JPH09289127A - Manufacture of rare earth permanent magnet, and the rare earth permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the oxidation of material even in handling in the open air by finely crushing rare earth permanent magnet material in an inert gas atmosphere, and collecting and keeping it in an oleaginous solvent, and adjusting the mixed slurry into the preset concentration, and removing the oleaginous solvent from the molded item after molding of the slurry, and sintering the molded item. SOLUTION: Rough powder is crushed (1) in are inert gas atmosphere, and the fine powder is collected into an oleaginous solvent without exposing it to the open air. The mixture of the fine powder in a recovery container and the oleaginous solvent is agitated and mixed (3) so that air may not get in, and then it is adjusted to slurry concentration suitable for the supply to the mold of a molding machine (4), and the slurry is supplied to the mold of a molding machine, and while filtration the oleaginous solvent in slurry, orientation of magnetic field is applied to get a molded item (5), and then the solvent in the molded item is removed at a specific temperature in vacuum (6), and the molded item is sintered in vacuum atmosphere to draw out magnetic property (7). Hereby, the oxidation can be suppressed in the manufacture process.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rare earth permanent magnet,
Preferably, the present invention relates to a method for producing a rare earth permanent magnet and a rare earth permanent magnet, in which R—Fe—B system (R is one or more of rare earth elements including Y).

[0002]

2. Description of the Related Art Rare earth permanent magnets dissolve raw material metals,
It is manufactured by crushing, molding and sintering an ingot obtained by pouring the molten metal into a mold. By the way, rare earth powders become chemically very active after fine grinding. For this reason, there is a problem in that the magnetic characteristics are rapidly oxidized when exposed to the atmosphere after the pulverization, especially during the molding, and the magnetic characteristics are deteriorated. As a method for preventing this, for example, JP-A-58-157924 is disclosed. This creates a mixture of raw powder and organic solvent,
This is supplied to a mold cavity, pressure molding is performed while filtering the organic solvent in the mixture, and then the organic solvent remaining in the molded body is removed in a vacuum atmosphere, and sintering is performed.

[0003]

However, organic solvents generally have strong volatility at room temperature, and when a molded product is handled in the air, the surface of the molded product may be dried and exposed to the air. There is a problem that the rare earth magnetic material in the body is oxidized and the magnetic characteristics are deteriorated. Further, there is a problem that the organic solvent generally has a low flash point and is dangerous to handle, and that the vaporized vapor at room temperature affects the human body.

[0004]

[Means for Solving the Problems] In a method for producing a rare earth permanent magnet, a fine pulverizing step of finely pulverizing a rare earth permanent magnet raw material in an inert atmosphere, and the fine powder produced above in an inert atmosphere to an oil solvent. A collecting step of collecting and storing, a slurry concentration adjusting step of adjusting the slurry, which is a mixture of the fine powder and an oily solvent, to a preset concentration, a molding step of molding the slurry whose concentration is adjusted, and an oily material formed from the molded body. It is characterized by having a solvent removal step of removing the solvent and a sintering step of sintering the molded body from which the oily solvent has been removed. Further, in weight percentage, R (R is one or more of rare earth elements including Y) is 28.0 to 31.0%, and B is 0.5.
~ 2.0%, N 0.02 ~ 0.15%, O 0.25% or less, C 0.1
It is also characterized in that it is a rare earth permanent magnet manufactured by the above manufacturing method, having a composition of 5% or less and the balance of Fe.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A method for manufacturing a rare earth permanent magnet will be described with reference to the manufacturing process chart of FIG. The rare earth permanent magnet raw material is an alloy having the composition described below, which is crushed to have an average particle size of 20 to 500 μm and an oxygen content of 500 to 2
000 ppm of coarse powder is used. Here, the average particle size is 20
If it is less than μm, the amount of oxygen in the coarse powder increases, and the coercive force of the rare earth permanent magnet when it becomes a product is lowered, and if it is more than 500 μm, the pulverizability in the fine pulverization step described later is lowered. Also, it is better that the amount of oxygen is as small as possible, but oxidation in the course of coarse crushing is unavoidable, and it is technically difficult to be less than 500 ppm. If it exceeds 2000 ppm, the coercive force of the rare earth permanent magnet when it becomes a product is descend. In the fine pulverization step 1, the coarse powder is pulverized in an inert gas atmosphere to obtain fine powder having an average particle size of 2 to 6 μm, preferably 3 to 5 μm, and the oxygen concentration in the atmosphere is less than 30 ppm, desirably Adjust to a few ppm. For this, a jet mill pulverization method in which the coarse powder is introduced into a high-pressure inert gas jet and the particles are made to collide with each other to obtain fine powder is suitable. If the average particle size is less than 2 μm, the orientation of the fine powder deteriorates during the molding in a magnetic field in the molding step described later, and the residual magnetic flux density decreases. If it is larger than 6 μm, the sinterability in the sintering step described later is poor, the density of the sintered body is reduced, and the coercive force is also rapidly reduced.

