WO2006098238A1

WO2006098238A1 - Method for producing rare earth magnet and impregnation apparatus

Info

Publication number: WO2006098238A1
Application number: PCT/JP2006/304731
Authority: WO
Inventors: Akihito Tsujimoto; Yuji Kaneko
Original assignee: Neomax Co., Ltd.
Priority date: 2005-03-14
Filing date: 2006-03-10
Publication date: 2006-09-21
Also published as: JPWO2006098238A1; JP4743120B2; CN1989581A

Abstract

Disclosed is a method for producing an R-Fe-B rare earth magnet comprising a pressing step (A) wherein a molded body (20) is formed by compression molding a rare earth alloy powder by dry pressing; a step (B) wherein the molded body (20) is impregnated with an antioxidant through the surface thereof; and a step (C) wherein the molded body (20) is sintered. In the step (B), the molded body (20) is impregnated with the antioxidant within a container (100) wherein the pressure is reduced.

Description

Specification

Rare earth magnet manufacturing method and impregnation apparatus

Technical field

The present invention relates to a method for manufacturing a rare earth magnet and an impregnation apparatus. More specifically, the present invention relates to the production of high performance rare earth sintered magnets produced from rare earth alloy powders with reduced oxygen content.

Background art

[0002] R—Fe—B rare earth magnets (R is a rare earth element) are mainly composed of tetragonal R Fe B compounds.

2 14

Main phase, R rich phase rich in rare earth elements such as Nd, and B rich phase force rich in B (boron). In R—Fe—B rare earth magnets, the main phase is R Fe B

Increasing the abundance ratio of 2 14 tetragonal compound improves its magnetic properties.

[0003] The minimum amount of R-rich phase is required for liquid phase sintering. R reacts with oxygen, R

2

In order to make an oxide of O, a part of R is consumed in the part that is not useful for sintering. This

Three

For this reason, conventionally, an extra R is required for consumption by acid. R O

The generation of the oxide of 2 3 becomes more remarkable as the amount of oxygen increases. Therefore, by reducing the amount of oxygen in the atmosphere gas at the time of powder preparation, the R relative amount in the finally obtained R-Fe-B rare earth magnet can be reduced and the magnetic properties can be improved. Has been considered.

[0004] As described above, it is preferable that the amount of oxygen in the R-Fe-B-based alloy powder used for the production of the R-Fe-B-based magnet is small. However, the method of 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 technology. The reason for this is that when an R—Fe—B alloy powder is produced in an environment in which the oxygen concentration is controlled to be low and the oxygen content of the alloy powder is reduced to, for example, 4000 ppm or less by weight, the powder is separated from oxygen in the atmosphere. This is because it reacted violently and could ignite within a few minutes even at room temperature.

[0005] The hydrogen pulverization method has higher production efficiency than mechanical pulverization methods such as ball milling. However, magnetic properties (especially coercive force) can be obtained depending on the sintering conditions when using magnetic powder produced by the hydrogen pulverization method. There is a problem that ignition is likely to occur again as soon as it fluctuates. Especially magnetic The fluctuation in characteristics is remarkable when the oxygen content of the sintered body is suppressed to 4000 ppm or less by weight, and the force is relatively small when the rare earth element content is relatively small (for example, the rare earth element content is 32 mass% or less of the entire magnet). To occur.

[0006] From the above, even though it has been 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, It was extremely difficult to handle reduced R—Fe—B alloy powder at production sites such as factories.

[0007] In particular, in the pressing process for compressing and molding powders, the heat generated by the friction between the powders accompanying compression and the frictional heat generated between the powder and the inner wall surface of the cavity when the molded body is taken out is reduced. Due to the rise in temperature, there is a high risk of ignition. In order to prevent this ignition, a non-oxygen atmosphere around the press device may be considered, but it is not practical because it is difficult to supply raw materials and take out the molded body. In addition, it is impossible to avoid the problem of ignition if the individual compacts are sintered quickly each time the compact is taken out of the pressing equipment, but this is an extremely inefficient method and is not suitable for mass production. . Since the sintering process takes more than 4 hours, it is reasonable to treat many compacts simultaneously in one sintering process. In addition, it is difficult for mass production equipment to manage the compact in an atmosphere with an extremely low oxygen concentration until the pressing force reaches the sintering step.

[0008] Incidentally, a liquid lubricant such as a fatty acid ester is added to the fine powder before the pressing step to improve the compressibility of the powder. By adding such a liquid lubricant, a thin oily film is formed on the surface of the powder particles, but it is not possible to sufficiently prevent the oxidation of the powder having an oxygen concentration of 4000 ppm or less.

