JP4716020B2 - Method for producing rare earth permanent magnet and method for mixing raw material powder and lubricant - Google Patents

Description

  The present invention relates to a method for producing a rare earth permanent magnet, and more particularly to a method for producing a rare earth permanent magnet capable of obtaining high magnetic properties, particularly a residual magnetic flux density (Br).

  R-T-B rare earth permanent magnets (R is one or more rare earth elements, T is Fe, or Fe and Co) have excellent magnetic properties, and Nd as the main component is Since it is abundant in resources and relatively inexpensive, it is used in electrical equipment such as various motors.

  An example of a method for producing a rare earth permanent magnet is a powder metallurgy method. Powder metallurgy is widely used because it can be manufactured at low cost. In the powder metallurgy method, a raw material alloy is coarsely and finely pulverized to obtain a finely pulverized powder of several μm. The finely pulverized powder thus obtained is magnetically oriented in a static magnetic field, and press molding is performed while the magnetic field is applied. At this time, the degree of magnetic orientation does not increase due to friction between the powders during molding or friction between the powder and the mold wall surface, and the magnetic characteristics cannot be sufficiently improved. Further, the mold surface and the surface of the molded body are likely to be damaged, which is not preferable in terms of quality and product yield. For this purpose, a lubricant is added and the lubricant is coated on the finely pulverized powder surface. In other words, the lubricant is added for the purpose of improving the degree of orientation by ensuring the fluidity of the alloy powder during molding in a magnetic field and facilitating release from the mold, etc. Usually, an organic material such as zinc stearate is used.

  The aforementioned lubricant is extremely cohesive. Therefore, it exists as agglomerated particles even after stirring for a long time. Since the lubricant evaporates by sintering, the place where the aggregated particles of the lubricant existed becomes huge pores after sintering. In addition, if the lubricant is present as aggregated particles, a larger amount of lubricant than the ideal amount must be added in order to obtain a predetermined degree of orientation improvement effect and mold release effect, and residual carbon after sintering This causes a problem that the coercive force of the rare earth permanent magnet is reduced.

  In order to solve such problems, the timing of adding the lubricant is devised in order to improve the dispersibility of the lubricant. For example, in Patent Document 1, a lubricant is added after coarse pulverization and before fine pulverization.

Japanese Patent No. 2915560

However, in Patent Document 1, when an amount capable of sufficiently exhibiting lubricity by a lubricant is added, there arises a problem that wear of piping of a pulverizer becomes severe.
Therefore, the inventors have disclosed a relatively small amount of solid-state lubrication in Patent Document 2 and Patent Document 3 as a technique for reducing the wear of the pulverizing equipment while enjoying the effect of improving the degree of orientation by adding a lubricant. It is disclosed that a lubricating effect can be obtained with a small amount of lubricant by adding an agent before pulverization and adding a liquid lubricant or a solvent for dissolving the lubricant after pulverization.

JP 2004-6761 A JP 2003-68551 A

In Patent Document 2 and Patent Document 3, by adding a liquid lubricant after fine pulverization or a solvent that dissolves the lubricant, the effect of improving the orientation by adding the lubricant is obtained, and the wear of the pulverizer is lost. Can be reduced. However, for example, in Patent Document 2, 0.3 wt% of fatty acid amide is added before fine pulverization, and 0.2 wt% of fatty acid ester is further added after fine pulverization. It has not yet been reduced. Considering the magnetic properties of the rare earth permanent magnet, the smaller the amount of lubricant added, the better.
The present invention has been made based on such a technical problem, and provides a method for producing a rare earth permanent magnet that can sufficiently exhibit the effect as a lubricant even when a smaller amount of lubricant is added. With the goal. Another object of the present invention is to provide a method for mixing finely pulverized powder and a lubricant that can sufficiently exert the effect as a lubricant even when a smaller amount of lubricant is added.

  In order to ensure the dispersibility of the lubricant in the state after fine pulverization, it is preferable to perform fine pulverization by adding a lubricant after coarse pulverization as disclosed in Patent Document 1. However, this fine pulverization alone still does not provide sufficient dispersibility of the lubricant in the fine pulverized powder. Therefore, the present inventors studied to further agitate and mix the finely pulverized powder and lubricant mixture after the fine pulverization in order to enhance the dispersibility of the lubricant in the finely pulverized powder. As a result, as will be described in detail later, when processed using a certain type of mixer, the temperature of the untreated product rises, specifically, a temperature of 30 ° C. or higher, and the finely pulverized powder thus obtained The residual magnetic flux density (Br) was improved in the rare earth permanent magnets manufactured using

