JP2007318150A - Method for manufacturing rare earth permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of efficiently deoiling and sintering a rare earth permanent magnet compact formed by a wet forming method. <P>SOLUTION: In the process of forming the rare earth permanent magnet, an R-Fe-B (R is not less than a kind of rare earth element including Y) base permanent magnet coarse powder is pulverized in the gas flow of N<SB>2</SB>or Ar that contains oxygen of ≤0.01%. Fine powder obtained is collected in a mineral oil belonging to the fourth second petroleum having inflammation point of ≥21°C and <70°C as defined by the fire protection law, or in a synthetic oil to directly make a slurry in one atomic pressure without contacting to atmosphere. The slurried raw material was wet formed in magnetic field. The obtained compact was introduced into a deoling chamber and the chamber was evacuated. Evacuation was stopped and an inert gas was introduced into the deoiling chamber. The compact was heated while mixing the introduced inert gas. Further, the deoil chamber was evacuated and the compact was heated for deoiling. The deoiled formed body is sintered. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to the manufacture of a high-performance rare earth permanent magnet sintered body.

  Among the means to improve the performance of rare earth permanent magnets, low oxygen has a great effect on improving magnetic properties. Therefore, research on the method has been continued for many years, and many proposals have been made. Yes.

  Among these proposals, there is a wet molding method as a low oxygen reduction technology that has recently attracted particular attention. In this method, a raw material powder for a rare earth permanent magnet is produced under a substantially oxygen-free atmosphere, and this is recovered in a certain kind of mineral oil or synthetic oil without being exposed to the atmosphere to obtain a slurry-like raw material. The raw material is wet-molded in a magnetic field to form a molded body. Under certain conditions, oil is removed from the molded body and then directly sintered without exposure to the atmosphere to produce a sintered body. . The amount of oxygen contained in the sintered body thus obtained is much smaller than that of sintered bodies produced by other conventional methods, and thus high magnetic properties can be realized.

  Although the content of the molded body molded by the wet molding method varies depending on molding conditions, etc., it is generally from 2 to 20% by weight percentage of mineral oil, synthetic oil, vegetable oil, or a mixture of two or more of these. Contains blended oil made. Therefore, it is necessary to remove these oils from the molded body before the molded body is sintered. This is because, when directly sintered without removing the oil, carbon derived from the oil reacts with the rare earth element to form a carbide, thereby causing a decrease in magnetic properties.

  The mineral oil and synthetic oil used in the above-mentioned wet molding belong to, for example, the 3rd petroleum defined by the Fire Service Law with a flash point at 1 atm of 70 ° C or more and less than 200 ° C, and the fractional distillation point is 400 ° C or less. In which the kinematic viscosity at room temperature is 10 cSt or less is used (see Patent Document 1). Therefore, in order to remove such mineral oil and synthetic oil from the molded body, a method of heating at a temperature in the vicinity of the fractional distillation point is effective. However, since it is a molded body containing a large amount of rare earth elements that are easily oxidized, it is necessary to carry out in a substantial vacuum or in a non-oxidizing gas atmosphere. In addition, the molded body after the deoiling treatment is in a state in which oil for preventing oxidation is lost, so that the surface thereof is active against oxygen. Therefore, it is necessary to continue sintering without exposure to the atmosphere.

  However, if there is a large amount of the object to be heated consisting of a molded body to be processed in mass production, a container accompanying it, and a transport mechanism, and the total heat capacity thereof becomes large, mineral oil belonging to Class 4 and Class 3 petroleums The removal of synthetic oil took a long time, and there was a problem in production efficiency.

Japanese Patent Application No. 7-214667

  The present invention is intended to solve the above problems of the conventional proposal and to propose a method for efficiently deoiling and sintering a molded body for a rare earth permanent magnet molded by a wet molding method.

In the present invention, R-Fe-B (R is one or more of rare earth elements including Y) -based permanent magnets are finely pulverized in an N ₂ gas or Ar gas stream having an oxygen concentration of 0.01% or less. The obtained fine powder is recovered directly in mineral oil or synthetic oil belonging to Class 4 and Class 2 Petroleum as defined by the Fire Service Act with a flash point of 1 atm. The slurry is then wet-molded in a magnetic field, and the resulting molded product is carried into a deoiling chamber, evacuated, and then evacuated and the inert gas introduced into the deoiling chamber. Then, after heating the molded body while stirring the introduced inert gas, the deoiling chamber is further heated in a vacuum evacuated state, and the resulting deoiled molded body is fired. It is characterized by being sintered.