[0009] For the above reasons, when crushing R-Fe-B alloys, a small amount of oxygen is intentionally introduced into the atmosphere, thereby thinly oxidizing the surface of the finely pulverized powder and making it reactive. Is being reduced. For example, in Patent Document 1, a rare-earth alloy is finely pulverized by 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. This technique is disclosed. According to this technology, oxygen in the atmosphere is blocked by the acid coating on the surface of the powder particles, so heat generation and ignition by acid can be prevented. However, since there is an acid coating on the surface of the powder particles, The amount of oxygen contained will increase.

[0010] On the other hand, Patent Document 2 and Patent Document 3 disclose a technique in which R-Fe-B alloy powder having a low oxygen content (eg, 1500 ppm) is mixed with mineral oil and slurried. Yes. 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 oxygen content of the R—Fe—B alloy powder.

[0011] However, according to the above-described conventional technique, it is necessary to perform the pressing process while squeezing out the oil after filling the slurry-like R—Fe—B alloy powder into the cavity of the press device. Therefore, productivity is low. In addition, according to the conventional method for producing rare earth magnets, the crystal grains are likely to be coarsened in the sintering process, so that the magnetite characteristics (coercive force) are not sufficiently improved even when a magnet powder having a low oxygen concentration is used. There was also a problem.

[0012] On the other hand, in order to solve the above problem, the present applicant cuts the contact between the magnetic powder constituting the compact and the atmospheric atmosphere by impregnating the powder compact with an antioxidant, thereby oxidizing the powder. A technology for preventing this is developed and disclosed in Patent Document 4 and Patent Document 5.

Patent Document 1: Japanese Patent Publication No. 6-6728

Patent Document 2: U.S. Pat.No. 5,489,343

Patent Document 3: Japanese Patent Laid-Open No. 10-321451

Patent Document 4: Japanese Patent Laid-Open No. 2002-8935

Patent Document 5: Japanese Patent Laid-Open No. 2002-170728

Disclosure of the invention

Problems to be solved by the invention

[0013] However, according to the techniques disclosed in Patent Document 4 and Patent Document 5, when the molded body is dipped in the antioxidation agent, bubbles are generated and peeling occurs in the molded body. May collapse. Such a collapse of the molded body is considered to occur as follows.

That is, when the molded body is immersed in the antioxidant, the antioxidant soaks into the interior from the surface of the molded body. At this time, air existing in the gaps between the powder particles constituting the compact is confined in the compact. As a result, the air inside the compact loses its escape and the air pressure inside the compact increases as impregnation proceeds.

[0015] On the other hand, since the density of the molded product varies depending on the site, Compressed air in the molded body seeks escape and may leak out from the relatively low molding density. At this time, bubbles are generated in the solution of the antioxidant, and cracks and peeling occur in the molded body.

[0016] In a molded body pressed into a complicated shape (for example, a bow shape) like a rare earth sintered magnet for a voice coil motor (VCM), the molding density is adjusted to a low value as a whole. Also, when performing magnetic field orientation, the molding density is set low. In this way, in a molded body whose molding density is adjusted to a low value as a whole and whose strength is low, cracking and chipping are particularly likely to occur during the antioxidant impregnation process. In addition, if the molded body is cracked or peeled during the impregnation process, the production yield of the sintered magnet will be significantly reduced.

[0017] The present invention has been made in view of various advantages, and its main purpose is to provide a method and apparatus capable of producing a high-performance rare earth magnet having a low oxygen content and excellent magnetic properties with a high yield. It is to provide.

Means for solving the problem

[0018] The method for producing an R—Fe—B rare earth magnet according to the present invention includes a pressing step (A) for producing a compact by compressing a rare earth alloy powder by a dry press method, and a surface of the compact. The method includes a step (B) of impregnating the molded body with an antioxidant and a step (C) of sintering the molded body. In the step (B), the molded body is a decompressed container. And impregnated with the antioxidant.

In a preferred embodiment, the step (B) includes a step of storing the molded body in the container, a step of decompressing the inside of the container, and supplying the antioxidant to the inside of the container. Including the step of.

[0020] Preferably, in the embodiment, the rare earth alloy powder has an oxygen content of 50 ppm to 4000 ppm by weight and a nitrogen content of 150 ppm to 1500 ppm by weight.

[0021] Preferably, according to the embodiment, the step (C) includes a first step of holding at a temperature range of 700 ° C or higher and lower than 1000 ° C for a time of 10 minutes or longer and 420 minutes or shorter; And a second step in which sintering proceeds in a temperature range from C to 1200 ° C. In a preferred embodiment, the rare earth alloy powder has an average particle size of 1.0 / zm to 5. O / zm.

[0023] Preferably, in the embodiment, the antioxidant is composed of a volatile component.

[0024] In a preferred embodiment, after the step (B), by volatilization of the anti-oxidation agent.

