JPH0917670A - Rare earth sintered magnet manufacturing method - Google Patents

Abstract

(57) [Abstract] [Purpose] In a method for producing a rare earth sintered magnet by powder metallurgy, the reaction between the alloy powder and the binder is suppressed, and the residual oxygen content and residual carbon content of the sintered body are reduced. , Rare earth-based sintering with thin and complex shapes and excellent magnetic properties, which improves the fluidity and lubricity of powder during molding to improve the dimensional accuracy and productivity of molded products. Providing a method for manufacturing a magnet. [Structure] A binder composed of water and at least one polymer selected from polyethylene oxide, water-soluble polyvinyl acetal, polyacrylic acid, polyacrylic acid derivative, and water-soluble carboxyalkyl cellulose derivative is added to the rare earth alloy powder and kneaded. To form a slurry, and the slurry is granulated into a predetermined particle size by a spray dryer to improve the fluidity and lubricity of the powder during molding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare-earth sintered magnet by powder metallurgy, which is a spherical granulated powder having high fluidity and which has excellent magnetic properties.
This alloy powder is kneaded with a specific binder to form a slurry, and the slurry is sprayed by a spray dryer device and cooled to obtain a fluidity of the powder during compression molding,
A rare earth-based sintered magnet capable of improving the lubricity and improving the molding cycle and the dimensional accuracy of the molded body, and providing a sintered magnet having a small shape, a thin shape or a more complicated shape and excellent magnetic properties. Manufacturing method.

[0002]

2. Description of the Related Art Today, small motors and actuators used for computer peripherals such as home electric appliances, automobiles, etc. are required to have high performance as well as miniaturization. In addition to downsizing, weight reduction, and thinning, a product having a complicated shape is required, such as providing irregularities at predetermined positions on the surface of the magnet material or providing through holes. Typical representative permanent magnet materials at present are alnico magnets, ferrite magnets, rare earth cobalt magnets, R-Co magnets, and R-Fe-B magnets previously proposed by the applicant (Japanese Patent Publication No. 61-34242). etc)
Is mentioned.

Among the above, R-Co magnets and R
Rare earth magnets such as -Fe-B magnets are mainly composed of light rare earth elements, which are abundant in resources, so that the magnets can be stably supplied, and compared with other magnet materials. It is widely used for various purposes because of its outstanding magnetic properties. The above-mentioned rare earth magnet, for example, R-Fe-
The B-based sintered permanent magnet has a maximum energy product ((BH) ma
x) exceeds 40 MGOe, and exceeds 50 MGOe at the maximum, and has extremely excellent magnetic properties. In order to exhibit the excellent magnetic properties, an alloy having the required composition should be crushed to an average particle size of about 1 to 10 μm. Is required.

When the grain size of the alloy powder is reduced, the fluidity of the powder during molding deteriorates, which causes variations in the density of the compact and shortens the life of the molding machine, and also causes variations in the dimensional accuracy after sintering. Especially, it was difficult to obtain a product having a thin shape or a small shape. Further, since the rare earth magnet contains a rare earth element or iron which is easily oxidized in the atmosphere, there is a problem that the magnetic characteristics are deteriorated by the oxidation when the grain size of the alloy powder is reduced, and in particular, the R-Fe-B permanent magnet is used. The magnet exhibits excellent magnetic properties by generating a specific structure of rare earth and boron as well as a specific compound or compound phase with these or iron due to a specific composition, but when the grain size of the alloy powder is reduced, the above-mentioned active There is also a problem that the magnetic characteristics are deteriorated by the oxidation of the compound or the compound phase.

[0005]

Therefore, in order to improve the moldability in particular, an alloy powder before molding is added with polyoxyethylene alkyl ether or the like (Japanese Patent Publication No. Hei 4-
80961), those to which paraffin or stearate is further added (Japanese Patent Publication No. 4-80962, Japanese Patent Publication No. 5-53842), and those to which oleic acid has been added (Japanese Patent Publication No. 62-36365). Was done. However, although the moldability can be improved to some extent, the effect of the improvement is limited, and it has been still difficult to form a thin or small shape required in recent years.

Further, as a method for manufacturing thin-walled shaped products and small-sized shaped products by further improving the moldability together with the addition of the above-mentioned binder and lubricant, saturated alloyed carboxylic acid and unsaturated fat are added to the alloy powder before molding. A method of adding a lubricant composed of a saturated or unsaturated aliphatic ester to an aromatic carboxylic acid, kneading the mixture, and then granulating the mixture (JP-A-62-245604).
No.), or a method in which a saturated aliphatic carboxylic acid, an unsaturated aliphatic carboxylic acid or the like is added to a paraffin mixture, kneaded, granulated and then molded (JP-A-63-237402).

