JP4391980B2 - Manufacturing method and manufacturing apparatus for magnetic anisotropic rare earth sintered magnet - Google Patents

Description

  The present invention relates to a method for manufacturing a high performance rare earth magnet and a manufacturing apparatus therefor.

  Rare earth / iron / boron sintered magnets (hereinafter referred to as “RFeB magnets”) not only far surpass the properties of permanent magnet materials but also use abundant raw materials such as neodymium, iron and boron. Therefore, it is inexpensive, and since its appearance in 1982, it has been steadily expanding its market 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. Furthermore, practical use is also being promoted in a hybrid car driving motor.

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. 2561704) and quenching alloys can be used A method of upsetting (US Pat. 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.

[Manufacturing process]
The RFeB sintered magnet is manufactured through steps of composition blending, melting, casting, grinding, compression molding in a magnetic field, sintering, and heat treatment.

[composition]
After the RFeB magnet was discovered, additive elements (Patent No. 1606420, etc.), heat treatment (Patent No. 1818977, etc.), crystal grain size control (Patent No. 1662257, etc.), etc. to improve the coercive force and other characteristics However, the most effective method for improving the coercive force is addition of heavy rare earth elements (Dy, Tb) (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 hybrid cars and industrial / household motors that are expected to increase in demand in the future.

[Dissolution]
Sintered magnets require a dense and uniform 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 α 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.) .

[Crushing]
When RFeB alloy occludes hydrogen, microcracks are generated in the alloy, which facilitates pulverization (Japanese Patent No. 1675022). 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 method of obtaining magnetically anisotropic sintered magnets by compression molding powder in a magnetic field originated from the invention of ferrite magnets (Japanese Patent Publication No. 29-885, US Pat. No. 2,762,778), and then RCo magnets and RFeB 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 the same year that Went et al. Invented a ferrite magnet in 1951 (JP-B 35-8281, US Pat. No. 2,762,777), Gulther et al. Invented a magnetic anisotropic sintered ferrite magnet (JP-B 29-29). 885, US Pat. No. 2,762,778). For the first time, the method of compression molding and sintering in a magnetic field was used for the production of a magnetic anisotropic permanent magnet. 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 fine powder during molding, and to reduce friction between powder and powder or between powder and mold, there is a method of adding a lubricant (Patent No. 2254603, No. 3454777, 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 at high pressure and wet compression molded in a magnetic field (Patent No. 1). No. 2731337). In this case, there is a report that 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. As a method of applying pressure isotropically, there is a method of applying cold isostatic pressing (CIP) (Patent No. 3383448) by putting fine powder in a rubber container and applying a magnetic field from the outside.

[RIP]
As a method for obtaining the same effect as CIP, the present inventors previously proposed a RIP (Rubber Isostatic Pressing) method in which a rubber mold is placed in a mold press machine and isotropic pressure is applied (Patent No. 2030923). . Because this method is easy to automate, it is much more suitable for mass production than CIP.

[AT]
As a method for filling a cohesive fine powder into a die-capacity such as a die press, an air tapping (Air Tapping, AT) method has been proposed (Japanese Patent Laid-Open Nos. 9-78103 and 9-95). No. 169301, JP-A-11-49101). Air tapping is a technique in which a high-speed airflow is intermittently applied to a powder to uniformly and uniformly fill the die cavity with the powder. Furthermore, a method has been proposed in which a near net shape molded body is obtained by solidification using an air tapping method (Japanese Patent Laid-Open No. 2000-96104).

[Pulse magnetic field]
In order to align the direction of the powder, a method of applying a magnetic field from the outside is adopted. In the case of an RFeB magnet, the c-axis direction of the tetragonal structure corresponds to the easy magnetization axis, and the powder is oriented in one direction when a magnetic field is applied. In the case of a normal die press, a static magnetic field is applied by an electromagnet, and the magnitude is about 15 kOe at the maximum. 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 when a high magnetic field is actually applied (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 uniform microstructure can be obtained. In rare earth cobalt magnets and RFeB magnets, there is no better method than powder metallurgy to obtain high performance permanent magnets by taking advantage of the properties of each material.

[Press forming in magnetic field]
Ferrite magnet was invented by Went et al. In 1951 (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 the liquid component by compression and to fix the 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.

[Reason for selecting a die press]
The reason why the die press is used is that a product (net shape) almost similar to the final shape and size is obtained, the yield is good, and automation is possible. 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.

[RIP]
As a method for obtaining the same effect as CIP, the present inventors previously proposed the RIP 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 magnetic properties are higher than with the die press method. This method is suitable for mass production because it is possible to automate the process of rubber mold filling, pulse magnetic field application, compression molding, and demagnetization continuously.

[Details of pressing process in 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.
・ Pressure is applied 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, the green compacts 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. The die press used in powder metallurgy is a precision machine, and it is relatively easy to align punches and dies if it is a single (single) picking press, but it is complicated in the case of multiple picking. . Magnets are required to have various shapes and dimensions, such as discs, rectangles, perforated discs, and arcuate shapes, 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 by JMD Coey, CLARENDON PRESS, OXFORD, 1996, pp. 340-341, "The pressing load is sufficient to make compacts having enough strength to be "handed but without significant misorientation of the crystallites." stated that the applied pressure is sufficient to produce a green compact with sufficient strength for handling without causing any significant disturbance in the particle arrangement. Has been. Also, J. Ormerod, "Powder Metallurgy of rate earth permanent magnets", Powder Metallurgy 1989, Vol. 32, No. 4, p. 247, "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 should be sufficient to give the green compact sufficient mechanical strength to handle, but not high enough to cause disruption of particle orientation.) ). 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 will be disturbed if pressurized with a large pressure. ing.

[Problems inherent in rare earth magnets]
Rare earth magnets contain about 30% by weight of chemically active and easily oxidizable rare earth elements. In the rare earth sintered magnet manufacturing process, there is a process for handling fine powders containing a large amount of chemically active rare earth elements and having an average particle size of about 3 μm. Since it is necessary to orient each fine powder in a certain direction in a magnetic field, it is not possible to use a means for granulating in advance and improving the fluidity of the powder 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 increase the orientation]
In order to increase the degree of orientation of the fine powder during molding, a method of adding a lubricant has been proposed (Japanese 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 compressing while applying a magnetic field. However, if a large amount of lubricant is added for the purpose of obtaining a sufficient lubricating effect, a long time is required for degreasing. Certain liquid lubricants (for example, JP 2000-306753 A) are excellent in volatility and hardly remain in the sintered body. However, when a large amount of a lubricant is added for the purpose of improving the degree of orientation, the green compact strength after the die press becomes weak, which causes handling problems. In the die press machine, a static magnetic field is applied by an electromagnet. The static magnetic field generated by the electromagnet is at most about 10 to 15 kOe (1 to 1.5 T) because of 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. In order to prevent this, an alignment method using a pulsed magnetic field has been proposed (Japanese Patent No. 3307418). A pulsed magnetic field of 1.5 to 5.5 T can be applied, and the effect of improving B _r (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, organic binders and lubricants have been added, and wet molding methods have been proposed, but all of them are premised on compression with a strong pressure. This component is strongly confined in the green compact and is not easily removed in the degreasing step prior to sintering. Degreasing is performed completely by heating at a low temperature for a long time, but the productivity is significantly reduced. When the organic component is left overheated at a high temperature, impurities such as carbon react with the constituent elements to deteriorate the magnetic characteristics and the like, resulting in poor corrosion resistance.

[Wet molding method]
In order to achieve a high degree of orientation while preventing oxidation of fine powder, a method of wet compression molding of a mixture of mineral oil / synthetic oil and fine powder in a magnetic field has been proposed (Japanese 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, while rare earth magnets cannot use water, and use solvents and oils. However, oil contains many components that become impurities such as carbon and is difficult to escape during 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 to deteriorate the magnetic properties and deteriorate the corrosion resistance.

[Oxygen-free process]
In the mold press method, fine powder is put into the atmosphere. There is a proposal that, after producing a fine powder, the process from pressing in a magnetic field to loading into a sintering furnace is performed in an inert gas atmosphere (Japanese Patent Laid-Open No. 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. Rare earth magnets cannot produce a strong green compact by molding using a large amount of binder and high pressure as in general crystals. Therefore, the green compact is fragile and easily broken. It is dangerous and inefficient to work with a human hand in the press like a glove box. That is, the concept of placing the entire process including the mold press machine in an inert atmosphere is extremely difficult to achieve in mass production.

[Reason for not using fine powder]
Regardless of how small the die punch clearance 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. In the magnet manufacturer with the most advanced technology in the world, the powder particle size of RFeB sintered magnet used for mass production is 4.5 to 6 μm, D ₅₀ which is the median value of particle size measured by laser type powder particle size distribution analyzer It is said that. 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 nonmagnetic oxide in the sintered magnet, which causes a decrease in magnetic properties. However, in the conventional method, it is inevitable that the fine powder is exposed to the atmosphere during the molding process and the process of bringing the compact into the sintering furnace. As described above, the particle size of the finely pulverized powders of the world's top manufacturers is about 4.5 to 6 μm in D ₅₀ , and if it is finer than this, even if it is a molded body, oxidation easily occurs. 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 powder having D ₅₀ = 4 μm or less cannot be practically handled by the conventional mold press method.

As described above, the first problem of the RFeB-based sintered magnet manufacturing method and manufacturing apparatus is that it is difficult to make the manufacturing line completely closed. It is known that RFeB-based sintered magnets can have higher characteristics as the oxidation of powder and green compacts during the manufacturing process is kept as low as possible and the particle size of the powder is reduced. However, little oxidation of the surface layer, as powder particle size smaller powder active, the production line must be kept filled with an inert gas such as always N _2. When air enters even a little, the powder generates heat. In the mass production line, there is a large amount of powder, so there is a concern that small heat generation will lead to large heat generation and fire. At present, most RFeB anisotropic sintered magnets are produced by production lines using the die press method or the RIP method. Some of these production lines are designed to be operated by being filled with an inert gas, and RFeB anisotropic sintered magnets produced by these production lines have low oxidation and high characteristics. However, these low-oxygen production lines have not eliminated the worry of a major accident leading to a fire or explosion. Therefore, even if it turns out that the further improvement of a characteristic is possible, it is difficult to activate a powder more than the present condition. The reason why it is difficult to make the current production line into a complete closed system is as follows.

