JP4167290B2 - Magnet manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a magnet, and more particularly to a method for manufacturing a magnet by wet molding.

  As a method of manufacturing a sintered magnet obtained by sintering magnetic powder, a wet molding method in which a slurry obtained by mixing magnetic powder as a raw material of a magnet with a solvent such as oil is molded and then sintered. The method of going through the process is known. Among magnets, rare earth magnets containing rare earth elements have excellent magnetic properties, and thus are applied to applications that require high magnetic properties even though they are small in size. A production method by wet molding is effective.

For example, as a method for producing rare earth magnets by wet molding, the following Patent Document 1 discloses that rare earth permanent magnet fine powder is recovered in a solvent such as oil, concentrated to a predetermined concentration, and then the resulting slurry is pressure molded. A method of further sintering is disclosed. According to such a manufacturing method, the rare earth permanent magnet fine powder can be made into a slurry so as not to be exposed to the atmosphere. Further, it is described that by setting the slurry concentration to a predetermined value, it is possible to suppress the generation of a supernatant to stabilize the supply amount of the raw material powder, and to improve the filling property into the mold cavity.
Japanese Patent Laid-Open No. 10-241981

  The magnetic characteristics of the magnet are generally indicated by the maximum value of the maximum energy product (BH), which is the product of the residual magnetic flux density (Br) and the coercive force (Hc), and the larger this value, the stronger the magnet. Therefore, in order to obtain high magnetic properties, it is necessary to increase both Br and Hc. Conventionally, however, it has been particularly difficult to increase Br while maintaining high Hc. It was important for high magnetic properties. Further, even for rare earth magnets obtained by the above-described conventional manufacturing method, higher Br is required so as to obtain further high magnetic properties.

  Then, this invention is made | formed in view of such a situation, and it aims at providing the manufacturing method of the magnet which can obtain the magnet which has high Br.

  In order to achieve the above object, as a result of intensive studies by the present inventors, the degree of orientation of the magnet is improved by performing kneading at the time of adjusting the slurry under specific conditions, and as a result, high Br is obtained. As a result, the present invention has been completed.

That is, the method for producing a rare earth magnet of the present invention includes a step of finely pulverizing an alloy by dry pulverization to obtain a magnetic powder, a mixing step of mixing a solvent with the magnetic powder to obtain a mixture, and a kneaded product obtained by kneading the mixture. A kneading step for forming a kneaded product to obtain a molded product, and a firing step for firing the molded product. After the kneading step and before the molding step, a solvent is further added to dilute the kneaded product. The kneaded product is further kneaded in a state where the concentration of the magnetic powder in the mixture is 85 to 95% by mass in the kneading step.

  In such a method for producing a rare earth magnet of the present invention, molding is performed after kneading a mixture containing magnetic powder and a solvent, but kneading is performed in a state where the concentration of the magnetic powder is high (85 to 95% by mass). Is going. Conventionally, in the manufacture of magnets, finely pulverized magnetic powder as a raw material has been used to increase the density of sintered magnetic powder, but the surface of fine particles after pulverization is activated. Therefore, they tend to aggregate and tend to form secondary particles and the like very easily. On the other hand, in the present invention, since kneading is performed at a high concentration as described above, contact / collision of magnetic powders can be caused with high frequency in the mixture during kneading. Therefore, in the kneading step, aggregation of primary particle aggregates (secondary particles and the like) in the magnetic powder can be sufficiently unwound (pulverized). Here, in this specification, “kneading” refers to an operation of repeatedly applying pressure to a mixture having fluidity that can maintain a lump shape.

  And, for example, when forming the orientation by molding in a magnetic field, if the magnetic powder is agglomerated, the orientation of each particle becomes difficult to occur. Since most of the magnetic powder is primary particles, each particle can be well oriented during molding. As a result, a magnet having a high degree of orientation is formed. And since Br of a magnet improves by raising the orientation degree of a magnet, according to the manufacturing method of this invention, it becomes possible to obtain the magnet which has high Br.