[0007] However, in the above method, it was difficult to realize sufficient fluidity of the powder because the binding force of the powder particles was not sufficient and the granulated powder was easily broken. The amount of various binders and lubricants added may be increased in order to improve the moldability and the binding force of the powder particles. However, if added in large amounts, the R component in the rare earth-containing alloy powder and the binder may be added. Due to the reaction, the amount of residual oxygen and the amount of residual carbon in the sintered body after sintering increase, which causes deterioration of magnetic properties, so that the addition amount is also limited.

Although not intended for rare earth-containing alloy powders, it is used as a binder for compression molding of Co-based superalloy powders in an amount of 1.5 to 3.5 wt% with respect to the target alloy powder. A composition is proposed (USP 4,118,480) in which methyl cellulose and a predetermined amount of additive glycerin and boric acid are mixed, and a special composition is used as a binder for injection molding of alloy powder for tools. 0.5 to 2.5 wt
A composition in which water, a plasticizer such as glycerin, a lubricant such as a wax emulsion, and a release agent is added to 100% methylcellulose has been proposed (JP-A-62-37302).

However, in order to ensure a predetermined fluidity and compact strength, all of them use a relatively large amount of binder such as 0.5 wt% or more with respect to the target alloy powder as described above. In addition, it is indispensable to add various binder additives, for example, plasticizer such as glycerin in the same amount as that of methyl cellulose. Carbon and oxygen remain, and in particular, in the case of the rare earth-based sintered magnet that is the subject of the present invention, the magnetism is deteriorated, so it cannot be easily applied.

Polyvinyl alcohol used as a binder is used for producing oxides such as sintered ferrite,
For example, a calcined powder of ferrite is wet pulverized with a ball mill to an average particle size of about 1 μm, then a binder such as polyvinyl alcohol is added by 0.6 to 1.0 wt% and a granulated powder of 50 to 100 μm is produced by a spray dryer. Then, the granulated powder is molded and sintered.

However, all of them use a large amount of binder of 0.6 wt% or more with respect to the oxide powder, and a considerable amount of carbon and oxygen remain in the sintered body after the degreasing treatment. Therefore, the rare-earth alloy powder of the present invention, which has the property of being extremely easily oxidized and carbonized and whose magnetic characteristics are extremely deteriorated even by a little oxidation or carbonization, is made of the above oxides. The method cannot be applied as is. In particular, in the case of an oxide, even if a relatively large amount of binder is used, it can be degreased and sintered in the air, so that the binder burns during degreasing and sintering, and it is possible to suppress residual carbon to some extent. In the case of the rare earth-containing alloy powder that is the subject of the invention, since the magnetic properties deteriorate due to oxidation, it is impossible to degrease and sinter in the air, so addition of a large amount of binder is fatal to the magnetic properties of the obtained sintered magnet. It will have an adverse effect.

As described above, in the method for producing a rare earth sintered magnet, various attempts have been made to improve the formability by adding various binders and lubricants to the alloy powder before forming and further granulating. Although proposed, it has been difficult to produce a rare-earth sintered permanent magnet having a thin shape or a small shape and excellent magnetic characteristics, which is required in recent years, by any of the methods.

The present invention is a method for producing a rare earth-based sintered magnet by powder metallurgy, which suppresses the reaction with an alloy powder binder to reduce the residual carbon content and residual oxygen content of the sintered body and further Rare earth with thin and complex shapes and excellent magnetic characteristics, which improves the fluidity and lubricity of the powder at the time to improve the dimensional accuracy of the molded body, productivity and magnetic characteristics. An object of the present invention is to provide a method for manufacturing a sintered sintered magnet.

[0014]

Means for Solving the Problems The inventors of the present invention have studied various methods of suppressing the reaction between the rare earth-containing alloy powder and the binder and reducing the residual carbon content and residual oxygen content of the sintered body. Rare earth in the step before sintering by using a binder composed of at least one polymer selected from the group consisting of water, polyethylene oxide, water-soluble polyvinyl acetal, polyacrylic acid, polyacrylic acid derivative, and water-soluble carboxyalkyl cellulose derivative. It was found that the reaction between the contained alloy powder and the binder can be suppressed, and the residual oxygen content and residual carbon content of the sintered body after sintering can be significantly reduced.

Further, when the above-mentioned binder uses polyethylene oxide, water-soluble polyvinyl acetal, polyacrylic acid, polyacrylic acid derivative, and water-soluble carboxyalkyl cellulose derivative alone, the addition amount thereof is based on 100 parts by weight of alloy powder. Even if the amount is 0.5 parts by weight or less, sufficient interparticle bonding force of primary particles, sufficient fluidity and molded body strength to sufficiently withstand vibration in a feeder for supplying powder to a mold during molding. What can be obtained, polyethylene oxide,
When a water-soluble polyvinyl acetal, a polyacrylic acid, a polyacrylic acid derivative, and a water-soluble carboxyalkyl cellulose derivative are respectively compounded, and these polymers and polymers such as polyvinyl alcohol, methyl cellulose, and polyacrylamide that the present inventors have already found. It has been found that in the case of compounding with, even if the addition amount is 0.4 parts by weight or less based on 100 parts by weight of the alloy powder, the same function and effect as described above can be obtained.