Production line using die press:
(1) The space that must be enclosed is large.
(2) It is difficult to replace a large mold without introducing air into the system.
(3) Powder filling, compression, green compact removal, green compact cleaning (removal of excess powder), green compacts aligned on the base plate, packing the base plate with the green compact, pressure A series of steps of charging the powder box into the sintering furnace must be performed in a short cycle time in order to improve productivity. In actual processes, various troubles frequently occur during these processes. In order to solve the trouble, human labor is inevitably required, and there often occurs a situation that cannot be solved without introducing air into the system.

Production line using RIP:
Filling rubber mold with high-density powder, magnetic field orientation, compression, green compact removal, rubber mold cleaning, aligning green compact to base plate, packing base plate with green compact, box containing green compact Even in a series of steps of charging a furnace into a sintering furnace, shortening the cycle time is indispensable for improving productivity, and trouble frequently occurs. As with a production line using a die press, there are often situations where air must be introduced into the system to solve the problem.

  In the above-mentioned two types of production lines, the first reason why the system cannot be completely sealed is that after the powder is compressed, the green compact must be taken out from the mold or rubber mold. When the green compact is taken out from the mold or rubber mold, the green compact breaks, is chipped, or excessive powder is sucked in, causing trouble. Troubles due to cracking or chipping of the green compact also occur during the subsequent green compact handling process. Since such a trouble cannot be dealt with by a robot, air is introduced into the system and the trouble is dealt with manually. In this way, with the conventional production line, it is possible to temporarily produce RFeB anisotropic sintered magnets in a closed system, but continuous operation for a long time is extremely difficult, and the powder is more active than it is at present. Is not only rejected from the production site, but is actually dangerous.

As mentioned above, the production method of RFeB anisotropic sintered magnets using the conventional mold press method and RIP method is inappropriate as a process for handling active powder, and as a mass-produced product, it is more than ever. In order to produce a magnet having a high magnetic property, particularly a high coercive force, there has been a limit to reducing the particle size of the powder or reducing the amount of oxygen contained in the powder. When measured with the laser particle size distribution measurement method, the powder used in the conventional production system has a median particle size distribution of about 5 μm, expressed as D ₅₀ , even in the production of the world's top-level RFeB magnets. Met.

  Another problem of the RFeB anisotropic sintered magnet production system is that the productivity of flat plate and arcuate plate magnets is low. The proportion of flat and arcuate plate magnets is extremely high among all RFeB anisotropic sintered magnets. In these magnets, the magnetization direction is a direction perpendicular to the plate surface.

  One method for producing a flat magnet by a conventional method is a method in which a large block-shaped sintered body is sliced with an outer cutter. A disadvantage of this method is that a part of the expensive sintered body after sintering becomes chipped, and the ratio increases as the thickness of the product decreases. Another problem is that machining (cutting) takes time and the tool is consumed much.

  Another method for producing a flat magnet by a conventional method is a method in which a green compact is formed by pressing in a magnetic field one by one by a die pressing method, and each is separately sintered one by one. The disadvantage of this method is that the parallel magnetic field press method must be used to form the flat magnet. According to the parallel magnetic field press method, the orientation of the powder is disturbed during compression, and the maximum energy product of the magnet produced by sintering is nearly 10 MGOe lower than that of a press product in a perpendicular magnetic field. Further, the method of pressing and sintering flat magnets one by one is low in productivity. A multi-cavity press method can be used in which several die cavities are made to produce a plurality of green compacts and sintered, but due to the limitation of applied pressure, the number of green compacts that can be molded at one time is two. About 4 or so will not be a big improvement.

  In order to produce an arcuate plate magnet by a conventional method, a pressing method in a parallel magnetic field is usually used. This method has the same problem as the above-described flat magnet. In other words, because the magnet orientation after sintering is low, the maximum energy product of the magnet is low, and even if the method of molding one by one or the multi-cavity molding method with multiple die cavities is used. This means that the productivity from the process to the sintering is low.

  When producing an arcuate plate magnet by the conventional method, the maximum energy product of the magnet after sintering can be improved by using the perpendicular magnetic field press method. However, even in this case, the disadvantage of low productivity remains. In addition, there is a problem that the height of the arcuate plate-shaped green compact cannot be increased too much.

  Another disadvantage of the conventional production method is that it is not possible to produce a long sintered body having a circular or irregular cross section. In the mold pressing method, there are problems that the length (height) of the green compact that can be molded is limited and the maximum energy product of the magnet is low in the case of the parallel magnetic field press method. When a long product is manufactured by a press method in a perpendicular magnetic field, the cross-sectional shape of the green compact that can be formed is limited, and a near net shape cannot be formed.

  Furthermore, a disadvantage of the conventional production method is that it is difficult to produce a flat ring magnet having high characteristics. A flat ring magnet is used by being magnetized in a direction perpendicular to the disk surface. To produce a flat ring magnet, a parallel magnetic field press method is used, but this method can only produce a magnet whose maximum energy product is nearly 10MGOe lower than a magnet made by a perpendicular magnetic field press method. The RIP method is expected to have high performance as a production method for flat ring magnets, but flat ring magnets are not produced by the RIP method due to problems such as distortion of the shape during molding.

  Another problem with the conventional method is that a thin plate-like magnet with a thickness of 1 mm or less, a deformed long section with a side or diameter of 1 mm or less, or a sintered magnet with a long circular section In other words, it cannot be directly produced by sintering a green compact having a small size. The reason is that it is difficult to produce a compact with such a small size by means of a die press or RIP method. This is because it is difficult to handle them so as not to break when they are arranged in line, packed in a box, or charged in a sintering furnace. The metal injection molding (MIM) method is known as one possible method, but due to problems such as residual carbon impurities, it is not widely used in the production of RFeB anisotropic sintered magnets. Absent.

[Object of the present invention]
The object of the present invention is to eliminate the fundamental problems of the manufacturing method and manufacturing apparatus of the sintered magnet including the current die press method and RIP method in the manufacturing method and manufacturing apparatus of the magnetic anisotropic rare earth sintered magnet. , Providing RFeB sintered magnets with higher maximum energy product and higher coercive force, improving productivity of flat magnets and arcuate plate magnets, and means for producing ring magnets with high degree of orientation And a means for producing a long-sized sintered body having a circular or irregular cross section and a sintered body having a small dimension of 1 mm or less.

The first aspect of the method for producing a high-density, high-orientation magnetic anisotropic rare earth sintered magnet according to the present invention made to solve the above problems is as follows:
a) filling a container having a cavity corresponding to the shape of the product (hereinafter referred to as a mold) with a high density of alloy powder;
b) applying a high magnetic field to the alloy powder to orient the alloy powder;
c) a step of heating and sintering the gas component released from the alloy powder in a state where the alloy powder can be discharged out of the mold while the alloy powder is put in the mold;
d) removing the sintered body of the alloy powder from the mold;
It is characterized by having.
Here, it is desirable to design the cavity in consideration of the desired shape and size of the product and shrinkage during sintering. A high-density, high-orientation sintered body has a density of 97% or more of the theoretical density, and when the orientation degree is measured by a pulse magnetization measurement method with a maximum applied magnetic field of 10 T, the saturation magnetization J _s of the residual magnetization J _r The ratio J _r / J _s is determined to be 93% or more.

The second aspect of the production method according to the present invention is:
a) filling the mold with a high density of alloy powder;
b) applying a high magnetic field to the alloy powder to orient the alloy powder;
c) heating the gas component released from the alloy powder in a state capable of being discharged out of the mold while the alloy powder is still in the mold, and producing a temporary sintered body of the alloy powder;
d) removing the temporary sintered body from the mold or removing a part of the mold, and then heating the temporary sintered body to a temperature higher than the temporary sintering temperature to perform main sintering;
e) a step of taking out the sintered body obtained by subjecting the temporary sintered body to main sintering from the remainder of the mold;
It is characterized by having.

A third aspect of the production method according to the present invention is characterized in that, in the first or second aspect, the filling density of the alloy powder in the mold is 35 to 60% of the true density of the alloy.
Normally, according to the powder filling method in which the alloy powder is simply dropped into the cavity, the packing density of the powder is about 20% of the theoretical density. In the method of the present invention, it is preferable to fill with high density to 35% or more. If it is 35% or less, the density of the sintered body after sintering is low, and a large nest is formed in the sintered body, so that it cannot be a practical sintered magnet. If the packing density is too high and exceeds 60%, magnetic field orientation of the alloy powder becomes difficult.

According to a fourth aspect of the production method of the present invention, in the third aspect, the filling density is 40 to 55% of the true density.
A more preferable range is given than the third embodiment.

According to a fifth aspect of the manufacturing method of the present invention, in any one of the first to fourth aspects, the orientation magnetic field is 2T or more.
In order for the degree of orientation J _r / J _{s of the} sintered magnet to be 93% or more, the orientation magnetic field is preferably at least 2 T or more.

  A sixth aspect of the manufacturing method according to the present invention is characterized in that, in the fifth aspect, the orientation magnetic field is 3T or more. A more preferable range of the orientation magnetic field is given.

  A seventh aspect of the manufacturing method according to the present invention is characterized in that, in the sixth aspect, the orientation magnetic field is 5T or more. This gives a more preferred range of orientation magnetic field.

  According to an eighth aspect of the manufacturing method of the present invention, in any one of the first to seventh aspects, the orientation magnetic field is a pulsed magnetic field.

  According to a ninth aspect of the manufacturing method of the present invention, in the eighth aspect, the orientation magnetic field is an alternating magnetic field.

  According to a tenth aspect of the manufacturing method of the present invention, in any one of the first to ninth aspects, the orientation magnetic field is applied a plurality of times.

  An eleventh aspect of the production method according to the present invention is characterized in that, in the tenth aspect, the orientation magnetic field is a combination of a DC magnetic field and an alternating magnetic field.

  A twelfth aspect of the production method according to the present invention is characterized in that, in any one of the first to eleventh aspects, a lubricant is added to the alloy powder.

  A thirteenth aspect of the production method according to the present invention is characterized in that, in the twelfth aspect, the lubricant is a solid lubricant, a liquid lubricant, or both.