The present invention made on the basis of the above examination results is the production of R-T-B (R: one or more rare earth elements, T: Fe, or Fe and Co, B: boron) -based rare earth permanent magnets. A coarse pulverization step of coarsely pulverizing a raw material alloy, a step of adding a lubricant to the coarsely pulverized powder obtained in the coarse pulverization step, and a fine pulverization step of finely pulverizing the coarsely pulverized powder to which the lubricant has been added. And a mixing step of stirring the mixture of the finely pulverized powder and the lubricant obtained in the pulverizing step in a temperature range of 30 ° C. or higher and lower than the melting point of the lubricant, and forming the finely pulverized powder after the mixing step in a magnetic field And a sintering step for sintering the molded body obtained in the molding step, and in the mixing step, the finely pulverized powder is heated by friction between the finely pulverized powders in a deposited state. And That is, in the present invention, as a method of heating the finely pulverized powder to which the lubricant is added to the above temperature range, a method of spontaneously generating heat by the stirring is adopted. Compared to the method of heating the finely pulverized powder by an external heating means, it is preferable from the viewpoint of energy consumption to use spontaneous heat generation. In addition, the suitable stirring method for heating to the temperature range required by this invention is mentioned later.
In the method for producing a rare earth permanent magnet of the present invention, in the mixing step, it is preferable to stir the mixture in a temperature range of 35 to 70 ° C. in order to obtain a high residual magnetic flux density (Br).

The method for producing a rare earth permanent magnet of the present invention makes it possible to obtain a high degree of orientation with a small amount of addition of a lubricant of 0.01 to 0.2 wt%, and thus has a high residual magnetic flux density (Br). A rare earth permanent magnet can be obtained. In addition, according to the present invention, there is an advantage that a high residual magnetic flux density (Br) can be obtained in a small amount as described above by using only a solid lubricant.
In the present invention, a part of the lubricant to be added can be added after pulverization before the mixing step. This is effective for preventing wear of the grinding equipment during fine grinding.

  The present invention specifies the temperature range when mixing the finely pulverized powder to which the lubricant has been added as described above. In order to heat the finely pulverized powder to this temperature range, It is preferable to use the friction of That is, the present invention relates to a raw material powder and a solid state used for the production of RTB (R: one or more of rare earth elements, T: Fe, or Fe and Co, B: boron) based rare earth permanent magnets. In which a mixture containing raw material powder and a lubricant is stored in a predetermined container in a deposited state, and is rotated by a rotating body in a partial region of the deposited mixture. While stirring the mixture by applying force, the mixture is heated by friction between finely pulverized powders.

In the present invention, the lubricant is preferably maintained in a solid state during the mixing process. This is because if the lubricant is melted, the finely pulverized powder may be aggregated during the solidification process.
In the present invention, the mixing is preferably performed in a low oxygen atmosphere having an oxygen content of 100 ppm or less. This is because the finely pulverized powder is easily oxidized due to heat generated by friction between the finely pulverized powders.

  As described above, according to the present invention, a rare earth permanent magnet having a high residual magnetic flux density (Br) can be produced by sufficiently exerting the effect as a lubricant even when a smaller amount of lubricant is added. be able to. In addition, according to the present invention, since the amount of lubricant added can be suppressed, wear of the pulverizer during fine pulverization can be prevented.

This embodiment is a method for producing a rare earth permanent magnet using a powder metallurgy method, adding a solid lubricant before pulverization, and stirring the lubricant and pulverized powder in a predetermined temperature range after pulverization, It is characterized by mixing. Hereafter, the manufacturing method by this invention is explained in full detail.
As shown in FIG. 1, the method of manufacturing a rare earth permanent magnet according to the present embodiment includes a raw material alloy production process, a coarse pulverization process, a lubricant addition process, a mixing process, a fine pulverization process, a heating agitation / mixing process, and a magnetic field molding. Process, sintering process and aging heat treatment process.
<Raw material alloy production process>
The raw material alloy can be produced by a strip casting method or other known melting methods in a vacuum or an inert gas, preferably an argon atmosphere. In the strip casting method, a molten metal obtained by melting a raw metal in a non-oxidizing atmosphere such as an argon gas atmosphere is jetted onto the surface of a rotating roll. The melt rapidly cooled by the roll is rapidly solidified in the form of a thin plate or flakes (scales). The raw material alloy can be obtained not only by the strip casting method but also by other melting methods such as high frequency induction melting. An alloy obtained by the reduction diffusion method can also be used as a raw material alloy.
When an R-T-B rare earth permanent magnet is obtained, an alloy mainly composed of R ₂ T ₁₄ B crystal grains (low R alloy) and an alloy containing more R than low R alloys (high R alloy) are used. A mixing method can also be applied to the present invention.