Further, a slurry having a rare earth-containing alloy powder and the above binder added and kneaded is used to produce a highly fluid spherical granulated powder by a spray dryer device, and the granulated powder is used. By molding, the granulated powder has a sufficient binding force, combined with the excellent fluidity of the binder itself, the fluidity of the powder is significantly improved, the variation of the compact density and the life of the molding machine are shortened. The present invention has been completed based on the finding that a rare-earth sintered magnet having a thin shape and a small shape and excellent magnetic properties, which is excellent in dimensional accuracy after sintering without being made, can be efficiently obtained.

That is, the present invention comprises a rare earth-containing alloy powder, and at least one polymer selected from polyethylene oxide, water-soluble polyvinyl acetal, polyacrylic acid, polyacrylic acid derivative, and water-soluble carboxyalkyl cellulose derivative, and water. Add binder,
A method for producing a rare earth-based sintered magnet, which comprises kneading to form a slurry, forming the slurry into a granulated powder by a spray dryer device, and using the granulated powder to obtain a sintered magnet by a powder metallurgy method. Is.

Rare Earth-Containing Alloy Powder In the present invention, the target rare earth-containing alloy powder is
Any composition containing the rare earth element R is applicable, but among them, R-Fe-B based alloy powder and R-Co.
-Based alloy powder, or those obtained by substituting an element other than the rare earth element (R) in the alloy powder with another element, for example, R
-Fe-B system Fe is a transition metal such as Co, B is C or S
Those substituted with a semimetal such as i are most suitable. In particular, as the rare earth-containing alloy powder, a powder obtained by pulverizing a single alloy having the required composition, a powder prepared by mixing alloy powders having different compositions to obtain the required composition, for improving coercive force and improving manufacturability. Known alloy powders can be used, such as those in which additional elements are added at the time of blending the raw materials or before and after crushing.

As the production method, a known method such as a dissolution / pulverization method, an ultra-quenching method, a direct reduction diffusion method, a hydrogen-containing disintegration method, an atomization method can be appropriately selected, and the particle size thereof is also particularly limited. However, if the average particle size of the alloy powder is less than 1 μm, it is not preferable because it reacts easily with oxygen in the atmosphere or with a binder and a solvent to easily oxidize, which may deteriorate the magnetic properties after sintering, and exceeds 10 μm. The average particle size is not preferable because the particle size is too large and the sintered density is saturated at about 95%, and improvement in the density cannot be expected. Therefore, the average particle size of 1 to 10 μm is a preferable range. Particularly preferably, it is in the range of 1 to 6 μm.

Binder Component In the present invention, the binder component added to make the alloy powder into a slurry is polyethylene oxide,
A material comprising at least one polymer selected from water-soluble polyvinyl acetal, polyacrylic acid, polyacrylic acid derivative, and water-soluble carboxyalkyl cellulose derivative and water is used. The polymer selected from the above-mentioned polyethylene oxide, water-soluble polyvinyl acetal, polyacrylic acid, polyacrylic acid derivative, and water-soluble carboxyalkyl cellulose derivative forms a uniform slurry with a small amount of addition, and the slurry viscosity is spray granulated. It is easy to adjust the viscosity to a suitable level for carrying out, and it is possible to maintain a high binding force even after drying, and since a small addition amount is sufficient, the residual oxygen amount and residual carbon amount in the powder can be controlled. It can be reduced.

In the polymer used in the present invention, polyethylene oxide is easily dissolved in water, does not gel even when heated, has a good thermal decomposability, and has a powder dispersibility during the preparation of a slurry. Since it is excellent and has excellent lubricity during press molding, it is suitable as a polymer used in the present invention. In order to make full use of these characteristics, those having an average molecular weight of 20,000 to several million are preferable. Molecular weight 2
If it is less than 10,000, the polymer itself will change from a waxy solid to a liquid and the strength of the polymer itself will not be sufficient, and as a result, the binding force to the alloy particles after drying in the granulation process will be insufficient and the granulation will not be complete. , May remain as fine powder.
Further, when the molecular weight exceeds several million, the binding force is improved, but the viscosity of the aqueous solution is significantly increased, and the slurry viscosity becomes high even when added in a small amount during the preparation of the slurry, so that the supply stability to the rotating disk becomes poor. , The particle size distribution of the obtained granulated powder may be disturbed. Further, those having a molecular weight higher than this are not industrially and universally produced, and are economically disadvantageous.

