JP2018078190A - Method for manufacturing rare earth magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a rare earth magnet capable of improving the shape retention of a compact formed from metal powders containing a rare earth element.SOLUTION: A method for manufacturing a rare earth magnet comprises: a molding step of forming a compact 10b by supplying metal powders containing a rare earth element into a die 2; an orientating step of orientating the metal powders contained in the compact 10b by applying a magnetic field to the compact 10b held in the die 2; a separating step of separating the compact 10b from at least a part of the die 2 after the orientating step; and a sintering step of sintering the compact 10b after the separating step. The die 2 includes a lower die 8, a cylindrical side die 6 arranged on the lower die 8, and an upper die 4 inserted into the side die 6 from above the side die 6. The separating step separates the compact 10b from the side die 6 and the upper die 4 by extracting the compact 10b held in the side die 6 from below the side die 6.SELECTED DRAWING: Figure 2

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 yield rate 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.

International Publication No. 2016/047593 Pamphlet

  When the metal powder is molded at a low pressure as in the molding method described in Patent Document 1, durability against high pressure is not required for the mold, and a large-scale and complicated molding apparatus is not required. Therefore, when molding metal powder at a low pressure, the material, size and shape of the mold are not limited, and various types of rare earth magnets can be manufactured relatively easily using molds having various sizes and shapes. it can. The high-pressure magnetic field press method takes a long time to form and orient the metal powder, but by forming the metal powder at a low pressure, the time required for the forming and orientation is greatly shortened and the productivity of the rare earth magnet is improved. To do.

  However, in the molding method described in Patent Document 1, since the metal powder is molded at a low pressure, the metal powder is difficult to solidify. Therefore, the molded body obtained by the molding method described in Patent Document 1 is inferior in shape retaining ability and easily collapses compared to the molded body obtained under high pressure. For this reason, the molded body is damaged when the molded body is taken out of the mold, or the molded body is damaged when the molded body is transported to a facility in a subsequent process (for example, a sintering process).

  The present invention has been made in view of such problems of the prior art, and provides a method for producing a rare earth magnet that improves the shape retention of a compact formed from a metal powder containing a rare earth element. Objective.

  A method for producing a rare earth magnet according to one aspect of the present invention includes supplying a metal powder containing a rare earth element into a mold to form a molded body, and applying a magnetic field to the molded body held in the mold. (Apply) to align the metal powder contained in the molded body, after the alignment process, to separate the molded body from at least a part of the mold, and after the separating process, to sinter the molded body A separating step including a lower mold, a cylindrical side mold disposed on the lower mold, and an upper mold inserted into the side mold from above the side mold. Then, the molded body is separated from the side mold and the upper mold by extracting the molded body held in the side mold from below the side mold.

  In one aspect of the invention, the side mold may be seamless.

  In one aspect of the present invention, the space surrounded by the cylindrical side mold may expand as it approaches the lower surface of the side mold.

  In the separation step according to one aspect of the present invention, the upper mold may penetrate the side mold.

  In one aspect of the present invention, the pressure exerted on the metal powder by the mold may be adjusted to 0.049 MPa or more and 20 MPa or less.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the rare earth magnet which improves the shape retention of the molded object formed from the metal powder containing rare earth elements is provided.

It is a typical perspective view of the type | mold (an upper mold | type, a side mold | type, and a lower mold | type) used for a formation process. (A) in FIG. 2, (b) in FIG. 2, (c) in FIG. 2 and (d) in FIG. 2 are schematic cross-sectional views of the mold and the molded body, in which the molding process and separation are performed. An example of a process is shown. (A) in FIG. 3, (b) in FIG. 3, (c) in FIG. 3 and (d) in FIG. 3 are schematic cross-sectional views of the mold and the molded body. An example is shown. 4A is a side view and a bottom view of a modification of the side mold used in the molding process, and FIG. 4B is a side view of another modification of the side mold used in the molding process. 4C is a side view and a bottom view of another modification of the side mold used in the molding process, and FIG. 4D is a side mold used in the molding process. It is the side view and bottom view of other modifications.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals. The present invention is not limited to the following embodiment. 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 drawings.

In the present embodiment, the rare earth magnet means a sintered magnet. In the rare earth magnet manufacturing method, an alloy is first cast. The casting method may be, for example, a strip casting method. The alloy may be in the form of flakes or ingots. The alloy includes a rare earth element R. The rare earth element R 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. In addition to the rare earth element R, 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. It may contain at least one element selected. 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 material for the alloy may be prepared by weighing and blending the starting materials containing the above 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 R is larger than that of the main phase. The grain boundary phase may include a B-rich phase, an oxide phase, or a carbide phase.

