Method for manufacturing rare earth sintered magnet

Abstract

To provide a rare earth sintered magnet having a shape, size, and electrical characteristics that are difficult to obtain by grinding.SOLUTION: A manufacturing method of the rare earth sintered magnet includes the steps of: producing a plurality of sintered body materials from a compact of alloy powders including a rare earth element; producing a laminated sintered body by joining at least two of the sintered body materials using an adhesive layer; and dividing crosswise over the adhesive layer the laminated sintered body into a plurality of sintered body pieces.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application relates to a method for manufacturing a rare earth sintered magnet.

Background Art

[0002] An R-T-B sintered magnet (where R is a rare earth element, including at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one transition metal and necessarily includes Fe, and B is boron), which is a representative example of rare earth sintered magnets, is composed of a main phase of a compound having an R2Fe 14 B-type crystal structure, a grain boundary phase located at the grain boundary portion of this main phase, and a compound phase generated by the influence of trace additive elements and impurities. The R-T-B sintered magnet has a high residual magnetic flux density B r (hereinafter, may be simply referred to as "B r ") and a high coercive force H cJ (hereinafter, may be simply referred to as "H cJ "), and is known as the highest performance magnet among permanent magnets because it has excellent magnetic properties.

[0003] Therefore, R-T-B sintered magnets are used in various motors in the automotive field such as electric vehicles (EV, HV, PHV), the renewable energy field such as wind power generation, the household electrical appliance field, and the industrial field. The R-T-B sintered magnet is an indispensable material for reducing the size and weight of these motors and improving their efficiency and energy conservation (improvement of energy efficiency). In addition, the R-T-B sintered magnet is used in the drive motors of electric vehicles, and by replacing internal combustion engine vehicles with electric vehicles, it also contributes to preventing global warming by reducing greenhouse gas emissions such as carbon dioxide (reduction of fuel and exhaust gas). Thus, the R-T-B sintered magnet greatly contributes to the realization of a green energy society.

[0004] Rare-earth sintered magnets such as R-T-B sintered magnets are manufactured, for example, through a process of preparing alloy powder, a process of press-forming the alloy powder to produce a formed body, and a process of sintering the formed body. The alloy powder is produced, for example, by the following method.

[0005] First, an alloy is produced from the molten metal of various raw material metals by a method such as the ingot method or the strip casting method. The obtained alloy is subjected to a pulverization process to obtain alloy powder having a predetermined particle size distribution. This pulverization process usually includes a coarse pulverization process and a fine pulverization process. The former is performed, for example, by utilizing the phenomenon of hydrogen embrittlement, and the latter is performed, for example, using an air-flow pulverizer (jet mill).

[0006] The sintered body obtained by the process of sintering the formed body is then subjected to mechanical processing such as grinding and cutting, and is fragmented into individual pieces having a desired shape and size. Also, there are cases where electrical insulation (electrical resistance) is required for the sintered body. More specifically, the sintered body is first compression-molded with an R-T-B rare-earth magnet powder using a pressing device to produce a formed body having a size larger than the final magnet product. Then, the formed body is sintered by a sintering process to produce a sintered body. The sintered body may be subjected to a diffusion treatment in which a diffusion source containing the rare-earth element R is diffused from the magnet surface to the inside as needed. And, the sintered body after sintering or diffusion is ground, for example, with a carbide blade saw or a rotary grinding wheel to impart a desired shape. For example, after first producing a sintered body having a block shape, a plurality of plate-shaped sintered body portions are cut out by slicing the sintered body with a blade saw or the like.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] As described above, rare-earth sintered magnets are used in a wide variety of applications, and since their shapes and required characteristics are also diverse, it has sometimes been difficult to efficiently obtain a sintered body having a desired shape, size, and electrical characteristics by simply grinding the sintered body after sintering or after diffusion.

[0009] Embodiments of the present disclosure provide a method for manufacturing a rare-earth sintered magnet that can solve such problems.

Means for Solving the Problems

[0010] The method for manufacturing a rare-earth sintered magnet of the present disclosure includes, in an exemplary embodiment, a step of producing a plurality of sintered body materials from a molded body of an alloy powder containing a rare-earth element, a step of joining at least two of the sintered body materials with an adhesive layer to produce a laminated sintered body, and a step of cutting the laminated sintered body so as to cross the adhesive layer to divide it into a plurality of laminated sintered body pieces.

[0011] In a certain embodiment, in the laminated sintered body, a coating layer is provided between one of the two sintered body materials sandwiching the adhesive layer and the adhesive layer.

[0012] In a certain embodiment, in the laminated sintered body, coating layers are provided between both of the two sintered body materials sandwiching the adhesive layer and the adhesive layer, respectively.

[0013] In a certain embodiment, the total thickness of the adhesive layer and the coating layer is 4 μm or more and 250 μm or less.

[0014] In a certain embodiment, each of the plurality of laminated sintered body pieces includes at least two portions electrically separated by the adhesive layer and the coating layer.

[0015] In a certain embodiment, the coating layer is formed on the surface after diffusing a rare-earth element from the surface of the plurality of sintered body materials.