  A fourteenth aspect of the production method according to the present invention is characterized in that, in the thirteenth aspect, the liquid lubricant contains a fatty acid ester or a depolymerized polymer as a main component.

  The sixth to fourteenth aspects provide means for improving the degree of orientation.

According to a fifteenth aspect of the production method of the present invention, in any one of the first to fourteenth aspects, the alloy powder has a particle size of 4 μm or less.
This makes it possible to produce high-performance RFeB anisotropic sintered magnets that have been difficult to mass-produce due to the powder being too active by conventional magnet manufacturing methods including the die press method or the RIP method.

  The sixteenth aspect of the production method according to the present invention is characterized in that, in the fifteenth aspect, the particle diameter of the alloy powder is 3 μm or less. This makes it possible to produce a magnet with higher characteristics than in the fifteenth aspect.

  A seventeenth aspect of the production method according to the present invention is characterized in that, in the sixteenth aspect, the particle diameter of the alloy powder is 2 μm or less. This makes it possible to produce a magnet with higher characteristics than in the sixteenth aspect.

  An eighteenth aspect of the production method according to the present invention is characterized in that, in the seventeenth aspect, the particle diameter of the alloy powder is 1 μm or less. This makes it possible to produce a magnet with higher characteristics than in the seventeenth aspect.

A nineteenth aspect of the production method according to the present invention is characterized in that, in any one of the sixteenth to eighteenth aspects, the particle diameter of the alloy powder is 3 μm or less and the sintering temperature is 1030 ° C. or less. .
This makes it possible to improve the characteristics of the RFeB sintered magnet and to greatly extend the life of the mold.

  A twentieth aspect of the production method according to the present invention is characterized in that, in the nineteenth aspect, the alloy powder has a particle size of 2 μm or less and a sintering temperature of 1010 ° C. or less. As a result, the RFeB sintered magnet is further improved in characteristics compared with the nineteenth aspect, and the mold life is further improved.

A twenty-first aspect of the manufacturing method according to the present invention is characterized in that in any one of the first to twentieth aspects, a part or all of the mold is used a plurality of times.
This is essential for improving productivity when the present invention is industrially implemented.

  A twenty-second aspect of the manufacturing method according to the present invention is characterized in that, in any of the first to twenty-first aspects, the mold has a plurality of cavities.

A twenty-third aspect of the manufacturing method according to the present invention is characterized in that, in any one of the first to twenty-second aspects, the cavity is columnar.
This is a method of producing a long product having a circular cross section or a modified cross section by a net shape.

  A twenty-fourth aspect of the manufacturing method according to the present invention is characterized in that, in any one of the first to twenty-third aspects, a columnar core is arranged at the center of the cylindrical cavity.

According to a twenty-fifth aspect of the manufacturing method of the present invention, in the twenty-fourth aspect, the alloy powder is filled in the cavity and oriented by applying a magnetic field, and then the mold core is removed, or the mold core It is characterized in that is replaced with a thin one and sintered.
The twenty-fourth and twenty-fifth aspects enable the production of a cylindrical ring-shaped magnet having high characteristics similar to those of a press product in a perpendicular magnetic field, which was impossible with the conventional method.

  A twenty-sixth aspect of the manufacturing method according to the present invention is characterized in that, in any one of the twenty-third to the twenty-fifth aspects, the alloy powder is oriented by applying a magnetic field in the direction of the principal axis of the cavity.

The twenty-seventh aspect of the manufacturing method according to the present invention is characterized in that, in the twenty-sixth aspect, a material corresponding to a lid and a bottom part at both ends of the cavity in the principal axis direction is made of a ferromagnetic material.
The twenty-sixth and twenty-seventh aspects provide means for obtaining a columnar or cylindrical sintered body with as little distortion as possible.

  A twenty-eighth aspect of the production method according to the present invention is characterized in that, in the twenty-second aspect, the cavity is flat. This provides a high productivity production method for flat magnets.

  A twenty-ninth aspect of the manufacturing method according to the present invention is characterized in that, in the twenty-second aspect, the cavity has an arcuate plate shape. This provides a high productivity production method for arcuate plate magnets.

  A thirtieth aspect of the production method according to the present invention is characterized in that, in the twenty-eighth or the twenty-ninth aspect, the alloy powder is oriented by applying a magnetic field in a direction perpendicular to the hollow flat plate surface or the arcuate plate surface. .

  The thirty-first aspect of the manufacturing method according to the present invention is that in the thirty-third aspect, the material of the portion forming the hollow flat plate surface or the arcuate plate surface is a non-magnetic material or has a saturation magnetization of 1.5 T or less. It is characterized by.

A thirty-second aspect of the manufacturing method according to the present invention is characterized in that, in the thirty-first aspect, the saturation magnetization is 1.3 T or less.
The thirtieth to thirty-second embodiments provide means for obtaining a high-density sintered body without a nest when producing a flat plate or arcuate plate magnet.

  A thirty-third aspect of the manufacturing method according to the present invention is characterized in that, in any of the twenty-second to thirty-second aspects, a plurality of cavities are arranged in two or more rows in the mold.

  A thirty-fourth aspect of the production method according to the present invention is the part of the mold according to any one of the first to thirty-third aspects, wherein a part or all of the part constituting the wall parallel to the magnetic field orientation direction of the alloy powder among the parts of the mold. Is a ferromagnetic material.

  A thirty-fifth aspect of the production method according to the present invention is characterized in that, in any one of the first to thirty-fourth aspects, an anti-seizure coating is applied to the inner wall of the cavity.

  A thirty-sixth aspect of the manufacturing method according to the present invention is the method according to any one of the first to thirty-fifth aspects, wherein a mechanical tapping method using mechanical vibration, a pusher method by pressing a push rod, or a gas flow The mold is forcibly filled with alloy powder by an air tapping method using impact or a combination thereof.

  A thirty-seventh aspect of the production method according to the present invention is characterized in that, in any one of the first to thirty-sixth aspects, a fine powder obtained by pulverizing an alloy obtained by a molten metal quenching method is used as an alloy powder. To do.

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

The second aspect of the apparatus for producing a magnetic anisotropic rare earth sintered magnet according to the present invention is:
a) Alloy powder filling means for filling the mold with alloy powder obtained by finely pulverizing the alloy;
b) magnetic field orientation means for orienting the alloy powder in a magnetic field;
c) pre-sintering means for pre-sintering the alloy powder while retaining its shape until the shape is retained;
d) a main sintering means for main sintering the pre-sintered alloy powder;
e) Conveying means for conveying the mold in the order of alloy powder supply means, magnetic field orientation means, pre-sintering means, and main sintering means;
f) a container containing alloy powder filling means, magnetic field orientation means, pre-sintering means, main sintering means and conveying means;
g) atmosphere adjusting means for making the inside of the container an inert gas atmosphere or a vacuum;
It is characterized by providing.
This provides a means to increase the safety of the apparatus embodying the present invention.

  A third aspect of the production apparatus according to the present invention is characterized by comprising an external container for housing the container. This provides a means to further increase the safety of the apparatus implementing the present invention.

Embodiments and effects of the invention

  According to the present invention, in a method for producing a magnetic anisotropic rare earth sintered magnet, a mold having a cavity is filled with fine powder, and a magnetic field is applied from the outside to orient the powder, followed by sintering. Here, the shape and dimensions of the cavity are designed corresponding to the desired shape and dimensions of the product. In that case, it is desirable to design in consideration of shrinkage during sintering.

  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 mold, 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 processes from filling of fine powder, application of a magnetic field, and carrying into a sintering furnace are performed in an inert gas atmosphere such as argon or nitrogen, or in a vacuum. Rare earth magnets are affected by impurities such as oxygen. Whether it is an RFeB magnet or an SmCo magnet, it is necessary to select a composition on the rare earth-rich side of the 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 a rare earth magnet such as an RFeB magnet or an SmCo magnet, there is no opportunity to come into contact with oxygen in the atmosphere in the form of fine powder, so that 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.

In the present invention, sintering (in the case of the first aspect) or pre-sintering (in the case of the second aspect) is performed in a state where the gas component released from the alloy powder can be discharged out of the mold. Therefore, it is necessary that the mold be formed with openings for degassing, pores, slits, grooves or the like during sintering or preliminary sintering. These deaeration openings and the like may be formed from the beginning, or may be formed after the alloy powder filling and magnetic field orientation steps.
The powder may store a large amount of hydrogen absorbed in the alloy at the time of hydrogen crushing, and adsorbed gas components such as nitrogen and moisture are always present. Furthermore, a part or all of the lubricant and binder mixed in the fine powder is vaporized at a high temperature. These gas components must be discharged out of the mold during sintering or pre-sintering. If these gas components remain sealed in the mold, the density of the sintered body does not increase during sintering, or the sintered body reacts with these gas components and is contaminated, which adversely affects the magnetic properties. Such gas component discharge slits and pores are provided in the mold in advance, or the mold is filled with alloy powder, the lid is closed, and the magnetic field is oriented. The opening may be formed by removing the 24th or 25th aspect. The above-mentioned slits and pores may be natural gaps such as fitting between the cavity and its lid.

  According to the present invention, a fine powder is filled in a mold having a predetermined cavity according to the target size and shape, and the powder is oriented by applying a magnetic field from the outside, and then sintered or pre-sintered as it is. Can do.

  The magnetic alloy fine powder is densely filled in the mold. The degree of high density filling is higher than the degree of filling in the conventional mold press method, and is lower than the relative density 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 the green compact handling. However, in the present invention, since there is no green compact handling step, it is not necessary to compress.

  The alloy powder must be filled in the mold sufficiently densely and uniformly. Otherwise, the density of the sintered body will be reduced, or powder will be biased during the orientation of the pulse magnetic field, and a nest will be formed in the sintered body.

The rare earth magnet of the present invention is preferably an RFeB magnet.
The RFeB magnet is composed of R (at least one of rare earth elements including Y): 12 to 20%, B: 4 to 20%, 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.
Even if Ti, Ni, V, Nb, Ta, Cr, Mo, W, Mn, Al, Sn, Zr, Hf, Ga, etc. are added to improve coercive force, sinterability and other manufacturability Good. These additive elements may be added in combination, but in any case, the total amount is preferably 6 atomic% or less. In particular, Cu, Al, V, and Mo are preferable.
In the case of RFeB magnets, sintering is performed between 900-1200 ° C.

