Manufacturing method of rare earth magnet

Abstract

To provide a method for manufacturing a rare earth magnet capable of improving magnetic properties and productivity of the magnet.SOLUTION: Disclosed is a method for producing a rare earth magnet comprising: a step of pressurizing and sintering a raw material powder by pressing the raw material powder with a punch while heating the raw material powder and applying pressure with the punch on the surface of molding holes of first and second magnetic plates, by using a mold; and a step of applying a magnetic field to the filled raw material powder with the first and second magnets from before pressurization and sintering and continuing the application of the magnetic field until at least the middle of pressurization and sintering. The mold comprises a die having a molding hole and having first and second magnet holes respectively provided on both sides thereof to communicate with the molding hole, a punch, first and second magnets respectively embedded in the first and second magnet holes, the first magnetic plate embedded on the molding hole side closer than the first magnet of the first magnet hole so as to block the communication port with the molding hole, and the second magnetic plate embedded on the molding hole side closer than second magnet the second magnet hole so as to block the communication port with the molding hole.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for producing a rare earth magnet by pressure sintering magnetic powder. [Background technology]

[0002] Conventionally, a method for manufacturing a rare earth magnet is adopted in which a magnet having a sintered body is manufactured by pressure sintering a magnetic powder. As a method for manufacturing such a rare earth magnet, a method for imparting magnetic anisotropy to a sintered body in order to improve magnetic properties is known. For example, a method is known in which a magnetic field molding method is used, which includes sandwiching a raw material powder containing a magnetic powder between a pair of first members, further sandwiching the raw material powder and the pair of first members between a pair of second members to obtain a laminate, and compressing the raw material powder in the laminate by applying pressure to the laminate in the stacking direction, in which at least a part of the first member is a rare earth magnet and at least a part of the second member is a permendur-based alloy, and then pressure sintering the magnetic field molding to obtain a magnetic field molding (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-141121 Summary of the Invention [Problem to be solved by the invention]

[0004] In response to this, there is a demand for a method for producing rare earth magnets that further improves the magnetic properties of the magnets by imparting more sufficient magnetic anisotropy to the sintered body. At the same time, there is a demand for improving the productivity of rare earth magnets. The present invention has been made in light of these circumstances, and its object is to provide a method for producing rare earth magnets that can improve the magnetic properties and productivity of magnets. [Means for solving the problem]

[0005] In order to solve the above problems, a method of manufacturing a rare earth magnet of the present invention includes the steps of: preparing a powder molding die including a die having a molding hole and first and second magnet holes on either side of the molding hole that communicate with the molding hole; a punch to be fitted into the molding hole of the die; a first magnet embedded in the first magnet hole; a first magnetic plate embedded in the first magnet hole on the molding hole side of the first magnet so as to close the communication opening with the molding hole; a second magnet embedded in the second magnet hole; and a second magnetic plate embedded in the second magnet hole on the molding hole side of the second magnet so as to close the communication opening with the molding hole; preparing raw material powder including magnetic powder; The method includes a filling step of filling the raw material powder into the cavity surrounded by the punch and the surfaces of the first and second magnetic plates facing the forming hole in the forming hole of the die; a step of pressing the filled raw material powder with the punch while heating the raw material powder, thereby applying pressure to the surfaces of the first and second magnetic plates facing the forming hole and the punch, thereby performing pressure sintering of the raw material powder to obtain a sintered body; and a step of applying a magnetic field to the filled raw material powder by the first and second magnets before the pressure sintering, thereby orienting the magnetic powder, and continuing the application of the magnetic field to the raw material powder until at least halfway through the pressure sintering. Effect of the Invention

[0006] According to the present invention, the magnetic properties and productivity of magnets can be improved. [Brief description of the drawings]

[0007] [Figure 1] 1A is a schematic perspective view of a die of a powder molding die according to one embodiment, and FIG. 1B is a schematic top view and schematic cross-sectional view of the die, upper punch, and lower punch of the powder molding die according to one embodiment. [Diagram 2] 1 is a schematic process diagram of a method for manufacturing a magnet according to one embodiment. FIG. [Diagram 3] 1 is a schematic process diagram of a method for manufacturing a magnet according to one embodiment. FIG. [Figure 4]1 is a schematic process diagram of a method for manufacturing a magnet according to one embodiment. FIG. [Diagram 5] FIG. 2 is a schematic diagram showing a mold according to an example and a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] First, the outline of the method for producing a rare earth magnet according to the embodiment will be described by exemplifying the method for producing an SmFeN magnet according to one embodiment. FIG. 1(a) is a schematic perspective view of a die of a powder molding die according to one embodiment. FIG. 1(b) is a schematic top view and schematic cross-sectional view of the die, upper punch, and lower punch of a powder molding die according to one embodiment. FIGS. 2(a) to 4(c) are schematic process diagrams of a method for producing a magnet according to one embodiment. In these figures, the depth direction of the molding hole of the die of the die is the Z direction, one direction perpendicular to the Z direction is the X direction (width direction), and the direction perpendicular to the Z direction and the X direction is the Y direction (opposing direction). Each top view shown in FIG. 1(b) is a plan view from the Z direction, and each cross-sectional view shown in FIG. 1(b) is a view showing a cross section perpendicular to the Y direction passing through the center in the Y direction. The cross sections of the die shown in FIG. 2(c) to FIG. 4(b) are cross sections perpendicular to the X direction passing through the center in the X direction of the die, and the upper punch and the lower punch.

