JP2008274420A - METHOD FOR PRODUCING R-Fe-B BASED RARE EARTH MAGNET - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce an R-Fe-B based rare earth magnet having excellent oxidation resistance by performing dry pressing to a rare earth alloy powder having an oxygen content of ≤1,500 mass ppm. <P>SOLUTION: The method for producing an R-Fe-B based magnet comprises: a stage where rare earth alloy powder having a rare earth content of 27.5 to 30.5 mass% and an oxygen content of ≤1,500 mass ppm is subjected to compression molding by a dry pressing process so as to produce a molding; a stage where an oil agent is impregnated from the surface of the molding into the molding; and a stage where the molding is sintered. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a rare earth magnet. More specifically, the present invention relates to a method for producing a rare earth sintered magnet having excellent magnetic properties using a rare earth alloy powder having a reduced oxygen content.

An R—Fe—B rare earth magnet (R is a rare earth element including Y) is mainly composed of a main phase composed of a tetragonal compound of R ₂ Fe ₁₄ B, an R rich phase composed of Nd, and a B rich phase. ing. In the R—Fe—B rare earth magnet, the magnetic properties are improved by increasing the abundance ratio of the main phase R ₂ Fe ₁₄ B tetragonal compound.

The R-rich phase requires a minimum amount for liquid phase sintering, but R reacts with oxygen in the atmosphere to form an oxide of R ₂ O _3, so a part of R is not useful for sintering. It will be consumed by the part. For this reason, extra R is required for the consumption by oxidation. The generation of the oxide of R ₂ O ₃ becomes more remarkable as the oxygen concentration in the atmosphere is higher. Therefore, it has been studied so far to suppress the generation of R ₂ O ₃ by reducing the amount of oxygen in the atmosphere at the time of powder production, thereby improving the magnetic properties of the sintered magnet.

  Thus, it is preferable that the amount of oxygen in the R—Fe—B alloy powder used for the production of the R—Fe—B magnet is small. However, the method for improving the magnet characteristics by reducing the amount of oxygen in the R—Fe—B alloy powder has not been realized as a mass production technique. The reason is that when an R—Fe—B alloy powder is produced in an environment where the oxygen concentration is controlled to be low and the oxygen content of the alloy powder is reduced to, for example, 4000 mass ppm or less, the powder reacts violently with oxygen in the atmosphere. This is because there was a risk of ignition in a few minutes even at room temperature. In addition, when pulverized by the hydrogen storage method, the rare earth element is often exposed on the surface of the pulverized powder because it breaks from the rare earth-rich portion of the alloy. As a result, ignition is more likely to occur.

  Therefore, even though it is understood that it is desirable to reduce the amount of oxygen in the R—Fe—B based alloy powder in order to improve the magnetic properties, in practice, the R—Fe— with a low oxygen content is used. It has been extremely difficult to handle B-based alloy powder at production sites such as factories.

  In particular, in the pressing process for compression molding of powder, the temperature of the molded body rises due to frictional heat between the powders accompanying compression and frictional heat generated between the powder and the inner wall of the cavity when the molded body is taken out. High risk. In order to prevent this ignition, a non-oxygen atmosphere around the press apparatus may be considered, but it is not practical because it is difficult to supply raw materials and take out the molded body. In addition, if each compact is taken out of the press machine, the individual compacts may be sintered quickly, which may avoid the problem of ignition, but this is an extremely inefficient method and is suitable for mass production. Absent. In addition, it is difficult for mass production equipment to manage the compact in a non-oxygen atmosphere from the press to the sintering process.

  In addition, liquid lubricants, such as fatty acid ester, are added to the fine powder before the pressing process to improve the compressibility or moldability of the powder. By adding such a liquid lubricant, a thin oily film is formed on the surface of the powder particles, but the oxidation of the powder having an oxygen concentration of 4000 mass ppm or less could not be sufficiently prevented.

  For the above reasons, when pulverizing an R—Fe—B alloy, a small amount of oxygen is intentionally introduced into the atmosphere, thereby thinly oxidizing the surface of the finely pulverized powder and reducing the reactivity. ing. For example, Patent Document 1 discloses a technique in which a rare earth alloy is finely pulverized with a supersonic inert gas stream containing a predetermined amount of oxygen, and a thin oxide film is formed on the surface of fine powder particles generated by the pulverization. ing. According to this technique, since oxygen in the atmosphere is blocked by the oxide film on the surface of the powder particles, heat generation and ignition due to oxidation can be prevented.

  On the other hand, Patent Document 2 discloses a technique (wet forming method) in which a low oxygen content R—Fe—B alloy powder is slurried by mixing with mineral oil and the like, and a molded body is produced using this slurry. ) Is disclosed. Since the powder particles in the slurry do not come into contact with the atmosphere, heat generation and ignition can be prevented while reducing the amount of oxygen contained in the R—Fe—B alloy powder.

