JP6809150B2 - Rare earth magnet manufacturing method - Google Patents

Description

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

Rare earth magnets are parts such as motors or actuators, such as hard disk drives, hybrid vehicles, electric vehicles, magnetic resonance imaging (MRI), smartphones, digital cameras, thin TVs, scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners. , Used in various fields such as washing and drying machines, elevators and wind power generators. The dimensions and shapes required for rare earth magnets vary according to these diverse uses. Therefore, in order to efficiently produce a wide variety of rare earth magnets, a molding method capable of easily changing the size and shape of the rare earth magnet is desired.

In the conventional production of a rare earth magnet, a magnetic field is applied to the metal powder while pressurizing a metal powder containing a rare earth element (for example, an alloy powder) at a high pressure (for example, 50 MPa or more and 200 MPa or less). As a result, a molded product is formed from the metal powder oriented along the magnetic field. Such a molding method will be referred to as a "high pressure magnetic field press method" below. According to the high-pressure magnetic field pressing method, the metal powder is easily oriented, and it is possible to obtain a molded product having a high residual magnetic flux density Br and excellent shape retention. A magnet product is completed by obtaining a sintered body by sintering the molded body and processing the sintered body into a desired shape.

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 the molding die are limited. Due to this limitation, the general shape of the compact obtained by the high pressure magnetic field press method is limited to coarse blocks. Therefore, when a wide variety of magnet products are manufactured by a conventional method, a block-shaped molded body is sintered to obtain a sintered body, and then the sintered body is formed according to the dimensions and shape required for the magnet product. Need to be processed. In the processing of the sintered body, since the sintered body is cut and polished, waste containing expensive rare earth elements is generated. As a result, the yield rate of the magnet product decreases. Further, in the high-pressure magnetic field pressing method, the mold or the molded body is easily damaged by galling between the dies or galling between the mold and the molded body. For example, cracks may occur in the molded product obtained by the 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 wide variety or a small amount of magnet products. As a molding method alternative to the high-pressure magnetic field pressing method, Patent Document 1 below discloses a method of molding an alloy powder at a low pressure (0.98 MPa or more and 2.0 MPa or less). The method for manufacturing this rare earth magnet is a step of producing a molded body (filling step) by filling the mold with an alloy powder and pressurizing the alloy powder at a low pressure, and applying a magnetic field to the molded body in the mold. The process includes a step of aligning the alloy powder in the molded body (alignment step) and a step of sintering the molded body taken out from the mold (sintering step). Then, in the production method described in Patent Document 1 below, the filling step and the orientation step are performed at different places.

International Publication No. 2016/047593 Pamphlet

When molding a metal powder at a low pressure as in the molding method described in Patent Document 1, the mold is not required to have durability against a high pressure, and a large-scale and complicated molding apparatus is not required. Therefore, when molding metal powder at low pressure, the material, size and shape of the mold are not limited, and it is relatively easy to manufacture a wide variety of rare earth magnets using molds having various sizes and shapes. it can. Further, in the high-pressure magnetic field press method, it takes a long time to form and orient the metal powder, but by forming the metal powder at low pressure, the time required for forming and orienting is significantly 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 hard to solidify. Therefore, the molded product obtained by the molding method described in Patent Document 1 is inferior in shape-retaining availability and easily collapses as compared with the molded product obtained under high pressure. Therefore, the molded body may be damaged when the molded body is taken out from the mold, or the molded body may be damaged when the molded body is transported to the equipment in a subsequent process (for example, a sintering process).