[0009] In a manufacturing method of a magnet according to one embodiment, a powder molding die 10 according to one embodiment shown in Fig. 1 and Fig. 2 is prepared in advance (die preparation step). The powder molding die 10 is a die used for molding raw material powder including magnetic powder, and includes a die 20, an upper punch 80, and a lower punch 90. The die 20 has a right cylindrical shape having an upper surface 20t and a lower surface (bottom surface) 20b parallel to the XY plane, and includes a frame portion 22 and an insert portion 30. The frame portion 22 and the insert portion 30 are made of a non-magnetic cemented carbide. The frame portion 22 is provided with a fitting hole 24 that penetrates in the Z direction from a central portion of the upper surface 22t to the lower surface 22b. The insert portion 30 is fitted into the fitting hole 24 of the frame portion 22. The upper opening 24t of the fitting hole 24 and the upper surface 30t of the insert part 30 are generally rectangular with short sides parallel to the X direction and long sides parallel to the Y direction with rounded corners. The lower opening 24b of the fitting hole 24 and the lower surface 30b of the insert part 30 are rectangular with short sides parallel to the X direction and long sides parallel to the Y direction. The side surfaces 24x on both sides in the X direction of the fitting hole 24 and the side surfaces 30x on both sides in the X direction of the insert part 30 have a tapered shape that inclines toward the center of the fitting hole 24 and the insert part 30 in the X direction (the center of the die in the X direction) as it moves from the upper end to the lower end along the Z direction. The side surfaces 30x on both sides in the X direction of the insert part 30 abut against the side surfaces 24x on both sides in the X direction of the fitting hole 24, respectively, so that the insert part 30 does not fall off the frame part 22. On the other hand, side surfaces 24y on both sides in the Y direction of the fitting hole 24 and side surfaces 30y on both sides in the Y direction of the insert portion 30 are provided parallel to the ZX plane. The side surfaces 30y on both sides in the Y direction of the insert portion 30 are in contact with the side surfaces 24y on both sides in the Y direction of the fitting hole 24, respectively.

[0010] The insert part 30 is provided with a molding hole 32 that penetrates in the Z direction from the center of the upper surface 30t to the lower surface 30b. The cross section of the molding hole 32 perpendicular to the Z direction is a square with two sides parallel to the X direction and two sides parallel to the Y direction. The insert part 30 is provided with a first magnet hole 34 and a second magnet hole 36 that penetrate in the Z direction from the upper surface 30t to the lower surface 30b on both sides of the molding hole 32 in the Y direction and communicate with the molding hole 32 from the upper end to the lower end along the Z direction. The first magnet hole 34 and the second magnet hole 36 have the same shape and size. The upper opening 34t of the first magnet hole 34 and the upper opening 36t of the second magnet hole 36, and the lower opening 34b of the first magnet hole 34 and the lower opening 36b of the second magnet hole 36 are approximately rectangular with long sides parallel to the X direction and short sides parallel to the Y direction and rounded corners. The side surfaces 34x on both sides in the X direction of the first magnet hole 34 and the side surfaces 36x on both sides in the X direction of the second magnet hole 36 have a tapered shape that inclines toward the center of each magnet hole in the X direction (the center of the die in the X direction) from the upper end to the lower end along the Z direction. Meanwhile, the side surfaces 34yf, 34yr on both sides in the Y direction of the first magnet hole 34 and the side surfaces 36yf, 36yr on both sides in the Y direction of the second magnet hole 36 are provided parallel to the ZX plane. The long sides of the upper opening 34t of the first magnet hole 34 and the upper opening 36t of the second magnet hole 36, and the long sides of the lower opening 34b of the first magnet hole 34 and the lower opening 36b of the second magnet hole 36 (the widths of the parts adjacent to the communication openings of the first and second magnet holes with the molding hole) are longer than the two sides parallel to the X direction of the cross section perpendicular to the Z direction of the molding hole 32 (the widths of the parts adjacent to the communication openings of the molding hole equal to the widths of the communication openings).