[0016] In one embodiment, the surfaces of the plurality of sintered body materials are roughened before the coating layer is formed.

[0017] In one embodiment, the step of producing the plurality of sintered body materials includes a step of compression molding the alloy powder in an oriented magnetic field to produce the molded body, a step of cutting the molded body to divide it into a plurality of molded body pieces, and a step of sintering the plurality of molded body pieces to obtain the plurality of sintered body materials.

Effects of the Invention

[0018] According to the embodiment of the present disclosure, a sintered body having a shape, size, and electrical characteristics that are difficult to obtain by grinding can be efficiently obtained.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

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Figure 9

DETAILED DESCRIPTION OF THE INVENTION

[0020] As described above, it may be difficult to obtain a sintered body having a desired shape and size by simply grinding the sintered body after sintering or after diffusion. For this reason, bonding a plurality of sintered bodies with an adhesive is considered an effective countermeasure. When the adhesive has insulating properties, an effect of reducing eddy currents is also expected. However, according to the study by the present inventor, it has been found that applying an adhesive to each of the small-sized processed sintered bodies and joining the sintered bodies together is not suitable for mass production. This is because it takes a long time to apply the adhesive to a large number of small sintered bodies. As a result of further study by the present inventor, if a laminated structure is produced by joining a plurality of relatively large sintered body materials in the stage before being processed small with an adhesive layer, and the laminated structure is cut to produce a small-sized laminated sintered body, it becomes unnecessary to apply the adhesive to a large number of small sintered bodies, and it is possible to produce the sintered body efficiently, so that it is possible to improve mass productivity, and the present invention has been completed.

[0021] Hereinafter, an embodiment of a method for manufacturing a rare earth sintered magnet according to the present disclosure will be described. The method for manufacturing a rare earth sintered magnet in the present embodiment, as shown in the flowchart of FIG. 1, · a step (S10) of producing a plurality of sintered body materials from a molded body of an alloy powder containing a rare earth element; · a step (S20) of producing a laminated sintered body by joining at least two sintered body materials with an adhesive layer; · a step (S30) of cutting the laminated sintered body so as to cross the adhesive layer and dividing it into a plurality of laminated sintered body pieces; is included.

[0022] According to the manufacturing method of the present disclosure, since an adhesive is formed and laminated on a relatively large sintered body material before division, it is more efficient than forming and laminating an adhesive on a relatively small number of individual pieces after division.

[0023] FIG. 2 is a diagram schematically showing a cross section of two laminated sintered body materials 16. An adhesive layer 18 is provided between the sintered body materials 16. FIG. 3 is a diagram schematically showing a cross section of a plurality of laminated sintered body pieces 30 obtained by cutting and dividing the laminated sintered body 22 so as to cross the adhesive layer 18. A cut surface 21 is formed on the laminated sintered body piece 30 by cutting. The adhesive layer 18 is formed of an insulating material and can electrically separate the laminated sintered body materials 16 from each other. Each of the plurality of laminated sintered body pieces 30 includes at least two portions electrically separated by the adhesive layer 18, and a structure that functions as a so-called "segmented magnet" to suppress the generation of eddy currents is realized. Thus, according to the rare earth sintered magnet finally obtained from each laminated sintered body piece 30, in applications such as being incorporated into a rotor of an electric motor, for example, the generation of eddy currents due to an alternating magnetic field is suppressed, so that the effect of reducing eddy current loss can be obtained.

[0024] The adhesive layer 18 can be formed of materials such as an epoxy-based adhesive layer, an acrylic-based adhesive layer, and a urethane-based adhesive layer. The thickness of the adhesive layer 18 is preferably 1 μm or more and 50 μm or less, and more preferably 2 μm or more and 30 μm or less.

[0025] When the adhesive is unevenly applied, minute gaps may occur in the adhesive layer 18. When the laminated sintered body 22 is cut in such a state, a part of the grinding powder (cutting powder) of the sintered body material 16 may penetrate through the minute gaps in the adhesive layer 18 and enter between the laminated sintered body materials 16, which may reduce the electrical insulation (electrical resistance) between the laminated sintered body materials 16. The size of the grinding powder (cutting powder) is about the crystal particles constituting the sintered body material 16, for example, 10 μm or less. Therefore, when the thickness of the adhesive layer 18 is less than 10 μm, the possibility of such a phenomenon occurring is high.

[0026] In addition, fine irregularities with a size equal to or smaller than the diameter of crystal grains may be formed on the surface of the sintered body material 16. Even if the surface of the sintered body material 16 is roughened, such fine irregularities may remain. For this reason, there is also a possibility that the adhesive layer 18 penetrates through the fine convex portions present on the surface of the sintered body material 16, reducing the electrical resistance of the adhesive layer 18.

[0027] FIG. 4 is a diagram schematically showing a cross section of an example in which a coating layer 19 is provided between one of the two sintered body materials 16 sandwiching the adhesive layer 18 and the adhesive layer 18. FIG. 5 is a diagram schematically showing a cross section of a plurality of laminated sintered body pieces 30 obtained by cutting and dividing the laminated sintered body 22 so as to cross the adhesive layer 18. Also in this example, a cut surface 21 is formed on the laminated sintered body piece 30 by cutting. In the example of the figure, the coating layer 19 is formed on one of the two sintered body materials 16, but the coating layer 19 may be formed on both of the sintered body materials 16.

