JP4819103B2 - Manufacturing method and manufacturing apparatus for magnetic anisotropic rare earth sintered magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a magnetically anisotropic rare earth sintered magnet that involves no orientation disturbance causing coercive force deterioration and does not scatter fine powders to be used as materials. <P>SOLUTION: Fine powders available as materials for magnetically anisotropic rare earth sintered magnets are filled into a charge container up to a predetermined density in a scale/charger 41 and a densifier 42 the powders are oriented in a magnetic orientation facility 43 via a pulse magnetic field, and then the oriented powders are sintered in a sintering furnace 44 without pressing them. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a high-performance rare earth magnet and an apparatus for manufacturing the same.

  Rare earth / iron / boron-based sintered magnets (hereinafter referred to as “RFeB magnets”) not only far surpass the properties of permanent magnet materials, but also include resources such as neodymium (a kind of rare earth elements), iron and boron. It is inexpensive because it uses abundant raw materials, and since its appearance in 1982, the market has been steadily expanding as an ideal permanent magnet material. Main applications include computer HDD (hard disk drive) magnetic head drive motor VCM (voice coil motor), luxury speakers, headphones, battery-assisted bicycles, golf carts, permanent magnet magnetic resonance diagnostic equipment (MRI), etc. is there. In addition, practical applications are also being promoted in hybrid car (electric vehicle) drive motors, energy-saving, low-noise, large household appliances (coolers and refrigerators), and industrial motors.

  RFeB magnets have high magnetic properties but have the disadvantage of poor temperature characteristics. In particular, the temperature characteristic of the coercive force is important. RFeB magnets have become widely used since their advent, but the most used fields are VCM and MRI for computer HDDs. These are all used at a stable room temperature.

  When used in home appliances and industrial motors, temperature rise due to coil current cannot be avoided. Further, since a reverse magnetic field acts from the motor armature, irreversible demagnetization occurs in the permanent magnet when the temperature rises and the coercive force decreases. In order to prevent irreversible demagnetization, the coercive force must be increased in advance.

The RFeB magnet was discovered by the present inventors in 1982 (Patent Document 1). This RFeB magnet has a tetragonal crystal structure and an R ₂ Fe ₁₄ B intermetallic compound having magnetic anisotropy as a main phase. In order to obtain high magnetic properties, it is necessary to take advantage of the characteristics of magnetic anisotropy. In addition to the sintering method, casting, hot working, aging treatment methods (patent No. 2,561,704) and quenching alloys can be used. A method for upsetting (Patent No. 4,792,367) has been proposed. However, these methods are inferior to the sintering method in terms of both magnetic properties and productivity. The sintering method is the best method for obtaining a dense and homogeneous microstructure required for permanent magnets.

[Sintering process]
RFeB sintered magnets are manufactured through the steps of compounding, melting, casting, grinding, compression molding in a magnetic field, sintering, and heat treatment.

[composition]
After the RFeB magnet was discovered, additional elements (Patent No. 1606420, etc.), heat treatment (Patent No. 1818977, etc.), crystal grain size control (Patent No. 1662257, etc.) were improved to improve the coercive force and other characteristics. Although the effect has been clarified, addition of heavy rare earth elements (Dy, Tb) is the most effective for improving the coercive force (Japanese Patent No. 1802487). If a large amount of heavy rare earth elements is used, the coercive force will surely increase, but the saturation magnetization will decrease and the maximum energy product will decrease. In addition, Dy and Tb are limited in resources and are expensive, so it is impossible to cover electric vehicles and industrial / household motors that are expected to be in the future.

[Dissolved]
Sintered magnets require a dense and homogeneous microstructure. Initially, a method of casting and finely pulverizing molten alloy was common (for example, Japanese Patent No. 1431617). If the molten alloy is rapidly cooled by the strip cast method, the appearance of alpha iron can be suppressed, and a high energy product can be obtained by reducing the amount of non-magnetic rare earth elements (Patent No. 2665590, JP 2002-208509, etc.) .

[Reduction diffusion method]
There is a method of directly obtaining RFeB alloy powder by mixing and heating rare earth oxide powder, iron powder, ferroboron powder and the like with metal Ca.

[Crushing]
When the RFeB alloy occludes hydrogen, microcracks are generated in the alloy, and pulverization is facilitated (Japanese Patent No. 1674022). For fine pulverization, a powder having a sharp particle size distribution is obtained, and jet mill pulverization using an inert gas such as nitrogen is mainly used (Japanese Patent No. 1883860).

[Molding]
The manufacturing method for obtaining a magnetic anisotropic sintered magnet by compression molding powder in a magnetic field originated from the invention of a ferrite magnet (Japanese Patent Publication No. 29-885, US Pat. No. 2,762,778), and then RCo magnet and RFeB Applied to magnets (US Pat. No. 3,684,593, etc., patent 1431617).
Fine powder is formed with the c-axis of the RFeB tetragonal crystal structure aligned in one direction. A die press method is generally used, but there are a CIP method (Patent No. 3383448) and a RIP method (Patent No. 2030923) as a method for obtaining a higher degree of orientation and a higher energy product.

[Die pressing method]
In 1951, ferrite magnets were invented by Went et al. (Japanese Patent Publication No. 35-8281, US Pat. No. 2,762,777). In the same year, a magnetic anisotropic sintered ferrite magnet was invented by Golter et al. (Japanese Patent Publication No. 29-885, US Pat. No. 2,762,778). Since then, many improvements have been made to overcome the drawbacks of the mold press process.

[Addition of lubricant]
In order to increase the orientation of the fine powder during molding, there is a method of adding a lubricant to reduce friction between the powder and the powder and between the powder and the mold (Patent Nos. 2254603, 3447947, etc.).

[Wet magnetic field press]
In order to achieve high orientation while preventing oxidation of fine powder, there is a method in which a mixture of mineral oil, synthetic oil or vegetable oil and fine powder is injected into a mold under high pressure and wet compression molding is performed in a magnetic field (patented) No. 2731337). In this case, there is a report that high sintering density and high magnetic properties can be obtained by pressurizing and filling the slurry (Patent No. 2859517).

[CIP]
The die molding method can only apply pressure from one direction, which is the cause of disturbing the orientation. If pressure can be applied isotropically from all directions, the disorder of orientation becomes small. There is a method (Patent No. 3383448, etc.) in which a fine powder is put in a rubber container, a magnetic field is applied from the outside, and cold isostatic pressing (CIP) is performed.

[RIP]
As a method of obtaining the same effect as that of the cold isostatic press, the present inventors previously proposed a RIP (Rubber Isostatic Pressing) method as a method of applying an isotropic pressure by installing a rubber mold in a die press machine. (Patent No. 2030923). Because this method is easy to automate, it is much more suitable for mass production than CIP.

[MIM]
There has been proposed a method in which a large amount of binder and fine powder are kneaded to increase the temperature and lower the viscosity, and then injection molding into a mold (Japanese Patent No. 3087363).

[AT]
Air tapping (Air Tapping, AT) has been proposed as a method for filling a coagulating fine powder into a die cavity such as a die press (Japanese Patent Laid-Open Nos. 9-78103 and 9-169301). No. 9-25693). Air tapping is characterized in that a high-speed air stream flows from the powder supply hopper toward the cavity, and when returning, it is slower than that. A method has been proposed in which a powder previously mixed with a binder is filled in a cavity using an air tapping method and solidified by means of heating or the like to obtain a near net shape molded body (Japanese Patent Laid-Open No. 2000-96104). ).

[Pulse magnetic field]
A method of applying a magnetic field from the outside is used to align the powder direction. In the case of an RFeB magnet, the c-axis direction of the tetragonal structure corresponds to the easy magnetization axis, and when a magnetic field is applied, the powder is oriented in one direction. In the case of a normal die press, a static magnetic field is applied by an electromagnet, and the maximum is about 15 kOe. However, a pulse magnetic field using an air-core coil can apply a strong magnetic field of 15 to 55 kOe, and the magnetic characteristics are improved by actually applying a high magnetic field (Japanese Patent No. 3307418).

[Closed system]
In order to avoid oxidation of the powder, it has been proposed to perform the pulverization step and the molding step in an inert atmosphere (Japanese Patent Laid-Open No. 6-108104).

Patent No. 1431617

[Effect of sintering method]
In the powder metallurgy (sintering) method, a dense and homogeneous microstructure can be obtained. In rare earth cobalt magnets and R-Fe-B magnets, there is no better method than powder metallurgy to obtain high-performance permanent magnets by taking advantage of the characteristics of each material.

[Press forming in magnetic field]
In 1951, ferrite magnets were invented by Went et al. (Japanese Patent Publication No. 35-8281, US Pat. No. 2,762,777). The first magnetically anisotropic sintered ferrite magnets appeared by Galter et al. (Japanese Patent Publication No. 29-885, US Pat. No. 2,762,778). The purpose of compression molding is to squeeze out a liquid binder component by compression and to fix oriented particles. Further, compression molding is considered preferable for obtaining a desired shape. There is an example of heating with a container in a magnetic field without compression molding, but the density is lower and the magnetic properties are lower than in the example of compression molding.
After that, compression molding and sintering methods in a magnetic field were succeeded by RCo sintered magnets (US Pat. No. 3,684,593, etc.) and RFeB sintered magnets (Patent No. 1431617). Applying a magnetic field is an essential step for orienting the particles, but no particular consideration has been given to the effect of compression.
The die press has a perpendicular magnetic field method and a parallel magnetic field method. Consider x-, y-, and z-axes. In the parallel magnetic field method, a magnetic field is applied in the z-axis direction, and pressure is applied in the z-axis direction at the same time. The fine particles arranged in the z-axis direction by the magnetic field are also pressurized from the z-axis direction, and are tilted in the x-axis direction and the y-axis direction by friction to disturb the arrangement. On the other hand, in the perpendicular magnetic field method, a magnetic field is applied in the x-axis direction and the pressure is applied from the z-axis direction. Similarly, it tilts in the x-axis direction and y-axis direction due to friction, but when it tilts in the y-axis direction, the powder only rotates and the arrangement itself is small. In other words, the parallel magnetic field method disturbs the arrangement in two directions with respect to the ideal arrangement, but the perpendicular magnetic field method disturbs the arrangement only in one direction, and the perpendicular magnetic field method has higher characteristics.

[Reason for choosing a die press]
One of the reasons why the die press is used is that it is possible to obtain a product (net shape) that is almost close to the final shape and dimensions, and can be automated with a good yield. In particular, from the viewpoint of net shape and yield, the die press method has been widely adopted as a method suitable for mass production.

[CIP]
There is a method in which fine powder is put in a rubber container in advance and sealed, and a magnetic field is applied from the outside, followed by CIP (Cold Isostatic Pressing) (Patent No. 3383448, etc.). Since the pressure is applied isotropically rather than the pressurization from one direction that disturbs the orientation of the particles as in the mold press, the orientation is less disturbed. A high magnetic field by a pulse magnetic field can be applied to orient the powder. A high pressure can be applied, and a robust green compact can be obtained. However, a degaussing process for handling is necessary. Since it is not possible to obtain a green compact with a desired shape, the yield is poor and the processing step is troublesome. Also, manual work is inevitable, so it is not suitable for mass production.