[0011] The mold 10 further includes a first magnet 40, a first magnetic plate 50, a second magnet 60, and a second magnetic plate 70. The first and second magnets have the same shape and dimensions, and are generally rectangular prisms with the Z direction as the height direction. The first and second magnets are SmCo magnets (samarium-cobalt magnets). Before the mold 10 is used in the manufacturing method according to one embodiment, the first and second magnets are not magnetized. The first and second magnetic plates are rectangular flat plates separated from the insert portion 30. The first and second magnetic plates have the same shape and dimensions, and are plate-shaped parallel to the ZX plane. The material of the first and second magnetic plates is SKD61.

[0012] The first magnet 40 and the second magnet 60 are embedded in the first magnet hole 34 and the second magnet hole 36 of the insert part 30, respectively, with a gap between them and the molding hole 32. The upper surface 40t of the first magnet 40 and the upper surface 60t of the second magnet 60 are flush with the upper surface 30t of the insert part 30. The lower surface 40b of the first magnet 40 and the lower surface 60b of the second magnet 60 are flush with the lower surface 30b of the insert part 30. The upper surface 40t and the lower surface 40b of the first magnet 40 and the upper surface 60t and the lower surface 60b of the second magnet 60 are approximately rectangular with long sides parallel to the X direction and short sides parallel to the Y direction, and with rounded corners. The side surface 40yr of the first magnet 40 opposite the molding hole 32 side in the Y direction abuts against the side surface 34yr of the first magnet hole 34 opposite the molding hole 32 side in the Y direction. The short side and the long side of the lower surface 40b of the first magnet 40, which are opposite to the molding hole 32 side, are in contact with the short side and the long side of the lower opening 34b of the first magnet hole 34, which are opposite to the molding hole 32 side. Similarly, the side surface 60yr of the second magnet 60, which is opposite to the molding hole 32 side in the Y direction, is in contact with the side surface 36yr of the second magnet hole 36, which is opposite to the molding hole 32 side in the Y direction. The short side and the long side of the lower surface 60b of the second magnet 60, which are opposite to the molding hole 32 side, are in contact with the short side and the long side of the lower opening 36b of the second magnet hole 36, which are opposite to the molding hole 32 side. The first magnetic plate 50 is embedded in the gap on the molding hole 32 side of the first magnet hole 34 of the insert part 30 from the first magnet 40 so as to close the communication opening 35 with the molding hole 32, so that the thickness direction is the Y direction. Similarly, the second magnetic plate 70 is embedded in the gap on the molding hole 32 side of the second magnet 60 in the second magnet hole 36 of the insert portion 30 so that its thickness direction is in the Y direction and so as to block the communication opening 37 with the molding hole 32.

[0013] The side faces 50x on both sides in the X direction of the first magnetic plate 50 and the side faces 70x on both sides in the X direction of the second magnetic plate 70 have a tapered shape that inclines toward the center of each magnetic plate in the X direction (the center of the die in the X direction) from the upper end to the lower end along the Z direction. The side faces 50x on both sides in the X direction of the first magnetic plate 50 and the side faces 70x on both sides in the X direction of the second magnetic plate 70 are in contact with the side faces 34x on both sides in the X direction of the first magnet hole 34 and the side faces 36x on both sides in the X direction of the second magnet hole 36, respectively, so that the first magnetic plate 50 and the second magnetic plate 70 are fixed so as not to move downward relative to the insert part 30. Furthermore, the first magnet 40 and the second magnet 60 are fixed to the first magnetic plate 50 and the second magnetic plate 70 by magnetic force, respectively, so that they do not fall from the insert part 30. On the other hand, the surface 50yf of the first magnetic plate 50 on the molding hole 32 side in the Y direction and the surface 70yf of the second magnetic plate 70 on the molding hole 32 side in the Y direction are in contact with the side surfaces 34yf located on both sides of the communication opening of the first magnet hole 34 on the molding hole 32 side in the Y direction and the side surfaces 36yf located on both sides of the communication opening of the second magnet hole 36 on the molding hole 32 side in the Y direction, respectively, blocking the communication opening 35 of the first magnet hole 34 with the molding hole 32 and the communication opening 37 of the second magnet hole 36 with the molding hole 32. The surface 50yr of the first magnetic plate 50 opposite the molding hole 32 side in the Y direction and the surface 70yr of the second magnetic plate 70 opposite the molding hole 32 side in the Y direction are in contact with the side surface 40yf of the first magnet 40 on the molding hole 32 side in the Y direction and the side surface 60yf of the second magnet 60 on the molding hole 32 side in the Y direction, respectively.