In the polymer used in the present invention, the water-soluble polyvinyl acetal is a polymer obtained by the condensation reaction of polyvinyl alcohol and aldehyde. The properties of the polymer obtained by this reaction vary greatly depending on the molecular weight of the starting polyvinyl alcohol, the degree of saponification, the degree of acetalization, and the like. In the present invention, as long as it has a desired binding force and can obtain an appropriate slurry viscosity and slurry dispersibility, it is not limited to these values, but generally the saponification degree is 70 to 99, A polymer obtained by using polyvinyl alcohol having a degree of polymerization of several hundreds to several thousands and acetalizing several mol% to several tens mol% is preferable.

In the polymer used in the present invention, the polyacrylic acid and the polyacrylic acid derivative are water-soluble polyacrylic acid, polymethacrylic acid and their metal salts, ammonium salts and the like. Since polyacrylic acid and polymethacrylic acid are amorphous and are extremely hard polymers, they give sufficient bond strength to alloy particles, and as a result, granulation can be imparted with a small amount of addition. Is. Further, although those salts are inferior in strength to the above-mentioned two kinds of polymers, they have a peptizing action,
It is suitable for improving the uniformity of the slurry in the process of preparing the slurry.

In the polymer used in the present invention, the water-soluble carboxyalkyl cellulose derivative is a metal salt, ammonium salt or the like for partially etherifying the three hydroxyl groups of the cellulose skeleton and further making it water-soluble.

Slurry In the present invention, a slurry is prepared by adding the above polymer and water as a solvent to alloy powder, and stirring and kneading the mixture. The slurry concentration is slurry viscosity, alloy powder dispersibility, and spray granulation. It can be appropriately selected from the viewpoint of the amount of treatment in the process, and it is generally desirable that the alloy powder concentration in the slurry is 40 to 80% by weight. If the above concentration is less than 40% by weight, solid-liquid separation occurs in the stirring and kneading step, the dispersibility of the slurry decreases, and not only a non-uniform slurry is formed, but also the slurry is supplied from the stirring and kneading tank to the spray dryer during the supply. Sedimentation occurs in the pipe, and fine powder that has not been granulated is mixed with the obtained granulated powder, or non-spherical granulated powder is formed. On the other hand, when the concentration exceeds 80% by weight, the viscosity of the slurry is significantly increased and uniform stirring and kneading cannot be performed, and the slurry cannot be supplied from the stirring and kneading tank to the spray dryer device.

In the present invention, the slurry supplied to the spray dryer comprises at least alloy powder, polymers containing the above polymer, and water as a solvent. The amount of the polymers added at this time is 100 weight% of the alloy powder. It is 0.05 to 0.7 parts by weight, preferably 0.05 to 0.5 parts by weight, based on parts. If the addition amount is less than 0.05 parts by weight, the bond between the particles in the granulated powder is weak, and the ungranulated fine powder is mixed in the powder, or the granulated powder is broken during powder feeding before molding and the powder Is not preferable because the fluidity of the powder is remarkably reduced, and when it exceeds 0.7 parts by weight, the residual oxygen amount and the residual carbon amount in the sintered body are increased, the coercive force is lowered, and the magnetic properties are deteriorated, which is not preferable. .

Water, which is a solvent in the present invention, suppresses the reaction with the R component of the rare earth-containing alloy powder as much as possible.
It is desirable to use pure water that has been treated with dissolved oxygen or water that has undergone bubbling substitution with an inert gas such as nitrogen.

The addition and stirring of the binder to the alloy powder is preferably carried out within the temperature range of 0 ° C. to 30 ° C., so that the oxidation reaction between the alloy powder and water can be further suppressed. On the contrary, stirring at a temperature higher than 30 ° C. is not preferable because it promotes the oxidation reaction between the alloy powder and water. 0 ° C ~
In order to maintain the temperature within the temperature range of 30 ° C., it is possible to use water which has been cooled to the temperature in advance, or a means for cooling the stirring container with cooling water or the like.

When a plasticizer is added to the above slurry, the powder form can be permanently deformed with a little force when press-molding the granulated powder. The polymers according to the present invention have a high interparticle bonding force for facilitating granulation, and thus have excellent shape-retaining properties, but retain their shape-retaining properties even under constant pressure during press molding. As a result, the green compact density decreases, and sometimes the magnetic field applied during molding in a magnetic field does not completely align due to its excellent interparticle bonding force, and as a result, the residual magnetic flux density of the resulting sintered body is reduced. This causes deterioration of magnetic properties. Therefore, it is preferable to add a plasticizer in order to lower the intermolecular interaction of the polymer chains and lower the glass transition temperature.

As the plasticizer, in consideration of its plasticizing effect, compatibility with a polymer, chemical stability, physical properties (boiling point, vapor pressure, etc.), reactivity with an alloy powder, etc., a generally known plasticizer is used. Agents can be used, and in the case of an aqueous slurry using a water-soluble polymer as in the present invention, ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, propylene glycol, glycerin, butanediol. , Diethylene glycol, triethylene glycol and the like can be used.

