Method for producing rare earth sintered magnet and wet molding apparatus

Abstract

The method for manufacturing a rare earth-based sintered magnet of the present invention includes: a step of compressing a slurry containing alloy powder containing rare earth elements and a dispersion medium using a wet molding apparatus to produce a molded body; and a step of sintering the molded body, wherein when the slurry is injected into the space of the cavity forming the wet molding apparatus, no magnetic field is applied, and the dispersion medium contained in the slurry is discharged from the space by pressing the slurry.

Description

Technical Field

[0001] This invention relates to a method for manufacturing rare earth sintered magnets and a wet forming apparatus. Background Technology

[0002] In recent years, rare earth sintered magnets have shown high demand. Among them, R-T-B sintered magnets (R is at least one of the rare earth elements, T is mainly iron, and B is boron) are known as the highest performance magnets and are used in voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), motors for industrial equipment, and various other motors and home appliances.

[0003] R-T-B series sintered magnets are mainly composed of R2T 14 Compound B consists of a main phase and a grain boundary phase located at the grain boundary portion of the main phase. R2T is the main phase. 14 B compounds are ferromagnetic materials with high saturation magnetization and anisotropic magnetic fields. The grain boundary phase consists of a low-melting-point R-rich phase that is nonmagnetic and contains concentrated rare earth elements (R). As a method to improve the magnetic properties of R-T-B sintered magnets, (1) R2T 14 Miniaturization of phase B, (2) Improvement of R2T 14 (3) Reduce oxygen content, (4) Increase R2T 14 The ratio of phase B.

[0004] In the manufacture of rare-earth sintered magnets such as R-T-B series sintered magnets, for example, an ingot is obtained by casting a molten metal or other raw material into a mold, or alloy powder with a specified particle size is obtained by crushing a raw material alloy casting material with a desired composition, such as a sheet obtained by strip casting. This alloy powder is then compressed in an orientation magnetic field to form a powder molded body (pressed powder body), and then sintered to manufacture a rare-earth sintered magnet. However, if the powder particles oxidize during crushing and molding, it will hinder the improvement of magnetic properties.

[0005] However, in the molding methods for producing powder molded articles, there are two methods: dry molding and wet molding. Patent Document 1 discloses a wet molding method. It is believed that according to this wet molding method, the oxidation of powder particles can be suppressed, so compared with the dry molding method, it is less likely to hinder the improvement of magnetic properties.

[0006] Existing technical documents and patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 8-88133 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] In the wet molding method disclosed in Patent Document 1, a slurry containing rare earth alloy powder is injected under pressure into the cavity (space) of the mold. However, according to the inventor's research, even under such circumstances, it is easy to produce "density deviation of powder molded body" and "orientation disorder" caused by compression in orientation magnetic field.

[0010] The former, "density deviation of the powder molded body," may cause cracking or fissures when the powder molded body is removed or during subsequent sintering. Furthermore, the latter, "orientation disorder," may lead to a decrease in magnetic properties. In particular, the degree of density deviation and orientation disorder of the powder molded body varies depending on the relationship between the pressing direction when the slurry is pressurized into the mold cavity and the direction of the magnetic field, as well as the condition of the slurry within the mold cavity. Therefore, it is difficult to stably produce the required high magnetic properties.

[0011] This invention provides a new method for manufacturing rare earth sintered magnets and a wet forming apparatus that can solve the above-mentioned problems.

[0012] Methods for solving problems

[0013] In a non-limiting embodiment of the method for manufacturing a rare-earth-based sintered magnet of the present invention, a slurry comprising alloy powder containing rare-earth elements and a dispersion medium is supplied into the space of a mold, and a molded body obtained by pressing the supplied slurry is sintered. When the slurry is supplied into the space of the mold, no magnetic field is applied; however, when the dispersion medium is discharged from the space of the mold, a transverse magnetic field in a direction orthogonal to the pressing direction is applied before the discharge.

[0014] In one embodiment, the dimensions of the molded body are 90 mm or more in length, 90 mm or more in width, and 90 mm or more in height.

[0015] In one embodiment, the method includes: a first dividing step, which divides the molded body into 10 or more molded body pieces by cutting it; and a sintered body raw material production step, which, after the first dividing step, produces a plurality of sintered body raw materials by sintering the plurality of molded body pieces respectively.

[0016] In one implementation, it includes:

[0017] The second dividing process, after the above-mentioned sintered body raw material production process, involves cutting multiple of the above-mentioned sintered body raw materials into more than 100 sintered body pieces.

[0018] In one embodiment, a gap is formed between the device for pressing the slurry and the upper surface of the slurry before the transverse magnetic field is applied.

[0019] In a non-limiting embodiment, the method for manufacturing rare-earth sintered magnets of the present invention includes: a step of preparing a wet forming apparatus, the wet forming apparatus comprising: a mold having a through hole; a lower punch that moves up and down relative to the mold with at least its front end inserted into the through hole; and an upper punch that moves up and down relative to the lower punch, the upper punch having a lower end with a plurality of discharge holes for liquid to pass through, a cavity being formed inside the through hole by the upper end of the lower punch and the lower end of the upper punch, the volume of the cavity being reduced by reducing the distance between the upper end of the lower punch and the lower end of the upper punch;

[0020] The process of preparing a slurry containing alloy powder with rare earth elements and a dispersion medium.

[0021] The process includes: a step of filling the space by injecting slurry into the space formed by the inner wall of the through hole in the wet forming apparatus and the upper end of the lower punch; a step of sealing the space with the lower end of the upper punch to form a cavity filled with slurry; a step of reducing the distance between the lower end of the upper punch and the upper end of the lower punch while applying a transverse magnetic field perpendicular to the direction of the up-and-down movement of the lower punch to the cavity, and discharging the dispersion medium contained in the slurry through the plurality of discharge holes in the upper punch to produce a molded body of the alloy powder; and a step of sintering the molded body. When injecting the slurry into the space, no magnetic field is applied to the space, and the space is temporarily or intermittently covered with a non-magnetic cover. Before applying the transverse magnetic field to the cavity, the non-magnetic cover can be moved from the position covering the space.

[0022] In one embodiment, during the process of manufacturing the molded body of the alloy powder while reducing the distance between the lower end of the upper punch and the upper end of the lower punch, a filter cloth or filter is disposed between the slurry in the cavity and the lower end of the upper punch.

[0023] In one embodiment, the process includes the following steps: after filling the space with the slurry, moving the non-magnetic cover from the position covering the space, and at least before the application of the transverse magnetic field, causing the lower punch to descend relative to the mold, thereby forming a gap between the lower end of the upper punch and at least one of the filter cloth and the slurry.

[0024] In one embodiment, the size of the aforementioned gap is 2 mm or more and 4 mm or less.

[0025] In one embodiment, after the space is filled with the slurry, the non-magnetic cover is moved from the position covering the space, and the transverse magnetic field is applied before the dispersion medium contained in the slurry is discharged through the plurality of discharge holes in the upper punch.

[0026] In one embodiment, the process includes a step of temporarily connecting the interior of the space with the exterior by moving the non-magnetic cover up and down when injecting the slurry into the interior of the space.

[0027] In one embodiment, the concentration of the alloy powder in the slurry during injection is 75-88% by mass.

[0028] The wet forming apparatus of the present invention is a wet forming apparatus for producing a molded body of rare earth alloy powder, comprising: a mold having a through hole; a lower punch that moves vertically relative to the mold with at least its front end inserted into the through hole; an upper punch that moves vertically relative to the lower punch and has a lower end having a plurality of discharge holes for liquid to pass through; and an electromagnetic coil that applies a transverse magnetic field in a direction perpendicular to the direction of vertical movement of the lower punch to the interior of the through hole of the mold. The mold has an injection port that injects a slurry containing the rare earth alloy powder into the space formed by the inner wall of the through hole and the upper end of the lower punch. The wet forming apparatus further comprises a non-magnetic cover that temporarily or intermittently covers the space when the slurry is injected into the space.

[0029] In one embodiment, the wet forming apparatus includes a control device for controlling the movement of the upper punch, lower punch, mold, electromagnetic coil, and non-magnetic cover. The aforementioned control device performs the following steps: forming the space by the inner wall of the through hole in the wet forming device and the upper end of the lower punch, injecting the slurry into the space, and filling the space with the slurry; forming a cavity filled with the slurry by closing the space with the lower end of the upper punch; and reducing the gap between the lower end of the upper punch and the upper end of the lower punch while applying a transverse magnetic field perpendicular to the direction of the up-and-down movement of the lower punch to the cavity, discharging the dispersion medium contained in the slurry through the plurality of discharge holes in the upper punch, and producing a molded body of the rare earth alloy powder. Furthermore, when injecting the slurry into the space, no magnetic field is applied to the space, and the space is temporarily or intermittently covered with the non-magnetic cover. Before applying the transverse magnetic field to the cavity, the non-magnetic cover is moved from the position covering the space.