  By coarse pulverization of the above alloy, a coarse alloy powder is obtained. In the coarse pulverization, for example, the alloy may be pulverized by occluding hydrogen in the alloy grain boundaries (R-rich phase). In the coarse pulverization of the alloy, a mechanical pulverization method such as a disk mill, a jaw crusher, a brown mill, or a stamp mill may be used. The particle size of the coarse powder obtained by coarse pulverization may be, for example, 10 μm or more and 100 μm or less.

  Fine powder of the alloy is obtained by fine grinding of the coarse powder. In the fine pulverization, the alloy powder may be pulverized by a jet mill, a ball mill, a vibration 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, 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 pulverization. An organic substance may be added to the fine powder obtained by fine pulverization. That is, the organic substance may be mixed with the metal powder either before or after pulverization. The organic substance functions as a lubricant, for example. By adding the lubricant to the metal powder, the aggregation of the metal powder is suppressed by adding the lubricant to the metal powder. Further, by adding the lubricant to the metal powder, the friction between the mold and the metal powder is easily suppressed in the subsequent process. As a result, the metal powder is easily oriented in the orientation step, and it is easy to suppress scratches on the surface of the molded body or the surface of the mold obtained from the metal powder. The organic substance may be, for example, a fatty acid or a fatty acid derivative. Organic substances include, for example, oleic acid amide, zinc stearate, calcium stearate, stearic acid amide, palmitic acid amide, pentadecylic acid amide, myristic acid amide, lauric acid amide, capric acid amide, pelargonic acid amide, caprylic acid amide, enanthic acid It may be at least one selected from the group consisting of amide, caproic acid amide, valeric acid amide and butyric acid amide. The lubricant may be a powdery organic material. The lubricant may be a liquid organic material. An organic solvent in which a powdery 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 the mold to form a formed body. Part or all of the mold is made of resin. 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 (punched) disposed on the side mold 6. And). A space 6a corresponding to the shape and size of the rare earth magnet penetrates the side mold 6 in the vertical direction. The side mold 6 may be rephrased as a mold side wall. The lower mold 8 may be plate-shaped. The position of the side mold 6 in the horizontal direction may be fixed by fitting the lower part of the side mold 6 to a claw portion (stops) formed on the surface of the lower mold 8.

  As shown in FIG. 1 and FIG. 2A, in the molding process, the side mold 6 is placed on the lower mold 8, and the opening 6co (hole) on the lower surface 6c side of the side mold 6 is formed. Close with lower mold 8. With such an arrangement, the side mold 6 and the lower mold 8 constitute a cavity (female mold). Subsequently, the alloy powder 10 a is introduced into the cavity (the space 6 a penetrating the side mold 6) from the opening 6 bo (hole) on the upper surface 6 b side of the side mold 6. The cavity may be filled with the alloy powder 10a. That is, the cavity may be filled with the alloy powder 10a. The upper mold 4 may be rephrased as a core (male mold). The upper mold 4 has a shape that fits into a cavity (a space 6 a that penetrates the side mold 6). The length of the upper mold 4 in the vertical direction (Z-axis direction) may be longer than the height of the side mold 6. In this case, the upper mold 4 easily penetrates the side mold 6 in the separation step described later. As shown in FIG. 2B, the upper die 4 is inserted into the side die 6 (inside the cavity), and the end surface of the upper die 4 is pressed against the alloy powder 10a. As a result, the alloy powder 10a is molded in the cavity so as to correspond to the shape and size of the rare earth magnet, and a molded body 10b is obtained. The compact 10b (alloy powder 10a) in the cavity may be compressed by the upper mold 4. However, since the density of the compact 10b is sufficiently increased and a rare earth magnet having a desired density is obtained only by sintering the alloy powders in the compact 10b in the sintering process, the alloy powder in the cavity is not compressed. May be. As long as the relative positional relationship among the lower mold 8, the side mold 6 and the upper mold 4 shown in FIGS. 1 and 2 is maintained, in the molding process, the lower mold 8, the side mold 6 and the upper mold 4 are vertical. It may be inclined with respect to the direction. In other words, as long as the upper mold 4 is positioned on the side mold 6 and the side mold 6 is positioned on the lower mold 8, the entire mold 2 is inclined with respect to the vertical direction in the molding process. Good. For example, in the molding step, the angle formed by the entire mold 2 with respect to the vertical direction (Z-axis direction) may be 0 degree or greater and 45 degrees or less.

In the molding process, the pressure mold 2 on the alloy powder 10a, 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 on the alloy powder 10a by the end surface of the upper mold 4. Thus, by forming the molded body 10b from the alloy powder 10a at a lower pressure than the conventional high-pressure magnetic field pressing method, the friction between the mold 2 and the molded body 10b is easily suppressed, and the mold 2 or the molded body 10b is damaged. (For example, cracks in the molded body 10b) are easily suppressed. When the pressure is too high, the mold 2 is bent, it is difficult to secure the capacity of the target cavity, and it is difficult to obtain the density of the target molded body 10b. 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 this embodiment, since it is not necessary to perform shaping | molding and orientation simultaneously, an orientation process can be performed after a shaping | molding process. By separating the molding process and the orientation process, apparatuses that are smaller and less expensive than conventional ones (for example, a press molding apparatus and a magnetic field application apparatus) can be used for each process. You may perform a shaping | molding process and an orientation process substantially simultaneously.

