JP2019114608A - Method of manufacturing rare earth magnet - Google Patents

Abstract

To provide a method of manufacturing rare earth magnets capable of suppressing a variation in a degree of orientation in the rare earth magnets and suppressing deformation of the rare earth magnets.SOLUTION: The method of manufacturing rare earth magnets includes: a forming step of supplying a metal powder containing a rare earth element into a die 2 to form a molded body 10; an orientation step of applying a pulse magnetic field H to the molded body 10 held in the die 2 to orient the metal powder contained in the molded body 10; and a sintering step of sintering the molded body 10 after the orientation step. In the orientation step, a pulse magnetic field H is applied to the molded body 10 using at least two coils 17a, 17b arranged to have a same central axis A.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method of manufacturing a rare earth magnet.

  The rare earth magnet is a component such as a motor or an actuator, and for example, a hard disk drive, a hybrid car, an electric car, a magnetic resonance imaging apparatus (MRI), a smartphone, a digital camera, a thin TV, a scanner, an air conditioner, a heat pump, a refrigerator, a vacuum cleaner It is used in various fields such as washing and drying machines, elevators and wind power generators. Depending on these various applications, the required size and shape of the rare earth magnet will vary. Therefore, in order to efficiently produce a wide variety of rare earth magnets, a molding method that can easily change the size and shape of the rare earth magnets is desired.

  In the manufacture of a conventional rare earth magnet, a magnetic field is applied to the metal powder while pressing the metal powder (for example, alloy powder) containing the rare earth element under 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. Such a forming method is hereinafter referred to as "high pressure magnetic field pressing method". According to the high-pressure magnetic field pressing method, it is possible to obtain a molded body in which the metal powder is easy to be oriented and which has high residual magnetic flux density Br and excellent shape retention. A sintered body is obtained by sintering the molded body, and the sintered body is processed into a desired shape to complete a magnet product.

  However, high pressure magnetic field pressing requires high pressure to be applied to the metal powder in a magnetic field, which requires a large-scale and complicated forming apparatus, which limits the size and shape of the mold for forming. Due to this limitation, the general shape of the shaped body obtained by high-pressure magnetic field pressing is limited to coarse blocks. Therefore, when producing various kinds of magnet products by the conventional method, after sintering the block-like molded body to obtain a sintered body, the sintered body is produced according to the size and shape required for the magnet product. It is necessary to process. In the processing of the sintered body, scraps containing expensive rare earth elements are generated because the sintered body is cut or polished. As a result, the yield rate of the magnet product is reduced. Further, in the high-pressure magnetic field pressing method, the mold or the molded body is easily broken by galling between the molds or by the galling between the mold and the molded body. For example, a crack may occur in a compact obtained by high-pressure magnetic field pressing.

  For the reasons as described above, the manufacturing method using the conventional high-pressure magnetic field pressing method is not suitable for the manufacture of a large variety 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 an alloy powder at a low pressure (0.98 MPa or more and 2.0 MPa or less). In the method of manufacturing a rare earth magnet, the alloy powder is filled in a mold and the alloy powder is pressurized at a low pressure to apply a magnetic field to the step of producing a compact (filling step) and the compact in the mold. And a step of orienting the alloy powder in the compact (orientation step), and a step of sintering the compact taken out of the mold (sintering step). And in the manufacturing method of following patent document 1, a filling process and an orientation process are performed in another place.

International Publication No. 2016/047593 Brochure

  When molding a metal powder at low pressure as in the molding method described in Patent Document 1, durability against high pressure is not required of the mold, and a large-scale complex molding apparatus is also unnecessary. Therefore, when molding metal powder under low pressure, it is relatively easy to manufacture various kinds of rare earth magnets using molds having various sizes and shapes without being limited in material, size and shape of the mold. it can. In addition, in the high-pressure magnetic field pressing method, although it takes a long time to form and orientate the metal powder, by shaping the metal powder under a low pressure, the time required for the shaping and orientation is significantly shortened and the productivity of the rare earth magnet is improved. Do.

  However, in the manufacturing method described in Patent Document 1 described above, since the magnetic field is generated using one air core coil, the degree of orientation of the metal powder in the compact tends to vary, and the compact shrinks uniformly during the sintering step. It is difficult to do. As a result, the degree of orientation in the obtained rare earth magnet (sintered body) also tends to vary, and the rare earth magnet is easily deformed.

  The present invention has been made in view of the problems of the prior art described above, and a method of manufacturing a rare earth magnet capable of suppressing variation in orientation (variatilon) of the rare earth magnet and suppressing deformation of the rare earth magnet. Intended to be provided.

  In the method of manufacturing a rare earth magnet according to one aspect of the present invention, a metal powder containing a rare earth element is supplied into a mold to form a molded body, and a pulse magnetic field is applied to the molded body held in the mold. And an orientation step of applying and orienting the metal powder contained in the formed body, and a sintering step of sintering the formed body after the orientation step, wherein the orientation step is arranged to have the same central axis A pulsed magnetic field is applied to the compact using at least two coils.

  The inner diameter of one coil may be equal to the inner diameter of the other coil, the inner diameter of each of the two coils may be represented by 2R, and the maximum width of the molded body in the direction perpendicular to the central axis is represented by W And R may be equal to or greater than W, and in the orientation step, the compact may be disposed inside the two coils.

  The inner diameter of one coil may be equal to the inner diameter of the other coil, the inner diameter of each of the two coils may be represented by 2R, and the distance between the two coils in the direction parallel to the central axis may be represented by D. , D / 2R may be greater than 0 and less than or equal to 0.55, and in the orientation step, the shaped body may be disposed inside the two coils.

Before the orientation step, the density of the molded body may be adjusted to 3.0 g / cm ³ or more and 4.4 g / cm ³ or less.

  At least a portion of the mold may be formed of nonmagnetic material.

  At least a portion of the mold may be formed of a resin.

  In the sintering step, the compact separated from the mold may be sintered.

  According to the present invention, there is provided a method of manufacturing a rare earth magnet capable of suppressing variation in the degree of orientation in the rare earth magnet and suppressing deformation of the rare earth magnet.

It is a typical perspective view of a model (an upper model, a side model, and a lower model) used for a forming process. It is a typical perspective view of a pair of coils (double coil) with which a magnetic field orientation device is provided. It is typical sectional drawing of the double coil, the type | mold arrange | positioned inside a double coil, and the molded object hold | maintained in the type | mold. It is a typical perspective view of a double coil and a forming object arranged inside a double coil. FIG. 5 is a schematic cross-sectional view of the double coil and the molded body shown in FIGS. 3 and 4. (A) in FIG. 6 is a schematic top view of the molded body and double coil shown in FIGS. 3 to 5, and (b) in FIG. 6 is another molded body and double coil. It is typical sectional drawing of. (A) in FIG. 7 is a schematic cross-sectional view of another molded body and each double coil, and (b) in FIG. 7 is a schematic upper surface of each other molded body and the double coil. FIG. It is a schematic perspective view of the rare earth magnet obtained from the molded object shown by FIG. It is a figure which shows an example of the pulse magnetic field applied to a molded object in a formation process.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the drawings, equivalent components are denoted by the same reference numerals. The present invention is not limited to the following embodiments. X, Y and Z shown in each figure mean three coordinate axes orthogonal to each other. The direction indicated by each coordinate axis is common to all the drawings. Although the mold is omitted in FIGS. 4 to 7 for the convenience of description, the molded body shown in FIGS. 4 to 7 is actually held in the mold.

In the present embodiment, the rare earth magnet means a sintered magnet. In the method of manufacturing a rare earth magnet, an alloy is first cast. The casting method may be, for example, a strip casting method. The alloy may be flake-like or ingot-like. The alloy contains a rare earth element. Examples of the 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 may be at least one selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The raw material alloy is selected from the group consisting of B, N, Fe, Co, Cu, Ni, Mn, Al, Nb, Zr, Ti, W, Mo, V, Ga, Zn, Si and Bi in addition to the rare earth elements. And at least one element. The chemical composition of the alloy may be adjusted according to the chemical composition of the main phase and the grain boundary phase of the rare earth magnet to be finally obtained. That is, the starting materials of the alloy may be prepared by weighing and blending the respective starting materials containing the above-mentioned elements according to the composition of the target rare earth magnet. The rare earth magnet may be, for example, a neodymium magnet, a samarium cobalt magnet, a samarium-iron-nitrogen magnet, or a praseodymium magnet. The main phase of the rare earth magnet may be, for example, Nd ₂ Fe ₁₄ B, SmCo ₅ , Sm ₂ Co ₁₇ , Sm ₂ Fe ₁₇ N ₃ , Sm ₁ Fe ₇ N _x , or PrCo ₅ . The grain boundary phase may be, for example, a phase (R-rich phase) in which the content of the rare earth element is larger than that of the main phase. The grain boundary phase may contain a B-rich phase, an oxide phase or a carbide phase.

  Rough grinding of the above-mentioned alloy gives a rough powder of the alloy. In the coarse grinding, for example, the alloy may be crushed by storing hydrogen in the grain boundary (R rich phase) of the alloy. In rough grinding of the alloy, mechanical grinding methods such as a disc mill, a jaw crusher, a brown mill or a stamp mill may be used. The particle size of the coarse powder obtained by the coarse grinding may be, for example, 10 μm or more and 100 μm or less.