The recovery step 2 is a step of recovering the fine powder obtained above in an oily solvent without exposing it to the atmosphere. Therefore, it is preferable to set the recovery container containing the oily solvent directly connected to the fine powder discharge port of the crusher used above.
Here, as the oily solvent, one or a mixture of two or more kinds of mineral oil, synthetic oil or vegetable oil having a distillation point of 400 ° C. or less, a kinematic viscosity at room temperature of 10 cst or less, and a vaporization starting temperature of about 150 ° C. is used. Slurrying step 3 is a step of thoroughly stirring and mixing a mixture of fine powder and an oily solvent (hereinafter referred to as slurry) in the recovery container. This may be performed during the recovery of fine powder, or may be performed after the recovery container is separated from the crusher, but it is desirable to prevent air from entering the recovery container.

In the slurry concentration adjusting step 4, the concentration is adjusted to be suitable for supplying the slurry to the molding die. After leaving the collection container subjected to the above treatment for a predetermined time,
The supernatant is removed, and the slurry is transferred to the concentration adjusting means again while stirring and mixing, and the slurry concentration is 50 to 85% by weight,
It is preferably 75 to 80% by weight. As the slurry concentration adjusting means, one having a frame structure in which the outer shell of the slurry passage is made of a stainless mesh filter,
A pressure filtration type such as a filter press or a centrifugal filtration type may be used. This treatment is preferably performed in conjunction with the supply of the slurry to the next pressure molding step, but the slurry after the treatment concentration adjustment may be temporarily stored. Also in this case, it is desirable to prevent air from entering the storage container. When the slurry concentration is less than 50% by weight, the solvent and the fine powder are severely separated, and the amount of the fine powder supplied during the slurry supply in the molding step to be described later varies greatly.
When it is more than 85% by weight, it is almost like a solid matter, the feedability is deteriorated, and the orientation of the fine powder during the molding in a magnetic field is poor and the residual magnetic flux density is lowered. In the molding step 5, the slurry whose treatment concentration has been adjusted is supplied to the mold of the molding machine, and the magnetic field orientation is applied while filtering the oily solvent in the slurry to obtain a molded body. It is desirable to supply a certain amount of slurry to the cavity in the mold, and it is preferable to use a screw pump or a plunger pump. The molded body is stored in a container filled with an inert gas such as Ar or N or a container containing an oily solvent.

In the desolvation step 6, the solvent contained in the molded body is removed. In a vacuum with a vacuum degree of 1 Torr or less, the molded body is heated to 100 to 250 ° C., preferably 150 to
It is carried out by keeping it at 200 ° C. for 30 minutes or more, but it can also be carried out in an inert gas or reducing gas atmosphere while exhausting under reduced pressure. Here, it is important to almost completely remove the solvent from the molded body and to exhaust the vaporized solvent or its decomposition product so as not to adhere to the molded body. Here, if the temperature of the molded body is less than 100 ° C., it takes a very long time that degreasing cannot be completed even in one day,
If the temperature is higher than 250 ° C., the rare earth element in the molded body reacts with C in the solvent to lower the coercive force. The sintering step 7 is for sintering the molded body after removing the solvent so as to obtain magnetic characteristics. Therefore, it is necessary to transfer the molded body after the desolvation treatment to this step without exposing it to the atmosphere. Sintering is vacuum 10 ^-1
1000 to 1150 in a vacuum atmosphere below Torr
It hold | maintains at (degree C.), preferably 1050-1100 degreeC for a predetermined time, and performs it. If the temperature is less than 1000 ° C, the residual magnetic flux density is low,
If the temperature is higher than 1150 ° C, the crystal grains grow abnormally and the coercive force decreases.