  Mineral oils and synthetic oils belonging to Class 4 and 2 Petroleum (as flash point is 21 ℃ or more and less than 70 ℃) as defined by the Fire Service Act include kerosene, light oil, xylene and turpentine oil. . These mineral oils and synthetic oils can be removed at lower temperatures because they have lower molecular weight and higher vapor pressure than mineral oils and synthetic oils belonging to Class 4 and 3 petroleums as stipulated in the Fire Service Law. . Removal of mineral oil and synthetic oil by vacuum heating is disadvantageous in that the heating efficiency is poor and it takes a long time for the deoiling treatment, but this problem becomes more noticeable in mass production with a large amount of treatment. Use of mineral oils and synthetic oils belonging to the 4th class 2nd petroleum makes it possible to remove at a lower temperature, that is, in a shorter time, and is suitable for mass production.

There is no particular limitation on the method for removing the oil from the molded product containing the mineral oil and the synthetic oil belonging to the above-mentioned fourth and second petroleums, but the temperature for vacuum heating is preferably 40 to 120 ° C. If the heating temperature is less than 40 ° C, the removal efficiency decreases. Also, heating temperatures higher than 120 ° C. are not preferable because a long time is required for mass processing. The degree of vacuum is preferably 5 × 10 ⁻¹ torr or less, more preferably 5 × 10 ⁻² torr or less.

  Further, in order to further shorten the deoiling treatment time in the vacuum heating, an inert gas such as argon is provided in the deoiling chamber from the start of heating after the vacuum exhaust is stopped until the product temperature reaches a certain stage. In addition, the introduced inert gas is heated with stirring to enhance heat transfer, and then it is necessary to heat the vacuum at the above degree of vacuum for a time to reach and maintain a predetermined temperature.

The molded body from which the oil has been removed is directly sintered without being exposed to the atmosphere. The sintering conditions in this case are also not particularly limited. Particularly, the sintering temperature is selected according to the composition of the rare earth permanent magnet, but the sintering temperature is generally in the range of 1000 to 1150 ° C. When vacuum sintering is employed, the degree of vacuum is 5 × 10 ⁻³ torr or less, more preferably 5 × 10 ⁻⁴ torr or less. Sintering in an Ar atmosphere is also used in some cases.

  Another advantage of the selection of mineral oils and synthetic oils belonging to Group 4 and 2 petroleums is that the residual carbon after sintering is low because the molecular weight is smaller than mineral oils and synthetic oils belonging to Group 4 and 3 petroleums. The level of quantity will be less. This is extremely advantageous for stabilizing the coercive force of the permanent magnet.

In the present invention, it is preferable to use a jet mill for fine pulverization. The oxygen concentration in the N ₂ gas or Ar gas, which is a pulverization medium in fine pulverization, is 0.01% or less, preferably 0.005% or less, more preferably 0.002% or less. When the oxygen concentration is higher than 0.01%, the fine powder during the pulverization becomes intensely oxidized, the amount of oxygen in the finally obtained sintered body increases, and a good coercive force cannot be obtained.

  The fine powder after pulverization is directly collected and slurried in mineral oil or synthetic oil belonging to the second petroleum installed in the fine powder discharge port of a fine pulverization apparatus such as a jet mill without being exposed to the atmosphere. Since the surface of the fine powder is covered with mineral oil or synthetic oil and shielded from the atmosphere, oxidation is prevented even if the slurry-like raw material is handled in the atmosphere. The slurry-like raw material thus prepared is wet-molded in a magnetic field, and the resulting molded body is deoiled under the above-described removal conditions, and then sintered, so that both the amount of oxygen and the amount of carbon are small. A rare earth permanent magnet sintered body having high magnetic properties can be produced.