[0028] The coating layer 19 is formed of an insulating material and exhibits a function of increasing the electrical resistance (insulating property) between the sintered body materials 16 facing each other through the adhesive layer 18. Further, according to the study by the present inventors, it was found that when the laminated sintered body 22 is cut, even if a part of the grinding powder of the sintered body material 16 penetrates the adhesive layer 18, the electrical insulation can be ensured due to the presence of the coating layer 19. Thus, by providing both the adhesive layer 18 and the coating layer 19 on one of the two sintered body materials 16 sandwiching the adhesive layer 18, electrical insulation can be more reliably ensured. The coating layer 19 is formed by coating the surface of the magnet and can be formed of materials such as epoxy resins, acrylic resins, urethane resins, and silicone resins. The thickness of the coating layer 19 is preferably 3 μm or more and 100 μm or less, and more preferably 5 μm or more and 70 μm or less. Also, the total thickness of the adhesive layer and the coating layer is preferably 4 μm or more and 150 μm or less.

[0029] In addition, when the coating layer is included in both of the two sintered body materials sandwiching the adhesive layer 18, it is preferable to set the total thickness of the coating layer in both the adhesive layer and the sintered body material to be 5 μm or more and 250 μm or less.

[0030] In addition, in order to improve the magnetic properties of the magnet, rare earth element R may be diffused from the surface of the plurality of sintered body materials 16 before forming the coating layer 19. Further, the surface of the plurality of sintered body materials 16 is preferably flattened by processing before forming the adhesive layer 18 and the coating layer 19.

[0031] Hereinafter, the manufacturing method of the rare earth sintered magnet in the present embodiment will be described in detail.

[0032] First, the step (S10) of producing a plurality of sintered body materials from a molded body of alloy powder containing rare earth elements will be described. This step may include, for example, a step (1) of compression molding alloy powder in an orientation magnetic field to produce a molded body, a step (2) of cutting the molded body and dividing it into a plurality of molded body pieces, and a step (3) of sintering the plurality of molded body pieces to obtain a plurality of sintered body materials. Further, before laminating the plurality of sintered body materials, a step (4) of diffusing rare earth elements from the surface of each sintered body material may be performed. Hereinafter, examples of these steps will be sequentially described.

[0033] (1) Step of compression molding alloy powder in an orientation magnetic field to produce a molded body <Composition of alloy> In the present embodiment, an alloy for an R-T-B system sintered magnet is used. Here, R is a rare earth element and necessarily contains at least one selected from the group consisting of Nd, Pr, and Ce. Preferably, a combination of rare earth elements represented by Nd-Dy, Nd-Tb, Nd-Dy-Tb, Nd-Pr-Dy, Nd-Pr-Tb, Nd-Pr-Dy-Tb is used.

[0034] Among R, Dy and Tb are particularly H cJIt is effective for the improvement. In addition to the above elements, other rare earth elements such as La may be contained, and misch metal or didymium can also be used. Further, the content is, for example, 27% by mass or more and 35% by mass or less. Preferably, the R content of the rare earth sintered magnet is 31% by mass or less (27% by mass or more and 31% by mass or less, preferably 29% by mass or more and 31% by mass or less).

[0035] T is at least one of transition metals and necessarily contains Fe, and up to 50% of Fe by mass ratio may be replaced with cobalt (Co) (including the case where T consists essentially of iron and cobalt). Co is effective for improving temperature characteristics and corrosion resistance, and the alloy powder may contain 10% by mass or less of Co. The content of T may occupy the remainder of R and B or R, B, and M described later.

[0036] The content of B may also be a known content, for example, a preferable range is 0.9% by mass to 1.2% by mass. If it is less than 0.9% by mass, high H cJ may not be obtained, and if it exceeds 1.2% by mass, B r may decrease. Note that a part of B can be replaced with C (carbon).

[0037] In addition to the above elements, an M element can be added for the improvement of H cJ The M element is one or more selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, and W. The addition amount of the M element is preferably 5.0% by mass or less. This is because if it exceeds 5.0% by mass, Br may decrease. Also, inevitable impurities can be tolerated.

[0038] <Fabrication of the alloy> The manufacturing process of the alloy for rare earth sintered magnets is illustrated. An alloy ingot can be obtained by melting a metal or alloy pre-adjusted to have the above-described composition and using an ingot casting method of pouring it into a mold. Also, the molten metal is brought into contact with a single roll, double roll, rotating disk, rotating cylindrical mold, etc. and rapidly cooled, and alloy flakes can be manufactured by a rapid cooling method typified by a strip casting method or a centrifugal casting method for producing a solidified alloy thinner than the alloy made by the ingot method.