<Coarse grinding process>
In the coarse pulverization step, the raw material alloy is coarsely pulverized to a particle size of about several hundred μm to obtain a coarsely pulverized powder. The coarse pulverization is desirably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. Prior to coarse pulverization, it is effective to perform pulverization by allowing hydrogen to be stored in the raw material alloy and then releasing it. The hydrogen releasing treatment is performed for the purpose of reducing hydrogen as an impurity as a rare earth permanent magnet. Hydrogen storage is performed at room temperature to 200 ° C. for 30 minutes or longer, preferably 1 hour or longer, and dehydrogenation is performed at 350 to 650 ° C. in a vacuum or with an argon gas flow. Note that the hydrogen storage process and the dehydrogenation process are not essential processes. This hydrogen pulverization can be regarded as coarse pulverization, and mechanical coarse pulverization can be omitted.

<Lubricant addition process>
A lubricant is added to the coarsely pulverized powder obtained in the coarsely pulverized step. Although the kind of lubricant in this invention is not ask | required, it is preferable to use a fatty-acid type compound from viewpoints, such as availability. As the fatty acid compounds, fatty acids such as stearic acid, metal soaps of fatty acids such as zinc stearate and calcium stearate, fatty acid amides and the like are preferable, and among these, fatty acid amides are particularly preferable. Among fatty acid amides, it is particularly preferable to use one or more of caprylic acid amide, capric acid amide, lauric acid amide, stearic acid amide, oleic acid amide, and behenic acid amide. It is also possible to use camphor or paraffin as the lubricant.
The form of the lubricant to be added is not particularly limited, but a powdery lubricant is preferable for efficient and uniform dispersion. The particle size of the lubricant at the time of addition is not particularly limited, but preferably has a particle size equal to or smaller than that of the coarsely pulverized powder.

The addition amount of the lubricant is preferably as much as possible from the viewpoint of improving the grindability, but is preferably as small as possible from the viewpoint of the magnetic properties and the strength of the molded body. Therefore, the lubricant can be added in the range of 0.01 to 1 wt%. In particular, in the present invention, even with a small amount of lubricant, the effect of improving the degree of orientation can be maximized, so the amount of lubricant added can be 0.01-0.2 wt%. Furthermore, it can be 0.01-0.15 wt%.
<Mixing process>
The mixing step after the addition of the lubricant is not essential, but it is preferable to mix the coarsely pulverized powder and the lubricant after the addition of the lubricant. The effect of improving the dispersibility of the lubricant with respect to the coarsely pulverized powder during fine pulverization described later is expected. This mixing may be performed for about 5 to 30 minutes using a screw type mixing device (for example, Nauta mixer manufactured by Hosokawa Micron Corporation).

<Fine grinding process>
A finely pulverized powder (crushed powder) having an average particle size of 2.5 to 6 μm, preferably 3 to 5 μm is mainly used for finely pulverizing the coarsely pulverized powder to which a lubricant is added. ) The jet mill releases a high-pressure inert gas from a narrow nozzle to generate a high-speed gas flow, accelerates the coarsely pulverized powder with this high-speed gas flow, collides with the coarsely pulverized powder, and collides with the target or the container wall. It is a method of generating a collision and crushing. In this fine pulverization step, not only the coarsely pulverized powder but also the solid state lubricant is pulverized. Furthermore, in the obtained mixture of finely pulverized powder and lubricant, the dispersion state of the lubricant with respect to the finely pulverized powder is remarkably improved as compared with that before pulverization. However, the purpose of the present invention is to further increase the dispersion state of the lubricant with respect to the finely pulverized powder in order to obtain a high degree of orientation with a smaller amount of lubricant.

<Heating and mixing process>
In the present invention, a mixture of finely pulverized powder and a lubricant is stirred. This is for increasing the dispersion state of the lubricant with respect to the finely pulverized powder. In the present invention, this stirring is performed in a temperature range of 30 ° C. or higher. As shown in the Example mentioned later, a high residual magnetic flux density (Br) can be obtained by stirring in the temperature range of 30 degreeC or more. However, if the temperature of stirring is too high and the lubricant is melted, the lubricants or finely pulverized powders are agglomerated in the solidification process, which is not preferable. Therefore, the temperature in this step is less than the melting temperature of the lubricant. The more preferable temperature range of stirring is 35-70 degreeC, and a more preferable temperature range is 40-60 degreeC. The melting points of some lubricants are shown below.
Stearic acid: 72 ° C
Zinc stearate: 140 ° C
Caprylic acid amide: 110 ° C
Capric acid amide: 100 ° C
Lauric acid amide: 110 ° C
Stearamide: 108 ° C
Oleamide: 75 ° C
Behenamide: 111 ° C
Behenic acid: 81 ° C

