JPH1012473A - Manufacture of rare-earth permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method wherein a molding is efficiently deoiled and sintered in the manufacturing process of an R-Fe-B system permanent magnet in which a wet molding method is employed. SOLUTION: R-Fe-B (wherein R denotes at least one of rare-earth elements including Y) system permanent magnet raw powder is pulverized into fine powder in the flow of N2 gas or Ar gas with oxygen concentration not higher than 0.01%. The fine powder after pulverization is directly collected into mineral oil or synthetic oil which belongs to the 4th type 2nd petroleum group whose flash point is more than 21 deg.C and less than 70 deg.C specified in the Fire Service Act to make slurry. The slurry material is subjected to the wet molding in a magnetic field and, after the mineral oil or synthetic oil in a molding is removed by vacuum heating, the molding is sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the production of high performance rare earth permanent magnet sintered bodies.

[0002]

2. Description of the Related Art Among the means for improving the performance of rare earth permanent magnets,
Since hypoxia has a large effect of contributing to the improvement of magnetic properties, the method has been studied for many years and many proposals have been made. Among these proposals, there is a wet molding method as a low-oxygenation technology that has recently attracted particular attention. In this method, a raw material fine powder for a rare earth permanent magnet is produced under a substantially oxygen-free atmosphere, and the fine powder is recovered into a certain kind of mineral oil or synthetic oil without being exposed to the atmosphere to obtain a raw material in the form of a slurry. 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 this is directly sintered without being exposed to the atmosphere to produce a sintered body. . The sintered body thus obtained has a much lower oxygen content than those of the sintered bodies manufactured by other conventional methods, so that high magnetic properties can be realized.

The content of a molded article formed by a wet molding method varies depending on molding conditions and the like, but is generally 2 to 20% by weight of a mineral oil, a synthetic oil, a vegetable oil or two or more kinds of these oils. Contains a blended oil made from blending. Therefore, it is necessary to remove these oils from the molded body before sintering the molded body. 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 deterioration in magnetic properties. The mineral oil and the synthetic oil used in the wet molding are, for example, a third petroleum as defined by the Fire Service Law having a flash point of 70 ° C. or more and less than 200 ° C. at 1 atm, and a fractionation point of 400 ° C. or less. Kinematic viscosity at room temperature is 1
0 cst or less is used (Japanese Patent Application No. Hei 7-21).
No. 4667). Therefore, in order to remove such mineral oil and synthetic oil from the compact, a method of heating at a temperature near the fractionation point is effective. However, since the molded body contains a large amount of rare earth elements that are easily oxidized, it is necessary to perform the molding in a substantial vacuum or in a non-oxidizing gas atmosphere. In addition, the surface of the molded body after the deoiling treatment is active with respect to oxygen because oil for preventing oxidation has been lost. Therefore, it is necessary to continue sintering without exposure to the atmosphere. However, in the case where the amount of the object to be heated composed of the molded body to be processed in mass production, its associated container, and the transport mechanism is large, and the total heat capacity thereof is large, the fourth
It takes a long time to remove mineral oil and synthetic oil belonging to the third petroleum class, and there is a problem in production efficiency.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior proposals and proposes a method for efficiently deoiling and sintering a rare earth permanent magnet formed by a wet forming method. What you want to do.

[0005]