Patent Document 3 discloses that a rare earth alloy powder having an oxygen content of 4000 mass ppm or less is compression-molded by a dry press method, thereby producing a molded body, and an organic solvent is impregnated into the molded body from the surface of the molded body. The process to make is disclosed. According to such a process, oxidation of rare earth elements is efficiently suppressed and ignition can be prevented.
Japanese Patent Publication No. 6-6728 JP 10-32451 A JP 2002-8935 A

  According to the technique of Patent Document 1, since an oxide film is present on the surface of the powder particles, the amount of oxygen contained in the powder increases. Therefore, the amount of oxygen contained in the sintered body after sintering increases (that is, the amount of rare earth oxide increases), and the magnetic properties of the obtained sintered magnet can deteriorate.

  On the other hand, in the technique of Patent Document 2, since it is necessary to perform a pressing process while squeezing out oil after filling slurry-like R—Fe—B alloy powder into a cavity of a press apparatus, productivity is low. There is a problem.

  In addition, according to the prior art of Patent Document 3, since the ratio between the rare earth content and the oxygen content is not taken into consideration, the oxidation increase is increased by slightly touching the atmosphere with the powder, and the oxygen content is 1500 mass ppm. It was difficult to produce the following rare earth alloy powders.

  In addition, it is known that in an R—Fe—B based sintered magnet, the magnetic properties deteriorate as the amount of carbon contained in the magnet increases. Therefore, in order to obtain a rare earth magnet having excellent magnetic properties after sintering, it is necessary to perform a deoiling process at a high temperature in order to volatilize the oil used to form the slurry. However, in the above-described prior art, the oil agent remains over the entire molded body after the molded body is produced, and the amount thereof is large, so that the time required for the deoiling process becomes longer. For this reason, the problem that productivity becomes low arises.

  The present invention has been made in view of the above points, and its main object is to provide a method for safely and efficiently producing a rare-earth magnet that is difficult to oxidize while using a rare earth alloy powder having a low oxygen concentration. is there.

  The method for producing an R—Fe—B rare earth magnet according to the present invention is a dry pressing method of rare earth alloy powder having a rare earth content of 27.5 mass% to 30.8 mass% and an oxygen content of 1500 mass ppm or less. A pressing process for forming a molded body by compression, a step of impregnating the molded body with an oil from the surface of the molded body, and a process of sintering the molded body.

  It is preferable that the rare earth alloy powder is placed in an inert atmosphere gas having an oxygen concentration of 20000 ppm by volume or less until the cavity of a press apparatus for producing the compact is filled.

  When the oil agent removing step for substantially removing the oil agent is performed before sintering the molded body, it is preferable that the molded body is not brought into contact with the atmosphere after the oil agent removing step until sintering.

  The oil agent removing step is preferably performed at 100 ° C. to 600 ° C. under reduced pressure for 0.1 to 8.0 hours.

  In a preferred embodiment, it is preferable to store a molded body having a surface temperature of a predetermined level or less in a recoverable collection box.

  In a preferred embodiment, the impregnation step is performed using an impregnation tank provided with an opening for taking in and out the molded body and a shutter capable of closing the opening.

  In a preferred embodiment, after the impregnation step, the compact is placed on a sintering base plate in an inert atmosphere before sintering. Instead of doing this, after the impregnation step, the compact may be housed in a sintered case in an inert atmosphere before sintering.

  In the present specification, the “oil agent” is a hydrophobic liquid and includes a hydrocarbon solvent, a lubricant, and the like.

The R—Fe—B rare earth magnet of the present invention has a rare earth content of 27.5 mass% to 30.8 mass%, an absolute value of oxygen content of 1500 mass ppm or less, and 300 hours or more. In the PCT test, the oxidative depletion amount is 2.0 g / m ² or less.

  By limiting the rare earth content to 27.5 mass% to 30.8 mass% and setting the oxygen content to 1500 mass ppm or less, the oxidation resistance of the rare earth alloy powder is improved.

  If the content of the rare earth element R is limited to 27.5% by mass to 30.8% by mass, the present inventor makes the rare earth element R that becomes a liquid phase that easily oxidizes even if the oxygen content is 1500 mass ppm or less. Therefore, it is possible to suppress the formation of oxides formed on the surface of the sintered body (particularly the grain boundary phase portion).

  Hereinafter, an embodiment of a method for producing a rare earth magnet according to the present invention will be described in detail.

  First, R (where R is at least one of rare earth elements including Y): 27.5% by mass to 30.8% by mass, B: 0.85% by mass to 1.1% by mass, balance: Fe, And an R-Fe-B alloy melt containing inevitable impurities is prepared.

  However, a part of Fe may be substituted with one or two of Co and Ni, or a part of B may be substituted with C. According to the present invention, since the oxygen content can be reduced and the generation of oxides of the rare earth element R can be suppressed, the amount of the rare earth element R can be kept as low as necessary.

Next, the molten alloy is rapidly solidified into a thin plate having a thickness of 0.03 mm to 10 mm at a cooling rate of 10 ² to 10 ⁴ ° C./second by an appropriate rapid cooling method such as a strip casting method (or melt spinning method). And after casting to the slab which has the structure | tissue which the R rich phase disperse | distributed by the fine size of 5 micrometers or less, a slab is accommodated in a container and this is accommodated in the chamber which can be inhaled / exhausted. After evacuating the inside of the chamber, H ₂ gas having a pressure of 0.03 MPa (megapascal) to 1.0 MPa is supplied into the chamber to form decay alloy powder. The decay alloy powder is pulverized in an inert gas stream after dehydrogenation.