[RIP]
As a method for obtaining the same effect as CIP, the present inventors previously proposed a RIP (Rubber Isostatic Pressing) method (Japanese Patent No. 2030923). In RIP, a fine powder is put into a rubber mold, a pulse magnetic field is applied, and the entire rubber mold is pressurized with a die press. As is the case with the CIP method, pressure is applied isotropically and a pulsed magnetic field can be used, so the characteristics are higher than the die press method. This method is suitable for mass production because it can automate the process of rubber mold filling, pulse magnetic field application, compression molding, and demagnetization continuously.
Because it is a floating die method, it does not require a precise die set like a die press machine, and does not require a coil or magnetic circuit for an electromagnet. A fraction of the press is enough. Because of its small size, it can be sealed in a glove box type atmosphere. Since a large pressure can be applied, a robust green compact can be obtained without using a binder.
However, the fine powder of this magnet is a crushed intermetallic alloy lump, and it is not a uniform spherical powder, but has a fracture surface of various shapes, and when a large force is applied, whether it is CIP or RIP In addition, it was difficult to remove the disorder of orientation due to friction between powders. Moreover, since a rubber mold is used, it takes a lot of time to take out the green compact, and it is difficult to automate the process up to the sintering furnace conveyance.

[MIM]
MIM (Metal Injection Molding) is an injection molding process in which a kneaded mixture consisting of alloy powder and a large amount of binder (40-50% by volume) is heated to reduce its viscosity. Thus, the molded body is obtained, put into a furnace, and the binder removal treatment is performed while gradually raising the temperature. In the case of a magnetic anisotropic magnet, a static magnetic field is applied in advance from outside the mold. A method using a paraffin wax as a binder (Japanese Patent Laid-Open No. 64-28302) and a method using agar or methylcellulose (Japanese Patent No. 3086333) are known. Although net shape properties have been realized, the reported magnetic properties are quite low. Since a binder removal process is required for a long time in a low temperature range where the binder evaporates and the binder component does not react with the rare earth element, it takes time and the production efficiency is very poor.
The MIM method is a filling method by high-pressure injection, and there is no compression process. Since a large amount of binder is used, the characteristics deteriorate due to the influence of residual carbon and the like. Although it is excellent from the viewpoint of net shape, its magnetic properties are low.

[Details of pressing process in a magnetic field]
Throughout its long history, the die press method has been automated for efficient work. The process is roughly as follows.
-Fine powder is fed into the mold through the feeder.
-Lower the upper punch to seal the cavity.
・ A magnetic field is applied.
・ Pressurize with upper and lower punches while applying a magnetic field.
・ Demagnetize the compact by applying a reverse magnetic field or an alternating magnetic field.
・ The upper punch goes up.
・ The lower punch goes up (or the die goes down), and the green compact is pushed out onto the mold.
・ The robot arm carries the green compact to the conveyor.
・ Green compact is collected in one place.
・ Arranged on the sintering platen.
At this time, they are arranged at intervals in order to avoid collision and welding. Depending on the working conditions, the green compact may be stored for several days.
A mold press used in powder metallurgy is a precision machine. With a single (single) picking press, it is relatively easy to align punches and dies, but with multiple picking it is complicated. Magnets are required to have various shapes and dimensions, such as discs, rectangles, perforated discs, and bows, and each time a complicated mold replacement operation is required.

[Purpose and effect of compression molding in a magnetic field]
Regarding the role of compression molding, for example, "Rare-earth Iron Permanent Magnet" edited JMDCoey, CLARENDON PRESS, OXFORD, 1996, pp340-341 states "The pressing load is sufficient to make compacts having enough strength to be handled but without significant misorientation of the crystallites. (The applied pressure is sufficient to make a compact with sufficient strength for handling without causing any significant disturbance in the particle arrangement).
Also in J. Ormerod "Powder Metallurgy of rare earth permanent magnets" Powder Metallurgy 1989, Vol.32, No.4, p247, `` The pressing pressure should be sufficient to give the powder compact enough mechanical strength to withstand handling, but not high enough to cause particle misorientation. (The applied pressure is sufficient to give the compact a sufficient mechanical strength to withstand handling, but it must not be so high as to disturb the orientation of the particles).
In any document, it is recognized that it is necessary to compress strongly in order to give the green compact sufficient strength for handling while recognizing that the orientation is disturbed if pressurized with a large pressure. Yes.

[Problems specific to rare earth magnets]
Rare earth magnets contain about 30 weight percent of chemically active and easily oxidized rare earth elements. In the rare earth sintered magnet manufacturing process, there is a process for handling fine powder containing a large amount of chemically active rare earth elements and having an average particle size of about 3 microns.
Since it is necessary to orient each fine powder in a certain direction in a magnetic field, it is not possible to use means for improving the fluidity of the powder by granulating in advance, as used in general powder metallurgy. Since the fine powder is bulky and each powder has the properties of a magnet, even if the powder is supplied into the mold cavity, a bridge is formed and uniform filling is difficult.

[To raise the orientation]
In order to enhance the orientation of the fine powder during molding, a method of adding a lubricant has been proposed (Patent No. 3345947, Japanese Patent Laid-Open No. 8-167515, etc.). The lubricant has the effect of reducing the friction of the fine powder, and improves the degree of orientation when compressed while applying a magnetic field. However, if a large amount of lubricant is added for the purpose of obtaining a sufficient lubricating effect, it takes a long time for degreasing.
Certain liquid lubricants (for example, JP 2000-306753 A) are excellent in volatility and hardly remain in the sintered body. However, if a large amount of a lubricant is added for the purpose of improving the orientation, the green compact strength after the die press becomes weak, which causes a handling problem.
In the die press machine, a static magnetic field is applied by an electromagnet. The static magnetic field generated by the electromagnet remains at most about 10 to 15 Oe (1 to 1.5 T) due to the saturation of the magnetic flux caused by the iron core. When pressure is applied with a magnetic field applied, the frictional force between the powders becomes larger, the powders rotate, and the orientation is disturbed.
An alignment method using a pulsed magnetic field has been proposed (Japanese Patent No. 3307418). In the pulsed magnetic field, a magnetic field of 1.5 to 5.5 Tesla can be applied, and the effect of improving Br (residual magnetic flux density) has been confirmed. However, when a pulse magnetic field is applied in the mold press as in the present invention, eddy current loss and hysteresis loss occur each time the magnetic field is applied, and the mold generates heat. In addition, a momentary impact is applied to the metal mold, which shortens the life of the precision press and is not practical.

[To increase the green strength]
In order to improve the workability of the mold press method, methods such as adding a binder and a lubricant and wet molding have been proposed, but all of them are premised on compressing with a strong pressure. It is strongly confined inside the green compact and is not easily removed in the degreasing process prior to sintering. Degreasing may be carried out completely by heating at a low temperature for a long time, but the productivity is significantly reduced. If the component is left overheated at a high temperature, impurities such as carbon react with the constituent elements to deteriorate the characteristics and deteriorate the corrosion resistance.

[Wet molding method]
In order to achieve high orientation while preventing fine powder oxidation, a method of wet compression molding of a mixture of mineral oil / synthetic oil and fine powder in a magnetic field has been proposed (Patent No. 2859517, etc.). Powders finely pulverized by a jet mill are accumulated in mineral oil or synthetic oil, mixed, and then injected into a mold cavity and pressurized and filled. Wet molding is an application of Sr ferrite magnet manufacturing technology, but ferrite magnets use water, whereas rare earth magnets cannot use water, and use solvents and oils. However, the oil contains many components that become impurities such as carbon and is difficult to be removed at the sintering stage. Oils that evaporate easily and do not remain have been studied, but it is difficult to remove the carbon trapped in the compacted green compact. An operation of degreasing at a temperature at which the oil evaporates and does not react with the rare earth is necessary, but for that purpose, it must be kept at a relatively low temperature for a long time, and the mass production efficiency is remarkably deteriorated. If the degreasing is not sufficiently performed, it easily reacts with a rare earth element at a high temperature, thereby deteriorating the magnetic properties and deteriorating the corrosion resistance.

[Anoxic process]
In the mold press method, fine powder is exposed to the atmosphere. There is a proposal that, after producing a fine powder, the process from pressing in a magnetic field to carrying it into a sintering furnace is carried out in an inert gas atmosphere (JP-A-6-108104). However, in practice, it is indispensable to clean the fine powder scattered around the mold and change the mold frequently. If the scattered fine powder is left as it is, it is very dangerous when opening. Magnet fine powder is bulky and easy to make a bridge, so the quantitative supply is not successful, and it is necessary to periodically measure the weight of the green compact and feed it back. It is not possible with rare earth magnets to form a strong green compact by molding using a large amount of binder and high pressure as in a general sintered product. Therefore, the green compact is fragile and easily broken. However, since the die press is large, it cannot be operated with human hands inserted like a glove box. That is, the idea of placing the entire process including the mold press machine in an inert atmosphere is not realistic.

[Demagnetization]
The green compact after the die press is conveyed and arranged on the sintering platen. The green compact pressed in the magnetic field is an assembly of small magnets, and the green compact also has the properties of a magnet. Therefore, it collides with the suction repulsive force between the green compacts, and chipping and cracking occur. Therefore, a method of previously demagnetizing the green compact is employed. Actually, it is performed by applying a reverse magnetic field or an alternating attenuation magnetic field in the most compressed state in the die press. Since the particles cannot move in the compressed state, the orientation of the particles is not disturbed even if a reverse magnetic field or an alternating magnetic field is applied.

[Reason for not using fine powder]
No matter how small the clearance of the die punch is, it is impossible to confine the fine powder of 3 μm, and every time the fine powder is compressed, the fine powder ejected will fly around the mold. They have a risk of fire and explosion. It can be collected with an automatic dust collector, but it needs regular cleaning.
The actual powder particle size of the RFeB sintered magnet is such that D _50, which is the median value of the particle size measured by a laser-type powder particle size distribution measuring device, is about ₅ to 10 μm. It is known that the measured value of D ₅₀ is close to the actual value measured by a microscope. The single domain particle diameter of the R ₂ Fe ₁₄ B intermetallic compound is even smaller (0.2 to 0.5 μm). Accordingly, even in the case of a sintered magnet, a higher coercive force can be expected with a smaller powder particle size. Actually, however, as is apparent from FIG. 3 of JP-A-59-163802, the coercive force rapidly decreases as the particle diameter decreases. This indicates that oxidation is inevitable in the conventional process for handling fine powder.
RFeB alloy fine powder containing a chemically active rare earth element is very easily oxidized and may ignite if left in the atmosphere. The smaller the powder particle size, the greater the risk of ignition. Even if it does not ignite, it oxidizes easily and exists as a non-magnetic oxide in the sintered magnet, which causes deterioration of characteristics. However, in the conventional method, exposure to the atmosphere is inevitable in the molding process and the process of bringing the compact into the sintering furnace.
The actual finely pulverized powder has a D ₅₀ particle size of about 3 to 5 μm, and if it is finer than this, oxidation easily occurs even if it is a molded body. There is an attempt to add oil or liquid lubricant to fine powder in advance to have a synergistic effect of preventing oxidation, but adding a large amount of lubricant etc. will weaken the green compact strength and leave carbon etc. To reduce the magnetic properties. That is, fine powders of 3 μm or less cannot be practically handled by the conventional mold press method.
A method has been proposed in which the pulverization / molding / sintering furnace carrying-in process is performed in an inert gas atmosphere such as nitrogen (JP-A-6-108104). However, in the conventional mold press system, the press machine must be large from the viewpoint of mass productivity, and it is necessary to clean the excess fine powder or replace the mold for each product number. It is impractical to cover the entire die press with an inert atmosphere.

