JP6668289B2 - Method of manufacturing RTB-based permanent magnet and RTB-based permanent magnet - Google Patents

Description

  The present invention relates to a method for manufacturing an RTB-based permanent magnet and an RTB-based permanent magnet.

  2. Description of the Related Art Conventionally, there has been an axial gap type motor as means for realizing miniaturization and thinning of a device. Patent Literature 1 describes a permanent magnet used in the axial gap type motor and a method for manufacturing the same. In the method for manufacturing a permanent magnet described in Patent Document 1, first, a compound is generated by mixing a magnet powder and a binder. Next, the compound is formed into a sheet to form a green sheet. The green sheet is subjected to a magnetic field orientation, and the green sheet subjected to the magnetic field orientation is deformed and formed into a product shape. Next, this is sintered to produce a permanent magnet. In the annular permanent magnet obtained by this manufacturing method, the axis of easy magnetization is oriented in the axial direction, and the waveform of the magnetic flux density distribution in the circumferential direction of the surface in the axial direction is approximated to a sine wave shape. As a result, the torque ripple is reduced, and an attempt is made to reduce noise and vibration of the rotating electric machine.

JP-A-2006-32023

  However, the method for manufacturing a permanent magnet described in Patent Document 1 is not simple.

  In view of the above, the present invention has been made in view of the above, and has a simple and simple R-T-B system in which the magnetic flux density on the side surface of the cylinder continuously changes along the circumferential direction. It is an object to provide a method for manufacturing a magnet.

  In order to solve the above-described problem and achieve the object, a method for manufacturing an RTB-based permanent magnet according to one embodiment of the present invention provides an RTB-based magnet powder (R is Nd and / or A billet forming step of forming a polygonal pillar-shaped billet by forming a rare earth element containing Pr, T representing Fe, or Fe and Co), and forming an opening at one end and closing the other end. The polygonal column-shaped billet obtained in the billet forming step is placed in a cylindrical die, pressure is applied to the billet from the opening side, and the billet is heated to form the polygonal column-shaped billet. And a hot working step of producing a cylindrical R-T-B-based permanent magnet from the above, in the billet forming step, the polygonal column-shaped billet is formed such that the bottom surface of the billet is polygonal, The hot working In the cylindrical R-T-B based permanent magnet, the bottom surface of the the R-T-B-based permanent magnet is hot worked such that the circle.

  According to one embodiment of the present invention, it is possible to easily manufacture an R-T-B-based permanent magnet having a columnar shape, in which the magnetic flux density on the side surface of the cylinder changes continuously along the circumferential direction.

FIG. 1 is a flowchart schematically showing a method for manufacturing an RTB-based permanent magnet according to the embodiment. FIG. 2 is a diagram for further explaining the flowchart of FIG. FIG. 3 is a diagram for explaining an RTB-based permanent magnet obtained by the method of manufacturing an RTB-based permanent magnet according to the embodiment. FIG. 4 is a diagram for explaining the shape of the bottom surface of the billet. FIG. 5 is a diagram for explaining the example. FIG. 6 is a diagram for explaining the example. FIG. 7 is a diagram for explaining the embodiment. FIG. 8 is a diagram showing the measurement results of the surface magnetic flux density of the RTB-based permanent magnet (after magnetization) manufactured in the example. FIG. 9 is a diagram showing a measurement result of a surface magnetic flux density of the RTB-based permanent magnet (after magnetization) manufactured in the example. FIG. 10 is a diagram showing the measurement results of the magnetic flux density of the RTB-based permanent magnet (after magnetization) manufactured in Example 5. FIG. 11 is a diagram showing measurement results of demagnetization curves of the RTB-based permanent magnets manufactured in the examples. FIG. 12 is a diagram illustrating the relationship between the hot working time and the coercive force of the RTB-based permanent magnet manufactured in the example.

  Hereinafter, embodiments will be described in detail. In addition, it is not limited at all by the following embodiments.