  The slab of magnet material used in the present invention is preferably manufactured by rapidly cooling a molten alloy having a specific composition by a strip casting method using a single roll method or a twin roll method. Depending on the plate thickness of the slab to be produced, the single roll method and the twin roll method can be used properly. When the slab is thick, the twin roll method is preferably used, and when the slab is thin, the single roll method is preferably used. Further, as a quenching method other than the strip casting method, a centrifugal casting method can also be adopted. When an alloy produced by such a rapid cooling method is used, the particle size of the main phase becomes uniform and fine, so that it is possible to retain the permanent magnet obtained compared to using an alloy of the same composition produced by the ingot method. Magnetic force can be improved.

  If the thickness of the slab (flaked alloy) is less than 0.03 mm, the rapid cooling effect increases, and therefore the crystal grain size may be too small. If the crystal grain size is too small, the individual particles are polycrystallized when powdered, and the crystal orientation cannot be aligned, leading to deterioration of magnetic properties. On the contrary, if the thickness of the slab exceeds 10 mm, the cooling rate becomes slow, so that α-Fe is easily crystallized, and the Nd-rich phase is unevenly distributed.

  The hydrogen storage process can be performed as follows, for example. That is, after a cast piece broken to a predetermined size is inserted into a raw material case, the raw material case is inserted into a sealable hydrogen furnace, and the hydrogen furnace is sealed. Next, after sufficiently evacuating the hydrogen furnace, hydrogen gas having a pressure of 30 kPa to 1.0 MPa is supplied into the furnace, and hydrogen is stored in the slab. Since the hydrogen occlusion reaction is an exothermic reaction, it is preferable to provide a cooling pipe for supplying cooling water around the outer periphery of the furnace to prevent temperature rise in the furnace. Due to the absorption and absorption of hydrogen, the slab naturally collapses and becomes brittle (partially powdered).

  After cooling the alloy that has been subjected to hydrogen storage treatment, dehydrogenation treatment is performed by heating in a vacuum. Since there are fine cracks in the particles of the alloy powder obtained by dehydrogenation treatment, the alloy powder having a predetermined particle size distribution should be prepared in a short time by ball mill, jet mill, etc. Can do. A preferred embodiment of the hydrogen pulverization treatment is disclosed in Japanese Patent Laid-Open No. 7-18366.

The above-mentioned fine pulverization is preferably performed by a jet mill using an inert gas (for example, N ₂ or Ar), but is performed by a ball mill or attritor using an organic solvent (for example, benzene or toluene). Also good.

  In the above pulverization step, the oxygen concentration in the atmospheric gas is controlled to be low (for example, 20000 ppm by volume or less) so that the amount of oxygen contained in the powder can be kept low.

  Further, it is preferable to add a liquid lubricant or binder mainly composed of a fatty acid ester or the like to the raw material alloy powder. The addition amount is, for example, 0.15 to 5.0% by mass. Examples of fatty acid esters include methyl caproate, methyl caprylate, and methyl laurate. The important point is that the lubricant can be volatilized and removed in a later step. In addition, when the lubricant itself is a solid that is difficult to be uniformly mixed with the alloy powder, the lubricant may be diluted with a solvent. As the solvent, a petroleum solvent typified by isoparaffin, a naphthene solvent, or the like can be used. The timing of addition of the lubricant is arbitrary, and may be any of before pulverization, during pulverization, and after pulverization. The liquid lubricant coats the surface of the powder particles and exhibits the effect of preventing the oxidation of the particles, and also exhibits a function of making the density of the molded body uniform during pressing and suppressing disorder of orientation.

  Next, magnetic field orientation and compression molding are performed using the press apparatus shown in FIG. The apparatus 10 of FIG. 1 includes a die 1 having a through hole, and punches 2 and 3 that sandwich the through hole of the die 1 from above and below. The raw material powder 4 is filled in a space (cavity) formed by the die 1 and the lower punch 2, and is compressed by reducing the distance between the lower punch 2 and the upper punch 3 (pressing process). The press apparatus 10 of FIG. 1 includes coils 5 and 7 for performing magnetic field orientation.

  The packing density of the powder 4 is set within a range that enables magnetic field orientation and that hardly disturbs the orientation of the magnetic powder after the magnetic field is removed. In the case of this embodiment, it is preferable that the filling density is, for example, 30 to 40% of the true density.

After the powder filling, an orientation magnetic field is formed in the space filled with the powder 4, and the magnetic field orientation of the powder 4 is executed. This is effective not only in the case of parallel magnetic field shaping in which the direction of the magnetic field and the pressing direction are matched, but also in the case of vertical magnetic field shaping in which the direction of the magnetic field and the pressing direction are perpendicular. In addition, as for the molded object density which the oil agent impregnated in the oil agent impregnation process mentioned later has sufficient intensity | strength, it is desirable to set a molded object density to 3.6-4.8 g / cm < ³ >.