  In order to perform stirring in the above temperature range, in the present invention, frictional heat between finely pulverized powders by stirring can be used. An outline of the configuration of the apparatus for heating by using friction in this way is shown in FIG. The stirring device 10 includes a container 1 that stores finely pulverized powder P, an agitating blade 2 that agitates the finely pulverized powder P, and a motor 3 that rotationally drives the agitating blade 2. A predetermined amount of finely pulverized powder P is stored in the container 1 in a deposited state, and a rotational force by the stirring blade 2 is applied to a partial region of the finely pulverized powder P in the deposited state. When the rotational force of the stirring blade 2 is applied to some areas of the finely pulverized powder P, some areas of the finely pulverized powder P and other areas are in a fluid state, and the finely pulverized powders P are in contact with each other. Friction occurs and the finely pulverized powder P spontaneously generates heat without being heated from the outside. This mixing by stirring can be referred to as a high-speed fluid mixing method. As long as the flow state of the powder is maintained, the higher the rotational speed of the stirring blade 2, the faster the heating by friction. The number of rotations of the stirring blade 2 varies depending on the amount of the finely pulverized powder P to be processed, but if it is about several hundred to several thousand rpm, the finely pulverized powder P can be heated to the temperature required by the present invention in several minutes. . According to the study by the present inventors, in a known mixing or pulverizing method, in a ball mill or screw type mixing apparatus, if the treatment is not performed for a considerable time, self-heating of the finely pulverized powder P causes 30 ° C. or higher. It was difficult to heat to this temperature.

Needless to say, in order to perform the stirring in the above temperature range, a heating means can be used in addition to utilizing self-heating due to friction between finely pulverized powders. For example, the mixture of finely pulverized powder and lubricant may be stirred in an atmosphere heated to the above temperature range.
Moreover, it is preferable to perform the mixing process by stirring of this invention in a low oxygen atmosphere. R and Fe constituting the finely pulverized powder are easily oxidizable elements, and oxidation is promoted by heating. Therefore, the mixing step by stirring with heating is preferably performed in an atmosphere having an oxygen content of 100 ppm or less, more preferably 50 ppm or less. In addition to this process, in order to obtain a rare earth permanent magnet with high magnetic properties, it is necessary to create a low oxygen atmosphere with an oxygen content of 100 ppm or less from other processes, that is, from the coarse pulverization process to the sintering process. preferable. By carrying out each step in such a low oxygen atmosphere, an RTB-based rare earth permanent magnet having an oxygen content of 2000 ppm or less can be obtained.

  The present invention is based on the premise that a lubricant is added before pulverization, but it is not essential to add the entire amount of lubricant to be added before pulverization. For example, 50% of the lubricant to be added may be added before pulverization, and the remaining 50% may be added during the heating and stirring / mixing step performed after pulverization. In this case, the type of lubricant added before pulverization and the type of lubricant added after pulverization can be changed. This includes adding a solid state lubricant before pulverization and adding a liquid lubricant after pulverization. As the liquid lubricant, fatty acid esters are preferable. Among them, ethyl caprylate, ethyl laurate, butyl laurate, methyl oleate, ethyl oleate, and butyl oleate are preferably used. It is of course possible to add a solid lubricant before pulverization and to add a solid lubricant after pulverization.

<Molding process in magnetic field>
The finely pulverized powder obtained as described above is filled in a mold cavity and subjected to molding in a magnetic field. What is necessary is just to let the shaping | molding pressure in shaping | molding in a magnetic field be the range of 0.3-3 ton / cm < ² >. The molding pressure may be constant from the start to the end of molding, may increase or decrease gradually, or may vary irregularly. The lower the molding pressure, the better the degree of orientation. However, if the molding pressure is too low, the strength of the molded body becomes insufficient and handling problems occur. Therefore, the molding pressure is selected from the above range in consideration of this point. The final relative density of the molded body obtained by molding in a magnetic field is usually 50 to 60%.
The applied magnetic field may be about 12 to 20 kOe. Further, the applied magnetic field is not limited to a static magnetic field, and may be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

  Since the lubricant is sufficiently dispersed in the finely pulverized powder in the heating and stirring / mixing step prior to molding in a magnetic field, the present invention is highly oriented in molding in a magnetic field even if the amount of lubricant added is small. You can get a degree. A high degree of orientation can be judged from the value of residual magnetic flux density (Br) as a rare earth permanent magnet. Further, since the lubricant is sufficiently dispersed in the finely pulverized powder, there is no risk that the molded body will adhere to the mold wall surface, and stable molding in a magnetic field can be performed.