  The magnet production method of the present invention preferably includes a dilution step in which a solvent is further added to the kneaded product to dilute the kneaded product after the kneading step and before the forming step. When such dilution is performed, the magnetic powder easily moves in the solvent, and therefore, the magnetic powder is more easily oriented in the molding process. As a result, a magnet having a higher degree of orientation and thus Br can be obtained. In addition, since the fluidity of the kneaded product is enhanced by performing the dilution as described above, for example, the transportability when moving the kneaded product to the molding machine is higher than when a high-concentration kneaded product is used. The work advantage of being good is also obtained.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the magnet which can obtain the magnet which has high Br.

  Hereinafter, preferred embodiments of the present invention will be described. In the following description, a method for producing a rare earth magnet particularly suitable for the present invention will be described. However, the method for producing a magnet of the present invention is not limited to a rare earth magnet, and other metal magnets, ferrite magnets, etc. Any sintered magnet obtained by sintering can be applied without particular limitation.

  FIG. 1 is a flowchart showing a manufacturing process of a rare earth magnet according to a preferred embodiment.

  In manufacturing the rare earth magnet, first, an alloy is prepared so that a rare earth magnet having a desired composition can be obtained (step S11). In this process, for example, a simple substance, an alloy, a compound, or the like containing an element such as a metal corresponding to the composition of the rare earth magnet is dissolved in an inert gas atmosphere such as vacuum or argon, and then used for casting or stripping. An alloy having a desired composition is manufactured by performing an alloy manufacturing process such as a casting method.

  Here, examples of rare earth magnets include those containing mainly Nd and Sm as rare earth elements, and those having a composition in which a rare earth element and a transition element other than the rare earth element are combined are suitable. Specifically, R—Fe containing at least one of Nd, Pr and Dy as a rare earth element (represented by “R”), 1 to 12 atomic% of B as an essential element, and the balance being Fe. Those having a -B composition are preferred. Such a rare earth magnet has a composition further containing other elements such as Co, Ni, Mn, Al, Nb, Zr, Ti, W, Mo, V, Ga, Zn, and Si as required. May be.

Next, the obtained alloy is coarsely pulverized to form fine particles having a particle size of about several hundred μm (step S12), and further finely pulverized (step S13), preferably 1 to 10 μm, more preferably A magnetic powder having a particle size of about 3 to 5 μm is obtained. The coarse pulverization of the alloy is performed by using a coarse pulverizer such as a jaw crusher, a brown mill, a stamp mill, or the like, or after the alloy has occluded hydrogen, it is self-destructive based on the difference in hydrogen occlusion between different phases It can be performed by causing pulverization (hydrogen occlusion pulverization). Also, milling, the coarse ground powder, while appropriately adjusting the conditions such as the grinding time can be done by further pulverized using a jet mill, a ball mill, a pulverizer such as a vibration mils.

  Next, a solvent is mixed with the magnetic powder (step S14; mixing step). As a solvent, the solvent used for the slurry in the wet molding of a magnet can be applied without particular limitation. Examples thereof include oils such as mineral oil, synthetic oil and vegetable oil, and organic solvents such as acetone and alcohol. Of these, oil is preferable in order to prevent oxidation of the magnetic powder.

  In the mixing step, in addition to the solvent, other additives capable of obtaining desired characteristics can be further added. Examples of the additive include dispersants such as cationic, anionic, betaine, and nonionic surfactants that can promote dispersion of the magnetic powder. Such an additive may be added not in the mixing step but in a kneading step or a dilution step described later.

  Then, a mixture obtained by adding a solvent to the pulverized magnetic powder is kneaded to obtain a kneaded product (first slurry) (step S15; kneading step). The kneading can be performed by a method such as a pressure kneader, an open kneader, a twin screw extruder, or a planetary mixer.