  As shown in FIG. 1, the side mold 6 may be seamless. That is, the side mold 6 may be seamless. If there is a seam in the side mold 6 (for example, when the side mold 6 can be disassembled into a plurality of members), the alloy powder 10a is transferred from the seam (gap) of the side mold 6 to the mold 2 May leak out. As a result, the shape retention of the molded body 10b is impaired, and for example, a burr may be formed on the molded body 10b. When the side mold 6 is separated from the molded body 10b by disassembling the side mold 6 into a plurality of members, a force may be applied to the molded body 10b by mistake and the molded body 10b may be damaged. When the alloy powder 10a leaks from the joint of the side mold 6 to the outside of the mold 2, the size, density, and shape of the molded body 10b vary, and the size, shape, and magnetic characteristics of the finally obtained rare earth magnet also vary. There is also. These problems are easily suppressed by using the side mold 6 without a seam.

  In the orientation step, a magnetic field is applied to the compact 10b held in the mold 2 so that the alloy powder 10a constituting the compact 10b is oriented in the mold 2 along the magnetic field. The magnetic field may be a pulsed magnetic field or a static magnetic field. For example, the molded body 10b held in the mold 2 is placed inside the air core coil (solenoid coil) together with the mold 2, and an electric current (alternating current) is passed through the air core coil, so that the molding in the mold 2 is performed. A magnetic field may be applied to the body 10b. You may apply a magnetic field to the molded object in a type | mold by sending an electric current through a double coil or a Helmholtz coil. A double coil is a magnetic field generator arranged such that two coils have the same central axis. 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. A magnetic field may be applied to the molded body 10b in the mold 2 using a magnetized yoke. The strength of the magnetic field applied to the molded body 10b in the mold 2 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.

  While pressing the alloy powder 10a in the mold 2, the alloy powder 10a may be oriented by a magnetic field. That is, in the orientation process, the molded body 10b in the mold 2 may be compressed. The pressure exerted on the molded body 10b by the mold 2 may be adjusted to 0.049 MPa or more and 20 MPa or less for the above reason.

  As shown in (b) in FIG. 2 and (c) in FIG. 2, in the separation step, the side mold 6 is moved upward with the position of the upper mold 4 fixed in the vertical direction (Z-axis direction). Move. As a result, the upper mold 4 inserted into the side mold 6 passes through the side mold 6, and the end surface of the upper mold 4 pushes the molded body 10 b downward to the side mold 6. That is, the molded body 10 b held in the side mold 6 is extracted from the lower surface 6 c of the side mold 6. Subsequently, as shown in FIG. 2 (d), by moving the side mold 6 and the upper mold 4 upward, the molded body 10b placed on the lower mold 8 becomes the side mold 6 and Separate from the upper mold 4. Thus, by extracting the molded body 10b from the lower side of the side mold 6, the molded body 10b can be extracted from the mold 2 while maintaining the shape of the molded body 10b. If the molded body 10b is directly gripped by a chuck or the like and taken out from above the side mold 6 (on the upper surface 6b side), the molded body 10b is easily damaged. In the present embodiment, the molded body 10b can be easily separated from the side mold 6 and the upper mold 4 without directly gripping the molded body 10b. If the side mold 6 is separated from the molded body 10b by disassembling the side mold 6 into a plurality of members, a force may be applied to the molded body 10b by mistake and the molded body 10b may be damaged. In the present embodiment, the molded body 10 b can be easily separated from the side mold 6 and the upper mold 4 without disassembling the side mold 6. As long as the relative positional relationship of the lower mold 8, the side mold 6 and the upper mold 4 shown in FIGS. 1 and 2 is maintained, in the separation process, the lower mold 8, the side mold 6 and the upper mold 4 are vertical. It may be inclined with respect to the direction. In other words, as long as the upper mold 4 is positioned on the side mold 6 and the side mold 6 is positioned on the lower mold 8, the entire mold 2 is inclined with respect to the vertical direction in the separation step. Good. For example, in the separation step, the angle formed by the entire mold 2 with respect to the vertical direction (Z-axis direction) may be not less than 0 degrees and not more than 45 degrees.