The addition amount of the plasticizer can be appropriately selected depending on the above-mentioned characteristics of the plasticizer, but it is usually 2 to 100 parts by weight with respect to 100 parts by weight of the polymer added to the slurry, and if the addition amount is less than 2 parts by weight. However, the plasticity effect is not sufficient, the orientation in a magnetic field is not improved, and the magnetic properties (residual magnetic flux density) of the obtained sintered body are reduced. In addition to lowering the granulation property and lowering the fluidity, these water-soluble plasticizers generally have high hygroscopicity, which reduces the drying property in the granulation process and increases the residual water content in the powder. However, there are problems such as causing oxidation and absorbing moisture during storage of the powder. More preferably 5
~ 70 parts by weight addition. Further, if necessary, additives such as a deflocculant (dispersant), a lubricant, an antifoaming agent and a surface treatment agent can be added within a range in which the residual carbon concentration of the sintered body does not significantly increase. .

Granulation Method In the present invention, the slurry obtained by adding the above-mentioned binder to the alloy powder and kneading the mixture into granulated powder by a spray dryer device. First, a method for producing granulated powder using a spray drier will be described. A slurry is supplied from a slurry stirrer to a spray drier, for example, sprayed by centrifugal force of a rotating disk, or atomized by a pressure nozzle tip. The sprayed droplets are instantaneously dried by hot air of the heated inert gas to become granulated powder, and fall naturally to the lower part in the collection unit.

The structure of the spray dryer device is as follows.
Any of the above disk rotating type and pressure nozzle type may be used, and a known open type spray dryer device may be used. However, since the rare earth-containing alloy powder to be granulated is very easy to oxidize, the slurry storage of the device is performed. It is preferable that the inside of the unit or the inside of the unit for collecting the granulated powder can be replaced with an inert gas or the like, and the oxygen concentration can be constantly maintained at 3% or less.

As for the structure in the recovery part of the spray dryer device, in order to instantly dry the liquid droplets sprayed from the rotating disk or the pressure nozzle, it is heated above the rotating disk or above the pressure nozzle. An injection port for injecting an inert gas is arranged, and a discharge port for discharging the injected gas to the outside of the recovery unit is provided in the lower part inside the recovery unit.At that time, a heater external to the device or attached to the device in advance. In order not to lower the temperature of the inert gas heated to the required temperature in 1., it is preferable to maintain the injection port at a temperature corresponding to the temperature of the inert gas, for example, 60 to 150 ° C.

That is, when the temperature of the inert gas is lowered, the sprayed liquid droplets cannot be dried sufficiently in a short time, so that the slurry supply amount must be reduced and the efficiency is lowered. . When making granulated powder with a relatively large particle size, the rotation speed of the rotating disk or the pressure of the pressure nozzle is lowered, but if the temperature of the inert gas is lowered at that time, it is sprayed. The droplets cannot be dried sufficiently, and as a result, the supply amount of the slurry is reduced, resulting in extremely low efficiency when obtaining granulated powder having a large particle size. Therefore, in order to feed the preheated inert gas into the recovery unit while maintaining the temperature of the inert gas as it is, it is preferable to maintain the temperature of the injection port at 60 to 150 ° C, and most preferably around 100 ° C.

Further, when the temperature difference between the inert gas injection port and the exhaust port is small, the processing efficiency tends to decrease, so that
It is desirable to set the temperature of the discharge port at 50 ° C. or lower, preferably 40 ° C. or lower, and particularly preferably about room temperature. As the inert gas, nitrogen gas or argon gas is preferable,
The heating temperature is preferably 60 to 150 ° C.

The particle size of the granulated powder includes the slurry concentration and slurry viscosity to be supplied to the spray dryer device, its supply amount,
Alternatively, it can be controlled by the rotation speed of the rotating disk or the pressure of the pressure nozzle, but the average particle size is 10 μm.
If it is less than the above, the effect of improving the fluidity of the granulated powder is not so much seen, and if the average particle size exceeds 400 μm, the particle size is too large and the packing density in the mold at the time of molding decreases and It is not preferable because the body density also lowers, which in turn lowers the density of the sintered body after sintering. Therefore,
The average particle size of the granulated powder is preferably 10 to 400 μm, particularly preferably 40 to 200 μm.

Further, by performing undercutting and overcutting with a sieve, it is possible to obtain a granulated powder having an extremely high fluidity. Further, by adding a small amount of a lubricant such as zinc stearate, magnesium stearate, calcium stearate, and aluminum stearate to the obtained granulated powder, it is possible to further enhance the fluidity.