  The fine powder of the alloy is obtained by pulverizing the above-mentioned coarse powder. In pulverizing, the alloy powder may be pulverized by a jet mill, a ball mill, a vibrating mill, a wet attritor, or the like. The particle size of the fine powder obtained by pulverization may be, for example, 0.5 μm or more and 5 μm or less. Below, a coarse powder or fine powder may be described as alloy powder or metal powder.

  An organic substance may be added to the alloy powder obtained by coarse grinding. An organic substance may be added to the fine powder obtained by pulverization. That is, the organic substance may be mixed with the metal powder either before or after the pulverization. The organic matter functions, for example, as a lubricant. The addition of the lubricant to the metal powder suppresses aggregation of the metal powder. In addition, by adding a lubricant to the metal powder, the friction between the mold and the metal powder is easily suppressed in the subsequent step. As a result, the metal powder is easy to be oriented in the orientation step, and it is easy to suppress scratches on the surface of the molded body obtained from the metal powder or the surface of the mold. The organic matter may be, for example, a fatty acid or a derivative of a fatty acid. Organic substances are, for example, oleic acid amide, zinc stearate, calcium stearate, stearic acid amide, palmitic acid amide, pentadecyl acid amide, myristic acid amide, lauric acid amide, capric acid amide, pelargonic acid amide, caprylic acid amide, enanthate It may be at least one selected from the group consisting of amides, caproic acid amides, valeric acid amides and butyric acid amides. The lubricant may be a powdered organic matter. The lubricant may be a liquid organic substance. An organic solvent in which a powdered lubricant is dissolved may be added to the alloy powder.

  In the forming step, the alloy powder obtained by the above procedure is supplied into a mold to form a formed body. The size, shape and structure of the mold are not limited. For example, as shown in FIG. 1, the mold 2 includes a lower mold 8, a cylindrical side mold 6 disposed on the lower mold 8, and an upper mold 4 disposed on the side mold 6 (punch And. A space corresponding to the shape and size of the rare earth magnet penetrates the side mold 6 in the vertical direction. Side mold 6 may be reworded as the side wall of the mold. The lower mold 8 may be plate-shaped. The lower portion of the side mold 6 may be engaged with the stops formed on the surface of the lower mold 8 to fix the position of the side mold 6 in the horizontal direction. In the molding process, the side mold 6 is placed on the lower mold 8, and the opening (hole) on the lower surface side of the side mold 6 is closed by the lower mold 8. By such an arrangement, the side mold 6 and the lower mold 8 constitute a cavity (female mold). Subsequently, the alloy powder is introduced into the cavity from the opening (hole) on the upper surface side of the side mold 6. As a result, the alloy powder is shaped to correspond to the shape and size of the rare earth magnet in the cavity. Alloy powder may be loaded into the cavity. That is, the cavity may be filled with alloy powder. The upper mold 4 may be reworded as a core (male mold). The upper mold 4 may have a shape that fits in the cavity. The upper mold 4 may be inserted into the cavity. The compact 10 (alloy powder) in the cavity may be compressed at the end face of the upper mold 4. However, it is not necessary to compress the alloy powder in the cavity because the density of the formed body 10 is sufficiently increased and the rare earth magnet having the desired density is obtained only by sintering the alloy powders in the sintering step.

In the molding process, the pressure type is on the alloy powder, may be adjusted to more than 0.049 MPa 20 MPa or less (0.5 kgf / cm ² or more 200 kgf / cm ² or less). The pressure may be, for example, the pressure exerted by the end face of the upper mold 4 on the alloy powder. Thus, by forming the compact 10 from the alloy powder at a lower pressure than the conventional high-pressure magnetic field pressing method, the friction between the mold 2 and the compact 10 is easily suppressed, and damage to the mold 2 or the compact 10 ( For example, cracks in the molded body 10 are easily suppressed. If the pressure is too high, the mold 2 will bend, making it difficult to secure the volume of the intended cavity, and it is difficult to obtain the density of the targeted compact 10. In the conventional high pressure magnetic field pressing method, it has been necessary to simultaneously form and orient the alloy powder under high pressure. On the other hand, in the present embodiment, since it is not necessary to simultaneously perform molding and orientation, the orientation process can be performed after the molding process. By separating the forming step and the orienting step, smaller and less expensive apparatuses (for example, a press forming apparatus and a magnetic field application apparatus) can be used in each step than in the prior art. The molding process and the orientation process may be performed substantially simultaneously.

The density of the molded body 10 (the molded body 10 before the orientation step) subjected to the molding step is 3.0 g / cm ³ or more and 4.4 g / cm ³ or less, preferably 3.2 g / cm ³ or more and 4.2 g / cm ³ or less, more preferably it may have been adjusted to below 3.4 g / cm ³ or more 4.0 g / cm ^3. The density of the molded body 10 may be adjusted, for example, by the pressure exerted by the mold 2 on the molded body 10 in the molding process. The density of the compact 10 may be adjusted, for example, by the mass of the alloy powder supplied into the mold 2. When the density of the compact 10 before the orientation step is in the above range, the residual magnetic flux density Br of the finally obtained rare earth magnet tends to increase. As the density of the green body 10 before the orientation step is lower, the alloy powder constituting the green body 10 is more easily rotated and oriented along the magnetic field. As a result, the residual magnetic flux density Br of the rare earth magnet tends to increase. When the density of the molded body 10 before the orientation step is too low, the shape retention property (mechanical strength) of the molded body 10 is insufficient, and the surface of the molded body 10 is formed by the friction between the molded body 10 and the mold in a later step. The degree of orientation of the alloy powder located at is disturbed. As a result, the residual magnetic flux density Br of the rare earth magnet tends to decrease. In addition, when the density of the molded body 10 before the orientation step is too low, the shape retention property (mechanical strength) of the molded body 10 is insufficient, and thus the rare earth magnet is easily cracked. When the density of the green body 10 before the orientation step is too high, deformation of the rare earth magnet is easily suppressed, but the alloy powder constituting the green body 10 is hard to rotate freely and is hard to orient along the magnetic field. As a result, the residual magnetic flux density Br of the rare earth magnet tends to decrease.

  In the orientation step, a pulse magnetic field is applied to the compact 10 held in the mold 2 to orient the alloy powder constituting the compact 10 in the mold 2 along the pulsed magnetic field. In the orientation step, a pulse magnetic field is applied to the compact 10 using a magnetic field generator provided with a double coil.

  As shown in FIGS. 2 to 5, the double coil 15 is at least two coils 17 a and 17 b arranged to have the same central axis A. The inner diameter of one coil 17a may be equal to the inner diameter of the other coil 17b. One coil 17a and the other coil 17b may be completely the same coil. The two coils 17 a and 17 b may be disposed parallel to a plane (XY plane) perpendicular to the central axis A. When viewed in the direction parallel to the central axis A, one coil 17a may overlap the other coil 17b. That is, the two coils 17a and 17b may be arranged straight as seen from the direction parallel to the central axis A. The magnitude and direction of the current I applied to each of the two coils 17a and 17b may be the same. The distance D between one coil 17a and the other coil 17b may be different from the inner radius R of the coils 17a and 17b. The distance D may be restated as the shortest distance between the end surface (lower surface) of one coil 17a and the end surface (upper surface) of the other coil 17b facing the end surface (lower surface). If the distance D is equal to the radius R, the double coil 15 is a Helmholtz coil.

  As shown in FIG. 3, in the orientation step, the compact 10 held in the mold 2 is placed inside the double coil 15 together with the mold 2. The molded body 10 may be disposed on the central axis A of the double coil 15. The center of the molded body 10 may be located on the central axis A of the double coil 15. The center of the molded body 10 may be located at a midpoint between the center of one coil 17a and the center of the other coil 17b. By passing the current I through the double coil 15, a pulse magnetic field H parallel to the central axis A is generated inside and outside the two coils 17a and 17b. The pulse magnetic field H is applied to the compact 10 in the mold 2. The number of times of applying the pulse magnetic field H to the compact 10 may be one or more than one. The double coil 15 and the other coils may be arranged to have the same central axis A. A pulse magnetic field H formed by the double coil 15 and another coil may be applied to the compact 10 in the mold 2. In the orientation step, a plurality of molds for holding the compact may be disposed inside the double coil. That is, in the orientation step, a plurality of molded bodies may be disposed inside the double coil together with the mold. The coils 17a and 17b may be arranged diagonally along the same central axis. Each of the coils 17a and 17b may be an air core coil. A soft magnetic material may be disposed inside the coils 17a and 17b. The coils 17a and 17b may be embedded in the resin.