  In the separation step, the molded body 10b may be transferred from the lower mold 8 to the heating step tray by the following procedure. For example, as shown in FIG. 3A, the side mold 6 and the upper mold 4 are moved together with the molded body 10b from the lower mold 8 while the side mold 6 and the upper mold 4 hold the molded body 10b. To separate. Even if the molded body 10b is separated from the lower mold 8, the molded body 10b is unlikely to fall out from below the side mold 6 due to the friction between the molded body 10b and the side mold 6 or the spring back of the molded body 10b. Subsequently, as shown in FIG. 3B, the molded body 10 b held by the side mold 6 and the upper mold 4 is placed on the heating process tray 32 together with the side mold 6 and the upper mold 4. Put. Subsequently, as shown in FIG. 3C, the side mold 6 is moved upward in a state where the position of the upper mold 4 in the vertical direction (Z-axis direction) is fixed. As a result, the upper mold 4 inserted into the side mold 6 passes through the side mold 6, and the end surface of the upper mold 4 pushes the molded body 10 b downward to the side mold 6. That is, the molded body 10 b held in the side mold 6 is extracted from the lower surface 6 c of the side mold 6. Subsequently, as shown in FIG. 3 (d), by moving the side mold 6 and the upper mold 4 upward, the molded body 10b placed on the heating process tray 32 becomes the side mold. 6 and upper mold 4 are separated. As long as the relative positional relationship of the heating process tray 32, the side mold 6 and the upper mold 4 shown in FIG. 3 is maintained, in the separation process, the heating process tray 32, the side mold 6 and the upper mold 4 are It may be inclined with respect to the vertical direction. In other words, as long as the upper mold 4 is positioned on the side mold 6 and the side mold 6 is positioned on the heating process tray 32, in the separation process, the heating process tray 32, the side mold 6, and The upper mold 4 may be inclined with respect to the vertical direction.

  As shown in (a) in FIG. 4, (b) in FIG. 4, (c) in FIG. 4, and (d) in FIG. 4, a space 6 a ( The cavity) may expand as it approaches the lower surface 6 c of the side mold 6. Such a structure of the side mold 6 may be rephrased as “reverse taper”.

  In the molding step, since the upper part of the molded body 10b is pressurized by the upper mold 4, the density of the upper part of the molded body 10b tends to be higher than the density of the lower part of the molded body 10b. The upper part of the compact 10b, which is denser than the lower part of the compact 10b, is less likely to shrink during the sintering process than the lower part of the compact 10b. In other words, the lower part of the molded body 10b that is less dense than the upper part of the molded body 10b is more likely to shrink during the sintering process than the upper part of the molded body 10b. Accordingly, when the thickness of the molded body 10b is uniform, the lower part of the sintered body (rare earth magnet) obtained from the molded body 10b is thinner than the upper part of the sintered body due to the density difference in the vertical direction of the molded body 10b. It is easy to become. In order to obtain a sintered body having a uniform thickness from the molded body 10b having a density difference in the vertical direction, the lower part of the molded body 10b that easily contracts by sintering may be made thicker than the upper part of the molded body 10b. . According to each side mold 6 shown in FIG. 4, a molded body 10 b whose bottom is thicker than the top is easily formed so as to correspond to the shape of the space 6 a (cavity) that expands as it approaches the lower surface 6 c of the side mold 6. Is possible.

  When the molded body 10b is compressed in the mold 2 in the molding process, the molded body 10b may be difficult to be extracted from below the side mold 6 due to the spring back. Here, the spring back is a phenomenon in which the molded body 10b expands when the pressure is released after the alloy powder 10a is pressed and molded. Since the space 6a (cavity) surrounded by each side mold 6 shown in FIG. 4 is enlarged as it approaches the lower surface 6c of the side mold 6, the lower part of the molded body 10b is the upper part of the molded body 10b in the cavity. It is harder to be pressurized than. Therefore, the spring back of the molded body 10 b hardly occurs below the side mold 6, and the molded body 10 b can be easily pulled out from below the side mold 6.

  In the case of the side mold 6 shown in FIG. 4A, the space 6 a surrounded by the cylindrical side mold 6 continuously expands as it approaches the lower surface 6 c of the side mold 6. The opening 6co formed in the lower surface 6c of the side mold 6 is wider than the opening 6bo formed in the upper surface 6b of the side mold 6. The opening 6co formed in the lower surface 6c of the side mold 6 is similar to the opening 6bo formed in the upper surface 6b of the side mold 6. The inner wall of the side mold 6 surrounding the space 6a is a flat surface.

  In the case of the side mold 6 shown in FIG. 4B, the space 6a surrounded by the side mold 6 has a constant width (width), and the space 6a surrounded by the side mold 6 has a lower surface 6c. There is a part that expands as it approaches.

  In the case of the side mold 6 shown in FIG. 4C, the space 6a surrounded by the side mold 6 has a constant width (width), and the space 6a surrounded by the side mold 6 has a lower surface 6c. There is a part that expands as it approaches. In a portion where the space 6a surrounded by the side mold 6 expands as it approaches the lower surface 6c, at least a part of the inner wall of the side mold 6 is formed of a curved surface.