<Method for producing RTB-based permanent magnet>
The method for manufacturing the RTB-based permanent magnet according to the embodiment will be described in detail. FIG. 1 is a flowchart schematically showing a method for manufacturing an RTB-based permanent magnet according to the embodiment. FIG. 2 is a diagram for further explaining the flowchart of FIG. FIG. 3 is a diagram for explaining an RTB-based permanent magnet obtained by the method of manufacturing an RTB-based permanent magnet according to the embodiment.

  As shown in FIG. 1, the method for manufacturing an RTB-based permanent magnet according to the embodiment includes a magnet powder preparation step (ST1), a billet forming step (ST2), a hot working step (ST3), and a post-treatment. Step (ST4) is included.

  The method of manufacturing an RTB-based permanent magnet according to the embodiment is different from the method of manufacturing a general sintered magnet that performs magnetic field orientation. In the method of manufacturing an RTB-based permanent magnet according to the embodiment, the easy axis of magnetization is oriented by hot plastic working in the hot working step (ST3).

  Specifically, in hot plastic working, pressure is applied from one bottom surface to a billet having the shape of a regular quadratic prism (right prism) to obtain a permanent magnet having the shape of a cylinder (right cylinder). In hot plastic working, the height of the square pillar is reduced, and the bottom is pushed out to form a cylinder. FIG. 3 shows a column-shaped RTB-based permanent magnet obtained by hot plastic working. A square indicated by a broken line on the bottom surface represents a cross section of a square pillar-shaped billet before hot plastic working.

As can be seen from FIG. 3, almost no plastic deformation occurs at the sides of the square prism in the height direction. On the other hand, plastic deformation occurs on the side surface of the square prism. The amount of plastic deformation increases from the side in the height direction to the center of the side surface, and the amount of plastic deformation becomes maximum at the center of the side surface. For example, in the case of an R ₂ Fe ₁₄ B crystal (R = Nd, Pr, etc.), the crystal grains grow anisotropically in the direction perpendicular to the c-axis of the crystal due to plastic deformation, and become flat crystal grains. The flat crystal grains are stacked in the c-axis direction. It is considered that the greater the amount of plastic deformation, the greater the degree of stacking in the c-axis direction. In the R ₂ Fe ₁₄ B crystal (R = Nd, Pr, etc.), the c-axis direction matches the direction of the easy axis. Therefore, it is considered that the greater the amount of plastic deformation, the greater the degree of orientation of the easy axis. Also, it is considered that the direction of the plastic deformation corresponds to the direction of the axis of easy magnetization.

  Here, the degree of orientation of the axis of easy magnetization and the direction of the axis of easy magnetization for the columnar RTB-based permanent magnet obtained by hot plastic working (specifically, the outer peripheral edge of the column in the permanent magnet). Is represented by an arrow, for example, it is considered as shown by an arrow in FIG. Specifically, in the portion where the center of the side surface of the square prism is plastically deformed, the degree of orientation of the axis of easy magnetization becomes the largest. In this portion, the axis of easy magnetization is oriented in the direction in which the pressure is applied. Further, in the cylindrical RTB-based permanent magnet, the degree of orientation of the axis of easy magnetization continuously decreases toward the portion that was the side in the height direction of the square prism before hot plastic working. Become.

  In the case of a cylindrical R-T-B permanent magnet obtained by hot plastic working, when the magnetic flux density of the side surface of the cylinder (specifically, the outer peripheral edge of the cylinder) is measured, the magnetic flux density becomes It changes continuously along the direction. It is considered that this continuous change corresponds to the degree of orientation of the easy axis. Such a permanent magnet can be applied to an axial gap type motor. Since the magnetic flux density changes continuously along the circumferential direction, low cogging and low torque ripple can be realized.

  As described above, by using the hot plastic working, the magnetic flux density on the side surface of the column can be more easily and continuously reduced at a lower cost than the manufacturing method of Patent Literature 1 along the circumferential direction. Can be manufactured.