  In the kneading step, kneading is performed in a state where the content of the magnetic powder (magnetic powder concentration) in the mixture is 85 to 95% by mass, preferably 88 to 94% by mass, with respect to the total mass of the mixture. When the magnetic powder concentration of the mixture in the kneading step is less than 85% by mass, the fluidity of the mixture increases, the load applied to the mixture decreases, and the magnetic powder in the mixture is less likely to contact and collide with each other. Sometimes the primary particle aggregates of the magnetic powder are not sufficiently broken up. On the other hand, when it exceeds 95% by mass, the mixture is not sufficiently wetted by the solvent of the magnetic powder, and kneading itself becomes difficult and it becomes difficult to obtain a good kneaded product.

  In this kneading step, the magnetic powder concentration of the mixture may be gradually changed, for example, by adding a solvent. In this case, during the kneading step, the mixture does not always have to have the above-mentioned suitable magnetic powder concentration, and it is sufficient that the mixture has a suitable magnetic powder concentration for at least a certain time.

  Here, the fixed time is a time that can sufficiently crush the aggregates of primary particles contained in the mixture. Conditions such as pressure and shear force applied to the mixture, and aggregation of the magnetic powder before kneading. It depends on the degree of For example, in the case of a mixture prepared under normal conditions, in order to sufficiently break up the aggregate of the magnetic powder, at least 5 minutes, preferably 10 minutes or more, more preferably 20 minutes or more, as described above. It is preferable to knead at the magnetic powder concentration. If this time is less than 5 minutes, kneading is insufficient, and the aggregates of primary particles may not be sufficiently crushed.

  After the kneading step, a solvent is further added to the obtained kneaded material, and the kneaded material is diluted to obtain a slurry (second slurry) having a lower magnetic powder concentration and improved fluidity than the kneaded material. (Step S16; dilution process). This dilution step can be performed, for example, by adding a solvent while stirring the kneaded product obtained in the above-described kneading step. The solvent used in the dilution step may be the same as or different from the solvent used in the mixing step. However, from the viewpoint of removing the solvent later, it is possible to remove under the condition for one kind of solvent, and therefore, the same solvent as that in the mixing step is preferable.

  In this dilution step, at least the magnetic powder concentration is made smaller than that of the kneaded product. For example, it is preferable that the magnetic powder concentration be smaller by about 5 to 35% by mass than the kneaded product. Specifically, the magnetic powder concentration of the obtained slurry is preferably 60 to 80% by mass, more preferably 65 to 78% by mass. In this case, the magnetic powder is easily oriented by an orientation operation such as molding described later, and the slurry can be easily supplied to the molding machine. However, if the magnetic powder concentration of the slurry is too small in the dilution step, the magnetic powder in the slurry may be easily settled.

  The three steps of the mixing step, the kneading step and the dilution step described above may be performed independently or as a series of operations. That is, mixing of magnetic powder and solvent, kneading of the mixture, and dilution of the kneaded material may be performed in separate tanks, and after mixing and kneading in one tank, only the dilution is different. You may perform in a tank and you may perform all of mixing, kneading | mixing, and dilution in one tank. However, since it is difficult to move the mixture in which only the solvent is added to the magnetic powder, it is preferable to perform mixing and kneading by at least a series of operations. In this case, for example, mixing and kneading can be continuously performed by adding the solvent while stirring the magnetic powder, or adding the magnetic powder while stirring the solvent.

  In addition, when performing the kneading step and the dilution step as a series of operations, the solvent is gradually added to the kneaded product to gradually decrease the magnetic powder concentration of the kneaded product. Alternatively, kneading and dilution may be performed in a two-stage operation in which kneading and dilution are performed at a constant magnetic powder concentration, and then a desired dilution concentration is obtained by adding a solvent once.

  Thereafter, before forming the slurry, it is preferable to perform a step of dispersing the magnetic powder and the solvent again as necessary (step S17; dispersion step). In the slurry obtained after the dilution step, the magnetic powder and the solvent are separated during the supply to the molding machine, and the supernatant of the solvent may be generated. If this slurry is used for molding as it is, the amount of magnetic powder charged into the molding machine may not be constant depending on the degree of separation, and as a result, the amount of magnetic powder in the compact may vary. On the other hand, if the dispersion is performed after the dilution and before the molding, the molding can be performed in a state where the separation of the slurry is small, and the variation of the molded body can be suppressed. In addition, although it is thought that the primary particle obtained by the kneading | mixing process mentioned above hardly produces aggregation again, for example, when aggregation has arisen in part, an aggregate is disintegrated also by this dispersion | distribution process. It is considered possible.