[0030] Invention Effects

[0031] According to an embodiment of the present invention, slurry can be uniformly supplied into the space of the mold in a manner that suppresses concentration deviation. This suppresses density deviation and orientation disorder of the powder molded body, and inhibits cracking and fissures caused therefrom, thus enabling stable production of the required high magnetic properties. Attached Figure Description

[0032] Figure 1 This is a diagram showing a basic configuration example of the wet forming apparatus 100 in this embodiment.

[0033] Figure 2 This is a perspective view schematically showing an example of the configuration of the mold 10 included in the wet forming apparatus 100.

[0034] Figure 3 This is a perspective view schematically representing an example of a non-magnetic cover 34.

[0035] Figure 4 This is an explanatory diagram illustrating the manufacturing method of the rare earth sintered magnet in this embodiment.

[0036] Figure 5 This is an explanatory diagram illustrating the manufacturing method of the rare earth sintered magnet in this embodiment.

[0037] Figure 6 This is an explanatory diagram illustrating a portion of the manufacturing method in this embodiment. Detailed Implementation

[0038] The inventors conducted research and found that by not applying a magnetic field when supplying slurry into the space of the mold, and by applying the transverse magnetic field molding method described later after the slurry is supplied, the slurry can be uniformly supplied into the space of the mold in a way that suppresses concentration deviation.

[0039] Before describing the embodiments of the present invention, the insights discovered by the inventors and their technical background will be explained.

[0040] In methods for manufacturing powder-formed bodies for rare-earth-based sintered magnets, there are dry forming methods that press rare-earth alloy powder in a dry state and wet forming methods that press a slurry obtained by dispersing alloy powder in a dispersion medium such as oil into a mold cavity. Furthermore, pressing in a magnetic field is divided into transverse magnetic field forming methods where the direction of compression (pressing direction) is orthogonal to the direction of the magnetic field applied to the alloy powder, and longitudinal magnetic field forming methods where the pressing direction is parallel to the direction of the magnetic field applied to the alloy powder.

[0041] In dry forming, the pressing device (forming device) has a relatively simple structure, eliminating the need for processes such as removing the dispersion medium during pressing and removing the dispersion medium from the formed body after pressing. In particular, according to the transverse magnetic field forming method, since the pressing direction is orthogonal to the magnetic field application direction, the orientation of the alloy powder oriented towards the magnetic field application direction is not disturbed, enabling the production of formed bodies with high orientation. In contrast, the longitudinal magnetic field forming method, where the pressing direction is parallel to the magnetic field application direction, tends to cause orientation disorder in the alloy powder during pressing, resulting in lower orientation compared to the transverse magnetic field forming method. Therefore, the transverse magnetic field forming method is primarily used in dry forming, while shapes that are difficult to form using the transverse magnetic field forming method, such as circular plates, rings, and thin plates, are mainly manufactured using the longitudinal magnetic field forming method.

[0042] However, in dry forming, contact between the alloy powder and the atmosphere is unavoidable during the supply of alloy powder to the cavity and during pressing. Furthermore, the molded body also comes into contact with the atmosphere when it is removed after pressing. Therefore, the oxygen content of the molded body increases, leading to a decrease in magnetic properties. Additionally, since it is difficult to avoid large friction between the alloy powder particles or between the alloy powder and the mold, the resistance to rotation and orientation of the alloy powder under the applied magnetic field increases, and there is a limit to improving the degree of orientation.

[0043] On the other hand, wet forming requires slurry supply and dedispersing medium, making the forming device more complex. However, by using a dispersing medium to suppress oxidation of the alloy powder and the formed body, the oxygen content of the formed body can be reduced. Furthermore, since a dispersing medium exists between the alloy powder and the forming material during pressing in a magnetic field, the constraint caused by friction is weaker, allowing the alloy powder to rotate more easily in the direction of the applied magnetic field. Therefore, a higher degree of orientation can be obtained. Thus, it has the advantage of being able to produce rare-earth-based sintered magnets with superior magnetic properties compared to dry forming. In this way, if wet forming is used, a higher degree of orientation and superior oxidation suppression effect can be obtained compared to dry forming, and there is a tendency for the resulting rare-earth-based sintered magnets to have higher magnetic properties.

[0044] However, this wet molding method also has problems. In wet molding, when the slurry is placed into the cavity and pressed under a magnetic field, most of the dispersion medium (oil, etc.) in the slurry needs to be discharged outside the cavity. Therefore, at least one of the upper or lower punches is provided with a discharge hole for the dispersion medium. Furthermore, as the volume of the cavity decreases due to the movement of the upper and / or lower punches, the dispersion medium contained in the pressurized slurry is discharged from this discharge hole. At this time, the dispersion medium in the slurry is filtered out from the part near the discharge hole, so in the initial stage of pressing, a layer with a high density of alloy powder, called a "filter cake layer," is formed in the part near the discharge hole.

[0045] The upper and / or lower punches move to press and shape the material, and more dispersion medium is filtered out, expanding the area of ​​the filter cake layer within the cavity. Ultimately, the entire area within the cavity becomes a filter cake layer with high alloy powder density (low dispersion medium concentration), resulting in a molded body with relatively weak bonding between the alloy powder particles.

[0046] In the initial stage of compression molding, if a filter cake layer is formed near the discharge hole, there is a tendency for the magnetic field direction to bend in the transverse magnetic field molding method. This is because the alloy powder in the filter cake layer has a high density (a large amount of alloy powder per unit volume), so its permeability is higher compared to the parts of the slurry outside the filter cake layer (a smaller amount of alloy powder per unit volume). Therefore, the magnetic field tends to concentrate in the filter cake layer. Thus, even if the magnetic field is applied approximately perpendicularly to the side of the cavity on the outside of the cavity, the magnetic field will bend towards the filter cake layer inside the cavity. Therefore, since the alloy powder is oriented along this bent magnetic field, there are sometimes oriented bends in the molded body after compression molding. If oriented bends are present, the degree of orientation in the molded body is reduced, so sometimes sufficient magnetic properties cannot be obtained in rare earth sintered magnets. The problem of reduced magnetic properties of rare earth sintered magnets due to such magnetic field bending is more pronounced the larger the size of the cavity in the direction of magnetic field application (e.g., more than 15 mm, typically more than 30 mm). Furthermore, if the cavity size in the pressing direction is 90 mm or more, the magnetic field bends significantly, resulting in a substantial reduction in the magnetic properties of the rare-earth-based sintered magnet and causing numerous cracks after sintering. Therefore, such large-sized molded bodies cannot be mass-produced using wet molding methods. Thus, to make the molded body elongated in the pressing direction, the aforementioned problems need to be addressed. Moreover, research by the inventors has shown that such problems are particularly prone to occur when the slurry concentration inside the cavity is uneven or when the slurry is not supplied evenly to the cavity.

[0047] On the other hand, in the longitudinal magnetic field forming method, the magnetic field is applied in a direction parallel to the pressing direction, i.e., parallel to the direction from the upper punch to the lower punch. Therefore, even if a filter cake layer is formed in the portion of the upper and / or lower punches near the dispersion medium outlet, the magnetic field is difficult to bend and easily enters the filter cake layer straight in the portion without a filter cake layer. Thus, it is not constrained by the size of the cavity in the direction of magnetic field application, as is the case in the transverse magnetic field forming method. However, in the longitudinal magnetic field forming method, the rotation of alloy powder particles during pressing easily causes orientation disorder, making it difficult to uniformly achieve a high residual magnetic flux density B. r .

[0048] To date, large-sized molded articles in the direction of magnetic field application have been mainly manufactured using transverse magnetic field forming based on dry forming. However, in dry forming, the oxygen content of the molded article increases, leading to a decrease in magnetic properties, and there are limits to improving the degree of orientation.

[0049] According to the method for manufacturing rare-earth-based sintered magnets and the wet forming apparatus of the present invention, the aforementioned problems of wet forming methods during transverse magnetic field forming can be solved. Therefore, rare-earth-based sintered magnets with a pressing direction of 90 mm or more can be stably manufactured by transverse magnetic field forming. Specifically, it is possible to stably manufacture rare-earth-based sintered magnets with dimensions of 90 mm or more (either longitudinal or transverse, where the magnetic field is applied and the height is the pressing direction), preferably 100 mm or more (either longitudinal or transverse, where the magnetic field is applied and the height is the pressing direction). Here, "dimensions of 90 mm or more (either longitudinal or transverse, where the magnetic field is applied and the height is the pressing direction)" means that the longitudinal dimension is 90 mm or more, the transverse dimension is 90 mm or more, and the height dimension is 90 mm or more. The same applies to "100 mm or more (length or width or height)". The shape of the molded body is preferably a cuboid. If it is a cuboid, it is easy to divide it into multiple molded body pieces. However, the molded body can also have other shapes.