The temperature of the molded body is lowered at least temporarily.

[0025] Preferably, in the embodiment, the antioxidant is isoparaffin.

[0026] The impregnation apparatus includes a container for storing a molded body of rare earth alloy powder, a means for supplying an antioxidant used for impregnation of the molded body to the inside of the container, and a reduced pressure for reducing the internal pressure of the container. Device.

The invention's effect

[0027] In the present invention, since the molded product is impregnated with an antioxidant under reduced pressure, the antioxidant can be impregnated quickly without causing cracks or chips in the molded product during the impregnation process. As a result, while reducing the oxygen content of the magnet powder, it is possible to suppress the oxidation of the powder compact with good yield.

[0028] According to the present invention, the risk of heat generation and ignition can be reduced, and the amount of the main phase of the magnet can be increased safely and practically, so that the magnet characteristics of the rare earth magnet can be greatly improved. become.

Brief Description of Drawings

[0029] FIG. 1 is a schematic view showing a configuration of an impregnation apparatus used in the present invention.

FIG. 2 (a) to (c) are process cross-sectional views showing an impregnation process (conventional example) performed under atmospheric pressure.

FIG. 3 (a) to (c) are process cross-sectional views showing an impregnation process performed under reduced pressure according to the present invention.

FIG. 4 is a cross-sectional view showing a schematic configuration of a press apparatus used for molding magnetic powder.

FIG. 5 is a view showing a temperature profile of a sintering process, and shows a profile 30 related to a conventional sintering process and a profile 32 related to the sintering process of the present invention.

[Fig. 6] (a) is a diagram showing a molded body in which cracks occurred when impregnation was performed at atmospheric pressure. (B) and (c) are views showing a molded body in an example of the present invention.

FIG. 7 is a graph showing the relationship between the pressure during impregnation (impregnation pressure) and the amount of impregnation.

8] A graph showing the relationship between the compact density and the amount of impregnation.

Explanation of symbols

1 die

2 Bottom punch

3 Top punch

4 Raw material powder

5 Coinole

7 Koinole

10 Press equipment

20 Molded body

21 Antioxidants

22 Solution tank

23 Air

24 crack

BEST MODE FOR CARRYING OUT THE INVENTION

[0031] In the present invention, after performing a pressing process for producing a molded body by compression molding rare earth alloy powder by a dry press method, the molded body is impregnated with an antioxidant before performing the sintering process of the molded body. The process to make is performed. The main feature of the present invention is that the antioxidant impregnation step is performed under reduced pressure.

Hereinafter, a method for producing an R—Fe—B rare earth magnet according to the present invention will be described with reference to FIG.

[0033] FIG. 1 schematically shows a main part of an apparatus suitably used in the impregnation step in the present invention. This device reduces the internal pressure of the decompression vessel 100, the decompression vessel 100 that houses the rare earth alloy powder compact 20 produced in the pressing process, the supply unit 110 that supplies the antioxidant to the interior of the decompression vessel 100, and And a decompression device 120 for performing the above operation.

[0034] In a preferred embodiment, the decompression vessel 100 is easy to observe the contents from the outside. In this way, a transparent member such as acrylic or glass can also be produced.

[0035] In the illustrated example, the decompression vessel 100 is connected to the decompression device 120 via a pipe line, and after the molded body 20 is set in the decompression vessel 100, evacuation in the decompression vessel 100 is executed. It is done. In the example shown in the drawing, the support base 130 on which the molded body 20 is placed rises to the drive unit 140 and is stored in the decompression container 100. The decompression device 120 is a vacuum pump such as an ejector, and can reduce the internal pressure of the decompression vessel 100 to a range of, for example, −50 kPa to 1 lOOkPa. Here, “−50 kPa” and “one 100 kPa” mean “50 kPa lower than atmospheric pressure, pressure” and “lOOkPa lower than atmospheric pressure, pressure”, respectively.

[0036] The ejector operates using jet steam or the like as a drive source, has no mechanical drive unit, and is a vacuum pump. Therefore, the ejector has an advantage that the structure is simple and failure is unlikely to occur. However, the decompression device 120 is not limited to an ejector, and may be another type of vacuum device.

In a preferred embodiment, when the internal pressure of the decompression vessel 100 reaches the range of −50 kPa to −lOOkPa, the antioxidant is supplied into the decompression vessel 100. The reservoir (supply unit 110) in which the antioxidant is stored and the decompression vessel 100 are connected via a valve (not shown). When the valve is opened while the inside of the decompression vessel 100 is decompressed, the acid / antioxidant flows from the reservoir into the decompression vessel 100 and flows into the decompression vessel 100.

Next, the impregnation process of the molded body will be described with reference to FIG. 2 and FIG. FIG. 2 is a diagram showing an impregnation process (comparative example) performed under atmospheric pressure, and FIG. 3 is a diagram showing an impregnation process (present invention) performed under reduced pressure.