[Limit of die press method]
From the viewpoint of net shape and yield, the die press method is excellent. Despite sacrificing magnetic properties, the die press method is considered the most mass-productive because of its net shape. A large press is used from the viewpoint of efficiency, but the size and shape of the press are limited due to the magnetic field conditions of the electromagnet. Pulse magnetic field cannot be used. Lubricants are necessary to aim for high orientation, but depending on the lubricant, the properties may deteriorate due to residual carbon, and the green compact strength will decrease, resulting in poor yield. Oriented particles are disturbed due to unidirectional pressing. Further, the orientation is disturbed in the demagnetization process. There are various restrictions on installing a large press in the atmosphere to achieve full automation.
RFeB alloy is composed of intermetallic compounds, has almost no ductility and malleability, and is hard and brittle. Therefore, the mold is worn and the life is shortened. Also, since granulated powder cannot be used, it is necessary to use fine powder with poor fluidity as it is, and it is necessary to apply a magnetic field from the outside during compression molding, so the press cycle must inevitably be slow. I don't get it. Nevertheless, in order to make the pressing process efficient, a method of compressing and molding a large number of presses at a time is common. However, since it is necessary to give a magnetic field of a certain strength with an electromagnet, the press machine can be made large indefinitely for reasons such as the uniformity of the magnetic field in the mold, the size of the power supply, and the effect of the magnetic field on the surrounding work environment. It cannot be done and is limited to a few hundred tons.

[Object of the present invention]
Initially, large cast ingots were being crushed. In the casting method, since the cooling rate is slow, α-iron is likely to precipitate locally, which causes a significant decrease in coercive force. In order to suppress the precipitation of α-iron, a larger amount of rare earth element must be added than the composition ratio of R ₂ Fe ₁₄ B, and the rare earth element lowers the saturation magnetization of the alloy and lowers the maximum energy product. In the rapid cooling method (strip casting method), precipitation of α-iron can be suppressed and the amount of rare earth can be reduced, so that a high energy product can be obtained (JP 2002-208509 A, etc.). However, even in this case, as long as the conventional molding method is employed, it is not possible to suppress a decrease in the degree of orientation during molding.
The process for handling powder will be described in detail. Coarse pulverization is performed using the hydrogen storage properties of this alloy. If an alloy such as an ingot is left in hydrogen, microcracks enter the alloy. The particle size is then trimmed by mechanical grinding. At this stage, the size is several tens to several hundreds μm. Since it is easy to ignite while storing hydrogen, heat treatment for dehydrogenation may be performed.
A ball mill, an attritor, a vibration mill, a jet mill, etc. are used for fine grinding. Among these, jet mills that can remove ultrafine powder and obtain fine powder with a sharp particle size distribution are widely used. In a jet mill, grinding is performed in a high-speed stream of inert nitrogen gas. In order to increase the stability of the metal powder, a small amount of oxygen (atmosphere) is intentionally mixed in the stream to form an oxide film on the particle surface. May form. Such a powder is relatively stable. The ultrafine powder that has become too fine is conveyed to a high-speed air stream and discharged outside the crusher (dust collector).
There was a time when ball milling or attritor grinding in an organic solvent was carried out to avoid oxidation during fine grinding. Ultra fine powder is mixed in, or the carbon component in the organic solvent remains in the sintered magnet and deteriorates the characteristics and corrosion resistance. At present, jet mill grinding is the mainstream. Since jet mill pulverization produces fine powder with a sharp particle size distribution, the jet mill pulverization method is superior in terms of magnetic properties.
The above description mainly focused on the RFeB magnet, but the same situation applies to the other rare earth magnet, samarium-cobalt magnet (1-5 type, 2-17 type). The device is also applicable to samarium-cobalt magnets.
In any of the die pressing method, CIP, and RIP methods, the purpose is to make a strong green compact by compressing strongly. One is to facilitate handling and the other is to obtain a sufficient sintered density. However, strong compression causes a disorder of orientation.
The present invention provides a completely new method for producing a magnetically anisotropic rare earth sintered magnet that does not include a conventional mold pressing process including various problems and contradictions.
The initial RFeB sintered magnet product has a magnetic property level of maximum energy product ((BH) max) = 35MGOe for high energy materials and coercive force (iHc) = 12kOe class, (BH) max = 30MGOe for high coercivity materials The coercive force was 17 kOe class. High-energy materials have been mainly used for MRI devices and speakers that are relatively unaffected by the environment, such as temperature, and high-coercivity materials have been mainly used for motors that receive temperature rise and reverse magnetic fields from coils. An object of the present invention is to provide an RFeB sintered magnet having a high coercive force while maintaining a high maximum energy product.

[To obtain high coercivity]
RFeB magnets and SmCo ₅ magnets are single-domain fine-particle magnets, and the maximum coercive force can be obtained at the size of single-domain fine particles. In the case of an NdFeB magnet, the size of the single domain particle diameter is about 0.2 to 0.3 μm. Only when these fine particles are oriented by a magnetic field and sintered without causing grain growth, a dense and uniform microstructure is formed. However, in the current mass production method, particularly the method using a die press, the size of the crystal grain size of the obtained sintered magnet is about 5 to 10 μm, which is an order of magnitude larger than the ideal size. The particle size of the powder used at this time is also about ₅ to 10 μm in D50. This is considered to be due to restrictions on the process of the die press. In other words, in the current manufacturing process, exposure to the atmosphere is inevitable in the steps from the die press to the sintering furnace loading. When the mold press is compressed, fine powder pops out from the mold clearance, and the fine powder is attracted to the magnetic field every time a magnetic field is applied to the mold press and flies around the die set. In order to avoid such a situation, when trying to make a strong green compact by adding a large amount of binder in advance and pressing strongly, the binder component strongly contained in the green compact reacts with the magnet component during sintering. As a result, the characteristics deteriorate, or the powder orientation is disturbed by strong pressure.
Therefore, it is impossible to obtain an ideal single domain fine particle sintered magnet by the conventional die pressing method.

The first aspect of the method for producing a magnetic anisotropic rare earth sintered magnet according to the present invention, which has been made to solve the above problems,
A method of manufacturing a magnetic anisotropy rare earth sintered magnet to perform alignment and sintered without applying a pressure to the alloy fine powder after filling the filled container, filled container provided with a deaerating pores or grooves In addition, a step of filling an alloy fine powder of an NdFeB magnet having an average particle diameter D50 of 0.5 μm or more and 5 μm or less and not containing Dy and Tb as measured by a laser-type powder particle size distribution analyzer, and filling the filling container A step of orienting the alloy fine powder in a magnetic field in a state and a step of sintering the alloy fine powder in a state of being filled in the filling container, and performing each of the above steps in an oxygen-free or inert gas atmosphere. And
Or a method of manufacturing a magnetic anisotropy rare earth sintered magnet to perform alignment and sintered without applying a pressure to the alloy fine powder after filling the filled container, provided with a degassing pores or grooves Fill the filling container with fine NdFeB magnet alloy powder containing Dy and / or Tb with an average particle size D50 of 0.5 μm or more and 5 μm or less and 6% by weight or less as measured by a laser type powder particle size distribution analyzer. And a step of orienting the alloy fine powder in a magnetic field in a state in which the filling container is filled, and a step of sintering the alloy fine powder in a state of being filled in the filling container. It is characterized by being performed in an inert gas atmosphere.

The second aspect of the method for producing a magnetic anisotropic rare earth sintered magnet according to the present invention is:
A method of manufacturing a magnetic anisotropy rare earth sintered magnet to perform alignment and sintered without applying a pressure to the alloy fine powder after filling the filled container, filled container provided with a deaerating pores or grooves Filling the alloy fine powder of the NdFeB magnet not containing Dy and Tb in the step, orienting the alloy fine powder in a magnetic field in the state filled in the filled container, and the alloy fine powder in the state filled in the filled container. A step of pre-sintering until shape retention, and a step of removing the pre-sintered body from the filled container and then sintering, and performing each of the above steps in an oxygen-free or inert gas atmosphere. To do.
Or a method of manufacturing a magnetic anisotropy rare earth sintered magnet to perform alignment and sintered without applying a pressure to the alloy fine powder after filling the filled container, provided with a degassing pores or grooves A step of filling a filling container with a fine alloy powder of NdFeB magnet containing 6% by weight or less of Dy and / or Tb; a step of orienting the fine alloy powder in a magnetic field in a state filled with the filling container; and the filling container And pre-sintering the alloy fine powder until it retains its shape in a state of being filled, and a step of taking out the pre-sintered body from the filling container and then sintering it. It is characterized by being performed in an active gas atmosphere.

  In the manufacturing method of the second aspect, it is desirable that the pre-sintering temperature is between 500 ° C. and 10 ° C. lower than the sintering temperature. Moreover, a part or all of a filling container can be replaced | exchanged after preliminary sintering.

  In the method for producing a magnetic anisotropic rare earth sintered magnet of the present invention, filling from fine powder to sintering can be performed in an oxygen-free or inert gas atmosphere.

  In the method for producing a magnetic anisotropic rare earth sintered magnet of the present invention, the magnetic anisotropic rare earth sintered magnet may be a rare earth iron boron magnet or a rare earth cobalt magnet.

  In the method for producing a magnetic anisotropic rare earth sintered magnet according to the present invention, the filling container can be single or multiple. Part or all of the filling container can be made of a non-magnetic material. Alternatively, a part of the filling container can be made of a ferromagnetic material. This ferromagnetic material can be one in which a ferromagnetic material is disposed at both ends of the magnetic pole of the filling container. Moreover, it is desirable that the fine powder in the filled container after orientation in a magnetic field is uniformly filled. Furthermore, the filling container can be a net shape.

In the method for producing a magnetic anisotropic rare earth sintered magnet of the present invention, the average particle size of the alloy fine powder can be 5 μm or less. The average particle diameter can be 2 μm or less, and can be 1 μm or less. Here, the median value (D ₅₀ ) of particle diameters measured by a laser type powder particle size distribution measuring device can be used as the average particle diameter.

  It is desirable to fill the filling container with fine powder with a filling density between 40% and 55% of the true density. Further, the fine powder can be forcibly filled into the filling container using a mechanical tapping method or an air tapping method.

  The magnetic field can be a pulsed magnetic field. The intensity of this pulse magnetic field is desirably 3 Tesla or higher. Further, the pulse magnetic field can be an alternating magnetic field of one cycle or more.

  An alloy obtained by the molten metal quenching method can be used for the fine powder.

  The filling container can be filled with fine powder mixed with a lubricant. This lubricant can be a liquid lubricant. As this liquid lubricant, one having a fatty acid ester or a depolymerized polymer as a main component can be used.

The first aspect of the apparatus for producing a magnetic anisotropic rare earth sintered magnet according to the present invention is:
a) a fine powder filling means for high-density filling a fine powder of finely pulverized alloy;
b) a magnetic field orientation means for orienting the fine powder in the magnetic field;
c) sintering means for sintering the fine powder in the filled container;
d) conveying means for conveying the filled container in the order of fine powder supply means, magnetic field orientation means, and sintering means;
e) a container containing fine powder filling means, magnetic field orientation means, sintering means, and conveying means;
f) atmosphere adjusting means for making the inside of the container an oxygen-free or inert gas atmosphere;
It is characterized by providing.

In the second aspect of the apparatus for producing a magnetic anisotropic rare earth sintered magnet according to the present invention,
a) a fine powder filling means for high-density filling a fine powder of finely pulverized alloy;
b) a magnetic field orientation means for orienting the fine powder in the magnetic field;
c) pre-sintering means for pre-sintering the fine powder in the filled container until the shape is retained;
d) a sintering means for sintering the pre-sintered fine powder;
e) conveying means for conveying the filled container in the order of fine powder supply means, magnetic field orientation means, pre-sintering means, sintering means;
f) a container containing fine powder filling means, magnetic field orientation means, pre-sintering means, sintering means and conveying means;
g) atmosphere adjusting means for making the inside of the container an oxygen-free or inert gas atmosphere;
It is characterized by providing.