[0050] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0051] <Basic Component Example>

[0052] First, refer to Figure 1 and Figure 2 A basic configuration example of the wet forming apparatus in the embodiments of the present invention will be described. Figure 1 This is a diagram showing a basic configuration example of the wet forming apparatus 100 in this embodiment. Figure 2 This is a perspective view schematically illustrating an example of the configuration of the mold 10 included in the wet forming apparatus 100. For reference, the mutually orthogonal X-axis, Y-axis, and Z-axis are shown in the figure. The Z-axis is parallel to the vertical direction, and the Y-axis is perpendicular to the plane of the paper. The XY plane, including the X-axis and Y-axis, is horizontal.

[0053] The wet forming apparatus 100 in this embodiment includes, for example, Figure 2(a) A mold 10 with a through hole 10H, as illustrated. The mold 10 is formed of a magnetic material through which magnetic flux passes. The through hole 10H extends from the upper end to the lower end of the mold 10 in the Z-axis direction. The through hole 10H has an inner wall 10W. The cross-section of the through hole 10H perpendicular to the Z-axis has a specific shape and size along the Z-axis direction. In this example, the through hole 10H has a cuboid shape, but the shape of the through hole 10H is not limited to this example. The inner wall 10W of the through hole 10H is not limited to a plane, and may contain a curved surface in part or all of it.

[0054] The shape and size of the molded body to be manufactured depend on the shape and size of the through hole 10H. For example, if the dimensions of the molded body are 100mm long × 100mm wide × 90mm high, the dimensions of the cross-section of the through hole 10H parallel to the XY plane can be less than 100mm long × less than 100mm wide. When manufacturing larger molded bodies, for example, if the dimensions of the molded body are 150mm long × 150mm wide × 100mm high or more, the dimensions of the cross-section of the through hole 10H parallel to the XY plane can be less than 150mm long × less than 150mm wide.

[0055] Refer again Figure 1 The wet forming apparatus 100 includes: a lower punch 12, which moves vertically relative to the mold 10 with at least its front end inserted into the through hole 10H; and an upper punch 14, which moves vertically relative to the lower punch 12. In this embodiment, the upper punch 14 has a lower end 14U with a plurality of discharge holes 14H through which the liquid (liquid component) contained in the slurry passes. The slurry, for example, contains an alloy powder (R-T-B alloy powder) containing rare earth elements, iron, and boron, and a dispersion medium.

[0056] In this invention, "up and down movement" refers to movement in the vertical direction. Furthermore, "A moving up and down relative to B" means that the distance between A and B in the vertical direction increases or decreases. Therefore, the up and down movement of the lower punch 12 relative to the mold 10 includes the following scenarios: the lower punch 12 moving up and down while the mold 10 is stationary; the mold 10 moving up and down while the lower punch 12 is stationary; and the mold 10 and the lower punch 12 moving up and down in the same or opposite directions. Figure 1 (b) in the state, with Figure 1 Compared to state (a), the lower punch 12 remains stationary, while the mold 10 and upper punch 14 descend. As a result, the lower punch 12 rises relative to the mold 10.

[0057] exist Figure 1In the state shown in (a), a space 16 is formed by the inner wall 10W of the through hole 10H of the mold 10 and the upper end 12T of the lower punch 12. The space 16 has a volume for receiving slurry. The upper punch 14 is located above the space 16, but the upper surface of the space 16 is open. In other words, a portion of the lower punch 12 is inserted into the lower part of the through hole 10H of the mold 10, but the space 16 is not closed by the upper punch 14. Figure 2 (b) Schematic representation of the state in which the space 16 is formed by the inner wall 10W of the through hole 10H of the mold 10 and the upper end 12T of the lower punch 12. The lower punch 12, inserted into the through hole 10H of the mold 10, is in sliding contact with the inner wall 10W of the through hole 10H. The inner wall 10W and the lower punch 12 are connected in such a way that the liquid components of the slurry can be retained leak-free in the space 16.

[0058] Reference Figure 1 (b). In Figure 1 In state (b), the lower end 14U of the upper punch 14 descends by pressing downwards against the mold 10. As a result, the space 16 is closed by the upper punch 14, forming a cavity. Figure 1 In example (b), a "filter cloth" 32 is disposed between the upper punch 14 and the mold 10. The filter cloth 32 is a cloth-like filter material made of woven synthetic fibers, etc., and can also be called a filter. Examples of filters include filter cloth, filter paper, porous filters, and metal filters. By setting such a filter, it is possible to more reliably prevent alloy powder particles from entering the discharge holes 14H, and to allow only the dispersion medium to pass through. The size of the pores present in the filter cloth 32 is determined in such a way that particles of rare earth alloy powder can hardly pass through. Specifically, the filter cloth 32 is installed on the upper punch 14 in such a way that it covers the multiple discharge holes 14H provided at the lower end 14U of the upper punch 14. In the figure, only a part of the filter cloth is shown for simplicity, but the filter cloth can be extended longer along the X-axis direction and used by winding it around a roller. When such a roller is rotated, the part of the filter cloth 32 that contacts the lower end 14U of the upper punch 14 can be switched. As a result, it is easy to switch the area of ​​the filter cloth that was contaminated in the pressing process to the area of ​​the new filter cloth to perform the next pressing process.

[0059] exist Figure 1 In example (b), with Figure 1 Compared to state (a), not only does the upper punch 14 descend, but the mold 10 also descends. By shortening the distance between the upper end 12T of the lower punch 12 and the lower end 14U of the upper punch 14, the volume of the cavity 10C can be reduced. Figure 1 (a) After the space 16 is filled with slurry, it becomes Figure 1 During the process of (b), the liquid components in the slurry are discharged from the inside of the cavity 10C to the outside through the discharge hole 14H of the filter cloth 32 and the upper punch 14.

[0060] like Figure 1 As shown, the mold 10 has an injection port 10P for injecting slurry into the interior of the space 16 formed by the inner wall 10W of the through hole 10H and the upper end 12T of the lower punch 12. The injection port 10P need not be one; there can be multiple injection ports. Furthermore, the number of through holes 10H in one mold 10 is not limited to one; there can be multiple through holes. When one mold 10 has multiple through holes 10H, the wet forming apparatus 100 includes multiple sets of lower punches 12 assigned to each through hole 10H. The injection port 10P is connected to a slurry supply device (a hydraulic device with a hydraulic cylinder), and the slurry 30 pressurized by the hydraulic cylinder, etc., is supplied to the interior of the space 16 through the injection port 10P.

[0061] The wet forming apparatus 100 includes an electromagnetic coil 20 that applies a transverse magnetic field perpendicular to the direction of the vertical movement of the lower punch 12 (Z-axis direction, i.e., vertical direction) to the interior of the through hole 10H of the mold 10 (horizontal transverse direction). Figure 1 In this example, the electromagnetic coil 20 is able to generate a transverse magnetic field within the cavity 10C, with the magnetic flux extending in the X-axis direction. As described later, in this embodiment, when injecting slurry into the interior of the space 16 from the injection port 10P, as... Figure 1 As shown in (a), the upper punch 14 is located away from the mold 10 and no magnetic field is applied.

[0062] The wet forming apparatus 100 in this embodiment also includes Figure 1 The "non-magnetic cover" not shown in the text. This non-magnetic cover temporarily or intermittently covers the space 16 when the slurry is injected into the interior of the space 16. Figure 3 This is a perspective view schematically illustrating an example of a non-magnetic cover 34. Figure 3 In the example, the non-magnetic cover 34 completely covers the through hole 10H of the mold 10. Figure 3 The dashed line schematically indicates that the non-magnetic cover 34 is in the avoidance position. The function of the non-magnetic cover 34 will be described later.

[0063] In order to implement the manufacturing method of rare earth sintered magnets of the present invention, a "non-magnetic cover" is not necessarily an indispensable element.

[0064] The wet forming apparatus in embodiments of the present invention includes a control device for controlling the movement of the upper punch 14, the lower punch 12, the mold 10, the electromagnetic coil 20, and the non-magnetic cover 34. Such a control device can be implemented by a computer that operates according to a program stored in a storage device.

[0065] <Manufacturing Method>

[0066] The following is for reference Figure 4 and Figure 5 The manufacturing method of the rare earth sintered magnet in the embodiments of the present invention will be described. Figure 4 This is an explanatory diagram illustrating the manufacturing method of the rare earth sintered magnet in this embodiment. Figure 5 This is an explanatory diagram illustrating the manufacturing method of the rare-earth sintered magnet in this embodiment. Figure 4 The description of electromagnetic coil 20 is omitted in the text.

[0067] In the manufacturing method of the rare earth sintered magnet of this embodiment, the following steps are performed.