Any known powder metallurgical means can be adopted as the conditions, means and the like of the steps after granulation, that is, the steps such as molding, sintering and heat treatment. Below is R-Fe-B
An example of preferable conditions in the case of a system magnet will be shown. The molding can be carried out by any known molding method, but compression molding is most preferable, and the pressure is 0.3 to 2.0 ton.
/ Cm ² is preferred. The magnetic field strength in the case of applying a magnetic field for molding is preferably in the range of 10 to 20 kOe. Before sintering, a general method of heating in vacuum,
The temperature is raised at 100 to 200 ° C./hour in a hydrogen stream to 300
The binder removal treatment is preferably performed by a method of holding at 600 ° C for 1 to 2 hours. Almost all carbon in the binder is decarburized by applying the debinding process,
Magnetic properties are improved.

Since the alloy powder containing the R element easily absorbs hydrogen, it is preferable to perform the dehydrogenation treatment after the debinding treatment in the hydrogen stream. Dehydrogenation process,
In vacuum, the temperature is raised at a heating rate of 50 to 200 ° C./hour,
By holding at 500 to 800 ° C. for about 1 to 2 hours, the stored hydrogen is almost completely removed. Note that after the dehydrogenation treatment, it is preferable to subsequently perform heating and heating to perform sintering, and the temperature rising rate after exceeding 500 ° C. may be arbitrarily selected, for example, 100 to 300 ° C./hour. A known heating method that is generally adopted in sintering is possible.

The sintering of the molded product after the binder removal treatment and the heat treatment conditions after the sintering are appropriately selected according to the selected alloy composition powder, but the sintering and the heat treatment conditions after the sintering are from 1000 to 1,000. A sintering step of holding at 1200 ° C for 1 to 2 hours, an aging treatment step of holding at 450 to 800 ° C for 1 to 8 hours, and the like are preferable.

[0042]

The present invention provides a binder comprising a rare earth-containing alloy powder, at least one polymer selected from polyethylene oxide, water-soluble polyvinyl acetal, polyacrylic acid, polyacrylic acid derivative, and water-soluble carboxyalkyl cellulose derivative, and water. Is added and kneaded to form a slurry, and the slurry is formed into a highly fluid spherical granulated powder by a spray dryer device, and the granulated powder is molded, sintered, and heat treated to form a binder. Combined with the excellent lubricity of itself, the fluidity of the powder is remarkably improved, the molding cycle is improved, and there is no variation in the density of the molded body or reduction in the life of the molding machine.
It is possible to obtain a rare earth-based sintered magnet having a small shape, a thin shape, and excellent magnetic characteristics, which has a small amount of residual oxygen and residual carbon in the sintered body after sintering and is excellent in dimensional accuracy.

Since the granulated powder in the present invention is isotropic in itself, when it is molded without applying a magnetic field, it naturally becomes an isotropic sintered body. When molding while applying, due to the action of the compressive stress and the magnetic field, the granulated powder is broken into the original primary particles, and the primary particles are oriented by the magnetic field, so that an anisotropic molded body is obtained.
It also has the advantage that both isotropic magnets and anisotropic magnets can be manufactured depending on the application.

[0044]

【Example】

Example 1 Nd: 13.3 atomic%, Pr: 0.31 atomic%, Dy:
A raw material consisting of 0.28 atomic%, Co: 3.4 atomic%, B: 6.5 atomic%, the balance: Fe and unavoidable impurities,
High-frequency melting was performed in an Ar gas atmosphere to obtain a button-shaped ingot alloy. Next, the alloy was coarsely crushed, then crushed with a jaw crusher or the like to have an average particle size of 15 μm, and further with a jet mill to obtain a powder having an average particle size of 3 μm.

Polyethylene oxide (average molecular weight: 500000) was used as a polymer in the obtained powder, and water and a plasticizer were added to 100 parts by weight of the alloy powder.
To prepare a slurry by stirring and kneading the mixture at room temperature, and using a disk rotary spray dryer, nitrogen was used as an inert gas, the hot air inlet temperature was 100 ° C, and the outlet temperature was 40 ° C. Granulation was performed by setting the temperature to ° C. The resulting granulated powder was undercut with fine particles through a # 440 sieve, and overcut with coarse particles through a # 70 sieve. Table 1 shows the average particle size of the granulated powder and the yield of # 440 to # 70.

The above granulated powder was compressed by using a compression magnetic field press.
Magnetic field strength 15 kOe, pressure 1 ton / cm ² 10 mm
After forming into a shape of × 15 mm × thickness 10 mm, the binder was removed by heating to a room temperature of 300 ° C at a temperature rising rate of 100 ° C / hour in a hydrogen atmosphere. Sequentially, the temperature is raised to 1100 ° C. in vacuum and the sintering is performed for 1 hour. After the completion of the sintering, Ar gas is introduced and the temperature is cooled to 800 ° C. at a rate of 7 ° C./min. An aging treatment was performed by cooling at a speed and holding at 550 ° C. for 2 hours to obtain an anisotropic sintered body.

The average particle size of the granulated powder, the fluidity of the granulated powder during molding, the size of the molded body, the density of the molded body, and the residual oxygen content, residual carbon content, and magnetic properties of the obtained sintered magnet were measured. The results are shown in Table 1. In addition, cracks, cracks, and deformation were not observed in the obtained sintered body at all. The liquidity is
The measurement was performed in the time required for 50 g of the powder to spontaneously drop and pass through a funnel tube having an inner diameter of 5 mm.

Example 2 Water-soluble polyvinyl acetal (average molecular weight: 30,000, acetal group: 10 mo) was added to the R-Fe-B alloy powder used in Example 1 as a polymer component in the binder.
1%, acetyl group: 5 mol%, hydroxyl group 85 mol%)
Was mixed with the composition shown in Table 1 to prepare a slurry, and granulated powder was obtained in the same manner as in Example 1, followed by molding, binder removal treatment, sintering, and aging treatment. The same measurement results as in Example 1 are shown in Table 1. No cracks, cracks, or deformations were found in the obtained sintered body.

Example 3 A slurry prepared by compounding the R-Fe-B alloy powder used in Example 1 with polyacrylic acid (average molecular weight: 10000) as a polymer component in the binder in the composition shown in Table 1 was used. Was obtained, and after obtaining a granulated powder in the same manner as in Example 1,
Molding, binder removal treatment, sintering, and aging treatment were performed.
The same measurement results as in Example 1 are shown in Table 1. No cracks, cracks, or deformations were found in the obtained sintered body.

Example 4 Ammonium polyacrylate (average molecular weight: 20000) was used as the polymer component in the binder in the R-Fe-B alloy powder used in Example 1 and blended in the composition shown in Table 1. A slurry was prepared and granulated powder was obtained in the same manner as in Example 1, followed by molding, binder removal treatment, sintering, and aging treatment. The same measurement results as in Example 1 are shown in Table 1.
No cracks, cracks, or deformations were found in the obtained sintered body.

Example 5 A slurry was prepared by compounding the R-Fe-B alloy powder used in Example 1 with carboxymethyl cellulose ammonium salt as a polymer component in the binder in the composition shown in Table 1 to prepare a slurry. After obtaining the granulated powder as in Example 1,
Molding, binder removal treatment, sintering, and aging treatment were performed.
The same measurement results as in Example 1 are shown in Table 1. No cracks, cracks, or deformations were found in the obtained sintered body.

Example 6 Two types of polymers, polyethylene oxide and polyvinyl acetal, were used as the polymer component in the binder in the R-Fe-B alloy powder used in Example 1 and Table 1
In the same manner as in Example 1, a slurry was prepared by blending with the composition shown in 1 above, and then granulated powder was obtained, followed by molding, debinding and sintering, and aging treatment. The same measurement results as in Example 1 are shown in Table 1. No cracks, cracks, or deformations were found in the obtained sintered body.

Example 7 The R-Fe-B alloy powder used in Example 1 was blended in the composition shown in Table 1 using two kinds of polymers, polyethylene oxide and polyacrylic acid, as polymer components in the binder. Then, a slurry was prepared, and in the same manner as in Example 1, after obtaining a granulated powder, molding, binder removal treatment, sintering, and aging treatment were performed. The same measurement results as in Example 1 are shown in Table 1. No cracks, cracks, or deformations were found in the obtained sintered body.

Example 8 In the composition shown in Table 1, two kinds of polymers, polyethylene oxide and ammonium polyacrylate, were used as polymer components in the binder in the R-Fe-B alloy powder used in Example 1. After blending to prepare a slurry and obtaining a granulated powder in the same manner as in Example 1, molding, binder removal treatment, sintering, and aging treatment were performed. The same measurement results as in Example 1 are shown in Table 1. The obtained sintered body was cracked,
There were no cracks or deformations.

Example 9 Two kinds of polymers, polyethylene oxide and carboxymethyl cellulose ammonium salt, were used as polymer components in the binder in the R-Fe-B type alloy powder used in Example 1, and the composition shown in Table 1 was used. After blending to prepare a slurry and obtaining a granulated powder in the same manner as in Example 1, molding, binder removal treatment, sintering, and aging treatment were performed. Example 1
Table 1 shows the measurement results similar to the above. No cracks, cracks, or deformations were found in the obtained sintered body.

Example 10 In the R-Fe-B alloy powder used in Example 1, the polyethylene oxide of the present invention was used as the polymer component in the binder, and the polyvinyl alcohol (average molecular weight: 70,000, saponification degree) already found. : 88%),
After mixing with the composition shown in Table 1 to prepare a slurry and obtaining granulated powder in the same manner as in Example 1, molding, debinding treatment,
Sintered and aged. The same measurement results as in Example 1 are shown in Table 1. No cracks, cracks or deformations were found in the obtained sintered body.