  In the space surrounded by the two coils 17a and 17b, a homogeneous pulsed magnetic field H (a pulsed magnetic field having uniform direction and intensity) is formed. The magnetic lines of force of the pulse magnetic field H formed by the double coil 15 are likely to be distributed parallel to each other not only in the space surrounded by the double coil 15 but also near the end portions of the coils 17a and 17b. Therefore, by using the double coil 15, a more homogeneous pulse magnetic field H can be applied to the molded body 10 as compared with the case where only one coil is used. As a result, as compared with the case where only one coil is used, the individual alloy powders contained in the compact 10 can be easily oriented uniformly along the pulse magnetic field H, and the degree of orientation of the alloy powder in the compact 10 (oriented direction) Is less likely to vary. The compact 10 tends to shrink in the orientation direction of the alloy powder. Therefore, by sintering the shaped body 10 in which the variation in the degree of orientation of the alloy powder is suppressed, the shaped body 10 shrinks uniformly along the orientation direction of the alloy powder (the direction of the pulse magnetic field H). As a result, a sintered body (rare earth magnet) is obtained in which the variation in the degree of orientation is suppressed and the thickness in the orientation direction is uniform. That is, by suppressing the variation in the degree of orientation of the alloy powder in the compact 10, the variation in the degree of orientation in the rare earth magnet is suppressed, and the deformation of the rare earth magnet is suppressed.

  When the magnetic field is formed by only one conventional air core coil, the magnetic field lines are parallel to the central axis near the central axis of the coil. However, as the magnetic field lines move away from the central axis of the coil, they tend to face the outside of the coil. In particular, in the vicinity of both ends of the coil, a magnetic field which is not parallel to the central axis of the coil is formed. When a magnetic field that is not homogeneous as described above is applied to the compact, the degree of orientation of the alloy powder in the compact tends to vary depending on the positional relationship with the central axis of the coil. When a compact having a variation in the degree of orientation of the alloy powder is sintered, the compact shrinks unevenly. As a result, a sintered body (rare earth magnet) having a large variation in the degree of orientation and an uneven thickness is formed. When ferromagnetic materials are disposed at both ends of one air core coil, the magnetic field generated in the air core coil tends to be in a direction parallel to the central axis of the air core coil. However, when a high-intensity pulse magnetic field is generated in the air core coil, the ferromagnetic members disposed at both ends of the air core coil tend to saturate magnetically, and the magnetic lines of force at both ends of the air core coil become the air core coil. Easy to turn outward from the central axis of the That is, even when ferromagnetic materials are disposed at both ends of one air core coil, the magnetic fields at both ends of the air core coil are unlikely to be parallel to the central axis of the air core coil.

  Since the compact 10 formed at low pressure is relatively brittle, it is difficult to directly measure the degree of orientation of the alloy powder in the compact 10. Therefore, the degree of orientation of the alloy powder in the compact 10 and the variation thereof are retrospectively estimated from the degree of orientation in the rare earth magnet (sintered body) and the variation thereof. As described below, the degree of orientation in a rare earth magnet is measured by the Lotgering method applying X-ray diffraction (XRD). The detail of the measuring method of the orientation degree in a rare earth magnet is described in Unexamined-Japanese-Patent No. 2006-258616.

In the Lotgering method, the degree of orientation fc (unit:%) in the rare earth magnet is defined by the following equation 1.

  I (001) in Equation 1 is the diffraction intensity of the reflected X-ray on the (001) plane of the rare earth magnet. I (hk0) in Equation 1 is the diffraction intensity of the reflected X-ray on the (hk0) plane of the rare earth magnet. In the numerator of Formula 1, only the reflection component (component in the orientation direction) of the (001) plane is integrated. On the other hand, a diffraction peak having an orientation slightly different from the orientation direction is regarded as a reflection component (component perpendicular to the orientation direction) of the (hk0) plane and is excluded from the molecules of Formula 1. Therefore, the calculated degree of orientation fc is a smaller value than the actual degree of orientation. In order to calculate fc as close as possible to the actual degree of orientation, it is preferable to perform vector correction on the diffraction peak. In the vector correction, a diffraction peak whose direction is different from that of the (001) reflection X-ray is separated into a reflection component of the (001) plane and a reflection component of the (hk0) plane orthogonal thereto. The reflection component of the separated (001) plane is added to the numerator in Eq. For example, when the plane orientation of a certain crystal plane X is different from (001), the diffraction peak corresponding to the plane orientation of the crystal plane X is multiplied by cos α based on the inclination angle α of the diffraction peak. By this multiplication, the reflection component of the (001) plane among the reflection components of the crystal plane X is calculated. The reflection component of (001) calculated from the reflection component of the crystal plane X is integrated in the numerator in Equation 1.

  The variation of the orientation degree fc of the rare earth magnet is calculated by the following method.

The rare earth magnet is divided substantially equally to form a plurality of magnet pieces. For example, as shown in FIG. 8, the rectangular parallelepiped rare earth magnet 100 is equally divided to form nine magnet pieces a, b, c, d, e, f, g, h and i. However, the number of magnet pieces formed by division of the rare earth magnet is not limited to nine. Subsequently, the XRD pattern of each magnet piece is measured, and the degree of orientation fc of each magnet piece is calculated by the Lotgering method described above. For example, as shown in FIG. 8, in the measurement of the XRD pattern of each magnet piece, the plane on which X-rays are incident belongs to the plane 100s perpendicular to the central axis A (pulsed magnetic field H) of the double coil 15 in the orientation step. It may be the side that was The orientation degree of the magnet piece having the highest degree of orientation fc among the plurality of magnet pieces is expressed as fc (max). The orientation degree of the magnet piece having the lowest degree of orientation among the plurality of magnet pieces is expressed as fc (min). Based on the above premise, the variation Vf of the orientation degree fc of the rare earth magnet is defined by the following equation 2. The smaller the variation Vf in the orientation degree fc of the rare earth magnet, the better.
Vf (%) = fc (max)-fc (min) (2)

  When the inner diameter of each of the coil 17a and the coil 17b is represented by 2R and the maximum value of the width of the molded body 10 in the direction perpendicular to the central axis A is represented by W, 2R may be W or more. That is, 2R / W may be 1 or more. For example, as shown in (a) in FIGS. 4 and 6, when the molded body 10 is a rectangular solid and the surface of the molded body 10 perpendicular to the central axis A is rectangular, the maximum width of the molded body 10 is The value W corresponds to the length of the diagonal Ld of the surface of the molded body 10 perpendicular to the central axis A. The cross section of each of the molded body 10 and the double coil 15 cut parallel to the central axis A along the diagonal Ld of the surface of the molded body 10 is shown in FIG.

  When 2R is equal to or greater than W, the entire compact 10 is likely to fit inside the double coil 15, and the pulse magnetic field H is likely to act uniformly on the entire compact 10. As a result, the variation in the degree of orientation of the alloy powder in the compact 10 is easily suppressed, the variation in the degree of orientation in the rare earth magnet is also easily suppressed, and the deformation of the rare earth magnet is also easily suppressed. For the same reason, 2R / W is 0.9 or more and 7.5 or less, 1.7 or more and 7.5 or less, 2.8 or more and 7.5 or less, 3.7 or more and 7.5 or less, or 5.0 It may be 7.5 or less. As 2R / W narrows in this order, the variation in the degree of orientation is further suppressed, and the deformation of the rare earth magnet tends to be further suppressed.

  The shape of the top surface of the molded body 10 (the surface of the molded body 10 perpendicular to the central axis A) is not limited to the polygon shown in (a) in FIG. As shown in (b) in FIG. 6, the cross section of the molded body 10a (the cross section of the molded body 10 in the plane direction parallel to the central axis A) or the side surface may have a semi-cylindrical shape. As shown in (a) in FIG. 7, the cross section of the molded body 10 b (the cross section of the molded body 10 in the plane direction parallel to the central axis A) or the side surface may be C-shaped. As shown in (b) in FIG. 7, the upper surface of the molded body 10 c (the surface of the molded body 10 perpendicular to the central axis A) may be circular. Regardless of the shape of these compacts, when 2R is W or more, the pulse magnetic field H tends to act uniformly on the entire compact.

  When the inner diameter of each of the coil 17a and the coil 17b is represented by 2R and the distance between the two coils in the direction parallel to the central axis A is represented by D, D / 2R is greater than 0 and 0.55 or less You may When D / 2R is more than 0 and not more than 0.55, the direction and the intensity of the pulse magnetic field H generated by the double coil 15 tend to be uniform. As a result, the variation in the degree of orientation of the alloy powder in the compact 10 is easily suppressed, the variation in the degree of orientation in the rare earth magnet is also easily suppressed, and the deformation of the rare earth magnet is also easily suppressed. For the same reason, D / 2R may be 0.17 or more and 0.55 or less, preferably 0.17 or more and 0.48 or less, and more preferably 0.23 or more and 0.43 or less.

  The pulsed magnetic field H may be an alternating magnetic field. That is, the pulsed magnetic field H may be a magnetic field that repeats the change in intensity and direction as time passes. The pulsed magnetic field H may be an alternating magnetic field that decays. In other words, the pulse magnetic field H may be attenuated while repeating inversion as time passes. An example of the pulsed magnetic field H is shown in FIG. The vertical axis of FIG. 9 is the magnetic flux density (unit: T) of the pulse magnetic field H, and the horizontal axis of FIG. 9 is time (unit: second). As shown in FIG. 9, the maximum intensity (amplitude) of the pulse wave (the first pulse wave PW1) of the magnetic field initially applied to the formed body 10 is applied to the formed body 10 following the first pulse wave PW1. May be larger than the maximum intensity of the pulse wave of the magnetic field (second pulse wave PW2). The direction of the second pulse wave PW2 may be opposite to the direction of the first pulse wave PW1. The alloy powder constituting the compact 10 may be oriented by the application of the first pulse wave PW1, and the compact 10 may be degaussed by the application of the second pulse wave PW2. The method of generating the alternating magnetic field may be an alternating current method or a direct current inversion method.