[0039] As shown in Fig. 2 (a), when the molded product 20 is immersed in the anti-oxidation agent stored in the solution tank, the impregnation of the antioxidant proceeds from the surface of the molded product 20, and the impregnated portion 20a However, the inside will spread and become stronger. However, as impregnation proceeds as shown in FIG. 2 (b), the air 23 trapped inside the compact 20 (between the powder) is compressed and its internal pressure rises. As a result, even if the strength of the molded body 20 is low, the air 23 escapes to the outside, and cracks 24 are generated as shown in FIG. 2 (c).

[0040] On the other hand, when the molded body 20 is placed inside the vacuum container 100 and impregnated with the antioxidant under reduced pressure, the antioxidant is obtained as shown in FIGS. 3 (a) to (c). Impregnation proceeds rapidly. If the pressure in the decompression vessel 100 is reduced to, for example, −90 kPa or less, the impregnated part 20a extends to the center of the compact 20 because almost no air that impedes impregnation exists in the compact. It spreads quickly.

[0041] As described above, when impregnation is performed under reduced pressure, air pressure that resists impregnation is hardly formed inside the molded body 20, so that the molded body is not cracked or chipped due to air leakage.

[0042] According to the present invention, after forming a molded body of low oxygen concentration magnet powder in the pressing process, the impregnation process described above is performed, whereby the molded body generates heat without causing cracks. Can be solved.

[0043] It should be noted that an antioxidant effective for preventing heat generation and ignition of the molded body is considered preferable for a rare earth sintered magnet, and is a force containing carbon and other impurities. Since it is sufficiently removed by the previous debinding process, the final magnet properties are not adversely affected. When a volatile antioxidant is used, when the molded body after the impregnation process is taken out of the pressure reducing container, the temperature of the molded body temporarily decreases due to volatilization of the anti-oxidation agent, thus preventing ignition. The effect is more remarkable and preferable.

[0044] In the above example, after the reduced pressure state is formed in the reduced pressure vessel, the antioxidant is supplied into the reduced pressure vessel. However, when the reduced pressure is started after the antioxidant is supplied into the reduced pressure vessel, There is a possibility that the antioxidant having boilability will boil and the molded body will be cracked or chipped. For this reason, it is preferable to supply the antioxidant into the vacuum container after the pressure in the vacuum container has been sufficiently reduced.

Hereinafter, embodiments of the present invention will be described in more detail.

[0046] (Embodiment)

First, the rare earth element R is at least one element selected from the group force consisting of Y, La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu): 10 atomic% ˜30 atomic%, B: 0.5 atomic% to 28 atomic%, balance: Fe, and a molten R—Fe—B alloy containing inevitable impurities is prepared. However, one 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 production of rare earth element R oxides can be suppressed, the amount of rare earth element R can be minimized. Can be kept low. In addition, the rare earth element R preferably contains 10 atomic% or more of heavy rare earth elements such as Dy, Tb, and Ho.

[0047] Next, the molten alloy is lowered to a temperature of 1000 ° C or lower by a rapid cooling method such as a strip cast method at a cooling rate of 10 ² to 10 ⁴ ° C / second to a thickness of 0.03mn! Rapidly solidifies into a thin plate of ~ 10mm. Then cooled at a cooling rate of 10 to 10 ² ° CZ seconds to room temperature. In this manner, the R-rich phase is fabricated into a piece having a structure separated in a fine size of 5 m or less, and then the piece is accommodated in a container that can be inhaled and exhausted. After evacuating the inside of the container, H gas at a pressure of 0.03 MPa to l. OMPa is supplied into the container to form a collapsed alloy powder. This collapse

2

Gold powder is finely pulverized in an inert gas stream after dehydrogenation.

[0048] The piece of magnet material used in the present invention is preferably manufactured by a strip casting method using a molten alloy having a specific composition by a single roll method or a twin roll method. Depending on the thickness of the piece to be produced, the single roll method and the twin roll method can be used properly. If the piece is thick, it is preferable to use the twin roll method. If the piece is thick, it is preferable to use the single roll method.

. In addition, since the alloy by the rapid cooling method has a sharp particle size distribution and can have a uniform particle size, the squareness after sintering is improved.

[0049] When the thickness of the piece is less than 0.03 mm, the rapid cooling effect is increased, so that the crystal grain size may be too small. If the crystal grain size force is too large, the individual particles will be polycrystallized when powdered and the crystal orientation cannot be aligned, leading to deterioration of magnetic properties. On the other hand, if the thickness of the flake exceeds 10 mm, the cooling rate slows down, and a Fe crystallizes out and the N d rich phase is unevenly distributed.