  The apparatus for producing a magnetic anisotropic rare earth sintered magnet according to the present invention can include an external container for housing the container.

Embodiments and effects of the invention

  According to the present invention, in the method for producing a magnetic anisotropic rare earth sintered magnet, a fine container is filled with a fine powder in a predetermined size and shape, and the powder is oriented by applying a magnetic field from the outside. After that, it is sintered as it is.

  The production method of the present invention is applied to the production of RCo (rare earth cobalt) magnets and RFeB (rare earth / iron / boron magnets).

  According to the present invention, after the fine powder is confined in the filling container, a magnetic field is applied and the process proceeds to the sintering process. Fine powder does not fly, and even rare earth magnet fine powder can be handled safely.

  According to the present invention, all the processes from filling of fine powder, application of a magnetic field, and carrying into a sintering furnace are performed in an oxygen-free or inert gas atmosphere. Rare earth magnets are affected by impurities such as oxygen. Whether it is an RFeB magnet or a 1-5 type SmCo magnet, it is necessary to select a composition on the rare earth-rich side with respect to its stoichiometric composition in anticipation of the amount of rare earth to be oxidized in advance. However, the nonmagnetic phase increases correspondingly, and the characteristics deteriorate. When the process according to the present invention is applied to rare earth magnets such as NdFeB magnets and SmCo magnets, there is no opportunity to come into contact with oxygen in the atmosphere in the form of fine powder, so oxygen in the sintered body can be reduced. In this case, since it is not necessary to anticipate the amount of rare earth to be oxidized in advance, the amount of rare earth (Nd, Sm) can be reduced to the limit, and high magnetic characteristics can be obtained. At the same time, since there is no compression process, high orientation is maintained and a high Br / high energy product is realized.

  The filling container in the present invention is provided with pores or grooves for deaeration. Even when finely pulverized using an inert gas such as nitrogen, adsorbed gas components such as hydrogen, nitrogen and moisture are always present in the fine powder. They evaporate when the temperature rises during sintering, but when the filled container is sealed, the reactivity increases at high temperatures and reacts with the magnet components. Any number of pores or grooves for degassing may be provided in one filled container, but it is preferable to have a plurality of pores or grooves for enhancing the degassing effect.

  In the die press method, it is impossible to contain 3 μm fine powder, no matter how small the clearance between the die and the punch is. Japanese Patent Laid-Open No. 6-108104 proposes a method for consistently processing the processes from pulverization, molding, and carrying into a sintering furnace in an inert gas atmosphere such as nitrogen, but the fine powder discharged from the mold press is closed. It is extremely dangerous to enclose it in an open space. The actual mold press must be large in terms of mass production efficiency, and it is necessary to replace the mold for each product number, and the discharged fine powder must be cleaned each time. Risk of fire and explosion if exposed to air with fine powder floating. Therefore, it is not practical to contain the entire large press in the atmosphere.

  It is possible to presinter as it is after filling fine powder into a pre-filled container according to the intended size and shape, orienting the powder by applying a magnetic field from the outside.

  The magnet alloy fine powder is filled in the filling container at a high density. The degree of high-density filling is higher than the degree of filling in the conventional mold press method, CIP method, and RIP method, and is lower than the degree of filling of the compression molded body in the conventional die press method, CIP method, and RIP method. In the conventional method, a strong green compact strength is required for green compact handling. However, since there is no green compact handling step in the present invention, there is no need to compress.

  The powder filled in the filling container at a high density may be of such a degree that the container is uniformly filled so that a sufficient density can be obtained in the sintered body. Specifically, it is sufficient that the powder is not biased after the pulse magnetic field orientation. Such a state can be confirmed by the presence or absence of fine pores in the cross section of the sintered body after sintering, and a state in which almost no pores are present is preferable.

The reason why the pores or grooves for deaeration are provided in a part of the filling container used in the present invention is to prevent the gas component evaporating from the powder during the sintering heating from staying in the filling container. Since the raw material powder of the present invention has an intermetallic compound as a main phase, adsorbed gases such as hydrogen and moisture cannot be avoided. If the container is sealed, the gas component may expand. In the present invention, it is preferable to add a liquid lubricant in order to enhance the orientation. The liquid lubricant component may react with the magnet component at high temperatures. The reason why the degassing pores or grooves are provided in a part of the filling container used in the present invention is to prevent these gas components from remaining in the container.
The size of the pores or grooves is desirably small enough that the powder in the container does not jump out of the container due to an impact such as a magnetic field pulse.

The rare earth magnet of the present invention is preferably an RFeB magnet.
The RFeB magnet is composed of 2 to 30% R (R is at least one kind of rare earth elements including Y), B2 to 28%, and the balance substantially Fe in atomic percent.
In order to improve the temperature characteristics and corrosion resistance of the magnet and to improve the stability of the fine powder, less than 50% of Fe may be replaced with Co.
To improve coercive force, sinterability and other manufacturability, part of Fe is Ti, Ni, Bi, V, Nb, Ta, Cr, Mo, W, Mn, Al, Sb, Ge, Sn , Zr, Hr, Ga, etc. These additive elements may be added in combination, but in any case, the total amount is preferably 6 atomic% or less. V and Mo are particularly preferable.
Furthermore, the sum of R1 (one or more of Dy, Tb, Gd, Ho, Er, Tm, Yb) and R2 (one or more rare earth elements including Y other than R1 with a total of Nd / Pr of 80% or more) When R is R, a composition comprising R1 12 to 20%, B 4 to 20% and the balance Fe is a preferable composition range in which high squareness of the demagnetization curve and high coercive force can be obtained.
In the case of an RFeB magnet, sintering is performed between 950-1200 ° C.

The rare earth magnet of the present invention can also be applied to a cobalt magnet (RCo magnet).
Among RCo magnets, the composition range of 1-5 type magnets is RTx (R is Sm or Sm and one or a combination of two or more of La, Ce, Pr, Nd, Y, Gd, and T is Co or Co. One or a combination of two or more of Mn, Fe, Cu, and Ni, represented by 3.6 <x <7.5), and its sintering temperature is 1050-1200 ° C.
The composition range of type 2-17 RCo magnet is R (where R is Sm or two or more rare earth elements containing 50% by weight or more of Sm) 20-30% by weight, Fe 10-45% by weight, Cu 1-10 % By weight, one or more of Zr, Nb, Hf, V 0.5-5% by weight, balance Co and inevitable impurities, sintering temperature is 1050-1250 ° C.
In both the 1-5 type and the 2-17 type, the coercive force can be increased by performing a heat treatment at 900 ° C. or lower during sintering.

  In order to obtain a magnet having high magnetic properties, it is desirable to increase the coercive force by increasing the sintering density and sintering without causing grain growth as described above. The optimum sintering temperature can be defined as a sintering temperature at which the sintering density can be sufficiently increased and no grain growth occurs. The optimum sintering temperature varies depending on the magnet composition, powder particle size, sintering time, and the like.

  In the present invention, pre-sintering is performed until a part of the powder is bonded and the shape can be preserved. For this purpose, the pre-sintering temperature is preferably 500 ° C. or higher. On the other hand, in consideration of the life of the container, and in order to prevent the product from being packed and fired in the container and the container from being baked, the pre-sintering temperature is preferably 10 ° C. or lower than the optimum sintering temperature. This is because, at the optimum sintering temperature, the reactivity of the filled powder is high, and the baking onto the container tends to be strong.

RFeB magnets and RCo ₅ type magnets contain more rare earth elements than the equilibrium composition of intermetallic compounds (R ₂ Fe ₁₄ B and RCo ₅ ). They promote liquid phase sintering through a low melting eutectic composition with other constituent elements. That is, powder binding occurs due to the presence of the liquid phase, and then proceeds to the contraction stage. If pre-sintering is performed in a filled container, the target shape is preserved. The pre-sintered body can be taken out from the filling container and subjected to original sintering using another sintering base plate or the like.

  At the stage where the pre-sintering is completed, there is no possibility that the fine powder is oxidized, so that it can be taken out into the atmosphere. At this time, it is also possible to transfer the pre-sintered body from the filled container to a sintering base plate or the like and perform sintering. When a cylindrical or ring-shaped filling container is filled with powder and sintered, the inner diameter portion contracts and cracks occur. In such a case, after preliminary sintering, it is necessary to transfer from the filled container to the sintered container. Moreover, it is more preferable to transfer from the viewpoint of the life of the filled container.

The simplest filling container is a “single-piece” which obtains one magnet from one container. However, considering productivity, it is efficient to use a “multi-piece” filling container in which a plurality of magnets are obtained from one filling container.
In the conventional mold press method, a large number of pieces are adopted from the viewpoint of production efficiency, but the press machine must be large in terms of mold strength. In the multi-cavity manufacturing according to the present invention, it is only necessary to have a thin spacer between adjacent ones.

  A magnetic field is applied from the outside in order to orient the fine powder filled in the filling container. If the entire filling container is non-magnetic, it is preferable because the external magnetic field works effectively on the magnetic powder that is a magnetic substance.

  After applying the external magnetic field, the powder in the filling container is in a movable state. The orientation of the powder may be disturbed by the magnetic moment of each magnetized powder or the magnetic field formed by the entire powder in the filled container. Dispersion of powder after application of a magnetic field can be avoided by disposing ferromagnetic materials at both ends or part of side surfaces of the filling container to change the flow of magnetic flux.

  When a non-magnetic material is used on the side surface of the filling container, it is effective to dispose a ferromagnetic material at both ends of the filling container in order to prevent disorder of the orientation of the powder after application of a magnetic field. The demagnetizing field formed by the whole powder in the filling container is reduced, and the influence of the magnetic field on the powder can be reduced by changing the flow of magnetic flux.

  The powder in the filling container is sintered while preserving the shape of the filling container. Therefore, if the shrinkage rate by sintering is calculated | required previously, the sintered compact of the target dimension shape can be obtained by calculating backward.

The crystal grain size of an actual neodymium magnet sintered body that is commercially available is ₅ to 10 μm, and the particle size of the fine powder before sintering is 3 to 5 μm at D ₅₀ . Here, D ₅₀ represents the median value of the particle size distribution measured with a laser particle size distribution measuring instrument or the like. The particle size of fine particles having a measured value of 3 μm by an air permeation type particle size distribution analyzer (Fischer's Sub-Seeve Sizer, FSSS) that has been used once is displayed as 4 to ₅ μm in D50. The FSSS method is not suitable for the measurement of rare earth alloy powders that are highly cohesive and chemically active.
The rare-earth magnet alloy composition comprising 30 percent or more rare earth elements by weight, in the conventional die-pressing method has been difficult to D ₅₀ of handle 5 [mu] m (3 [mu] m in FSSS) following fine powder.
In the present invention, the fine powder is filled in a filled container in an inert atmosphere such as oxygen-free or nitrogen, oriented by a magnetic field, and carried into a sintering furnace, so there is no step of touching air, even if it is fine powder. However, there is no danger in handling.