[0068] (1): Preparation of slurry

[0069] For example, the process of preparing a slurry containing alloy powder containing rare earth elements (preferably alloy powder containing rare earth elements, iron and boron) and a dispersion medium is performed.

[0070] • Composition of alloy powder

[0071] The composition of the alloy powder may, for example, include known rare earth sintered magnet compositions containing R-T-B sintered magnets (R refers to at least one rare earth element (including the concept of yttrium (Y)), T refers to iron (Fe) or iron and cobalt (Co), and B refers to boron) and samarium-cobalt sintered magnets.

[0072] R-T-B sintered magnets are preferred. This is because they exhibit the highest magnetic energy product among various magnets and are relatively inexpensive.

[0073] The following describes the composition of a preferred R-T-B sintered magnet.

[0074] R is selected from at least one of Nd, Pr, Dy, and Tb. Preferably, R includes either Nd or Pr. More preferably, a combination of rare earth elements represented by Nd-Dy, Nd-Tb, Nd-Pr-Dy, or Nd-Pr-Tb is used.

[0075] In R, Dy and Tb are especially relevant to H. cJ To enhance performance. In addition to the elements mentioned above, small amounts of other rare earth elements such as Ce or La can be included, as well as cerium-containing mixed rare earth metals (misch metals) and neodymium-praseodymium mixtures (didymium). Furthermore, R may not be a pure element; within industrially available limits, it may contain unavoidable manufacturing impurities. The content can be of a level known in the prior art, preferably in the range of 25% by mass or more and 35% by mass or less. This is because, below 25% by mass, high magnetic properties, especially high H, are sometimes not obtained. cJ When it exceeds 35% by mass, sometimes B r reduce.

[0076] T contains iron (including cases where T is substantially composed of iron), and may be replaced by cobalt (Co) at a mass ratio of less than 50% (including cases where T is substantially composed of iron and cobalt). Co is effective in improving temperature characteristics and corrosion resistance, and the alloy powder may contain less than 10% by mass of Co. The content of T may be the remainder other than R and B, or the remainder other than R, B and M as described later.

[0077] Regarding the content of B, it can be a known content, for example, 0.8% to 1.2% by mass is a preferred range. Below 0.8% by mass, sometimes a high H content cannot be obtained. cJ When it exceeds 1.2% by mass, sometimes B r The concentration of B is reduced. A portion of B can be replaced by C (carbon). Substitution with C can sometimes improve the corrosion resistance of magnets. When the total content is B+C (including both B and C), it is preferable to convert the number of C atoms substituted into the number of B atoms and set it within the range of the aforementioned B concentration.

[0078] In addition to the elements mentioned above, in order to improve H cJ Furthermore, element M can be added. Element M is selected from one or more of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, and W. The amount of element M added is preferably 5.0% by mass or less. This is because if it exceeds 5.0% by mass, sometimes B... r Reduced. In addition, it also allows for unavoidable impurities.

[0079] • Method for manufacturing alloy powder

[0080] Alloy powder is produced, for example, by melting to form ingots or sheets of rare earth magnet raw material alloys (preferably R-T-B magnet raw material alloys) with the desired composition, and the alloy ingots and sheets are hydrogen-pulverized by absorbing (storing) hydrogen to produce coarse powder.

[0081] Then, coarse powder can be further pulverized using a grinding mill or similar device to produce fine powder (alloy powder).

[0082] An example of the manufacturing method of raw material alloys for R-T-B series magnets.

[0083] Alloy ingots can be produced by melting metal that has been pre-adjusted to the final desired composition and casting it into a mold.

[0084] In addition, alloy sheets can be produced by strip casting, which produces solidified alloys thinner than those produced by ingot casting, by contacting molten metal with a single roll, double roll, rotating disk, or rotating cylindrical mold and rapidly cooling it. This method can also be used to produce alloy sheets by rapid cooling, such as centrifugal casting.

[0085] In this invention, alloys produced by either the ingot casting method or the quenching method can also be used, but alloys produced by the quenching method are preferred.

[0086] The thickness of R-T-B series magnet raw material alloys (quenched alloys) produced by the quenching method is typically in the range of 0.03 mm to 10 mm, and they are in the form of thin sheets or plates. The alloy molten metal begins to solidify from the contact surface with the cooling rollers (roller contact surface), and crystals grow in a columnar shape from the roller contact surface along the thickness direction. Compared to alloys produced by the existing ingot casting method (mold casting method) (ingot alloys), quenched alloys are cooled in a short time, resulting in a finer microstructure and smaller crystal grain size. Furthermore, the grain boundary area is large. The R-rich phase diffuses significantly within the grain boundaries, resulting in excellent dispersion of the R-rich phase in quenched alloys.

[0087] Therefore, grain boundary fracture is easily achieved by hydrogen pulverization. By hydrogen pulverizing the rapidly cooled alloy, the size of the hydrogen-pulverized powder (coarse powder) can be set to, for example, below 1.0 mm.

[0088] By further pulverizing the coarse powder obtained in this way using a jet mill or similar method, it is possible to produce D-type lasers obtained using airflow dispersion laser analysis. 50 R-T-B alloy powder with a particle size of 2-7 μm.

[0089] The grinding mill is preferably operated in an atmosphere consisting of (a) nitrogen and / or argon (Ar) with an oxygen content of substantially 0% by mass, or (b) an atmosphere consisting of nitrogen and / or Ar with an oxygen content of 0.005 to 0.5% by mass.

[0090] In order to control the nitrogen content in the obtained sintered body, it is more preferable to set the atmosphere in the shot blasting mill to Ar gas and introduce a small amount of nitrogen gas into it to adjust the nitrogen concentration in the Ar gas.

[0091] • Dispersion medium

[0092] A dispersion medium is a liquid in which alloy powder is dispersed to make a slurry.

[0093] Mineral oil or synthetic oil can be cited as preferred dispersion media used in this invention.

[0094] There are no particular restrictions on the type of mineral oil or synthetic oil, but when the kinematic viscosity at room temperature exceeds 10 cst, the increased viscosity strengthens the bonding force between alloy powders, which can sometimes have an adverse effect on the orientation of alloy powders during wet forming in a magnetic field.

[0095] Therefore, the kinematic viscosity of mineral oil or synthetic oil at room temperature is preferably below 10 cst. In addition, when the fractionation point of mineral oil or synthetic oil exceeds 400°C, degreasing after obtaining the molded body becomes difficult, which may sometimes increase the residual carbon content in the sintered body and reduce the magnetic properties.

[0096] Therefore, the fractionation point of mineral oil or synthetic oil is preferably below 400°C.

[0097] Alternatively, vegetable oils can also be used as a dispersion medium. Vegetable oils refer to oils extracted from plants, and the types of plants are not limited to specific plants. Examples include soybean oil, rapeseed oil, corn oil, safflower oil, or sunflower seed oil.

[0098] • Preparation of slurry

[0099] It is possible to prepare a slurry by mixing the obtained alloy powder with a dispersion medium.

[0100] The mixing ratio of alloy powder to dispersion medium is not particularly limited, but the concentration of alloy powder in the slurry is preferably 70% or more by mass (i.e., 70% by mass or more). This is because, in the range of 20–600 cm⁻¹, 3 At a flow rate of / second, alloy powder can be efficiently supplied into the space, and excellent magnetic properties can be obtained.

[0101] Furthermore, the concentration of alloy powder in the slurry is preferably 90% or less by mass. This is to reliably ensure the fluidity of the slurry.

[0102] More preferably, the concentration of alloy powder in the slurry is 75% to 88% by mass. This is because the alloy powder can be supplied more effectively, and the flowability of the slurry can be ensured more reliably. More preferably, the concentration of alloy powder in the slurry is 84% ​​or more by mass. There is no particular limitation on the mixing method of the alloy powder and the dispersion medium. It can also be prepared by separately preparing the alloy powder and the dispersion medium, weighing a specified amount of both and mixing them. Alternatively, when preparing alloy powder by dry grinding coarse powder using a jet mill or the like, a container containing the dispersion medium can be placed at the alloy powder discharge port of the grinding device such as the jet mill, and the alloy powder obtained from grinding can be directly recycled into the dispersion medium in the container to obtain a slurry. In this case, it is preferable that the atmosphere inside the container is also composed of nitrogen and / or argon, so that the obtained alloy powder is directly recycled into the dispersion medium without contacting the atmosphere to make a slurry. Furthermore, it is also possible to wet grind the coarse powder while it is in the dispersion medium using a vibratory mill, ball mill, or grinding mill to produce a slurry composed of alloy powder and dispersion medium.

