JP2006265643A - Sintered magnet containing rare-earth metal and manufacturing method therefore - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a sintered magnet containing a rare-earth metal having excellent magnetic properties while improving the accuracy of the dimension of a formed body and improving productivity, by producing a granulated powder having excellent flowability. <P>SOLUTION: The method for manufacturing a sintered magnet containing the rare-earth metal comprises the steps of: charging a raw powder for the sintered magnet containing the rare-earth metal and a liquid into a chamber 11; agglomerating the raw powder through the liquid by relatively rotating a main wing 12 placed in the chamber 11 with respect to the chamber 11; and loosening the obtained agglomerate with an aileron 13 placed in the chamber 11 to prepare the granulated powder; uniformizing the grain size of the granulated powder by using an oscillating sieve; charging the powder into a mold cavity; applying a magnetic field to the granulated powder; pressing the powder into the formed body; and sintering the formed body. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a rare earth sintered magnet typified by an Nd-Fe-B system, and in particular, by adjusting the particle size after granulating raw material powder, the filling property to a mold during molding in a magnetic field is improved. The present invention relates to a technique for obtaining a rare earth sintered magnet having improved magnetic properties and improved magnetic properties.

When manufacturing rare earth sintered magnets, magnetic properties such as saturation magnetic flux density and coercive force are ensured by refining the raw material powder used for sintering. However, the refinement of the raw material powder is a factor that hinders the dimensional accuracy and productivity of the molded body.
The raw material powder forms a compact by pressure molding in a magnetic field. In the molding in the magnetic field, the raw powder particles are oriented by applying a static magnetic field or a pulsed magnetic field. At the time of molding in this magnetic field, the finer the raw material powder, the lower the fluidity and the problem of filling into the mold. If the powder filling property is inferior, the powder cannot be sufficiently filled into the die, so the dimensional accuracy of the molded product cannot be obtained, or the filling of the die itself takes time and productivity. There is a problem of inhibiting. In particular, it is difficult to accurately and efficiently produce a molded body having a thin shape or a complicated shape.

Attempts have been made to granulate raw material powder as one means for improving the fluidity of raw material powder.
In order to granulate raw material powder, a proposal has been made to granulate by spray-drying a slurry in which a binder is added to a rare earth metal powder (see, for example, Patent Document 1).
In addition, a technique has been proposed in which a flow of fluid (airflow) is generated in the chamber, and kinetic energy is given to the raw material powder in the chamber by this flow to achieve granulation (see, for example, Patent Document 2). .

JP-A-8-107034 JP 2004-131815 A

  However, in the technique using the spray dryer as in the technique of Patent Document 1, granules are formed by blowing slurry containing raw material powder into hot air from a nozzle. The formed granules are sprayed at high speed. Because the granules fall on the inner wall of the slab and repeatedly collide with each other in the air stream, the granule diameter increases and the shape of the granules is not uniform. Also, in the technique of forming granules by the flow of fluid in the chamber as in the technique of Patent Document 2, the raw material powder (granules) repeatedly rises and falls in the chamber by the air flow, and collides with the inner wall of the chamber and Repeat the collision between each other. These impacts are accompanied by the problem that the granules collapse and the yield of the granules decreases.

  The present invention has been made on the basis of such a technical problem. By producing granules having excellent fluidity and further adjusting the particle size of the granules, the dimensional accuracy of the molded body is improved and the productivity is improved. It aims at providing the method of manufacturing the rare earth sintered magnet which has the outstanding magnetic characteristic.

  When the present inventors produced granules by rolling, they were able to efficiently produce granules having high fluidity. However, it was confirmed that this granule has a large particle size distribution. When this granule was supplied on the vibrating body, it was found that the particle size distribution could be adjusted to be small. That is, a method for producing a rare earth sintered magnet of the present invention, a step of rolling a raw material composition containing a raw material powder of a rare earth sintered magnet and a granulating aid, and obtaining granules, and supplying the granules onto the vibrating body, A step of adjusting the particle size distribution of the granules, a step of feeding the granules into the mold cavity, a step of obtaining a molded body by applying a magnetic field to the granules and press-molding, and a step of sintering the molded body It is characterized by providing.

  In the method for producing a rare earth sintered magnet of the present invention, it is preferable to use a vibrating sieve as the vibrating body. Since the particle size distribution can be adjusted and the granule having a particle size equal to or smaller than the predetermined particle size passes through the sieve openings, a granule having the predetermined particle size and particle size distribution can be obtained efficiently.

In the method for producing a rare earth sintered magnet according to the present invention, the step of obtaining granules includes putting the raw material composition into the chamber and relatively rotating the chamber and the main wing provided in the chamber. It is preferable to produce granules by agglomerating the raw material powder through a loosening and loosening the obtained agglomerates with an auxiliary blade provided in the chamber.
As described above, when the raw material powder and the granulation aid are agglomerated by rotating the chamber and the main wing relatively, and further, the granule is produced at a high speed by loosening the obtained agglomerate with the auxiliary wing. Granules are produced well without hitting the chamber or other agglomerates.

As the granulation aid used in the present invention, any granule may be used as long as it assists (promotes) granulation of the raw material powder.
By the way, when the raw material powder is granulated, the fluidity is improved, but due to the binding force between the raw material powders constituting the granule, the raw material powder is less likely to be magnetically oriented and the magnetic properties, particularly the residual magnetic flux density, are reduced. There is a problem of doing. For this reason, it is desirable that the granule is configured with a weak binding force that can be easily broken by applying a magnetic field during magnetic field orientation.
In particular, as shown in Patent Document 1, when a raw material powder is attached using a binder such as PVA (polyvinyl alcohol) as a granulating aid, the adhesive force between the raw material powders is relatively strong. Even if the granules having such strong adhesion are subjected to molding in a magnetic field, it is not easy to orient each raw material powder. Further, since carbon contained in the binder causes a decrease in magnetic characteristics, a step of removing the binder is necessary.