The rare earth magnet manufacturing method of the present invention can also be applied to rare earth cobalt magnets (RCo magnets).
Among RCo magnets, the composition range of 1-5 type magnet is RTx (R is Sm or Sm and one or more combinations of La, Ce, Pr, Nd, Y, Gd, T is Co or Co and One or a combination of two or more of Mn, Fe, Cu, and Ni, 3.6 <x <7.5), and the sintering temperature is 1050 to 1200 ° C.
The composition range of the 2-17 type RCo magnet is R (where R is Sm or two or more rare earth elements containing 50% by weight or more of Sm): 20 to 30% by weight, Fe: 10 to 45% by weight, Cu: 1 to 10% by weight, one or more of Zr, Nb, Hf and V: 0.5 to 5% by weight, balance Co and unavoidable impurities, sintering temperature is 1050 to 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 mold, in order to prevent seizure between the product to be sintered and the mold, the pre-sintering temperature is preferably 30 ° 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 seizure to the mold tends to be strong.

RFeB magnets and RCo magnets contain more rare earth elements than the stoichiometric composition of intermetallic compounds (R ₂ Fe ₁₄ B and RCo ₅ ). They form a low melting point alloy with other constituent elements and cause liquid phase sintering. By liquid phase sintering, the alloy powder filled in the mold shrinks from the filled state to become a high-density sintered body. When powder is filled into a cylindrical ring-shaped mold in which a columnar core is placed in the center of the cylindrical cavity and sintered, the core of the mold is prevented from shrinking and cracks are formed in the inner diameter portion of the sintered body. Occurs. In such a case, after preliminary sintering, the core is removed, or the temporary sintered body is transferred to a container for main sintering, or the powder is filled in a mold and magnetically oriented and then temporarily sintered. Alternatively, if the core is removed before the heating for sintering is started, or if sintering is performed instead of the thin core, a sintered body without cracks can be produced.

  One of the features of the present invention is to use a mold with a cavity designed to obtain a sintered magnet having a desired shape and size after sintering, and repeatedly use the mold. Considering that rare-earth sintered magnets are often produced in units of 1 million for one product, this is an essential requirement for industrial technology. The inventor has demonstrated that it is industrially possible to repeatedly use a mold when the proposed technique satisfies certain conditions.

  The present invention proposes the use of a mold having a large number of cavities in order to achieve higher productivity. The overwhelming advantage over the conventional mold pressing and RIP methods is that the number of flat magnets and arcuate plate magnets that can be produced with one mold is many times larger. The characteristics of the magnets to be produced are very uniform with little variation among the magnet pieces. This is because in the present invention, a very long air-core coil can be used for the orientation of the alloy powder. For example, if a bitter-type coil is used as the coil and the length of the coil is 20 cm, 30 typical rare earth sintered magnets having a flat plate shape or an arcuate plate shape can be manufactured in one mold. Since the magnetic field in the coil is uniform, the magnetic properties of the flat plate or arcuate plate magnet produced in this way are uniform with little variation for each magnet piece. The reason why the bitter type coil is used is that this type of coil has a longer life as a coil that repeatedly generates a high magnetic field than a normal winding type coil.

  The selection of the material constituting the mold is important for using the present invention as an industrial technology. For example, when an iron mold is used as a mold for a flat magnet, when a pulse magnetic field is applied, the alloy powder in the mold is pressed against the outer periphery of the flat plate, and if sintered as it is, a large nest is formed in the central portion of the flat plate. A sintered body with The portions other than the nest are high-density and highly oriented sintered bodies. Naturally, such a magnet is not suitable as an industrial material. Select the material of the mold appropriately, that is, use a non-magnetic material for the part that forms the flat plate surface or arcuate plate surface of the cavity, or the saturation magnetization is 1.5T or less, more preferably 1.3T or less By using the material, such a problem is solved.

  Also, if part or all of the part of the mold part that forms the wall parallel to the magnetic field orientation direction of the alloy powder is made of a ferromagnetic material, the orientation of the alloy powder after the magnetic field orientation is fixed and stabilized as a magnetic circuit. It becomes. Thereby, even if some impact force is applied to the mold during handling of the mold after the magnetic field orientation, the orientation is not disturbed, so that the production apparatus can be sped up and the production can be stabilized. Similarly, when the cavity has a columnar shape or a cylindrical ring shape, it is desirable to use a ferromagnetic material for the lid and the bottom portions at both ends of the cavity in the principal axis direction (depth direction). By doing so, the orientation of the alloy powder after the magnetic field orientation is kept stable.

In order to use the mold repeatedly, a coating can be applied to prevent the alloy powder from being baked on the mold. An effective coating for preventing seizure is BN (boron nitride) coating. As a BN coating method, even if BN powder is mechanically applied, it is effective to some extent for preventing seizure. In order to prevent more complete seizure, it is desirable to fix the BN powder to the mold more strongly. When a resin is used as a binder for fixing, coating is performed every time sintering is performed. Using metal or glass as a binder and baking BN on the inner surface of the mold allows a coating that can be used multiple times. Further, sputtering, ion plating, TiN by the CVD method or the like, TiC, TiB various nitrides such as _2, carbides, borides, or thin film coating consisting of an oxide such as alumina is durable, the surface is smooth It is effective as an anti-seizure coating that can be used multiple times.

The world's top-level neodymium magnet sintered body has a crystal grain size of 5 to 15 μm, and the fine powder before sintering has a grain size of D ₅₀ and 4.5 to 6 μm. Here, D ₅₀ represents the median value of the particle size distribution measured with a laser type particle size distribution measuring instrument (eg, manufactured by Sympatech, manufactured by Horiba, Ltd.). The particle size of fine particles having a measured value of 3 μm by an air permeation type particle size distribution measuring instrument (Fischer's sub-sieve sizer, FSSS) which has been used once is displayed as about 4.5 to ₅ μm in D50. With a rare earth magnet alloy composition containing 30% by weight or more of rare earth elements, it was difficult to handle fine powders having a D ₅₀ of 4.5 μm (FSSS 3 μm) or less by the conventional mold pressing method. In the present invention, the fine powder is filled in the mold in an inert atmosphere such as nitrogen, oriented by a magnetic field, and carried into the sintering furnace, so there is no step of touching air, even if it is a fine powder. There is no danger.

The conventional die press, CIP and RIP manufacturing processes are not suitable for handling RFeB magnetic alloy fine powder containing a large amount of chemically active rare earth elements. If unoxidized RFeB alloy powder with a small particle size of 4 μm or less is exposed to the atmosphere, there is a risk of ignition and explosion, and stable production cannot be achieved. Even if it is not necessary to ignite, since the fine powder has a large surface area, the amount of oxygen increases and the magnetic properties deteriorate. Since these effects cannot be avoided by the conventional method, a fine powder of 4.5 μm or less could not be handled industrially in large quantities.
When a sintered magnet is made using an RFeB alloy powder having a D ₅₀ value of 4 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 can be obtained.
According to the present invention, it is possible to stably use RFeB magnets having high coercive force, which are used for hybrid cars and industrial motors, with little or no amount of Dy and Tb, which are rare and expensive. Can be mass-produced.

One of the features of the present invention is that pressure molding is not performed after the powder is oriented, as in a die press, CIP, or RIP. The powder oriented in the mold is sintered while maintaining high orientation without being disturbed by application of pressure as in the conventional method. A high degree of orientation achieves a high residual magnetic flux density (B _r ) 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 3 μm or less, 2 μm or less, or even 1 μm or less in order to further increase the coercive force. According to the present invention, the process from preparation of fine powder to sintering can be processed in a completely inert atmosphere, and even rare earth-containing magnet powder having a D ₅₀ value of 0.5 μm or less can be handled.

  The magnet alloy powder is obtained by pulverizing a cast ingot obtained by melting the composition in a melting furnace or a cast piece obtained by a molten metal quenching method (strip casting method). In order to obtain a fine powder of several μm, the pulverization is generally divided into coarse pulverization and fine pulverization. Coarse pulverization includes a mechanical pulverization method and a hydrogen pulverization method (hydrogen pulverization method), and is often used because the hydrogen pulverization method is excellent in productivity. As the 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 is generally used. In the present invention, a fine powder having a size of several μm 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.

In the present invention, the packing density of the powder in the mold is preferably 35% to 60%, more preferably 40% to 55% 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, in order to obtain sufficient magnetic characteristics, the above-described strong pressing force is required. 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 using mechanical vibration, a pusher method in which a push rod is pushed into a mold, or an air tapping method (Japanese Patent Laid-Open No. 2000-96104). Micron-sized magnet powders tend to agglomerate and form a bridge easily when filling a mold, making uniform filling difficult. The bridge is mechanically broken by mechanical tapping method or pusher method to perform high density filling. Alternatively, the powder can be uniformly and uniformly filled in the mold at high density by applying a periodic air impact to the powder in the powder feeder by the air tapping method.
In JP 2000-96104 A, a powder with a binder 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 subsequent 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) as it is in a mold. In the present invention, a binder for obtaining a powder molded body is not used, and it is not necessary to handle a powder molded body hardened with a binder.

The external magnetic field generating source used for powder orientation is preferably a pulsed magnetic field. The mold filled with powder is placed in an air coil and a pulsed magnetic field is applied. In the static magnetic field method using an electromagnet used in the mold press method, the applied magnetic field is 1.5 T at most, whereas in the pulse magnetic field method, a much higher magnetic field can be applied. The magnitude of the pulse magnetic field in the present invention is 2T or more, 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 type waveform magnetic field is applied in advance, and then a DC pulse magnetic field is applied, rather than applying a DC pulse only once.
Japanese Patent No. 3307418 confirms that magnetic properties are improved by applying a magnetic field of 1.5 to 5 T in the manufacture of RFeB magnets. However, when a pulse magnetic field is applied to a conventional mold press, eddy current loss and hysteresis loss occur in the mold 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 powder orientation magnetic field in the present invention may be any as long as a strong magnetic field can be obtained by a superconducting coil or the like.