  In the case of the side mold 6 shown in FIG. 4D, the opening 6co formed in the lower surface 6c of the side mold 6 is not similar to the opening 6bo formed in the upper surface 6b of the side mold 6. The vertical width in the horizontal direction of the space 6a (cavity) surrounded by the side mold 6 is constant, and the horizontal width in the horizontal direction of the space 6a (cavity) surrounded by the side mold 6 increases as it approaches the lower surface 6c. Yes.

  As shown in (a) in FIG. 3 and (b) in FIG. 3, in the process of separating the molded body 10 b from the lower mold 8 and transferring it to the heating process tray 32, the molded body 10 b is removed from the side mold 6. It may fall out. When the space 6 a (cavity) in the side mold 6 has a reverse taper shape, the molded body 10 b easily falls out from below the side mold 6. In order to prevent the molded body 10b from falling off the side mold 6, the mold shown in FIG. 3A and the entire molded body 10b are rotated so that the lower surface 6c of the side mold 6 is directed in the horizontal direction. Thereafter, the lower mold 8 may be replaced with a heating process tray 32.

  Part or all of the mold 2 may be formed of a resin. The lower mold 8, the side mold 6, and the upper mold 4 may all be formed from a resin. Of the lower mold 8, the side mold 6, and the upper mold 4, only the side mold 6 may be formed of 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 resin. Resins used for forming the mold 2 are, for example, acrylic resin, polyethylene, polyethylene terephthalate, polypropylene, polystyrene, ABS resin (acrylonitrile, butadiene and styrene copolymer), ethyl cellulose, paraffin wax, and styrene / butadiene copolymer. One or more selected from the group consisting of ethylene / vinyl acetate copolymer, ethylene / ethyl acrylate copolymer, atactic polypropylene, methacrylic acid copolymer, polyamide, polybutene, polyvinyl alcohol, phenol resin and polyester resin It may be.

  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 from a resin, and the lower mold 8 may be formed from 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 from a resin, and the upper mold 4 may be formed from 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 the resin. When a part of the mold 2 is made of resin, parts other than the resin of the mold 2 are, for example, iron, silicon steel, stainless steel, permalloy, aluminum, molybdenum, tungsten, carbonaceous material, ceramics, and silicon resin. It may be formed from at least one selected from the group consisting of: Portions other than the resin of the mold 2 may be formed from an alloy (for example, an aluminum alloy). The whole mold | type 2 may be formed from compositions other than resin.

  If all of the lower mold 8, the side mold 6, and the upper mold 4 are made of metal, the metal scrap is generated by the friction between the side mold 6 and the upper mold 4 in the molding process. May be detached from the surface and mixed into the compact 10b. Metal scraps (for example, aluminum or aluminum alloy) mixed in the molded body 10b may impair the magnetic characteristics of the finally obtained rare earth magnet. In contrast, when part or all of the mold 2 is made of resin, the wear scrap (resin) of the mold 2 has a magnetic property of the rare earth magnet as compared with the case where the mold 2 is made of only metal. The effect is suppressed. For example, when one (for example, the side mold 6) of the side mold 6 and the upper mold 4 that rubs in the molding process is a resin and the other (for example, the upper mold 4) is a metal, the side mold 6 and the upper mold 4 Due to the friction with the mold 4, resin scraps having hardness lower than that of metal are easily generated instead of metal scraps. Resin scrap is less likely to impair the magnetic properties of rare earth magnets than metal scrap. For example, only the side mold 6 may be formed from a resin, and the lower mold 8 and the upper mold 4 may be formed from a metal (for example, aluminum or an aluminum alloy).

  If a pulse magnetic field is applied to the molded body 10b 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 10b in the mold is effective. The strength of the magnetic field that acts on the metal is lower than the strength of the pulse magnetic field outside the mold. On the other hand, when the mold 2 is made of resin, a strong pulse magnetic field can be applied to the molded body 10b in the mold 2 and the orientation of the alloy powder 10a is improved.

  Since the shrinkage rate of the neodymium magnet in the sintering process is anisotropic, it is difficult to accurately predict the shape (particularly complicated shape) of the neodymium magnet (sintered body) after shrinkage. Therefore, trial and error for adjusting the size and shape of the mold 2 is necessary for the net shape, 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 uses, the mold 2 made of resin is suitable. Conventional molds are difficult to process and expensive, and are not suitable for manufacturing a wide variety of rare earth magnets for various applications.