  The slurry can be dispersed by using a ball mill, ultrasonic diffusion, homogenizer, optimizer, or the like. For example, it is possible to achieve good dispersion by incorporating an apparatus for performing these operations in the middle of a supply pipe that supplies the diluted slurry to the molding machine. From the viewpoint of obtaining a good effect by the dispersion, it is preferable to perform the dispersion just before the molding as much as possible.

  Thereafter, the dispersed slurry is put into a molding machine, and the molded product is obtained by molding the slurry while applying a magnetic field (step S18; molding process). By the molding step, a molded body having a predetermined degree of orientation is obtained. The molding can be performed, for example, by press molding. Specifically, after the slurry is filled in the mold cavity, the filled slurry is pressurized so as to be sandwiched between the upper punch and the lower punch, It is processed into a predetermined shape while extracting the solvent. At this time, the upper punch or the lower punch may be provided with a hole communicating with the outside in order to extract the solvent that has flowed out. However, it is preferable to place a cloth or paper filter on the punch surface, or to make the upper punch or the lower punch partly porous so that the magnetic powder does not flow out. The shape of the molded body obtained by molding is not particularly limited, and can be changed according to the desired shape of the rare earth magnet, such as a columnar shape, a flat plate shape, or a ring shape.

The pressing direction during molding may be the same as the magnetic field application direction, or may be perpendicular to the magnetic field application direction, but more excellent magnetic properties can be obtained by applying pressure perpendicular to the magnetic field application direction. There is a tendency. Moreover, the magnetic field intensity at the time of shaping | molding can be 15-20 kOe, and pressurization can be 0.3-3 ton / cm < ² >. Furthermore, the molding time is preferably several seconds to several tens of seconds. By forming in a magnetic field under such conditions, a rare earth magnet having good magnetic properties tends to be easily obtained.

  Next, a desolvation process is performed on the compact to remove the solvent and additives remaining in the compact by, for example, vacuum heating (step S19). The solvent removal is performed under such conditions that most of the solvent in the molded body can be removed. For example, the solvent is preferably heated at 100 to 160 ° C. for 1 to 5 hours under a reduced pressure of about 10 to 3000 Pa. In this solvent removal step, sintering of the molded body usually does not proceed, but partial sintering may proceed.

  Thereafter, the desolvated shaped body is fired to obtain a sintered body (step S20; firing step). Sintering can be performed, for example, by heating the molded body at 1000 to 1200 ° C. for 1 to 10 hours in a vacuum or in the presence of an inert gas and then rapidly cooling.

  After the sintering, the obtained sintered body is heated at a temperature lower than that at the time of firing, etc., and then subjected to an aging treatment (step S21). The aging treatment is, for example, two-stage heating for 1 to 3 hours at 700 to 900 ° C., and further 1 to 3 hours at 500 to 700 ° C. Perform under conditions. Such an aging treatment can improve the magnetic properties of the sintered body.

  And the target rare earth magnet is obtained by performing the process which cut | disconnects to the desired size with respect to the sintered compact obtained in this way, or smoothes the surface. The obtained rare earth magnet may further be provided with a protective layer for preventing deterioration of the oxide layer, the resin layer, etc. on the surface.

  According to the method for producing a rare earth magnet of the above-described embodiment, the magnetic powder is constituted at the time of kneading because the mixture having a high magnetic powder concentration (85 to 95% by mass) is kneaded in the kneading step. The particles can be contacted and collided with each other at a high frequency, whereby the aggregates of the primary particles of the magnetic powder contained in the mixture are crushed well. Further, since the kneaded product is diluted in the dilution step after kneading, the primary particles of the magnetic powder are widely dispersed in the resulting slurry. Therefore, in the molding step, magnetic field orientation of the magnetic powder in the slurry is satisfactorily generated, and thereby a molded body having a high degree of orientation can be obtained. As a result, a rare earth magnet having a high Br can be obtained.