[0039] In the embodiments of the present disclosure, materials manufactured by either the ingot method or the rapid cooling method can be used, but it is preferable to be manufactured by a rapid cooling method such as the strip casting method. The thickness of the rapidly cooled alloy produced by the rapid cooling method is usually in the range of 0.03 mm to 1 mm and is in the form of flakes. The alloy melt starts to solidify from the surface in contact with the cooling roll (roll contact surface), and crystals grow columnarly in the thickness direction from the roll contact surface. The rapidly cooled alloy is cooled in a short time compared to an alloy (ingot alloy) produced by a conventional ingot casting method (die casting method), so the structure is refined and the crystal grain size is small. Also, the area of the grain boundaries is large. Since the R-rich phase spreads widely within the grain boundaries, the rapid cooling method is excellent in the dispersibility of the R-rich phase. For this reason, it is easy to break at the grain boundaries by the hydrogen pulverization method. By hydrogen-pulverizing the rapidly cooled alloy, the size of the hydrogen-pulverized powder (coarse pulverized powder) can be made, for example, 1.0 mm or less. The coarse pulverized powder thus obtained is pulverized with a jet mill.

[0040] <Fine pulverization process of alloy> The powder of the alloy for rare earth sintered magnets is active and easily oxidized. For this reason, as the gas used in the jet mill, for example, an inert gas such as nitrogen, argon, or helium is used in order to avoid the risk of heat generation and ignition and to reduce the oxygen content as an impurity to improve the performance of the magnet.

[0041] The material to be pulverized (coarse pulverized powder) fed into the jet mill is pulverized into fine powder having a particle size distribution with an average particle size (median diameter: d50) of 2.0 μm or more and 4.5 μm or less, and is collected by the cyclone collector 0. The cyclone collector is used to separate powder from the air stream carrying the powder. Specifically, the coarse pulverized powder of the alloy for rare earth sintered magnets is pulverized by the jet mill in the previous stage, and the fine powder generated by the pulverization is supplied to the cyclone collector together with the gas used for the pulverization. A mixture of an inert gas (pulverization gas) and the pulverized fine powder forms a high-speed air stream and is sent to the cyclone collector. The cyclone collector is used to separate these pulverization gases and fine powder. The fine powder separated from the pulverization gas is recovered by a powder collector.

[0042] <Step of manufacturing a compact> Next, a compact is manufactured from the above fine powder by pressing in a magnetic field. In pressing in a magnetic field, from the viewpoint of oxidation suppression, it is preferable to form a compact by pressing in an inert gas atmosphere or by wet pressing. In particular, in wet pressing, the surface of the particles constituting the compact is coated with a dispersant such as an oil agent, and contact with oxygen and water vapor in the air is suppressed. Therefore, it is possible to prevent or suppress the oxidation of the particles by the air before, during, or after the pressing step.

[0043] When performing wet pressing in a magnetic field, a slurry in which a dispersion medium is mixed with the fine powder is prepared, supplied to the cavity in the mold of the wet pressing apparatus, and press-molded in a magnetic field.

[0044] ·Dispersion medium The dispersion medium is a liquid capable of obtaining a slurry by dispersing alloy powder therein.

[0045] Preferred dispersion media for use in the present disclosure include mineral oil or synthetic oil. The type of mineral oil or synthetic oil is not specified, but if the kinematic viscosity at room temperature exceeds 10 cSt, the binding force between alloy powders may increase due to increased viscosity, which may adversely affect the orientation of alloy powders during wet forming in a magnetic field. Therefore, the kinematic viscosity of the mineral oil or synthetic oil at room temperature is preferably 10 cSt or less. Also, if the distillation point of the mineral oil or synthetic oil exceeds 400 °C, it becomes difficult to remove the oil after obtaining the compact, and the amount of residual carbon in the sintered body may increase, resulting in a decrease in magnetic properties. Therefore, the distillation point of the mineral oil or synthetic oil is preferably 400 °C or less. Also, vegetable oil may be used as the dispersion medium. Vegetable oil refers to oil extracted from plants, and the type of plant is not limited to a specific plant.

[0046] · Preparation of slurry A slurry can be obtained by mixing the obtained alloy powder and the dispersion medium.

[0047] The mixing ratio of the alloy powder and the dispersion medium is not particularly limited, but the concentration of the alloy powder in the slurry is preferably 70% or more (i.e., 70 mass% or more) by mass ratio. This is because the alloy powder can be efficiently supplied into the cavity at a flow rate of 20 to 600 cm 3 / s, and excellent magnetic properties can be obtained. The concentration of the alloy powder in the slurry is preferably 90% or less by mass ratio. The method of mixing the alloy powder and the dispersion medium is not particularly limited. The alloy powder and the dispersion medium may be prepared separately, weighed in predetermined amounts, and mixed together. Also, when obtaining the alloy powder by dry pulverizing the coarsely pulverized powder with a jet mill or the like, a container containing the dispersion medium may be placed at the alloy powder discharge port of the pulverizing device such as a jet mill, and the alloy powder obtained by pulverization may be directly recovered into the dispersion medium in the container to obtain a slurry. In this case, it is preferable that the inside of the container is also an atmosphere composed of nitrogen gas and / or argon gas, and the obtained alloy powder is directly recovered into the dispersion medium without being exposed to the atmosphere to form a slurry. Furthermore, it is also possible to obtain a slurry composed of the alloy powder and the dispersion medium by wet pulverizing the coarsely pulverized powder using a vibration mill, a ball mill, an attritor, or the like while holding it in the dispersion medium.