  After the molded body is taken out from the press apparatus 10 of FIG. 1, it is immediately subjected to an impregnation treatment with an oil agent such as an organic solvent. FIG. 2 is a drawing showing the state of the impregnation process. In the present embodiment, a saturated hydrocarbon solvent such as isoparaffin is used as the solvent to be impregnated into the molded body 20. The organic solvent 21 is placed in a solvent tank 22 as shown in FIG. 2 and the molded body 20 is immersed in the organic solvent 21 in the solvent tank 22. The organic solvent 21 is impregnated into the molded body from the surface of the molded body 20 (the surface defined by the outer shape of the molded body (outer surface)), whereby the molded body 20 is substantially covered with the organic solvent. Direct contact with atmospheric oxygen is suppressed. As a result, even if the molded body 20 is left in the atmosphere, the risk of heat generation and ignition in a short time is greatly reduced.

  In this impregnation step, it is not necessary for the entire surface of the powder particles constituting the molded body to be covered with an organic solvent (oil agent). By substantially covering at least the surface of the powder particles in the surface region of the molded body with the oil agent, the reaction between oxygen present around the molded body and the molded body can be prevented.

  Moreover, in the said impregnation process, the surface of a powder particle should just be covered substantially and it is not necessary to fill the bubble in a molded object with an oil agent.

  It is sufficient that the time (immersion time) for immersing the molded body 20 in the organic solvent 21 is 0.5 seconds or more. When the immersion time is long, the amount of the organic solvent contained in the molded body increases, but this does not cause a problem such as the collapse of the molded body. Therefore, until the sintering process is started, the molded body may be continuously immersed in the organic solvent, or the impregnation process may be repeated a plurality of times.

  As the organic solvent used for the impregnation treatment, the same material as the liquid lubricant added to the powder for the purpose of improving the moldability and the degree of orientation can be used. However, since it is necessary to be an organic solvent having a surface antioxidant function, petroleum solvents such as isoparaffin, naphthenic solvents, fatty acid esters such as methyl caproate, methyl caprylate, methyl laurate, and higher alcohols. Higher fatty acids are considered particularly preferable.

  The organic solvent used for the impregnation treatment is not limited to the saturated hydrocarbon solvent as described above, and an unsaturated hydrocarbon solvent formed from α-pinene, cyclobutene, cyclohexene, diethylbenzene, or the like can also be used. However, since the unsaturated hydrocarbon solvent may react with the powder in which the active surface is exposed through the pulverization step, it is preferable to use a saturated hydrocarbon solvent.

  After the impregnation treatment, the molded body 20 finally becomes a permanent magnet product through known manufacturing processes such as a preheating step (deoiling step), a sintering step, and an aging treatment step. Since carbon (C) contained in the oil component deteriorates the magnetic properties of the rare earth magnet, an oil agent to be impregnated in the compact 20 is selected from those that are detached from the compact during the preheating step and the sintering step. Therefore, the oil agent does not adversely affect the magnet characteristics. The oil preferably has a vapor pressure of 8 Pa or higher at 20 ° C. After the oil has volatilized by a preheating step before sintering, it is necessary to place the compact in an environment with a low oxygen concentration without contacting the molded product with the atmosphere. For this reason, it is preferable to connect the furnace which performs a preheating process and a sintering process, and to move between furnaces so that a molded object may not contact directly with air | atmosphere. It is desirable to use a continuous furnace.

  In addition, when the above organic solvents are used, since carbon in these organic solvents is relatively easily removed, it is not necessary to use hydrogen or the like that promotes carbon removal in the preheating step. Therefore, it is possible to perform the deoiling process in a shorter time than when mineral oil is used, and productivity is improved.

  Further, as described above, the oil agent is removed from the molded body in the preheating process, the sintering process, or the like. In order to remove the oil agent, it is preferable to heat the molded body at 100 to 600 ° C. for 0.1 to 8.0 hours under reduced pressure.

  In the present embodiment, an example in which the raw material alloy is produced by the strip casting method (for example, described in US Pat. No. 5,383,978) has been described, but other methods (for example, the ingot method, the direct reduction method, the atomizing method) are described. , Centrifugal casting method).

  Next, another embodiment of the method for producing a rare earth magnet according to the present invention will be described with reference to FIG. FIG. 4 shows a pressing device (pressing machine) 10, an impregnation tank 42, a sintering case 58, and the like used in this embodiment. In the present embodiment, the molded body 20 produced by the press device 10 is sent to the temperature detection unit 30. The temperature detector 30 is provided with an infrared temperature measuring device 32, and the measuring device 32 measures the surface temperature of the molded body 20 after pressing. If the infrared temperature measuring device 32 is used, the temperature can be measured quickly and easily without directly touching the molded body 20.

  When the surface temperature of the molded body 20 measured by the temperature measuring device 32 is equal to or higher than a preset level (for example, 40 ° C. or 45 ° C.), the molded body 20 is excluded from being impregnated with an oil agent ( For example, it is discarded by the robot arm 34 into the collection box 36. The collection box 36 is preferably composed of a sealed container that can be opened and closed, and is preferably disposed in the vicinity of the conveyance path of the molded body 20. With such a configuration, for example, even when the discarded molded body 20 is ignited, the molded body 20 is sealed in the collection box 36 and shielded from the surrounding atmosphere (oxygen and water vapor), thereby preventing this. Can be extinguished. Further, in order to further facilitate extinguishing the fired molded body 20, the inside of the collection box 36 may be filled with an inert gas such as nitrogen gas.