  When the molding process and the orientation process using the same mold 2 are repeated, the interior of the mold 2 may be cleaned each time molding and orientation are performed. For example, the inside of the mold 2 may be cleaned by attracting excess alloy powder 10a remaining in the mold 2 with a magnetic field. By cleaning the inside of the mold 2 each time it is molded and oriented, the accuracy of weighing the alloy powder 10a molded in the mold 2 is improved, and the density and dimensional variations of the resulting molded body 10b are suppressed. As a result, variations in the density, size, and magnetic properties of the finally obtained rare earth magnet are suppressed. If the mold 2 is made of a ferromagnetic metal (for example, iron), the mold 2 itself is attracted by a magnetic field when the mold 2 is cleaned, so that the mold 2 is difficult to clean. However, when the mold 2 is formed of a resin that does not have ferromagnetism, the mold 2 itself is not attracted by the magnetic field, so that the interior of the mold 2 can be easily cleaned. If the mold 2 is formed of a ferromagnetic metal (for example, iron), the mold 2 itself is magnetized in the orientation process, and the alloy powder 10a adheres to the mold 2. Therefore, the alloy powder 10a The orientation may be disturbed, or the shape retention of the molded body 10b may be impaired. However, when the mold 2 made of resin is used, the magnetization of the mold 2 itself is suppressed.

  While supplying the alloy powder 10 a into the mold 2, the mass of the alloy powder 10 a molded in the mold 2 may be measured together with the mass of the mold 2. When simultaneously measuring the mass of the alloy powder 10a 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 scale, and the measurement of the mass of the alloy powder 10a itself. The accuracy of the is also reduced. However, when the mold 2 made of a resin lighter than the conventional metal is used, the mass of the alloy powder 10a can be measured with high accuracy together with the mass of the mold 2 itself.

The density of the molded body 10b (molded body 10b before the sintering process) that has undergone the molding process and the orientation process is, for example, 3.0 g / cm ³ or more and 4.4 g / cm ³ or less, preferably 3.2 g / cm ³ or more. It may be adjusted to 4.2 g / cm ³ or less, more preferably 3.4 g / cm ³ or more and 4.0 g / cm ³ or less.

  A heating step may be performed following the separation step. In the heating step, the molded body 10b may be heated to adjust the temperature of the molded body 10b to 200 ° C. or higher and 450 ° C. or lower. In the heating step, the temperature of the molded body 10b may be adjusted to 200 ° C. or higher and 400 ° C. or lower, or 200 ° C. or higher and 350 ° C. or lower. In the molding step, the pressure applied to the alloy powder 10a is lower than that of the conventional high-pressure magnetic field pressing method, so that the alloy powder 10a is hard to be pressed and hardened, and the resulting molded body 10b is likely to collapse. However, the shape retention of the molded body 10b is improved by the heating process.

  In the heating step, when the temperature of the molded body 10b is 200 ° C. or higher, the molded body 10b starts to harden and the shape retention of the molded body 10b is improved. In other words, when the temperature of the molded body 10b is 200 ° C. or higher, the mechanical strength of the molded body 10b is improved. Since the shape-retaining property of the molded body 10b is improved, the molded body 10b is unlikely to be damaged when the molded body 10b is transported or handled in the subsequent process. For example, when the molded body 10b is gripped by a transport chuck or the like and arranged on the sintering tray, the molded body 10b is unlikely to collapse. As a result, defects in the finally obtained rare earth magnet are suppressed.

  If the temperature of the molded body 10b exceeds 450 ° C. in the heating process, cracks are easily formed in the molded body 10b in the sintering process performed after the heating process. The reason for the formation of cracks is not clear. For example, there is a possibility that a crack is formed in the molded body 10b because hydrogen remaining in the molded body 10b blows out as a gas to the outside of the molded body 10b due to a rapid temperature rise of the molded body 10b in the heating process. However, by adjusting the temperature of the molded body 10b to 450 ° C. or lower in the heating process, cracks in the molded body 10b in the sintering process are suppressed. As a result, cracks in the finally obtained rare earth magnet are easily suppressed. In addition, since the temperature of the molded body 10b is adjusted to 450 ° C. or lower in the heating step, the time required for raising or cooling the molded body 10b is suppressed, and the productivity of the rare earth magnet is improved. Further, since the temperature of the molded body 10b in the heating process is 450 ° C. or lower and lower than a general sintering temperature, even if the molded body 10b is heated together with a part of the mold 2 (for example, the lower mold 8), the mold 2 or a chemical reaction between the molded body 10b and the mold 2 hardly occurs. Therefore, even the mold 2 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 10b is improved by adjusting the temperature of the molded body 10b 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 10a becomes carbon in the heating process, and the alloy powder 10a (alloy particles) are bound to each other via carbon. As a result, the shape retention of the molded body 10b may be improved. If the temperature of the molded body 10b exceeds 450 ° C. in the heating step, metal carbide constituting the alloy powder 10a may be generated, or the alloy powder 10a (alloy particles) may be directly sintered. . On the other hand, when the temperature of the compact 10b is adjusted to 200 ° C. or higher and 450 ° C. or lower, metal carbides are not necessarily generated, and alloy particles are not necessarily sintered directly.

  The time for maintaining the temperature of the molded body 10b 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 10b.