[0048] By forming the slurry thus obtained using a known wet pressing apparatus, a molded body having a predetermined size and shape can be obtained. Conventionally, it is normal to sinter this powder molded body to obtain a sintered body. However, in the present embodiment, as will be described below, the molded body is divided by a wire saw before sintering.

[0049] (2) Step of cutting the molded body to divide it into a plurality of molded body pieces Here, with reference to FIGS. 6(a) to 6(d), an example of the step of cutting the molded body to divide it into a plurality of molded body pieces will be described.

[0050] First, as shown in FIG. 6(a), a molded body 10 of the alloy powder produced through the above steps is prepared. In the example of FIG. 6(a), the molded body 10 has a block shape. For reference, the direction M of the orientation magnetic field is indicated by an arrow. This direction M is referred to as the "magnetic field orientation direction". The orientation magnetic field is applied to the powder particles when pressing the powder of the alloy for a rare earth sintered magnet to produce a molded body, and the orientation of each powder particle is oriented in the magnetic field orientation direction M. Finally, magnetization is performed in a direction parallel to this magnetic field orientation direction M.

[0051] Next, as shown in FIG. 6(b), the molded body 10 is cut (sliced) to divide the molded body 10 into a plurality of molded body pieces. In a preferred embodiment, the molded body 10 can be performed using a wire saw. Details of the wire saw will be described later.

[0052] In the example of FIG. 6(b), the molded body 10 is cut into a plurality of molded body pieces 12 along a direction parallel to the magnetic field orientation direction M of the molded body. That is, in each molded body piece 12, the length direction is the magnetic field orientation direction M. Note that the cutting of the molded body 10 may be performed a plurality of times to divide the molded body piece 12 as needed. However, in order to perform the step (S30) of cutting the laminated sintered body into a plurality of laminated sintered body pieces, the molded body piece 12 is divided into a shape and size larger than the final magnet component. In the present embodiment, as shown in FIG. 6(c), the molded body piece 12 divided into a plate shape is further cut as shown in FIG. 6(d) to obtain a plurality of bar-shaped molded body pieces 12. The magnetic field orientation direction M in each molded body piece is not limited to the illustrated example.

[0053] In the manufacturing method of the present disclosure, after the step (S20) of producing a laminated sintered body by joining a plurality of sintered body materials with an adhesive layer, a step (S30) of cutting the laminated sintered body into a plurality of laminated sintered body pieces is performed. Therefore, the shape and size of the sintered body material at the stage before joining are defined by the shape and size of the molded body piece 12. Therefore, it is preferable that the portion of the surface of the molded body piece 12 that will eventually become the region where the adhesive layer is formed has a flat surface. Also, in order to efficiently apply the adhesive, the area of the flat surface where the adhesive layer is planned to be formed among the individual molded body pieces is, for example, 25 cm 2 It is preferably set to the above or more.

[0054] Cutting of such a molded body 10 and molded body piece 12 can be performed, for example, by a wire saw apparatus shown in FIG. 7.

[0055] Here, with reference to FIG. 7, a configuration example of a wire saw apparatus that can be used in the present embodiment will be described. FIG. 7 is a perspective view showing a configuration example of a wire saw apparatus 100 in an embodiment of the present disclosure. The figure shows an xyz coordinate system including an x-axis, a y-axis, and a z-axis that are orthogonal to each other for reference. In this example, the xy plane is horizontal and the z-axis is oriented in the vertical direction.

[0056] The wire saw apparatus 100 in FIG. 7 has rollers 50a, 50b, 50c arranged such that their rotation central axes are parallel to each other, and a single continuous wire 60. The molded body 10 prepared in step S10 is supported by the fixing base 40.

[0057] The fixing base 40 moves up and down in the z-axis direction with the molded body 10 fixed. This up and down movement can be executed by a driving device (not shown). The driving device may obtain a driving force by a hydraulic cylinder or may operate by a motor.

[0058] The rollers 50a, 50b, 50c are arranged at a predetermined interval such that when viewed from a direction parallel to the x-axis, the axes of the rotation centers are located at the vertices of a triangle. A plurality of grooves are provided on each side surface of the rollers 50a, 50b, 50c. The wire 60 is wound around the plurality of grooves of the rollers 50a, 50b, 50c in order. The center interval (pitch) of the plurality of grooves defines the width of the element to be divided by cutting with the wire saw. Both ends of the wire 60 are wound around a recovery bobbin (not shown), for example.

[0059] During cutting, the rollers 50a, 50b, 50c and the recovery bobbin rotate. The rotation directions of the rollers 50a, 50b, 50c depend on their arrangement and the way the wire 60 is hung. In the wire saw apparatus 100 shown in FIG. 7, the rollers 50a, 50b, 50c rotate in the same direction.

[0060] When a wire 60 of a predetermined length is wound around one recovery bobbin, the recovery bobbin and the rollers 50a, 50b, 50c are rotated in the reverse direction. Thereby, the wire 60 moves in the reverse direction, and by repeating this, the wire 60 can be reciprocated (moved).