[0050] The hydrogen storage treatment can be performed, for example, as follows. That is, after a piece of a piece that has been 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 the inside of the hydrogen furnace is sufficiently evacuated, hydrogen gas having a pressure of 3 OkPa to l.OMPa is supplied into the container, and hydrogen is occluded in the piece. Since the hydrogen absorption 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. As a result of absorption and absorption of hydrogen, the splinters spontaneously collapse and become powder.

[0051] After cooling the powdered alloy, it is heated in vacuum to perform a dehydrogenation treatment. For dehydrogenation treatment As a result, fine cracks are present in the resulting alloy powder grains, so that it can be finely pulverized in a short time by a ball mill, a jet mill or the like to produce an alloy powder having the particle size distribution described above. it can. A preferred embodiment of the hydrogen pulverization treatment is disclosed in JP-A-7-18366.

[0052] The fine pulverization is preferably performed by a dry pulverization apparatus such as a jet mill, an attritor, and a vibration mill using an inert gas containing nitrogen and substantially free of oxygen. It is desirable to use high-purity nitrogen gas with a purity of 99.99% or more as the inert gas whose oxygen concentration in the inert gas is preferably controlled to 500 ppm or less. By performing the powdering process in such an atmosphere of high purity nitrogen gas, a finely pulverized powder having a low oxygen concentration and a thinly nitrided surface can be obtained. The average particle size (pulverized particle size) of the powder is preferably in the range of 1. to 5.5 μm. The smaller the average particle size, the more acidic the powder particles become. Therefore, when the powder particle size is 5.0 m or less (especially 2.0 m or less), even if the oxygen concentration exceeds 4000 ppm. There is an advantage of implementing the manufacturing method of the present invention.

[0053] It is preferable to add a liquid lubricant containing a fatty acid ester or the like as a main component to the magnet powder thus produced. The addition amount is, for example, 0.15 to 5.0% by mass. Examples of fatty acid esters include methyl methyl pronate, methyl caprylate, and methyl laurate. The lubricant may contain components such as a binder. The important point is that the lubricant volatilizes and can be removed later. In addition, when the lubricant itself is a solid that is difficult to mix uniformly with the alloy powder, it may be diluted with a solvent. As the solvent, petroleum solvents such as isoparaffin and naphthenic solvents 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 an anti-oxidation effect on the particles, and also has a function of uniforming the density of the compact during pressing and suppressing the disorder of orientation.

Next, magnetic field orientation and compression molding are performed using a press apparatus as shown in FIG. 4 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 the space (cavity) formed by the die 1, the lower punch 2 and the upper punch 3, and the distance between the lower punch 2 and the upper punch 3 is reduced. Compression molding is performed by a small amount (pressing process). The pressing device 10 of FIG. 4 is provided with coils 5 and 7 for magnetic field orientation!

[0055] 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 20 to 30% of the true density. As a result, the density of the green body shows a value included in the range of 3.8 to 4.2 g / cm 3.

[0056] 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. Even in the case of vertical magnetic field shaping in which the direction of the magnetic field and the pressing direction are perpendicular to each other, it is effective not only in the case of parallel magnetic field shaping in which the direction of the magnetic field matches the pressing direction. The magnetic field applied for orientation may be a static magnetic field or a pulsed magnetic field. In order to prevent acidity of the powder, it is preferable to perform the pressing process itself in an inert gas such as nitrogen.

[0057] After the molded body is taken out from the press apparatus 10, it is immediately subjected to an impregnation treatment with an antioxidant. In this embodiment, the molded body 20 is impregnated with isoparaffin in a reduced pressure state (pressure: about −50 kPa to about 1 lOOkPa) using an apparatus having the configuration shown in FIG.

[0058] By the above impregnation, the surface of the rare earth magnet alloy powder constituting the compact 20 is coated with an antioxidant, so that even if the compact 20 is exposed to the atmosphere, the powder particles are in direct contact with oxygen. Is suppressed. As a result, even if the molded body 20 is left in the atmosphere, the possibility of heat generation or ignition in a short time is greatly reduced.

[0059] As the anti-oxidation agent used for the impregnation treatment, a liquid lubricant added to the powder for the purpose of improving the moldability and the degree of orientation and the same substance as the antioxidant for diluting the liquid lubricant are used. Can be. However, since it is necessary to be an acid / antioxidant having a surface acid / antioxidation function, petroleum-based solvents such as isoparaffin, naphthenic solvents, methyl caprate, methyl caprylate, methyl laurate, etc. Fatty acid esters, higher alcohols, and higher fatty acids are particularly preferred.