  The composition of the R—Fe—B permanent magnet in the present invention is not limited to a specific one. However, in order to further manifest the effects of the present invention such as a low sintered body oxygen content and carbon content, a rare earth element is used. The elemental content should be 28.0-31.5% by weight percentage, more preferably 28.5-30.5%. When the rare earth element content is less than 28.0%, the coercive force decreases. On the other hand, if it exceeds 31.5%, the residual magnetic flux density Br decreases. The B content is 0.9 to 1.5%, more preferably 0.95 to 1.2% by weight. When the B content is less than 0.9%, the coercive force decreases. On the other hand, if it exceeds 1.5%, the residual magnetic flux density Br decreases. Furthermore, a part of Fe can be replaced by at least one of the elements of Co, Al, Nb, Ga, and Cu. The content of each element after the substitution is 0.5 to 5.0% by weight with respect to the total composition of the R-Fe-B permanent magnet sintered body, 0.5 to 5.0% for Co, 0.02 to 0.3% for Al, 0.2 to 2.0% for Nb, Ga is preferably 0.02 to 0.2%, and Cu is preferably 0.02 to 0.2%.

  The method for producing the coarse powder for R—Fe—B permanent magnets used for jet mill pulverization in the present invention is not particularly limited. The composition of the R-Fe-B permanent magnet sintered body to be finally obtained is used as a melting composition, an ingot is produced by a casting method, and this is pulverized to a predetermined particle size and used. If necessary, a method of increasing the pulverizability by subjecting the ingot to heat treatment, hydrogen storage treatment, or the like is also employed. Further, a ribbon-like alloy having a predetermined composition may be produced by a so-called strip casting method of a rapid cooling method, and this may be used after being pulverized to a predetermined particle size. Also in this case, the ribbon-shaped alloy is subjected to heat treatment or hydrogen storage treatment as necessary. Furthermore, two or more types of ingots and ribbon-like alloys with different compositions are prepared, and after these are coarsened by the above method, the composition of the R-Fe-B permanent magnet sintered body to be finally obtained Thus, these coarse powders can be mixed to adjust the composition to obtain coarse powder for pulverization.

  As described above, according to the present invention, it is possible to efficiently deoil and sinter a large amount of R-Fe-B rare earth permanent magnet compacts containing a large amount of oil. As a result, R-Fe-B rare earth permanent magnets with low oxygen content and carbon content and high magnetic properties can be industrially mass-produced, and its significance is truly great.

  The details of the manufacturing method of the present invention have been described above. The effect will be clarified by the following examples. The scope of the present invention is not limited by this embodiment.

(Reference Example 1)
Nd-Fe-B system consisting of Nd 22.5%, Pr 6.3%, Dy 1.0%, B 1.0%, Co 2.2%, Al 0.08%, C 0.01%, O 0.12%, N 0.007%, balance Fe The raw material coarse powder is jet mill pulverized in nitrogen gas with an oxygen concentration of 0.001%, and this is recovered directly without exposure to the air in light oil in a container installed at the fine powder discharge port of the pulverizer. did.

This raw material was wet-molded in a magnetic field to obtain a molded body of 50 mm × 50 mm × 10 mm (110 g / ke). This molded body contained 10% by weight of light oil. The molded body total 110 kg, the container in which the molded body is installed, and the transport mechanism are combined to obtain a heated object 6 having a total weight of 250 kg. This heated object 6 was placed in the compact storage chamber 1 on one side of the sintering furnace shown in FIG. 1, and after vacuum evacuation, it was transported to a deoiling chamber 2 that was also evacuated. The internal heater and the external heater were energized to heat the heated object 6 and the inner wall of the deoiling chamber 2, respectively. When heating was continued with the internal heater while continuing evacuation, the temperature of the compact reached 100 ° C. 3 hours after the start of energization. The temperature of the inner wall surface of the deoiling chamber 2 at this time was 120 ° C. The degree of vacuum in the deoiling chamber 2 at this stage was 4 × 10 ⁻² torr. Later investigations did not show any indoor contamination with evaporated oil. The article 6 to be heated after the deoiling treatment was transferred to the sintering chamber 4 via the adjustment chamber 3 that had been evacuated in advance. In the sintering chamber 4, the temperature was raised under vacuum exhaust conditions, and after 2 hours, the temperature of the compact reached 1090 ° C. The degree of vacuum in the room at this time was 5 × 10 ⁻⁴ torr. After holding at this temperature for 3 hours, heating was stopped, and when the temperature of the molded body reached 900 ° C., it was transferred to the cooling chamber 5 that had been evacuated in advance. In the cooling chamber 5, helium gas was blown onto the object 6 to be cooled forcibly. After 3 hours, the article 6 to be heated was taken out of the furnace.