The inventors have intensively studied for such a problem. In the conventional granulation technology using a binder, a slurry containing a predetermined amount of a so-called organic solvent is prepared as a solvent for dissolving the binder and as a dispersion medium for dispersing the raw material powder. The present inventors paid attention to this organic solvent. As a result, it is possible to produce granules only with an organic solvent without using a binder. This granule is excellent in fluidity when filled with a mold. Since the adhering force was relatively weak, it was confirmed that it was separated into raw material powder by a magnetic field applied during molding in a magnetic field and a good orientation state could be realized. Moreover, it confirmed that a granule could be similarly produced also by using water instead of an organic solvent.
Based on such knowledge, the granulation aid used in the method for producing a rare earth sintered magnet of the present invention is an organic liquid, water, or the like, a saturated vapor pressure at 20 ° C. of 75 mmHg (10.0 kPa) or less, and a surface at 20 ° C. It is preferable that the tension is 20 dyn / cm or more and the viscosity at 20 ° C. is 0.35 cp or more. Note that a substance similar to an organic solvent is used, but the substance is expressed as an organic liquid because it does not function as a solvent.

  In addition, when using organic liquid or water as granulation aid, the amount of granulation aid required as moisture for preparing the granule and granulation necessary for maintaining the shape of the granule It was found that there was a difference in the amount of auxiliaries, the latter being less. It can be said that the granulation aid has a very small effect on the magnetic properties compared to conventional binders such as PVA, but the amount of granulation aid in the state of forming the granules is equivalent to the magnetic properties of the rare earth sintered magnet. It was also confirmed to have an effect. For this reason, it is preferable to remove a part of the granulation aid after preparing the granules. Furthermore, the granulation aid may be completely removed as long as the granules can be maintained by van der Waals force between the raw material powders. As one criterion, if it is desired to obtain high magnetic properties, the granulation aid is completely removed, and if it is desired to prioritize the fluidity of the granules over the magnetic properties, the granulation aid may be left. .

  As described above, by providing a process for removing part or all of the granulation aid at any stage after granule formation, the problem of magnetic properties can be solved. It is desirable that the granulation aid removal step be simple. In order to satisfy this requirement, it has been found that it is effective to achieve the object of the present invention, once the granules are produced, and then removing other granulation aids, leaving the amount necessary for maintaining the shape of the granules. . That is, if a granule is prepared using a liquid component that is easy to remove after granule formation and the first organic liquid that is harder to remove than this liquid component, then only the liquid component that is easy to remove is preferentially removed from the granule. On the other hand, the first organic liquid that is difficult to remove can remain in the granules. That is, as the granulation aid, the first organic liquid and a liquid component having a higher saturated vapor pressure than the first organic liquid are used. The liquid component may be water or the like, but an organic liquid (second organic liquid) having a saturated vapor pressure higher than that of the first organic liquid can be used.

According to the present invention, a rare earth sintered magnet obtained by applying a magnetic field to a granule containing raw material powder of a rare earth sintered magnet, press-molding, and sintering the granule, the granule comprising the raw material powder and the granulation aid A rare earth sintered magnet is provided which is rolled and granulated by a main wing rotating in a chamber and an auxiliary wing rotating in a direction different from the main wing, and further subjected to a vibrating sieve after the rolling granulation.
This raw material powder has an R ₂ T ₁₄ B phase (R is one or more elements selected from rare earth elements, T is one or two elements selected from transition metal elements including Fe, Fe and Co) It is preferable to have a composition containing the above elements) and have an average particle size of 2.5 to 6 μm.

  According to the present invention, a granule having excellent fluidity is obtained, and a method for producing a rare earth sintered magnet having excellent magnetic properties and improving the dimensional accuracy and productivity of a molded body is provided. It becomes possible to do.

Hereinafter, the present invention will be described in detail based on embodiments.
In the present embodiment, the powder is granulated by adhering the primary alloy particles (raw material powder) to each other with an organic liquid as a granulating aid. The presence of the organic liquid between the particles causes liquid cross-linking and causes the primary alloy particles to adhere to form granules. When the granules are applied to a vibrating body, preferably a vibrating sieve, the granules that have become large lumps by adhering to each other can be broken into granules of an appropriate size. On the other hand, a fine powder or granule that has failed to become a moderately sized granule can be rolled into the granule with an organic liquid to obtain a moderately sized granule. As a result, granules having a narrow particle size distribution can be obtained. Moreover, granules having a predetermined particle size can be obtained by passing through the openings of the vibrating sieve.
The adhesion force of the granules obtained above is extremely weak compared to the adhesion force of conventional binders such as PVA, so it easily collapses and separates into primary alloy particles by a magnetic field applied during molding in a magnetic field, and has high orientation. You can get a degree. Furthermore, since this granule has a narrow particle size distribution, it is possible to obtain a rare earth sintered magnet having excellent fluidity, improving the dimensional accuracy of the molded body, improving productivity, and having excellent magnetic properties.