[0060] After the impregnation treatment, the molded body 20 finally becomes a permanent magnet product through a production process such as a binder removal step, a sintering step, and an aging treatment step. The carbon contained in the oil component deteriorates the magnetic properties of the rare earth magnet. In the process and the sintering step, one that is detached from the molded body is selected. For this reason, the oil does not adversely affect the magnet characteristics. After the oil has volatilized, such as in the binder removal process before sintering, it is necessary to place the compact in an environment with a low oxygen concentration without contacting it with the atmosphere. For this reason, it is preferable that the furnaces for performing the binder removal process and the sintering process are connected and moved between the furnaces so that the compact does not directly contact the atmosphere. It is more desirable to perform the above treatment using a batch furnace.

[0061] In the present invention, the crystal grain size in the finally obtained sintered magnet is 3 μm or more and 9 μm or less, preferably 3 μm or more, by performing a two-step sintering process described later. It can be controlled within the range of 6 μm or less. In the conventional sintering process, crystal grains are coarsened by grain growth during sintering, and it was difficult to sufficiently improve the coercive force even when low oxygen magnetic powder was used. According to the process, the effect of using the low oxygen magnetic powder can be sufficiently exhibited.

FIG. 5 shows a temperature profile in the sintering process. In FIG. 5, the profile indicated by reference numeral “30” is adopted in the conventional sintering process, and the profile indicated by reference numeral “32” is adopted in the sintering process of the present invention. Is.

[0063] In the sintering process used in this embodiment, two-stage heat treatment is performed. First, in the first stage, a relatively long time (preferably 10 to 420 minutes) is maintained in a relatively low temperature range (preferably 700 to: L 000 ° C.), and then the process proceeds to the second stage. In the second stage, a relatively short temperature (for example, 30 to 240 minutes) is maintained in a relatively high temperature range (preferably 1000 to 1200 ° C). The atmosphere during sintering is preferably an inert gas such as nitrogen, hydrogen, or argon.

[0064] During the hydrogen crushing process using the hydrogen occlusion / release phenomenon by the rare earth alloy, the hydrogen remaining in the R Fe B phase, which is the main phase, is removed from the binder at about 500 ° C before the sintering process.

2 14

Released by the process. However, rare earth hydrogen compounds (RH) formed by combining rare earth elements and hydrogen contained in the R-rich phase etc. during hydrogen crushing treatment do not metallize at about 500 ° C (hydrogen does not release into a metallic state) ). However, according to the sintering process of the present invention, the rare earth hydrogen compound (RH) releases hydrogen and metallizes it in the first stage. The That is, RH → R + (x / 2) H x 2 in the first stage heat treatment performed at a temperature of 700 ° C or higher

As a result of the reaction represented by the chemical reaction formula †, the R-rich phase at the grain boundary quickly becomes a liquid phase in the second stage heat treatment, and the sintering reaction proceeds rapidly. As a result, the sintering process is completed in a short time and the coarsening of the crystal grains is suppressed, so that the coercive force is improved and the sintering density is also improved.

According to the experiments of the present inventors, the change in coercive force due to the difference in crystal grain size in the sintered magnet is remarkable when the amount of oxygen contained is small. For example, when the oxygen content is 7000 mass ppm, the coercive force of both is 10%, regardless of whether the crystal grain size is about 3-6 / ζ πι or 12-15 / ζ πι. When the oxygen content was 3000 ppm by mass or less, there was a difference of about 10% or more in coercive force between magnets with an average crystal grain size of 9 m or less and magnets with an average crystal grain size of more than 9 m. The average grain size of R-Fe-B rare earth magnets is 3 μm or more and 9 μm or less, the oxygen concentration is 50 ppm to 4000 ppm by weight, and the nitrogen concentration is 150 ppm to 1500 ppm by weight. Is preferred. After sintering, perform aging treatment at 400-900 ° C.

In this embodiment, an example in which the raw material alloy is produced by the strip casting method has been described, but other methods (for example, an ingot method, a direct reduction method, an atomizing method, a centrifugal forging method) may be used.

[0067] In the present specification, ¾? "6-8 rare earth magnets" broadly includes those in which the-part of 6 is replaced with a metal such as 0) and rare earth magnets in which part of B (boron) is replaced with C (carbon). R-Fe-B rare earth magnets have a tetragonal structure R Fe

twenty one

B-type compound power The structure surrounding the main phase, which is surrounded by the R-rich phase and B-rich phase (grain boundary phase)

Four

Has a structure. The structure of such an R—Fe—B rare earth magnet is disclosed in US Pat. No. 5,564,565.

[0068] <Example>

First, an alloy melt having the composition Nd + Pr (30.0 mass%) — Dy (l. 0 mass%) — B (l. 0 mass%) — Fe (remainder) was prepared by a high-frequency melting furnace. Then, the molten metal was cooled by a water-cooled roll type strip casting method to produce a thin plate-like piece (flaked alloy) having a thickness of about 0.5 mm. This flaky alloy contains 150 mass ppm of oxygen was.