  On the other hand, when the measured surface temperature of the molded body 20 is lower than the set level, the molded body 20 is sent to the oil agent impregnation unit 40 without being discarded by the exclusion device 34. The oil agent impregnation unit 40 is provided with an impregnation tank 42 in which an oil agent 41 is accommodated. Openings 42 a that can be opened and closed by a shutter 44 are provided at both ends of the upper surface of the impregnation tank 42. Thereby, the impregnation tank 42 can take in and out the molded body 20 inside thereof, and can substantially seal the inside of the tank. Inside the impregnation tank 42, a cooler 48 for cooling the oil agent 41 is provided, and the oil agent temperature is controlled so as not to rise to a high risk level of ignition. Moreover, if the inside of an impregnation tank is made into inert atmosphere, it can work more safely.

  The molded body 20 sent to the oil agent impregnation part 40 is immersed in the oil agent 41 by a descending belt 46a extending from the opening 42a on one end side of the impregnation tank 42 into the tank. The molded body 20 immersed in the oil agent 41 is then moved in the oil agent 41 by the translation belt 46b, and the oil agent 41 is impregnated from the surface during the movement. Next, the molded body 20 is pulled up from the oil agent 41 by the rising belt 46c extending from the inside of the tank to the opening 42a on the other end side, and is taken out of the tank.

  In this impregnation step, the molded body 20 at about 40 ° C. is sequentially immersed in the oil agent 41 in the impregnation tank 42. Thereby, the temperature of the oil agent 41 rises gradually, and a part of the oil agent 41 may vaporize accordingly. In order to prevent the vaporized oil 41 from being released outside the tank, the opening 42 a of the impregnation tank 42 can be closed by the shutter 44. Even when the oil agent 41 is ignited due to the temperature rise described above, if the opening 42 a is closed using the shutter 44, the flame can be confined in the tank, so that the safety is high. Moreover, if the inside of an impregnation tank is made into inert atmosphere, ignition of a molded object and an oil agent can be suppressed more effectively.

  Furthermore, if the cooler 48 is appropriately operated, even when the temperature of the oil agent 41 is increased by the molded body 20, it can be maintained at a predetermined temperature (for example, approximately room temperature). In order to monitor the temperature of the oil agent 41, it is preferable to provide a thermometer for measuring the oil agent temperature inside the impregnation tank 42. The operation of the cooler 48 may be automatically controlled based on the oil temperature measured by the thermometer.

  After such an impregnation step, the molded body 20 impregnated with the oil agent 41 is sent to a sintering preparation unit 50 for preparing a subsequent sintering process of the molded body 20. The sintering preparation section 50 is preferably provided in a space substantially isolated from the outside air by an enclosure (partition) 52. In the sintering preparation unit 50, the molded body 20 is placed on the sintering base plate 56 in a desired arrangement by a placing device (for example, a robot arm) 54. Thereafter, the sintered base plate 56 on which the predetermined number of molded bodies 20 are placed is accommodated in the sintered case 58.

  In this sintering preparation step, an inert gas such as argon is supplied into the enclosure 52 through the opening 52a. If the molded body 20 is placed on the sintered base plate 56 and the sintered case 58 in an inert atmosphere, oxidation of the molded body 20 can be suppressed.

  According to the present embodiment, it is possible to prevent the molded body that has ignited or the molded body immediately before reaching the ignition from being put into the impregnation tank. For this reason, the oil agent in an impregnation tank is not heated too much, and the danger that an oil agent is ignited can be avoided. When pressing rare earth alloy powders with low oxygen concentration, the possibility of heat generation and ignition is the strongest after the molded body is extracted from the die of the press device. However, according to this embodiment, oil agent ignition is reliably prevented. Thus, the impregnation process can be performed safely.

  Next, still another embodiment of the method for producing a rare earth magnet according to the present invention will be described with reference to FIG. Also in the present embodiment, as in the embodiment shown in FIG. 4, when the surface temperature of the molded body 20 measured by the infrared temperature measuring device 32 is equal to or higher than a preset level (for example, 50 ° C.), an oil agent is applied to the molded body 20. Without impregnating 61, the molded body 20 is discarded into the collection box 36, and when the measured surface temperature falls below a preset level, a step of impregnating the molded body 20 with the oil agent 61 is executed. However, this embodiment is different from the embodiment shown in FIG. 4 in that a plurality of impregnation tanks 62 are used in the oil agent impregnation unit 60.

  The disposal of the molded body 20 into the collection box 36 and the transfer to the oil agent impregnation unit 60 are performed by an exclusion / injection device 70 configured using a robot arm or the like. Only when the surface temperature measured by the measuring instrument 32 is lower than a set level, the rejection / dosing device 70 immerses the molded body 20 in the oil 61 stored in any impregnation tank 62. Operate.