[0014] The upper punch 80 has a spacer 82 (plate portion) having a right circular cylindrical shape, and a punch portion 84 extending downward along the Z direction from the center of the lower surface 82b of the spacer 82. The lower punch 90 has a spacer 92 (plate portion) having a right circular cylindrical shape, and a punch portion 94 extending upward along the Z direction from the center of the upper surface 92t of the spacer 92. The punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90 have substantially the same dimensions and shapes of the cross section perpendicular to the Z direction as the forming hole 32 so that they can be fitted into the forming hole 32 from the upper end and the lower end, respectively, and can slide against the inner surface 32s of the forming hole 32. The material of the upper punch 80 and the lower punch 90 is a non-magnetic cemented carbide.

[0015] Next, in a manufacturing method of a magnet according to one embodiment, as shown in Fig. 2(a), an SmFeN magnetic powder 4 including magnetic particles 2 containing Sm, Fe, and N, and a metal zinc powder 8 (modifier powder) including metal zinc particles 6 are prepared, and then, as shown in Fig. 2(b), the magnetic powder 4 and the metal zinc powder 8 are mixed to obtain a mixed powder 1A and prepared as a raw material powder (powder preparation step). Next, as shown in Fig. 2(c), the punch portion 94 of the lower punch 90 is fitted from the lower end into the molding hole 32 of the insert portion 30 of the die 20 until the upper surface 92t of the spacer 92 of the lower punch 90 abuts against the lower surface 30b of the insert portion 30 of the die 20. Then, in the air or inert gas atmosphere (e.g., an argon gas atmosphere, a nitrogen gas atmosphere, etc.) at room temperature, the mixed powder 1A (raw material powder) is filled into the cavity C surrounded by the inner surface 32s (shown in Figure 1 (b)) of the forming hole 32 of the insert portion 30 of the die 20, the surface 50yf of the first magnetic plate 50 facing the forming hole 32, the surface 70yf of the second magnetic plate 70 facing the forming hole 32, and the punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90 (powder filling process).

[0016] Next, as shown in Fig. 3(a), in the air or inert gas atmosphere at room temperature, the punch portion 84 of the upper punch 80 is fitted into the molding hole 32 of the insert portion 30 of the die 20 from the upper end and moved downward along the Z direction to press the mixed powder 1A filled in the cavity C with the punch portion 84 of the upper punch 80. As a result, the mixed powder 1A filled in the cavity C is compressed by the inner surface 32s of the molding hole 32, the surface 50yf of the first magnetic plate 50 on the molding hole 32 side and the surface 70yf of the second magnetic plate 70 on the molding hole 32 side, as well as the punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90. In this way, the filled mixed powder 1A is compressed to adjust the bulk density of the mixed powder 1A (powder density adjustment process).

[0017] Next, as shown in FIG. 3(b), in the air or inert gas atmosphere at room temperature, a pulsed magnetic field is applied along the Y direction to both the filled mixed powder 1A and the first magnet 40 and the second magnet 60 by electromagnetic coils (not shown) arranged on both sides of the die 20 in the Y direction (magnetic field application step). In this way, the magnetic aggregation of the magnetic powder 4 contained in the mixed powder 1A is alleviated by the pulsed magnetic field, and the magnetic powder 4 is oriented. At the same time, the first magnet 40 and the second magnet 60 are magnetized by the pulsed magnetic field, so that the magnetic powder 4 contained in the mixed powder 1A is oriented by applying a magnetic field to the mixed powder 1A by the first magnet 40 and the second magnet 60 from before the pressure sintering, and the application of the magnetic field to the mixed powder 1A is continued until the completion of the pressure sintering (at least halfway through the pressure sintering).

[0018] Next, as shown in FIG. 3(c), in an inert gas atmosphere, the filled mixed powder 1A is heated by a heater (not shown) equipped with a high-frequency induction coil arranged around the die 20 in a direction perpendicular to the Z direction. In this way, the mixed powder 1A is heated to the temperature of pressure sintering (heating process). As a result, the α-Fe phase on the surface of the magnetic particles of the magnetic powder 4 contained in the mixed powder 1A reacts with the zinc component of the metal zinc powder 8 on the surface of the magnetic particles to form an Fe-Zn phase (modified phase). Even during this process, the first magnet 40 and the second magnet 60 continue to apply a magnetic field to the mixed powder 1A, and the orientation of the magnetic powder 4 progresses.

[0019] Next, as shown in FIG. 4(a), in an inert gas atmosphere, the filled mixed powder 1A is continuously heated by the heater (not shown) while the punch portion 84 of the upper punch 80 is further moved downward along the Z direction to further press the mixed powder 1A with the punch portion 84 of the upper punch 80. As a result, the mixed powder 1A is pressurized with the inner surface 32s of the molding hole 32, the surface 50yf of the first magnetic plate 50 facing the molding hole 32 and the surface 70yf of the second magnetic plate 70 facing the molding hole 32, as well as the punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90 while being continuously heated. In this manner, the mixed powder 1A is pressure-sintered to obtain a sintered body 1C (pressure-sintering process). In the pressure-sintering, an Fe-Zn phase (modified phase) is formed in which the α-Fe phase of the surface portion of the magnetic particles of the magnetic powder 4 reacts with the zinc component of the metal zinc powder 8. Even during the pressure sintering process, the first magnet 40 and the second magnet 60 continue to apply a magnetic field to the mixed powder 1A, and the orientation of the magnetic powder 4 progresses.