The rare-earth magnet alloy composition containing a rare earth element 30 weight percent or more, in the conventional die-pressing method was impossible to handle a fine powder D ₅₀ The following 2 [mu] m.
The RFeB magnet is a single-domain fine particle type, and the size of the single-domain particle is about 0.2 to 0.3 microns. However, the crystal grain size of the actual RFeB sintered magnet is about 5 to 10 μm, and the particle size of the fine powder before sintering is about 4 to ₅ μm at D ₅₀ . A large coercive force can be obtained if the crystal particle size is the size of a single domain particle. But to achieve that, smaller powders must be used. When handling RFeB magnet alloy fine powder containing a large amount of chemically active rare earth elements, the conventional die press, manufacturing process by CIP and RIP avoids the influence of oxygen and moisture contained in the atmosphere. Impossible. If RFeB alloy powder with a particle size as small as 2 μm is exposed to the atmosphere, the possibility of ignition and explosion increases, and stable production cannot be achieved. If it is not necessary to ignite, the fine powder has a large surface area, so the amount of oxygen increases and the magnetic properties deteriorate. In order to avoid oxidation, if a chemical substance such as that used in binders, lubricants, and wet presses is used in combination, the chemical component reacts with the powder component because of the large surface area of the fine powder. A remarkably long time is required in the degreasing process, and the productivity is deteriorated and the magnetic properties are deteriorated. Since these effects cannot be avoided by conventional methods, such fine powders cannot be handled.
When a sintered magnet is obtained using an RFeB alloy powder having a D ₅₀ value of 2 μm or less according to the present invention, a neodymium sintered magnet having a high orientation, a high energy product, and a high coercive force is obtained.

For example, in the commercially available material class with the highest coercive force ((BH) max = 32MGOe (255kJ / m3), iHc = 30kOe (2387kA / m)), heavy rare earth elements such as Dy and Tb of about 10% by weight It is known that Nd is substituted for Nd. Addition of Dy or Tb has the effect of increasing the coercive force of the magnet by increasing the anisotropic energy of the R ₂ Fe ₁₄ B intermetallic compound. The crustal abundance of heavy rare earth elements such as Dy and Tb is small compared to Nd, the price is expensive, and the saturation magnetization decreases when a large amount of heavy rare earth elements is added. Therefore, demand for electric vehicles, hybrid cars, home appliances and industrial motors cannot be covered by Dy and Tb.
According to the present invention, a high coercive force equal to or higher than that of the conventional product can be obtained with little or no amount of Dy or Tb, which is rare and expensive, even if it is used.

  One of the features of the present invention is that there is no need to perform pressure molding with a large pressure as in a die press, CIP, or RIP. The powder oriented in the filling container is sintered while maintaining a high orientation without applying a force that disturbs the orientation when further pressure is applied. A high degree of orientation achieves a high residual magnetic flux density (Br) and a high maximum energy product ((BH) max).

In the conventional method, there is no means for handling rare earth-containing magnet powder having a D ₅₀ value of 1 μm or less. Japanese Patent Application Laid-Open No. 6-108104 proposes a rare earth magnet manufacturing apparatus for processing all of the space between the pulverizing means, the forming means and the sintering means in an inert atmosphere.
According to this method, the fine powder is formed by the die press machine, and the green compact reaches the sintering furnace inlet via the conveyance path. However, the mold press method cannot avoid the opportunity for the fine powder to be exposed to the atmosphere, such as cleaning of the fine powder leaking from the mold clearance or changing the mold when changing the product number. In the case of a method using a conventional mold press, for example, as described in JP-A-2002-208509, fine powder having a particle size of 1 μm or less had to be removed.
According to the present invention, the process from preparation of fine powder to sintering can be processed in a complete oxygen-free or inert atmosphere, and the rare earth-containing magnet powder having a D ₅₀ value of 1 μm or less can be handled safely. Thus, a magnet having a high coercive force can be obtained.

The RFeB magnet is a single-domain fine particle type, and the single-domain particle diameter is about 0.2 to 0.3 μm. Therefore, the sintered body crystal grain diameter is preferably close to that. For this purpose, the powder particle size needs to be 0.5 μm or less. In the conventional method, there is no means for handling rare earth-containing magnet powder having a D ₅₀ value of 0.5 μm or less. According to the present invention, the process from preparation of fine powder to sintering can be processed in a complete oxygen-free or inert atmosphere, and the rare earth-containing magnet powder having a D ₅₀ value of 0.5 μm or less can be handled safely. Can do.

The magnet alloy powder is obtained by pulverizing a cast ingot obtained by melting a compounding composition in a melting furnace or a cast piece obtained by a rapid cooling method (strip casting method). In order to obtain a fine powder of several microns, generally, coarse pulverization and fine pulverization are often separated. Coarse pulverization includes a mechanical pulverization method and a hydrogen pulverization method (hydrogen pulverization method), and hydrogen pulverization method is excellent in productivity and is often used. There is also a method (reduction diffusion method) in which rare earth oxide, iron powder, and ferroboron powder are mixed and stirred and heated to directly obtain RFeB intermetallic powder. As a fine pulverization method, a method using a ball mill or an attritor, a jet mill pulverization method in which pulverization is performed using an air current such as nitrogen, and the like are common. In the present invention, a fine powder of several microns or less is used. However, the method for obtaining the fine powder is not limited, and methods other than those described above may be used.
However, if the powder is too small, it exhibits superparamagnetic (superpara) properties. Therefore, in order to avoid such ultrafine powder, a pulverization method with classification means is a preferable method.

The filling density of the powder in the filling container in the present invention is preferably between 40 percent and 55 percent with respect to the true density.
In the conventional method (die press method, CIP, RIP), a robust green compact is required for handling that leads to the subsequent process. For this reason, a stronger pressing force than that required to achieve a sintering density necessary for obtaining sufficient magnetic properties is required.
In other words, the green density in the conventional method has been obtained from the viewpoint of the green strength for handling, and in order to obtain the sintered density necessary for magnetic properties, It has been found that a small packing density is sufficient.
In the present invention, since there is no green compact handling step, it is not necessary to consider the green compact strength as in the conventional method.

For powder filling, it is preferable to use a mechanical tapping method or an air tapping method (Japanese Patent Laid-Open No. 2000-96104). Micron-sized magnet powder easily aggregates and forms a bridge when filling a container, making uniform filling difficult. If the mechanical tapping method or the air tapping method is used, the powder can be uniformly and uniformly filled in the container by applying periodic mechanical impact or air impact to the powder in the powder feeder.
In JP-A-2000-96104, a powder to which a binder or the like has been added in advance is filled into a mold by an air tapping method, the binder is solidified by a method such as heating, and the powder is bonded to obtain a molded body. A method of sintering is described. However, the present invention is not a method related to a magnet, there is no orientation by a magnetic field, and there is no idea of sintering (or pre-sintering) with a filled container. In the present invention, a binder for obtaining a powder molded body is not used, and handling is not necessary.

The external magnetic field generating source used for powder orientation is preferably a pulsed magnetic field. The pulsed magnetic field is applied by placing a filling container in the air core coil. The static magnetic field method using an electromagnet used in the die press method is 1.5 T (15 kOe) at most, while the pulse magnetic field method can give a high magnetic field strength. The magnitude of the pulse magnetic field in the present invention is preferably 3T or more, and more preferably 5T or more. The pulse magnetic field for orienting the powder is preferably a method in which an alternating decay waveform magnetic field is applied in advance, and then a direct current pulse magnetic field is applied, rather than a single direct current pulse.
Patent No. 3307418 gives a magnetic field of 15 to 50 kOe in the manufacture of RFeB magnets, and it has been confirmed that the magnetic properties are improved. However, the conventional die press method uses a pulse magnetic field in combination. When a pulse magnetic field is applied to the die press, eddy current loss and hysteresis loss occur in the die and cannot be used continuously. Moreover, since the impact force by the pulse magnetic field is applied to the mold, the mold may be damaged.
The magnetic field in the present invention needs to be a strong magnetic field, but may be any magnetic field as long as a strong magnetic field can be obtained by a superconducting coil in addition to the pulsed magnetic field.
The conventional method requires a demagnetization step after forming in a magnetic field. If not demagnetized, the green compacts collide with each other during handling, causing chipping or the like in the green compact. Demagnetization is performed by applying a reverse magnetic field or a damped alternating magnetic field, but the reverse magnetic field and the damped alternating magnetic field disturb the direction of the powder once oriented. According to the present invention, since the demagnetization step is not required, the orientation is not disturbed.

  Rare earth sintered magnets with excellent magnetic properties require a dense and homogeneous microstructure. In order to obtain such a sintered body, a strip casting method has been proposed as a method for obtaining a fine and dense alloy ingot (Japanese Patent No. 2665590). However, in Japanese Patent No. 2665590, the average crystal grain size of the strip cast slab is 3 to 20 μm. Since the sintered magnet of the present invention requires a smaller crystal grain size, the average crystal grain size of the strip cast alloy is preferably 3 μm or less, more preferably 1 μm or less.

  In the present invention, all the steps from taking out the fine powder to carrying it into the sintering furnace are performed in an oxygen-free or inert atmosphere. Fine powder placed in the hopper is filled into a filling container installed in an oxygen-free or inert gas atmosphere through high-density filling means such as mechanical tapping and air tapping, capped, and oriented in a magnetic field Move to the place where the means are provided. The filled container in which the powder is oriented by a magnetic field orientation means such as a pulsed magnetic field is conveyed to the sintering furnace entrance as it is.

Filling a filling container with a fine powder to which a liquid lubricant has been added in advance is a preferable method in order to facilitate orientation in a magnetic field and increase the degree of orientation.
In general, solid lubricants have low vapor pressure and high boiling point, while liquid lubricants have high vapor pressure and low boiling point. Considering that it is easy to spread over the whole fine powder and that it is easy to come off, a liquid lubricant is preferable.

It is known to use methyl caproate or methyl caprylate together with a saturated fatty acid as a liquid lubricant (Japanese Patent Laid-Open No. 2000-109903). However, when these lubricants are used in the mold press method, only a very small amount of 0.005 to 0.5% by weight can be used. These have good volatility and do not remain in the sintered body. However, when sintering green compacts that have been strongly compression-molded with a die press, the lubricant component trapped inside the green compacts It is difficult to remove the magnetic properties, and there is a risk that the lubricant component and the magnet component react at a high temperature to deteriorate the magnetic properties.
In the present invention, the powder in the filling container is not compressed, and the lubricant component is gasified and easily removed. Therefore, it is preferable that the amount of the liquid lubricant of the present invention is large. However, when it is too much, there is a possibility that high density filling is not possible. A preferable addition amount of the liquid lubricant is 0.5 to 1%.
The liquid lubricant of the present invention is only required to have lubricity and easily volatilize, such as methyl octylate, methyl decanoate, methyl caprylate, methyl laurate, methyl myristate, methyl palmitate, methyl stearate, etc. Can be used.

[Effect of the present invention]
The present invention has been found as a method for solving problems and contradictions of conventional methods in a method for producing a magnetically anisotropic sintered magnet of a rare earth magnet such as an RFeB magnet or an RCo magnet. That is, according to the present invention, there is no need for a large molding device such as a die press, and there is no need to make a robust green compact for handling, so there is no disturbance in orientation, and a net shape shape along the shape of the filled container The magnetically anisotropic sintered magnet is obtained. A strong pulse magnetic field can be applied by the air-core coil, and since there is no step of demagnetizing the green compact, a sintered body having a high orientation can be obtained. In addition, since chemically active fine powders containing rare earth elements can be processed without exposure to the atmosphere, powders with a small particle size can be handled, and rare earth magnets with high coercive force can be obtained without using Tb or Dy.