The manufacturing method of the rare earth sintered magnet of the present invention will be described below.
The raw material alloy used as the raw material of the sintered magnet can be produced by a strip casting method or other known melting methods in a vacuum or an inert gas, preferably in an Ar atmosphere. In the strip casting method, a molten metal obtained by melting a raw metal in a non-oxidizing atmosphere such as an Ar gas atmosphere is ejected onto the surface of a rotating roll. The melt rapidly cooled by the roll is rapidly solidified in the form of a thin plate or flakes (scales). This rapidly solidified alloy has a homogeneous structure with a crystal grain size of 1 to 50 μm. The raw material alloy can be obtained not only by the strip casting method but also by a melting method such as high frequency induction melting. In order to prevent segregation after dissolution, for example, it can be solidified by pouring into a water-cooled copper plate. An alloy obtained by the reduction diffusion method can also be used as a raw material alloy.
When obtaining an RTB-based sintered magnet, a so-called alloy using a R ₂ T ₁₄ B crystal grain (low R alloy) and an alloy containing more R than a low R alloy (high R alloy) is used. A mixing method can also be applied to the present invention.

The raw material alloy is first subjected to a grinding process. In the case of the mixing method, the low R alloy and the high R alloy are pulverized separately or together. The pulverization process includes a coarse pulverization process and a fine pulverization process.
In the coarse pulverization step, first, the raw material alloy is coarsely pulverized until the particle diameter becomes about several hundred μm. The coarse pulverization is desirably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. Prior to coarse pulverization, it is effective to perform pulverization by occluding hydrogen in the raw material alloy and then releasing it. The hydrogen releasing treatment is performed for the purpose of reducing hydrogen as an impurity as a rare earth sintered magnet. The temperature of heating and holding for releasing hydrogen is 200 ° C. or higher, desirably 350 ° C. or higher. The holding time varies depending on the relationship with the holding temperature, the thickness of the raw material alloy, etc., but is at least 30 minutes or longer, preferably 1 hour or longer. The hydrogen releasing treatment is performed in a vacuum or Ar gas flow. The hydrogen storage process and the hydrogen release process are not essential processes. This hydrogen pulverization can be regarded as coarse pulverization, and mechanical coarse pulverization can be omitted.

  After the coarse pulverization step, the coarse pulverization step is further pulverized in the fine pulverization step to obtain a raw material powder (fine pulverized powder). A jet mill is mainly used for fine pulverization, and a coarsely pulverized powder having a particle size of about several hundreds of μm has an average particle size of 2.5 to 6 μm, preferably 3 to 5 μm. The jet mill releases a high-pressure inert gas from a narrow nozzle to generate a high-speed gas flow, accelerates the coarsely pulverized powder with this high-speed gas flow, collides with the coarsely pulverized powder, and collides with the target or container wall. It is a method of generating a collision and crushing.

  In the case of the mixing method, the timing of mixing the two kinds of alloys is not limited. However, when the low R alloy and the high R alloy are separately pulverized in the pulverization step, the pulverized low R alloy powder is used. And high R alloy powder in a nitrogen atmosphere. The mixing ratio of the low R alloy powder and the high R alloy powder may be about 80:20 to 97: 3 by weight. The mixing ratio when the low R alloy and the high R alloy are pulverized together is the same. Fatty acids or fatty acid derivatives and hydrocarbons for the purpose of improving lubrication and orientation during molding, such as zinc stearate, calcium stearate, aluminum stearate, stearamide, olein, which are stearic acid and oleic acid Acid amide, ethylenebisisostearic acid amide, hydrocarbon paraffin, naphthalene and the like can be added in an amount of about 0.01 to 0.3 wt% during pulverization.

The raw material powder obtained above is granulated to produce granules.
In the production of granules, granules can be obtained by using a granulating apparatus 10 as shown in FIGS. 1 and 2 to give the finely pulverized powder a roll, that is, a movement that rolls individual raw material powders.
As shown in FIGS. 1 and 2, the granulating apparatus 10 has a configuration in which a main wing 12 and an auxiliary wing 13 are provided in a chamber 11.
The chamber 11 includes an openable / closable lid (not shown) and is hermetically sealed with the lid closed. Moreover, an organic liquid can be added to the chamber 11 by a fluid spray nozzle or a dropping nozzle (not shown).
The main wing 12 is provided with a plurality of wing members 12b on a rotary shaft 12a, and is driven to rotate around the axis of the rotary shaft 12a by a drive motor (not shown). Similarly, the auxiliary wing 13 is provided with a plurality of wing members 13b on the rotating shaft 13a, and a driving force such as a gear or a timing belt is transmitted from a driving motor (not shown) or a driving motor for rotating the main wing 12. The drive force transmitted through the mechanism is rotationally driven around the axis of the rotary shaft 13a.

Such a granulating apparatus 10 includes a vertical type as shown in FIG. 1 and a horizontal type as shown in FIG. 2 depending on the installation form of the main wing 12.
In the vertical granulator 10V shown in FIG. 1, the main wing 12 is provided such that the rotating shaft 12a has an axis line in a substantially vertical direction in the chamber 11. The auxiliary wing 13 is provided above the main wing 12, and the rotating shaft 13 a is provided so as to have an axis in the horizontal direction in the chamber 11.
Further, in the horizontal granulator 10H shown in FIG. 2, the main wing 12 is provided such that the rotating shaft 12a has an axis in the substantially horizontal direction in the chamber 11. The wing member 12b of the main wing 12 extends along the peripheral wall 11a continuous in the circumferential direction of the chamber 11, and the auxiliary wing 13 is provided so as to be located inward of these wing members 12b.