  The strength of the pulse magnetic field H applied to the compact 10 in the mold 2 is, for example, 796 kA / m to 5173 kA / m (10 kOe to 65 kOe), or 2387 kA / m to 3979 kA / m (30 kOe to 50 kOe). May be there. When the intensity of the pulse magnetic field H is 796 kA / m or more, the degree of orientation of the alloy powder is likely to be sufficiently improved. The higher the degree of orientation of the alloy powder, the higher the residual magnetic flux density Br of the obtained rare earth magnet. When the intensity of the pulse magnetic field H exceeds 5173 kA / m, it becomes difficult to improve the degree of orientation of the alloy powder even if the intensity of the pulse magnetic field H increases. In addition, when the intensity of the pulse magnetic field H exceeds 5173 kA / m, a large-sized magnetic field generator is required, and the cost of the alignment process becomes high. The intensity of the pulsed magnetic field applied to the compact 10 in the mold 2 is not necessarily limited to the above range.

  The duration of the pulse magnetic field H may be, for example, 10 μsec or more and 0.5 sec or less. The duration of the pulse magnetic field H is the time from the start of the application of the pulse magnetic field H to the molded body 10 to the end of the application. When the duration of the pulse magnetic field H is 10 μsec or more, the degree of orientation of the alloy powder tends to be sufficiently increased. The longer the duration of the pulse magnetic field H, the larger the amount of heat generation in the double coil 15 that generates the pulse magnetic field H, and power tends to be wasted. The period of the first pulse wave PW1 first applied to the compact 10 as the pulse magnetic field H may be, for example, 0.01 ms or more and 100 ms or less, preferably 1 ms or more and 30 ms or less. When the period of the first pulse wave PW1 is within the above range, the rotation of the individual alloy powder tends to follow the application of the pulse magnetic field H, and the alloy powder tends to be oriented. As a result, the magnetic properties (for example, residual magnetic flux density Br) of the finally obtained rare earth magnet can be easily improved. Even in the case of using either the high flowability alloy powder or the low flowability alloy powder, the shorter the period of the first pulse wave PW1, the better the degree of orientation of the alloy powder, and the residual magnetic flux of the rare earth magnet The density Br tends to increase.

  The pulse magnetic field H has a magnetic field strength higher than that of the static magnetic field frequently used in the conventional high-pressure magnetic field pressing method, and is applied to the compact 10 in a short time. Therefore, by the orientation process using the pulse magnetic field H, the compact 10 having a high degree of orientation can be obtained in a short time as compared to the case where the static magnetic field is used, and as a result, a rare earth magnet having a high residual magnetic flux density Br is manufactured. . However, if a pulse magnetic field H is applied to the molded body 10 held in a mold made of an electrical conductor (for example, metal), the magnetic field acting on the mold will be lower than when a static magnetic field is applied. Since the intensity rapidly changes in a short time, the eddy current is likely to flow to the mold by electromagnetic induction, and the reverse magnetic field is easily generated.

  The impact associated with the application of the pulsed magnetic field H may cause the mold 2 to move within the double coil 15. The movement of the mold 2 may cause a gap in the mold 2 and the alloy powder may leak from the gap. Therefore, in order to suppress the movement of the mold 2, the mold 2 disposed in the double coil 15 may be fixed by a jig or the like.

  Part or all of the mold 2 may be formed of nonmagnetic material (nonferromagnetic material). In other words, part or all of the mold 2 may be formed of at least one selected from the group consisting of a diamagnetic body, a paramagnetic body and an antiferromagnetic body. When part or all of the mold 2 is formed of a nonmagnetic material, the vibration of the mold 2 due to the magnetism of the mold 2 itself is easily suppressed in the orientation step, and breakage of the molded body held in the mold 2 It is easy to be suppressed. The nonmagnetic material contained in the mold 2 may be, for example, a resin described later. As the nonmagnetic material other than resin, for example, at least one selected from the group consisting of stainless steel, aluminum, molybdenum, tungsten, a carbonaceous material, and ceramics may be included in the mold 2. The lower mold 8, the side mold 6, and the upper mold 4 may all be formed of nonmagnetic material. Of the lower mold 8, the side mold 6, and the upper mold 4, only the side mold 6 may be formed of a nonmagnetic material. Of the lower mold 8, the side mold 6, and the upper mold 4, only the lower mold 8 may be formed of a nonmagnetic material. Of the lower mold 8, the side mold 6, and the upper mold 4, only the upper mold 4 may be formed of a nonmagnetic material. Of the lower mold 8, the side mold 6, and the upper mold 4, the side mold 6 and the upper mold 4 may be formed of a nonmagnetic material, and the lower mold 8 may be formed of a composition other than the nonmagnetic material. . Of the lower mold 8, the side mold 6 and the upper mold 4, the lower mold 8 and the side mold 6 may be formed of a nonmagnetic material, and the upper mold 4 may be formed of a composition other than a nonmagnetic material . Of the lower mold 8, the side mold 6, and the upper mold 4, the lower mold 8 and the upper mold 4 may be formed of a nonmagnetic material, and the side mold 6 may be formed of a composition other than the nonmagnetic material .

  Part or all of the mold 2 may be formed of a resin. When part or all of the mold 2 is formed of resin, when applying a pulse magnetic field H to the metal powder disposed in the mold 2, eddy current does not easily flow in the mold 2 and a reverse magnetic field is also generated. hard. Therefore, the phenomenon in which the metal powder constituting the molded body 10 is attracted to the surface of the mold 2 by the reverse magnetic field is suppressed. As a result, the density of the molded body 10 is likely to be uniform, and cracks are less likely to occur in the sintered body (rare earth magnet) in the sintering step. Further, by suppressing the eddy current and the reverse magnetic field in the orientation step, the degree of orientation of the metal powder is improved, and as a result, the magnetic properties of the rare earth magnet are also improved. Furthermore, since part or all of the mold 2 is formed of resin, temperature increase of the mold 2 due to eddy current loss is suppressed in the orientation step, and impact (magnetic force) acts instantaneously on the mold 2 itself. hard. As a result, the mold 2 becomes difficult to wear out.

  If the pulse magnetic field H is applied to the molded body 10 temporarily held in the mold, the saturation magnetic flux density of the metal (for example, iron) constituting the mold is limited, so that the molded body 10 in the mold is effective. The strength of the acting magnetic field is lower than the strength of the pulse magnetic field H outside the mold. However, if the mold 2 is made of resin, a strong pulsed magnetic field H can be applied to the compact 10 in the mold 2.

The resin constituting the mold 2 may be an insulating resin. By using the mold 2 made of an insulating resin, eddy current and reverse magnetic field are easily suppressed in the orientation step, and it is difficult for an impact to act instantaneously on the mold 2 itself. The resistivity of the resin may be, for example, 1 Ω · m or more and 1 × 10 ²⁰ Ω · m or less, preferably 1 × 10 ⁹ Ω · m or more and 1 × 10 ¹⁶ Ω · m or less. By forming the mold 2 from a resin having a high resistivity in this manner, eddy currents and a reverse magnetic field are easily suppressed in the orientation step, and it is difficult for an impact to act instantaneously on the mold 2 itself. The resin used to form mold 2 is, for example, acrylic resin, polyethylene, polyethylene terephthalate, polypropylene, polystyrene, ABS resin (copolymer of acrylonitrile, butadiene and styrene), ethyl cellulose, paraffin wax, styrene butadiene copolymer Ethylene / vinyl acetate copolymer, ethylene / ethyl acrylate copolymer, atactic polypropylene, methacrylic acid copolymer, polyamide, polybutene, polyvinyl alcohol, phenol resin and polyester resin, and silicone resin (silicone) It may be one or more selected. You may use the type | mold 2 comprised from electroconductive plastics whose resistivity is higher than metal and graphite. As a result, charging of the mold 2 is suppressed, and adhesion of the alloy powder to the mold 2 due to charging of the mold 2 is suppressed.

  As the contact area between the portion where the eddy current flows in the mold 2 and the compact 10 is wider, cracking of the sintered body due to the eddy current and deterioration of the magnetic characteristics are more likely to occur. In the present embodiment, among the lower mold 8, the side mold 6 and the upper mold 4, the contact area between the side mold 6 and the molded body 10 is the contact area between the lower mold 8 and the upper mold 4 and the molded body 10. It is wider than. Therefore, at least the side mold 6 of the lower mold 8, the side mold 6, and the upper mold 4 may be formed of a resin. By forming the side mold 6 having a large area in contact with the molded body 10 from resin, generation of eddy current and reverse magnetic field in the side mold 6 is effectively suppressed, and cracking of the rare earth magnet caused by eddy current and reverse magnetic field And deterioration of the magnetic properties are easily suppressed.

  In the mold 2, the position of the portion formed of the resin is not limited. Depending on the size and shape of the mold 2 or the direction of the pulse magnetic field H, the part of the mold 2 in which the eddy current needs to be suppressed may be formed of resin. For example, in the part of the mold 2 that forms a circuit that circulates in the direction of the pulse magnetic field H that orients the alloy powder, an eddy current and a reverse magnetic field easily occur. That is, when the penetration part of the side die 6 (the inner wall 6a of the side die 6) is parallel to the direction of the pulse magnetic field H, an eddy current and a reverse magnetic field are easily generated. Therefore, in the case where the side mold 6 which is a portion forming the circuit which circulates in the direction of the pulse magnetic field H for orienting the alloy powder in the mold 2 is formed from resin, the eddy current and the reverse magnetic field are easily suppressed .

  The lower mold 8, the side mold 6, and the upper mold 4 may all be formed of resin. Of the lower mold 8, the side mold 6, and the upper mold 4, only the side mold 6 may be formed of a resin. Of the lower mold 8, the side mold 6, and the upper mold 4, only the lower mold 8 may be formed of a resin. Of the lower mold 8, the side mold 6, and the upper mold 4, only the upper mold 4 may be formed of a resin. Of the lower mold 8, the side mold 6, and the upper mold 4, the side mold 6 and the upper mold 4 may be formed of a resin, and the lower mold 8 may be formed of a composition other than a resin. Of the lower mold 8, the side mold 6, and the upper mold 4, the lower mold 8 and the side mold 6 may be formed of a resin, and the upper mold 4 may be formed of a composition other than a resin. Of the lower mold 8, the side mold 6, and the upper mold 4, the lower mold 8 and the upper mold 4 may be formed of a resin, and the side mold 6 may be formed of a composition other than a resin. When a part of the mold 2 is formed of resin, the part of the mold 2 other than the resin is, for example, iron, silicon steel, stainless steel, permalloy, aluminum, molybdenum, tungsten, carbonaceous material, ceramics, and silicon resin And at least one selected from the group consisting of The portion of the mold 2 other than the resin may be formed of an alloy (for example, an aluminum alloy).

  If all of the lower mold 8, the side mold 6, and the upper mold 4 are made of metal, metal scraps are scraped from the side mold 6 or the upper mold 4 due to the friction between the side mold 6 and the upper mold 4 in the molding process. And may be mixed into the molded body 10. Metal scrap (e.g., aluminum or aluminum alloy) mixed in the compact 10 may impair the magnetic properties of the finally obtained rare earth magnet. In contrast, when part or all of the mold 2 is formed of resin, wear debris (resin) of the mold 2 affects the magnetic characteristics of the rare earth magnet as compared to the case where the mold 2 is made of metal only. The impact is reduced. For example, when one of the side molds 6 and the upper mold 4 which rubs in the molding process (for example, the side mold 6) is a resin and the other (for example, the upper mold 4) is a metal, The friction with the mold 4 tends to generate resin scrap having a hardness lower than that of metal instead of metal scrap. Resin scrap is less likely to damage the magnetic properties of the rare earth magnet than metal scrap. For example, only the side mold 6 may be formed of a resin, and the lower mold 8 and the upper mold 4 may be formed of a metal (eg, aluminum or an aluminum alloy).

  Since the contraction rate of the neodymium magnet in the sintering process is anisotropic, it is difficult to accurately predict the shape (especially complicated shape) of the neodymium magnet (sintered body) after contraction. Therefore, for the net shape, trial and error are required to adjust the size and shape of the mold 2, and as the material of the mold 2, a resin that is easy to cut is suitable. That is, in order to efficiently produce a wide variety of rare earth magnets according to various applications, the mold 2 made of resin is suitable. Conventional molds are difficult to process and expensive, so they are not suitable for producing a wide variety of rare earth magnets suitable for various applications.

  When the molding process and orientation process using the same mold 2 are repeated, the inside of the mold 2 may be cleaned each time of molding and orientation. For example, the inside of the mold 2 may be cleaned by attracting the excess alloy powder remaining in the mold 2 with a magnetic field. By cleaning the inside of the mold 2 at each molding and orientation, the accuracy of weighing of the alloy powder molded in the mold 2 is improved, and variations in density and size of the obtained molded body 10 are suppressed. As a result, variations in density, size and magnetic properties of the finally obtained rare earth magnet are suppressed. If the mold 2 is formed of a ferromagnetic metal (for example, iron), the mold 2 itself is attracted by a magnetic field when cleaning the inside of the mold 2, and it is difficult to clean the mold 2. However, when the mold 2 is formed of a resin having no ferromagnetism, the inside of the mold 2 is easy to clean because the mold 2 itself is not attracted by the magnetic field. If the mold 2 is formed of a metal (for example, iron) having ferromagnetism, the mold 2 itself is magnetized in the orientation step, and the alloy powder adheres to the mold 2. Therefore, the degree of orientation of the alloy powder Or the shape retention of the molded body 10 is impaired. However, by using the mold 2 made of resin, the magnetization of the mold 2 itself is suppressed.

  While supplying the alloy powder into the mold 2, the mass of the alloy powder to be formed in the mold 2 may be measured in combination with the mass of the mold 2. When simultaneously measuring the mass of the alloy powder molded in the mold 2 and the mass of the mold 2, the heavier the mass of the mold 2, the lower the accuracy of the balance, and the accuracy of the measurement of the mass of the alloy powder itself Also falls. However, by using the mold 2 made of a resin lighter than the conventional metal, it is possible to measure the mass of the alloy powder together with the mass of the mold 2 itself with high accuracy.

  The alloy powder may be oriented in a pulse magnetic field H while pressing the alloy powder in the mold 2. That is, also in the orientation step, the compact 10 in the mold 2 may be compressed. The pressure exerted on the compact 10 by the mold 2 may be adjusted to 0.049 MPa or more and 20 MPa or less for the above-mentioned reason.

  In the separation step, at least a part of the mold 2 is separated from the compact 10. For example, in the separation step, the molded body 10 may be placed on the lower mold 8 by separating and removing the upper mold 4 and the side mold 6 from the molded body 10. The side mold 6 and the upper mold 4 holding the molded body 10 may be separated from the lower mold 8, and the side mold 6 and the upper mold 4 holding the molded body 10 may be placed on the heating process tray. Then, the side mold 6 and the upper mold 4 may be separated from the compact 10 and the compact 10 may be placed on the heating process tray. One or both of the upper mold 4 and the side mold 6 may be capable of disassembly and assembly. In the separation step, one or both of the upper mold 4 and the side mold 6 may be removed from the molded body 10 by decomposing one or both of the upper mold 4 and the side mold 6.

The density of the formed body 10 (the formed body 10 before the heating step) subjected to the forming step and the orientation step is 3.0 g / cm ³ or more and 4.4 g / cm ³ or less, preferably 3.2 g / cm ³ or more and 4.2 g / cm ³ or less, more preferably it has been adjusted to be equal to or less than 3.4 g / cm ³ or more 4.0 g / cm ^3. The density of the shaped body 10 may be adjusted, for example, by the pressure exerted by the mold 2 on the shaped body 10. The density of the compact 10 may be adjusted, for example, by the mass of the alloy powder supplied into the mold 2.

  Following the separation step, a heating step may be performed. In the heating step, the temperature of the green body 10 may be adjusted to 200 ° C. or higher and 450 ° C. or lower by heating the green body 10. In the heating step, the temperature of the molded body 10 may be adjusted to 200 ° C. or more and 400 ° C. or less, or 200 ° C. or more and 350 ° C. or less. In the forming step, since the pressure applied to the alloy powder is lower than that of the conventional high-pressure magnetic field pressing method, the alloy powder is hard to be pressed and solidified, and the obtained molded body 10 is easily broken. However, the shape retention property of the molded body 10 is improved by the heating step.

  In the heating step, when the temperature of the formed body 10 reaches 200 ° C. or more, the formed body 10 starts to solidify, and the shape retention property of the formed body 10 is improved. In other words, when the temperature of the formed body 10 becomes 200 ° C. or more, the mechanical strength of the formed body 10 is improved. Since the shape retention property of the molded body 10 is improved, the molded body 10 is less likely to be broken during transportation of the molded body 10 or handling of the molded body 10 in a later step. For example, when the green body 10 is gripped by a transport chuck or the like and arranged on the sintering tray, the green body 10 is unlikely to collapse. As a result, defects of the finally obtained rare earth magnet are suppressed.

  If the temperature of the molded body 10 exceeds 450 ° C. in the heating step, cracks are likely to be formed in the molded body 10 in the sintering step performed after the heating step. It is not clear why the crack is formed. For example, there is a possibility that a crack may be formed in the compact 10 by blowing out the hydrogen remaining in the compact 10 as a gas to the outside of the compact 10 due to the rapid temperature rise of the compact 10 in the heating step. However, by adjusting the temperature of the green body 10 to 450 ° C. or less in the heating step, cracking of the green body 10 in the sintering step is suppressed. As a result, cracks in the finally obtained rare earth magnet are also easily suppressed. Moreover, in order to adjust the temperature of the molded object 10 to 450 degrees C or less in a heating process, the time which temperature rising or cooling of the molded object 10 requires is suppressed, and productivity of a rare earth magnet improves. In addition, since the temperature of the molded body 10 in the heating step is 450 ° C. or lower and lower than a general sintering temperature, even if the molded body 10 is heated with a part of the mold 2 (for example, the lower mold 8), It is difficult for the deterioration of No. 2 or the chemical reaction between the molded body 10 and the mold 2 to occur. Therefore, even the mold 2 composed of a composition (resin) which is not necessarily high in heat resistance can be used.

  By adjusting the temperature of the molded body 10 to 200 ° C. or more and 450 ° C. or less, the mechanism for improving the shape retention property of the molded body 10 is not clear. For example, an organic substance (for example, a lubricant) added to the alloy powder may become carbon in the heating step, and the alloy powder (alloy particles) may be bound to each other via the carbon. As a result, the shape retention of the molded body 10 may be improved. If the temperature of the molded body 10 exceeds 450 ° C. in the heating step, carbides of the metal constituting the alloy powder may be generated, or the alloy powders (alloy particles) may be directly sintered to each other. On the other hand, when the temperature of the formed body 10 is adjusted to 200 ° C. or more and 450 ° C. or less, metal carbides are not necessarily generated, and the alloy particles are not necessarily directly sintered.

  The time for maintaining the temperature of the formed body 10 at 200 ° C. or more and 450 ° C. or less in the heating step is not particularly limited, and may be appropriately adjusted according to the size and shape of the formed body 10.

  In the heating step, the formed body 10 may be heated by irradiating the formed body 10 with infrared radiation. By directly heating the formed body 10 by irradiation of infrared rays (that is, radiant heat), the time required for the temperature rise of the formed body 10 is shortened, and the production efficiency and the energy efficiency are increased, as compared with the case of heating by conduction or convection. However, in the heating step, the formed body 10 may be heated by heat conduction or convection in the heating furnace. The wavelength of the infrared light may be, for example, 0.75 μm or more and 1000 μm or less, preferably 0.75 μm or more and 30 μm or less. The infrared radiation may be at least one selected from the group consisting of near infrared radiation, short wavelength infrared radiation, middle wavelength infrared radiation, long wavelength infrared radiation (thermal infrared radiation), and far infrared radiation. Of the above infrared rays, near infrared rays are relatively easily absorbed by metals. Therefore, when irradiating a near infrared ray to a molded object, it is easy to heat up a metal (alloy powder) in a short time. On the other hand, among the above infrared rays, far infrared rays are relatively easily absorbed by the organic matter and easily reflected by the metal (alloy powder). Therefore, when far-infrared rays are irradiated to the molded object 10, the organic substance (for example, lubricant) mentioned above is easily heated selectively, and the molded object 10 tends to be hardened by the above-mentioned mechanism resulting from the organic substance. When irradiating the infrared rays to the molded body 10, for example, an infrared heater (ceramic heater or the like) or an infrared lamp may be used.

  When the molded body 10 separated from part or all of the mold 2 is heated in the heating step, deterioration of the mold 2 due to heating (for example, deformation, hardening or wear of the mold 2) is easily suppressed, and the molded body 10 and the mold The burn-in with 2 is also easily suppressed. Moreover, when heating the molded object 10 isolate | separated from one part or all part of the type | mold 2, the type | mold 2 is hard to thermally insulate a heat | fever and the molded object 10 tends to be heated. As a result, the shape retention of the molded body 10 is improved. When heating the molded body 10 separated from part or all of the mold 2, the possibility of the mold 2 chemically reacting with the molded body 10 is low. Therefore, heat resistance is not necessarily required for the mold 2, and the material of the mold 2 is not easily restricted. Therefore, it is easy to process as a raw material of type | mold 2 to a desired size and shape, and to select cheap material. Temporarily, when the molded body 10 and the whole of the mold 2 are collectively heated in the heating step, stress acts on the molded body 10 due to the difference in the thermal expansion coefficient between the molded body 10 and the mold 2 The molded body 10 is easily deformed or broken. Moreover, when the molded object 10 and all of the type | mold 2 are heated collectively in a heating process, the volume and heat capacity of the whole heating object are large. As a result, the number of molded bodies 10 heated collectively is limited, the time required for the heating process is extended, energy is wasted, and the productivity of the rare earth magnet is reduced.

  In the heating step, for example, the compact 10 placed on the lower mold 8 may be heated. In the heating step, the formed body 10 placed on the heating step tray may be heated. In the heating step, the molded body 10 may be heated in an inert gas or vacuum to suppress oxidation of the molded body 10. The inert gas may be a noble gas such as argon.

  In the heating step, after the temperature of the formed body 10 is adjusted to 200 ° C. or more and 450 ° C. or less, the formed body 10 may be cooled to 100 ° C. or less. When the surface of the chuck used to convey the formed body 10 after the heating step is made of a resin, the cooling of the formed body 10 suppresses the chemical reaction between the surface of the chuck and the formed body 10 to deteriorate the chuck, Contamination of the surface of the molded body 10 is suppressed. The cooling method may be, for example, natural cooling.

  In the sintering step, the compact after the orientation step is heated and sintered. In the sintering step, the alloy particles in the compact 10 are sintered to obtain a sintered body (rare earth magnet). After the orientation step, the sintering step may be performed without the above heating step. After the orientation step, the sintering step may be performed through the above heating step.

The density of the compact 10 to be sintered in the sintering step (the density of the compact 10 immediately before the sintering step) may be adjusted to 3.0 g / cm ³ or more and 4.4 g / cm ³ or less. The density of the compact 10 to be sintered in the sintering step (the density of the compact 10 immediately before the sintering step) is preferably 3.2 g / cm ³ or more and 4.2 g / cm ³ or less, more preferably 3.4 g / cm ^3. cm ³ or more 4.0 g / cm ³ may have been adjusted as follows. The lower the pressure exerted by the mold on the compact 10 (alloy powder) in the compacting process and the orienting process, the lower the density of the compact 10 immediately before the sintering process tends to be. Further, as the pressure exerted by the mold on the compact 10 (alloy powder) in the forming step and the orientation step is lower, the alloy powder constituting the compact 10 is more easily rotated and oriented along the magnetic field. As a result, the residual magnetic flux density Br of the finally obtained rare earth magnet tends to increase. Therefore, it can be said that the residual magnetic flux density Br of the rare earth magnet is easily increased as the density of the compact 10 immediately before the sintering step is lower. However, if the pressure exerted on the compact 10 (alloy powder) by the mold in the compacting step and the orienting step is too low, the shape retention property (mechanical strength) of the compact 10 is insufficient, and the compact 10 associated with the separation step. The friction between the mold and the mold disturbs the degree of orientation of the alloy powder located on the surface of the compact 10. As a result, the residual magnetic flux density Br of the finally obtained rare earth magnet decreases. Therefore, when the density of the compact 10 immediately before the sintering step is too low, it can be said that the residual magnetic flux density Br of the rare earth magnet is low. On the other hand, the higher the pressure applied to the formed body 10 (alloy powder) from the forming step to the sintering step, the higher the density of the formed body 10 immediately before the sintering step, and the shape retention of the formed body 10 (machine Strength) is high. As a result, cracks in the finally obtained rare earth magnet are easily suppressed. Therefore, it can be said that cracks in the rare earth magnet are more easily suppressed as the density of the compact 10 immediately before the sintering step is higher. However, if the pressure exerted by the mold on the compact 10 (alloy powder) in the forming step and the orientation step is too high, cracks are likely to be formed in the compact 10 due to springback, and the rare earth magnet obtained from the compact 10 is cracked. Will remain. Springback is a phenomenon in which the compact 10 expands when the pressure is released after the alloy powder is pressed and shaped. As described above, the density of the compact 10 immediately before the sintering step is correlated to the residual magnetic flux density Br and the crack of the rare earth magnet. By adjusting the density of the compact 10 immediately before the sintering step within the above range, the residual magnetic flux density Br of the rare earth magnet is likely to increase, and cracking in the rare earth magnet is likely to be suppressed.

  The density of the formed body 10 immediately before the sintering step may be adjusted by the mass of the alloy powder introduced into the mold 2 in the forming step and the pressure exerted on the formed body 10 (alloy powder) by the mold 2 in the forming step. The density of the formed body 10 immediately before the sintering step may be adjusted within the above numerical range by compressing the formed body 10 (alloy powder) a plurality of times between the forming step and the sintering step. That is, the molded body 10 may be further pressurized in a process different from the molding process. In order to suppress the cracks in the rare earth magnet, it is better to adjust the pressure exerted on the metal powder to 0.049 MPa or more and 20 MPa or less between the molding process and the sintering process.

  In the sintering step, the compact 10 may be heated together with the mold 2. In the sintering step, it is preferable to sinter the compact 10 separated from part or all of the mold 2.

  If the molded body 10 and the mold 2 are heated together without separating the molded body 10 from the resin mold 2 in the sintering step, the resin constituting the mold 2 is decomposed, and the carbon component derived from the resin Is mixed into the molded body 10. Even if the mold composed of the resin is burnt away in the process of the sintering step, it is difficult to sufficiently suppress the carbon component generated along with the burnout from being mixed in the molded body 10. As a result, the carbon component remains in the sintered body (rare earth magnet), and the carbon component impairs the magnetic properties (for example, coercivity) of the rare earth magnet. On the other hand, when the molded body 10 separated from the mold 2 is heated, the carbon component derived from the resin is less likely to be mixed into the molded body 10, and the magnetic properties (for example, coercivity) of the rare earth magnet are less likely to be impaired by the carbon component.