[Filling container]
The filling container is preferably made of a material that can withstand a high sintering temperature (˜1100 ° C.). Part or all of the filled container can be transferred to another container in a state in which the particles are bonded and retained in shape (pre-sintering) in the process of raising the temperature of the filled powder in advance. Since the pre-sintering temperature is desirably between 500 ° C. and a temperature 10 ° C. lower than the sintering temperature, the filling container used at the time of pre-sintering may be made of a material that can withstand this temperature.
As the material of the filling container, iron, iron alloy, stainless steel, permalloy, heat-resistant alloy, ceramics such as ferrite and alumina, and the like are used. In order to prevent the rearrangement of particles after applying a pulse magnetic field, iron-based magnetic materials can be used at both ends and side surfaces of the filling container. In the case where the preliminary sintering and the sintering process are performed separately, the heat-resistant alloy and oxide used conventionally can be used for the base plate used in the sintering process.

[Inner wall coating]
In order to avoid fusion between the sintered body and the container during sintering, it is also effective to apply a release agent such as BN (boron nitride) to the inside of the filling container in advance. By applying BN to the inner wall of the container, or spraying a high melting point metal such as Mo or W by spraying to form these films on the inner wall, the sintered body adheres to the interior of the container during sintering. Preventing the sintered body from being deformed or cracked due to the adhesion is effective in producing a high-quality sintered magnet.

[Filling method]
In the present invention, the filling method is important. The permanent magnet alloy fine powder that cannot be granulated is easily agglomerated because it has the properties of a magnet, and it is difficult to form a bridge and quantitatively fill the container. For forced filling used in the present invention, for example, a mechanical tapping method or an air tapping method (Japanese Patent Laid-Open No. 2000-96104) by the present inventor is used. High pressure filling methods used for wet molding and MIM can also be used.

[Packing density]
The packing density is a preferred range for high density packing of 40 to 55 percent of the true density of the alloy. If it is 40 percent or less, uniform filling cannot be obtained, and a homogeneous sintered body cannot be obtained. In order to avoid partial porosity and deformation, the packing density should be 40 percent or more. Above 55 percent, the range of forced filling according to the present invention is exceeded and a conventional compression molding process is required. In addition, since a magnetic field is applied after filling, sufficient orientation cannot be obtained at a filling rate of 55% or more. One of the objects of the present invention is to remove orientation disturbance due to compression. In the case of the RFeB magnet powder, a more preferable packing density range that can be sufficiently oriented to obtain a sufficient sintered density is 44 to 53%.

  As the filling container, a single container according to each shape as shown in FIG. 1 is used. In order to increase the efficiency, a multi-piece container as shown in FIG. 2 can be used. The partition of each cavity may be a detachable thin partition (for example, the partition 21 in FIG. 2 (3)). In the sintering process of the present invention using the fine powder, particles near the surface of the container boundary are combined, the desired shape is preserved, and then shrinkage proceeds with increasing temperature. Therefore, if a filled container having a predetermined shape calculated in advance from the shrinkage rate is prepared and subjected to predetermined forced filling, a sintered body having a uniform and predetermined shape can be obtained.

  The perforated cylindrical magnet manufactured by the filling container of FIG. 1 (3) or (4) was possible only when a parallel magnetic field was applied by the conventional mold pressing method. However, the magnetic characteristics of the parallel magnetic field type are low, and magnetic characteristics equivalent to or higher than that of a right angle press have been desired. Attempts have been made to install a metal rod in the center of a rubber container and compress it with CIP or RIP after applying a pulsed magnetic field, but the net shape property is poor and mass production efficiency is low. In the production method according to the present invention, the fine powder may be put into a filling container and pulsed and then sintered as it is. Since the shrinkage occurs in the inner diameter portion, it can be taken out from the filling container shown in FIG. 1 (3) or (4) in a pre-sintered state and transferred to another sintering container.

  Many filling containers having a shape close to the final shape (net shape) may be prepared. However, in order to extend the life of the container by repeatedly using the container, it is preferable to transfer the container after the preliminary sintering is completed. In this case, the process from powder filling to pre-sintering can be carried out in a filled container, and the subsequent sintering can be placed on another container or on a conventional sintering base plate. In this case, since the pre-sintering temperature is higher than the Curie temperature (˜310 ° C.) of the RFeB magnet, it is no longer magnetized and it is not necessary to use nerves for placement on the sintering base plate.

FIG. 1 (2) shows an example of a large block. According to the present invention, the conventional mold press method can easily achieve a size that is difficult due to the limit of the pressing pressure and the limit of the uniform magnetic field region.
FIG. 2 (3) shows a filled container divided by thin partitions. Multiple containers can be taken with this container.
FIG. 2 (4) shows the case of a segment magnet used in a motor or the like. In the present invention, it is also possible to easily achieve a shape that is difficult for the conventional mold press method. The partition portion may be as shown in FIG. 2 (3).

[lid]
A fine container is filled with a fine powder as shown in FIG. 1 or FIG. 2, and is simply sealed using a lid as shown in FIG. The purpose of the lid is to prevent scattering of the powder, not to seal it. The lid is usually provided with one or a plurality of deaeration holes for evaporating the lubricant on the end face or side face. The lid should be lightly press-fitted. Since it can be performed in a closed system, the container is not deteriorated by the influence of oxygen or the like. Since the influence of oxygen can be blocked, it is not necessary to select a rare earth element-rich composition as in the case of a conventional rare earth magnet, and therefore the reaction between the rare earth element and the container components can be minimized.
The size of the deaeration holes is preferably a few mm or less than 1 mm in diameter. What is necessary is just to adjust the magnitude | size and number of deaeration holes, seeing the state of deaeration.
The container and lid can be used repeatedly. The lid should be lightly press-fit. Since the purpose is to fix the lid, screwing or screwing may be used. A removal handle or the like may be provided on a part of the lid so that removal after the sintering is easy.

[Rare earth magnet]
The present invention is applied to a method for producing a rare earth magnet containing R (R is at least one rare earth element including Y) and a transition element.
The composition of the rare earth magnet is not particularly limited as long as it contains a rare earth element and a transition element. In particular, the present invention is an RFeB-based sintered magnet (part of Fe can be replaced by Co), or Suitable for manufacturing RCo-based sintered magnets.
The composition of the RFeB rare earth magnet usually preferably contains 27 to 38% by weight of R, 51 to 72% by weight of Fe, and 0.5 to 4.5% by weight of B. If the R content is too small, a phase rich in iron will precipitate and a high coercive force will not be obtained, and if the R content is too large, the residual magnetic flux density will decrease.
Examples of the rare earth element R include Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Tm, Yb, Lu, and the like. In particular, it is preferable that Nd and / or Pr is included. . Furthermore, if a part of R is replaced with dysprosium (Dy) or terbium (Tb) of heavy rare earth elements, a high coercive force can be obtained. However, since the residual magnetic flux density decreases when the substitution of heavy rare earth elements is excessive, the substitution amount of heavy rare earth elements is preferably 6% by weight or less. If the B content is too small, a high coercive force cannot be obtained, and if the B content is too large, a high residual magnetic flux density cannot be obtained. When a part of Fe is replaced with Co, the coercive force decreases as the amount of replacement increases, so the Co amount is preferably 30% by weight or less. Furthermore, in order to improve coercive force and sinterability, elements such as Al, Cu, Nb, Cr, Mn, Mg, Si, C, Sn, W, V, Zr, Ti, Mo, and Ga are added. However, if the total amount of addition exceeds 5% by weight, the residual magnetic flux density decreases, which is not preferable.
In addition to these elements, the magnet alloy may contain, for example, carbon or oxygen as an inevitable impurity or a trace additive in production.
A magnet alloy having such a composition has a main phase with a substantially tetragonal crystal structure. Further, it usually contains a nonmagnetic phase of about 0.1 to 10% by volume.
The method for producing the magnet powder is not particularly limited, but it is usually produced by casting a mother alloy ingot and pulverizing it, or by pulverizing an alloy powder obtained by the reduction diffusion method.
The RCo-based rare earth magnet contains R, one or more metals selected from Fe, Ni, Mn, and Cr, and Co. In this case, it preferably further contains one or more metals selected from Cu or Nb, Zr, Ta, Hf, Ti and V in addition to the above, and particularly preferably further contains Cu and Nb, Zr, Ta. And one or more metals selected from Hf, Ti and V. Among these, in particular, an intermetallic compound of Sm and Co, preferably SmCo ₅ or Sm ₂ Co ₁₇ intermetallic compound is the main phase, and this main phase has a substantially hexagonal or rhombohedral crystal structure. What has is preferable. The specific composition may be appropriately selected according to the production method, the required magnetic properties, and the like, and for example, the following composition is preferable.
R: 20 to 30% by weight, especially 22 to 28% by weight, one or more of Fe, Ni, Mn and Cr: 1 to 35% by weight, one or more of Nb, Zr, Ta, Hf, Ti and V: 0 ~ 6 wt%, especially 0.5-4 wt%, Cu: 0-10 wt%, especially 1-10 wt%, Co: balance.
Specific examples of the rare earth element include, for example, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and the like. And / or Ce is preferred.
Further, as one or more of Fe, Ni, Mn and Cr, Fe is preferable, and in particular, it is preferable to include Fe and to include one or more of Ni, Mn and Cr as necessary.
Further, Zr is preferable as one or more of Nb, Zr, Ta, Hf, Ti and V, and it is particularly preferable that Zr is included and one or more of Nb, Ta, Hf, Ti and V are included as necessary.
Moreover, you may add 1 or more types of other elements, such as Si, Mo, Ca, O, and C other than the said element as needed about 3 weight% or less of the whole. These may be contained as impurities by about 3% by weight or less.
The method for producing the R—Co based magnet powder is not particularly limited.

[Strip cast]
The RFeB alloy produced by the strip cast method (Patent No. 2665590, etc.) has almost no precipitation of αFe which adversely affects the magnetic properties due to the rapid cooling method. In order to prevent this, the composition on the rare earth-rich side was selected, and excessive rare earth elements became non-magnetic and caused a decrease in magnetic properties. Alloys made by the strip cast method were able to minimize the amount of rare earth, which realized the high characteristics of RFeB magnets. However, mold presses that require exposure to the atmosphere with a small amount of rare earth elements have inherent limitations. In the production method of the present invention, there is no step of exposing the fine powder to the atmosphere, and high magnetic characteristics can be obtained while keeping the amount of rare earths to a minimum. In the present invention, particularly when reducing the particle size of the powder, in the production of the strip cast alloy, the solidification rate and the cooling rate after solidification are set so that the structure of columnar crystals (interval of Nd-rich phase) is made fine. It is preferable to adjust.

[Powder particle size]
The average particle diameter of the magnet fine powder is preferably 0.5 to 5 μm in the case of the RFeB magnet. In the conventional method, a process of exposing fine powder or green compact to the atmosphere cannot be avoided, so fine powder of 3 μm or less could not be used. According to the present invention, since the fine powder is not exposed to the atmosphere, a powder of 2 μm or less can be used. Since the size of the single domain particle diameter of the RFeB type magnet is 0.2 to 0.3 μm, it is desirable that the crystal grain size of the sintered body is also in order to obtain a high coercive force. In order to realize this, it is desirable that the particle size of the fine powder is also fine.
As the particle size of the fine powder, a value measured by a sub-sieve-sizer (FSSS) manufactured by Fisher was used (for example, JP-A-59-163802). At present, however, laser-type particle size distribution measuring devices are common, and are defined by the value of R50 indicating the median value of the particle size distribution. For example, a powder with an FSSS value indicated as 3 μm is indicated as 5 to 6 μm at D ₅₀ , and it is known that there is a difference of 1.5 to 2 times in the measured value. Therefore, 3 μm referred to in the present invention indicates a particle size different from 3 μm of the conventional FSSS measurement value.
In the present invention, a preferable powder particle size is 5 μm or less in the case of an RFeB magnet at D ₅₀ . In order to obtain a large coercive force, the preferred size is 3 μm or less. Since the process of the present invention is performed in a complete closed system, the preferred size is 2 μm or less. Furthermore, the optimum size for obtaining the crystal grain size of the single domain particle size of the RFeB intermetallic compound is 1 μm or less.
In the case of the RCo magnet, the preferred powder particle size is 1 to 5 μm in both cases of the 1-5 type and the 2-17 type.