Next, the rare earth permanent magnet will be described. The present magnet is characterized by its composition as well as its manufacturing method, and the manufacturing method is as described above. The reasons for limiting the composition will be described below. The amount of rare earth element is 28.0 to 31.0% by weight. If the amount of rare earth element exceeds 31.0%, the amount of Rrich phase inside the sintered body increases, and the morphology becomes coarse, resulting in poor corrosion resistance. On the other hand, if the amount of the rare earth element is less than 28.0%, the amount of liquid phase required for densification of the sintered body is insufficient and the density of the sintered body decreases, and at the same time, the residual magnetic flux density Br of the magnetic properties is reduced.
And the coercive force iHc both decrease. Therefore, the amount of rare earth element is set to 28.0 to 31.0%. The amount of B is 0.1% by weight.
5 to 2.0%. When the amount of B exceeds 2.0%, the residual magnetic flux density decreases, and when it is less than 0.5%, the coercive force decreases, so the amount of B is preferably 0.5-2.0%. O
The amount is 0.05 to 0.25% by weight. The amount of O
When it exceeds 0.25%, a part of the rare earth element forms an oxide, and the magnetically effective rare earth element is reduced to decrease the coercive force i.
Hc decreases. On the other hand, since the maximum level of O in the ingot produced by melting is 0.04%, the O of the final sintered body is
It is difficult to keep the amount below this value, and the O amount is 0.05-
It is preferably 0.25%. The amount of C is 0.1% by weight.
It is set to 01 to 0.15%. When the amount of C is more than 0.15%, a part of the rare earth element forms a carbide, the magnetically effective rare earth element decreases, and the coercive force iHc decreases. C
The amount is more preferably 0.12% or less, still more preferably 0.10% or less. On the other hand, the level of C content of the ingot produced by melting is 0.008% at maximum, and it is difficult to keep the C content of the final sintered body at or below this value.
The C content of the sintered body is preferably 0.01 to 0.15%.

According to the research results of the present inventors, R-Fe
In order to improve the corrosion resistance of the -B rare earth permanent magnet, it is a necessary condition but not a sufficient condition to set the amount of rare earth element to 31.0% or less. This further requires strict control of the amount of N in the sintered body. In the R—Fe—B rare earth permanent magnet having the rare earth content, the O content, and the C content in the above composition range, excellent corrosion resistance and high magnetic properties can be obtained by setting the N content in the sintered body to a predetermined range. It can be compatible. The amount of N in the sintered body must be 0.02 to 0.15% by weight. Although the mechanism of the effect of improving the corrosion resistance due to the inclusion of N is not always clear, N in the sintered body is mainly present in the Rrich phase and forms a nitride by combining with a part of the rare earth element. Therefore, it is considered that the formation of this nitride suppresses the anodic oxidation of the Rrich phase. If the amount of N is less than 0.02%, the effect of improving the corrosion resistance of the sintered body cannot be seen, probably because the amount of nitride formed is small. When the amount of N is 0.02% or more, the corrosion resistance of the sintered body improves as the amount of N increases, but when the amount of N exceeds 0.15%, the coercive force iHc drops sharply. This is considered to be due to the reduction of magnetically effective rare earth elements due to the formation of nitrides. For the above reasons, the N content is 0.02 to 0.15
%. Further, the N content is preferably 0.03 to 0.13%.

In the R-Fe-B rare earth permanent magnet of the present invention, a part of Fe is Nb, Al, Co, G.
It can be replaced by one or more of a and Cu. The reason for limiting the substitution amount of each element (here, the weight percentage with respect to the total composition of the rare earth permanent magnet after substitution) will be described. The substitution amount of Nb is set to 0.1 to 2.0%. Nb
Addition of Nb produces Nb boride during the sintering process,
This suppresses abnormal grain growth of crystal grains. The amount of Nb substitution is
If it is less than 0.1%, the effect of suppressing abnormal grain growth of crystal grains becomes insufficient. On the other hand, when the substitution amount of Nb exceeds 2.0%, the amount of boride of Nb generated increases, and the residual magnetic flux density Br decreases. The substitution amount of Al is 0.02 to 2.0
%. The addition of Al has the effect of increasing the coercive force iHc. When the substitution amount of Al is less than 0.02%, the effect of improving the coercive force is small. When the substitution amount exceeds 2.0%, the residual magnetic flux density Br drops sharply.