[0020] Next, as shown in Fig. 4(b), in an inert gas atmosphere, the punch portion 84 of the upper punch 80 and the punch portion 94 of the lower punch 90 are moved downward along the Z direction, so that the sintered body 1C is moved downward in the molding hole 32 of the insert portion 30 of the die 20 while sliding against the inner side surface 32s of the molding hole 32, the surface 50yf of the first magnetic plate 50 facing the molding hole 32, and the surface 70yf of the second magnetic plate 70 facing the molding hole 32, and is ejected from the lower end of the molding hole 32 (ejection process). Next, as shown in Fig. 4(c), the sintered body 1C is heat-treated in a heating furnace 100 (heat treatment process). In this way, a SmFeN-based magnet 1 (rare earth magnet) including the sintered body 1C is manufactured.

[0021] In the magnet manufacturing method according to the embodiment described above, the first and second magnets are magnetized by a pulse magnetic field, and the magnetic field is applied to the filled mixed powder by the first and second magnets from before pressure sintering to orient the magnetic powder contained in the mixed powder, and the application of the magnetic field to the mixed powder is continued until the completion of pressure sintering (at least halfway through pressure sintering). This allows the orientation of the magnetic powder to be sufficiently maintained until the mutual bonding of the magnetic particles of the magnetic powder contained in the mixed powder occurs. Therefore, the sintered body can be sufficiently given magnetic anisotropy, and the residual magnetization of the SmFeN magnet can be improved. In addition, by using the powder molding die according to the embodiment, during pressure sintering, the filled mixed powder is pressed by the inner side of the molding hole, the surfaces of the first and second magnetic plates facing the molding hole, and the punch parts of the upper punch and the lower punch, without directly pressing the filled mixed powder with the first and second magnets. This makes it possible to avoid pressure being concentrated and directly applied to a part of the contact area of ​​the side surfaces of the first and second magnets facing the molding hole in the Y direction. This makes it possible to prevent cracking of the first and second magnets. Furthermore, when the sintered body is pulled out from the lower end of the molding hole, the sintered body is moved downward while sliding against the inner side surface of the molding hole and the molding hole side surfaces of the first and second magnetic plates without sliding against the side surfaces of the first and second magnets on the molding hole side in the Y direction. This makes it possible to avoid direct application of downward forces such as frictional force and peeling force of the sintered body to a contact area of ​​a part of the side surfaces of the first and second magnets on the molding hole side in the Y direction from the sintered body. This makes it possible to prevent cracking of the first and second magnets. In addition, the first and second magnetic plates are fixed so as not to be able to move downward relative to the insert part. This makes it possible to prevent a downward load from being applied to the first and second magnets from the first and second magnetic plates, even though a downward force is applied to the molding hole side surfaces of the first and second magnetic plates. This makes it possible to prevent cracking of the first and second magnets. Therefore, according to the manufacturing method of the rare earth magnet according to the embodiment, the magnetic properties and productivity of the magnet can be improved. Next, the manufacturing method of the rare earth magnet according to the embodiment will be described in detail.

[0022] 1. Mold preparation process In the die preparation step, a powder molding die is prepared. The powder molding die further includes a die having a molding hole and first and second magnet holes on either side of the molding hole that communicate with the molding hole, a punch to be fitted into the molding hole of the die, a first magnet embedded in the first magnet hole, a first magnetic plate embedded in the first magnet hole on the molding hole side of the first magnet so as to close the communication opening with the molding hole, a second magnet embedded in the second magnet hole, and a second magnetic plate embedded in the second magnet hole on the molding hole side of the second magnet so as to close the communication opening with the molding hole.

[0023] The die is not particularly limited and may be a single member, but is preferably divided into a frame portion (plate portion) with a fitting hole and an insert portion that fits into the fitting hole of the frame portion. This is because maintenance of only the insert portion is required, thereby reducing costs. The material of the die is not particularly limited, but is preferably a non-magnetic material such as non-magnetic cemented carbide or Inconel (registered trademark).

[0024] The first and second magnets are permanent magnets. The permanent magnets are not particularly limited, and examples thereof include alnico magnets and rare earth magnets (e.g., SmCo magnets, etc.), but rare earth magnets are preferred in terms of applying a strong magnetic field. The material of the first and second magnetic plates is not particularly limited as long as it is a magnetic material, and for example, SKD61 is preferred. The thickness of the first and second magnetic plates is not particularly limited, and for example, it is preferred to be 1 mm or more and 2 mm or less. This is because the magnetic plates are not too thin, which can prevent damage to the magnetic plates, and the magnetic plates are not too thick, which can prevent a decrease in the internal magnetic field.