[lubricant]
In the present invention, the lubricant is effective. In order to obtain a sufficient density after sintering, it is necessary to forcibly fill the filled container with fine powder. Since the bulk density of the fine powder is small and the fine powder forms a bridge, the predetermined purpose cannot be achieved only by filling by free fall. In this case, there is friction between the powders during orientation, which may interfere with orientation. In the conventional method, since the addition of the lubricant reduces the strength of the green compact, the amount used must be minimized. In the present invention, since there is no handling step, a lubricant sufficient for orientation can be used.
Lubricants used for rare earth magnets include solid lubricants and liquid lubricants. As solid lubricants, stearic acid-based lubricants such as zinc stearate and calcium stearate are well known and widely used since they have a sufficient lubricating effect. However, solid lubricants are not sufficiently removed in the degreasing process, and the characteristics are deteriorated because carbon tends to remain. In recent years, liquid lubricants such as borate esters, methyl caproate, and methyl caprate have been applied. In the case of a liquid lubricant, it is known that since the vapor pressure is high and the boiling point is low, it easily evaporates in a degreasing process and carbon does not remain so much. In the process according to the present invention, the powder and the lubricant are mixed in the hermetic container. However, it is desirable to evaporate from the small deaeration holes provided in the container, and a liquid lubricant is preferable. In the degreasing step before sintering, the temperature is raised in a vacuum or a reduced pressure state, so a liquid lubricant having a high vapor pressure and a low boiling point is desirable.
Liquid lubricants include fatty acid ester lubricants (laurate ester lubricants, oleate ester lubricants, methyl caproate, methyl caprate, methyl octylate, methyl decanoate, methyl caprylate, methyl laurate, A lubricant having a high vapor pressure and a low boiling point is preferred, such as methyl myristate, methyl palmitate, and methyl stearate.
The purpose of adding the lubricant is to reduce the friction between the powders during orientation, and since the strength of the green compact is not required in the present invention, an amount that can provide a sufficient lubricating effect may be added. The addition method may be performed by mixing fine powder and a predetermined amount of lubricant with a rocking mixer or the like.

[Pulse magnetic field]
The powder packed in the filling container is oriented by receiving a required magnetic field. In the present invention, the demagnetization process for handling required in the case of the die press method and the CIP or RIP method is not necessary.
A stronger magnetic field is preferred. In the electromagnet system used in the mold press, a magnetic field exceeding the saturation magnetization of the mold material cannot be obtained, and the maximum is 1.5 Tesla. There is also a proposal to apply a strong pulsed magnetic field to a die press, but this is not practical because it increases the temperature due to hysteresis loss and eddy current loss, and shock force is applied to a precision press to shorten the die life. The pulsed magnetic field in the present invention is given by an air-core coil in which a filling container filled with powder is arranged in a continuous device.
An air-core coil usually provides a magnetic field of 3 Tesla or higher. A stronger magnetic field for orientation is preferred. In reality, however, the strength is limited by the size of the power source, the strength of the coil, and the frequency of continuous use. A preferable magnetic field strength considering these is 5 Tesla or more. In the conventional example, a method of applying a pulse magnetic field by a coil installed in a die press machine has been proposed. However, the die press cannot be used continuously because of temperature rise and impact force. The pulsed magnetic field according to the present invention is an air-core coil type. In the case of a die press, the coil diameter is limited due to the presence of the die. The air-core coil in the present invention may have a small diameter because it can be large enough to contain a filling container. In the case of the air-core coil, in the case of the same ampere-turn, the smaller the inner diameter, the larger the magnetic field strength. Therefore, in the case of the air-core coil according to the present invention, no burden is imposed on the power source and the coil, which is realistic.
The fine powder in the filled container oriented by the pulsed magnetic field is conveyed without demagnetization to the degreasing process which is the pre-sintering process of FIG. Since the process according to the present invention is a closed system with no opportunity to contact oxygen, it is desirable that the sintering furnace be a continuous processing furnace. However, it is also possible to place the sealed container on the sintering base plate in an atmosphere chamber provided in the front chamber of the sintering furnace by putting the sealed container in a transfer chamber filled with an inert gas.

[Before sintering]
In the pre-sintering chamber, the temperature is raised in a vacuum or an inert gas decompression atmosphere. If a lubricant is used, it is degreased at this stage. In the case of a green compact that is strongly compressed using a conventional mold press or CIP, RIP, the lubricant component trapped inside the green compact cannot easily escape, but in the present invention there is no compacting powder. In this case, the filler component easily evaporates through the degassing deaeration holes provided in the filling container.

  In the case of a ring or the like, if it is sintered as it is in a filled container, it may break due to shrinkage of the inner diameter portion during sintering. In such a case, presintering is performed at 500 ° C. to 1000 ° C., and the particles are lightly bonded to each other and taken out from the filled container before shrinkage starts, and the container may be replaced. At temperatures lower than 500 ° C, particle bonding does not occur, and at temperatures above 1000 ° C, shrinkage begins and cracks occur. When such a crack occurs, even if the sintering temperature exceeds 1010 ° C. (a temperature that is 10 ° C. lower than the sintering temperature is 1000 ° C.), the upper limit temperature of pre-sintering is 1000 ° C. A more preferred temperature range is 600-800 ° C. to avoid particle binding and shrinkage.

In the case of an RFeB magnet, the sintering temperature is preferably in the range of 900 ° C. to 1200 ° C. in a reducing or non-oxidizing atmosphere. In order to obtain higher magnetic properties, a range of 1000 ° C. to 1150 ° C. is more preferable.
In the case of 2-17 type RCo magnet, it is sintered at 1,100-1250 ° C, and then it is solutionized at a temperature 0-50 ° C lower than the sintering temperature. The time required for sintering and solution treatment is appropriately 0.5 to 5 hours. Finally, as the aging treatment, the normal aging is usually held at 700 to 950 ° C. for a certain period of time, and then continuous cooling or multi-stage aging is performed. Each of the above steps is performed in a vacuum or in a non-oxidizing atmosphere in order to prevent the deterioration of characteristics when the R ₂ Co ₁₇ alloy is oxidized.
For 1-5 type RCo magnet, sintered stuffed flour rare earth rich side of the alloy composition granularity FSSS is ground to about 3 [mu] m (at D ₅₀ about 5 [mu] m) to the filling container. The sintering temperature is about 1100 ° C to 1250 ° C. It is necessary to cool rapidly from around 800 ℃.

[Manufacturing equipment]
The manufacturing apparatus of the present embodiment will be described with reference to FIGS.
As shown in FIG. 4, the entire apparatus (hereinafter referred to as a system) is surrounded by a partition wall 40, and the region surrounded by the partition wall 40 is filled with an inert gas such as Ar gas or N ₂ gas. As shown in FIG. 4, the system is continued to a sintering furnace 44 through a powder weighing and filling unit 41, a densifying unit 42 by tapping, and a magnetic field orientation unit 43. These processes are connected by a conveyor 45, and the container 46 and the powder packed in the container are intermittently conveyed by the conveyor 45, and a predetermined process is performed at each stage.
In the weighing / filling unit 41, a certain amount of powder is supplied to the container 46 from a hopper 47 provided with a vibrator. At this stage, since the powder packing density is close to the natural packing density, the bulk density is small, and a guide 48 is attached to the upper portion of the container 46 in order to hold a predetermined amount of powder in the container 46.
In the next densification section 42, a lid 49 is placed on the upper surface of the powder at the top of the container, and as shown in FIG. Thus, the powder is densified. The tapping device is a vibration exciter that intermittently applies downward acceleration to the powder in the container (tamping). The powder in the container 46 is pushed down from the upper end of the container (the lower end of the guide) by tamping, and the lid 49 is mounted on the upper surface of the container. Thereafter, the holder 53 and the guide 48 at the time of tapping are removed from the container 46, and the powder and the container 46 are conveyed by the conveyor to the magnetic field orientation stage in a state where the powder with the lid is filled with the powder at high density.
In the magnetic field orientation unit 43, the container 46 filled with the powder is directed in a predetermined direction, installed at a predetermined position (center part of the coil), and a large pulse current is applied to the coil 54 installed outside the partition wall 40. Washed away. Thus, the powder in the container is oriented in a predetermined direction by the pulsed magnetic field generated. After the powder orientation, the container 46 filled with the powder is conveyed and enters the sintering furnace.

The features of this system are that the powder is carried in a container, so it is easy to handle (delivery and transfer), and there is no need for a robot or manual operation (manual operation) that requires complicated movement for automation. The entire system is completely surrounded by the partition wall 40 as shown in FIG. 4 because a huge press device such as a total pressure of 10 to 200 tons used in a press is unnecessary. Is easy to do. In the process aimed at in the present invention, the powder particle diameter is ultimately D ₅₀ = 1 μm and 2 μm, so safety is a very important factor. This is because if the partition wall is even pierced or cracked, the entire system may explode. In that sense, in the system of the present invention, as shown in FIG. 5, the outer partition wall 55 is installed outside the partition wall 40 shown in FIG. At this time, an inert gas is also filled between the outer and inner partition walls. In this way, even if the partition breaks during the filling, tapping and magnetic field orientation processes at each stage, the outer partition prevents air from entering, so there is a risk of powder burning or explosion. Absent. Such a system can be said to be a fail-safe system.

Next, an experiment performed in this example will be described.
[Experiment 1]
An alloy of Nd = 31.5% by weight, B = 0.97% by weight, Co = 0.92% by weight, Cu = 0.10% by weight, Al = 0.26% by weight and the balance Fe was prepared by a strip cast method. This alloy was crushed into 5-10 mm flakes, and fine powder with D ₅₀ = 4.9 μm was obtained by hydrogen cracking and jet mill. In the pulverization step, the oxygen concentration was set to 0.1% or less so as to keep the amount of oxygen contained in the fine powder as low as possible. After jet milling, 0.2% by weight of methyl caproate, a liquid lubricant, was added to the powder, and the mixture was stirred and mixed with a mixer.
This powder is filled into a stainless steel pipe with an inner diameter of 10 mm, an outer diameter of 12 mm, and a length of 30 mm so that the powder packing density is 3.0, 3.2, 3.4, 3.6, 3.8, 4.0 g / cm ^3. A lid made of metal was attached. A pulse magnetic field was applied to the NdFeB magnet powder packed in the stainless steel pipe in a direction parallel to the axis of the pipe. The peak value of the intensity of the pulsed magnetic field is 8T, and it is an alternating attenuation magnetic field (hereinafter referred to as AC pulse) that attenuates while changing the direction alternately, and after reaching the peak value of 8T, it attenuates without changing the magnetic field direction. Two types of pulsed magnetic fields were used: a pulsed magnetic field (hereinafter referred to as DC pulse). In this example, a pulse magnetic field having a peak value of 8T was applied to magnet powder filled in a stainless steel pipe in the order of AC, DC, and DC. After applying the magnetic field, the stainless steel pipe filled with the magnet powder was put in a sintering furnace and sintered at 1050 ° C. for 1 hour. In this experiment, the filling of the powder into the stainless steel pipe, the pulsed magnetic field orientation, the charging into the sintering furnace, and all the conveyance in the middle are all carried out in an inert gas, and the magnet powder is not exposed to air and is crushed. Up to sintering was performed. After sintering, when the sintered body is taken out from the stainless steel pipe, there are many nest-like cavities in the sintered body when the powder packing density into the stainless steel pipe is 3.0 g / cm ³ or 3.2 g / cm ^3. However, when the packing density is 3.4 g / cm ^3, there are no cavities except for a small part that touches the lid, and for 3.6 g / cm ³ or more, there are very few or no cavities. It was confirmed that a high-density sintered body was formed. The sintered body was processed into a cylinder having a diameter of 7 mm and a height of 7 mm, and a magnetic field was measured by applying a pulse magnetic field having a maximum magnetic field of 8T. The ratio of the remanent magnetization to the magnetization value at 8T was obtained from magnetic measurement by applying a pulsed magnetic field, and the degree of orientation in the sintered body was measured. As a result, the degree of orientation of the sintered body produced with the packing density = 3.6 g / cm ³ was 97.0%, and the degree of orientation of 3.8 g / cm ³ was 96.0%. For comparison, the degree of orientation of the sintered body produced by the conventional molding method in the mold magnetic field was 95.6%.