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

The method for producing a rare earth magnet according to one aspect of the present invention includes a molding step of supplying a metal powder containing a rare earth element and a lubricant into a mold to form a molded body, and a molded body held in the mold. An alignment step of applying a magnetic field (apply) to orient the metal powder contained in the molded body, a separation step of separating the molded body from at least a part of the mold after the alignment step, and baking of the molded body after the separation step. It is provided with a sintering process for binding, the lubricant is a powdered organic substance, and the molds are a lower mold, a tubular side mold arranged on the lower mold, and a side mold from above the side mold. In the molding process, including the upper mold inserted into the cavity, the side mold and the lower mold form the cavity, and the metal powder is molded in the cavity so as to correspond to the shape of the rare earth magnet. A molded body is obtained, and the shape of the rare earth magnet is a rectangular shape, a cubic shape, a polygonal columnar shape, a segment shape, a fan shape, a rectangular shape, a plate shape, a disk shape or a columnar shape, and the pressure exerted by the mold on the metal powder is determined. It is adjusted to 0.049 MPa or more and 20 MPa or less, and in the separation step, the molded body held in the side mold is extracted from below the side mold to separate the molded body from the side mold and the upper mold.
Part or all of the mold may be made of resin.
The density of the molded product that has undergone the molding step and the orientation step may be 3.0 g / cm ³ or more and 4.4 g / cm ³ or less.

In one aspect of the invention, the side molds need not be seamless.

In one aspect of the present invention, the space surrounded by the tubular 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 die may penetrate the side die.

According to the present invention, there is provided a method for producing a rare earth magnet that improves the shape retention of a molded product formed from a metal powder containing a rare earth element.

It is a schematic perspective view of the mold (upper mold, side mold and lower mold) used in a molding process. (A) in FIG. 2, (b) in FIG. 2, (c) in FIG. 2, and (d) in FIG. 2 are schematic cross-sectional views of a mold and a molded product, and are a molding process and separation. An example of the 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 a mold and a molded product, and are other than the separation step. An example is shown. FIG. 4A is a side view and a bottom view of a modified example of the side mold used in the molding process, and FIG. 4B is a side view of another modified example of the side mold used in the molding process. And bottom view, (c) in FIG. 4 is a side view and a bottom view of another modified example of the side mold used in the molding step, and (d) in FIG. 4 is a side mold used in the molding step. It is a side view and the bottom view of another modification.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the drawings, equivalent components are designated 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 drawings.

In the present embodiment, the rare earth magnet means a sintered magnet. In the method of manufacturing rare earth magnets, 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 contains the 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. The raw material alloy consists of 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 element R. It may contain at least one element of choice. 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, each starting material containing the above elements may be weighed and blended according to the composition of the target rare earth magnet to prepare the raw material for the alloy. The rare earth magnet may be, for example, a neodymium magnet, a samarium-cobalt magnet, a samarium-iron-nitrogen magnet, or a placeodim 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 in which the content of the rare earth element R is larger than that of the main phase (R-rich phase). The grain boundary phase may include a B-rich phase, an oxide phase or a carbide phase.

Coarse powder of the alloy is obtained by coarse pulverization of the above alloy. In coarse pulverization, for example, the alloy may be pulverized by occluding hydrogen at the grain boundaries (R-rich phase) of the alloy. In the coarse grinding of the alloy, a mechanical grinding method such as a disc mill, a jaw crusher, a Braun 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 finely pulverizing the above coarse powder. In 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. In the following, coarse powder or fine powder may be referred to as alloy powder or metal powder.

Organic substances may be added to the alloy powder obtained by coarse grinding. Organic substances 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 the fine grinding. The organic matter functions, for example, as a lubricant. By adding the lubricant to the metal powder, by adding the lubricant to the metal powder, the aggregation of the metal powder is suppressed. 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 alignment step, and scratches on the surface of the molded product or the surface of the mold obtained from the metal powder are easily suppressed. The organic matter may be, for example, a fatty acid or a derivative of a fatty acid. Organic substances include, for example, oleic acid amide, zinc stearate, calcium stearate, stearic acid amide, palmitate amide, pentadecyl acid amide, myristic acid amide, lauric acid amide, capric acid amide, pelargonic acid amide, capric acid amide, enanthic acid 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 substance .

In the molding step, the alloy powder obtained in the above procedure is supplied into a mold to form a molded product. Part or all of the mold is made of resin. For example, as shown in FIG. 1, the mold 2 has a lower mold 8, a tubular side mold 6 arranged on the lower mold 8, and an upper mold 4 (punch) arranged 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 side wall of the mold. 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 portion of the side mold 6 to the claws (stops) formed on the surface of the lower mold 8.