  In addition, based only on the viewpoint of obtaining a high Br, for example, by using a magnetic powder that is very finely pulverized as a raw material, or by pulverizing and pulverizing the magnetic powder in the slurry after slurry preparation, A method for easily causing the orientation of the magnetic powder is also conceivable. However, in the case of such a method, excessively fine magnetic powder generated by pulverization is also included in part, so there is a possibility that the degree of orientation obtained may vary, and when discharging the solvent during molding There is a tendency that inconveniences such as clogging of the solvent discharge filter are likely to occur. On the other hand, in the present invention, by kneading at a high concentration, the primary powder aggregates can be mainly crushed, not the magnetic powder. Therefore, the occurrence of excessively small particles is extremely reduced. As a result, the variation in the degree of orientation is reduced, and the filter is hardly clogged during molding.

  As mentioned above, although the manufacturing method of the rare earth magnet was demonstrated as suitable embodiment of the manufacturing method of the magnet of this invention, this invention is not necessarily limited to embodiment mentioned above. For example, the magnet manufacturing method of the present invention is a manufacturing method including at least a kneading step, a molding step, and a firing step, and other partial steps may be omitted as long as the effects of the present invention are sufficiently obtained. . Specifically, for example, after the kneading step, even if the kneaded product is used as it is, it can be supplied to a molding machine or the like, and if a magnet having a sufficient degree of orientation is obtained, the dilution step is not necessarily performed. May be.

  Moreover, when there is little separation of the slurry before shaping | molding, such as when using the obtained slurry for shaping | molding immediately after a dilution process, the dispersion | distribution process before shaping | molding can also be skipped. Further, when sufficient magnetic properties are obtained only by firing after the firing step, the aging treatment after the firing step is not necessarily performed. Furthermore, the manufacturing method of the magnet of this invention may further include processes other than the process mentioned above as needed.

  Furthermore, as described above, the production method of the present invention is not limited to rare earth magnets, and can be applied to the production of magnets other than rare earth magnets such as other metal magnets and ferrite magnets. And even if it is a case where it applies to another magnet, it becomes possible to manufacture the magnet which has high orientation degree and high Br similarly to embodiment mentioned above.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.
[Preparation of rare earth magnets]

(Example 1)
Nd: 30%, Dy: 1.8%, Al: 0.2%, Co: 0.5%, B: 1.0%, coarsely pulverized ingot made of Fe, then nitrogen was used using a jet mill Fine pulverization was carried out under an atmosphere until the average particle size became 4 μm to obtain a magnetic powder. Next, after the obtained magnetic powder was mixed with synthetic oil (Idemitsu Supersol FP30) having a fractional distillation point of 200 to 250 ° C., the resulting mixture was mixed with a planetary disperser (Asada with a magnetic powder concentration of 91%. Kneading). At this time, the kneading time was 60 minutes.

  Next, a slurry having a solid content concentration of 70% was prepared by further adding and diluting the same synthetic oil as described above to the obtained kneaded product. The slurry was molded in a magnetic field orientation of 15 kOe using a wet press machine to obtain a molded body. At this time, a cloth filter cloth (aperture 2 μm) was used as a filter on the press surface so that the synthetic oil that flowed out during molding was well removed.

  Then, the obtained molded object was heated at 150 degreeC in the vacuum of 100 Pa, and the synthetic oil contained in the molded object was removed. And after baking a molded object on the conditions of 1100 degreeC and 5 hours in the vacuum of 0.067 Pa, it gave Example 1 by giving an aging treatment on the conditions of 500 degreeC and 1 hour. A rare earth magnet was obtained.

(Example 2)
A rare earth magnet of Example 2 was obtained in the same manner as in Example 1 except that the mixture was kneaded at a magnetic powder concentration of 94% using a pressure kneader (manufactured by Moriyama).

(Example 3)
A rare earth magnet of Example 3 was obtained in the same manner as in Example 1 except that the mixture was kneaded using an open kneader (manufactured by Moriyama) at a magnetic powder concentration of 94%.