<Sintering process>
The molded product obtained by molding in a magnetic field is subjected to lubricant removal treatment. This is to prevent a decrease in magnetic properties due to carbon residue. The lubricant removal treatment is preferably performed under a predetermined heat treatment condition in a vacuum or in a hydrogen atmosphere. It is efficient to carry out the lubricant removal process during the heating process of sintering.
After the lubricant removal treatment, the compact is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, a difference of an average particle diameter, and a particle size distribution, what is necessary is just to sinter at 1000-1200 degreeC in vacuum for about 1 to 10 hours.

<Aging heat treatment process>
After sintering, the obtained sintered body can be subjected to an aging treatment. This step is an important step for controlling the coercive force (HcJ), and it is preferable to perform an aging treatment in an inert gas atmosphere or in a vacuum. As this aging treatment, a two-stage aging treatment is preferable. In the first stage aging treatment step, the temperature is maintained within a range of 700 to 900 ° C. for 1 to 3 hours. Next, a first quenching step is provided for quenching to room temperature to 200 ° C. In the second stage aging treatment step, the temperature is maintained within a range of 500 to 700 ° C. for 1 to 3 hours. Next, a second quenching step for quenching to room temperature is provided. Since the coercive force (HcJ) is greatly increased by heat treatment near 600 ° C., when aging treatment is performed in one stage, it is preferable to perform aging treatment near 600 ° C.

<Magnet composition>
The present invention can be applied to, for example, a rare earth permanent magnet, particularly an R-T-B rare earth permanent magnet.
This RTB-based rare earth permanent magnet contains 25 to 37 wt% of rare earth element (R). Here, R in the present invention has a concept including Y, and therefore 1 of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It is selected from species or two or more species. If the amount of R is less than 25 wt%, the R ₂ T ₁₄ B phase, which is the main phase of the R—T—B system rare earth permanent magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. The magnetic force is significantly reduced. On the other hand, when R exceeds 37 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 37 wt%. A desirable amount of R is 28 to 35 wt%, and a more desirable amount of R is 28.5 to 33 wt%.

The RTB-based rare earth permanent magnet contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. On the other hand, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit of B is set to 4.5 wt%. A desirable amount of B is 0.5 to 1.5 wt%, and a more desirable amount of B is 0.8 to 1.2 wt%.
This R-T-B rare earth permanent magnet can contain Co of 3 wt% or less (not including 0), preferably 0.1 to 2 wt%, and more preferably 0.3 to 1.5 wt%. . Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.

Moreover, this R-T-B type rare earth permanent magnet can contain 1 type or 2 types of Al and Cu in the range of 0.02-0.5 wt%. By including one or two of Al and Cu in this range, it is possible to increase the coercive force, the corrosion resistance, and the temperature characteristics of the obtained permanent magnet. In the case of adding Al, the desirable amount of Al is 0.03 to 0.3 wt%, and the more desirable amount of Al is 0.05 to 0.25 wt%. Further, in the case of adding Cu, the desirable amount of Cu is 0.15 wt% or less (not including 0), and the more desirable amount of Cu is 0.03 to 0.12 wt%.
Furthermore, this RTB-based rare earth permanent magnet allows the inclusion of other elements. For example, elements such as Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. In particular, when producing an RTB-based rare earth permanent magnet having a low oxygen content, one or more of Zr, Ti, Nb, and Ta should be added to prevent crystal grain coarsening. Is preferred. On the other hand, it is desirable to reduce impurity elements such as oxygen, nitrogen, and carbon as much as possible. In particular, the amount of oxygen that impairs magnetic properties is preferably 2000 ppm or less, more preferably 1500 ppm or less. This is because when the amount of oxygen is large, the rare-earth oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated. Moreover, in this invention, since the addition amount of a lubrication agent can be reduced, carbon content can be controlled to 1500 ppm or less, Furthermore, 1000 ppm or less.

28.1 wt% Nd-0.06 wt% Cu-0.12 wt% Al-0.2 wt% Zr-1.1 wt% B-Fe. a low R alloy having a composition of bal, 35 wt% Nd-0.5 wt% Cu-0.1 wt% Al-10 wt% Co-Fe. A high R alloy having a bal composition was prepared.
Next, after blending the low R alloy and the high R alloy in a weight ratio of 90:10, hydrogen was occluded at room temperature. Thereafter, dehydrogenation treatment was performed in an Ar atmosphere at 600 ° C. for 1 hour. By the dehydrogenation treatment, the low R alloy and the high R alloy were roughly pulverized to about several hundred μm. In addition, each process was implemented in the atmosphere whose oxygen amount is 100 ppm or less from the process of this hydrogen crushing process to the sintering process mentioned later. Of course, the amount of oxygen in each process is also regulated to 100 ppm or less.

  0.1 wt% oleic acid amide was added as a lubricant to the coarsely pulverized powder obtained by the hydrogen pulverization treatment. The melting point of oleic amide is 75 ° C. The coarsely pulverized powder to which oleic acid amide was added was finely pulverized with a jet mill until the average particle size became 3.5 to 4 μm.