  The sintered body is in good shape, and the analysis values are Nd 22.5%, Pr 6.3%, Dy 1.0%, B 1.0%, Co 2.2%, Al 0.08%, C 0.05%, O 0.15% in weight percentage. N 0.055%, balance Fe. The sintered compact density was 7.62 g / cc.

  When this sintered body was heat-treated and its magnetic properties were measured, good values of Br 13.9 kG, iHc 14.4 kOe, (BH) max 46.3 MGOe were obtained. In the form of following the lot, the same amount of the molded body was processed in the other oil removal chamber 2 of this sintering furnace, and the subsequent steps were also performed in the same procedure. Good results were also obtained for this processing lot.

Example 1
Nd 23.5%, Pr 4.3%, Dy 1.8%, B 1.1%, Co 2.2%, Al 0.12%, Ga 0.1%, Cu 0.1%, C 0.02%, O 0.014%, N 0.008%, balance Fe Nd-Fe-B raw material coarse powder consisting of Nd-Fe-B raw material is milled by jet mill in argon gas with an oxygen concentration of 0.0005%, and this is not exposed to the atmosphere in turpentine oil in a container installed at the fine powder outlet of the grinder The slurry was directly recovered and used as a slurry raw material. This raw material was wet-molded under the same conditions as in Reference Example 1 to prepare a total of 165 kg of 50 mm × 50 mm × 10 mm molded bodies. A total of 330 Kg of the object to be heated 12 was configured by combining the container and the transport mechanism, and was carried into one of the deoiling chambers 9 via the compact storage chamber 7 and the adjustment chamber 8 of the sintering furnace shown in FIG. In the oil removal chamber 9, after evacuation is stopped, argon gas is introduced up to 650 mmHg, and the internal heater and the external heater are energized while stirring the gas. The inner wall was heated. When the temperature of the molded body reached 45 ° C., evacuation was performed again to remove the previously introduced argon gas. The temperature of the inner wall surface of the deoiling chamber 9 at this time was 80 ° C. When heating was continued with the internal heater while continuing evacuation, the temperature of the compact reached 80 ° C. and the degree of vacuum in the room reached 3 × 10 ⁻² torr 2 hours after the start of energization. At this time, the temperature of the inner wall surface of the deoiling chamber 9 was 120 ° C. Later investigations did not show any indoor contamination with evaporated oil.

The article to be heated 12 was transferred again to the sintering chamber 10 via the procurement chamber 8 and sintered in the same procedure as in Reference Example 1. Since the temperature of the molded body reached 1080 ° C. 3 hours after the start of temperature increase, the temperature was maintained at this temperature for 4 hours and sintered. The degree of vacuum in the furnace at 1080 ° C. was 4 × 10 ⁻⁴ torr. After confirming that the temperature of the sintered body reached 900 ° C. after stopping the energization, the sintered body was transferred to the cooling chamber 11 and forcedly cooled in the same manner as in Reference Example 1. The article to be heated 12 was taken out of the furnace after 4 hours.

  The sintered body is a good sintered form, and the analysis values are Nd 23.5%, Pr 4.3%, Dy 1.8%, B 1.1%, Co 2.2%, Al 0.12%, Ga 0.1%, Cu 0.1%, C 0.05 %, O 0.17%, N 0.006%, and the balance Fe. The density of this sintered body was 7.61 g / cc. When the sintered body was heat-treated and its magnetic properties were measured, good values of Br 13.6 KG, iHc 15.9 KOe, (BH) max 44.8 MGOe were obtained. Following this lot, a second lot consisting of the same amount of compacts having the same contents is prepared and processed in the other deoiling chamber 9 of the sintering furnace of FIG. 2, and the subsequent steps are also the same. The procedure was performed. As a result, good results were obtained as described above.