According to the present invention, R- gas is supplied in an N2 gas or Ar gas stream having an oxygen concentration of 0.01% or less.
Fe-B (R is at least one of the rare earth elements including Y) -based permanent magnet coarse powder is finely pulverized, and the pulverized fine powder is exposed directly to the atmosphere at a flash point of 21 ° C. or more at 1 atm. It is recovered and slurried in mineral oil or synthetic oil belonging to Class 4 and 2 petroleums as specified by the Fire Service Law of less than 70 ° C, and the slurried raw material is wet-formed in a magnetic field to form After removing oil and synthetic oil by vacuum heating, the molded body is sintered to form a sintered body. Mineral oil belonging to Class 4 Class 2 Petroleum as defined by the Fire Services Act,
Specific examples of the synthetic oil include kerosene, light oil, xylene, and turpentine. These mineral oils and synthetic oils are smaller in molecular weight and higher in vapor pressure than those of mineral oils and synthetic oils belonging to Class 4 and 3 petroleums as defined by the Fire Service Law, so they can be removed at lower temperatures. . The disadvantage of removing mineral oils and synthetic oils by vacuum heating is that the heating efficiency is poor and the deoiling process requires a long time, but this problem becomes more pronounced in mass production with a large amount of treatment. By using mineral oil and synthetic oil belonging to the fourth class and the second petroleum, the oil can be removed at a lower temperature, that is, in a shorter time, and the production method is suitable for mass production. There is no particular limitation on the method of removing oil from a molded product containing mineral oil or synthetic oil belonging to the above-described fourth and second petroleums, but the temperature of vacuum heating is preferably 40 to 120 ° C. When the heating temperature is lower than 40 ° C., the removal efficiency decreases. Further, a heating temperature higher than 120 ° C. is not preferable because it requires a long time in the case of mass processing. The degree of vacuum is 5
It is desirably not more than × 10 -1 torr, more preferably not more than 5 × 10 -2 torr. In the vacuum heating, an inert gas such as argon is introduced into the deoiling chamber from the start of the heating until the temperature of the molded article reaches a certain stage in order to further reduce the deoiling time. It is also possible to increase the heat conductivity, and then perform vacuum heating under the above-mentioned degree of vacuum 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 not particularly limited. In particular, the sintering temperature is selected according to the composition of the 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 set to 5 × 10 −3 torr or less, more preferably 5 × 10 −4 torr or less. Ar
Sintering in an atmosphere is also employed in some cases. Another advantage of selecting mineral oils and synthetic oils belonging to Class 4 and 2 petroleums is that the molecular weight is smaller than that of mineral oils and synthetic oils belonging to Class 4 and 3 petroleum, so that residual carbon The point is that the level of quantity will be lower. 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 N2 gas or Ar gas, which is a grinding medium in the fine grinding, is 0.0
The content is 1% or less, preferably 0.005% or less, and more preferably 0.002% or less. Oxygen concentration is 0.01%
If the amount is larger, the oxidation of the fine powder during pulverization becomes severe, the amount of oxygen in the finally obtained sintered body increases, and a good coercive force cannot be obtained. The fine powder after the pulverization is directly collected into a mineral oil or a synthetic oil belonging to the second petroleum, which is provided at a fine powder discharge port of a fine pulverizer such as a jet mill, without being exposed to the atmosphere, and is slurried. Since the surface of the fine powder is coated with mineral oil or synthetic oil and is shielded from the atmosphere, oxidation is prevented even if the slurry-like raw material is used in the atmosphere. The slurry-like raw material thus produced is wet-molded in a magnetic field, and the obtained molded body is deoiled under the above-described removal conditions, and then sintered to reduce both the oxygen content and the carbon content. A rare earth permanent magnet sintered body having high magnetic properties can be manufactured. RF in the present invention
The composition of the eB-based permanent magnet is not limited to a specific one, but the content of the rare earth element must be It is necessary to be 28.0-31.5%, more preferably 28.5-30.5% by weight percentage. If the content of the rare earth element is less than 28.0%, the coercive force decreases. If it is more than 31.5%, the residual magnetic flux density Br decreases. The content of B is 0.9 to 0.9% by weight.
1.5%, more preferably 0.95 to 1.2%. If the B content is less than 0.9%, the coercive force decreases.
If it is more than 1.5%, the residual magnetic flux density Br decreases. Further, part of Fe is changed to Co, Al, Nb, G
It can be replaced by at least one or more of the elements a and Cu. The content of each element after substitution is 0.5 to 5.0% for Co, 0.02 to 0.3% for Al, and 0.2 for Nb in percentage by weight with respect to the entire composition of the permanent magnet sintered body. -2.0%, Ga is preferably 0.02-0.2%, and Cu is preferably 0.02-0.2%. The method for producing the R-Fe-B-based permanent magnet coarse powder to be subjected to jet mill pulverization in the present invention is not particularly limited. An ingot is produced by a casting method using the composition of the permanent magnet sintered body to be finally obtained as a melting composition, and this is ground to a predetermined particle size for use. If necessary, the ingot may be subjected to a heat treatment, a hydrogen storage treatment, or the like to improve the pulverizability. Alternatively, a strip-shaped alloy having a predetermined composition may be prepared by a so-called strip casting method of a quenching method, and the alloy may be pulverized to a predetermined particle size before use. Also in this case, a heat treatment or a hydrogen storage treatment is applied to the ribbon-shaped alloy as necessary. Further, two or more kinds of ingots and ribbon-shaped alloys having different compositions are prepared, and after coarsening them by the above-described method, the composition of the permanent magnet sintered body finally obtained is adjusted. Can be mixed to adjust the composition to obtain a coarse powder for pulverization.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the sintering furnace of the present invention have been described above. Hereinafter, the effect will be clarified by examples. The scope of the present invention is not limited by this embodiment.