In such granulators 10V and 10H, predetermined amounts of the finely pulverized powder and organic liquid obtained in the above-described steps are put into the chamber 11, respectively, and the main wing 12 and the auxiliary wing 13 are driven to rotate. Granulate the granules. At this time, the finely pulverized powder and the organic liquid are rolled in the chamber 11 by the main wing 12 to agglomerate the finely pulverized powder via the organic liquid to form an agglomerate, and the agglomerated by the rotatable auxiliary wing 13. By loosening the material, the granule can be satisfactorily produced without colliding with the chamber 11 or other aggregates at high speed.
In the granulating apparatus 10V, 10H, the above granulation is performed for a predetermined time, so that the finely pulverized powder is aggregated and granulated through the organic liquid in the chamber 11 to produce granules. Is done.
Note that after the finely pulverized powder is introduced into the chamber 11, the inside of the chamber 11 is preferably replaced with an inert gas such as nitrogen in order to prevent oxidation of the finely pulverized powder. At this time, it is more preferable to rotate the main wing 12 for a certain period of time to loosen the finely pulverized powder and to replace the inside of the chamber 11 with an inert gas while expelling air present in the voids of the finely pulverized powder.
In addition, the timing of adding the organic liquid may be the same as that of the finely pulverized powder, but it is preferable that the organic liquid is charged after the main wing 12 is rotated for a certain time after the finely pulverized powder is charged.
Further, after the predetermined amount of the organic liquid is added, it is preferable to rotate the main wing 12 for a certain period of time so that the organic liquid is adapted to the finely pulverized powder to promote granulation.

At this time, the organic liquid to be used includes hydrocarbon compounds, alcohol compounds, ether compounds (including glycol ether compounds), ester compounds (including glycol ester compounds), ketone compounds, fatty acid compounds, terpene compounds. One or two of the compounds can be selected. Specific examples of such organic liquids include hydrocarbons such as toluene, xylene, alcohols as terpineol, ethanol, and ethers as butyl cellosolve, cellosolve, carbitol, butyl carbitol, Examples of ester compounds include ethyl acetate, and examples of ketone compounds include acetone (dimethyl ketone), methyl isobutyl ketone, and methyl ethyl ketone.
Of course, the organic liquid is not limited to the organic liquids listed here, and other organic liquids such as ethylene glycol, diethylene glycol, and glycerin can also be used.
The organic liquid includes a substance generally called an organic solvent, but is called an organic liquid because it does not function as a solvent in the present invention.

  In the granule produced using an organic liquid, the organic liquid is present at least at the contact point between the finely pulverized powders, and the finely pulverized powders are adhered to each other by the liquid crosslinking force. At this time, the contact between the finely pulverized powders does not substantially contain a solid component such as a binder for adhering the finely pulverized powders in the liquid. However, when a lubricant is added to improve the grindability and the orientation during molding, the solid component of the lubricant is allowed to be present in the liquid.

  Granules produced using an organic liquid need to maintain their shape until a predetermined step. Once the produced granule cannot maintain its shape, the fluidity of the granule decreases due to the dropping of fine primary alloy particles. Therefore, in the present invention, it is desirable to use an organic liquid having a saturated vapor pressure at 20 ° C. of 75 mmHg (10.0 kPa) or less. The saturated vapor pressure at 20 ° C. is more preferably 20 mmHg or less, and the more desirable saturated vapor pressure at 20 ° C. is 5 mmHg or less.

  The organic liquid used in the present invention must also provide sufficient adhesion to maintain the granules between the primary alloy particles. Therefore, it is desirable in the present invention to specify the surface tension and viscosity of the organic liquid. The surface tension of the desired organic liquid is 20 dyn / cm or more at 20 ° C. The more desirable surface tension at 20 ° C. is 25 dyn / cm or more, and the more desirable surface tension at 20 ° C. is 30 dyn / cm or more. The desirable viscosity of the organic liquid is 0.35 cp or more at 20 ° C. A more desirable viscosity at 20 ° C. is 1 cp or more, and a further desirable viscosity at 20 ° C. is 2 cp or more.

  The amount of the organic liquid added to the finely pulverized powder is not particularly limited, but if the amount of the organic liquid added is too small, the amount of liquid sufficient to cause liquid crosslinking between primary alloy particles cannot be secured. Is difficult. On the other hand, when there is too much addition amount of an organic liquid, when removing an organic liquid from the obtained granule, it may become difficult to remove an organic liquid within predetermined time. From the above, it is recommended that the amount of organic liquid added to the finely pulverized powder be 1.0 to 20.0 wt%. A more desirable addition amount of the organic liquid is 2.0 to 18.0 wt%, and a more desirable addition amount of the organic liquid is 4.0 to 15.0 wt%.

  Moreover, when forming a granule, a granule can also be produced using a 1st organic liquid and a liquid component whose saturation vapor pressure is higher than a 1st organic liquid. In this case, the liquid component is preferably an organic liquid (second organic liquid), but a liquid other than an organic liquid such as water may be used. Water (saturated vapor pressure at 20 ° C. = 17.5 mmHg) may oxidize the primary alloy particles, but the amount to be added is small, and furthermore, pure water or the like that is less likely to oxidize the primary alloy particles should be used. Therefore, in the present invention, liquid components other than the organic liquid are allowed.