(Reference Example 2)
Nd 25.5%, Dy 4.5%, B 1.1%, Nb 0.25%, Al 0.08%, Co 2.0%, Ga 0.08%, Cu 0.1%, C 0.01%, O 0.14%, N 0.007%, balance Fe The Nd-Fe-B raw material coarse powder is crushed by jet mill in nitrogen gas with an oxygen concentration of 0.0001% or less (below the detection limit), and this is put into kerosene in a container installed at the fine powder outlet of the pulverizer The slurry was directly recovered without direct contact with the atmosphere to obtain a slurry-like raw material. This raw material was molded under the same conditions as in Reference Example 1, and a total of 50 kg of 50 mm × 50 mm × 10 mm molded bodies were prepared. A total of 170 kg of the object to be heated 19 was constituted by combining the container and the transport mechanism, and was placed in the compact storage chamber 13 of the sintering furnace shown in FIG. In the deoiling chamber 14, the deoiling treatment was performed in the same procedure as in Reference Example 1. One hour after the start of energization, the temperature of the molded body reached 60 ° C., and the degree of vacuum in the chamber reached 3 × 10 ⁻² torr. At this time, the temperature of the inner wall surface of the deoiling chamber 14 was 120 ° C. Later investigations did not show any indoor contamination with evaporated oil. After deoiling treatment, the object to be heated 19 was transferred to the sintering chamber 15 and heated up under vacuum exhaust. After 1.5 hours from the start of temperature increase, the temperature of the compact reached 1090 ° C. and the vacuum in the furnace reached 5.0 × 10 ⁻⁴ torr. When this temperature was maintained for 2 hours, evacuation was stopped, and argon gas was introduced into the furnace until it reached 500 mmHg, and then the sintering temperature was raised to 1100 ° C. After holding at this temperature for 2 hours, the energization was stopped. During this time, automatic control was performed by the exhaust systems 16 and 17 so that the internal pressure of the argon gas in the furnace did not exceed 500 mmHg. After the normal stop, it was confirmed that the temperature of the sintered body reached 900 ° C. or less, and it was conveyed to the cooling chamber 18 and forcedly cooled in the same manner as in Reference Example 1. The object to be heated 19 was taken out of the furnace after 2 hours. The sintered body is a good sintered form, and the analysis values are Nd 25.5%, Dy 4.5%, B 1.1%, Nb 0.25%, Al 0.08%, Co 2.0%, Ga 0.08%, Cu 0.1%, C 0.04 %, O 0.18%, N 0.06%, and the balance Fe. The density of this sintered body was 7.64 g / cc. When the sintered body was heat-treated and its magnetic properties were measured, good values of Br 12.9 KG, iHc 22 KOe, (BH) max 40.1 MGOe were obtained. Following this lot, a lot consisting of the same amount of compacts of the same content was prepared and processed in the sintering furnace in FIG. 3 under the same conditions as above. Results were obtained.

It is a top view which shows the sintering furnace for enforcing the reference example 1. FIG. 1 is a plan view showing a sintering furnace for carrying out Example 1. FIG. It is a top view which shows the sintering furnace for enforcing the reference example 2. FIG.

Explanation of symbols

1 molded body storage room, 2 deoiling room, 3 adjustment room, 4 sintering room,
5 Cooling room, 6 Object to be heated, 7 Molded body storage room, 8 Adjustment room, 9 Deoiling room, 10 Sintering room, 11 Cooling room, 12 Object to be heated, 13 Molded object storage room,
14 deoiling chamber, 15 sintering chamber, 16 mechanical booster pump,
17 Rotary pump, 18 Cooling chamber, 19 Object to be heated,
20 introduction gas piping, 21 heater, 22 rotary pump,
23 Pressure Cooling Device, 24 Thermal Insulation Door, 25 Mechanical Booster Pump 26 Rotary Pump

Claims (2)

Obtained by finely pulverizing R-Fe-B (R is one or more of rare earth elements including Y) -based permanent magnets in an N ₂ or Ar gas stream with an oxygen concentration of 0.01% or less. Without being exposed to the atmosphere, the fine powder is recovered directly in mineral oil or synthetic oil belonging to the 4th class 2nd class petroleum oil as defined by the Fire Service Act with a flash point of 21 ° C or higher and less than 70 ° C at 1 atm. The slurryed raw material is wet-molded in a magnetic field, and the resulting molded product is carried into a deoiling chamber and evacuated. Then, evacuation is stopped and an inert gas is introduced into the deoiling chamber. The molded body is heated while stirring the inert gas, and then the deoiling treatment is performed by heating the molded body in a state where the deoiling chamber is evacuated, and the resulting molded body after deoiling treatment is baked. A method for producing a rare earth permanent magnet. 2. The method for producing a rare earth permanent magnet according to claim 1, wherein the introduced inert gas is an argon gas.

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