Example 4
A rare earth magnet of Example 4 was obtained in the same manner as in Example 1 except that the mixture was kneaded at a magnetic powder concentration of 93% using a twin screw extruder (KEX Extruder manufactured by Kurimoto Seiko).

(Example 5)
A rare earth magnet of Example 5 was obtained in the same manner as in Example 1 except that kneading was performed at a magnetic powder concentration of 95%.

(Example 6)
A rare earth magnet of Example 6 was obtained in the same manner as in Example 1 except that kneading was performed at a magnetic powder concentration of 85%.

(Example 7)
A rare earth magnet of Example 7 was obtained in the same manner as in Example 1 except that the kneading time was 10 minutes.

(Comparative Example 1)
Nd: 30%, Dy: 1.8%, Al: 0.2%, Co: 0.5%, B: 1.0%, coarsely pulverized ingot made of Fe, then nitrogen was used using a jet mill Fine pulverization was performed under an atmosphere until the average particle size became 4 μm to obtain a magnetic powder. Next, the obtained magnetic powder was mixed with synthetic oil (Idemitsu Supersol FP30) having a fractional distillation point of 200 to 250 ° C. using a paddle type stirrer to prepare a slurry having a magnetic powder concentration of 70%.

  The obtained slurry was molded in a magnetic orientation of 15 kOe using a wet press machine to obtain a molded body. At this time, a cloth filter cloth (aperture 2 μm) was used as a filter on the press surface so that the synthetic oil that flowed out during molding was well removed.

  Then, the obtained molded object was heated at 150 degreeC in the vacuum of 100 Pa, and the synthetic oil contained in a molded object was removed. And after baking a molded object on the conditions of 1100 degreeC and 5 hours in the vacuum of 0.067 Pa, the obtained sintered compact is given an aging process on the conditions of 500 degreeC and 1 hour, and is comparative example 1 A rare earth magnet was obtained.

(Comparative Example 2)
A rare earth magnet of Comparative Example 2 was obtained in the same manner as Comparative Example 1 except that a dissolver type agitator was used instead of the paddle type agitator.

(Comparative Example 3)
A rare earth magnet of Comparative Example 3 was obtained in the same manner as in Example 1 except that kneading was performed at a magnetic powder concentration of 97%.

(Comparative Example 4)
A rare earth magnet of Comparative Example 4 was obtained in the same manner as in Example 1 except that kneading was performed at a magnetic powder concentration of 80%.
[Characteristic evaluation]

  The sintered compact density and magnetic characteristics of the rare earth magnets obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were measured, and the residual magnetic flux density (Br) and the degree of orientation of each magnet were calculated. The results obtained are summarized in Table 1.

  From Table 1, the rare earth magnets of Examples 1 to 7 that were kneaded at a predetermined magnetic powder concentration were kneaded at Comparative Examples 1 and 2 that were not kneaded, and at a concentration outside the range of the present invention. Compared to the cases of Comparative Examples 3 and 4, it was confirmed that the orientation was high and high Br was obtained.

  For each of the examples and comparative examples, the production of rare earth magnets was repeated using the same molding machine, and the number of times until the filter cloth placed on the press surface was clogged and needed to be replaced (number of continuous shots) ), It was confirmed that the number of continuous shots exceeded 20 in all cases.

It is a flowchart which shows the manufacturing process of the rare earth magnet which concerns on suitable embodiment.

Claims (2)

A step of finely pulverizing the alloy by dry pulverization to obtain a magnetic powder;
A mixing step of mixing the magnetic powder with a solvent to obtain a mixture;
A kneading step of kneading the mixture to obtain a kneaded product;
A molding step of molding the kneaded product to obtain a molded body;
A firing step of firing the molded body,
After the kneading step, before the molding step, further has a dilution step of further adding a solvent to dilute the kneaded product,
In the kneading step, the kneaded material is kneaded in a state where the content of the magnetic powder in the mixture is 85 to 95% by mass. The method for producing a rare earth magnet according to claim 1, wherein in the kneading step, the mixture is kneaded for 5 minutes or more.

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