The substitution amount of Co is set to 0.3 to 5.0%. C
The addition of o brings about an improvement in the Curie point, that is, an improvement in the temperature coefficient of saturation magnetization. When the substitution amount of Co is less than 0.3%, the effect of improving the temperature coefficient is small. When the substitution amount of Co exceeds 5.0%. , Residual magnetic flux density Br, coercive force iH
Both c decrease sharply. The replacement amount of Ga is 0.01 to 0.5
%. Although the addition of a small amount of Ga improves the coercive force iHc, when the substitution amount is less than 0.01%, the addition effect is small. On the other hand, when the Ga substitution amount exceeds 0.5%,
The residual magnetic flux density Br is significantly reduced and the coercive force is also reduced. The substitution amount of Cu is 0.01 to 1.0%.
Although the addition of a trace amount of Cu improves the coercive force iHc,
If the amount added exceeds 1.0%, the effect of addition becomes saturated. If the added amount is less than 0.01%, the effect of improving the coercive force iHc is small.

[0013]

EXAMPLES An example of the present invention for Nd-Fe-B rare earths will be described below. In the pulverizing step 1, the average particle size is 20
Fine powder was obtained by a jet mill pulverization method in which a coarse powder having a particle size of 0 μm and an oxygen content of 1300 ppm was used to collide particles in an inert high pressure gas atmosphere to obtain a fine powder. Inert gas is A
Oxygen concentration in crushed gas atmosphere is 1ppm using r gas
And the average particle size of the obtained fine powder is about 5 μm,
The composition is Nd 28.01%, Pr 0.57%, D by weight percentage.
y1.01%, B1.06%, Co2.06%, Nb0.67%, Al0.
The content was 10%, Ga 0.08%, Cu 1.06%, and the balance Fe. In the fine powder recovery step 2, as an oil solvent, Idemitsu Kosan Co., Ltd.
A mineral oil manufactured by LA35 was used. The mineral oil has a distillation point of about 272 ° C, a kinematic viscosity of 2.4 cst, and a flash point of 10.
7 ° C. Since the amount of the solvent was increased so that the fine powder after collection was sufficiently wet, the weight ratio of the fine powder and the solvent was 4: 6 (concentration 40% by weight). In the slurry forming step 3, the fine powder and the solvent in the recovery container were sufficiently mixed into a slurry by a stirrer equipped with a paddle type stirring blade.

In the slurry concentration adjusting step 4, the 40% by weight slurry is adjusted to 75-80% by weight. Fine powder precipitated during storage in the slurry in the collection container, and when the supernatant was removed, the slurry concentration was about 60% by weight. The slurry was uniformly stirred using a stirrer having a paddle type stirring blade and transferred to a concentration adjusting device using a pressure pump. In the concentration adjusting device, the pressure of the pressure pump is 1k
By pushing the 60 wt% slurry at gf / cm 2 into a stainless mesh filter (mesh opening 3 μm) and discharging only an appropriate amount of solvent out of the filter, the slurry concentration in the filter could be 75 to 80 wt%. . In the molding step 4, 75 to 80% by weight of the slurry is quantitatively supplied to the mold (width 15, depth 50, depth 50 mm) of the molding machine by controlling the rotational speed of the screw type positive displacement pump, and the horizontal direction is 1
While the orientation magnetic field of 2 kOe was applied, the solvent in the slurry was filtered through a cloth filter cloth and vertically pressed at a pressure of 1 ton / cm 2 to obtain a molded body. About 10% by weight of the solvent remained in the molded body. The molded body was stored in a container into which N gas was introduced for about 6 hours until the solvent removal sintering treatment.

In the desolvation step 6, the molded body was rapidly supplied to a degreasing furnace and heated in vacuum to remove the solvent contained in the molded body. Vacuum 10-2 ² Torr stand, moldings temperature 200 ° C., the solvent in a heating time of 1 hour it was confirmed that can be removed. In the sintering step 7, and transfers the molded body after leaving the solvent removed maintaining the vacuum state in a sintering furnace for continuous degreasing furnace, vacuum degree of 10 over ⁴ Torr stand, moldings temperature 1080 ° C., the sintering time 2 Sintering was performed for a time to obtain a sintered body. The oxygen content of the rare earth permanent magnet sintered body obtained under the above manufacturing conditions is 1580 p.
pm. The initial amount of oxygen in coarse powder was 1300 ppm, but only an increase of 280 ppm. Further, the residual magnetic flux density Br13.7 kG and the coercive force iHc15.3 kO
e, maximum energy product (BH) max45.2MGOe
That is, high magnetic characteristics were obtained. .