[0069] Next, the flaky alloy was accommodated in a hydrogen furnace. After evacuating the furnace, hydrogen gas was supplied into the furnace for 2 hours in order to embrittle hydrogen. The hydrogen partial pressure in the furnace was 200 kPa. After the flakes spontaneously collapsed due to hydrogen occlusion, they were evacuated with heating and dehydrated. Argon gas was introduced into the furnace and cooled to room temperature. When the alloy temperature was cooled to 20 ° C, the hydrogen reactor power was also removed. At this stage, the oxygen content of the alloy was 1000 ppm by mass.

[0070] Thereafter, the alloy was pulverized by a jet mill filled in the pulverization chamber with a nitrogen gas atmosphere in which the oxygen concentration was controlled to 200 mass ppm or less to produce magnet powders having various oxygen concentration values. In addition, by adjusting the grinding conditions such as grinding time, the average particle size (grinding particle size) of the magnet powder was changed in the range of 1.5 to 7. Various powders with different average particle sizes were prepared. Also, during pulverization, the amount of oxygen contained in the nitrogen atmosphere was controlled, and the oxygen content of the powder was changed to a maximum of about 7000 mass ppm. The nitrogen concentration of the powder thus obtained was in the range of 100-900 mass ppm.

[0071] Thereafter, 0.5% by mass of a liquid lubricant was added to the pulverized powder using a rocking mixer. This lubricant was mainly composed of methyl cabronate. Then, using the apparatus shown in FIG. 1, a compact was produced from the powder by a dry press method. The term “dry” as used herein refers to a powder that includes a case where the powder contains a relatively small amount of lubricant (oil agent) as in this embodiment, and does not require a step of squeezing the oil agent. The size of the molded body was 30 mm X 50 mm X 30 mm, and the density was 4.2 to 4.4 gZcm ³ .

Next, using the apparatus having the configuration shown in FIG. 1, a step of impregnating the molded body with an antioxidant from the surface of the molded body under reduced pressure was performed. Isoparaffin was used as the anti-oxidation agent.

[0073] For comparison, when impregnation was performed under atmospheric pressure by the method shown in Fig. 2, cracks occurred as shown in Fig. 6 (a). On the other hand, according to this example, as shown in FIGS. 6 (b) and 6 (c), cracks did not occur, and the impregnation of the antioxidant proceeded rapidly to the inside of the molded body. Fig. 6 (b) shows a case where the impregnation time is relatively short and the entire molded body is not impregnated, but the impregnation part is formed on the surface of the molded body, so that ignition is prevented. The effect is sufficiently obtained. Fig. 6 (c) shows a state where the impregnated part has spread over the entire compact. In the molded body shown in FIG. 6, a portion indicated as a region with more dense points is a portion where the antioxidant is impregnated.

FIG. 7 is a graph showing the relationship between the pressure in the decompression vessel and the amount of impregnation. The amount of impregnation increases as the pressure in the vacuum vessel becomes lower than the atmospheric pressure. If the difference between the pressure in the vacuum vessel and atmospheric pressure is 35kPa or less, the molded body may crack. For this reason, the pressure in the decompression vessel is preferably 40 kPa or more lower than the atmospheric pressure.

FIG. 8 is a graph showing the relationship between the molding density (the density of the molded body) and the amount of impregnation. As can be seen from Fig. 8, if the pressure and impregnation time are the same, the amount of impregnation increases as the molding density decreases.

[0076] For the examples of the present invention, after impregnating almost all of the molded product with the anti-oxidation agent, the molded product was left in the atmosphere at room temperature, and the temperature of the molded product was measured. When the rare earth element in the molded body is oxidized, heat is generated. Therefore, it is possible to evaluate the progress of oxidation based on the molded body temperature.

[0077] The temperature of the compact immediately after the impregnation treatment was 40 ° C or less, and even after 600 seconds, the temperature remained below 50 ° C. Even with compacts made from powder with the lowest oxygen concentration, the maximum temperature is only around 70 ° C, and even if the compact is left in the atmosphere for a long time (eg 6 hours) There was no risk of ignition, and no deterioration of the magnetic properties was observed. In addition, a phenomenon was observed in which the temperature of the molded body decreased temporarily (about 2 to 3 minutes) after the impregnation treatment. This is because the antioxidant was volatilized from the surface of the molded body and the molded body was cooled by the heat of vaporization.