  Table 1 shows saturated vapor pressures of various organic liquids, and the first organic liquid and the second organic liquid may be selected based on this value. For example, as the first organic liquid, terpene compounds including pinene, menthane and terpineol, butyl carbitol acetate, cyclohexanol, ethylene glycol, butyl carbitol, diethylene glycol, carbitol, cellosolve, butyl cellosolve, and propionic anhydride are used. be able to. In addition, as the second organic liquid, toluene, xylene, ethanol, acetone, methyl isobutyl ketone, ethyl acetate, methyl ethyl ketone, isobutyl alcohol, n-butyl acetate, and dibutyl ether can be used. However, this is merely an example, and does not determine the scope of the present invention. For example, among the examples exemplified as the first organic liquid, the first organic liquid and the second organic liquid can be configured, and among the examples exemplified as the second organic liquid, An organic liquid and a second organic liquid can also be configured.

  When a granule is produced using the first organic liquid and a liquid component having a higher saturated vapor pressure than the first organic liquid, the amount of the first organic liquid added to the finely pulverized powder is 6.0 wt% or less (however, , 0 is not included). Without the first organic liquid, the formation of granules by liquid cross-linking is not easy, while addition of 6.0 wt% is sufficient to maintain the shape of the formed granules, and addition exceeding this is a factor that degrades magnetic properties. Become. Therefore, the amount of the first organic liquid added is preferably 6.0 wt% or less (however, not including 0). Further, it is desirable that the amount of the liquid component (second organic liquid) added is 20.0 wt% or less (however, 0 is not included). Without the liquid component (second organic liquid), it is difficult to give the moisture necessary for granule preparation to the finely pulverized powder. The removal of the organic liquid (2) takes time. Therefore, it is desirable that the amount of the liquid component (second organic liquid) added is 20.0 wt% or less (excluding 0).

  The granules obtained as described above are passed through a vibrating sieve. Granules obtained by the rolling include granules that have become large lumps by adhering to each other, and fine powders that have failed to become granules of an appropriate size. Therefore, by applying this granule to a vibrating sieve, a large lump can be loosened into moderately sized granules. Further, a fine powder can be rolled into other granules to form granules of an appropriate size. In particular, if the granule contains a liquid such as an organic liquid, the liquid oozes out from the surface of the granule, adheres to the fine powder that has come into contact, and is granulated to form an appropriately sized granule. . By passing through the vibrating sieve in this way, the particle size of the granules is adjusted to be small, and the particle size distribution is narrowed.

  As the vibration sieve, a generally used apparatus capable of sieving powder (granules) while applying vibration can be used. The granules are put into a predetermined container having a mesh-like horizontal surface provided in the vibration sieve device, and the container is automatically vibrated by a vibration machine provided in the device. Then, the granules freely rotate on the mesh in the container, the particle size is adjusted and falls from the mesh eyes. The mesh opening can be appropriately selected, and is, for example, 50 to 800 μm, preferably 100 to 500 μm. Note that the horizontal plane does not have an opening like a mesh, and may be an uneven horizontal plane without an opening or a flat horizontal plane. Even if a granule rolls only on a flat horizontal surface, granulation by rolling occurs and the particle size is adjusted. In the present invention, in order to narrow the particle size distribution of the granules and to make effective use of resources, all the mesh openings provided in the vibrating sieve are passed through and all the passed granules are used in the subsequent steps. However, if it takes time in the process to pass everything, use only the mesh that has passed through the mesh openings, or those that have passed through the mesh openings and those that remain on the mesh And may be mixed as appropriate.

As described above, the organic liquid can be partially or completely removed from the granulated sieve. Moreover, when a granule is produced using the first organic liquid and a liquid component having a higher saturated vapor pressure than the first organic liquid, the liquid component (second organic liquid) is removed.
Specific means for removing the organic liquid and liquid components are not particularly limited, but it is simple and effective to volatilize the granules by exposing them to a reduced pressure atmosphere. The reduced-pressure atmosphere may be room temperature, but may be a heated reduced-pressure atmosphere or a non-reduced heating atmosphere. If the pressure in the reduced pressure atmosphere is too low, the organic liquid will not volatilize sufficiently. Therefore, in the present invention, it is desirable that the pressure of the reduced pressure atmosphere is in the range of 10 ⁻¹ to 10 ⁻⁵ Torr (133 × 10 ⁻¹ Pa to 133 × 10 ⁻⁵ Pa). However, in the case of a heated reduced-pressure atmosphere, a range of 10 ⁰ to 10 ⁻² Torr (133 × 10 ⁰ Pa to 133 × 10 ⁻² Pa) is sufficient. If the heating temperature at this time is too low, the volatilization of the organic liquid does not proceed sufficiently. Conversely, if the heating temperature is too high, the primary alloy particles constituting the granules may be oxidized, leading to deterioration of magnetic properties. Therefore, in the present invention, the heating temperature is desirably 40 to 80 ° C.

  In addition, although the process of removing a liquid is implemented after applying a granule to a vibration sieve in the above, this invention is not limited to this, It can also carry out before applying a granule to a vibration sieve. However, it is easier to obtain a more uniform particle size when the granules are passed through a vibrating sieve in a state containing some liquid. Therefore, in the case of removing the liquid before the vibrating sieve, the organic liquid is not removed, for example, only the second organic liquid is removed and the first liquid is left as it is. Is preferably processed so that a certain amount of liquid is contained in the granule.

  As described above, the granule from which the organic liquid or liquid component has been removed maintains the shape of the granule by the liquid crosslinking force and van der Waals force of the remaining organic liquid when the organic liquid is partially removed. ing. Further, when the organic liquid is completely removed, the organic liquid is in a dry state, and the granule is easily disintegrated because the form of the granule is maintained only by van der Waals force. In addition, when a granule is produced using the first organic liquid and a liquid component having a higher saturated vapor pressure than the first organic liquid, the second organic liquid is removed from the granule from which the liquid component (second organic liquid) has been removed. If one organic liquid remains, it is easy to maintain the granular form. On the other hand, if the amount of the first organic liquid remaining in the granules is too large, the effect of improving the magnetic properties cannot be enjoyed. Therefore, in the present embodiment, the amount of the first organic liquid remaining in the granules is preferably in the range of 6.0 wt% or less (excluding 0). The amount of the first organic liquid remaining in the more desirable granules is 0.1 to 4.0 wt%, and the amount of the first organic liquid remaining in the more desirable granules is 0.2 to 3.0 wt%.

The granules are subjected to molding in a magnetic field.
The granule obtained by the present invention is excellent in filling property in a magnetic mold. Therefore, it is possible to obtain a molded body having a desired dimensional accuracy and to ensure high productivity. In particular, it is possible to produce a thin-walled shape or a complex shape with high accuracy and efficiency.
The molding pressure in the magnetic field molding may be in the range of 0.3 to 3 ton / cm ² (30 to 300 MPa). The molding pressure may be constant from the beginning to the end of molding, may be gradually increased or gradually decreased, or may vary irregularly. The lower the molding pressure is, the better the orientation is. However, if the molding pressure is too low, the strength of the molded body is insufficient and handling problems occur. Therefore, the molding pressure is selected from the above range in consideration of this point. The final relative density of the molded body obtained by molding in a magnetic field is usually 50 to 60%.
The applied magnetic field may be about 12 to 20 kOe (960 to 1600 kA / m). By applying a magnetic field of this level, the granules are broken down and decomposed into primary alloy particles. The applied magnetic field is not limited to a static magnetic field, and may be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

Next, the compact is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, the difference of an average particle diameter, and a particle size distribution, what is necessary is just to sinter at 1000-1200 degreeC for about 1 to 10 hours.
After sintering, the obtained sintered body can be subjected to an aging treatment. This step is an important step for controlling the coercive force. In the case where the aging treatment is performed in two stages, holding for a predetermined time at around 800 ° C. and around 600 ° C. is effective. When the heat treatment at around 800 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by heat treatment near 600 ° C., when aging treatment is performed in one stage, it is preferable to perform aging treatment near 600 ° C.

Next, a rare earth sintered magnet to which the present invention is applied will be described.
The present invention is particularly preferably applied to an RTB-based sintered magnet. This RTB-based sintered magnet contains 25 to 37 wt% of a rare earth element (R). Here, R in the present invention has a concept including Y, and therefore 1 of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It is selected from species or two or more species. If the amount of R is less than 25 wt%, the R ₂ T ₁₄ B phase, which is the main phase of the R-T-B system sintered magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. The magnetic force is significantly reduced. On the other hand, when R exceeds 37 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 37 wt%. A desirable amount of R is 28 to 35 wt%, and a more desirable amount of R is 29 to 33 wt%.

Further, the RTB-based sintered magnet to which the present invention is applied contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. On the other hand, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit of B is set to 4.5 wt%. A desirable amount of B is 0.5 to 1.5 wt%, and a more desirable amount of B is 0.8 to 1.2 wt%.
The RTB-based sintered magnet to which the present invention is applied has a Co content of 2.0 wt% or less (not including 0), preferably 0.1 to 1.0 wt%, more preferably 0.3 to 0. .7 wt% can be contained. Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.

Moreover, the RTB-based sintered magnet to which the present invention is applied can contain one or two of Al and Cu in a range of 0.02 to 0.5 wt%. By containing one or two of Al and Cu in this range, it is possible to increase the coercive force, the corrosion resistance, and the temperature characteristics of the obtained R-T-B sintered magnet. In the case of adding Al, the desirable amount of Al is 0.03 to 0.3 wt%, and the more desirable amount of Al is 0.05 to 0.25 wt%. Further, in the case of adding Cu, the desirable amount of Cu is 0.15 wt% or less (not including 0), and the more desirable amount of Cu is 0.03 to 0.12 wt%.
The RTB-based sintered magnet to which the present invention is applied allows the inclusion of other elements. For example, elements such as Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. On the other hand, it is desirable to reduce impurity elements such as oxygen, nitrogen, and carbon as much as possible. In particular, the amount of oxygen that impairs magnetic properties is preferably 5000 ppm or less, more preferably 3000 ppm or less. This is because when the amount of oxygen is large, the rare-earth oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated.

Although it is desirable to apply the present invention to an RTB-based sintered magnet, the present invention can also be applied to other rare earth sintered magnets. For example, the present invention can be applied to an R—Co based sintered magnet.
The R—Co based sintered magnet contains R, one or more elements selected from Fe, Ni, Mn, and Cr, and Co. In this case, it preferably further contains Cu or one or more elements selected from Nb, Zr, Ta, Hf, Ti and V, and particularly preferably from Cu and Nb, Zr, Ta, Hf, Ti and V. Containing one or more selected elements. Among these, an intermetallic compound of Sm and Co, preferably an Sm ₂ Co ₁₇ intermetallic compound, is the main phase, and a subphase mainly composed of SmCo ₅ exists at the grain boundary. The specific composition may be appropriately selected according to the production method, required magnetic characteristics, and the like. For example, R: 20 to 30 wt%, particularly about 22 to 28 wt%, Fe, Ni, Mn, and Cr Above: about 1 to 35 wt%, one or more of Nb, Zr, Ta, Hf, Ti and V: 0 to 6 wt%, especially about 0.5 to 4 wt%, Cu: 0 to 10 wt%, especially 1 to 10 wt% To the extent, Co: the balance composition is desirable.
The R-T-B sintered magnet and the R-Co sintered magnet have been described above, but the present invention does not prevent application to other rare earth sintered magnets.

A raw material alloy having a composition of 26.5 wt% Nd-5.9 wt% Dy-0.25 wt% Al-0.5 wt% Co-0.07 wt% Cu-1 wt% B-Fe was produced by strip casting.
Next, after hydrogen was occluded in the raw material alloy at room temperature, hydrogen pulverization treatment was performed in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere.
The alloy that has been subjected to the hydrogen pulverization treatment was mixed with 0.05 to 0.1% of a lubricant that contributes to improvement in pulverization and orientation during molding. The lubricant may be mixed for about 5 to 30 minutes using, for example, a Nauter mixer. Thereafter, a finely pulverized powder having an average particle size of 5.0 μm was obtained using a jet mill.

The above finely pulverized powder was put into a chamber of a granulator, and the inside of the chamber was filled with nitrogen to prevent oxidation. As the granulator, a horizontal type as shown in FIG. 2 (chamber volume is 1.5 liters: high-speed flow type Spartan Luzer (Dalton)) was used.
Thereafter, the main wing of the granulator was rotated at a predetermined speed to stir the finely pulverized powder. Furthermore, the auxiliary wing was rotated. As an organic liquid, 80 g of terpineol (first organic liquid) and 270 g of ethanol (second organic liquid) were added to 4000 g of finely pulverized powder over a predetermined time using a nozzle.
Even after all the organic liquid was added, the main wing and auxiliary wing were kept rotating for a certain period of time in order to make the organic liquid and finely pulverized powder blend together. Thereafter, the main wing and auxiliary wing were stopped, and the granulated material was taken out from the chamber.

Subsequently, ethanol, which is the second organic liquid contained in the extracted granule (granulated product), was removed by evaporation. In order to prevent oxidation of the finely pulverized powder, a vacuum chamber was used for evaporation, and evaporation was performed in a reduced pressure atmosphere. The granules from which ethanol was removed in this way were passed through a vibrating sieve. An electric sieve (Nitto: AFN-300, (2800 rpm)) was used as the vibration sieve. Granules of Example 1 were obtained by vibrating the granules for 1 minute using a stainless steel container having no mesh in the vibrating sieve. Moreover, the granule of Example 2 was obtained by vibrating the granule for 1 minute using a mesh having an opening of 500 microns in the vibrating sieve. Furthermore, before the removal of the ethanol, that is, the granules containing ethanol and terpineol were vibrated for 1 minute using a mesh having a mesh opening of 500 microns on a vibrating sieve, and then the ethanol was removed by the same method as described above. 3 granules were obtained.
Further, as Comparative Example 1, a granule from which ethanol was removed without passing through a vibrating sieve was obtained.
In order to examine the particle size distributions of Examples 1 to 3 and Comparative Example 1 obtained, sieving was performed little by little while applying a minimum force to pass through the mesh so as not to vibrate the granules as much as possible. The results are shown in the graph of FIG.

  As shown in FIG. 3, when Example 1 and Comparative Example 1 were compared, the granules were granulated by rolling only by applying vibration even if there was no mesh opening, and the fine powder decreased. In Example 2, when a vibrating sieve with openings is used, it can be seen that the particle size distribution is further narrowed and the granules are concentrated at a predetermined particle size. It is considered that the granules roll on the mesh due to vibration by the vibrating sieve, and as a result, the granulation further progresses. Moreover, since the granule granulated to 500 micrometers or less tries to pass a mesh, it does not enlarge by rolling. In Example 3 where granulation was performed by pulverizing the granules before drying through a vibrating sieve, the particle size distribution was narrower than in Example 2, indicating that the granules were concentrated at a predetermined particle size. Thus, when the granule containing the liquid was passed through a vibrating sieve, the fine powder was reduced by adhering to the granule for rolling operation. In addition, too large granules were broken by vibration, resulting in smaller, moderately sized granules. As a result, it is considered that the particle size distribution is narrowed.

FIG. 4 shows external SEM images of granules of 500 μm or less in Example 2, Example 3 and Comparative Example 1. As is clear from FIG. 4, the granules of Examples 2 and 3 to which the vibrating sieve is applied have few fine powders. In Example 3, which was passed through a vibration sieve before drying, the granule was more rounded, the particle size was small, and the particle size was uniform, probably because of the large amount of liquid. When the repose angle of these samples was measured based on the following method, Comparative Example 1 was 50.7 °, whereas Example 2 was 48.3 ° and Example 3 was 44.8 °. It was found that the use of a vibrating sieve reduced the fine powder and improved the fluidity.
Angle of repose measurement: Granules were dropped little by little through a sieve from a certain height on a 60 mmφ circular table. The granule supply was stopped just before the granule pile collapsed. The bottom angle of the pile of granules formed on the round table was measured. The circular table was rotated by 120 °, the angles were measured at a total of three locations, and the average was taken as the angle of repose.