[Experiment 2]
Using the same powder as in Experiment 1, the difference in the shape and density of the sintered body depending on the material (saturation magnetization Js) of the powder-filled container was examined. The size of the container cavity (the space filled with powder) is a flat cylinder with a diameter of 25 mm and a thickness of 7 mm. The container material is iron (Js = 2.15T), permalloy (Js = 1.4T, 1.35T, 0.73). T, 0.65T, 0.50T) and nonmagnetic stainless steel. These container walls were all 1 mm thick.
The powder is packed in these cavities to a packing density of 3.8 g / cm ³ , and the same AC → DC → DC (peak magnetic field is 8T) as in Experiment 1 is applied to the powder in the entire container. Oriented and then the powder was sintered. In Experiment 2, as in Experiment 1, the powder was not exposed to air in all steps, and a sintered body was obtained. The sintering conditions are the same as in Experiment 1. After sintering, the sintered body was taken out from the container. As a result, it was found that the shape of the sintered body varies greatly depending on the container material. A sintered body made of an iron container with the largest Js had a large hole of about 3 mm in the center, and a columnar body with a diameter of about 0.5 mm was taken around this hole, making the hole even larger. A similar tendency was seen when using Permalloy with a Js of 1.35T or higher as the container material, although not as much as the iron container. As for the stainless steel container, it was also found that a portion having a diameter of about 3 to 5 mm in the central portion of the sintered body was poorly sintered and the sintering density was low (a phenomenon in which water soaked into this portion was observed). And it was the sintered compact produced using the container made from a permalloy of Js = 0.5-0.73T that there was no defect and the shape was favorable. Among them, the sintered body produced with a permalloy container having Js = 0.73T had no defects and the shape was the best. From this, it can be seen that the material used for the powder-filled container used in the present invention is that Js is neither too large nor too small, and Js = 0.3-1T, preferably Js = 0.5-0.8T is optimal. It was. This optimum Js value is also related to the powder packing density and the magnetization of the powder. The best firing is obtained when the Js of the container material is close to the value of (powder magnetization) x (packing density expressed as a percentage of the powder). It was found that a knot was obtained. It has been found that such a difference in the shape of the sintered body due to the container material appears remarkably when the cavity shape, and hence the sintered body shape after sintering, is flat.

[Experiment 3]
The same strip cast alloy as in Experiment 1 was hydrocracked, and powders with different particle sizes were produced by changing the jet mill conditions. There are three types of D ₅₀ = 3.68 μm, 4.93 μm and 9.34 μm. For these powders, a permalloy container with the same shape as in Experiment 2 and Js = 0.73T was prepared, filled with the above three types of powders at a packing density of 3.8 g / cm ³ , and sintered. In this case as well, in all steps from pulverization to sintering, the work was performed in high purity Ar gas so that the powder was not exposed to air. For comparison, a sintered body was also produced by a conventional mold press. Also in the case of the conventional method, all operations were performed in an inert gas so that the powder and the compressed body did not come into contact with air before sintering. Sintering temperature, also in this embodiment, even when using a mold pressing method of the prior art, 1030 ° C. for D ₅₀ = 3.68μm, 1050 ℃ for D ₅₀ = 4.93μm, the D ₅₀ = 9.34μm Was 1110 ° C. An optimum sintered body in which abnormal grain growth was suppressed at these temperatures was obtained. Each sintered body was heat-treated at 500 ° C. for 1 hour after sintering. Table 1 shows the result of measuring the coercive force by the pulse magnetization measurement described in Experiment 1 and the result of analyzing the amount of oxygen in the sintered body. For comparison, Table 2 shows the coercive force and the amount of oxygen in the sintered body of a sintered body produced by a conventional mold press.

Comparing Table 1 and Table 2, it can be seen that when a powder having a small powder particle size is used, the method of the present invention can provide a larger coercive force than the conventional method. This is because, as shown in the respective tables, the degree to which the powder is oxidized during the process is reduced by the method of the present invention. It should be noted that the following accident occurred during the experiment of the comparative example. That is, during the comparative experiment with D ₅₀ = 3.68 μm powder, the powder started to burn out due to a slight air leak in the glove box. In general, in the production of NdFeB magnets by the conventional mold pressing method, after compacting, when the compact is taken out of the mold, heat is generated due to friction with the compact on the mold wall, or the press itself, Or it is designed so that oxygen can easily enter the system from outside due to malfunctions of the powder compaction, placement, and boxing robots, and various troubles that occur frequently, and the entire system operates in an Ar atmosphere. Even so, the amount of oxygen in the sintered body after sintering tends to increase. When the oxygen content exceeds a certain limit, the powder may be heated, causing an accident that may result in burning or explosion. On the other hand, the method of the present invention can keep oxygen from entering into the system very low and the state is stable. The amount of oxygen in the body can be extremely low, and a low-oxygen sintered body can be produced stably. Although the difference between Table 1 and Table 2 is a comparison of a few examples, the effect of the present invention is expected to be greater than the difference between Table 1 and Table 2 in mass production with a large amount of production.
According to this example, a considerably high coercive force was obtained with the powder of D ₅₀ = 3.68 μm. However, in the method of the present invention, a powder having a smaller D ₅₀ can also be used. It has been demonstrated that high coercivity can be achieved without the addition of expensive rare earth elements such as Tb.

The perspective view which shows the example of the single-piece filling container used for implementation of the manufacturing method of the magnetic anisotropic rare earth sintered magnet of this invention. The perspective view which shows the example of the multi-cavity filling container used for implementation of the manufacturing method of the magnetic anisotropic rare earth sintered magnet of this invention. The perspective view which shows the example of the lid | cover used for the filling container of a present Example. The schematic block diagram which shows an example of the manufacturing apparatus of the magnetic anisotropic rare earth sintered magnet of this invention. The schematic block diagram which shows an example of the manufacturing apparatus of the magnetic anisotropic rare earth sintered magnet of this invention.

Explanation of symbols

40 ... partition wall 41 ... weighing / filling unit 42 ... densification unit 43 ... magnetic field orientation unit 44 ... sintering furnace 45 ... conveyor 46 ... container 47 ... hopper 48 ... guide 49 ... lid 50 ... press cylinder 51 ... push rod 52 ... tapping Device 53 ... Holder 54 ... Coil 55 ... Outer partition

Claims (15)

A method of manufacturing a magnetic anisotropy rare earth sintered magnet to perform alignment and sintered without applying a pressure to the alloy fine powder after filling the filled container, filled container provided with a deaerating pores or grooves In addition, a step of filling an alloy fine powder of an NdFeB magnet having an average particle diameter D50 of 0.5 μm or more and 5 μm or less and not containing Dy and Tb as measured by a laser-type powder particle size distribution analyzer, and filling the filling container A step of orienting the alloy fine powder in a magnetic field in a state and a step of sintering the alloy fine powder in a state of being filled in the filling container, and performing each of the above steps in an oxygen-free or inert gas atmosphere. A method for producing a magnetic anisotropic rare earth sintered magnet. A method of manufacturing a magnetic anisotropy rare earth sintered magnet to perform alignment and sintered without applying a pressure to the alloy fine powder after filling the filled container, filled container provided with a deaerating pores or grooves And a step of filling an alloy fine powder of NdFeB magnet having an average particle diameter D50 of 0.5 μm or more and 5 μm or less and containing 6% by weight or less of Dy and / or Tb as measured by a laser-type powder particle size distribution analyzer. A step of orienting the alloy fine powder in a magnetic field in a state where the filling container is filled, and a step of sintering the alloy fine powder in a state where the filling container is filled. A method for producing a magnetic anisotropic rare earth sintered magnet, which is performed in a gas atmosphere. A method of manufacturing a magnetic anisotropy rare earth sintered magnet to perform alignment and sintered without applying a pressure to the alloy fine powder after filling the filled container, filled container provided with a deaerating pores or grooves Filling the alloy fine powder of the NdFeB magnet not containing Dy and Tb in the step, orienting the alloy fine powder in a magnetic field in the state filled in the filled container, and the alloy fine powder in the state filled in the filled container. A step of pre-sintering until shape retention, and a step of removing the pre-sintered body from the filled container and then sintering, and performing each of the above steps in an oxygen-free or inert gas atmosphere. A method for manufacturing a magnetic anisotropic rare earth sintered magnet. A method of manufacturing a magnetic anisotropy rare earth sintered magnet to perform alignment and sintered without applying a pressure to the alloy fine powder after filling the filled container, filled container provided with a deaerating pores or grooves Filling the alloy fine powder of NdFeB magnet containing 6% by weight or less of Dy and / or Tb, orienting the fine alloy powder in a magnetic field with the filled container filled, and filling the filled container And presintering the alloy fine powder until the shape is retained, and removing the presintered body from the filling container and thereafter sintering the process. The above steps are oxygen-free or inert gas. A method for producing a magnetic anisotropic rare earth sintered magnet, which is performed in an atmosphere.   5. The magnetic anisotropy according to claim 1, wherein, in the filling step, the alloy fine powder of the NdFeB magnet is densely filled at a density between 40% and 55% with respect to the true density. Of manufacturing a rare earth sintered magnet.   The method for producing a magnetic anisotropic rare earth sintered magnet according to any one of claims 1 to 5, wherein a material that can withstand 1100 ° C is used as a material of the filling container.   The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 6, wherein the material is iron, iron alloy, stainless steel, permalloy, heat-resistant alloy, or ceramics.   The method for producing a magnetic anisotropic rare earth sintered magnet according to any one of claims 1 to 7, wherein a part or all of the filled container is a non-magnetic material.   9. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein a part of the filling container is a ferromagnetic material.   The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 9, wherein a ferromagnetic material is disposed at both ends of the magnetic pole of the filling container.   The magnetic anisotropic rare earth sintering according to any one of claims 1 to 10, wherein the average particle diameter D50 of the alloy fine powder measured by a laser type powder particle size distribution measuring device is 0.5 µm or more and 2 µm or less. Magnet manufacturing method.   The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 11, wherein the average particle diameter D50 is 0.5 µm or more and 1 µm or less.   The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein the magnetic field is a pulse magnetic field.   The method for producing a magnetic anisotropic rare earth sintered magnet according to any one of claims 1 to 13, wherein an alloy fine powder to which a lubricant is added and mixed is filled in a filling container.   The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 14, wherein the lubricant is a liquid lubricant.

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