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). In the conventional RFeB magnet manufacturing method, the thickness of the strip cast alloy ribbon is about 300 μm, but in the method of the present invention, the thickness of the alloy ribbon is preferably 250 μm or less. Furthermore, as a thin ribbon for obtaining a fine powder having a powder particle diameter of D ₅₀ = 3 μm or less, a thickness of 200 μm or less is preferable. As a thin ribbon for obtaining a powder having D ₅₀ = 2 μm or less, a thickness of 150 μm or less is preferable. Thus, the coercive force of the finally obtained neodymium sintered magnet can be maximized by obtaining fine powder using an alloy ribbon having an appropriate thickness.

  In the present invention, all the steps from taking out the fine powder from the pulverizer to carrying it into the sintering furnace are performed in an inert atmosphere. The fine powder placed in the hopper is filled into a mold placed in an inert gas atmosphere through high density filling means such as mechanical tapping and air tapping, capped, and provided with means for orienting in a magnetic field. Move to a location. The powder in the mold is oriented by a magnetic field orientation means such as a pulsed magnetic field and conveyed to the sintering furnace entrance as it is.

Filling the mold with a fine powder to which a liquid lubricant has been added in advance is a preferable method because it facilitates orientation in a magnetic field and increases the degree of orientation.
In general, solid lubricants have low vapor pressure and high boiling point, whereas liquid lubricants have high vapor pressure and low boiling point. Considering that it is easy to spread all over the fine powder and that the degreasing property is easy, a liquid lubricant is preferable.
It is known to use methyl caproate or methyl caprylate together with saturated fatty acid as a liquid lubricant (Japanese Patent Laid-Open No. 2000-109903). However, when these lubricants are used in the die pressing method, only a very small amount of 0.05 to 0.5% by weight can be used with respect to the magnet powder. These are highly volatile and have the feature that they do not remain in the sintered body. However, when sintering green compacts that have been strongly compression-molded with a die press, even the lubricant components trapped inside the green compacts. This is because 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 mold 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 0.1 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. Lubricants that are solid at room temperature, such as zinc stearate, have the disadvantage that it is difficult to apply evenly to the surface of the powder particles compared to liquid lubricants. However, if a device that applies a solid lubricant to the surface of the powder particles is used, such as a mixer called Super Mixer (manufactured by Carita), the lubrication effect of the solid lubricant will be maximized. Become. A powder to which a solid lubricant is added by such a method has a feature that a solidification phenomenon due to compression hardly occurs as compared with a powder to which a liquid lubricant is added. When such a powder is used in the rare earth magnet manufacturing method of the present invention, it is possible to prevent the powder from being pressed against the outer peripheral portion during pulse orientation and to be hardened, and then to form a nest in the central portion of the sintered body due to subsequent sintering. .

[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 apparatus 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 the magnetic anisotropy of the net shape shape. A sintered magnet is obtained. The air-core coil can provide a strong pulsed magnetic field, and chemically active fine powders containing rare earth elements can be processed without exposure to the atmosphere, so it is possible to handle powders with low oxygen content and small particle sizes. Rare earth magnets with high coercivity can be obtained without using Dy. In addition, high-performance magnets of the product shape most frequently produced as rare earth magnet products such as thin plate shapes and arcuate plate shapes can be produced very efficiently.

[mold]
The mold is preferably made of a material that can withstand a high sintering temperature (up to 1100 ° C.). In the process of raising the temperature of the mold in advance, the particles are slightly bonded, and the object to be sintered is in a state capable of self-holding. In this pre-sintered state, part or all of the mold can be removed, and the pre-sintered body can be transferred to another mold or base plate. Since the pre-sintering temperature is desirably from 500 ° C. to a temperature 30 ° C. lower than the sintering temperature, the mold used at the time of pre-sintering may be any material that can withstand this temperature.
As the mold material, iron, iron alloy, stainless steel, permalloy, heat-resistant steel, heat-resistant alloy, superalloy, molybdenum, tungsten, or an alloy thereof, and ceramics such as ferrite and alumina can be used.

[Mold inner wall coating]
In order to avoid fusion of the sintered body and the inner wall of the mold during sintering, it is also effective to apply a release agent such as BN to the inner wall of the mold in advance. By applying BN to the inner wall of the mold 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 inner wall of the mold during sintering. Preventing the sintered body from being deformed or cracked due to the adhesion is effective in producing a high-quality sintered magnet. When a thin film such as TiN, TiC, TiB, Al ₂ O ₃ , or ZrO _{2 is} formed on a mold surface such as stainless steel by sputtering, CVD, or ion plating, a durable anti-fusing coating can be formed.

[Filling method]
In the present invention, the filling method is important. The permanent magnet alloy fine powder that cannot be granulated is easily agglomerated due to the properties of a magnet, and it is difficult to form a bridge and quantitatively fill the mold. For forced filling used in the present invention, for example, a mechanical tapping method, a pusher method, or an air tapping method developed by the present inventors (Japanese Patent Laid-Open No. 2000-96104) can be used.

[Packing density]
The filling density is preferably 35% to 60% of the true density of the alloy. If it is 35% or less, a large nest is formed in the sintered body, or the entire sintered body becomes low-density and porous, and a practical permanent magnet cannot be obtained. In order to obtain a high-quality permanent magnet that can be used practically, the packing density needs to be 35% or more. When the packing density exceeds 60%, sufficient orientation cannot be obtained due to magnetic field orientation. A more preferable range of the packing density for obtaining a high-density sintered body that is sufficiently oriented and free of nests and cracks is 40 to 55%.

  As the mold, a single mold corresponding to each shape as shown in FIG. 1 can be used. In order to increase the efficiency, a multi-piece mold as shown in FIG. 2 or 3 can be used. The partition of each cavity may be a detachable thin partition (for example, the partition 21 in FIG. 2 (3)). 2 (1), (2), (4), and (5) form a cavity of the desired shape directly in a solid material by cutting with a drill or end mill or electric discharge machining. Made by. If a mold having a cavity with a predetermined shape calculated in advance from the shrinkage rate is prepared and subjected to predetermined forced filling, a sintered body with a uniform predetermined shape can be obtained.

  The perforated cylindrical ring-shaped magnet manufactured by the mold of FIG. 1 (3) or (4) can be manufactured only by the parallel magnetic field pressing method in the conventional mold pressing method. Since the magnetic properties of sintered magnets manufactured by the parallel magnetic field press method are low, it has been desired to develop a method for manufacturing a cylindrical ring magnet having magnetic properties equivalent to or higher than those of a perpendicular magnetic field press. Attempts have been made to place a metal rod (core) in the center of the rubber mold and compress it with CIP or RIP after applying a pulsed magnetic field, but the net shape is poor and the productivity is low. In the production method according to the present invention, the fine powder may be put into a mold and subjected to pulse orientation and then sintered as it is. Since shrinkage occurs at the inner diameter part, the temporary sintered body is taken out from the mold shown in FIG. 1 (3) or (4) and transferred to another sintering mold at the stage where the shape is retained by temporary sintering, After the child is removed, the main sintering is performed. Alternatively, the core can be removed after the magnetic field orientation and before heating, or the main sintering can be performed in place of the thin core. In this way, a cylindrical ring-shaped RFeB sintered magnet having magnetic characteristics equivalent to or higher than that of a perpendicular magnetic field press can be manufactured. 1 (3) and 1 (4) show an example in which the mold cavity is cylindrical, the cavity may have another shape such as a hexagonal column. Further, the core is not limited to a columnar shape, but may be another shape such as a hexagonal column shape.

FIG. 1 (2) shows an example of a mold for 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 mold for a flat magnet divided by thin partitions. By using this mold, a large number of pieces can be obtained.
FIG. 2 (4) shows a mold for an arcuate plate magnet used in a motor or the like. In the present invention, it is possible to easily manufacture a shape that the conventional mold pressing method is not good at. The partition may be detachable as in FIG. 2 (3).
FIG. 2 (5) shows a mold for producing a columnar magnet having a fan-shaped cross section. A magnet obtained by cutting the produced sector-shaped cross-sectional columnar magnet into a predetermined thickness is used for a voice coil motor or the like.
FIG. 3 shows an example of a mold capable of producing a larger number of plate magnets at a time than the molds of FIGS. 2 (1) and (3). In the manufacturing method of the present invention, it is not necessary to use a die press, so that two rows of flat cavities can be arranged side by side. Moreover, three or more rows of such cavities can be arranged, and two or more rows of cavities of other shapes such as an arcuate plate shape can be arranged in place of the flat plate-shaped cavities (not shown). In the present invention, when orienting the fine powder, a coil having a larger capacity of the air core than in the past can be used. Therefore, even if two or more rows of cavities are arranged in this way, variation in magnet characteristics for each flat magnet can be sufficiently achieved. It can be kept small.

[lid]
A mold as shown in FIGS. 1 to 3 is filled with fine powder, covered, and then a pulsed magnetic field is applied to orient the powder. When a pulsed magnetic field is applied to the powder, the particles that make up the powder become magnets one by one, and the N and S poles of the magnet repel each other and the powder volume expands greatly. If the lid is not covered or the lid is incomplete, the powder will be scattered during pulsed magnetic field orientation.
The lid is designed to fit lightly into the mold. If the fit between the lid and the mouth of the mold is too tight, the inside of the cavity is sealed. If the inside of the cavity is in a sealed state, the density of the sintered body is coarsened during sintering, or the carbon component contained in the lubricant is contaminated, resulting in a decrease in magnetic properties. For this reason, the fitting is adjusted so that a small gap is formed between the lid and the mold, or a small hole for deaeration is formed as shown in FIGS.

[Rare earth magnet]
The present invention is applied to a method for producing a rare earth magnet containing R (R is at least one of rare earth elements 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, an iron-rich phase will precipitate and a high coercivity cannot be obtained. On the other hand, when there is too much R content, a residual magnetic flux density will fall.
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, when 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 amount of heavy rare earth element substitution is too large, the substitution amount of heavy rare earth element 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. It is also possible to replace part of Fe with Co. In this case, the Co amount is preferably 30% by weight or less because the coercive force decreases if the amount of substitution is too large.
Furthermore, in order to improve coercive force and sinterability, elements such as Al, Cu, Nd, Cr, Mn, Mg, Si, C, Sn, W, V, Zr, Ti, Mo, and Ga are added. However, if the total amount of these additives exceeds 5% by weight, the residual magnetic flux density decreases, which is not preferable.
In addition to these elements, for example, carbon and oxygen may be contained in the magnet alloy as inevitable impurities or trace additives 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.