[0061] For the wire 60, for example, a fixed abrasive wire is used. Specifically, one in which high-hardness abrasive grains suitable for cutting a high-hardness material are fixed to a base wire by electroplating can be used. The high-hardness abrasive grains are also called super abrasive grains, and a typical example is diamond abrasive grains.

[0062] FIG. 8 schematically shows a cross section of the wire 60. The wire 60 includes a core wire 62, abrasive grains 64 located on the outer peripheral surface of the core wire 62, and an adhesion layer 66. The adhesion layer 66 is formed of a plating metal such as Ni, for example. The abrasive grains 64 are located on the surface of the core wire 62, and the adhesion layer 66 covers the surface of the core wire 62 around the abrasive grains 64 and the abrasive grains 64 as a whole, so that the abrasive grains 64 can be adhered to the core wire 62. The adhesion of the abrasive grains 64 may be realized by other methods. The average particle size of the abrasive grains 64 is, for example, 1 μm or more and 24 μm or less.

[0063] The step of cutting the molded body 10 with a wire saw is preferably performed in a state where the molded body 10 is submerged in a liquid. When the molded body 10 is a molded body formed by wet pressing, a preferred example of this liquid is a dispersion medium such as an oil agent (mineral oil or synthetic oil) used in wet pressing.

[0064] (3) Step of sintering a plurality of molded body pieces to obtain a plurality of sintered body materials Next, the individual molded body pieces cut by the above wire saw process are sintered to obtain a rare earth sintered magnet body (sintered body material). The sintering process of the molded body pieces can be performed, for example, under a pressure of 0.13 Pa (10 -3 Torr) or less, preferably 0.07 Pa (5.0×10 -4 Torr) or less, for example, in the temperature range of 1000 °C to 1150 °C. In order to prevent oxidation during sintering, the residual gas in the atmosphere can be replaced with an inert gas such as helium or argon.

[0065] Hereinafter, with reference to FIGS. 9(a) to 9(d), an example of the step of creating a rare earth-based sintered magnet from a sintered body material will be described.

[0066] (4) Step of diffusing rare earth elements First, as shown in Fig. 9(a), a plurality of sintered body materials 16 produced from the molded body pieces 12 in the above process are prepared. Then, as shown in Fig. 9(b), the powder 20 of the diffusion source containing the rare earth element R is brought into contact with at least one of the upper surface and the lower surface in the thickness direction of each sintered body material 16, and heat treatment is performed. By this heat treatment, the elements contained in the powder 20 of the diffusion source diffuse from the surface of the sintered body material 16 into the interior. In order to obtain higher magnetic properties, it is preferable to perform heat treatment by bringing the powder 20 of the diffusion source into contact with both the upper surface and the lower surface of the sintered body material 16.

[0067] As the diffusion source, it is preferable to use an alloy containing Pr, Tb, and Ga. Hereinafter, the diffusion source containing Pr, Tb, and Ga is referred to as a "Pr-Tb-Ga-based alloy". By this heat treatment, at least a part of Pr, Tb, and Ga contained in the powder 20 of the Pr-Tb-Ga-based alloy diffuses from at least the upper surface and the lower surface of each sintered body material 16 into the interior. When these elements diffuse from the surface of the sintered body material into the interior, the coercive force can be efficiently increased. The method of the diffusion process is not particularly limited. A known method can be adopted.

[0068] Hereinafter, the Pr-Tb-Ga-based alloy will be described.

[0069] The Pr-Tb-Ga-based alloy may contain rare earth elements other than Pr and Tb. Preferably, the total amount of Pr and Tb contained in the Pr-Tb-Ga-based alloy is 65 mass% or more and 97 mass% or less of the entire Pr-Tb-Ga-based alloy, and Ga is 3 mass% or more and 35 mass% or less of the entire Pr-Tb-Ga-based alloy.

[0070] The content of Pr: The preferable content of Tb in the Pr-Tb-Ga alloy is 3 mass% or more and 24 mass% or less of the whole Pr-Tb-Ga alloy. Also, 50 mass% or less of Ga can be replaced by at least one of Cu and Sn. The Pr-Tb-Ga alloy may contain inevitable impurities. Note that "50% or less of Ga can be replaced by Cu" in the present disclosure means that taking the content (mass%) of Ga in the Pr-Tb-Ga alloy as 100%, 50% of it can be replaced by Cu. Preferably, the content of Pr in the Pr-Tb-Ga alloy is 50 mass% or more of the whole rare earth elements contained in the Pr-Tb-Ga alloy. The whole rare earth elements contained in the Pr-Tb-Ga alloy preferably consist of only Pr and Tb. By containing Pr, diffusion in the grain boundary phase proceeds more easily, so that Tb can be diffused more efficiently, and higher H cJ can be obtained.

[0071] The shape and size of the Pr-Tb-Ga alloy are not particularly limited and are arbitrary. The Pr-Tb-Ga alloy can take shapes such as films, foils, powders, blocks, and particles.

[0072] The Pr-Tb-Ga alloy can be prepared using the production methods of raw material alloys adopted in the production methods of general rare earth sintered magnets, for example, die casting method, strip casting method, single roll super rapid cooling method (melt spinning method), atomization method, etc. Also, the Pr-Tb-Ga alloy may be obtained by pulverizing the alloy obtained by the above method with known pulverizing means such as a pin mill.