[0025] The punch is not particularly limited, but preferably has an upper punch and a lower punch. The material of the punch is not particularly limited, but preferably is a non-magnetic material such as non-magnetic cemented carbide or Inconel (registered trademark).

[0026] As a powder molding die, for example, as in one embodiment, a die in which the side surfaces on both sides in the width direction of the first and second magnet holes of the die have a tapered shape that inclines toward the center of the width direction of each magnet hole as it moves from the upper end to the lower end along the depth direction, and the side surfaces on both sides in the width direction of the first and second magnetic plates have a tapered shape that inclines toward the center of the width direction of each magnetic plate as it moves from the upper end to the lower end along the depth direction, and each abuts against the side surfaces on both sides in the width direction of the first and second magnet holes. This is because the first and second magnetic plates can be fixed so that they cannot move downward relative to the die. As a powder molding die, for example, as in one embodiment, a die in which the first and second magnet holes of the die penetrate in the depth direction and communicate with the molding hole from the upper end to the lower end along the depth direction, and the width of the portion adjacent to the communication opening of the first and second magnet holes of the die is longer than the width of the communication opening, and the width of the communication opening is the same as the width of the portion adjacent to the communication opening of the molding hole. Among such dies, for example, as in one embodiment, a die in which the surfaces of the first and second magnetic plates on the molding hole side abut against the side surfaces located on both sides of the communication openings on the molding hole side of the first and second magnet holes, respectively, and close the communication openings of the first and second magnet holes with the molding holes is preferred. Among such dies, particularly, as in one embodiment, a die in which the side surfaces of the first and second magnets opposite the molding hole side abut against the side surfaces of the first and second magnet holes opposite the molding hole side, respectively, and the side surfaces of the first and second magnetic plates opposite the molding hole side abut against the side surfaces of the first and second magnets on the molding hole side, respectively, is preferred. Here, the "depth direction" refers to the depth direction of the molding hole, and the "opposing direction" refers to the opposing direction of the first and second magnets when viewed in a plan view from the depth direction. Also, the "width direction" refers to the direction perpendicular to the opposing direction when viewed in a plan view from the depth direction, and the "width" refers to the dimension in the width direction. Furthermore, the terms "lower" and "upper" used to indicate the parts refer to the vertical direction and the opposite direction, respectively, of the mold when in use.

[0027] 2. Powder preparation process In the powder preparation step, raw powder containing magnetic powder is prepared. The raw powder is not particularly limited as long as it contains magnetic powder, and may be a general one, but a mixed powder containing magnetic powder and modifier powder containing zinc component is preferable. This is because the zinc component can bond and modify the particles of the magnetic powder when the raw powder is heated and sintered under pressure.

[0028] The magnetic powder is not particularly limited as long as it is a powder applicable to sintered bodies used in rare earth magnets, and may be a general one, but rare earth magnetic powders such as SmFeN magnetic powders are preferable. The SmFeN magnetic powder is not particularly limited as long as it is a magnetic powder containing magnetic particles having a magnetic phase and containing Sm, Fe, and N, and may be a general one. The SmFeN magnetic powder is usually anisotropic magnetic powder. The magnetic phase of the magnetic particles of the SmFeN magnetic powder is not particularly limited, and may be a general one, but at least a part of the magnetic phase is preferably Th2Zn. 17 Type and Th2Ni 17 Examples of rare earth magnets include phases having at least one of the crystal structures of the above types. Sm is samarium, Fe is iron, and N is nitrogen. Th is thorium, Zn is zinc, and Ni is nickel. Rare earth magnets exhibit magnetization due to the magnetic phase of the magnetic particles in the magnetic powder. The cumulative 50% particle size D in the volumetric particle size distribution of the magnetic powder is 50 The median diameter is not particularly limited and may be a general one, but is preferably, for example, 2 μm or more and 5 μm or less. 50 can be determined, for example, by measurement using a laser diffraction particle size distribution measuring device.

[0029] The content of the modifier powder in the mixed powder is not particularly limited and may be a general amount, but for example, when the magnetic powder is SmFeN magnetic powder, from the viewpoint of residual magnetization, it is preferable that the content is 2 parts by mass or more and 20 parts by mass or less per 100 parts by mass of SmFeN magnetic powder. The method of mixing the magnetic powder and the modifier powder is not particularly limited and may be a general method, for example, a mortar. The modifier powder is not particularly limited and may be a general one, for example, a metal zinc powder containing metal zinc particles, a zinc alloy powder containing zinc alloy particles, etc. The cumulative 50% particle size D in the volume-based particle size distribution of the modifier powder is 50 The (median diameter) is not particularly limited and may be a general one, but is preferably, for example, 0.1 μm or more and 4 μm or less.