As shown in (a) in FIGS. 1 and 2, in the molding step, 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 form a cavity (female mold). Subsequently, the alloy powder 10a is introduced into the cavity (space 6a penetrating the side mold 6) from the opening 6bo (hole) on the upper surface 6b 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 paraphrased as a core (male mold). The upper mold 4 has a shape that fits into the cavity (space 6a penetrating the side mold 6). The length of the upper die 4 in the vertical direction (Z-axis direction) may be longer than the height of the side die 6. In this case, in the separation step described later, the upper mold 4 easily penetrates the side mold 6. As shown in (b) in FIG. 2, the upper mold 4 is inserted into the side mold 6 (inside the cavity), and the end face of the upper mold 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 the molded body 10b is obtained. The molded body 10b (alloy powder 10a) in the cavity may be compressed by the upper mold 4. However, in the sintering step, the density of the molded body 10b is sufficiently increased only by sintering the alloy powders in the molded body 10b, and a rare earth magnet having a desired density can be obtained, so that the alloy powder in the cavity is not compressed. You may. In the molding process, the lower mold 8, the side mold 6, and the upper mold 4 are vertical as long as the relative positional relationship between the lower mold 8, the side mold 6 and the upper mold 4 shown in FIGS. 1 and 2 is maintained. It may be tilted with respect to the direction. In other words, as long as the upper mold 4 is located above the side mold 6 and the side mold 6 is located above the lower mold 8, in the molding process, the entire mold 2 is tilted with respect to the vertical direction. 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 degrees or more 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 face of the upper mold 4. As described above, 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. If the pressure is too high, the mold 2 bends, 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 is 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 perform molding and orientation at the same time, the orientation step can be performed after the molding step. By separating the molding process and the orientation process, a device smaller and cheaper than the conventional one (for example, a press molding device and a magnetic field applying device) can be used for each step. The molding step and the orientation step may be performed substantially at the same time.

As shown in FIG. 1, the side mold 6 does not have to be seamless. That is, the side mold 6 may be seamless. If the side mold 6 has a seam (for example, when the side mold 6 can be decomposed into a plurality of members), the alloy powder 10a is transferred from the seam (gap) of the side mold 6 to the mold 2 in the molding step or the orientation step. It may leak out of the. As a result, the shape retention of the molded body 10b is impaired, and for example, burrs 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 erroneously applied to the molded body 10b to damage the molded body 10b. When the alloy powder 10a leaks out of the mold 2 from the seam of the side mold 6, the dimensions, density and shape of the molded body 10b vary, and the dimensions, shape and magnetic characteristics of the finally obtained rare earth magnet also vary. There is also. These problems are easily suppressed by using the seamless side mold 6.

In the alignment step, a magnetic field is applied to the molded body 10b held in the mold 2 to orient the alloy powder 10a constituting the molded body 10b along the magnetic field in the mold 2. 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 arranged inside the air core coil (solenoid coil) together with the mold 2, and a current (alternating current) is passed through the air core coil to form the molded body in the mold 2. A magnetic field may be applied to the body 10b. A magnetic field may be applied to the molded body in the mold by passing an electric current through the double coil or Helmholtz coil. A double coil is a magnetic field generator in which two coils are arranged so as to have the same central axis. By using the double coil or the Helmholtz coil, a more homogeneous magnetic field can be applied to the molded body as compared with the case of using the air core coil. As a result, the orientation of the alloy powder in the molded product is likely to be improved, and the magnetic properties of the finally obtained rare earth magnet are likely to be improved. A magnetic field may be applied to the molded body 10b in the mold 2 by using the magnetizing 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). After the alignment step, the molded body may be demagnetized. The strength of the magnetic field applied to the molded body in the mold is not necessarily limited to the above range.