[0103] (2): Pressurized injection of slurry

[0104] like Figure 4(a) and Figure 4 As shown in (b), from the state where the lower punch 12 is inserted into the through hole 10H of the mold 10 in the wet forming apparatus 100, the mold 10 is raised, thereby forming a space 16 by the inner wall 10W and the upper end 12T of the lower punch 12. Figure 4 As shown in (b), during the stage when the mold 10 is fully raised, the interior of the space 16 is connected to the injection port 10P of the mold 10.

[0105] Next, as Figure 4 As shown in (c), slurry 30 is injected into the interior of space 16 through injection port 10P. The supply rate of slurry 30 can be set, for example, to 20–150 cm³. 3 The range is [number] / second. Supply rate is less than 20cm. 3 At a flow rate of / second, it is difficult to adjust the flow rate. Additionally, sometimes slurry cannot be supplied to space 16 due to piping resistance. On the other hand, if the supply exceeds 150 cm... 3 If the density of the powder molded body deviates from its normal value per second, cracks may occur when the molded body is removed after pressing, or due to shrinkage during sintering. Furthermore, the likelihood of orientation disorder occurring near the injection port 10P also increases.

[0106] The preferred slurry supply amount is 30-100 cm³. 3 / second, more preferably 40-80 cm / s 3 / second. By adjusting the flow regulating valve of the hydraulic device, which functions as a slurry supply device, the flow rate of oil supplied to the hydraulic cylinder of the hydraulic device is varied, thereby changing the speed of the hydraulic cylinder and thus controlling the slurry supply. The supply pressure of slurry 30 is, for example, 1.96MPa~14.71MPa (20kgf / cm³). 2 ~150kgf / cm 2 The injection port 10P of slurry 30 is, for example, a hole with a diameter of 2mm to 30mm.

[0107] One of the features of this embodiment is that when the slurry 30 is injected into the interior of the space 16, the space 16 is temporarily or intermittently covered by a non-magnetic cover 34.

[0108] By using the non-magnetic cap 34, the slurry 30 can be uniformly supplied to the space 16 in a manner that suppresses concentration deviation. This suppresses orientation disorder in the powder molded body produced by subsequent compression in the orientation magnetic field. Details will follow.

[0109] Typically, when slurry 30 is injected into space 16 without using a non-magnetic cover, space 16 is covered by an upper punch 14. If space 16 is filled with slurry 30 using this conventional method, at least a portion of the slurry 30 on the upper surface of space 16 comes into contact with the plurality of discharge holes 14H of the upper punch 14 or the filter cloth 32 disposed between the upper punch 14 and the mold 10, absorbing the dispersion medium contained in the slurry 30. As a result, the concentration of the slurry near the upper punch 14 in space 16 becomes higher, causing a concentration deviation. Furthermore, even when a magnetic field is applied after slurry injection, the powder particles in the slurry 30 on the upper surface of space 16 are difficult to orient. Additionally, without covering space 16 with an upper punch or the like, the following situations occur: a portion of the slurry 30 flies out of space 16 due to injection, or unevenness forms on the upper surface of the slurry, causing a concentration deviation, or the slurry cannot be uniformly supplied to the cavity. In contrast, by covering the space 16 with a non-magnetic cap 34, even if the space 16 is filled with slurry 30 and at least a portion of the slurry 30 is in contact with the non-magnetic cap 34, the dispersion medium contained in the slurry will not be absorbed by the non-magnetic cap 34. Furthermore, since the space 16 is covered with the non-magnetic cap 34, no part of the slurry 30 will fly out of the space 16 or form unevenness on the upper surface of the slurry due to slurry injection. Therefore, the slurry 30 can be uniformly supplied to the space 16 in a manner that suppresses concentration deviation. This, in turn, can suppress density deviation and orientation disorder in the powder molded body.

[0110] The non-magnetic cap 34 is made of, for example, rubber or resin. The rubber cap 34 can fit snugly against the upper end of the mold 10. Besides rubber, the non-magnetic cap 34 can also be made of, for example, silicon, non-magnetic aluminum, stainless steel, etc. Furthermore, the non-magnetic cap 34 does not include a through-hole for the slurry 30 to pass through. This is because there is a possibility that the dispersion medium contained in the slurry 30 may be absorbed by the through-hole, causing a concentration deviation. Furthermore, if the non-magnetic cap 34 is not non-magnetic, during processes such as transverse magnetic field pressing, the cap may become magnetic, and the slurry 30 may adhere to the cap. Therefore, it may be impossible to supply the slurry 30 to the space 16 in a way that suppresses concentration deviation.

[0111] As mentioned above, the non-magnetic cap 34 is not necessarily an indispensable element for implementing the method of manufacturing rare-earth-based sintered magnets according to the present invention. After injecting the slurry 30 into the space 16 without using the non-magnetic cap 34, if the slurry 30 is stirred using a rod-shaped component, for example, the concentration deviation of the slurry 30 can be reduced, thereby improving uniformity. Furthermore, the slurry 30 is particularly difficult to enter the four corners of the space 16. Therefore, for example, by injecting the slurry 30 to the point of overflowing from the space 16, the concentration deviation of the slurry 30 can also be reduced.

[0112] Figure 4 (d) schematically illustrates a state in which the non-magnetic cover 34 is slightly raised from the mold 10 to allow communication between the space 16 and the atmosphere, creating a gap between them. Through this gap, the atmospheric components contained inside the space 16 are squeezed out to the outside as the slurry 30 increases. By intermittently creating a gap between the non-magnetic cover 34 and the mold 10, the pressure inside the space 16 can be maintained at approximately atmospheric pressure, thus allowing for a smooth supply of the slurry 30.

[0113] Figure 4 (e) indicates the state in which space 16 is filled with slurry 30. At this time, space 16 is sealed by non-magnetic cover 34, and the filling amount of slurry 30 reaches the specified value. If slurry 30 is supplied to space 16 without non-magnetic cover 34, as described above, it is possible to form unevenness on the upper surface of slurry 30 during filling. With non-magnetic cover 34, the interior of space 16 with a desired volume can be filled with slurry 30.

[0114] The space 16 is sealed with the non-magnetic cover 34, for example, when about half of the space 16 is filled with slurry 30. Subsequently, as the amount of slurry 30 supplied to the space 16 increases, the internal pressure of the space 16 rises, so the non-magnetic cover 34 is lifted once or multiple times, reducing the internal pressure to a level equal to atmospheric pressure. This action can be achieved, for example, by mounting the upper surface of the non-magnetic cover 34 to a cylinder and mechanically or electrically driving the cylinder in the vertical direction.

[0115] When the space 16 is filled with a specified amount of slurry 30, the space 16 is sealed by a non-magnetic cover 34. At this time, the slurry 30 preferably contacts the lower surface of the non-magnetic cover 34, but a small gap (less than 1 mm) may also exist.

[0116] Another feature of this embodiment is that no magnetic field is applied to the space 16 when the slurry 30 is injected into the space 16 (non-magnetic field injection). If the slurry is injected while a magnetic field is applied (magnetic field injection), there is a possibility that the density of different parts of the powder molded body obtained after pressing will vary significantly. This is believed to be because, just before the slurry 30 is injected, the alloy powder in the slurry is attracted by the mold 10 or the lower punch 12, thereby separating the solid alloy powder from the liquid dispersion medium (solid-liquid separation), and the separated dispersion medium accumulates around the space 16. If the slurry 30 is supplied under such conditions, and the space 16 is filled with the slurry 30 before pressing, the density of the alloy powder around the cavity 10C (the amount of alloy powder per unit volume) will be lower than that of the center and bottom of the cavity 10C. As a result, the density of the upper and surrounding parts may be lower than that of the center and bottom of the obtained molded body. If the density varies in different parts of the molded body, the magnetic properties of the sintered magnet obtained by sintering the molded body will decrease, and deviations will occur due to different locations. Furthermore, if such density deviations exist, cracks may sometimes occur in the molded body when it is removed after pressing. Even if cracks do not occur in the molded body, they may still occur due to shrinkage during sintering. In this embodiment, since no magnetic field is applied during slurry supply, this density deviation problem can be solved. In the prior art, it is believed that slurry needs to be injected under a magnetic field to obtain high magnetic properties. This is because, compared to injection in a magnetic field, it is particularly difficult to orient the central portion of the magnet when injection is performed without a magnetic field. However, the inventors conducted research and found that by using the above-described non-magnetic cap method, when the slurry 30 is supplied to space 16 in a manner that suppresses concentration deviation and then a transverse magnetic field molding method is applied, the central portion of the magnet is uniformly oriented, and the magnetic properties do not decrease. On the other hand, if a longitudinal magnetic field molding method is applied, the magnetic properties decrease due to the orientation disorder caused by pressing.