[Powder particle size]
The average particle size of the magnet fine powder is preferably 0.5 to 5 μm in the case of the RFeB magnet. In the conventional process, fine powder or green compact is exposed to the atmosphere, so fine powder of 4 μm or less cannot be used. In the process of the present invention, since the fine powder is not exposed to the atmosphere, a powder of 3 μm or less or 2 μm or less can be used. In order to obtain a high coercive force, it is desirable that the crystal grain size of the sintered body is as close as possible to 0.2 to 0.3 μm, which is the size of the single domain particle diameter of the RFeB type magnet. In order to realize this, it is desirable that the fine powder particle size is also fine.
As the particle size of the fine powder, a value measured by a Fisher sub-sieve-sizer (FSSS) has been used (for example, JP 59-163802). However, at present, it is generally defined by the value of the median value D ₅₀ of the particle size distribution obtained by a laser type particle size distribution measuring apparatus (eg, manufactured by Sympatech, manufactured by Horiba, Ltd.). It is known that there is a difference of 1.5 to 2 times in the measured values of both methods. In the present application, the value of D ₅₀ measured with a laser particle size distribution apparatus is used.
In the present invention, a preferable powder particle size is 4 μm or less as a value of D ₅₀ in the case of an RFeB magnet. In order to obtain a large coercive force, it is preferably 3 μm or less, and more preferably 2 μm or less because the process of the present invention is carried out in a complete closed system. Furthermore, the optimum size is 1 μm or less in order to approach the crystal grain size of the single domain particle size of the RFeB intermetallic compound.
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.

[Pulse magnetic field]
The powder packed in the mold is oriented by receiving a required magnetic field. At this time, a stronger magnetic field is preferable. In the electromagnet system with an iron core used in the die press method, the limit is 2.5T, which is the magnetic field of saturation magnetization of the iron core. There is also a proposal to use a strong pulsed magnetic field in the die press method, but this is not practical because it increases the temperature due to hysteresis loss and eddy current loss and imposes a shocking force on a precision press to shorten the life of the die. In the present invention, a pulse magnetic field is applied to a mold filled with powder by an air-core coil arranged in a continuous device. In the present invention, the demagnetization step for handling the green compact necessary for the die press method, CIP, and RIP method is unnecessary.

  A stronger magnetic field for orientation is preferable, but in reality, there are limits depending on the size of the power source, the strength of the coil, and the frequency of continuous use. In consideration of these, the preferable magnetic field strength is 2T or more, more preferably 3T or more, and further preferably 5T or more. However, such a magnetic field can be obtained by an air-core coil. When a pulse magnetic field is obtained by an air-core coil, the coil diameter must be larger than that of the mold in the mold press. Since the mold is much larger than the size of the cavity into which the powder enters, an air core coil with a large inner diameter that can contain such a mold is required. On the other hand, in the case of the present invention, the inner diameter of the air-core coil may be as large as the mold can enter. In the air-core coil, even if the ampere turns are the same, the magnetic field strength increases as the coil inner diameter decreases. Therefore, the coil inner diameter can be reduced using the method of the present invention, thereby reducing the burden on the power source and the coil. Can increase the sex.

  The fine powder in the mold oriented by the pulse magnetic field is usually conveyed to the degreasing process which is a pre-sintering process without demagnetization. In the present invention, the sintering furnace is preferably a continuous processing furnace because it can be a closed process without contact with oxygen. However, the mold is put into a sealed container, the sealed container is put into a transfer champ filled with an inert gas, and the mold is transferred from the sealed container to the sintering base plate in the atmosphere chamber provided in the front chamber of the sintering furnace. Is also possible.

[Before sintering]
In the pre-sintering chamber, the mold is heated in a vacuum or an inert gas decompression atmosphere. If a lubricant is used, it is degreased at this stage. When compacted strongly using a conventional mold press, CIP, or RIP, the lubricant component trapped inside the green compact cannot be easily degreased, but in the present invention, the powder is not compressed, The lubricant component applied to the particle surface easily evaporates through a gap between the mold and the lid or a deaeration hole provided in the mold or the lid.

  When sintering a green compact, particle bonding does not occur at temperatures lower than 500 ° C., but shrinkage may occur and cracks may occur at temperatures higher than the temperature at which sintering begins. When sintering into a ring shape, if the mold is sintered as it is, cracking may occur due to shrinkage of the inner diameter portion during sintering. In such a case, pre-sintering is performed at a temperature of 500 ° C. or higher and lower than the temperature at which sintering shrinkage starts, and the temporary sintered body is taken out of the mold before the particles are lightly bonded and shrinkage does not start. The main sintering may be performed by exchanging with a mold having no child. Alternatively, the main sintering may be performed by removing only the core.

[Manufacturing equipment]
The manufacturing apparatus of the present embodiment will be described with reference to FIGS.
As shown in FIG. 5, the entire apparatus (hereinafter referred to as a system) is surrounded by a partition wall 40 and filled with an inert gas such as Ar gas or N ₂ gas. As shown in FIG. 5, the system includes a powder weighing / filling unit 41, a densifying unit 42 by tapping, a magnetic field orientation unit 43, and a sintering furnace 44. These processes are connected by a conveyor 45, and the powder packed in the mold 46 is intermittently carried 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 mold 46 from a hopper 47 equipped with a vibrator. At this time, since the powder packing density is a small value close to the natural packing density, a guide 48 is attached to the upper part of the mold 46 in order to hold a predetermined amount of powder in the mold 46.
In the next densification section 42, a lid 49 is placed on the upper surface of the powder on the upper side of the mold 46, and as shown in FIG. The powder is densified by driving 52. The tapping device is a vibrator that intermittently applies a downward acceleration to the powder in the mold 46 (tapping). By tapping, the powder in the mold 46 is pushed down to the upper end of the mold 46 (the lower end of the guide) or slightly below it, and the lid 49 is attached to the upper surface of the mold 46. Thereafter, the holder 53 and the guide 48 at the time of tapping are removed from the mold 46, and are conveyed to the magnetic field orientation section by the conveyor in a state where the powder with a lid is filled with high density.
In the magnetic field orientation unit 43, the mold 46 filled with powder is directed in a predetermined direction and placed at a predetermined position (center portion of the coil). A large pulse current is passed through the coil 54 installed outside the partition wall 40, and the powder in the mold 46 is oriented in a predetermined direction by the pulse magnetic field generated thereby. After the powder orientation, the mold 46 filled with the powder is conveyed and enters the sintering furnace.

The features of this system are that the powder is carried in the mold, so it is easy to handle (delivery and transfer), and there is no need for complicated moving robots or manual operations (manual operation). It is easy to completely enclose the entire system by the partition wall 40 as highlighted in FIG. 5 because a huge press device having a total pressure of 10 to 200 tons is unnecessary. It can be done. In the present invention, safety is an extremely important factor since the process is aimed at a process in which the powder particle diameter is ultimately D ₅₀ = 1 μm to 2 μm. This is because if the partition wall is pierced or cracked, the entire system may explode. In that sense, in the system of the present invention, as shown in FIG. 6, 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 inner partition wall may break during any of the processes, the outer partition wall prevents air from entering, so there is no fear of powder combustion or explosion. In this way, the system can be made fail-safe.

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 casting method. This alloy was crushed into 5 to 10 mm flakes, and fine powder with D ₅₀ = 4.9 μm was obtained by hydrogen cracking and jet milling. In the pulverization step, the oxygen concentration was 0.1% or less, and the amount of oxygen contained in the fine powder was kept as low as possible. After jet milling, 0.5% 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 magnetic powder was transferred to 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 transportation in the middle are performed in an inert gas, and the magnet powder is pulverized without exposing it to air. To the sintering process. After sintering, the sintered body was taken out from the stainless steel pipe. The sintered compacts when the powder packing density was 3.0 g / cm ³ and 3.2 g / cm ³ had many nest-like cavities inside, but when the packing density was 3.4 g / cm ³ The ligation had no cavities except for a small portion that touched the lid. When the packing density is 3.6 g / cm ³ or more, the density of the sintered body reaches 98.7% of the theoretical density, and there are very few or no cavities, and a high-density, high-quality sintered body is formed. I was sure that. 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 10 T. The ratio of remanent magnetization to the value of magnetization at 10 T 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 a packing density of 3.6 g / cm ³ was 97.0%, and that 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]
D ₅₀ = 4.9μm and D ₅₀ = 2.9μm powder obtained by hydrogen crushing and jet mill from the same alloy as in Experiment 1, and mold material (saturation magnetization J _s ) affecting the shape and density of the sintered body Dependency was examined. The space filled with mold powder is a flat cylinder with a diameter of 25mm and a thickness of 7mm. The mold material is iron (J _s = 2.15T), permalloy (J _s = 1.4T, 1.35T, 0.73T) 0.65T, 0.50T) and nonmagnetic stainless steel. The wall thicknesses of these molds were all 1 mm.
The powder is packed into these cavities so that the packing density is 3.8 g / cm ³ , and the same AC → DC → DC (each peak magnetic field is 8T) magnetic field is applied to the powder as in Experiment 1, and this powder is oriented. And then sintered. Also in this experiment, as in Experiment 1, the powder was not exposed to air in all steps, and a sintered body was obtained. The sintering conditions were 1050 ° C. for the powder with D ₅₀ = 4.9 μm and 1020 ° C. for the powder with D ₅₀ = 2.9 μm. After sintering, the sintered body was taken out from the mold. As a result, it has been found that the shape of the sintered body varies greatly depending on the material of the mold. The sintered body made with an iron mold with the largest J _s has a large hole of about 2 mm in the center, and a columnar body with a diameter of about 0.5 mm is taken around this hole, making the hole even larger .

Even when Permalloy with a J _s of 1.35T or more was used as the mold material, the same tendency was observed, although not as much as the iron mold. In addition, with respect to the nonmagnetic stainless mold, a small nest was sometimes formed in the center of the sintered body. However, most of the nests at this time did not hinder practically many purposes. The sintered body produced using a permalloy mold with J _s = 0.5 to 0.73 T had no defect and good shape. Among them, the sintered body produced by a permalloy mold with J _s = 0.73T had no defects and the shape was the best. For this reason, the material used for the powder mold used in the present invention is that J _s is neither too large nor too small, and J _s = 0.3 to 1 T, preferably J _s = 0.5 to 0.8 T is optimal. I understood. The value of the optimum J _s is also related to the magnetization of the powder packing density and powder, best when close to the value of J _s of the mold material (the magnetization of the powder) × (filling density, expressed as a percentage of powder) It was found that a sintered body of It was found that the difference in the quality of the sintered body depending on the mold material depends on the cavity shape, and appears significantly when the sintered body shape after sintering is flat.