  The plurality of impregnation tanks 62 are placed on a rotary conveyor 66 that circulates in a substantially horizontal plane. Each impregnation tank 62 is provided with a shutter 64. The impregnation tank 62 accommodates the molded body 20 introduced from the opening 62a with the shutter 64 opened. FIG. 5 shows an example in which one molded body is accommodated in one impregnation tank 62, but a plurality of molded bodies may be accommodated in one impregnation tank 62. Good. Further, the impregnation tank 62 containing the molded body 20 is moved on the conveyor 66 with the shutter 64 closed, and the molded body 20 absorbs the oil agent 61 during this movement. After the impregnation, the shutter 64 is opened, the molded body 20 is taken out from the opening 62a, and placed on the sintering base plate 56. This take-out process is executed by a take-out / placement device 72 having a robot arm as shown in the figure, for example. The molded body 20 placed on the sintering base plate 56 is accommodated in the sintering case 58, and then a known sintering process is performed.

  According to the present embodiment, since the opening 62a can be closed by the shutter 64 except when the molded body 20 is put in and out, the vaporized oil agent is not easily released to the outside of the impregnation tank 62, and is temporarily impregnated. Even when the oil in the tank 62 ignites, it is easy to confine the flame in the tank. Furthermore, according to this embodiment, since the impregnation process of the molded body 20 is performed by dividing into a plurality of impregnation tanks 62 formed with relatively small dimensions, any one of the plurality of impregnation tanks 62 is ignited. Even in this case, the influence does not reach the other impregnation tank 62, and the safety is further improved. In order to surely control the temperature of the oil within a safe range, it is preferable to provide a cooler (not shown) inside each impregnation tank 62.

  As mentioned above, although embodiment of this invention has been described about the example which accommodates the some molded object 20 in the comparatively large sintered case 58, this invention is not limited to this. For example, after storing the compact 20 in a smaller box-shaped sintered pack, a plurality of sintered packs may be stacked and carried into the sintering furnace. Moreover, after arrange | positioning the molded object 20 on the sintering base plate 56, you may make it carry in in a sintering furnace, without sealing especially. However, in any case, the step of mounting the molded body on the sintered base plate 56 is preferably performed in an inert atmosphere.

<Example 1>
First, a molten alloy having a composition of Nd (28.5 mass%)-Dy (1.0 mass%)-B (1.0 mass%)-Al (0.1 mass%)-Fe (remainder) is prepared. It was produced by a high frequency melting furnace. The molten metal was cooled using a roll-type strip caster to produce a thin plate-shaped slab (flaked alloy) having a thickness of about 0.3 to 0.5 mm. The oxygen content of this flaky alloy was 150 mass ppm.

  Next, the flaky alloy was accommodated in a case and accommodated in a hydrogen furnace. After the inside of the furnace was evacuated, hydrogen gas was supplied into the furnace for 2 hours for hydrogen embrittlement. The hydrogen partial pressure in the furnace was 200 kPa. After the flakes spontaneously collapsed due to hydrogen storage, they were evacuated while being heated and subjected to dehydrogenation treatment. Argon gas was introduced into the furnace and cooled to room temperature. When the alloy temperature was cooled to 20 ° C., the alloy was removed from the hydrogen furnace. At this stage, the oxygen content of the alloy was 1000 ppm by mass.

  Then, it grind | pulverized with the jet mill managed so that the oxygen concentration in a grinding | pulverization chamber might be 0.1 volume% (1000 volume ppm) or less, and produced the powder raw material 1 whose average particle diameter is 4 micrometers.

  In this example, finely pulverized powder in which surface oxidation was suppressed was prepared by performing fine pulverization in an atmosphere in which the oxygen concentration was controlled to be low. The oxygen concentration contained in the raw material 1 was 1000 mass ppm. In the present specification, the “average particle diameter” refers to a mass median diameter (median diameter).

  Next, 0.4 mass% liquid lubricant was added with respect to said finely pulverized powder (raw material 1) using the rocking mixer. This lubricant was mainly composed of methyl caproate.

  Next, using the apparatus shown in FIG. 1, a compact was produced from the powder by the dry press method described above. The term “dry” as used herein widely includes a case where the powder contains a relatively small amount of lubricant (oil agent) as in the present embodiment, and means that the step of squeezing the oil agent is unnecessary.

Two molded bodies were prepared from the raw materials 1 described above. The size of the molded body was 30 mm × 50 mm × 30 mm, and the density of the molded body was 4.3 to 4.4 g / cm ³ .

  Next, a step for impregnating the molded body with the oil from the surface of the molded body was performed. Isoparaffin was used as the oil. The entire molded body was immersed in this oil for 2 seconds. Volatile oil may be used as the oil.

<Comparative Example 1>
As Comparative Example 1, an alloy having a composition of Nd (31.0 mass%)-Dy (1.0 mass%)-B (1.0 mass%)-Al (0.1 mass%)-Fe (remainder) The molten metal was prepared by a high frequency melting furnace. The molten metal was cooled using a roll-type strip caster to produce a thin plate-shaped slab (flaked alloy) having a thickness of about 0.3 to 0.5 mm. The oxygen concentration after pulverization was 4000 mass ppm (raw material 2).

<Comparative example 2>
As Comparative Example 2, an alloy having a composition of Nd (30.5 mass%)-Dy (1.0 mass%)-B (1.0 mass%)-Al (0.1 mass%)-Fe (remainder) The molten metal was prepared by a high frequency melting furnace. The molten metal was cooled using a roll-type strip caster to produce a thin plate-shaped slab (flaked alloy) having a thickness of about 0.3 to 0.5 mm. The oxygen concentration after pulverization was 2500 mass ppm (raw material 3).