[0117] Preferably, after filling space 16 with slurry, as Figure 4 As shown in (f), the lower punch 12 is lowered relative to the die 10, thereby, as Figure 5 As shown in (a), when the upper punch 14 is lowered to close the space 16, a gap is formed at the lower end of the upper punch 14 or (in the case of using filter cloth 32) between the filter cloth and the slurry 30. Specifically, the position of the lower punch 12 is lowered relative to the mold 10 by a distance of 1 mm or more and 30 mm or less (e.g., 3 mm). As a result, after the slurry 30 is filled, the space 16 expands, and an air layer gap is formed in the upper part of the space 16. The size of the gap is preferably 2 mm or more and 4 mm or less, for example, about 3 mm. Figure 4In example (f), the method of raising the mold 10 relative to the lower punch 12, but forming such an air gap on the upper surface of the slurry 30, is not limited to this example. For example, the lower punch 12 can be lowered while the position of the mold 10 is fixed. Additionally, a "locking structure" of the size and shape of the through hole 10H embedded in the mold 10 can be formed on the lower surface of the non-magnetic cover 34. Specifically, the non-magnetic cover 34 avoids the position covering the mold 10 before or after forming the air gap. Figure 3 That is, the non-magnetic cover 34 can be moved from the position of the covered space 16 before a transverse magnetic field is applied to the cavity 10C.

[0118] In addition, Figure 4 In state (f), the upper punch 14 is located away from the mold 10, but it can also begin to descend at the same time the mold 10 begins to rise. Importantly, even when the upper punch 14 descends, the filter cloth 32 located at its lower end will not come into contact with the slurry 30. If the upper punch 14 separates from the mold 10, even if the descent of the upper punch 14 begins at or just before the mold 10 begins to rise, the filter cloth 32 will not come into contact with the slurry 30.

[0119] (3): Preparations before pressing and shaping in the transverse magnetic field

[0120] Next, the lower end 14U of the upper punch 14 closes the space 16, thereby forming a cavity 10C filled with slurry 30. Specifically, as Figure 5 As shown in (a), the upper punch 14 is lowered relative to the mold 10, closing the space 16. At this time, a filter cloth 32 is disposed between the mold 10 and the upper punch 14, but as described above, it is preferable to form an air gap between the filter cloth 32 and the slurry 30 so that the filter cloth 32 does not come into contact with the slurry 30. This reliably avoids the following situations: the filter cloth 32 comes into contact with the slurry 30 before the magnetic field is applied, the dispersion medium contained in the slurry 30 is absorbed by the filter cloth 32, the concentration of alloy powder near the upper surface of the slurry 30 increases excessively, resulting in a concentration deviation, or even if a magnetic field is applied, it is difficult to produce the orientation of powder particles.

[0121] (4): Pressing and molding in a transverse magnetic field

[0122] Next, while applying a "transverse magnetic field" perpendicular to the direction of the up-and-down movement of the lower punch 12 to the cavity 10C, the gap between the lower end 14U of the upper punch 14 and the upper end 12T of the lower punch 12 is reduced. Figure 5 (b) and Figure 5(c) indicates the case where the distance between the lower end 14U of the upper punch 14 and the upper end 12T of the lower punch 12 is reduced. The dispersion medium contained in the slurry 30 is discharged through multiple discharge holes 14H in the upper punch 14, resulting in a molded body 50 of alloy powder. The magnitude of the magnetic field formed inside the cavity 10C is, for example, 1.0T or more and 1.5T or less. When the transverse magnetic field is applied, it is preferable that there is an air gap G between the filter cloth 32 and the slurry 30. When the transverse magnetic field is first applied, a portion of the alloy powder particles contained in the slurry 30 moves due to the magnetic force, and a protrusion or concave portion may be formed on the upper surface of the slurry 30. However, the direction of the magnetic field is horizontal and orthogonal to the pressing direction, so the orientation direction is aligned through the pressing process.

[0123] If the magnetic field strength is above 1.0T, the magnetization direction of the alloy powder contained in the slurry 30 will more reliably align with the direction of the magnetic field, resulting in a high degree of orientation. If it is less than 1.0T, the orientation degree of the alloy powder will decrease, or the orientation of the alloy powder will easily become disordered during pressing. The strength of the magnetic field inside the cavity 10C can be determined by measuring it with a gaussmeter or by magnetic field analysis.

[0124] The electromagnetic coil 20 is positioned near the side of the mold 10 and can form a uniform magnetic field perpendicular to the pressing direction within the cavity 10C.

[0125] To describe the state within the cavity 10C in more detail, during the pressing process in a magnetic field, if the volume of the cavity 10C decreases, as described above, the dispersion medium in the slurry 30 is filtered and discharged from the portion of the upper punch 14 near the discharge hole 14H through the discharge hole 14H, but the alloy powder contained in the slurry 30 remains in the cavity 10C. Therefore, a "filter cake layer" is formed from the portion near the discharge hole 14H. As previously described, the filter cake layer is a layer where the dispersion medium in the slurry is discharged to the outside of the cavity 10C, resulting in a higher concentration of alloy powder. During the pressing process, the filter cake layer eventually expands to the entire cavity 10C, resulting in a powder molded body where the alloy powder particles are in contact with each other. In this embodiment, no filter cake layer is formed when the transverse magnetic field is initially applied, resulting in the suppression of orientation disorder near the upper punch 14.

[0126] After forming the molded body 50, as Figure 5 As shown in (d), the mold 10 is lowered, as... Figure 5 As shown in (e), the molded body 50 is exposed outside the mold 10. Then, as... Figure 5 As shown in (f), the molded body 50 can be removed by raising the upper punch 14.

[0127] The molded body obtained through the above process contains residual dispersion media such as mineral oil or synthetic oil. If the molded body in this state is rapidly heated from room temperature to a sintering temperature of, for example, 950–1150°C, the internal temperature of the molded body rises sharply. Sometimes, the dispersion media remaining in the molded body reacts with the rare earth elements of the molded body to form rare earth carbides. When rare earth carbides are formed, they hinder the generation of a sufficient amount of liquid phase during sintering, sometimes resulting in a sintered body with insufficient density and reduced magnetic properties. Therefore, it is preferable to perform a degreasing treatment on the molded body before sintering. This is because it can effectively remove the residual dispersion media from the molded body.

[0128] (5): The process of dividing the material into shaped pieces (first dividing process)

[0129] In this embodiment, the molded body produced by pressing in a transverse magnetic field can also be divided into multiple molded body pieces. For example, a first dividing process can be performed after the process of producing the molded body and before the process of sintering the molded body, to cut each molded body into 10 or more molded body pieces.

[0130] In this embodiment, a molded body, for example, 100 mm long × 100 mm wide × 90 mm high, can be sliced ​​into plate-shaped molded body pieces, for example, 9.5 mm long (magnetization direction) × 100 mm wide × 90 mm high, using a wire saw. The number, size, and shape of the molded body pieces are not limited to this example. Alternatively, a known cutting blade can be used instead of a wire saw for cutting.

[0131] The larger the size of the molded body, the more sintered magnets can be produced from a single molded body. In existing methods, the larger the molded body, the more uneven the density of the slurry, making it difficult to increase its size. According to embodiments of the present invention, the dimensions of the molded body can be 90 mm or more in length, 90 mm or more in width, and 90 mm or more in height (preferably 100 mm or more in length, 100 mm or more in width, and 90 mm or more in height, more preferably 120 mm or more in length, 120 mm or more in width, and 100 mm or more in height, and most preferably 150 mm or more in length, 150 mm or more in width, and 100 mm or more in height).

[0132] (6): Sintering process (process for making raw materials for sintered bodies)

[0133] Next, the shaped body (the cut shaped body sheet) is sintered to produce a rare earth sintered magnet. In this invention, when the sintered body of the shaped body sheet is further cut, the sintered body of the shaped body sheet is referred to as the "sintered body raw material". Hereinafter, for simplicity, the shaped body sheet will sometimes be simply referred to as the "shaped body".

[0134] The sintering of the molded body is preferably carried out at 0.13 Pa (10). －3Torr) or less, more preferably at 0.07 Pa (5.0 × 10⁻⁶ Pa). －4 The process is carried out at pressures below Torr and temperatures ranging from 1000°C to 1150°C. To prevent oxidation caused by sintering, residual gases in the atmosphere can be replaced by inert gases such as helium or argon. The dimensions of the sintered body obtained by sintering the molded sheet can be, for example, 4 mm or more in the longitudinal direction, 40 mm or more in the transverse direction, and 5 mm or more in the height direction.

[0135] (7): The process of dividing the material into sintered sheets (second dividing process)

[0136] In this embodiment, a second dividing process is performed, in which the sintered raw material obtained by sintering the molded body sheets is cut into multiple sintered body sheets. This second dividing process allows for the production of more than 100 sintered body sheets from a single sintered raw material. The cutting of the sintered raw material can be performed, for example, by a cutting saw. According to this embodiment, more than 1000 (=10×100) rare earth sintered magnets can be produced from a single large molded body (90mm or more in length, 90mm or more in width, and 90mm or more in height), improving mass production capabilities.