[0073] In the diffusion process, powder of a diffusion source containing R (preferably a Pr-Tb-Ga alloy) is brought into contact with at least one of the upper surface and the lower surface in the thickness direction of the sintered body material, and the first heat treatment is carried out at a temperature of 450 °C or higher and 950 °C or lower in a vacuum or inert gas atmosphere. By this heat treatment, R (preferably Pr, Tb, and Ga) can be diffused into the interior of the sintered body material.

[0074] The diffusion temperature is, for example, 450°C or higher and 950°C or lower.

[0075] The above heat treatment can be carried out using a known heat treatment apparatus by arranging powder of a diffusion source having an arbitrary shape on the surface of the sintered body material. For example, the surface of the sintered body material can be covered with a powder layer of a Pr-Tb-Ga-based alloy, and the above heat treatment can be carried out. For example, after applying a slurry in which a Pr-Tb-Ga-based alloy is dispersed in a dispersion medium to the surface of the sintered body material, the dispersion medium may be evaporated to bring the Pr-Tb-Ga-based alloy into contact with the sintered body material. Examples of the dispersion medium include alcohol (such as ethanol), aldehyde, and ketone.

[0076] For the sintered body material subjected to the heat treatment for the above diffusion, heat treatment (second heat treatment) may be carried out in a vacuum or inert gas atmosphere at 450°C or higher and 750°C or lower and at a temperature lower than the temperature of the heat treatment for diffusion. By performing the second heat treatment, higher H cJ can be obtained. Note that the second heat treatment may be carried out after the step of S50, that is, on the laminated sintered body piece.

[0077] Next, the step (S20) of manufacturing a laminated sintered body will be described.

[0078] It is preferable to form a coating layer on at least one of the upper and lower surfaces of the sintered body material 16 by a method such as an electrodeposition method or a spray method. When forming a coating layer on one side of the sintered body material 16, the spray method is preferable. As described above, the coating layer can be formed from a material such as an epoxy resin. The thickness of the coating layer is preferably 3 μm or more and 100 μm or less, and more preferably 5 μm or more and 70 μm or less. Thereafter, an adhesive is applied to the coating layer to form an adhesive layer (when there is no coating layer, an adhesive is applied to the surface of the sintered body material). The application of the adhesive can be carried out by various methods. In order to apply it efficiently over a wide range, for example, the adhesive may be arranged in dots using a dispenser. As described above, the adhesive layer can be formed from a material such as a one-component epoxy-based adhesive. The thickness of the adhesive layer is preferably 1 μm or more and 50 μm or less, and more preferably 2 μm or more and 30 μm or less. Thereafter, as shown in FIG. 9(c), at least two sintered body materials 16 are laminated to produce a laminated sintered body 22. The number of laminated sintered body materials 16 included in the laminated sintered body 22 is not limited to two, and may be three or more. In the illustrated example, the sizes (thicknesses) in the lamination direction of the laminated sintered body materials 16 are equal, but these sizes (thicknesses) may be different from each other. The magnetic field orientation direction M does not need to be parallel to the lamination direction, and may be inclined or orthogonal to the lamination direction. Also, the magnetic field orientation directions M of the respective sintered body materials 16 to be laminated do not need to be parallel.

[0079] Next, a step (S30) of cutting the laminated sintered body 22 to divide it into a plurality of laminated sintered body pieces will be described.

[0080] In this embodiment, each laminated sintered body 22 is cut from the upper surface to the lower surface so as to cross the adhesive layer and the coating layer, and is divided into a plurality of laminated sintered body pieces 30 as shown in FIG. 9(d). From the viewpoint of mass productivity, the number of the plurality of laminated sintered body pieces 30 to be divided is preferably 3 or more, and more preferably 50 or more. This dividing step may be performed by the wire saw apparatus described above, or may be performed by another cutting apparatus. Further, in order to obtain the final product shape and size, the laminated sintered body pieces may be further ground. Each of the individual laminated sintered body pieces 30 may have a size (thickness) in the magnetic field orientation direction of about 1 to 5 mm, a width of about 3 to 20 mm, and a length of about 5 to 100 mm, for example.

[0081] According to this embodiment, each of the individual laminated sintered body pieces 30 is a "divided magnet" in which a plurality of divided portions insulated from each other are joined. Although the cutting step across the adhesive layer is performed, due to the presence of the coating layer, high electrical insulation (for example, a high resistance of 50 Ω or more) is more reliably maintained. Further, since the adhesive is applied to the relatively large sintered body material before division, it is more efficient than applying it to a relatively small number of individual pieces after division.

[0082] The final rare earth-based sintered magnet is completed through a surface treatment step and a magnetization step as necessary for the laminated sintered body pieces 30 thus obtained. Thus, in the method for manufacturing a rare earth-based sintered magnet of the present disclosure, no diffusion is performed after the final cutting. The treatment after adhesion may be performed at a temperature at which the adhesive does not melt (for example, 180° C. or lower).