<Comparative Example 3>
As Comparative Example 3, an alloy having a composition of Nd (30.5 mass%)-Dy (1.0 mass%)-B (1.0 mass%)-Al (0.1 mass%)-Fe (remainder) The molten metal was prepared by a high frequency melting furnace. The molten metal was cooled using a roll-type strip caster to produce a thin plate-shaped slab (flaked alloy) having a thickness of about 0.3 to 0.5 mm. The oxygen concentration after pulverization was 1000 mass ppm (raw material 4).

  In Example 1 and Comparative Examples 1 to 3, the reason for the difference in the oxygen concentration contained is the difference in the oxygen concentration of the atmospheric gas in the pulverization process, the length of time in contact with the atmosphere in the molding process and the sintering process caused by.

  In the same manner as in the above examples, molded bodies were prepared from the raw material 2, the raw material 3, and the raw material 4, respectively. Next, after performing the preheating process for 2 hours at 250 degreeC with respect to the molded object in which the surface was covered with the oil agent, the sintering process for 6 hours was performed at 1040 degreeC.

  FIG. 3 shows the sintered body produced in this way, from Example 1 produced from the raw material 1 and Comparative Example 1 produced from the raw material 2 and from the raw material 3 with the mass reduction amount of the sintered body as the oxidation depletion amount. The relationship between the standing time measured by PCT (pressure cooker test) and the amount of oxidation depletion is shown for the comparative example 2 and the comparative example 3 created from the raw material 4. The PCT conditions were 2 atm (atm), 125 ° C., and 85 RH. In this graph, ▪ represents the data of Example, Δ represents the data of Comparative Example 1, ● represents the data of Comparative Example 2, and ▲ represents the data of Comparative Example 3.

  The difference between the example and the comparative example is that the rare earth content of the alloy in the example does not exceed 30 mass% and the oxygen content is 1000 ppm or less, whereas in the comparative example, the rare earth content of the alloy is 31.5%. It is in the point exceeding mass%.

Therefore, oxidation attrition amount of the sintered body, whereas embodiments are -0.6g / m ^2, respectively Comparative Example 1 -10.7g / m ^2, the Comparative Example 2 -8.5G / M ² and Comparative Example 3 was −95.7 g / m ² . Thus, the oxidative depletion amount of the comparative example is 15 to 200 times the oxidative depletion amount of the example. Here, the “oxidative depletion amount” means that the oxide formed on the surface of the sintered body after PCT (rare earth oxide) and the main phase that has been degranulated by intergranular corrosion due to the rare earth oxide are removed from the sintered body. In this state, the weight of the sintered body is measured, and the weight of the sintered body before PCT is subtracted from the weight.

FIG. 3 shows that the example in which the amount of oxidative depletion is −0.6 g / m ² is superior in oxidation resistance as compared with the comparative example. The reason why the oxidative depletion amount decreases in this way is that the rare earth content is limited within the range of the present invention, and as a result, the amount of the rare earth that becomes the liquid phase is reduced, and the amount of the rare earth constituting the oxide can be reduced. It is.

The sintered body thus produced was magnetized and various magnetic properties were evaluated. In the case of the sintered magnet produced from the raw material 1 (Example 1), the oxygen content was 1000 mass ppm, the residual magnetic flux density Br was 1.45 T, and the coercive force H _cJ was 900 kA / m.

In the case of the sintered magnet produced from the raw material 2 (Comparative Example 1), the oxygen content was 4000 ppm by mass, the residual magnetic flux density Br was 1.38 T, and the coercive force H _cJ was 930 kA / m. In the case of the sintered magnet produced from the raw material 3 (Comparative Example 2), the oxygen content was 2500 ppm by mass, the residual magnetic flux density Br was 1.40 T, and the coercive force H _cJ was 910 kA / m. In the case of the sintered magnet produced from the raw material 4 (Comparative Example 3), the oxygen content was 1000 mass ppm, the residual magnetic flux density Br was 1.40 T, and the coercive force H _cJ was 920 kA / m.

By using a rare earth alloy powder having an oxygen content of 1500 mass ppm or less, a high _Br magnet can be obtained by increasing the proportion of the main phase as compared with a conventional rare earth alloy magnet.

  Next, sintering of Examples 2 to 5 and Comparative Examples 4 to 5 having a rare earth content (hereinafter referred to as “total R amount”) and oxygen amount different from those of Example 1 and Comparative Examples 1 to 3 above. A magnet was produced. These compositions are as shown in Table 1 below. These Examples and Comparative Examples were prepared under the same conditions as in Example 1 except for the composition and oxygen content.

