is tapping density B. The powder evaluation method according to 1.   3. The powder evaluation method according to claim 2, wherein the number of times of tapping is determined so that the tapping density A / tapping density B is 0.82 to 0.92.   4. The powder evaluation method according to claim 3, wherein the tapping frequency at the tapping density A is 15 to 120 times, and the tapping frequency at the tapping density B is 600 times or more.   The powder evaluation method according to claim 3 or 4, wherein the tapping frequency is a tapping frequency in tapping at 1 cm / sec.   The powder evaluation method according to claim 1, wherein the powder is a rare earth alloy powder.   The rare earth alloy powder is R (R is one or more of rare earth elements, where the rare earth element is a concept including Y), T (T is one or two essential elements of Fe, Fe, Co). The powder evaluation method according to claim 6, which comprises at least one kind of transition metal element) and B.   The powder evaluation method according to claim 6 or 7, wherein the rare earth alloy powder is used for a rare earth sintered magnet.   A correlation between the ratio of the tapping density and the strength of the molded article to be molded, or a correlation with the defect occurrence rate is obtained in advance, and the powder is evaluated based on the measured correlation of the tapping density. The powder evaluation method according to any one of claims 1 to 8.   A rare earth sintered magnet obtained by sintering a compact formed by using the rare earth alloy powder evaluated by the powder evaluation method according to any one of claims 2 to 9. After forming the rare earth alloy powder, the molded body is sintered and a rare earth sintered magnet is produced.
A method for producing a rare earth sintered magnet, comprising measuring the tapping density of the rare earth alloy powder at different tapping times and evaluating the rare earth alloy powder based on a ratio of the tapping densities.   The rare earth alloy powder is R (R is one or more of rare earth elements, where the rare earth element is a concept including Y), T (T is one or two essential elements of Fe, Fe, Co). 12. The method for producing a rare earth sintered magnet according to claim 11, comprising at least one kind of transition metal element) and B.   13. The method for producing a rare earth sintered magnet according to claim 11 or 12, comprising a coarse pulverization step for coarsely pulverizing the raw material alloy and a fine pulverization step for finely pulverizing, and evaluating the rare earth alloy powder after the fine pulverization step. Method.

Images