[Experiment 3]
After the same strip cast alloy as in Experiment 1 was hydrogen pulverized, fine powders having different particle diameters were produced by changing the pulverization conditions with a jet mill. The produced fine powder has three particle sizes of D ₅₀ = 2.91 μm, 4.93 μm and 9.34 μm. These powders were filled in a Permalloy mold (J _s = 0.73T) having the same shape as in Experiment 2 to 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 green compact 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, D ₅₀ = 2.91μm, 1020 ℃ for, 1050 ° C. for _{D 50 = 4.93μm, D 50 =} 9.34μm About 1100 degreeC. A good 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 results of measuring the coercive force by the pulse magnetization measurement described in Experiment 1 and the results 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 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 each table, in the method of the present invention, the degree to which the powder is oxidized during the process is low. It should be noted that during the experiment of the comparative example for the powder of D ₅₀ = 2.91 μm, there was an accident in which the powder was heated and burned due to a slight air leak in the press enclosure. Generally, in the conventional mold pressing method, when the green compact is taken out of the mold, heat is generated due to friction between the green compact and the mold, or the press itself or the green compact is taken out, arranged and packed. Due to various troubles that frequently occur during work, oxygen can easily enter the system from the outside, and even if the entire system is designed to operate in an Ar atmosphere, the amount of oxygen in the sintered body after sintering Is easy to increase. When the oxygen content exceeds a certain limit, the powder may be heated, causing an accident that may lead to burning or explosion. On the other hand, the method of the present invention has a simple process, so there are few troubles, and oxygen can be kept from entering the system very low, and since this state is stable, even if the powder particle size is small. The amount of oxygen in the sintered body after sintering can be made 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, it is possible to stably use a powder of D ₅₀ = 2.91 μm for the production of a NdFeB sintered magnet, and the method of the present invention does not use an expensive rare earth element such as Dy or Tb. It has been demonstrated that high coercivity can be achieved.

[Experiment 4]
The strip cast alloy of Experiment 1 was hydrogen pulverized, and a powder of D ₅₀ = 2.9 μm was produced by a jet mill. 0.5% by weight of methyl caproate was added to this powder and mixed well. On the other hand, a mold having a cavity with a diameter of 23 mm and a depth of 4 mm was made of four types of materials: iron, magnetic stainless steel (J _s = 1.4T), permalloy (J _s = 0.7T), and nonmagnetic stainless steel. The thickness of the mold was 3 mm on both end faces and 2 mm on the side. The inner surface of the mold was rubbed with a mixture of BN powder and solid wax to form a welding prevention film during sintering. In these molds, the above-mentioned powder of D ₅₀ = 2.9 μm added with methyl caproate has a packing density of 3.2 g / cm ³ , 3.3 g / cm ³ , 3.4 g / cm ³ , 3.5 g / cm ³ , and Filled to 3.6 g / cm ³ . Thereafter, the powder-filled mold was put in a coil, and the powder was oriented by applying an AC with a peak value of 9 T, then DC, and then a DC magnetic field in the axial direction of the cylindrical mold, followed by sintering. Sintering was performed in vacuum at 1010 ° C. for 2 hours and cooled. FIG. 7 shows photographs of the mold inner surface and sintered body after sintering. The size of the sintered body was 19.0 to 19.5 mm in diameter and 2.7 to 2.8 mm in thickness (the higher the packing density, the larger). It can be seen from the photograph that all of the sintered bodies produced using the iron mold have holes in the middle, and fragments of the sintered body remain in the mold side center. Thus, when a relatively thin sintered body is produced using an iron mold, a large hole is formed at the center even when the powder packing density is high. It can be seen that when a magnetic stainless steel (SUS440) mold is used, if the packing density is low, a nest tends to be formed at the center of the disk-shaped sintered body. If a permalloy or nonmagnetic stainless (SUS304) mold with a relatively small magnetization J _s is used, a hole cannot be formed in the center even at a low packing density (3.2 to 3.3 g / cm ³ ). In addition, the mold used in this experiment was set to such an extent that the lid was lightly closed (the fitting portion was not tightly fitted). The gas component released from the powder being sintered escaped from this loosely bonded portion.

[Experiment 5]
An experiment similar to Experiment 4 was performed using a mold having a cavity of 10 mm in diameter and 60 mm in length using the same powder as in Experiment 4. Put the lid on one of the cylindrical mold, filling the powder into the formed cavity density ^{3.4g / cm 3, 3.5 g /} cm 3, 3.6g / cm 3, 3.7g / cm 3, was filled to 3.8 g / cm ³ . In this experiment, an experiment was conducted in which the material of both lids and the material of the mold were changed independently. After filling the mold with powder and closing both lids, magnetic field orientation was performed in the axial direction of the cylindrical mold under the same conditions as in Experiment 4. Thereafter, sintering was performed under the same conditions as in Experiment 4. The fitting at both ends of the lid mold was loosened so that the released gas during sintering was easily discharged. The sintering conditions are the same as in Experiment 4. As a result of investigating the density, shape, and nest formation of the sintered body, the density of the sintered body was 7.5 g / cm ³ or more for all samples, and a long and thin cylindrical sintered body without defects could be produced. . However, when the material of the lids at both ends was non-magnetic SUS304, a tendency was observed that the middle part of the cylinder was thick and the barrels were narrow at both ends. When both ends were made of a ferromagnetic material, a cylindrical sample having a uniform thickness was formed.

[Experiment 6]
Using the same powder as in Experiment 4, a flat plate and an arcuate plate magnet were manufactured using the mold shown in FIG. 2 (3). However, the arc-shaped plate magnet mold was used by replacing the threshold plate 21 with a curved threshold plate. The mold was coated by rubbing a mixture of BN and solid wax before powder filling. The upper and lower lids use flat non-magnetic stainless steel plates with a thickness of 1 mm. Bolts are inserted into the holes in the four corners of this plate and the square screw holes in the mold not shown in Fig. 2 (3). The upper and lower lids and the mold body were fixed by tightening. Powder loadings varied at intervals of every 0.1 g / cm ³ from 3.2 g / cm ³ to 3.9 g / cm ^3, the sintering conditions were the same as Experiment 4. The direction of the orientation magnetic field was a direction parallel to the direction of the long side outside the mold. The main points of the experimental results are as follows.
(1) NdFeB sintered magnets with a high density and high magnetic properties without defects when the packing density is 3.4 g / cm ³ or higher, the mold material and the slab plate material are non-magnetic and permalloy. Flat and arcuate plate magnets could be made.
(2) When the flat plate and arcuate plate are made of iron or magnetic stainless steel, a nest similar to that shown in the photograph of Experiment 4 (Fig. 7) is formed at the center of the flat plate and arcuate plate. A good product could not be produced.
(3) The mold outer material is iron, magnetic stainless steel or permalloy, the top and bottom plates are non-magnetic stainless steel, and the partition plate is non-magnetic stainless steel or permalloy. Fill the mold with powder and close both lids. After the orientation of the pulse magnetic field, the upper and lower nonmagnetic stainless steel lids and the bottom plate were removed, but the powder in the oriented mold did not flicker or fall, and some mechanical vibration or It turns out that it is stable to shock. Thereafter, sintering was performed with the upper and lower lids and the bottom plate removed, and a sintered body having a high orientation and a high sintering density could be produced. However, when the material of the outer mold of the mold is iron or magnetic stainless steel, among the plural cavities partitioned by the partition plate, the cavity formed at both ends, that is, the flat plate surface or the arcuate plate surface is formed in the cavity in contact with the outer frame. The body had a nest. From these cavities other than both ends, a good sintered body with no nest formed was obtained.

[Experiment 7]
Using the same powder as in Experiment 4, an experiment was conducted to produce a cylindrical ring magnet oriented in the axial direction. The mold used has a hole in the center of the bottom lid, similar to the top lid, for the core to enter. A cylindrical ring-shaped cavity was formed by fitting the core into the bottom lid and the bottom lid into the mold. This cylindrical ring-shaped cavity was filled with alloy powder at a density of 3.4 to 3.8 g / cm ³ and the upper lid was closed. The fit between the core and the upper and lower lids and the mold and the upper and lower lids were adjusted so that they would not fall off when they were lifted up, but could be removed when pulled strongly. The experiment was performed by changing the material of the upper and lower lids, cores, and molds independently of each other in the same manner as in Experiment 4.
As a result, when the core is made of non-magnetic stainless steel and the upper and lower lids are made of a magnetic material (iron, magnetic stainless steel, permalloy), the cavity is filled with powder, and the magnetic field is axially directed to the cylindrical ring cavity. It was confirmed that the magnetized powder was adsorbed by the upper and lower lids, and the powder did not fall or collapse even when the core was pulled out. Then, with the core pulled out, the mold was placed in a sintering furnace with the cylinder axis vertical, and sintering was performed at 1010 ° C. for 2 hours. The sintered body produced in this manner had no deformation or distortion, and had a cylindrical ring shape as expected from sintering shrinkage. Moreover, it was confirmed that there was no defect such as a nest and the density was high. Results of measurement of magnetic properties, the cylindrical ring NdFeB sintered body produced in this experiment is much higher B _r than NdFeB sintered magnet made by a magnetic field parallel in the press of the conventional method (mold pressing) And (BH) _max , and it was confirmed that it had the same characteristics as magnets produced by pressing in a perpendicular magnetic field or higher characteristics depending on the conditions. FIG. 8 shows a photograph of the mold used in this experiment and the cylindrical ring-shaped NdFeB sintered magnet produced thereby. At this time, the outer diameter of the mold cavity was 23.0 mm, the inner diameter was 10.0 mm, and the height was 33.2 mm. The produced cylindrical ring-shaped magnet had an outer diameter of 19.1 mm, an inner diameter of 8.6 mm, and a height of 22.3 mm.