[0137] In this embodiment, a diffusion process can be further performed on the sintered raw material before cutting to diffuse a heavy rare earth element RH (RH being at least one of Tb, Dy, and Ho) from the surface to the interior. Diffusion of the heavy rare earth element RH from the surface to the interior of the sintered body effectively improves coercivity. This diffusion process is particularly effective when the sintered raw material has a plate-like shape with a thickness of 1 mm or more and 20 mm or less. By diffusing from two opposing surfaces in the thickness direction, the heavy rare earth element RH can be efficiently diffused deep into the interior of the sintered raw material. If the diffusion of the heavy rare earth element RH is performed after the sintered raw material is divided into sintered sheets, there is a tendency for an increase in the amount of heavy rare earth element RH consumed to obtain the desired magnetic properties. Therefore, the diffusion of the heavy rare earth element RH is preferably performed on the sintered raw material before it is divided into sintered sheets.

[0138] Reference Figure 6 The process flow from the cutting process of the shaped body sheet to the cutting process of the sintered body raw material in a preferred embodiment is summarized as follows. Additionally, in... Figure 6 In the diagram, the direction of the orientation magnetic field (magnetic field orientation direction) M is indicated by an arrow. Ultimately, the magnetized material is magnetized in a direction parallel to this magnetic field orientation direction M.

[0139] Figure 6 The process flow is illustrated schematically.

[0140] • The process of preparing the molded body 50 (S10),

[0141] • The process of cutting the molded body 50 and dividing it into multiple molded body pieces 52 (S20)

[0142] • Sintering process (S30): Multiple sintered raw materials 54 are produced by sintering multiple molded sheets 52 separately.

[0143] • A process (S40) in which powder 56 containing the heavy rare earth element RH from a diffusion source is brought into contact with at least one of the upper surface 54a and lower surface 54b in the thickness direction of each sintered raw material 54 and heat-treated to allow at least a portion of the R contained in the diffusion source powder to diffuse from the upper surface 54a and / or lower surface 54b of each sintered raw material into the interior.

[0144] • Includes a process (S50) of cutting each sintered body raw material 54 from the upper surface 54a to the lower surface 54b to divide it into multiple sintered body pieces 58.

[0145] After the sintering process, the sintered body (including the raw material or sheet) is preferably heat-treated at a temperature lower than the sintering temperature. Heat treatment improves the magnetic properties. Known conditions can be used for heat treatment temperature, heat treatment time, and other heat treatment conditions. The resulting rare-earth sintered magnet is then subjected to grinding, polishing, surface treatment, and coating processes as needed, followed by a magnetization process to complete the final rare-earth sintered magnet.

[0146] Example

[0147] (Example 1)

[0148] To form Nd 22 Pr6Dy3B 0.94 Co2Al 0.25 Cu 0.1 The raw alloy was melted in a high-frequency furnace with a balance of Fe (mass%), and the molten alloy was then rapidly cooled using a strip casting method to obtain thin sheet alloys with a thickness of 0.5 mm. The alloy was then coarsely pulverized using hydrogen pulverization, and subsequently finely pulverized using a jet mill. The particle size D of the obtained R-T-B alloy powder was... 50 The thickness was 4.7 μm. The above R-T-B alloy powder was impregnated in mineral oil with a fractionation point of 250 °C and a kinematic viscosity of 2 cSt at room temperature under a nitrogen atmosphere to prepare a slurry. The slurry concentration was 85% by mass.

[0149] wet molding Figure 1The wet molding apparatus shown is used. Mold 10 uses a space 16 with dimensions of 100mm in length and 100mm in width (in the direction of magnetic field application). The depth of space 16 is 90mm. A slurry supply device is used to supply slurry at a concentration of 85% by mass and a slurry supply rate of 50cm³. 3 Slurry is supplied from supply port 15 to space 16 at a rate of / second. When space 16 is approximately half-filled with slurry 30, a non-magnetic cover 34 is placed over it. Subsequently, as the amount of slurry 30 supplied to space 16 increases, the non-magnetic cover 34 is repeatedly lifted using a cylinder (not shown) to maintain the internal pressure at a level equal to atmospheric pressure. After space 16 is completely filled with slurry, the non-magnetic cover 34 is moved out of space 16.

[0150] Then, as Figure 4 As shown in (f), when the upper punch 14 is lowered, in order to form a gap between the filter cloth 32 and the slurry 30, the position of the lower punch 12 is lowered by 3 mm relative to the mold 10. Then, as... Figure 5 As shown in (a), the upper punch 14 is lowered relative to the mold 10 to close the space 16 and form a cavity 10C. Then, a magnetic field of 1.5T is applied in the cavity 10C in the transverse direction (100mm direction) of the cavity 10C, so that the gap between the lower end 14U of the upper punch 14 and the upper end 12T of the lower punch 12 is reduced, and the lower punch 12 is pressed and formed in the transverse magnetic field.

[0151] Density was measured at 17 different locations on the molded body produced under these conditions, and the resulting variance was 0.04 g / cm³. 3 The value is sufficiently low.

[0152] Next, before the sintering process of each molded body, these molded bodies are cut into 20 molded body pieces by wire machining.

[0153] The resulting molded sheets were heated in a vacuum from room temperature to 150°C at a rate of 1.5°C / min, held at that temperature for 1 hour, then heated to 500°C at a rate of 1.5°C / min to remove the mineral oil from the molded sheets. The temperature was then further increased from 500°C to 1100°C at a rate of 20°C / min, and held at 1100°C for 2 hours for sintering. This yielded sintered raw materials from each molded sheet. The sintered bodies were confirmed to be free of cracks. Subsequently, the sintered raw materials were divided into 200 sintered sheets.

[0154] The obtained sintered sheet was heat-treated at 900℃ for 1 hour, and then further heat-treated at 600℃ for 1 hour to obtain an R-T-B sintered magnet. The obtained R-T-B sintered magnet was machined to a size of 7×7×7 (mm), and the magnetic properties of 10 magnets were measured using a BH tracer. The magnetic properties of the magnets were then analyzed from the measured B... rFind B by subtracting the minimum value from the maximum value. r The deviation is 0.011T, which is a sufficiently low value.

[0155] (Example 2)

[0156] To form Nd 30.1 Pr 0.5 Dy 1.0 B 1.0 Co 1.0 Al 0.1 Cu 0.1 The raw alloy was melted in a high-frequency furnace with a balance of Fe (mass%), and the molten alloy was then rapidly cooled using a strip casting method to obtain thin sheet alloys with a thickness of 0.5 mm. The alloy was then coarsely pulverized using hydrogen pulverization, and subsequently finely pulverized using a jet mill. The particle size D of the obtained R-T-B alloy powder was... 50 The thickness was 4.7 μm. The above R-T-B alloy powder was impregnated in mineral oil with a fractionation point of 250 °C and a kinematic viscosity of 2 cSt at room temperature under a nitrogen atmosphere to prepare a slurry. The slurry concentration was 85% by mass.

[0157] wet molding Figure 1 The wet molding apparatus shown is used. Mold 10 uses a space 16 with dimensions of 90mm vertically and 100mm horizontally (in the direction of magnetic field application). The depth of space 16 is 85mm. A slurry supply device is used to supply slurry at a concentration of 85% by mass and a slurry supply rate of 50cm³. 3 Slurry is supplied from supply port 15 to space 16 at a rate of / second. When space 16 is approximately half-filled with slurry 30, a non-magnetic cover 34 is placed over it. Subsequently, as the amount of slurry 30 supplied to space 16 increases, the non-magnetic cover 34 is repeatedly lifted using a cylinder (not shown) to maintain the internal pressure at a level equal to atmospheric pressure. After space 16 is completely filled with slurry, the non-magnetic cover 34 is moved out of space 16.

[0158] Then, as Figure 4 As shown in (f), in order to create a gap between the filter cloth 32 and the slurry 30, the position of the lower punch 12 is lowered by 3 mm relative to the mold 10. Then, as... Figure 5 As shown in (a), the upper punch 14 is lowered relative to the mold 10 to close the space 16 and form a cavity 10C. Then, a magnetic field of 1.5T is applied in the cavity 10C in the transverse direction (100mm direction) of the cavity 10C, so that the gap between the lower end 14U of the upper punch 14 and the upper end 12T of the lower punch 12 is reduced, and the mold is pressed in the transverse magnetic field (condition A).

[0159] For comparison, pressing and forming in a longitudinal magnetic field was performed in the same manner as in condition A (condition B), except that the direction of the applied magnetic field was set to the depth direction (85mm direction). Furthermore, pressing and forming in a transverse magnetic field was performed under the same conditions (condition C), except that the space 16 was covered by an upper punch, without using a non-magnetic cover 34.