  The finely pulverized powder containing the lubricant obtained by the jet mill was mixed using a high-speed fluid type agitator 10 shown in FIG. In addition, the rotation speed of the rotary blade 2 was made into two types, 10000 rpm (Example A) and 4000 rpm (Example B). Further, a finely pulverized powder containing a lubricant obtained by a jet mill was stirred and mixed using the screw type mixer described above (Comparative Example A). Note that the processing was completed at various times.

After sufficient time had passed after the above treatment, the finely pulverized powder was molded in a magnetic field. In addition, shaping | molding in a magnetic field was performed on the conditions of shaping | molding pressure: 1.4ton / cm < ² >, and applied magnetic field: 17kOe.
The molded body obtained by molding in a magnetic field was sintered. Sintering was carried out under conditions of holding at 1090 ° C. for 4 hours in a vacuum. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 540 ° C. × 1 hour (both in an Ar atmosphere).

When the composition analysis of the obtained RTB-based rare earth permanent magnet was performed, it was as follows.
28.7 wt% Nd-0.1 wt% Cu-0.12 wt% Al-0.18 wt% Zr-1 wt% B-1 wt% Co-Fe. bal
Moreover, the oxygen content, nitrogen content, and carbon content of these R-T-B rare earth permanent magnets were as follows.
Oxygen content: 890-1020ppm
Nitrogen content: 320-380 ppm
Carbon content: 680-820 ppm

  The magnetic properties of the obtained RTB-based rare earth permanent magnet were measured. FIG. 3 (residual magnetic flux density (Br)) and FIG. 4 (coercive force (HcJ)) show the relationship between the processing time of mixing by stirring after pulverization and the magnetic characteristics. As shown in FIGS. 3 and 4, it was found that the residual magnetic flux density (Br) varies depending on the mixing time. However, the coercive force (HcJ) does not vary depending on the mixing time and the mixing method. This is because oxidation can be suppressed by performing each step after the hydrogen pulverization treatment in an atmosphere having an oxygen amount of 100 ppm or less.

  The present inventors measured the temperature of the finely pulverized powder every stirring processing time in order to confirm the reason why the magnetic characteristics fluctuate depending on the mixing processing time. The result is shown in FIG. As shown in FIG. 5, it can be seen that the temperature of the finely pulverized powder increases as the mixing treatment time increases. In particular, the temperature rise is remarkable when a high-speed fluid mixer of 10,000 rpm is used.

  Based on the above results, the relationship between the ultimate temperature during the mixing process and the magnetic properties of the rare earth permanent magnet is shown in FIGS. As shown in FIGS. 6 and 7, the coercive force (HcJ) does not vary with temperature, but the residual magnetic flux density (Br) varies with the ultimate temperature in the mixing process. In the case of oleic amide used in this example, it can be seen that the residual magnetic flux density (Br) is improved by 100 to 200 G when the temperature in the mixing process is in the range of 30 to 75 ° C.

A finely pulverized powder was obtained by a jet mill in the same manner as in Example 1 except that lauric acid amide (melting point: 110 ° C.) was used as the lubricant. Various addition amounts of lauric acid amide were changed.
The finely pulverized powder containing the lubricant obtained by the jet mill was mixed for 700 sec (attainment temperature: 60 ° C.) using the high-speed fluid type stirring device 10 shown in FIG. The rotational speed of the rotary blade 2 was 4000 rpm (Example C).

After sufficient time had passed after the above treatment, molding in an magnetic field and sintering were performed in the same manner as in Example 1 to obtain an RTB-based rare earth permanent magnet.
The magnetic properties of the obtained RTB-based rare earth permanent magnet were measured. In addition, the magnetic characteristics of the RTB-based rare earth permanent magnet (Comparative Example C) obtained in the same manner as in Example C were measured except that the mixing process using the high-speed flow type stirring device 10 was not performed. .

FIG. 8 (residual magnetic flux density (Br)) and FIG. 9 (coercive force (HcJ)) show the relationship between the amount of lubricant added and the magnetic properties. As shown in FIG. 8, it can be seen that the residual magnetic flux density (Br) obtained in Example C in which the mixing process using the stirring device 10 is performed is higher than that in Comparative Example C in which the process is not performed. 8 and 9, it can be seen that a high coercive force (HcJ) is obtained when the amount of lubricant added is small, and that a higher residual magnetic flux density (Br) is obtained when the amount of lubricant added is large. . This is understood to be caused by the residual amount of C caused by the lubricant.
In addition, when the composition of the obtained RTB system rare earth permanent magnet was confirmed, it was the same as that of Example 1.
The oxygen content, nitrogen content, and carbon content of the R-T-B rare earth permanent magnet were the same as in Example 1.