The alloy powder 10a may be oriented by a magnetic field while pressurizing the alloy powder 10a in the mold 2. That is, even in the orientation step, the molded body 10b in the mold 2 may be compressed. The pressure exerted by the mold 2 on the molded product 10b 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 while the position of the upper mold 4 in the vertical direction (Z-axis direction) is fixed. Move. As a result, the upper mold 4 inserted into the side mold 6 penetrates the side mold 6, and the end face of the upper mold 4 pushes the molded body 10b downward from the side mold 6. That is, the molded body 10b held in the side mold 6 is extracted from the lower surface 6c of the side mold 6. Subsequently, as shown in (d) in FIG. 2, by moving the side mold 6 and the upper mold 4 upward, the molded body 10b placed on the lower mold 8 is moved to the side mold 6 and Separate from the upper mold 4. By pulling out the molded body 10b from below the side mold 6 in this way, the molded body 10b can be taken out from the mold 2 while maintaining the shape of the molded body 10b. If the molded body 10b is directly grasped by a chuck or the like and taken out from above the side mold 6 (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 grasping 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 erroneously applied to the molded body 10b to damage the molded body 10b. In the present embodiment, the molded body 10b 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 between the lower mold 8, the side mold 6 and the upper mold 4 shown in FIGS. 1 and 2 is maintained, the lower mold 8, the side mold 6 and the upper mold 4 are vertical in the separation step. It may be tilted with respect to the direction. In other words, as long as the upper mold 4 is located above the side mold 6 and the side mold 6 is located above the lower mold 8, in the separation step, the entire mold 2 is tilted with respect to the vertical direction. 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 0 degrees or more and 45 degrees or less.

In the separation step, the molded body 10b may be transferred from the lower mold 8 to the tray for the heating step by the following procedure. For example, as shown in (a) in FIG. 3, in a state where the side mold 6 and the upper mold 4 hold the molded body 10b, the side mold 6 and the upper mold 4 are together with the molded body 10b from the lower mold 8. To separate. Even if the molded body 10b is separated from the lower mold 8, the molded body 10b is unlikely to come off from below the side mold 6 due to friction between the molded body 10b and the side mold 6 or the springback of the molded body 10b. Subsequently, as shown in (b) in FIG. 3, the molded body 10b held by the side mold 6 and the upper mold 4 is placed on the tray 32 for the heating process together with the side mold 6 and the upper mold 4. Place. Subsequently, as shown in (c) in FIG. 3, the side mold 6 is moved upward while 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 penetrates the side mold 6, and the end face of the upper mold 4 pushes the molded body 10b downward from the side mold 6. That is, the molded body 10b held in the side mold 6 is extracted from the lower surface 6c of the side mold 6. Subsequently, as shown in FIG. 3D, by moving the side mold 6 and the upper mold 4 upward, the molded body 10b placed on the tray 32 for the heating process is moved to the side mold. Separate from 6 and upper mold 4. As long as the relative positional relationship between the heating process tray 32, the side mold 6 and the upper mold 4 shown in FIG. 3 is maintained, in the separation step, the heating process tray 32, the side mold 6 and the upper mold 4 are used. It may be tilted with respect to the vertical direction. In other words, as long as the upper mold 4 is located above the side mold 6 and the side mold 6 is located above the heating process tray 32, in the separation step, the heating process tray 32, the side mold 6, and The upper mold 4 may be tilted 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, the space 6a surrounded by the tubular side mold 6 ( The cavity) may expand as it approaches the lower surface 6c 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 pressed 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 molded body 10b, which is denser than the lower part of the molded body 10b, is less likely to shrink in the sintering process than the lower part of the molded body 10b. In other words, the lower part of the molded body 10b, which is less dense than the upper part of the molded body 10b, is more likely to shrink in the sintering process than the upper part of the molded body 10b. Therefore, 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. 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 shrinks due to 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 10b whose lower portion is thicker than the upper portion is easily formed so as to correspond to the shape of the space 6a (cavity) which expands as it approaches the lower surface 6c of the side mold 6. It is possible to do.