Comparative Example 1 The R-Fe-B alloy powder used in Example 1 was molded, debindered, sintered and aged in the same manner as in Example 1 without spray granulation. It was The same measurement results as in Example 1 are shown in Table 1.

Example 11 Sm 11.9 at%, Cu 8.8 at%, Fe 12.6
A raw material comprising at%, Zr1.2 at%, balance Co and unavoidable impurities was subjected to high frequency melting in an Ar gas atmosphere to obtain a button-shaped ingot alloy. Next, after coarsely pulverizing the alloy, the average particle size is about 15 μm with a jaw crusher or the like.
m, and average particle size 3 μm by jet mill
Was obtained. Polyethylene oxide (average molecular weight = 500,000) was used as a polymer in the obtained powder, and water and a plasticizer were added to 100 parts by weight of the alloy powder.
Was mixed with the composition shown in Example 1 to prepare a slurry by stirring and kneading at room temperature, and the slurry was mixed with a disk rotary spray dryer using nitrogen as an inert gas and a hot air inlet temperature of 100 ° C. Outlet temperature 40
Granulation was performed by setting the temperature to ° C. The obtained granulated powder is # 440
Fine particles are undercut by a sieve of # 7
Coarse particles were overcut with a 0 sieve. Table 1 shows the average particle size of the granulated powder and the yield of # 440 to # 70.

Using a compression magnetic field press, the granulated powder was 10 mm × with a magnetic field strength of 15 kOe and a pressure of 1 ton / cm ^2.
After forming into a shape of 15 mm × thickness 10 mm, a binder removal treatment of heating from room temperature to 300 ° C. at a temperature rising rate of 100 ° C./hour is performed in a hydrogen atmosphere, and subsequently heated to 1200 ° C. in vacuum. Sintering is performed for a certain period of time, and after completion of sintering, solution treatment is performed at 1160 ° C.
Gas was introduced and multi-step aging treatment was performed from 800 ° C to 400 ° C. The average particle size of the granulated powder, the fluidity of the granulated powder at the time of molding, the size of the molded body, the density of the molded body, and the residual oxygen content, residual carbon content, and magnetic characteristics of the obtained sintered magnet were measured. It shows in Table 1. In addition, cracks, cracks, and deformation were not found in the obtained sintered body at all. The fluidity was measured by the time required for 50 g of the powder to spontaneously drop and pass through a funnel tube having an inner diameter of 5 mm.

Comparative Example 2 Using the same 3 μm powder as in Example 11, without granulation,
As it is, the same magnetic field pressing machine as in the example was used, with a magnetic field strength of 15 kOe and a pressure of 1 ton / cm ² , 10 mm × 15 m.
After molding into a shape of m × thickness 10 mm, 120 in vacuum
After sintering at 0 ° C for 1 hour, and after the completion of sintering,
Solution treatment was performed at 1160 ° C, Ar gas was introduced, and multi-step aging treatment was performed from 800 ° C to 400 ° C. The same measurement results as in Example 11 are shown in Table 1.

[0061]

[Table 1]

[0062]

According to the present invention, R-Fe-B system and R
-To rare earth-containing alloy powder such as Co, polyethylene oxide, water-soluble polyvinyl acetal, polyacrylic acid,
At least one polymer selected from a polyacrylic acid derivative and a water-soluble carboxyalkyl cellulose derivative and a binder consisting of water are added and kneaded to form a slurry, and the slurry is granulated by a spray dryer device and a rare earth-containing alloy. The binder itself of the granulated powder is used for molding, sintering, and heat treatment using spherical granulated powder with high fluidity that suppresses the reaction between the powder and the binder component and imparts sufficient fluidity to the kneaded product. Combined with the excellent fluidity of, the fluidity of the powder is remarkably improved, the molding cycle is improved, the dispersion of the density of the molded product and the life of the molding machine are not reduced, and as shown in Examples, A rare earth-based material that has a small amount of residual oxygen and residual carbon in the sintered body after sintering and has excellent dimensional accuracy and a small shape and thin shape and excellent magnetic characteristics. Sintered magnet can be efficiently obtained.

Claims (1)

[Claims] 1. A binder composed of at least one polymer selected from polyethylene oxide, water-soluble polyvinyl acetal, polyacrylic acid, polyacrylic acid derivative, and water-soluble carboxyalkyl cellulose derivative and water is added to the rare earth-containing alloy powder. , Manufacturing a rare earth-based sintered magnet, characterized by kneading to form a slurry, forming the slurry into a granulated powder by a spray dryer device, and using the granulated powder to obtain a sintered magnet by a powder metallurgy method Method.