  In the heating step, the molded body 10b may be heated by irradiating the molded body 10b with infrared rays. By directly heating the molded body 10b by irradiation with infrared rays (that is, radiant heat), the time required for raising the temperature of the molded body 10b 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 10b 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 the metal (alloy powder 10a). Therefore, when irradiating the molded body 10b with far-infrared rays, the organic material (for example, lubricant) described above is easily heated selectively, and the molded body 10b is easily cured by the above-described mechanism resulting from the organic material. When irradiating the molded object 10b with infrared rays, for example, an infrared heater (ceramic heater or the like) or an infrared lamp may be used.

  When the molded body 10b 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 10b and the mold 2 is also easily suppressed. Moreover, when heating the molded object 10b isolate | separated from a part or all of the type | mold 2, the type | mold 2 is hard to insulate heat and the molded object 10b is easy to be heated. As a result, the shape retention of the molded body 10b is improved. When the molded body 10b separated from part or all of the mold 2 is heated, the possibility that the mold 2 chemically reacts with the molded body 10b is low. Therefore, the mold 2 is not necessarily required to have heat resistance, and the material of the mold 2 is not easily limited. Therefore, as a raw material for the mold 2, it is easy to process into a desired size and shape, and it is easy to select an inexpensive material. If the molded body 10b and all of the mold 2 are heated together in the heating step, stress acts on the molded body 10b due to the difference in coefficient of thermal expansion between the molded body 10b and the mold 2. The molded body 10b is easily deformed or damaged. Moreover, when the molded object 10b and all the type | molds 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 compacts 10b that are heated together 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 10b placed on the lower mold 8 may be heated. In the heating step, the molded body 10b placed on the heating step tray 32 may be heated. In the heating step, the molded body 10b may be heated in an inert gas or vacuum to suppress oxidation of the molded body 10b. The inert gas may be a noble gas such as argon.

  In the heating step, after the temperature of the molded body 10b is adjusted to 200 ° C. or higher and 450 ° C. or lower, the molded body 10b may be cooled to 100 ° C. or lower. When the surface of the chuck used for transporting the molded body 10b after the heating step is made of resin, the cooling of the molded body 10b suppresses the chemical reaction between the surface of the chuck and the molded body 10b, and deterioration of the chuck. Contamination of the surface of the molded body 10b is suppressed. The cooling method may be natural cooling, for example.

  A sintering process is performed after an orientation process. After the alignment step, the sintering step may be performed without passing through the heating step. After the orientation step, the sintering step may be performed through the heating step. In the sintering step, the compact 10b separated from the entire mold 2 is heated and sintered. That is, in the sintering step, the alloy particles in the compact 10b are sintered to obtain a sintered body (rare earth magnet).

The density of the compact to be sintered in the sintering process (the density of the compact immediately before the sintering process) is, for example, 3.0 g / cm ³ or more and 4.4 g / cm ³ or less, preferably 3.2 g / cm ³ or more. It may be adjusted to 4.2 g / cm ³ or less, more preferably 3.4 g / cm ³ or more and 4.0 g / cm ³ or less. The lower the pressure exerted by the mold on the compact 10b (alloy powder 10a) in the molding process and the orientation process, the lower the density of the compact 10b immediately before the sintering process. Further, the lower the pressure exerted by the mold 2 on the compact 10b (alloy powder 10a) in the molding step and the orientation step, the easier the alloy powder 10a constituting the compact 10b rotates and the easier it is to align along the magnetic field. As a result, the residual magnetic flux density of the finally obtained rare earth magnet tends to increase. Therefore, it can be said that the lower the density of the molded body 10b immediately before the sintering step, the higher the residual magnetic flux density of the rare earth magnet. However, when the pressure exerted by the mold 2 on the compact 10b (alloy powder 10a) in the molding step and the orientation step is too low, the shape retention (mechanical strength) of the compact 10b is insufficient, and the molding accompanying the separation step Due to the friction between the body 10b and the mold 2, the orientation of the alloy powder 10a located on the surface of the molded body 10b is disturbed. As a result, the residual magnetic flux density of the rare earth magnet finally obtained decreases. Therefore, when the density of the molded body 10b immediately before the sintering process is too low, it can be said that the residual magnetic flux density of the rare earth magnet is low. On the other hand, the higher the pressure applied to the compact 10b (alloy powder 10a) from the molding step to the sintering step, the higher the density of the compact 10b immediately before the sintering step, and the shape retention ( Mechanical strength) is likely to increase. As a result, cracks in the finally obtained rare earth magnet are easily suppressed. Therefore, it can be said that the higher the density of the compact 10b immediately before the sintering step, the easier the cracks in the rare earth magnet are suppressed. However, if the pressure exerted by the mold on the molded body 10b (alloy powder) is too high in the molding process and the orientation process, cracks are easily formed in the molded body 10b due to the springback, and the rare earth magnet obtained from the molded body 10b is cracked. Will remain. The spring back is a phenomenon in which the molded body 10b expands when the pressure is released after the alloy powder is pressed and molded. As described above, the density of the compact 10b immediately before the sintering process correlates with the residual magnetic flux density and cracks of the rare earth magnet. By adjusting the density of the compact 10b immediately before the sintering step within the above range, the residual magnetic flux density of the rare earth magnet is likely to be increased, and cracks in the rare earth magnet are likely to be suppressed.