  Temporarily, in the sintering step, when the molded body 10 and part or all of the mold 2 are heated at one time, the molded body 10 is caused due to the difference in the coefficient of thermal expansion between the molded body 10 and the mold 2. Stress tends to act on the molded body 10, and the molded body 10 may be deformed or broken. Furthermore, when the compact 10 and the whole of the mold 2 are collectively heated in the sintering step, the volume and heat capacity of the entire object to be heated are large. As a result, the number of the compacts 10 heated collectively is limited, the time required for the sintering process becomes long, energy is wasted, and the productivity of the rare earth magnet is lowered. On the other hand, when heating the molded object 10 isolate | separated from the type | mold 2, compared with the case where the molded object 10 and all the type | molds 2 are heated collectively, the volume and heat capacity of whole heating object are small. As a result, it is easy to raise the temperature of a large number of compacts 10 collectively, the time and energy required for the sintering process are easily suppressed, and the productivity of the rare earth magnet is improved.

  In the sintering step, the compact 10 placed on the lower mold 8 may be transferred onto a sintering tray. In the sintering step, the compact 10 placed for the heating step may be transferred onto a sintering tray. Since the shape retention property of the green body 10 is improved in the heating step, breakage of the green body 10 is suppressed when the green body 10 is gripped by the transport chuck and aligned on the sintering tray.

  In the sintering step, the plurality of compacts 10 may be placed on the sintering tray, and the plurality of compacts 10 placed on the sintering tray may be heated at one time. The productivity of the rare earth magnet is improved by arranging a large number of compacts 10 at narrow intervals on the sintering tray and heating the large number of compacts 10 collectively.

  The composition of the tray for sintering may be any composition that does not easily react with the compact 10 at the time of sintering, and hardly produces a substance that contaminates the compact 10. For example, the sintering tray may be comprised of molybdenum or a molybdenum alloy.

  The sintering temperature may be, for example, 900 ° C. or more and 1200 ° C. or less. The sintering time may be, for example, 0.1 hours or more and 100 hours or less. The sintering process may be repeated. In the sintering step, the compact 10 may be heated in an inert gas or vacuum. The inert gas may be a noble gas such as argon.

  The sintered body may be subjected to an aging treatment. 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 example, for 0.1 hours or more and 100 hours or less. Aging treatment may be performed in an inert gas or vacuum. Aging treatment may consist of multi-step heat treatment with 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 of 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.

  The size and shape of the rare earth magnet vary depending on the application of the rare earth magnet and is not particularly limited. The shape of the rare earth magnet may be, for example, a rectangular parallelepiped, a cube, a polygonal prism, a segment, a fan, a rectangle, a plate, a sphere, a disc, a cylinder, a ring, or a capsule. The shape of the cross section of the rare earth magnet may be, for example, a polygon, a chord, an arc, or a circle. The size and shape of the mold 2 or cavity correspond to the size and shape of the rare earth magnet and is not limited.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Example 1
By the strip casting method, the composition is Nd ₂₉ Dy ₁ Fe _bal. A flake-like alloy of B ₁ was produced. The alloy was roughly crushed by a hydrogen storage method to obtain a coarse powder. Oleic acid amide (lubricant) was added to the crude powder. Subsequently, the coarse powder was pulverized by a jet mill in an inert gas to obtain a fine powder (a metal powder containing a rare earth element). The content of oleic acid amide in the fine powder was 0.1% by mass. The particle diameter D50 of the fine powder was adjusted to 4 μm. The content of oxygen in the fine powder was 800 mass ppm or less. The content of nitrogen in the fine powder was 500 mass ppm or less. The content of carbon in the fine powder was 1,500 ppm by mass or less.

  In the molding step, a fine powder to which oleic acid amide was added was fed into a mold to form a molded body. The details of the molding process were as follows.

  The mold was provided with a rectangular lower mold, a rectangular parallelepiped side mold arranged above the lower mold, and an upper mold arranged above the side mold. The upper and lower molds were formed of aluminum. The side mold was formed of acrylic resin. A rectangular parallelepiped space penetrates in the vertical direction at the central portion of the side mold. That is, the side mold was cylindrical. The upper mold had a shape fitted into the side mold. In the molding process, the side mold was placed on the lower mold, and the opening on the lower surface side of the side mold was closed with the lower mold. The dimensions of the side mold and the space enclosed by the lower mold (cavity) were 20 mm × 12 mm × 8 mm. Subsequently, fine powder of a predetermined mass was filled into the side mold through the opening on the upper surface side of the side mold. Leveling of the fine powder in the cavity was performed by vibrating the whole of the side mold and the lower mold in which the fine powder was held. Subsequently, the fine powder in the cavity was made more compact by tapping. After tapping, the upper mold was inserted into the side mold and the fine powder in the side mold was compressed at the tip face of the upper mold. In the molding step, the pressure exerted by the upper mold on the fine powder (molded body) in the mold was adjusted to 0.14 MPa.

Fifty molded articles were produced by the above procedure. As shown to (a) in FIGS. 3-5 and FIG. 6, the molded object 10 was a rectangular parallelepiped. The dimensions of the molded body 10 were 20 mm × 12 mm × 6 mm. The density of the compact 10 immediately after the molding process was calculated from the volume and mass of the compact 10. The density of the molded body of Example 1 immediately after the molding step (before the orientation step) was adjusted to 3.6 g / cm ³ .

  In the orientation step subsequent to the forming step, a magnetic field generator equipped with an AC power supply was used. The magnetic field generator was provided with the double coil 15 and the capacitor shown in FIGS. Both the inductance L of the double coil 15 and the capacitance C of the capacitor were freely variable, and according to the magnetic field generator, it was possible to generate a pulsed magnetic field having a desired alternating current decay waveform. The double coil 15 was provided with two coils 17a and 17b arranged to have the same central axis A. One coil 17a and the other coil 17b that constitute the double coil 15 are completely the same coil. When viewed in the direction parallel to the central axis A, one coil 17a completely overlapped with the other coil 17b. The distance D between the two coils 17a and 17b was freely variable.

  As shown in FIGS. 3 to 5, in the orientation step, the molded body 10 held in the mold 2 was placed in the double coil 15, and the mold 2 was fixed by a jig. As shown in (a) in FIG. 5 and FIG. 6, the inside of the mold 2 is such that the rectangular surface of the molded body 10 is perpendicular to the direction of the central axis A (pulsed magnetic field H) of the double coil 15. Were placed in the double coil 15. Then, a pulse magnetic field H which attenuates while being reversed as time passes is applied to the compact 10 in the mold 2. By the application of this pulse magnetic field H (attenuating alternating magnetic field), the individual fine powders constituting the compact 10 were oriented and demagnetized. In the orientation step, the intensity of the first wave (maximum magnetic field) of the pulsed magnetic field H was adjusted to 6.1 T, and the period of the first wave was adjusted to 9 milliseconds. As shown in FIG. 5, the distance between the two coils 17a and 17b in the direction parallel to the central axis A of the double coil 15 is represented by D, and the inner diameter of each of the coils 17a and 17b is 2R. Be done. D / 2R of Example 1 was a value shown in Table 1 below. As shown in (a) in FIGS. 4, 5 and 6, the maximum value of the width of the molded body 10 (length of the diagonal Ld) in the direction perpendicular to the central axis A of the double coil 15 is W expressed. 2R / W of Example 1 was a value shown in the following Table 1.

  After the orientation step, the upper mold and the side mold were separated from the compact. The molded body placed on the lower mold was heated by irradiation with infrared rays in a heating furnace together with the lower mold. The temperature of the molded body (maximum temperature) during heating was maintained at 300.degree.

  The compact after heating was separated from the lower mold, and 50 compacts were placed on a sintering tray. The sintering tray was composed of molybdenum. The density of the compact of Example 1 immediately before the sintering step was substantially the same as the density of the compact immediately after the molding step.

  In the sintering step, the compact on the sintering tray was sintered in a vacuum atmosphere. The sintering temperature (maximum temperature) was adjusted to 1080.degree. The sintering time was adjusted to 4 hours. Following the sintering step, aging treatment was performed. In the aging treatment, the sintered body was heated at 900 ° C. (maximum temperature) for 1 hour. Subsequently, the sintered body was heated at 500 ° C. (maximum temperature) for 1 hour.

  Fifty sintered bodies (rare earth magnets) were obtained by the above steps. All rare earth magnets were also rectangular parallelepipeds.

<Measurement of deformation amount ΔT of rare earth magnet>
Before polishing the rare earth magnet, the deformation amount ΔT of the rare earth magnet was measured by the following method.

  As shown in FIG. 8, the rectangular shaped surface of the rare earth magnet 100 is divided into nine equal areas a, b, c, d, e, f, g, h and i, and the thickness of each area is determined. T was measured. The partitioned surface corresponds to the surface of the molded body 10 disposed perpendicularly to the central axis A (pulsed magnetic field H) of the double coil 15 in the orientation step. The thickness T of each region corresponds to the thickness of the molded body 10 in the direction parallel to the central axis A (pulse magnetic field H) of the double coil 15 in the orientation step. The difference (the amount of deformation ΔT) between the maximum value and the minimum value among the thicknesses of the nine regions was calculated. The smaller the ΔT, the more the deformation of the rare earth magnet is suppressed. ΔT is preferably 140 μm or less, more preferably 120 μm or less, and most preferably 80 μm or less. ΔT of Example 1 was a value shown in Table 1 below.