[0083] Note that the method for manufacturing a rare earth-based sintered magnet according to the present disclosure is not limited to the above embodiment. The compact may be manufactured by a dry pressing method, and the shape and size before and after cutting of the compact are also arbitrary.

Example

[0084] Although it will be described in more detail with reference to examples, the present disclosure is not limited thereto.

[0085] Experimental Example 1 Alloy powder with a composition of Nd: 24.5 mass%, Pr: 5.5 mass%, B: 0.93 mass%, Cu: 0.3 mass%, Ga: 0.5 mass%, Co: 0.45 mass%, Al: 0.12 mass%, Zr: 0.05 mass%, and the balance being Fe was prepared. The particle size d50 was 3.5 μm. Using these powders, a compact was produced with a wet pressing apparatus. The obtained compact was sintered (selecting a temperature at which sufficient densification by sintering occurs) to produce a plurality of sintered body materials from the compact. The dimensions of the sintered body were 4 mm in thickness × 8 mm in width × 10 mm in length. Two obtained sintered body materials were joined by an adhesive layer (joining the 8 mm × 10 mm surface) to produce a laminated sintered body A. Note that, as the adhesive, a one-component epoxy-based adhesive was used, and the thickness of the adhesive layer was in the range of 5 to 20 μm. Also, electrodeposited resin coating was performed on one of the obtained sintered body materials to form a coating layer on the surface of the sintered body material. The thickness of the coating layer was in the range of 30 to 40 μm. The sintered body material with the coating layer formed and the sintered body material without the coating layer formed (without electrodeposited resin coating) were joined by an adhesive layer (joining the 8 mm × 10 mm surface) to produce a laminated sintered body B. The bonding conditions were the same as those for the laminated sintered body A. Then, the laminated sintered body A was cut across the adhesive layer and divided into two laminated sintered body pieces (sample A). Similarly, the laminated sintered body B was cut across the adhesive layer and divided into two laminated sintered body pieces (sample B). The electrical resistance of the obtained samples A and B was measured. Note that, in the present disclosure, it is determined that the electrical resistance is 1 Ω or more and electrical insulation is ensured. Further, when it is 50 Ω or more, it is further determined that electrical insulation is ensured. When the electrical resistance was measured, sample A was 7.3 Ω and sample B was 1000 Ω. Therefore, both samples A and B are more efficient than forming and laminating an adhesive on a large number of individual pieces after division, since an adhesive is formed and laminated on the sintered body material before division, and further, electrical insulation is ensured. Also, when comparing the electrical resistance of sample A and sample B, sample B (the sample in which a coating layer is provided between one of the two sintered body materials sandwiching the adhesive layer and the adhesive layer) has a significantly lower electrical resistance. Therefore, it is more excellent in electrical insulation.

Description of the reference numerals

[0086] 10··· green compact, 16··· sintered body material, 18··· adhesive layer, 19··· coating layer, 20··· laminated sintered body, 22··· cut surface, 30··· laminated sintered body piece, 40··· fixed base, 50a, 50b, 50c··· rollers, 60··· wire saw, 100··· wire saw apparatus

Claims

1. A step of producing a plurality of sintered body materials from a molded body of an alloy powder containing rare earth elements; A step of producing a laminated sintered body by joining at least two of the sintered body materials with an adhesive layer; A step of cutting the laminated sintered body so as to cross the adhesive layer and dividing it into a plurality of laminated sintered body pieces; comprising: The step of producing the plurality of sintered body materials is: A step of producing the molded body by compression molding the alloy powder in an oriented magnetic field; A step of cutting the molded body and dividing it into a plurality of molded body pieces; A step of sintering the plurality of molded body pieces to obtain the plurality of sintered body materials; A method for manufacturing a rare earth sintered magnet.

2. The method for manufacturing a rare earth sintered magnet according to claim 1, wherein in the laminated sintered body, a coating layer is provided between one of the two sintered body materials sandwiching the adhesive layer and the adhesive layer.

3. The method for manufacturing a rare earth sintered magnet according to claim 1, wherein in the laminated sintered body, coating layers are provided between both of the two sintered body materials sandwiching the adhesive layer and the adhesive layer, respectively.

4. The method for manufacturing a rare earth sintered magnet according to claim 2 or 3, wherein the total thickness of the adhesive layer and the coating layer is 4 μm or more and 150 μm or less.

5. The method for manufacturing a rare earth sintered magnet according to any one of claims 2 to 4, wherein each of the plurality of laminated sintered body pieces includes at least two portions electrically separated by the adhesive layer and the coating layer.

6. The method for manufacturing a rare earth sintered magnet according to any one of claims 2 to 5, wherein the coating layer is formed on the surface after diffusing rare earth elements from the surface of the plurality of sintered body materials.

7. The method for manufacturing a rare earth sintered magnet according to claim 6, wherein the surface of the plurality of sintered body materials is processed before the coating layer is formed.

8. The step of producing the molded body by compression molding the alloy powder in an oriented magnetic field is performed by wet pressing, The method for manufacturing a rare earth sintered magnet according to any one of claims 1 to 7, wherein the step of cutting the molded body and dividing it into a plurality of molded body pieces is performed in a state where the molded body is submerged in a liquid.

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