In the same manner as in Example 1, finely pulverized powder was obtained by a jet mill. The obtained finely pulverized powder was stirred and mixed using the screw mixer used in Comparative Example A of Example 1. However, the pulverized powder being treated was heated by circulating a heat medium (heated oil) around the outer periphery of the container of the screw mixer. Note that the processing was completed at various times.
After sufficient time had passed after the above treatment, molding in an magnetic field and sintering were performed in the same manner as in Example 1 to obtain an RTB-based rare earth permanent magnet. The magnetic properties of the obtained RTB-based rare earth permanent magnet were measured.

  FIG. 10 (residual magnetic flux density (Br)) and FIG. 11 (coercive force (HcJ)) show the relationship between the temperature at which the finely pulverized powder is heated during the stirring / mixing process and the magnetic properties. 10 and 11 also show the results of Example 1 described above. As shown in FIGS. 10 and 11, the effect of improving the residual magnetic flux density (Br) can be obtained even when the stirring / mixing process is performed exclusively while heating from the outside.

  Using oleic acid amide (melting point: 75 ° C.) as the first lubricant, finely pulverized powder was obtained by a jet mill in the same manner as in Example 1. To the finely pulverized powder containing the first lubricant obtained by the jet mill, stearic acid (melting point: 72 ° C.) is added as the second lubricant, and the high-speed fluid type stirring device 10 shown in FIG. A 700 sec mixing process (attainment temperature: 60 ° C.) was performed. At that time, the rotational speed of the rotary blade 2 was set to 4000 rpm. Although the addition amount of oleic amide was fixed at 0.1 wt%, the addition amount of stearic acid was variously changed as shown in Table 1.

After a sufficient amount of time had passed after the above treatment, R-T-B rare earth permanent magnets (Sample Nos. 1 to 3) were obtained by performing molding and sintering in a magnetic field in the same manner as in Example 1. .
The magnetic properties of the obtained RTB-based rare earth permanent magnet were measured. The magnetic properties of the R-T-B rare earth permanent magnet (sample No. 4) obtained in the same manner as described above except that the second lubricant was not added were also measured. Further, Sample No. was changed except that the amount of oleic amide added was changed to 0.125 wt%, 0.15 wt%, and 0.175 wt%. The magnetic properties of the RTB-based rare earth permanent magnets (sample Nos. 5 to 7) produced in the same manner as in Example 4 were also measured. These results are shown in Table 1. Sample No. 1 to 4, the relationship between the total addition amount of the lubricant (total addition amount of the first lubricant and the second lubricant) and the magnetic characteristics is shown in FIG. 12 (residual magnetic flux density (Br)) and FIG. Magnetic force (HcJ)).

  From FIG. 12 and FIG. 13, the same tendency as in Example 3 was confirmed. That is, even when the second lubricant is added after pulverization, a high coercive force (HcJ) can be obtained if the total amount of lubricant added is small, and conversely, the higher the total amount of lubricant added, the higher the residual magnetic flux. Density (Br) was obtained. However, since the residual magnetic flux density (Br) is equal between the case where the total amount of the lubricant is 0.15 wt% and the case where the total amount is 0.175 wt%, the residual magnetic flux density (Br) is improved by the addition of the lubricant. It can be said that there is an appropriate addition amount in order to enjoy the effect.

  Next, sample No. The abrasion state of the grinder after producing a predetermined number of 1 to 7 was examined. The results are also shown in Table 1. In investigating the wear state of the pulverizer, the bending portion where the wear was most likely to occur in the pulverizer piping was observed. In the column of “Wearing state of pulverizer” in Table 1, the criteria for “◯” and “x” are as follows.

○ (Wear of pulverizer is slight): When 500 kg of raw material is pulverized, the thickness of the bent portion in the pulverizer pipe is less than 3%.
X (Wear of pulverizer is remarkable): When 500 kg of raw material is pulverized, the wear of the thickness of the bent portion in the pulverizer pipe is reduced by 3% or more.