About the sintered magnet which concerns on said Example and comparative example, the feasibility of magnetization and the amount of oxidation depletion were measured. The results are shown in Table 2. In addition, judgment of magnetization was judged by whether it has a density required in order to show a magnet characteristic after sintering. Here, with respect to the case where the density after sintering was less than 7.45 g / cm ³ , the magnetization was denied and the sign of “x” is shown in Table 2. The oxidation depletion amount indicates the amount of oxide (rare earth oxide) formed on the surface of the sintered body after PCT and the main phase that has been degranulated by intergranular corrosion due to the rare earth oxide. For those whose density after sintering was 7.45 g / cm ³ or more, the magnetization was affirmed, and the symbol “◯” is shown in Table 2. Further, the amount of oxidative depletion after PCT (pressure cooker test) is shown in Table 2 after the lapse of 120 hours.

As is apparent from Table 2, when the total R amount is 27.5% by mass to 30.8% by mass and the oxygen amount is 1500 ppm or less, the oxidative depletion after 120 hours is 1.5 g / m ^2. As shown below, it is hardly oxidized and the oxidation resistance is high. In addition, the oxidation depletion amount of Example 1 was 0.66 g / m ² . That is, when the total amount of R is 27.5% by mass to 29.5% by mass, the oxidative depletion amount is 0.66 g / m ² or less, and it can be seen that it is not substantially oxidized. Since the required density could not be obtained after sintering, the oxidation depletion amount was not measured for Comparative Example 4 and Comparative Example 5 that were evaluated as x in the judgment of magnetization.

  FIG. 6 is a graph showing Table 4 in which the change with time in oxidation consumption measured for Example 6 and Comparative Examples 6 and 7 having the compositions and oxygen amounts shown in Table 3 below was measured. Example 6 and Comparative Examples 6 and 7 were produced under the same conditions as in Example 1 except for the composition and oxygen amount described in Table 3.

As can be seen from FIG. 6 and Table 4, in the PCT test of 300 hours or more, the oxidation consumption amount is 2.0 g / m ² or less in the examples of the present invention, whereas the oxidation consumption amount is 2. It has exceeded 0 g / m ² . Thus, in the present invention, it is possible to achieve high oxidation resistance that has not been obtained conventionally.

  The method for producing an R—Fe—B rare earth magnet of the present invention provides a method for producing a rare earth magnet that is difficult to oxidize safely and efficiently while using a rare earth alloy powder having a low oxygen concentration (1500 mass% or less). It becomes possible.

It is sectional drawing which shows schematic structure of the press apparatus used suitably for shaping | molding of magnetic powder. It is a figure which shows the impregnation process in one Embodiment of this invention. It is a graph which shows the relationship between the leaving time measured by PCT, and the amount of oxidation depletion about the Example and comparative example of this invention. It is drawing which shows the press apparatus, impregnation tank, sintering case, etc. which are used by other embodiment of this invention. It is drawing which shows the press apparatus, impregnation tank, sintering case, etc. which are used in other embodiment of this invention. It is a graph which shows a time-dependent change to 300 hours of oxidation loss.

Explanation of symbols

1 die 2 lower punch 3 upper punch 4 raw material powder 5 coil 7 coil 10 press device 20 molded body 21 organic solvent 22 solvent tank 30 temperature detection unit 32 infrared temperature measuring device 34 exclusion device 36 recovery box 40 oil agent impregnation unit 41 oil agent 42 impregnation Tank 42a opening 44 shutter 46b translation belt 46c ascending belt 48 cooler 50 sintering preparation section 52 enclosure 52a opening 54 mounting device 56 sintering base plate 58 sintering case

Claims (8)

A pressing step in which a rare earth alloy powder having a rare earth content of 27.5% by mass to 30.8% by mass and an oxygen content of 1500 ppm by mass or less is compression-molded by a dry press method, thereby producing a molded body;
Impregnating the molded body with an oil from the surface of the molded body;
A method for producing an R—Fe—B rare earth magnet comprising the step of sintering the compact.   The R-Fe-B according to claim 1, wherein the rare earth alloy powder is placed in an inert atmosphere gas having an oxygen concentration of 20000 ppm by volume or less until the cavity of a press apparatus for producing the compact is filled. Of manufacturing rare earth magnets.   The oil agent removing step of substantially removing the oil agent is performed before sintering the molded body, and the molded body is not brought into contact with the atmosphere after the oil agent removing step until sintering. The manufacturing method of the R-Fe-B type rare earth magnet of description.   The said oil agent removal process is a manufacturing method of the R-Fe-B type rare earth magnet of Claim 3 performed for 0.1 to 8.0 hours in the temperature range of 100 to 600 degreeC under pressure reduction.   The R-Fe-B rare earth according to any one of claims 1 to 4, wherein the impregnation step is performed using an impregnation tank provided with an opening for taking in and out the molded body and a shutter capable of closing the opening. Magnet manufacturing method.   The method for producing an R-Fe-B rare earth magnet according to any one of claims 1 to 5, wherein after the impregnation step, the compact is disposed on a sintered base plate in an inert atmosphere before sintering. .   The method for producing an R-Fe-B rare earth magnet according to any one of claims 1 to 6, wherein after the impregnation step, the compact is housed in a sintering case in an inert atmosphere before sintering. The rare earth content is 27.5 mass% to 30.8 mass%, and the oxygen content is 1500 mass ppm or less,
An R—Fe—B rare earth magnet having an absolute value of oxidative depletion of 2.0 g / m ² or less in a PCT test of 300 hours or more.

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