[0078] When the molded article was not subjected to the impregnation step with the antioxidant (comparative example), in the molded article in which the oxygen concentration was adjusted to about 2000 ppm by mass or less, the pressing device force was also taken out. After about 6 minutes and 45 seconds, it reached 80 ° C in the atmosphere and ignited. Since the heat generated by the acid promotes the oxidation of the surrounding powder, the temperature of the compact rapidly increases when the oxidation of V and oxidization starts, and the risk of ignition increases significantly. Even if such a compact is housed in a case of atmospheric gas with a relatively low oxygen concentration, it is thought that it gradually oxidizes in the case and accumulates heat inside the compact. . Therefore, eventually it will suddenly There is a risk of overheating and ignition.

[0079] The molded body impregnated with the antioxidant was subjected to a binder removal step at 250 ° C for 2 hours, and then a sintering step. When producing a sintered magnet using a magnet powder with a low oxygen concentration, it is particularly preferable to reduce the crystal grain size using a two-stage sintering process. When the oxygen concentration is, for example, 1000 mass ppm or more and 4000 mass ppm or less, it is preferable that the average crystal grain size range of the sintered magnet is 3 μm or more and 9 μm or less.

[0080] When the powder surface is not nitrided by, for example, pulverizing in an atmosphere of He or argon, a nitride layer is not formed on the surface of the powder particles, so that the process is easy to oxidize. Ignition and magnetic properties deteriorated. On the other hand, if the nitriding of the powder particle surface proceeds too much, the sintering process becomes difficult to proceed and the magnetic properties deteriorate. For this reason, it is preferable to control the nitrogen concentration in the magnet powder in the range of 150 mass ppm to 1500 mass ppm, and more preferably in the range of 200 mass ppm to 700 mass ppm. If the nitrogen concentration in the magnet powder is 150 mass ppm or more and 1500 mass ppm or less and the oxygen concentration is 50 mass ppm or less and 4000 mass ppm or less, the sintered magnet obtained in the embodiment of the present invention also has the same nitrogen concentration and oxygen concentration. Will have.

[0081] In addition, the raw material composition of the rare earth magnet used in the present invention is not limited to the composition of the above example! Needless to say, the low oxygen concentration at which there is a risk of heat generation and ignition due to an oxidation reaction in the atmosphere. The present invention is widely applicable to rare earth alloy powders.

[0082] In the above-described embodiment, V and deviation are also measured using a dry press method. However, the present invention is applied using a wet press method as disclosed in US Pat. No. 5,489,343. May be implemented. According to the present invention, since the effect of reducing the hydrogen concentration can be obtained regardless of the type of pressing method, the magnetic characteristics are improved. Moreover, when producing a molded body using a wet press, the step of impregnating the molded body with an oil after pressing may be omitted.

In the above embodiment, the pulverization step is performed in a nitrogen atmosphere, but argon or helium may be used instead of nitrogen or in place of nitrogen. When fine pulverization is not performed using nitrogen gas, the powder particle surface is not nitrided, but the effect of controlling the oxygen concentration and hydrogen concentration can be obtained.

Industrial applicability According to the present invention, the low-density, low-strength magnet powder molded body can be impregnated with the anti-oxidation agent without causing cracks and the like. It becomes possible to provide magnets with high yield.

Claims

The scope of the claims

[1] A pressing step (A) for producing a compact by compressing a rare earth alloy powder by a dry press method;

Surface force of the molded body Step (B) of impregnating the molded body with an anti-oxidation agent, Step (C) of sintering the molded body,

Including

In the step (B), the molded body is impregnated with the antioxidant in a decompressed container. The method for producing an R—Fe—B rare earth magnet.

[2] The step (B)

Storing the molded body in the container;

Depressurizing the interior of the container;

Supplying the antioxidant into the container;

The manufacturing method of Claim 1 containing this.

[3] The production method according to claim 1, wherein the rare earth alloy powder has an oxygen content of 50 ppm to 4000 ppm by weight and a nitrogen content of 150 ppm to 1500 ppm by weight.

[4] The step (C) includes

A first step of maintaining a temperature in a temperature range of 700 ° C or higher and lower than 1000 ° C for a period of 10 minutes to 420 minutes;

The manufacturing method according to claim 1, comprising: a second step in which sintering proceeds in a temperature range of 1000 ° C or higher and 1200 ° C or lower.

[5] The production method according to claim 1, wherein the rare earth alloy powder has an average particle size of 1.0 / z m or more and 5.0 m or less.

6. The production method according to claim 1, wherein the antioxidant is composed of a volatile component.

7. The method according to claim 6, wherein after the step (B), the temperature of the molded body is at least temporarily reduced by volatilization of the anti-oxidation agent.

8. The production method according to claim 1, wherein the antioxidant is isoparaffin. A container for storing a molded body of rare earth alloy powder;

Means for supplying an oxidization inhibitor used for impregnation of the molded body to the inside of the container; and a pressure reducing device for reducing the internal pressure of the container;

An impregnation apparatus comprising: