JP2018078183A - Rare earth magnet manufacturing method - Google Patents

Abstract

A method for manufacturing a rare earth magnet capable of suppressing non-uniformity in weight between compacts is provided. A method for producing a sintered magnet includes a step of supplying rare earth alloy powder P into a cavity V of a die 10 placed on a weight measuring instrument 50, and information on weight obtained from the weight measuring instrument 50. A step of controlling the weight of the rare earth alloy powder P in the cavity 50 so as to fall within a predetermined range based on and, after controlling the weight, compressing the rare earth alloy powder P in the cavity V with a punch to obtain a compact. and a step of sintering the compact. [Selection drawing] Fig. 1

Description

  The present invention relates to a method for producing a rare earth magnet.

  Rare earth magnets are components such as motors or actuators, such as hard disk drives, hybrid cars, electric cars, magnetic resonance imaging devices (MRI), smartphones, digital cameras, thin TVs, scanners, air conditioners, heat pumps, refrigerators, and vacuum cleaners. It is used in various fields such as washing and drying machines, elevators and wind power generators. Depending on these various applications, the dimensions and shape required for rare earth magnets vary. Therefore, in order to efficiently manufacture a wide variety of rare earth magnets, a molding method that can easily change the size and shape of the rare earth magnet is desired.

  In the production of a conventional rare earth magnet, a magnetic field is applied to the metal powder while pressing a metal powder (for example, an alloy powder) containing a rare earth element with a high pressure (for example, 50 MPa or more and 200 MPa or less). As a result, a compact is formed from the metal powder oriented along the magnetic field. Hereinafter, such a forming method is referred to as a “high-pressure magnetic field pressing method”. According to the high-pressure magnetic field pressing method, it is possible to obtain a molded body having a high residual magnetic flux density Br and excellent shape retention, since the metal powder is easily oriented. A sintered product is obtained by sintering the compact, and the sintered product is processed into a desired shape to complete a magnet product.

  However, in the high-pressure magnetic field pressing method, since it is necessary to apply a high pressure to the metal powder in a magnetic field, a large-scale and complicated molding apparatus is required, and the size and shape of a molding die are limited. Due to this limitation, the shape of a general molded body obtained by a high-pressure magnetic field pressing method is limited to a coarse block. Therefore, when manufacturing various types of magnet products by the conventional method, after obtaining the sintered body by sintering the block-shaped molded body, the sintered body is prepared according to the size and shape required for the magnet product. Need to be processed. In the processing of the sintered body, since the sintered body is cut or polished, scraps containing expensive rare earth elements are generated. As a result, the material yield of the magnet product is reduced. In the high-pressure magnetic field pressing method, the mold or the molded body is easily damaged due to galling between the molds or between the mold and the molded body. For example, cracks may occur in a molded body obtained by a high-pressure magnetic field pressing method.

  For the above reasons, the manufacturing method using the conventional high-pressure magnetic field pressing method is not suitable for manufacturing a variety of products or a small amount of magnet products. As a forming method that replaces the high-pressure magnetic field pressing method, Patent Document 1 below discloses a method of forming alloy powder at a low pressure (0.98 MPa to 2.0 MPa). In this rare earth magnet manufacturing method, alloy powder is filled in a mold, and the alloy powder is pressurized at a low pressure to produce a molded body (filling process), and a magnetic field is applied to the molded body in the mold. The step of orienting the alloy powder in the compact (orientation step) and the step of sintering the compact taken out from the mold (sintering step) are provided. And in the manufacturing method of the following patent document 1, a filling process and an orientation process are performed in another place.

WO2016 / 047593

  However, in the above method, there is a case where non-uniform shapes occur between the sintered bodies even when the same mold is used for sintering. If the shape becomes non-uniform between the sintered bodies, the portion to be removed by processing after sintering increases and the material yield decreases. This tendency is particularly remarkable in the case of low pressure molding.

  This invention is made | formed in view of the said subject, and it aims at providing the manufacturing method of the rare earth magnet which can suppress the nonuniformity of the shape between sintered compacts.

  The method for producing a sintered magnet according to the present invention includes a step of supplying a rare earth alloy powder into a cavity of a die placed on a weight measuring device, and the cavity based on information on the weight obtained from the weight measuring device. A step of controlling the weight of the rare earth alloy powder in a predetermined range, a step of pressing the rare earth alloy powder in the cavity with a punch after the weight control, and sintering the molded body And a step of performing.

  Conventionally, the weight of the rare earth alloy powder was measured in a container separate from the die, and then the rare earth alloy powder in the container was transferred into the cavity. However, since the rare earth alloy powder has strong adhesion, a part of the rare earth alloy powder often remains adhered to the container even after the transfer, and the weight is uneven among the compacts. According to the present invention, the rare earth alloy powder is supplied into the cavity V of the die placed on the weight measuring device, and the weight of the rare earth alloy powder in the cavity is determined based on the information on the weight obtained from the weight measuring device. Control within the range. Further, the powder is formed by punching without being transferred after the weight measurement. Therefore, the rare earth alloy powder of the compact can be controlled uniformly with high accuracy. And if the uniformity of the weight of a molded object becomes high, the uniformity of the shape between sintered bodies will also become high, the sintered compact close | similar to the shape of a final product will be obtained, and a material yield can be raised.

  Here, by controlling the amount of the rare earth alloy powder supplied into the cavity, the weight of the rare earth alloy powder in the cavity can be controlled within the predetermined range.

  This is preferable because the weight of the rare earth alloy powder can be easily controlled within a predetermined range.

  The die may be made of resin. According to this, since the weight of the die is reduced, the accuracy of powder weight measurement is improved.

  The rare earth alloy powder may be an Nd—Fe—B alloy powder. This powder is highly effective because it has adhesiveness and tends to be non-uniform in weight between molded bodies.

  The pressure of the press can be 0.049 to 20 MPa. When the molding pressure is so low, die consumption can be reduced, which contributes to a reduction in manufacturing cost.

  Further, the rare earth alloy powder can be supplied into the cavity by a circle feeder or a table feeder.

  Unlike feeders such as screw feeders, these feeders have little compressive action on the rare earth alloy powder during supply, so there are variations in density distribution inside the rare earth magnet-filled powder in the die, and variations in density distribution inside the compact. Can be reduced. Further, when the Nd-Fe-B alloy powder is used, the effect is high because the bulk is bulky and the density in the filled powder and the compact tends to vary.

  In addition, the method may further include a step of taking out the molded body from the cavity of the die, and the molded body taken out from the cavity can be sintered.

  Moreover, the heating process which heats the said molded object taken out from the said cavity to 200-450 degreeC before the said sintering can also be further provided.

  Further, it may further comprise an orientation step of orienting the rare earth alloy powder contained in the compact by applying a magnetic field to the compact held in the cavity of the punch.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the rare earth magnet which can suppress the nonuniformity of the weight between sintered compacts can be provided.

FIG. 1 is a schematic diagram showing a process of controlling the weight of the rare earth alloy powder in the die. 2A is a schematic cross-sectional view showing a circle feeder 40A which is an example of the feeder of FIG. 1, and FIG. 2B is an outline of a table feeder 40B which is another example of the feeder of FIG. It is sectional drawing. FIGS. 3A to 3C are schematic cross-sectional views showing a process of compressing the rare earth alloy powder in the die with a punch and then removing the molded body 5 from the cavity. 4 (a) to 4 (c) are schematic cross-sectional views showing a process of compressing the rare earth alloy powder in the die with a punch and then removing the molded body 5 from the cavity.

  A preferred embodiment of a method for producing a rare earth magnet will be described with reference to the drawings.

(Preparation process of rare earth alloy powder)
First, a rare earth alloy powder is prepared. A rare earth alloy is an alloy containing a rare earth element.

  Examples of rare earth elements include one or more elements selected from the group consisting of scandium (Sc), yttrium (Y) and lanthanoids belonging to Group 3 of the long-period periodic table. Here, the lanthanoid is lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy). , Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

Specific examples of the rare earth alloy are Sm—Co alloy, Nd—Fe—B alloy, and Sm—Fe—N alloy. Among these, an Sm—Co alloy represented by SmCo ₅ and Sm ₂ Co ₁₇ or an Nd—Fe—B alloy represented by Nd ₂ Fe ₁₄ B is preferable.

  When the rare earth alloy is an Nd—Fe—B alloy, the content of the rare earth element in the alloy is preferably 8 to 40% by mass, more preferably 15 to 35% by mass. Moreover, the content ratio of Fe in the Nd—Fe—B alloy is preferably 42 to 90% by mass, and more preferably 60 to 80% by mass. The content ratio of B in the Nd—Fe—B alloy is preferably 0.5 to 5% by mass. Further, a part of Fe may be substituted with cobalt (Co). A part of B may be substituted with one or more elements selected from the group consisting of carbon (C), phosphorus (P), sulfur (S), and copper (Cu).

  Rare earth alloys are made of aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), bismuth (Bi) from the viewpoint of improving coercive force, improving productivity and reducing costs. Niobium (Nb), Tantalum (Ta), Molybdenum (Mo), Tungsten (W), Antimony (Sb), Germanium (Ge), Tin (Sn), Zirconium (Zr), Nickel (Ni), Silicon (Si) , Gallium (Ga), copper (Cu) and / or hafnium (Hf) may be included.

  The rare earth alloy may contain oxygen (O), nitrogen (N), carbon (C), and / or calcium (Ca) as inevitable impurities.

  The rare earth alloy powder can be prepared by the following procedure. First, an alloy containing a rare earth metal constituent element in a desired ratio is cast by a slip casting method or the like to obtain rare earth alloy flakes. Next, the obtained flakes are coarsely pulverized using a pulverizer such as a stamp mill to obtain coarse powder having a particle size of about 10 to 100 μm. At this time, hydrogen may be occluded in the flakes before coarse pulverization, and hydrogen may be released from the coarse powder by heat treatment after coarse pulverization. Subsequently, a lubricant is added as necessary, and further pulverized to a particle size of about 0.5 to 10 μm using a jet mill or the like to obtain a rare earth alloy powder.

  Examples of lubricants include hydrocarbons such as paraffin wax; fatty acids such as stearic acid and stearyl alcohol; oleic acid amide, stearic acid amide, palmitic acid amide, pentadecylic acid amide, myristic acid amide, lauric acid amide, capric acid amide, Aliphatic amides such as pelargonic acid amide, caprylic acid amide, enanthic acid amide, caproic acid amide, valeric acid amide and butyric acid amide; organic substances such as metal soap such as metal stearate (zinc stearate, calcium stearate) . The lubricant can be a powder or a liquid. The density | concentration of the organic substance used as the lubrication agent in rare earth alloy powder can be 0.01-1.0 mass%.

(Die preparation)
Then, as shown to (a) of FIG. 1, the die | dye 10 which has the cylindrical part 10a and the flat bottom plate part 10b is prepared. A cylindrical portion 10 a is placed on the upper surface of the bottom plate portion 10 b, and a cavity V is formed in the die 10. The cavity V is opened upward.

  The material of the die 10 is not particularly limited, but is preferably made of resin from the viewpoint of reducing the weight of the die and increasing the accuracy of the weight measurement of the rare earth alloy powder. Examples of resins are acrylic resin, polyethylene, polyethylene terephthalate, polypropylene, polystyrene, ABS resin (acrylonitrile, butadiene and styrene copolymer), ethyl cellulose, paraffin wax, styrene / butadiene copolymer, ethylene / vinyl acetate copolymer It may be one or more selected from the group consisting of a coalescence, ethylene / ethyl acrylate copolymer, atactic polypropylene, methacrylic acid copolymer, polyamide, polybutene, polyvinyl alcohol, silicone resin, phenol resin and polyester resin. The die 10 may be made of a lightweight metal such as aluminum, aluminum alloy, magnesium, magnesium alloy, or a lightweight alloy, a carbonaceous material, or ceramics. Moreover, the die | dye 10 may be comprised from at least 1 type chosen from the group which consists of iron, silicon steel, stainless steel, a permalloy, molybdenum, tungsten, for example.

(Die placement on weight measuring device)
Subsequently, the die 10 is placed on the weight measuring device 50. The weight measuring device 50 outputs information regarding the weight of the placed object. There is no particular limitation on the weight measuring device 50. For example, a weight measuring device that measures weight with a load cell is preferably used. The weight measuring device 50 can output information on weight periodically at a predetermined time interval, and can output information on weight in response to a request from the outside such as a computer.

(Rare earth alloy powder filling)
Subsequently, the rare earth alloy powder P is supplied into the cavity V of the die 10 by the feeder 40.

  Although there is no limitation in particular in the feeder 40, the circle feeder 40A shown to (a) of FIG. 2 and the table feeder 40B shown to (b) of FIG. 2 are preferable.

  The circle feeder 40 </ b> A has a cylindrical portion 41 extending in the vertical direction, a disk-shaped table 42 facing the opening at the lower end of the cylindrical portion 41, and a rod shape provided on the table 42 and extending in the radial direction of the table 42. , And a motor 48 that rotates the rotating member 44 around the rotating shaft 46.

  A gap G is provided between the lower end of the cylindrical portion 41 and the upper surface of the table 42, and the rare earth alloy powder P supplied into the cylindrical portion 41 exits from the lower end of the cylindrical portion 41, and the table. The gap G is filled while forming a slope with a predetermined angle of repose on the outer side of the cylindrical portion 41 on 42. Then, when the rotating member 44 is rotated on the table 42 by the motor 48, the rare earth alloy powder P on the table 42 is gradually pushed out on the table 42 outward in the rotational radius direction of the rotating member 44, and from the end surface of the table 42. It is discharged downward.

  The supply amount of the rare earth alloy powder P can be controlled by the rotation speed of the rotating member 44. For example, when the rotation of the rotating member 44 is stopped, the supply of powder is stopped.

  As shown in FIG. 2B, the table feeder 40B rotates the cylindrical portion 41 extending in the vertical direction, the disk-shaped table 42 facing the opening at the lower end of the cylindrical portion 41, and the table 42. A motor 48 that rotates around the shaft 46 and a scraper 47 that is provided on the table 42 and extends in the radial direction of the table 42 and arranged in the vertical direction are provided. The scraper 47 does not rotate even when the motor 48 is driven.

  A gap G is provided between the lower end of the cylindrical portion 41 and the upper surface of the table 42, and the rare earth alloy powder P supplied into the cylindrical portion 41 exits from the lower end of the cylindrical portion 41, and the table. The gap G is filled while forming a slope with a predetermined angle of repose on the outer side of the cylindrical portion 41 on 42. When the table 42 is rotated by the motor 48, the rare earth alloy powder P on the table 42 is pushed out along the scraper 47 outward in the rotational radius direction of the table 42 and discharged downward from the end surface of the table 42.

  The supply amount of the rare earth alloy powder P can be controlled by the rotation speed of the table 42. When the rotation of the table 42 is stopped, the supply of the powder is stopped.

  Returning to FIG. 1, the computer 70 controls the weight of the rare earth alloy powder in the cavity V of the die 10 within a predetermined range based on the information regarding the weight output from the weight measuring device 50. Specifically, in this embodiment, based on the information about the weight obtained from the weight measuring device 50, the computer 70 makes the amount of the rare earth alloy powder supplied into the cavity of the die 10 fall within a predetermined range. The feeder 40 is controlled. The predetermined range is a predetermined target range of the weight of the rare earth alloy powder P, and is appropriately set according to the size and shape of the sintered magnet. For example, it can be within a range of ± 1% of the target weight.

  Specifically, for example, the computer 70 obtains information on the weight of only the die obtained from the weight measuring device 50 before supplying the rare earth alloy powder and the die obtained from the weight measuring device 50 during the supply of the rare earth alloy powder. The weight of the rare earth alloy powder supplied into the cavity can be estimated periodically or at any timing based on the information on the total weight of the supplied rare earth alloy powder. For example, the weight of only the powder can be obtained by subtracting the weight output from the weight measuring device before supplying the powder from the weight output from the weight measuring device during powder supply. And the computer 70 should just stop supply of the powder from the feeder 40, when the weight of only powder enters in the predetermined range.

  When the weight of the die 10 is known in advance, the computer 70 knows in advance information on the total weight of the die and the rare earth alloy powder obtained from the weight measuring device 50 during the supply of the rare earth alloy powder. The weight of the rare earth alloy powder supplied into the cavity can be estimated periodically or at any timing based on the information regarding the weight of the die that has been used. For example, the weight of only the supplied powder can be obtained by subtracting the weight of the die obtained in advance from the total weight of the die and the rare earth alloy powder obtained from the weight measuring device 50 during the powder supply. Further, information regarding the total value of the weight of the rare earth alloy powder to be supplied and the weight of the die is obtained in advance, and the supplied rare earth alloy is compared with this information related to the total weight obtained from the weight measuring device 50. It can also be determined whether the weight of the powder is within a predetermined range.

  When the computer 70 determines that the weight of the rare earth alloy powder supplied into the cavity is within a predetermined range, the computer 70 stops the supply of the rare earth alloy powder by the feeder 40.

  Thereafter, after filling the rare earth alloy powder, the surface of the rare earth alloy powder in the die 10 may be flattened, or the filling density may be increased by tapping the die.

(Rare earth alloy powder punching process)
Next, as shown in FIG. 3A, the punch 15 is inserted into the die 10 and the rare earth alloy powder is pressed to obtain the compact 5. The press pressure can be a low pressure, that is, 0.049 to 20 MPa. The press pressure is, for example, the pressure exerted by the punch tip surface on the alloy powder. Low pressure molding is preferable because the die 10 and punch 15 are less consumed. Accordingly, it is possible to use a resin die and punch, and it is possible to reduce the cost. Moreover, the protrusion 15b can be provided in the punch 15, and the punch 15 can restrict | limit the height after compression, and the press by the high pressure which is not intended can also be prevented.

(Orientation process of rare earth alloy powder)
After the punching, before the molded body 5 is taken out from the cavity V of the die 10, an alignment step of applying a magnetic field to the molded body may be performed.
In the alignment step, a magnetic field is applied to the compact 5 held in the cavity V of the die 10 to align the alloy powder constituting the compact 5 along the magnetic field in the cavity V. The magnetic field may be a pulsed magnetic field or a static magnetic field. For example, by arranging the molded body 5 held in the cavity V of the die 10 together with the die 10 (or with the punch 15) inside the air-core coil and passing an electric current (alternating current) through the air-core coil. A magnetic field may be applied to the molded body 5 in the die 10. A magnetic field may be applied to the molded body 5 in the die 10 using a magnetized yoke. You may apply a magnetic field to the molded object 5 in the cavity V by sending an electric current through a double coil or a Helmholtz coil. By using a double coil or a Helmholtz coil, a more homogeneous magnetic field can be applied to the molded body than when an air-core coil is used. As a result, the orientation of the alloy powder in the compact is easily improved, and the magnetic properties of the finally obtained rare earth magnet are easily improved.
The strength of the magnetic field applied to the molded body 5 in the cavity V may be, for example, 796 kA / m or more and 5173 kA / m or less (10 kOe or more and 65 kOe or less). You may demagnetize a molded object after an orientation process. The intensity of the magnetic field applied to the molded body in the mold is not necessarily limited to the above range.
During the punching, that is, while pressing the alloy powder in the cavity V, the above-described magnetic field may be applied to the alloy powder and oriented.

  After the orientation step, the molded body may be demagnetized in order to improve the handleability of the molded body.

(Process of separating the molded body from the cavity)
Thereafter, a separation step of taking out the molded body 5 from the cavity V of the die 10 is performed. Specifically, for example, as shown in FIG. 3B, in the separation step, the cylindrical portion 10a is moved upward with the position of the punch 15 in the vertical direction (Z-axis direction) fixed. Let As a result, the punch 15 inserted into the tubular portion 10a passes through the tubular portion 10a, and the end surface of the punch 15 pushes the molded body 5 downward of the tubular portion 10a. That is, the molded body 5 held in the cylindrical portion 10a is extracted from under the cylindrical portion 10a. Subsequently, as shown in FIG. 3C, the molded body 5 placed on the bottom plate portion 10 b is separated from the cavity V by moving the cylindrical portion 10 a and the punch 15 upward. Is done. Thus, the molded body 5 can be taken out from the cavity V while keeping the shape of the molded body 5 by extracting the molded body 5 from below the cylindrical portion 10a. If the molded body 5 is directly gripped by a chuck or the like and taken out from above the cylindrical portion 10a, the molded body 5 is easily damaged. In the present embodiment, the molded body 5 can be easily separated from the cavity V without directly gripping the molded body 5. If the molded body 5 is separated from the cavity V by disassembling the cylindrical portion 10a into a plurality of members, a force may be applied to the molded body 5 by mistake and the molded body 5 may be damaged. In the present embodiment, the molded body 5 can be easily taken out from the cavity V without disassembling the cylindrical portion 10a. The bottom plate portion 10b can be used as a heating process tray.

In the separation step, the molded body 5 may be taken out from the cavity V as shown in FIG. First, as shown in (a) of FIG. 4, with the cylindrical portion 10 a and the punch 15 holding the molded body 5, the cylindrical portion 10 a and the punch 15 are moved together with the molded body 5 from the bottom plate portion 10 b. To separate. Even if the molded body 5 is separated from the bottom plate portion 10b, the molded body 5 is unlikely to fall out from below the cylindrical portion 10a due to friction between the molded body 5 and the cylindrical portion 10a or spring back of the molded body 5. Subsequently, as shown in FIG. 4B, the molded body 5 held by the cylindrical portion 10a and the punch 15 is placed on the heating process tray 32 together with the cylindrical portion 10a and the punch 15. Put. Subsequently, as shown in FIG. 4C, the cylindrical portion 10a is moved upward in a state where the position of the punch 15 in the vertical direction (Z-axis direction) is fixed. As a result, the punch 15 inserted into the tubular portion 10a passes through the tubular portion 10a, and the end surface of the punch 15 pushes the molded body 5 downward from the tubular portion 10a. That is, the molded body 5 held in the cavity V is extracted from under the cylindrical portion 10a. Subsequently, as shown in FIG. 3 (d), the molded body 5 placed on the heating process tray 32 is formed into a cylindrical shape by moving the cylindrical portion 10a and the punch 15 upward. Separated from the part 10 a and the punch 15.
3 and 4, the axes of the cavity V and the punch 15 are in the vertical direction, but may be inclined within 45 ° with respect to the vertical.

The density of the molded body 5 separated from the cavity V is, for example, 3.0 to 4.4 g / cm ³ , preferably 3.2 to 4.2 g / cm ³ , and more preferably 3.4 to 4.0 g / cm ³ . It may be adjusted to cm ³ .

(Molded body heating process)
Subsequently, since the molded body 5 molded at low pressure has low strength and is difficult to handle, it is preferable to heat (heat treat) the molded body to increase the strength of the molded body.
The temperature of the molded body in the heating step can be adjusted to 200 to 450 ° C. In a heating process, you may adjust the temperature of a molded object to 200-400 degreeC or 200-350 degreeC.

  In the heating step, when the temperature of the molded body 5 becomes 200 ° C. or higher, the molded body 5 starts to harden, and the shape retention of the molded body 5, in other words, the mechanical strength of the molded body 5 is improved. Since the shape retaining property of the molded body 5 is improved, the molded body 5 is hardly damaged when the molded body 5 is conveyed or when the molded body% is handled in a subsequent process. For example, when the molded body 5 is gripped by a transport chuck or the like and arranged on the baking tray, the molded body 5 is unlikely to collapse. As a result, defects in the finally obtained rare earth magnet are suppressed.

  If the temperature of the molded body 5 exceeds 450 ° C. in the heating process, cracks are likely to be formed in the molded body 5 in the firing process performed after the heating process. The reason for the formation of cracks is not clear. For example, there is a possibility that cracks may be formed in the molded body 5 because hydrogen remaining in the molded body 5 blows out as a gas to the outside of the molded body 5 due to a rapid temperature rise of the molded body 5 in the heating process. However, the crack of the molded object 5 in a baking process is suppressed by adjusting the temperature of the molded object 5 to 450 degrees C or less in a heating process. As a result, cracks in the finally obtained rare earth magnet are easily suppressed. Moreover, since the temperature of the molded object 5 is adjusted to 450 degrees C or less in a heating process, the time required for the temperature rising or cooling of the molded object 5 is suppressed, and the productivity of a rare earth magnet improves. Further, since the temperature of the molded body 5 in the heating step is 450 ° C. or lower and lower than a general firing temperature, even if the molded body 5 is heated together with a part of the die 10 (for example, the bottom plate portion 10b), the die 10 Or chemical reaction between the molded body 5 and the die 10 hardly occurs. Therefore, even a die composed of a composition (for example, resin) that does not necessarily have high heat resistance can be used.

  The mechanism by which the shape retention of the molded body 5 is improved by adjusting the temperature of the molded body 5 to 200 ° C. or higher and 450 ° C. or lower is not clear. For example, there is a possibility that an organic substance (for example, a lubricant) added to the alloy powder becomes carbon in the heating process, and the alloy powders are bound via carbon. As a result, the shape retention of the molded body 5 may be improved. If the temperature of the molded body 5 exceeds 450 ° C. in the heating step, there is a possibility that metal carbide constituting the alloy powder is generated or the alloy powders are directly sintered. On the other hand, when the temperature of the molded body 5 is adjusted to 200 ° C. or higher and 450 ° C. or lower, metal carbide is not necessarily generated, and alloy particles are not necessarily sintered directly.

  The time for maintaining the temperature of the molded body 5 at 200 ° C. or higher and 450 ° C. or lower in the heating step is not particularly limited, and may be appropriately adjusted according to the size and shape of the molded body 5.

  In the heating step, the molded body 5 may be heated by irradiating the molded body 5 with infrared rays. By directly heating the molded body 5 by irradiation with infrared rays (that is, radiant heat), the time required for raising the temperature of the molded body 5 is shortened compared to heating by conduction or convection, and production efficiency and energy efficiency are increased. However, in the heating step, the molded body 5 may be heated by heat conduction or convection in the heating furnace. The infrared wavelength may be, for example, 0.75 μm to 1000 μm, preferably 0.75 μm to 30 μm. The infrared rays may be at least one selected from the group consisting of near infrared rays, short wavelength infrared rays, medium wavelength infrared rays, long wavelength infrared rays (thermal infrared rays), and far infrared rays. Of the above infrared rays, near infrared rays are relatively easily absorbed by metals. Therefore, when near-infrared rays are irradiated to the molded body, the temperature of the metal (alloy powder) is easily raised in a short time. On the other hand, far infrared rays among the above infrared rays are relatively easily absorbed by organic substances and easily reflected by metal (alloy powder). Therefore, when irradiating a far infrared ray to a molded object, the organic substance (for example, lubricant) mentioned above is easy to be selectively heated, and a molded object is easy to harden by the above-mentioned mechanism resulting from an organic substance. In the case of irradiating the molded body with infrared rays, for example, an infrared heater (such as a ceramic heater) or an infrared lamp may be used.

  When the molded body 5 separated from part or all of the die 10 is heated in the heating step, deterioration (for example, deformation, hardening, or wear) of the die 10 due to heating is easily suppressed, and the molded body 5 and the die 10 are Burn-in is also easily suppressed. Further, when the molded body 5 separated from the cavity of the die 10 is heated, the molded body 5 is easily heated because there is no heat insulation by the die. As a result, the shape retention of the molded body 5 is improved. When the molded body 5 separated from the cavity V is heated, the possibility that the die 10 chemically reacts with the molded body 5 is low. For this reason, the die 10 is not necessarily required to have heat resistance, and the material of the die 10 is not easily limited. Therefore, as a material for the die 10, it is easy to process into a desired size and shape, and it is easy to select an inexpensive material. If the molded body 5 held in the cavity is heated together with the die 10 in the heating step, stress is applied to the molded body 5 due to the difference in thermal expansion coefficient between the molded body 5 and the die 10. It is easy to act, and the molded body 5 is deformed or damaged. Moreover, since the volume and heat capacity of the whole heating target are large, the number of the molded bodies 5 is limited, the time required for the heating process is lengthened, energy is wasted, and the productivity of the rare earth magnet is reduced.

  In the heating step, for example, the molded body 5 placed on the bottom plate portion 10b may be heated. In the heating step, the molded body 5 placed on the heating step tray 32 may be heated. In the heating step, the molded body 5 may be heated in an inert gas or vacuum to suppress oxidation of the molded body 5. The inert gas may be a noble gas such as argon.

  In the heating step, after the temperature of the molded body 5 is adjusted to 200 ° C. or higher and 450 ° C. or lower, the molded body 5 may be cooled to 100 ° C. or lower. When the surface of the chuck used for transporting the molded body 5 after the heating step is made of resin, the chemical reaction between the surface of the chuck and the molded body 5 is suppressed by cooling of the molded body 5, deterioration of the chuck, and Contamination of the surface of the molded body 5 is suppressed. The cooling method may be natural cooling, for example.

When the strength of the molded body 5 is increased through the heating process, even the molded body 5 molded at a low pressure can be easily grasped by a robot hand or the like, and the handling property in the subsequent process is improved.
The density of the green body before sintering is also adjusted to 3.0 to 4.4 g / cm ³ , preferably 3.2 to 4.2 g / cm ³ , more preferably 3.4 to 4.0 g / cm ^3. It's okay.

(Sintering process of molded body)
Next, the compact is sintered to obtain a sintered magnet. In the sintering step, the molded body placed on the bottom plate portion 10b and the molded body placed on the heating process tray may be sintered as they are, but before the sintering step, the bottom plate portion 10b or It is preferable to transfer the molded body 5 on the heating process tray onto the sintering tray. In the case of undergoing the above-described heating step, since the shape retention of the molded body is improved, damage to the molded body is suppressed when the molded body is gripped by the conveyance chuck and arranged on the sintering tray.

  In the sintering step, a plurality of molded bodies may be placed on the sintering tray, and the plurality of molded bodies placed on the sintering tray may be heated together. By arranging a large number of compacts on a sintering tray at narrow intervals and heating a large number of compacts at once, the productivity of the rare earth magnet is improved.

  The composition of the sintering tray may be any composition that does not easily react with the molded body during sintering and does not easily generate a substance that contaminates the molded body. For example, the sintering tray may be made of molybdenum or a molybdenum alloy.

  The sintering temperature should just be 900 degreeC or more and 1200 degrees C or less, for example. The sintering time may be, for example, from 0.1 hours to 100 hours. The sintering process may be repeated. In the sintering step, the compact may be heated in an inert gas or vacuum. The inert gas may be a noble gas such as argon.

  An aging treatment may be applied to the sintered body. In the aging treatment, the sintered body may be heat-treated at, for example, 450 ° C. or more and 950 ° C. or less. In the aging treatment, the sintered body may be heat-treated for 0.1 hours to 100 hours, for example. The aging treatment may be performed in an inert gas or vacuum. The aging treatment may be composed of a multi-stage heat treatment at different temperatures.

  The sintered body may be cut or polished. A protective layer may be formed on the surface of the sintered body. The protective layer may be, for example, a resin layer or an inorganic layer (for example, a metal layer or an oxide layer). The method for forming the protective layer may be, for example, a plating method, a coating method, a vapor deposition polymerization method, a gas phase method, or a chemical conversion treatment method.

(Function)
Conventionally, the weight of the rare earth alloy powder is measured in a container separate from the die 10, and then the rare earth alloy powder in the container is transferred into the cavity. However, since the rare earth alloy powder has strong adhesiveness, when it is transferred into the cavity, a part of the rare earth alloy powder often remains attached to the container, and the weight is uneven among the compacts. According to the present embodiment, the rare earth alloy powder is supplied into the cavity V of the die placed on the weight measuring device, and the weight of the rare earth alloy powder in the cavity is determined based on the information on the weight obtained from the weight measuring device. Control within a predetermined range. Furthermore, after the weight measurement, the powder in the cavity is directly molded by a punch without being transferred elsewhere. Therefore, the weight of the rare earth alloy powder of the compact can be controlled with high accuracy. Among these, Nd—Fe—B alloy powder is particularly effective because of its particularly strong adhesion.
And if the uniformity of the weight of the molded body is high, variation in shape between the sintered bodies is suppressed, the amount of processing of the sintered magnet after sintering can be reduced, and the material yield can be increased. . In particular, in the case of low pressure molding, the effect is high because the shape of the compact and the shape of the sintered magnet vary greatly due to the weight variation between the compacts.

  Further, when the die is made of a light material such as resin, the weight of the die is reduced, and the measurement accuracy of the weight of the rare earth alloy powder is further improved.

  Further, as the feeder 40, a circle feeder 40A or a table feeder 40B is used. Since these feeders have little compaction action on the powder, it is difficult to cause lumps, and the density of the rare earth alloy powder to be filled can be suppressed. Accordingly, it is possible to suppress non-uniform density in the molded body and the sintered body. Further, when the Nd-Fe-B alloy powder is used, the effect is high because the bulk is bulky and the density in the filled powder and the compact tends to vary.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, in the above embodiment, a circle feeder and a table feeder are employed, but the present invention can also be implemented by employing other powder feeders such as a screw feeder.

  In the above embodiment, the computer 70 controls the weight of the rare earth alloy powder in the cavity V by controlling the feeder 40 based on the information about the weight obtained from the weight measuring device 50. Not limited. For example, when using a feeder with low supply accuracy or when it is necessary to increase the accuracy of the weight of the rare earth alloy powder to be supplied, the computer 70 is based on the weight-related information obtained from the weight measuring device 50. In some cases, it is necessary to partially remove the rare earth alloy powder in the cavity V to control the weight of the rare earth alloy powder in the cavity V within a predetermined range. As the powder removing device, for example, a suction nozzle can be used. The computer 70 can control both the amount of powder supplied by the feeder 40 and the amount of powder removed by the powder removing device based on the information obtained from the weight measuring device 50, or only the powder removing device. It is also possible to control.

  Moreover, in the said embodiment, although the feeder 40 is controlled by the computer 70, a person may judge according to the output result of the weight measuring device 50, and may control the feeder 40 grade | etc.,.

Further, the shape and structure of the die 10 and the punch 15 and the shape of the cavity V are not limited to the above embodiment, and various shapes can be taken according to the shape of the target magnet. For example, in the above-described embodiment, the die can be divided into two upper and lower dies, but may be divided into three or more or may not be divided.
The size and shape of the rare earth magnet vary depending on the use of the rare earth magnet and are not particularly limited. The shape of the rare earth magnet may be, for example, a rectangular parallelepiped shape, a cubic shape, a polygonal column shape, a segment shape, a fan shape, a rectangular shape, a plate shape, a spherical shape, a disc shape, a columnar shape, a ring shape, or a capsule shape. The cross-sectional shape of the rare earth magnet may be, for example, a polygonal shape, a chordal shape, an arc shape, or a circular shape.

  Moreover, in the said embodiment, although a shaping | molding pressure is made low and a heating process is performed, it is good also as a normal pressure (for example, 50-200 MPa) without making a shaping | molding pressure low, and a heating process is unnecessary in this case. Even in the case of high-pressure molding, non-uniformity in the weight of the compact results in non-uniform shape after sintering and increases the amount of processing after sintering, thus reducing the material yield. According to this embodiment, even in the case of high pressure molding, there is an effect of improving the uniformity of the shape between the molded bodies and between the sintered bodies.

  In the above embodiment, the molded body 5 is taken out from the cavity of the die 10 and sintered. However, the molded body can be sintered in a state of being accommodated in the die 10.

  DESCRIPTION OF SYMBOLS 5 ... Molded object, 10 ... Die, 15 ... Punch, 40A ... Circle feeder (feeder), 40B ... Table feeder (feeder), 50 ... Weight measuring instrument, 70 ... Computer, P ... Rare earth alloy powder, V ... Cavity.

Claims (9)

Supplying rare earth alloy powder into the cavity of the die placed on the gravimetric instrument;
Controlling the weight of the rare earth alloy powder in the cavity within a predetermined range based on information on the weight obtained from the weight measuring device;
After controlling the weight, pressing the rare earth alloy powder in the cavity with a punch to obtain a molded body; and
And a step of sintering the molded body.   The method according to claim 1, wherein the amount of rare earth alloy powder supplied into the cavity is controlled to control the weight of the rare earth alloy powder in the cavity within the predetermined range.   The method according to claim 1, wherein the die is made of resin.   The method according to any one of claims 1 to 3, wherein the rare earth alloy powder is an Nd-Fe-B alloy powder.   The method of any one of Claims 1-4 which makes the pressure of the said press 0.049-20MPa.   The method according to claim 1, wherein the rare earth alloy powder is supplied into the cavity by a circle feeder or a table feeder. Further comprising removing the molded body from the cavity of the die,
The method according to claim 1, wherein the molded body taken out from the cavity is sintered.   The method according to claim 7, further comprising a heating step of heating the molded body taken out from the cavity to 200 to 450 ° C. before the sintering.   The magnetic field is applied to the said molded object hold | maintained in the cavity of the said punch, and the orientation process of orientating the said rare earth alloy powder contained in the said molded object is further provided. the method of.

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