Example 1 Nd22.5 in weight percentage
%, Pr6.3%, Dy1.0%, B1.0%, Co
2.2%, Al 0.08%, C 0.01%, O 0.12
%, N 0.007% N-Fe-B-based raw material coarse powder composed of the balance Fe is jet mill-pulverized in nitrogen gas having an oxygen concentration of 0.001%, and this is placed in a container installed at the fine powder outlet of the pulverizer. Was directly collected in light oil without contacting the atmosphere to obtain a slurry raw material. This raw material was wet-molded in a magnetic field to obtain a molded body of 50 mm × 50 mm × 10 mm (110 g / piece). The molded product contained 10% by weight of light oil. A total of 110 kg of the molded body, a container in which the molded body was installed, and a transport mechanism were combined to obtain a heated object having a total weight of 250 kg. The object to be heated was placed in the compact storage room 1 on one side of the sintering furnace shown in FIG. 1, evacuated, and then transferred to a deoiling chamber 2 which was also evacuated. The internal heater and the external heater were energized to heat the object to be heated and the interior wall of the deoiling chamber, respectively. When the heating was continued by the internal heater while the evacuation was continued, the temperature of the molded body reached 100 ° C. 3 hours after the start of energization. At this time, the temperature of the wall surface of the deoiling chamber is 1
20 ° C. The degree of vacuum in the deoiling chamber at this stage is 4 ×
It was 10-2 torr. Subsequent investigations did not show any contamination of the room by the evaporated oil. The heated object after the deoiling treatment was conveyed to the sintering chamber 4 via the adjusting chamber 3 which had been evacuated in advance. In the sintering chamber, the temperature was raised under the condition of evacuation, and after 2 hours, the temperature of the compact reached 1090 ° C. At this time, the degree of vacuum in the room was 5.times.10@-4 torr. After maintaining at this temperature for 3 hours, heating was stopped, and when the temperature of the molded body reached 900 ° C., it was transported to the cooling chamber 5 which had been evacuated in advance. In the cooling chamber, a helium gas was sprayed on the object to be heated to forcibly cool the object. After 3 hours, the object to be heated was taken out of the furnace. The sintered body is in a good form, and its analysis value is Nd 22.5% by weight percentage, Pr
6.3%, Dy 1.0%, B 1.0%, Co 2.2%,
Al 0.08% C 0.05%, O 0.15%, N 0.0
The remaining Fe was 55%. The sintered body density is 7.62g / cc
Met. This sintered body was heat-treated and its magnetic properties were measured to find Br13.9KG, iHc14.4KO.
e, a good value of (BH) m46.3MGOe was obtained. In the form of following the lot, the same amount of the same shaped body was processed in another deoiling chamber of this sintering furnace, and the subsequent steps were performed in the same procedure. Good results were also obtained for this processing lot.

Example 2 Nd 23.5 in weight percentage
%, Pr 4.3%, Dy 1.8%, B1.1%, Co
2.2%, Al 0.12%, Ga 0.1%, Cu 0.1
%, C 0.02% O 0.014%, N 0.008% Nd-Fe-B-based raw material coarse powder consisting of the balance Fe is jet mill-pulverized in an argon gas having an oxygen concentration of 0.0005%. The turpentine in the container installed at the fine powder discharge port was directly recovered without contacting the atmosphere to obtain a slurry raw material. This raw material was wet-molded under the same conditions as in Example 1 to obtain a 50 mm × 50 mm × 10 mm molded body in a total of 1
65 kg was prepared. 330 in total including container and transport mechanism
A heated object of Kg was formed, 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 deoiling chamber, after stopping the evacuation, 65 g of argon gas was discharged.
The mixture was introduced to 0 mmHg, and while being stirred, the internal heater and the external heater were energized to heat the object to be heated and the inner wall of the deoiling chamber, respectively. When the temperature of the molded body reached 45 ° C., vacuum evacuation was performed again to remove the previously introduced argon gas. At this time, the temperature of the wall surface of the deoiling chamber was 80 ° C. When the heating was continued by the internal heater while continuing the evacuation, the temperature of the compact reached 80 ° C. and the degree of vacuum in the room reached 3 × 10 −2 torr two hours after the start of energization. At this time, the temperature of the wall surface of the deoiling chamber was 120 ° C. Subsequent investigations did not show any contamination of the room by the evaporated oil. The object to be heated was transported again to the sintering chamber 10 via the procurement chamber 8, and sintered in the same procedure as in Example 1. Since the temperature of the molded body reached 1080 ° C. in 3 hours after the start of the temperature rise, it was held at this temperature for 4 hours and sintered. The degree of vacuum in the furnace at 1080 DEG C. was 4.times.10@-4 torr. After the power supply was stopped, it was confirmed that the temperature of the sintered body had reached 900 ° C.
And forcedly cooled in the same manner as in Example 1. After 4 hours, the object to be heated was taken out of the furnace. The sintered body was in a good sintered form, and its analysis values were Nd 23.5%, Pr4.
3%, Dy 1.8%, B 1.1%, Co 2.2%, Al
0.12%, Ga 0.1%, Cu 0.1%, C0.05
%, O 0.17%, N 0.006% balance Fe.
The density of this sintered body was 7.61 g / cc. The sintered body was heat-treated and its magnetic properties were measured.
6KG, iHc15.9KOe, (BH) m 44.8M
A good value of GOe was obtained. Following this lot,
Prepare a second lot consisting of the same amount of compacts with the same contents,
This was processed in the other deoiling chamber of the sintering furnace shown in FIG. 2, and the same procedure was performed in the subsequent steps. As a result, similar to the above, good results were obtained.