When the molded body 10b is compressed in the mold 2 in the molding step, it may be difficult for the molded body 10b to be pulled out from below the side mold 6 due to the springback. Here, the springback 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 expands 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 pressurize than. Therefore, springback of the molded body 10b is unlikely to occur below the side mold 6, and the molded body 10b 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 6a surrounded by the tubular side mold 6 continuously expands as it approaches the lower surface 6c of the side mold 6. The opening 6co formed on the lower surface 6c of the side mold 6 is wider than the opening 6bo formed on the upper surface 6b of the side mold 6. The opening 6co formed on the lower surface 6c of the side mold 6 is similar to the opening 6bo formed on the upper surface 6b of the side mold 6. The inner wall of the side mold 6 surrounding the space 6a is composed of a flat surface.

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

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

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

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

Part or all of the mold 2 may be made of resin. 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 resin. Of the lower mold 8, the side mold 6, and the upper mold 4, only the lower mold 8 may be formed of 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. The resin used for forming the 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. It may be there.

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 the 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 the 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 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. It may be formed from 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). The entire mold 2 may be formed of a composition other than the resin.

If the lower mold 8, the side mold 6, and the upper mold 4 are all formed of metal, the metal scraps are generated by 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. It may be separated from the surface of the molded product and mixed with the molded product 10b. Metal scraps (for example, aluminum or aluminum alloy) mixed in the molded body 10b may impair the magnetic properties of the finally obtained rare earth magnet. In contrast, when part or all of the mold 2 is made of resin, the wear debris (resin) of the mold 2 has the magnetic properties 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) is a resin and the other (for example, the upper mold 4) is a metal among the side molds 6 and the upper molds 4 that rub against each other in the molding process, the side molds 6 and the upper molds are upper. Due to friction with the mold 4, resin scraps having a hardness lower than that of metal are likely to be formed in place of metal scraps. Resin scraps are less likely to impair the magnetic properties of rare earth magnets than metal scraps. For example, only the side mold 6 may be formed of resin, and the lower mold 8 and the upper mold 4 may be formed of a metal (for example, aluminum or an aluminum alloy).

If a pulsed magnetic field is applied to the molded body 10b held in the mold, the saturation magnetic field density of the metal (for example, iron) constituting the mold is limited, so that it is effective for the molded body 10b in the mold. The strength of the magnetic field acting on the mold is lower than the strength of the pulsed magnetic field outside the mold. On the other hand, when the mold 2 is formed of resin, a strong pulsed 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 neodymium magnets 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, for the net shape, trial and error is required to adjust the size and shape of the mold 2, and a resin that is easy to cut is suitable as the material of the mold 2. That is, in order to efficiently produce a wide variety of rare earth magnets for various purposes, the mold 2 formed 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 for various purposes.

When the molding step and the orientation step using the same mold 2 are repeated, the inside of the mold 2 may be cleaned every time the molding and the orientation are performed. For example, the inside of the mold 2 may be cleaned by attracting the excess alloy powder 10a remaining in the mold 2 with a magnetic field. By cleaning the inside of the mold 2 every time molding and orientation are performed, the accuracy of weighing the alloy powder 10a molded in the mold 2 is improved, and variations in the density and dimensions of the obtained molded body 10b are suppressed. As a result, variations in the density, dimensions, and magnetic properties of the finally obtained rare earth magnet are suppressed. If the mold 2 is made of a metal having ferromagnetism (for example, iron), it is difficult to clean the mold 2 because the mold 2 itself is attracted by the magnetic field when cleaning the inside of the mold 2. However, when the mold 2 is made of a resin having no ferromagnetism, the mold 2 itself is not attracted by the magnetic field, so that the inside of the mold 2 can be easily cleaned. If the mold 2 is formed of a metal having ferromagnetism (for example, iron), the mold 2 itself is magnetized in the alignment step and the alloy powder 10a adheres to the mold 2, so that the alloy powder 10a The orientation is disturbed, and the shape retention of the molded body 10b is impaired. However, when the mold 2 made of resin is used, the magnetism of the mold 2 itself is suppressed.