  If, in the sintering step, the molded body 10b is not separated from the mold 2 and the molded body 10b and the mold 2 are heated together, the components constituting the mold 2 are mixed into the molded body 10b, and the rare earth magnet obtained Magnetic characteristics may be impaired. For example, the resin constituting the mold 2 is decomposed, and a carbon component derived from the resin is mixed into the molded body 10b. Even if the mold composed of the resin disappears in the course of the sintering process, it is difficult to sufficiently suppress the carbon component generated along with the disappearance from being mixed into the molded body 10b. As a result, the carbon component remains in the sintered body (rare earth magnet), and the carbon component impairs the magnetic properties (eg, coercive force) of the rare earth magnet. On the other hand, in the sintering step, when the molded body 10b separated from the mold 2 is heated, components derived from the mold 2 are not easily mixed into the molded body 10b. Therefore, the magnetic characteristics (for example, coercive force) of the obtained rare earth magnet are not easily impaired by the component derived from the mold 2.

  If the molded body 10b and part or all of the mold 2 are heated together in the sintering step, the molded body 10b is caused by the difference in thermal expansion coefficient between the molded body 10b and the mold 2. Stress is easily applied to the molded body 10b, and the molded body 10b may be deformed or damaged. Furthermore, when the compact 10b and the entire mold 2 are heated together in the sintering process, the volume and heat capacity of the entire heating target are large. As a result, the number of compacts 10b that are heated together is limited, the time required for the sintering process is lengthened, energy is wasted, and the productivity of rare earth magnets is reduced. On the other hand, in the sintering process, when the molded body 10b separated from the mold 2 is heated, the volume and heat capacity of the entire heating target are smaller than when the molded body 10b and the entire mold 2 are heated together. . As a result, it is easy to raise the temperature of a large number of compacts 10b at once, 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 molded body 10b placed on the lower mold 8 may be transferred onto a sintering tray. In the sintering step, the molded body 10b placed for the heating step may be transferred onto the sintering tray. Since the shape-retaining property of the molded body 10b is improved in the heating step, the molded body 10b is prevented from being damaged when the molded body 10b is gripped by the conveying chuck and arranged on the sintering tray.

  In the sintering step, the plurality of molded bodies 10b may be placed on the sintering tray, and the plurality of molded bodies 10b placed on the sintering tray may be heated together. By arranging a large number of compacts 10b on a sintering tray at a narrow interval and heating the numerous compacts 10b at once, the productivity of the rare earth magnet is improved.

  The composition of the sintering tray may be a composition that does not easily react with the molded body 10b during sintering and does not easily generate a substance that contaminates the molded body 10b. 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 molded body 10b 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 example, for 0.1 hour or more and 100 hours or less. 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.

  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. The size and shape of the mold 2 or cavity correspond to the size and shape of the rare earth magnet and are not limited.

  According to the method for producing a rare earth magnet according to the present invention, it is possible to produce a wide variety of rare earth magnets according to various uses such as a hard disk drive, a hybrid vehicle, or an electric vehicle. Even in a small amount, the manufacturing cost can be suppressed.

  2 ... Mold, 4 ... Upper die, 6 ... Cylindrical side die, 6a ... Space surrounded by side die, 8 ... Lower die, 10a ... Alloy powder (metal powder), 10b ... Molded body.

Claims (5)

A metal powder containing rare earth elements is supplied into the mold to form a molded body,
An orientation step of orienting the metal powder contained in the compact by applying a magnetic field to the compact held in the mold;
A separation step of separating the molded body from at least a part of the mold after the orientation step;
After the separation step, a sintering step for sintering the molded body,
With
The mold includes a lower mold, a cylindrical side mold disposed on the lower mold, and an upper mold inserted into the side mold from above the side mold,
In the separation step, the molded body is separated from the side mold and the upper mold by extracting the molded body held in the side mold from below the side mold.
A method for producing a rare earth magnet. The side mold is seamless,
The method for producing a rare earth magnet according to claim 1. The space surrounded by the cylindrical side mold is enlarged as it approaches the lower surface of the side mold,
The method for producing a rare earth magnet according to claim 1 or 2. In the separation step, the upper mold penetrates the side mold,
The manufacturing method of the rare earth magnet as described in any one of Claims 1-3. Adjusting the pressure exerted on the metal powder by the mold to 0.049 MPa or more and 20 MPa or less,
The manufacturing method of the rare earth magnet as described in any one of Claims 1-4.

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