[Experiment 8]
Five types of alloys with different compositions and thicknesses as shown in Table 3 were prepared.
Hydrogen was occluded in these alloys and fine cracks were formed in the alloys, and then the alloys were heated to 400 ° C. to remove hydrogen in the main phase. The hydrogen pulverized alloy was pulverized by a jet mill. A powder having a particle size of D ₅₀ = 4 μm or less was prepared by pulverizing by changing the pulverization conditions of the jet mill. Before jet milling, zinc stearate powder (solid lubricant) at 0.05% of the alloy weight was added to the hydrogen-pulverized alloy. These powders were transferred to a high-performance glove box (dew point of about −80 ° C.) filled with high-purity Ar so as not to be exposed to air, and all subsequent powders were handled in this glove box. In the glove box, first, the liquid lubricant methyl caproate was added to 0.5% alloy powder, and the mixture was stirred for about 5 minutes with a mixer that rotates at high speed. These powders were filled into a permalloy mold having a cylindrical cavity having a diameter of 10 mm and a depth of 10 mm. Packing density was varied in 0.1 g / cm ³ increments from 2.5 g / cm ³ to 4.1 g / cm ^3. After filling the mold with the powder, the mold was capped. The lid was not particularly provided with small holes or grooves, and the clearance at the fitting portion between the lid and the mold mouth was used as a deaeration hole during sintering. The mold filled with the powder was put in a sealed container, and a pulsed magnetic field was applied to the powder and the mold while being put in the sealed container. The pulse magnetic field was changed in the range of 1.8T to 9T, and an AC decay pulse and a DC pulse were sequentially applied to perform magnetic field orientation of the powder. After the powder was magnetically oriented, the sealed container was coupled to the sintering furnace inlet, and the mold in the sealed container was transferred into the sintering furnace without any contact with air, and the sintering furnace inlet was closed. Sintering was performed in a high vacuum of 10 ⁻⁴ Pa or higher. The sintering temperature was changed in the range of 950 ° C. to 1050 ° C., and the lowest temperature at which the density of the sintered body after sintering (sintering density) exceeded 7.5 g / cm ³ was determined as the optimum temperature. The sintering time was 2 hours. After sintering, the sintered body was rapidly cooled from 800 ° C. to room temperature, and then rapidly cooled by heating at 500 to 600 ° C. for 1 h. After the heat treatment, all samples were processed into a cylinder having a diameter of 7 mm and a length of 7 mm, and a magnetization curve was measured by appearance inspection, density measurement, and pulse magnetization measurement with a maximum magnetic field of 10T. The main results of this experiment are shown in Table 4.
In Table 4, the orientation magnetic field of 9.0P or 1.8P means a pulse magnetic field having peak values of 9.0T and 1.8T, respectively. Then, a DC pulse having the same peak value was applied twice in the same direction. 2.5D indicates that a 2.5 T DC magnetic field was applied. At this time, a DC magnetic field was first applied in one direction of the mold, and then a DC magnetic field having the same strength was applied by changing the magnetic field application direction in the reverse direction while the mold was fixed.

In this experiment, by the method of the present invention, NdFeB having a high coercive force, which is difficult to achieve by the conventional method, can be safely used with a powder having an extremely small particle size, which is difficult to handle by the conventional mold press method and RIP method. It was confirmed that the sintered magnet can be manufactured industrially.
However, in order to obtain such high characteristics, it is desirable to appropriately set the packing density of powder in the mold, the orientation magnetic field, the sintering temperature, and the like. In samples 1 to 13, high residual magnetic flux density B _r , maximum energy product (BH) _max , coercive force H _cJ and orientation degree J _r / J _s are obtained. On the other hand, Samples 14 and 15 have a higher sintering temperature than the other samples, but (BH) _max and coercive force _HcJ are slightly lower than _those of the other samples. Sample 16 has a low orientation magnetic field, and B _r , (BH) _max and J _r / J _s are slightly lower than those of other samples. Sample 17 had a packing density lower than that of the other samples, but cavities were formed in the sintered body, and magnetic properties comparable to those of other samples could not be measured.
The comparative example shows an example of an NdFeB sintered magnet manufactured by using a conventional powder having a standard particle size by a conventional die press method. In the comparative example, the particle size of the powder cannot be made very small, so it can be seen that the coercive force obtained is smaller than that of the magnet of the present invention.

The perspective view which shows the example of the single piece mold 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-piece mold 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-piece mold 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 mold 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. The photograph of the disk-shaped NdFeB sintered magnet produced in a present Example, and the mold used for the production. The cylindrical ring-shaped NdFeB sintered magnet produced in a present Example (The magnetic field orientation direction is a direction parallel to an axis | shaft), and the photograph of the mold used for the production.

Explanation of symbols

40 ... Bulkhead
41 ... Weighing / filling section
42 ... Densification part
43 ... Magnetic field orientation part
44 ... Sintering furnace
45 ... conveyor
46 ... Mold
47 ... Hopper
48 ... Guide
49 ... lid
50 ... Press cylinder
51 ... Push bar
52 ... Tapping device
53 ... Holder
54 ... Coil
55… Outer bulkhead

Claims (27)

a) filling a mold having a cavity corresponding to the shape of the product with an alloy powder of NdFeB magnet not containing Dy and Tb at a density between 46.4% and 55% of the true density ;
b) applying a magnetic field to the alloy powder to orient the alloy powder;
c) a step of heating and sintering to a sintering temperature of 1010 ° C. or lower in a state where the alloy powder is filled in a mold and a gas component released from the alloy powder can be discharged out of the mold;
d) removing the sintered body of the alloy powder from the mold;
The method for producing a magnetic anisotropic rare earth sintered magnet is characterized in that the process from the filling step to the sintering step is performed consistently in a container in an oxygen-free or inert gas atmosphere. a) Fill a mold with a cavity corresponding to the shape of the product with an alloy powder of NdFeB magnet containing 6% by weight or less of Dy and / or Tb at a density between 46.4% and 55% of the true density. Process,
b) applying a magnetic field to the alloy powder to orient the alloy powder;
c) a step of heating and sintering to a sintering temperature of 1010 ° C. or lower in a state where the alloy powder is filled in a mold and a gas component released from the alloy powder can be discharged out of the mold;
d) removing the sintered body of the alloy powder from the mold;
The method for producing a magnetic anisotropic rare earth sintered magnet is characterized in that the process from the filling step to the sintering step is performed consistently in a container in an oxygen-free or inert gas atmosphere.   The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 2, wherein the alloy powder has a Dy and / or Tb content of 3% by weight or less. The method of manufacturing a magnetic anisotropic rare earth sintered magnet according to claim 1 or 2, wherein the magnetic field is 2T or more. The method of manufacturing a magnetic anisotropic rare earth sintered magnet according to claim 4, wherein the magnetic field is 3T or more. 6. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 5, wherein the magnetic field is 5 T or more. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein the magnetic field is an alternating magnetic field. The method of manufacturing a magnetic anisotropic rare earth sintered magnet according to any one of claims 1 to 7, wherein the magnetic field is applied a plurality of times. 9. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 8, wherein the magnetic field is a combination of a DC magnetic field and an alternating magnetic field.   The method for producing a magnetic anisotropic rare earth sintered magnet according to any one of claims 1 to 9, wherein a lubricant composed of a solid or both a solid and a liquid is added to the alloy powder.   The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 10, wherein the liquid lubricant contains a fatty acid ester or a depolymerized polymer as a main component. The magnetic anisotropic rare earth sintered magnet according to any one of claims 1 to 11, wherein an average particle diameter D50 of the alloy powder measured by a laser powder particle size distribution measuring device is 0.5 µm or more and 3 µm or less. Manufacturing method. 13. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 12, wherein the average particle diameter D50 is 0.5 μm or more and 2 μm or less.   The method for producing a magnetic anisotropic rare earth sintered magnet according to any one of claims 1 to 13, wherein a part or all of the mold is used a plurality of times. The alloy powder is filled in the cavity with the above density and oriented by applying a magnetic field, and then the mold core is removed or the mold core is replaced with a thin one and sintered. Item 15. A method for producing a magnetic anisotropic rare earth sintered magnet according to any one of Items 1 to 14.   16. The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1, wherein a magnetic field is applied in the direction of the main axis of the cavity to orient the alloy powder.   The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 16, wherein the material of the lid and the bottom of the cavity in the principal axis direction is made of a ferromagnetic material.   18. The alloy powder is oriented by applying a magnetic field in a direction perpendicular to the flat plate surface or the arcuate plate surface of the cavity using a mold having a flat plate or arcuate plate-like cavity. A method for producing a magnetic anisotropic rare earth sintered magnet according to claim 1.   The magnetic anisotropic rare earth sintered magnet according to claim 18, wherein a material of a portion forming the flat plate surface or the arcuate plate surface of the cavity is a non-magnetic material or has a saturation magnetization of 1.5 T or less. Production method.   The method for producing a magnetic anisotropic rare earth sintered magnet according to claim 19, wherein the saturation magnetization is 1.3 T or less.   The method for producing a magnetic anisotropic rare earth sintered magnet according to any one of claims 1 to 20, wherein the mold has a plurality of cavities arranged in two or more rows.   The magnetic anisotropy according to any one of claims 1 to 21, wherein a part or all of a part of the mold constituting a wall parallel to the magnetic field orientation direction of the alloy powder is a ferromagnetic material. Of manufacturing a rare earth sintered magnet.   A mold for producing a magnetic anisotropic rare earth sintered magnet, comprising: a cylindrical cavity; and a columnar core disposed at the center of the cylindrical cavity.   A mold for producing a magnetic anisotropic rare earth sintered magnet having a cylindrical or columnar cavity, wherein the material at the lid and the bottom of the cavity in the depth direction is a ferromagnetic material.   Magnetic anisotropic characterized by having a flat plate or arcuate plate-like cavity, and the material of the portion forming the flat plate surface or the arcuate plate surface of the cavity is a non-magnetic material or a saturation magnetization of 1.5 T or less Mold for producing rare earth sintered magnets.   The mold for manufacturing a magnetic anisotropic rare earth sintered magnet according to claim 25, wherein the saturation magnetization is 1.3 T or less.   A mold for producing a magnetic anisotropic rare earth sintered magnet, wherein a part or all of a portion constituting a wall parallel to the magnetic field orientation direction of the alloy powder is a ferromagnetic material.