While supplying the alloy powder 10a into the mold 2, the mass of the alloy powder 10a formed in the mold 2 may be measured together with the mass of the mold 2. When the mass of the alloy powder 10a formed in the mold 2 and the mass of the mold 2 are measured at the same time, 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 is also reduced. However, when the mold 2 composed 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 step) that has undergone the molding step and the orientation step 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 separation step may be followed by a heating step. In the heating step, the molded product 10b may be heated to adjust the temperature of the molded product 10b to 200 ° C. or higher and 450 ° C. or lower. In the heating step, the temperature of the molded product 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, since the pressure applied to the alloy powder 10a is lower than that of the conventional high-pressure magnetic field pressing method, the alloy powder 10a is hard to be compacted and the obtained molded body 10b is easily collapsed. However, the heating step improves the shape retention of the molded product 10b.

In the heating step, when the temperature of the molded body 10b becomes 200 ° C. or higher, the molded body 10b begins to solidify, and the shape retention of the molded body 10b is improved. In other words, when the temperature of the molded product 10b is 200 ° C. or higher, the mechanical strength of the molded product 10b is improved. Since the shape retention of the molded body 10b is improved, the molded body 10b is less likely to be damaged during transportation of the molded body 10b or handling of the molded body 10b in a subsequent process. For example, when the molded body 10b is grasped by a transport chuck or the like and arranged on a 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 step, cracks are likely to be formed in the molded body 10b in the sintering step performed after the heating step. The cause of the crack formation is unknown. For example, due to a sudden temperature rise of the molded body 10b in the heating step, hydrogen remaining in the molded body 10b is blown out as a gas to the outside of the molded body 10b, so that a crack may be formed in the molded body 10b. However, by adjusting the temperature of the molded product 10b to 450 ° C. or lower in the heating step, cracks in the molded product 10b in the sintering step are suppressed. As a result, cracks in the finally obtained rare earth magnet are also easily suppressed. Further, 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 step is 450 ° C. or lower, which is lower than the 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 is formed. Deterioration of 2 or chemical reaction between the molded product 10b and the mold 2 is unlikely to occur. Therefore, even a mold 2 composed of a composition (for example, a resin) whose heat resistance is not necessarily high can be used.

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

The time for maintaining the temperature of the molded product 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 dimensions and shape of the molded product 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 as compared with the case of heating by conduction or convection, and the production efficiency and energy efficiency are improved. However, in the heating step, the molded product 10b may be heated by heat conduction or convection in the heating furnace. The wavelength of infrared rays 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 ray may be at least one selected from the group consisting of near infrared ray, short wavelength infrared ray, medium wavelength infrared ray, long wavelength infrared ray (thermal infrared ray), and far infrared ray. Of the above infrared rays, near infrared rays are relatively easily absorbed by metals. Therefore, when the molded body is irradiated with near infrared rays, the temperature of the metal (alloy powder) can be easily raised in a short time. On the other hand, of the above infrared rays, far infrared rays are relatively easily absorbed by organic substances and easily reflected by a metal (alloy powder 10a). Therefore, when the molded body 10b is irradiated with far infrared rays, the above-mentioned organic substance (for example, a lubricant) is easily heated selectively, and the molded body 10b is easily cured by the above-mentioned mechanism caused by the organic substance. When irradiating the molded body 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 a 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 are easily suppressed. Seizure with 2 is also easily suppressed. Further, when the molded body 10b separated from a part or all of the mold 2 is heated, it is difficult for the mold 2 to insulate the heat, and the molded body 10b is easily heated. As a result, the shape retention of the molded product 10b is improved. When the molded product 10b separated from a part or all of the mold 2 is heated, it is unlikely that the mold 2 chemically reacts with the molded product 10b. 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 the raw material of 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 the entire mold 2 are heated together in the heating step, stress acts on the molded body 10b due to the difference in the coefficient of thermal expansion between the molded body 10b and the mold 2. It is easy for the molded body 10b to be deformed or damaged. Further, when the molded body 10b and the entire mold 2 are heated together in the heating step, the volume and heat capacity of the entire heating target are large. As a result, the quantity of the compact 10b to be heated in a batch is limited, the time required for the heating step becomes long, energy is wasted, and the productivity of the rare earth magnet is lowered.