Example 3 Nd25.5 in weight percentage
%, Dy4.5%, B1.1%, Nb0.25%, Al
0.08%, Co 2.0%, Ga 0.08%, Cu0.
1%, 0.01% C, 0.14% O, 0.007% N Nd-Fe-B-based raw material coarse powder consisting of Fe in a nitrogen gas having an oxygen concentration of 0.0001% or less (detection limit or less) is jetted. This was pulverized in a mill, and this was directly collected in kerosene in a container provided at a fine powder discharge port of the pulverizer without directly contacting the atmosphere to obtain a slurry raw material. This raw material was molded under the same conditions as in Example 1, and a total of 50 kg of a molded body of 50 mm × 50 mm × 10 mm was prepared. A total of 170 kg of an object to be heated was constituted by combining the container and the transfer mechanism, installed in the compact storage room 13 of the sintering furnace shown in FIG. In the deoiling chamber, the deoiling treatment was performed in the same procedure as in Example 1, and the temperature of the molded body was 60 hours after the start of energization.
℃, the degree of vacuum in the room reached 3 × 10 -2 torr. At this time, the temperature of the wall surface of the deoiling chamber was 120 ° C. Subsequent investigations did not show any contamination of the room by the evaporated oil.
After the deoiling treatment, the object to be heated was transferred to the sintering chamber 15 and heated under vacuum evacuation. 1.5 hours after the start of the temperature rise, the temperature of the compact reached 1090 ° C., and the degree of vacuum in the furnace reached 5.0 × 10 −4 torr. When the temperature was maintained at this temperature for 2 hours, the evacuation was stopped, argon gas was introduced into the furnace until the pressure reached 500 mmHg, and then the sintering temperature was raised to 1100 ° C. After maintaining 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 shutdown, it was confirmed that the temperature of the sintered body had reached 900 ° C. or less.
And forcedly cooled in the same manner as in Example 1. After 2 hours, the object to be heated was taken out of the furnace. The sintered body was in a good sintered form, and the analysis values were Nd 25.5%, Dy 4.5%, B
1.1%, Nb 0.25%, Al 0.08%, Co2.
0%, Ga 0.08%, Cu 0.1%, C 0.04%,
O was 0.18%, N was 0.06%, and the balance was Fe. The density of this sintered body was 7.64 g / cc. The sintered body was heat-treated and its magnetic properties were measured.
G, iHc22KOe, (BH) m40.1MGOe, good values were obtained. Following this lot, a lot consisting of the same amount of a compact having the same contents was prepared and was sequentially processed in the sintering furnace shown in FIG. 3 under the same conditions as above. Results were obtained.

[0011]

As described above, according to the present invention,
It is possible to efficiently deoil and sinter a rare earth magnet molded body containing a large amount of oil in a large amount. As a result, rare earth permanent magnets having a small amount of oxygen and a small amount of carbon and having high magnetic properties can be industrially mass-produced, and its significance is truly significant.

[Brief description of the drawings]

FIG. 1 is an example of a plan view of a sintering furnace for carrying out the present invention.

FIG. 2 is another example of a plan view of a sintering furnace for carrying out the present invention.

FIG. 3 is another example of a plan view of a sintering furnace for carrying out the present invention.

[Explanation of symbols]

1 molded product storage room, 2 deoiling room, 3 adjustment room, 4
Sintering room, 5 cooling room, 6 heated object, 7 compact storage room, 8 adjustment room, 9 deoiling room 10 sintering room, 11 cooling room, 12 heated object, 13
Molded body storage room, 14 Deoiling room, 15 Sintering room, 16
Mechanical booster pump, 17 rotary pump, 18 cooling chamber, 19 object to be heated, 20 introduced gas pipe, 21 heater, 22 rotary pump,
23 Pressurized cooling device, 24 Insulated door, 25 Mechanical booster pump 26 Rotary pump

Claims (1)

[Claims] 1. An R-Fe-B (R is one or more of rare earth elements including Y) -based permanent magnet coarse powder in an N2 gas or Ar gas stream having an oxygen concentration of 0.01% or less. In mineral oil or synthetic oil belonging to Class 4 Class 2 petroleum as defined by the Fire Service Law with a flash point at 1 atm or more and less than 70 ° C without directly contacting the fine powder after grinding with the atmosphere. The slurry is formed into a slurry, and the slurried raw material is wet-formed in a magnetic field, and after removing mineral oil and synthetic oil in the formed body by vacuum heating, the formed body is sintered. Manufacturing method of magnet.