[0016]

As described above, the present invention has the following effects by using the oily solvent having a lower volatility than the organic solvent. Fine pulverization of rare earth permanent magnet materials is carried out in an inert atmosphere, they are collected in an oily solvent without being exposed to the air as they are, made into slurries, molded, and supplied to the sintering process in a wet state. Also in the case, the surface can be covered with the oil solvent to suppress the oxidation of the material. That is, it is possible to thoroughly suppress the oxidation of fine powder of rare earth which is extremely easy to oxidize during the manufacturing process until sintering, and to obtain a rare earth permanent magnet having good magnetic characteristics. Further, since mineral oil, synthetic oil, and vegetable oil have a smaller amount of dissolved oxygen than the organic solvent which is a conventional solvent, even if the fine oil is stored in a slurry after being finely pulverized, the fine powder is less likely to oxidize and the magnetic properties are not deteriorated. Further, since mineral oil has a higher flash point than organic solvents, it can be safely handled at room temperature. further,
Mineral oil is less volatile than organic solvents at room temperature,
No one inhales the steam, and there is no effect on the human body.

[Brief description of drawings]

FIG. 1 shows a manufacturing process diagram of the present invention.

[Explanation of symbols]

 1: Fine pulverization step 2: Collection step 3: Slurrying step 4: Slurry concentration adjusting step 5: Molding step 6: Desolvation step 7: Sintering step

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display area H01F 1/08 H01F 1/08 B

Claims (6)

[Claims] 1. A method for producing a rare earth permanent magnet, comprising a fine pulverizing step of finely pulverizing a raw material of a rare earth permanent magnet in an inert atmosphere, and a step of recovering and storing the fine powder produced above in an oily solvent in an inert atmosphere. Steps, a slurry concentration adjusting step of adjusting the slurry, which is a mixture of the fine powder and the oily solvent, to a preset concentration, a molding step of molding the slurry of which the concentration is adjusted, and an oily solvent is removed from the molded body formed. A method for producing a rare earth permanent magnet, comprising a desolvation step and a sintering step of sintering a molded body from which an oily solvent has been removed. 2. A method for manufacturing a rare earth permanent magnet, wherein the average particle size is 20 to 500 μm and the oxygen content is 500 to 500 μm.
2000 ppm of R-Fe-B system (R is one or more kinds of rare earth elements including Y) rare earth permanent magnet raw material coarse powder having an average particle diameter of 2 to 6 μm in an inert atmosphere with an oxygen concentration of 30 ppm or less. A fine pulverization step of pulverizing, and a fine fraction produced as described above in an inert atmosphere with a fractionation point of 40.
A collecting step of collecting and storing in an oily solvent having a kinematic viscosity at room temperature of 0 ° C. or less and 10 cst or less, a slurrying step of mixing the fine powder and the oily solvent, and a concentration of the slurry of 50 to 85% by weight percentage of the fine powder. A slurry concentration adjusting step for adjusting the concentration to a mold, a forming step in which the slurry whose concentration is adjusted is quantitatively supplied to a mold, is molded while applying a magnetic field, and the molded body is stored in a substantially non-contact state with the atmosphere; Is 1 Torr or less, and the molded body temperature is 100 to 25
Desolvation step at 0 ° C. to remove the oily solvent from the molded product, and a molded product temperature of 1000 at a vacuum degree of 10 ⁻¹ Torr or less.
A sintering step of sintering the formed body from which the oily solvent has been removed at a temperature of ˜1150 ° C., and a method for producing a rare earth permanent magnet. 3. The method for producing a rare earth permanent magnet according to claim 1, wherein the oily solvent is one kind or a mixture of two or more kinds of mineral oil, synthetic oil and vegetable oil. 4. A rare earth permanent magnet, wherein R (R is one or more of rare earth elements including Y) is 28.0 to 31.0%, B is 0.5 to 2.0%, and N is 0.1% by weight.
02-0.15%, O less than 0.25%, C less than 0.15%, balance F
A rare earth permanent magnet having a composition of e and manufactured by the manufacturing method according to any one of claims 1 to 3. 5. The rare earth permanent magnet according to claim 4, wherein F
Part of e is Nb 0.1-2.0%, Al 0.02-2.0%, Co
The rare earth permanent magnet according to claim 4, which is substituted with one or more of 0.3 to 5.0%, Ga 0.01 to 0.5%, and Cu 0.01 to 1.0%. 6. The rare earth permanent magnet according to claim 4, wherein the value of the coercive force iHc is 13.0 kOe or more.