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 tray 32 for the heating step may be heated. In the heating step, the molded product 10b may be heated in an inert gas or vacuum in order to suppress the oxidation of the molded product 10b. The inert gas may be a rare gas such as argon.

In the heating step, the temperature of the molded product 10b may be adjusted to 200 ° C. or higher and 450 ° C. or lower, and then the molded product 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, resulting in deterioration of the chuck and deterioration of the chuck. Contamination of the surface of the molded product 10b is suppressed. The cooling method may be, for example, natural cooling.

After the alignment step, a sintering step is performed. After the alignment step, the sintering step may be performed without going through the above heating step. After the alignment step, the sintering step may be performed through the above heating step. In the sintering step, the molded body 10b separated from the entire mold 2 is heated and sintered. That is, in the sintering step, the alloy particles in the molded body 10b are sintered together to obtain a sintered body (rare earth magnet).

The density of the molded body to be sintered in the sintering step (density of the molded body immediately before the sintering step) 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 molded body 10b (alloy powder 10a) in the molding step and the orientation step, the lower the density of the molded body 10b immediately before the sintering step tends to be. Further, the lower the pressure exerted by the mold 2 on the molded body 10b (alloy powder 10a) in the molding step and the orientation step, the easier it is for the alloy powder 10a constituting the molded body 10b to rotate freely and to be easily oriented 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 easier it is for the residual magnetic flux density of the rare earth magnet to increase. However, if the pressure exerted by the mold 2 on the molded body 10b (alloy powder 10a) in the molding step and the orientation step is too low, the shape retention (mechanical strength) of the molded body 10b is insufficient, and the molding accompanying the separation step is performed. The friction between the body 10b and the mold 2 disturbs the orientation of the alloy powder 10a located on the surface of the molded body 10b. As a result, the residual magnetic flux density of the finally obtained rare earth magnet decreases. Therefore, if the density of the molded body 10b immediately before the sintering step 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 exerted on the molded body 10b (alloy powder 10a) from the molding step to the sintering step, the higher the density of the molded body 10b immediately before the sintering step, and the shape retention of the molded body 10b ( Mechanical strength) tends 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 molded body 10b immediately before the sintering step, the easier it is to suppress cracks in the rare earth magnet. However, if the pressure exerted by the mold on the molded body 10b (alloy powder) in the molding step and the orientation step is too high, cracks are likely to be formed in the molded body 10b due to springback, and the rare earth magnet obtained from the molded body 10b is cracked. Will remain. The springback is a phenomenon in which the molded body 10b expands when the pressure is released after the alloy powder is pressurized and molded. As described above, the density of the molded body 10b immediately before the sintering step correlates with the residual magnetic flux density and the cracks of the rare earth magnet. By adjusting the density of the molded body 10b immediately before the sintering step within the above range, the residual magnetic flux density of the rare earth magnet is likely to increase, 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 both the molded body 10b and the mold 2 are heated, the components constituting the mold 2 are mixed in the molded body 10b, and the obtained rare earth magnet The magnetic properties may be impaired. For example, the resin constituting the mold 2 is decomposed, and the carbon component derived from the resin is mixed in the molded product 10b. Even if the mold composed of the resin disappears in the process of the sintering step, it is difficult to sufficiently suppress the carbon component generated due to the disappearance from being mixed in the molded product 10b. As a result, a carbon component remains in the sintered body (rare earth magnet), and the carbon component impairs the magnetic properties (for example, coercive force) of the rare earth magnet. On the other hand, when the molded body 10b separated from the mold 2 is heated in the sintering step, the components derived from the mold 2 are unlikely to be mixed into the molded body 10b. Therefore, the magnetic properties (for example, coercive force) of the obtained rare earth magnet are not easily impaired by the components derived from the mold 2.