As shown in Table 1, sample No. 1 to which a lubricant was added in two portions before pulverization and after pulverization was divided. In the cases of 1 to 3, the wear of the pulverizer was slight. In contrast, Sample No. in which the lubricant was collectively added before pulverization. In the case of 4-7, sample no. 4 (lubricant addition amount: 0.1 wt%) and Sample No. No. 5 (lubricant addition amount: 0.125 wt%), although the wear of the pulverizer was slight, sample No. 5 in which the total addition amount of the lubricant was 0.15 wt% and 0.175 wt%, respectively. For 6 and 7, the wear of the pulverizer was significant.
In addition, Sample No. with the same total amount of lubricant added. 2 and sample no. Compared with 6, the former showed slight wear of the pulverizer, while the latter showed significant wear of the pulverizer. Similarly, sample no. 3 and sample no. Compared to 7, the former was slightly worn by the grinder, whereas the latter was significantly worn by the latter.
From the above results, it can be said that adding a part of the lubricant to be added in the mixing step after fine pulverization is effective in preventing wear of the pulverizer during fine pulverization. Further, it was found that when the amount of the lubricant added is 0.15 wt% or more, it is better to add a part of the lubricant after pulverization.
In addition, when the composition of the obtained RTB system rare earth permanent magnet was confirmed, it was the same as that of Example 1. The oxygen content, nitrogen content, and carbon content of the R-T-B rare earth permanent magnet were the same as in Example 1.

It is a flowchart which shows the manufacturing process of the RTB system rare earth permanent magnet by this invention. It is sectional drawing which shows the structure outline | summary of the stirring apparatus which can be applied to this invention. 6 is a graph showing the relationship between mixing processing time and magnetic characteristics (residual magnetic flux density (Br)) in Example 1. 3 is a graph showing the relationship between mixing processing time and magnetic characteristics (coercivity (HcJ)) in Example 1. 4 is a graph showing the relationship between the mixing processing time and the temperature of finely pulverized powder in Example 1. 6 is a graph showing the relationship between the ultimate temperature and magnetic characteristics (residual magnetic flux density (Br)) during mixing processing in Example 1. 6 is a graph showing the relationship between the ultimate temperature and magnetic characteristics (coercive force (HcJ)) during mixing processing in Example 1. It is a graph which shows the relationship between the lubricant addition amount in Example 2, and a magnetic characteristic (residual magnetic flux density (Br)). It is a graph which shows the relationship between the lubricant addition amount in Example 2, and a magnetic characteristic (coercive force (HcJ)). It is a graph which shows the relationship between the ultimate temperature at the time of the mixing process in Example 3, and a magnetic characteristic (residual magnetic flux density (Br)). It is a graph which shows the relationship between the ultimate temperature at the time of the mixing process in Example 3, and a magnetic characteristic (coercive force (HcJ)). It is a graph which shows the relationship between the total addition amount of the lubricant in Example 4, and a magnetic characteristic (residual magnetic flux density (Br)). It is a graph which shows the relationship between the total addition amount of the lubricant in Example 4, and a magnetic characteristic (coercive force (HcJ)).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Stirrer blade, 3 ... Motor, 10 ... Stirrer, P ... Finely pulverized powder

Claims (8)

R-T-B (R: one or more of rare earth elements, T: Fe, or Fe and Co, B: boron), a method for producing a rare earth permanent magnet,
A coarse pulverization step for coarsely pulverizing the raw material alloy;
Adding a lubricant to the coarsely pulverized powder obtained in the coarsely pulverized step;
A finely pulverizing step of finely pulverizing the coarsely pulverized powder to which the lubricant is added;
A mixing step of stirring the mixture of the finely pulverized powder obtained in the fine pulverization step and the lubricant in a temperature range of 30 ° C. or higher and lower than the melting point of the lubricant;
A molding step of molding the finely pulverized powder that has undergone the mixing step in a magnetic field;
A sintering step of sintering the molded body obtained in the molding step;
Equipped with a,
In the mixing step, the finely pulverized powder is heated by friction between the finely pulverized powders in a deposited state .   2. The method for producing a rare earth permanent magnet according to claim 1, wherein in the mixing step, the mixture is stirred in a temperature range of 35 to 70 ° C. 3. The method for producing a rare earth permanent magnet according to claim 1 or 2 , wherein the addition amount of the lubricant is 0.01 to 0.2 wt%. The lubricant, method for preparing a rare earth permanent magnet according to any one of claims 1 to 3, characterized in that a solid lubricant. In the mixing step, method for preparing a rare earth permanent magnet according to any one of claims 1-4, characterized by adding a predetermined amount of the lubricant. R-T-B (R: one or more of rare earth elements, T: Fe, or Fe and Co, B: boron) The raw material powder used for the production of the rare earth permanent magnet and the solid state lubricant are stirred. Mixing method,
Containing a mixture containing the raw material powder and the lubricant in a predetermined state in a predetermined container;
A raw material powder characterized by heating the mixture by friction between the raw material powders while stirring the mixture by applying a rotational force by a rotating body to a partial region of the mixture in a deposited state; Lubricant mixing method. The method according to claim 6 , wherein the lubricant maintains a solid state in the mixing process. The method of mixing raw material powder and lubricant according to claim 6 or 7 , wherein the mixing is performed in a low oxygen atmosphere having an oxygen content of 100 ppm or less.

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