[0030] 3.Powder filling process In the powder filling step, the raw material powder is filled into the cavity surrounded by the punch and the surfaces of the first and second magnetic plates facing the forming hole of the die. In the powder filling step, the raw material powder may be further filled into the cavity surrounded by the inner surface of the forming hole. The atmosphere in which the raw material powder is filled may be a general one.

[0031] 4. Pressure sintering process In the pressure sintering step, the filled raw material powder is pressed with the punch while being heated, thereby applying pressure to the surfaces of the first and second magnetic plates facing the molding hole and the punch, thereby performing pressure sintering of the raw material powder to obtain a sintered body. In the pressure sintering step, pressure may be applied to the inner surfaces of the molding hole, the surfaces of the first and second magnetic plates facing the molding hole, and the punch.

[0032] The temperature for pressure sintering is not particularly limited and may be a general one, but from the viewpoint of mutual bonding of the magnetic powders and avoiding decomposition of the magnetic phase, it is preferably, for example, 310° C. or more and 500° C. or less, and more preferably 350° C. or more and 450° C. or less. Furthermore, from the viewpoint of avoiding excessive reaction of the magnetic powder and the modifier powder, the temperature for pressure sintering is preferably, for example, 430° C. or less, and more preferably 390° C. or less.

[0033] The pressure for pressure sintering is not particularly limited and may be a general one, but from the viewpoint of increasing the density of the sintered body and suppressing distortion of the magnetic phase, the pressure is preferably, for example, 100 MPa or more and 2000 MPa or less, and more preferably 500 MPa or more and 1200 MPa or less.

[0034] The time for pressure sintering is not particularly limited and may be a general one, but from the viewpoint of increasing the density of the sintered body and suppressing distortion of the magnetic phase, it is preferably, for example, 1 minute or more and 60 minutes or less, and more preferably 3 minutes or more and 30 minutes or less. The atmosphere in which pressure sintering is performed may be a general one, but for example, an inert gas atmosphere is preferable.

[0035] 5.Magnetic field application process In the magnetic field application step, a magnetic field is applied to the filled raw material powder by the first and second magnets before the pressure sintering to orient the magnetic powder, and the application of the magnetic field to the raw material powder is continued until at least halfway through the pressure sintering. Since the mutual bonding of the magnetic powder occurs as early as halfway through the pressure sintering of the raw material powder, by continuing the application of the magnetic field until at least halfway through the pressure sintering, it is possible to impart sufficient magnetic anisotropy to the sintered body.

[0036] As the magnetic field application step, a step of applying a magnetic field along the facing direction of the first and second magnets to both the filled raw material powder and the first and second magnets before pressure sintering is preferable, thereby orienting the magnetic powder contained in the raw material powder and magnetizing the first and second magnets at the same time. This is because the application of a magnetic field to the raw material powder can be continued by the first and second magnets from before pressure sintering to at least halfway through pressure sintering after magnetization. In such a step, a method of applying a magnetic field to both the raw material powder and the first and second magnets is preferably a method of applying a pulse magnetic field or a static magnetic field by, for example, an electromagnetic coil, etc., and among them, a method of applying a pulse magnetic field is preferable. This is because the magnetic aggregation of the magnetic powder can be alleviated. The conditions of the pulse magnetic field are not particularly limited and may be general. The magnitude of the pulse magnetic field is not particularly limited, but is preferably, for example, 500 kA / m or more and 20000 kA / m or less. The number of times of application of the pulse magnetic field is preferable because the more times it is applied, the more effectively the magnetic aggregation of the magnetic powder can be alleviated. The atmosphere in which the magnetic field is applied may be general. EXAMPLES

[0037] The method for producing a rare earth magnet according to the embodiment will be described in more detail below with reference to examples and comparative examples.

[0038] [Example] An example of a manufacturing method of an SmFeN magnet according to one embodiment was carried out. First, a die having dimensions [mm] and a tapered inclination angle as shown in FIG. 5(a) was prepared as a powder molding die shown in FIG. 1 and FIG. 2 (die preparation step). The thickness of the first and second magnetic plates of the die was 1.45 mm. Next, SmFeN magnetic powder (D 50 A mixed powder (content of metal zinc powder: 5.0 mass%) containing a granular material (grain size: 3.08 μm) and metal zinc powder (modifier powder) was prepared. Next, the mixed powder was filled into the cavity in the molding hole of the insert part of the die (powder filling step).