If part or all of the molded body 10b and the mold 2 are heated together in the sintering step, the molded body 10b is caused by the difference in the coefficient of thermal expansion between the molded body 10b and the mold 2. Stress is likely to act on the molded product 10b, and the molded product 10b may be deformed or damaged. Further, in the sintering step, when the molded body 10b and the entire mold 2 are heated together, the volume and heat capacity of the entire object to be heated are large. As a result, the quantity of the compact 10b to be heated in a batch is limited, the time required for the sintering step becomes long, energy is wasted, and the productivity of the rare earth magnet is lowered. On the other hand, in the sintering step, 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 at once. .. As a result, it is easy to raise the temperature of a large number of molded bodies 10b at once, the time and energy required for the sintering step 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 the sintering tray. In the sintering step, the molded product 10b placed for the heating step may be transferred onto the sintering tray. Since the shape retention of the molded body 10b is improved in the heating step, damage to the molded body 10b is suppressed when the molded body 10b is grasped by the transport chuck and arranged on the sintering tray.

In the sintering step, a 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 at once. By arranging a large number of molded bodies 10b on the sintering tray at narrow intervals and heating the large number of molded bodies 10b at once, the productivity of the rare earth magnet is improved.

The composition of the sintering tray may be any composition that does not easily react with the molded body 10b at the time of 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 may be, for example, 900 ° C. or higher and 1200 ° C. or lower. The sintering time may be, for example, 0.1 hour or more and 100 hours or less. The sintering process may be repeated. In the sintering step, the molded product 10b may be heated in an inert gas or vacuum. The inert gas may be a rare gas such as argon.

The sintered body may be aged. In the aging treatment, the sintered body may be heat-treated at, for example, 450 ° C. or higher and 950 ° C. or lower. In the aging treatment, the sintered body may be heat-treated for, for example, 0.1 hour or more and 100 hours or less. The aging treatment may be carried out in an inert gas or vacuum. The aging treatment may consist of multi-step 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 vapor phase method, or a chemical conversion treatment method.

The dimensions 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 cube shape, a polygonal columnar shape, a segmental 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, polygonal, chordal, arched, or circular. The size and shape of the mold 2 or the 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, and the production amount thereof is high. It is possible to suppress the manufacturing cost even in a small amount.

2 ... mold, 4 ... upper mold, 6 ... tubular side mold, 6a ... space surrounded by side mold, 8 ... lower mold, 10a ... alloy powder (metal powder), 10b ... molded body.

Claims (6)

A molding process in which a metal powder containing a rare earth element and a lubricant are supplied into a mold to form a molded product.
An orientation step of applying a magnetic field to the molded body held in the mold to orient the metal powder contained in the molded body.
After the orientation step, a separation step of separating the molded product from at least a part of the mold,
After the separation step, a sintering step of sintering the molded body and
With
The lubricant is a powdery organic substance.
The mold includes a lower mold, a tubular side mold arranged on the lower mold, and an upper mold inserted into the side mold from above the side mold.
In the molding step, the side mold and the lower mold form a cavity, and the metal powder is molded in the cavity so as to correspond to the shape of a rare earth magnet, whereby the molded product is obtained. The shape of the rare earth magnet is a rectangular parallelepiped shape, a cube shape, a polygonal columnar shape, a segmental shape, a fan shape, a rectangular shape, a plate shape, a disc shape or a columnar shape, and the pressure exerted by the mold on the metal powder is 0.049 MPa. Adjust to 20 MPa or less,
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 manufacturing rare earth magnets. The side mold is seamless,
The method for producing a rare earth magnet according to claim 1. The space surrounded by the tubular side mold expands 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 method for producing a rare earth magnet according to any one of claims 1 to 3. Part or all of the mold is made of resin,
The method for producing a rare earth magnet according to any one of claims 1 to 4. The density of the molded product that has undergone the molding step and the orientation step is 3.0 g / cm ³ or more and 4.4 g / cm ³ or less.
The method for producing a rare earth magnet according to any one of claims 1 to 5.

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