[0160] Under conditions A, B, and C, 200 molded bodies were fabricated respectively. The resulting molded bodies were heated in a vacuum from room temperature to 150°C at a rate of 1.5°C / min, held at 1100°C for 1 hour, then heated to 500°C at a rate of 1.5°C / min to remove mineral oil. The temperature was further increased from 500°C to 1100°C at a rate of 20°C / min, and held at this temperature for 2 hours for sintering. The resulting sintered bodies were heat-treated at 900°C for 1 hour, then further heat-treated at 600°C for 1 hour to obtain R-T-B sintered magnets. The obtained R-T-B sintered magnets were machined to a size of 7×7×7 (mm), and their magnetic properties were measured using a BH tracer. The B-values ​​of the 200 magnets under conditions A, B, and C were measured respectively. r and H cJ Calculate their average value. The results are shown in Table 1. Additionally, by measuring B... r Find B by subtracting the minimum value from the maximum value. r Deviation, through the measurement of H cJ Find H by subtracting the minimum value from the maximum value. cJ Deviation. The results are also shown in Table 1.

[0161] [Table 1]

[0162]

[0163] As shown in Table 1, Example B of the present invention r and H cJ The deviation is small, enabling stable production of high magnetic properties. Compared with the example of the present invention (condition A), condition B has... r Significantly reduced; condition C compared to the present invention example (condition B), B r and H cJ The deviation is large.

[0164] Industrial availability

[0165] The method for manufacturing rare-earth sintered magnets and the wet forming apparatus of the present invention are suitable for manufacturing rare-earth sintered magnets with reduced oxygen concentration. Such rare-earth sintered magnets can be used in various motors such as voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), motors for industrial equipment, and household appliances.

[0166] Symbol Explanation

[0167] 10… Mold

[0168] 10H…through hole

[0169] 10W…inner wall

[0170] 12… Down punch

[0171] 12T… Upper end of the lower punch

[0172] 14…Upward punch

[0173] 14H… Discharge hole of the upper punch

[0174] 14U… Lower end of the upper punch

[0175] 20…electromagnetic coil

[0176] 16…space

[0177] 30…slurry

[0178] 100…wet forming device.

Claims

1. A method for manufacturing a rare-earth-based sintered magnet, comprising feeding a slurry containing alloy powder containing rare-earth elements and a dispersion medium into the space of a mold, pressing the supplied slurry to obtain a molded body, and sintering the molded body, characterized in that: When supplying the slurry into the space of the mold, no transverse magnetic field is applied, and the space is temporarily or intermittently covered with a non-magnetic cap that does not absorb the dispersion medium. Before applying the transverse magnetic field to the space, the non-magnetic cover is moved from its position covering the space. A filter cloth is provided above the space of the mold. When the dispersion medium is discharged from the space of the mold, a transverse magnetic field in a direction orthogonal to the pressing direction is applied before the discharge.

2. The method for manufacturing rare earth sintered magnets as described in claim 1, characterized in that: The dimensions of the molded body are 90mm or more in length, 90mm or more in width, and 90mm or more in height.

3. The method for manufacturing a rare-earth-based sintered magnet as described in claim 1 or 2, characterized in that, include: The first dividing process involves cutting the molded body into more than 10 molded body pieces. and The sintered body raw material production process involves, after the first division process, sintering multiple shaped body sheets to produce multiple sintered body raw materials.

4. The method for manufacturing rare earth-based sintered magnets as described in claim 3, characterized in that, include: The second dividing process, after the sintered body raw material production process, involves cutting multiple sintered body raw materials into more than 100 sintered body pieces.

5. The method for manufacturing a rare-earth-based sintered magnet as described in claim 1 or 2, characterized in that: Before the transverse magnetic field is applied, a gap is formed between the device for pressing and shaping the slurry and the upper surface of the slurry.

6. A method for manufacturing a rare-earth-based sintered magnet, characterized in that, include: A process for preparing a wet forming apparatus, the wet forming apparatus comprising: a mold having a through hole; a lower punch that moves vertically relative to the mold with at least its front end inserted into the through hole; and an upper punch that moves vertically relative to the lower punch, the upper punch having a lower end with a plurality of discharge holes for liquid to pass through, a cavity being formed inside the through hole by the upper end of the lower punch and the lower end of the upper punch, the volume of the cavity being reduced by decreasing the distance between the upper end of the lower punch and the lower end of the upper punch; The process of preparing a slurry containing alloy powder with rare earth elements and a dispersion medium. The process of injecting slurry into the space formed by the inner wall of the through hole in the wet forming device and the upper end of the lower punch, and filling the space with the slurry; The process of using the lower end of the upper punch to close the space and form the cavity filled with the slurry; Under the condition of applying a transverse magnetic field perpendicular to the direction of the up-and-down movement of the lower punch to the cavity, the gap between the lower end of the upper punch and the upper end of the lower punch is reduced, and the dispersion medium contained in the slurry is discharged through the plurality of discharge holes in the upper punch, in order to produce a molded body of the alloy powder; and The process of sintering the molded body, When injecting the slurry into the space, no magnetic field is applied to the space, and the space is temporarily or intermittently covered with a non-magnetic cap that does not absorb the dispersion medium. After the slurry is injected and before the non-magnetic cap is removed, an air gap is formed between the underside of the upper punch and the slurry, or optionally between the filter cloth and the slurry. Before applying the transverse magnetic field to the cavity, the non-magnetic cover is moved from its position covering the space.

7. The method for manufacturing a rare earth-based sintered magnet as described in claim 6, characterized in that: In the process of forming a molded body of the alloy powder while reducing the distance between the lower end of the upper punch and the upper end of the lower punch, a filter cloth or filter is disposed between the slurry in the cavity and the lower end of the upper punch.

8. The method for manufacturing a rare earth-based sintered magnet as described in claim 6 or 7, characterized in that: The process includes the following steps: after filling the space with the slurry, moving the non-magnetic cover from the position covering the space, and at least before the application of the transverse magnetic field, causing the lower punch to descend relative to the mold, thereby forming a gap between the lower end of the upper punch and at least one of the filter cloth and the slurry.

9. The method for manufacturing a rare earth-based sintered magnet as described in claim 8, characterized in that: The size of the gap is greater than 2mm and less than 4mm.

10. The method for manufacturing a rare earth-based sintered magnet as described in claim 6 or 7, characterized in that: After filling the space with the slurry, the non-magnetic cover is moved from its position covering the space. The transverse magnetic field is applied before the dispersion medium contained in the slurry is discharged through the plurality of discharge holes in the upper punch.

11. The method for manufacturing a rare earth-based sintered magnet as described in claim 6 or 7, characterized in that: This includes a process of temporarily connecting the interior and exterior of the space by moving the non-magnetic cover up and down when injecting the slurry into the space.

12. The method for manufacturing a rare earth-based sintered magnet as described in claim 6 or 7, characterized in that: The concentration of the alloy powder in the slurry during injection is 75-88% by mass.

13. A wet forming apparatus for producing molded bodies of rare earth alloy powder, characterized in that, include: A mold with a through hole; The lower punch moves up and down relative to the mold while at least its front end is inserted into the through hole; The upper punch moves up and down relative to the lower punch and has a lower end with a plurality of discharge holes for liquid to pass through. and An electromagnetic coil applies a transverse magnetic field, perpendicular to the direction of the up-and-down movement of the lower punch, to the interior of the through-hole of the mold. The mold has an injection port that injects a slurry containing the rare earth alloy powder into the space formed by the inner wall of the through hole and the upper end of the lower punch. The wet molding apparatus also includes a non-magnetic cover that does not absorb the dispersion medium, which temporarily or intermittently covers the space when the slurry is injected into the space. After the slurry is injected and before the non-magnetic cap is removed, an air gap is formed between the underside of the upper punch and the slurry, or between the filter cloth and the slurry, if optionally used.

14. The wet forming apparatus as described in claim 13, characterized in that: The wet forming apparatus includes a control device for controlling the upper punch, lower punch, mold, electromagnetic coil, and the movement of the non-magnetic cover. The control device performs the following procedures: The process of forming the space by the inner wall of the through hole in the wet forming device and the upper end of the lower punch, injecting the slurry into the space, and filling the space with the slurry; The process of forming a cavity filled with slurry by closing the space using the lower end of the upper punch; and Under the condition of applying a transverse magnetic field perpendicular to the direction of the up-and-down movement of the lower punch to the cavity, the gap between the lower end of the upper punch and the upper end of the lower punch is reduced, and the dispersion medium contained in the slurry is discharged through the plurality of discharge holes in the upper punch, thus forming a molded body of the rare earth alloy powder. Furthermore, when injecting the slurry into the space, no magnetic field is applied to the space, and the space is temporarily or intermittently covered by the non-magnetic cover. Before applying the transverse magnetic field to the cavity, the non-magnetic cover is moved from its position covering the space.

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