<Measurement of relative density of rare earth magnet>
Subsequently, the end face of each sintered body (rare earth magnet) was polished to adjust the size of each rare earth magnet to 15 mm × 10 mm × 4 mm.

  The weight of each of the 50 sized rare earth magnets was measured. The relative density of each rare earth magnet was calculated from the weight and size. The relative density of all 50 rare earth magnets was 99.5% or more.

<Measurement of crack occurrence rate>
By visually observing the 50 rare earth magnets, it was examined whether or not a crack was generated in each rare earth magnet. The incidence of cracks in Example 1 was less than 10%. The crack generation rate is a percentage of the number n of the rare earth magnets in which the crack was generated among the 50 rare earth magnets of Example 1 (that is, (n / 50) × 100 = 2 n).

<Measurement of variation Vf of orientation degree fc of rare earth magnet>
As shown in FIG. 8, the rare earth magnet 100 was equally divided by a diamond cutter to form nine magnet pieces a, b, c, d, e, f, g, h and i. The end face of each magnet piece was polished, and the dimensions of each magnet piece were adjusted to 4 mm × 3 mm × 4 mm. Subsequently, the XRD pattern for each magnet piece was measured. The surface of each magnet piece on which X-rays are incident in the measurement of the XRD pattern corresponds to the plane (the plane corresponding to the plane 100s in FIG. 8) perpendicular to the central axis A (pulse magnetic field H) of the double coil 15. It was The XRD pattern of each magnet piece was measured in the range where the diffraction angle 2θ is 20 ° or more and 70 ° or less. The angular step in the measurement of the XRD pattern was 0.1 ° per step. Based on the XRD pattern, the degree of orientation fc of each magnet piece was calculated by the Lotgering method described above. As shown in FIG. 8, among the plurality of magnet pieces obtained by equally dividing the rare earth magnet 100, the orientation degree of the magnet piece having the highest degree of orientation is represented as fc (max). The orientation degree of the magnet piece having the lowest degree of orientation among the plurality of magnet pieces is expressed as fc (min). Based on the above premise, the variation Vf of the degree of orientation fc of the rare earth magnet was calculated from the following formula 2. As described above, the smaller the variation Vf in the degree of orientation fc of the rare earth magnet, the better. It is preferable that Vf is 10% or less. The variation Vf of the degree of orientation fc of the rare earth magnet of Example 1 was a value shown in Table 1 below.
Vf (%) = fc (max)-fc (min) (2)

(Comparative example 1)
The magnetic field generator used in the orientation step of Comparative Example 1 was provided with one air core coil and a capacitor instead of the double coil 15. Both the inductance L of the air core coil and the capacitance C of the capacitor were freely variable, and according to the magnetic field generator, it was possible to generate a pulse magnetic field having a desired alternating current attenuation waveform.

  In the orientation step of Comparative Example 1, the molded body held in the mold was disposed in the air core coil, and the mold was fixed by a jig. Then, a pulse magnetic field which decays while being reversed as time passes was applied to the compact in the mold.

  As described above, the rare earth magnet of Comparative Example 1 was produced in the same manner as in Example 1 except that the double coil was not used. In the same manner as Example 1, ΔT and Vf of Comparative Example 1 were measured. ΔT and Vf of Comparative Example 1 were values shown in Table 1 below.

(Examples 2 to 7)
In the molding processes of Examples 2 to 7, the values of 2R / W shown in Table 1 below were obtained by changing the size of the molded body 10 using a mold having a size different from that of the mold used in Example 1. Adjusted to

  The rare earth magnets of Examples 2 to 7 were produced in the same manner as in Example 1 except for 2R / W. In the same manner as in Example 1, ΔT and Vf in each of Examples 2 to 7 were measured. The ΔT and Vf in Examples 2 to 7 were the values shown in Table 1 below.

(Example 8)
The dimensions of the mold used in the molding step of Example 8 were the same as those of the mold used in Example 1. However, the entire mold used in the molding step of Example 8 was made of carbon. Then, in the sintering step of Example 8, the compact 10 was not separated from the mold. That is, in the sintering step of Example 8, the compact 10 was heated together with the mold. The rare earth magnet of Example 8 was produced in the same manner as in Example 1 except for the composition of the mold and the sintering step. In the same manner as Example 1, ΔT and Vf of Example 8 were measured. ΔT and Vf of Example 8 were values shown in Table 1 below.

(Examples 9 to 15)
In the orientation steps of Examples 9-15, the D / 2 R of Examples 9-15 is adjusted to the values shown in Table 2 below by changing the distance D between the coil 17a and the coil 17b. did. Rare earth magnets of Examples 9 to 15 were produced in the same manner as in Example 1 except for D / 2R. In the same manner as in Example 1, ΔT and Vf in each of Examples 9 to 15 were measured. ΔT and Vf of Example 4 were values shown in Table 2 below.

(Examples 16 to 23)
In each of the forming steps of Examples 16 to 23, the density of the formed body immediately after the forming step (before the orientation step) was adjusted to the value shown in Table 3 below by changing the pressure exerted on the alloy powder by the mold. The rare earth magnets of Examples 16 to 23 were produced in the same manner as in Example 1 except for the density of the compact. In the same manner as in Example 1, ΔT and Vf in each of Examples 16 to 23 were measured. The ΔT and Vf of Examples 16 to 23 were values shown in Table 3 below.

<Measurement of residual magnetic flux density Br of rare earth magnet>
The residual magnetic flux density Br of 50 rare earth magnets of Example 16 was measured using a direct current BH tracer, and from these measured values, the average value of the residual magnetic flux density Br of the rare earth magnet of Example 16 was calculated. The average value of the residual magnetic flux density Br of each of the rare earth magnets of Examples 17 to 23 was calculated in the same manner. The average value of the residual magnetic flux density Br of Example 20 was the largest among the average values of the residual magnetic flux density Br of Examples 16-23. The average value of the residual magnetic flux density Br of Example 20 is hereinafter referred to as Brmax. The average value of the residual magnetic flux density Br of Example n (n is a natural number of 16 to 23) is represented as Brn. Based on these assumptions, the reduction rate ΔBr / Br of the residual magnetic flux density Br is defined by the following formula 3. The ΔBr / Br is preferably 2% or less, more preferably 1% or less. The ΔBr / Br in each of Examples 16 to 23 was a value shown in Table 3 below. It is inferred that the relatively high ΔBr / Br of Example 23 is due to the high density of the compact of Example 23.
ΔBr / Br (%) = (Brmax−Brn) ÷ Brmax × 100 (3)

  In the same manner as in Example 1, the incidence of cracks in Examples 16 to 23 was determined. The incidences of cracks in Examples 16 to 23 were all less than 10%. The incidence of cracks in Example 16 was higher than any of the incidences of cracks in Examples 17-23. It is assumed that the relatively high crack rate of Example 16 is due to the low density of the compact of Example 16.

  According to the method for producing a rare earth magnet according to the present invention, it is possible to produce various types of rare earth magnets according to various applications such as hard disk drive, hybrid car or electric car, and the production amount thereof is Even small amounts can reduce the manufacturing cost.

  DESCRIPTION OF SYMBOLS 2 ... type | mold 4 ... upper mold | type 6 ... side mold type | mold 8 ... lower mold | type 10, 10a, 10b, 10c ... molded body 15 ... double coil 17a, 17b ... coil 100 rare earth magnet, A ... two Central axis common to coils, D: Distance between two coils, R: Inner radius of coil, 2R: Inner diameter of coil, H: Pulsed magnetic field, W: Maximum width of molded body in a direction perpendicular to central axis value.

Claims (7)

A forming step of supplying a metal powder containing a rare earth element into a mold to form a formed body;
An orientation step of orientating the metal powder contained in the compact by applying a pulse magnetic field to the compact held in the mold;
A sintering step of sintering the compact after the orientation step;
Equipped with
In the orientation step, the pulse magnetic field is applied to the compact using at least two coils disposed to have the same central axis.
Method of manufacturing rare earth magnet. The inner diameter of one of the coils is equal to the inner diameter of the other of the coils,
The inner diameter of each of the two coils is represented by 2R,
The maximum value of the width of the compact in the direction perpendicular to the central axis is represented by W,
2R is W or more,
In the orientation step, the molded body is disposed inside the two coils.
The manufacturing method of the rare earth magnet of Claim 1. The inner diameter of one of the coils is equal to the inner diameter of the other of the coils,
The inner diameter of each of the two coils is represented by 2R,
The distance between the two coils in a direction parallel to the central axis is represented by D,
D / 2R is greater than 0 and less than or equal to 0.55,
In the orientation step, the molded body is disposed inside the two coils.
The manufacturing method of the rare earth magnet of Claim 1 or 2. Before the orientation step, the density of the molded body is adjusted to 3.0 g / cm ³ or more and 4.4 g / cm ³ or less.
The manufacturing method of the rare earth magnet as described in any one of Claims 1-3. At least a portion of the mold is formed of non-magnetic material,
The manufacturing method of the rare earth magnet as described in any one of Claims 1-4. At least a portion of the mold is formed of a resin,
The manufacturing method of the rare earth magnet as described in any one of Claims 1-5. In the sintering step, the compact separated from the mold is sintered.
The manufacturing method of the rare earth magnet as described in any one of Claims 1-6.

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