Next, the granules of Examples 4 to 6 and Comparative Example 2 were used in the same manner as Examples 1 to 3 and Comparative Example 1, respectively, except that 20 g of terpineol and 330 g of ethanol were used for 4000 g of finely pulverized powder as the organic liquid. Got. The angle of repose in the granules of Examples 4 to 6 and Comparative Example 2 obtained was measured.
Moreover, the filling dispersion | variation to a metal mold | die was measured in the following ways. A mold having an opening of 15 mm × 4 mm was attached to a molding machine in a magnetic field, the granules were supplied using a feeder, and the mold was ground and filled. This feeder is a box that reciprocates horizontally on a mold, and a supply hole is formed in the lower part of the box. A certain amount of granules are stored in the box, and when this box reciprocates, the powder falls from the supply hole at the bottom of the box into the mold. Granules with better fluidity will drop more granules with a certain number of reciprocating motions. After the granules were filled in the mold as described above, molding was performed with a magnetic field of 15 kOe and a pressure of 1.4 ton / cm ² to obtain a molded body. The weight of the obtained molded body was measured. Each granule was molded 50 times in a magnetic field, and the standard deviation σ of the weight of each compact was divided by the average weight σ / ave. A value obtained by multiplying 100 by 100 was defined as filling variation (%). In addition, the filling amount of each granule with different bulk density is standardized by dividing by the average weight.
Moreover, the measurement of the intensity | strength of the molded object which consists of the granule of Examples 4-6 and the comparative example 2 was also performed. For the strength of the compact, 10 g of each granule was weighed, filled in a mold having an opening of 18 mm × 20 mm, molded in a magnetic field under the same conditions as described above, and the bending strength was measured by a three-point bending test method.
Furthermore, the molded body obtained as described above was heated to 1080 ° C. in vacuum and Ar atmosphere and held for 4 hours for sintering. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 560 ° C. × 1 hour (both in an Ar atmosphere).
Table 2 shows the measurement results of the angle of repose, filling variation, and magnetic properties of the sintered magnets of Examples 4 to 6 and Comparative Example 2. Table 2 shows a sintered powder obtained by molding and sintering using finely pulverized powder of the same material as in Examples 4 to 6 without granulation for granule formation and without sieving. The magnetized magnet is also shown as the original material.

  As shown in Table 2, it can be seen that Examples 4 to 6 subjected to the vibration sieve have a smaller angle of repose and higher fluidity than Comparative Example 2 as well as the original material. In particular, Example 6 in which the granules were passed through a vibrating sieve while containing a liquid had the smallest angle of repose. It can also be seen that powder having a smaller angle of repose and better fluidity is easier to fill into the mold, and as a result, there is less filling variation. In addition, Example 6 was superior to Comparative Example 2, Examples 4 and 5 in terms of magnetic characteristics. The original material has higher magnetic properties than Comparative Example 2 and Examples 4 to 6, but the filling angle is extremely inferior because the angle of repose is large and the fluidity is poor.

In the above embodiment, the organic liquid is used to form the granules. However, the present invention is not limited to this, and water or the like can also be used.
In addition to this, as long as it does not depart from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

It is a figure which shows the structure of a vertical rolling type granulator, (a) is a front sectional view, (b) is a top view, (c) is a right view of (b). It is a figure which shows the structure of a horizontal type | mold rolling granulator, (a) is a front sectional view, (b) is a right view of (a). It is a graph which shows the particle size distribution of the granule produced by the Example and the comparative example. It is a SEM image which shows the granule appearance produced by the Example and the comparative example.

Explanation of symbols

  10, 10H, 10V ... Granulator, 11 ... Chamber, 12 ... Main wing, 13 ... Auxiliary wing

Claims (9)

Rolling a raw material composition containing a raw material powder of a rare earth sintered magnet and a granulation aid to obtain granules;
Supplying the granules onto a vibrating body to adjust the particle size distribution of the granules;
Introducing the granules into a mold cavity;
Applying a magnetic field to the granules, and obtaining a molded body by pressure molding;
Sintering the molded body;
A method for producing a rare earth sintered magnet.   The method of manufacturing a rare earth sintered magnet according to claim 1, wherein the vibrating body is a vibrating sieve.   In the step of obtaining the granules, the raw material composition is put into a chamber, and the raw material powder is agglomerated through the granulation aid by relatively rotating a chamber and a main wing provided in the chamber. The method for producing a rare earth sintered magnet according to claim 1 or 2, wherein the granules are produced by loosening the obtained agglomerates with an auxiliary blade provided in the chamber.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 3, wherein the granulation aid is made of an organic liquid.   The organic liquid has characteristics such that a saturated vapor pressure at 20 ° C. is 75 mmHg (10.0 kPa) or less, a surface tension at 20 ° C. is 20 dyn / cm or more, and a viscosity at 20 ° C. is 0.35 cp or more. Item 5. A method for producing a rare earth sintered magnet according to Item 4.   6. The rare earth sintered magnet according to claim 4, wherein the organic liquid includes a first organic liquid and a second organic liquid having a saturated vapor pressure higher than that of the first organic liquid. Method.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 6, further comprising a step of removing the organic liquid from the granules whose particle size distribution is adjusted. A rare earth sintered magnet obtained by applying a magnetic field to a granule containing raw material powder of a rare earth sintered magnet, press molding, and sintering,
The granules are rolled and granulated by a main wing rotating the raw material powder and the granulating aid in a chamber, and an auxiliary wing rotating in a direction different from the main wing, and after passing through the rolling granulation, the granules are passed through a vibrating sieve. Rare earth sintered magnet characterized by being made. The raw material powder is R ₂ T ₁₄ B phase (R is one or more elements selected from rare earth elements, T is one or two elements selected from transition metal elements including Fe, Fe and Co) The rare earth sintered magnet according to claim 8, wherein the rare earth sintered magnet has a composition containing the above elements) and has an average particle diameter of 2.5 to 6 μm.

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