[0039] Next, the packed mixed powder was compressed to a bulk density of 1.5 g / cm 3(powder density adjusting step). Next, a pulse magnetic field was applied along the Y direction to both the filled mixed powder and the first and second magnets (magnetic field application step). At this time, the magnitude of the pulse magnetic field was set to 4775 kA / m, the number of times that the magnetic field was applied in one direction was set to one time, and the number of times that the pulse magnetic field was applied was set to one time.

[0040] Next, the filled mixed powder was heated in an argon gas atmosphere to raise the temperature of the mixed powder to 380°C (heating step). Next, in an argon gas atmosphere, the mixed powder was pressure sintered at a temperature of 380°C and a pressure of 500 MPa for 30 minutes to obtain a sintered body (pressure sintering step). Next, the sintered body was extracted from the lower end of the molding hole (extraction step). Next, the sintered body was heat treated in a vacuum at a temperature of 390°C for 24 hours (heat treatment step). In this way, a SmFeN magnet (rare earth magnet) comprising a sintered body was manufactured.

[0041] [Comparative Example] In the mold preparation step, a mold having a die and first and second magnets as shown in Fig. 5(b) was prepared, and the same manufacturing method of the SmFeN magnet as in the embodiment was carried out, except that the mold was used in the subsequent steps. The mold shown in Fig. 5(b) does not have the first and second magnetic plates, the dimension of the first and second magnet holes in the Y direction is shortened by the thickness of the first and second magnetic plates (1.45 mm), and the side surfaces of the first and second magnets on the molding hole side in the Y direction are abutted against the side surfaces located on both sides of the communication openings on the molding hole side in the Y direction of the first and second magnet holes, respectively, blocking the communication openings of the first and second magnet holes with the molding holes. The mold shown in Fig. 5(b) is substantially the same as the mold shown in Fig. 5(a) in other respects.

[0042] [evaluation] The bulk density [g / cm3] of the sintered bodies of the SmFeN magnets produced in the examples and comparative examples was 3] and the degree of orientation were calculated to evaluate the magnetic properties. In calculating the degree of orientation, in the magnetization-magnetic field curve, the magnetization when the magnetic field was 0T was determined as M(0T) and the magnetization when the magnetic field was 8T was determined as M(8T), and the degree of orientation was calculated by M(0T) / M(8T). In evaluating the magnetic properties, the rare earth magnets of each example were pulse-magnetized at room temperature with a magnetizing magnetic field of 4775kA / m, and the residual magnetization [T] was measured using a direct current magnetization fluxmeter (TRF). The above results are shown in Table 1 below. Furthermore, for the manufacturing methods of the SmFeN magnets of the examples and comparative examples, a test was conducted multiple times in which the test was repeated until either the first or second magnet of the mold broke. In the comparative example, either the first or second magnet broke after roughly one or two runs. On the other hand, in the examples, neither the first nor the second magnet broke.

[0043] [Table 1]

[0044] [Consideration] As shown in Table 1 above, there was almost no difference in the bulk density and degree of orientation of the sintered body, as well as the residual magnetization, between the SmFeN magnets produced in the examples and those produced in the comparative examples. From these results and the evaluation results of the cracks in the magnets in the mold, it is believed that the manufacturing method of the SmFeN magnets in the examples can improve the magnetic properties and productivity of the magnets by using the first and second magnetic plates in the mold.

[0045] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as described in the claims. [Explanation of symbols]

[0046] 1: rare earth magnet, 1A: mixed powder (raw powder), 1C: sintered body, 10: mold, 20: die, 30: insert portion, 32: molding hole, 34: first magnet hole, 36: second magnet hole, 40: first magnet, 50: first magnetic plate, 60: second magnet, 70: second magnetic plate, 80: upper punch, 90: lower punch

Claims

[Claim 1] a step of preparing a powder molding die further comprising: a die having a molding hole and first and second magnet holes on either side of the molding hole that communicate with the molding hole; a punch to be fitted into the molding hole of the die; a first magnet embedded in the first magnet hole; a first magnetic plate embedded in the first magnet hole on the molding hole side of the first magnet so as to close the communication opening with the molding hole; a second magnet embedded in the second magnet hole; and a second magnetic plate embedded in the second magnet hole on the molding hole side of the second magnet so as to close the communication opening with the molding hole; A step of preparing a raw material powder including a magnetic powder; a filling step of filling the raw material powder into a cavity surrounded by the punch and the surfaces of the first and second magnetic plates on the forming hole side in the forming hole of the die; a step of pressing the filled raw material powder with the punch while heating the raw material powder, thereby applying pressure to the molding hole side surfaces of the first and second magnetic plates and the punch, thereby performing pressure sintering of the raw material powder to obtain a sintered body; a step of applying a magnetic field to the filled raw material powder using the first and second magnets before the pressure sintering to orient the magnetic powder, and continuing to apply the magnetic field to the raw material powder until at least halfway through the pressure sintering.

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