  JP-A-2-276210 discloses a method for producing a rare-earth permanent magnet in which Nd-Fe-B-based magnet powder is preformed and then hot-worked (hot extrusion). According to this manufacturing method, an anisotropic ring magnet having anisotropy in the radial direction can be obtained. JP-A-7-161523 describes a method of manufacturing a rare-earth permanent magnet in which a rare-earth magnet powder is placed in a cylindrical capsule, hot-extrusion-molded, processed into an arc shape, and magnetized. . With this manufacturing method, an arc-shaped magnet having a sinusoidal surface magnetic flux density waveform in the radial direction can be obtained. As described above, according to the method for manufacturing a rare earth permanent magnet described in the above patent document, a rare earth permanent magnet having anisotropy in the radial direction can be obtained. These rare-earth permanent magnets are usually used for radial gap type motors, but are not used for axial gap type motors.

[Magnetic powder preparation step (ST1)]
In the magnet powder preparing step (ST1), the RTB-based magnet powder (R represents a rare earth element containing Nd and / or Pr used in the billet forming step (ST2), and T is Fe, or Fe and Co Is prepared.) Note that the RTB-based magnet constituting the RTB-based magnet powder will be described in detail in the billet forming step (ST2).

  In the magnet powder preparation step (ST1), as shown in FIG. 2, first, the raw materials are weighed (ST1-1), and high-frequency induction melting is performed under reduced pressure or in an argon atmosphere (ST1-2). Next, the melted raw material is poured on a rotating roll and rapidly cooled to form a ribbon. Next, the ribbon is pulverized (ST1-3). For example, it is preferable to break the ribbon into several millimeters to several tens of millimeters and then pulverize it with a pulverizer or the like. By this magnet powder preparation step (ST1), an RTB-based magnet powder (a thin strip) having a flake shape and exhibiting magnetic isotropy is obtained.

[Billet forming process (ST2)]
In the billet forming step (ST2), RTB-based magnet powder (R represents a rare earth element containing Nd and / or Pr, and T represents Fe, or Fe and Co) is formed. Manufactures billets in the shape of a square prism (right prism). Specifically, the RTB-based magnet powder obtained in the magnet powder preparation step (ST1) is used.

Here, the RTB (boron) -based magnet constituting the RTB-based magnet powder will be described. The RTB-based magnet includes an R ₂ T ₁₄ B phase (for example, an Nd ₂ Fe ₁₄ B-type compound phase) that is a ternary tetragonal compound as a main phase. Further, the RTB-based magnet usually further includes an R-rich phase and the like.

  R represents a rare earth element containing Nd and / or Pr. In other words, R contains Nd and / or Pr as essential components. Rare earth elements include neodymium (Nd) and praseodymium (Pr), as well as scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), promethium (Pm), samarium (Sm), and europium (Eu). ), Gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). As the rare earth elements other than Nd and Pr, one kind may be used alone, or two or more kinds may be used in combination.

  Specifically, as R, only Nd may be used, only Pr may be used, or only Nd and Pr may be used. Further, Nd and a rare earth element other than Nd and Pr may be used, Pr and a rare earth element other than Nd and Pr may be used, and Nd and Pr and a rare earth element other than Nd and Pr may be used. Is also good. It is preferable to use at least Nd as R.

  T represents Fe, or Fe and Co. As described above, T may be Fe alone or may be partially substituted with Co. When the total amount of T is 100 atomic%, it is preferable that Fe is contained in an amount of 50 atomic% or more.

  The RTB-based magnet may include other elements. Other elements include titanium, zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W). As the other elements, one type may be used alone, or two or more types may be used in combination.

  In the RTB-based magnet, R is preferably contained in an amount of 12 atomic% or more and 15 atomic% or less. B is preferably contained in an amount of 6 atomic% or more and 8 atomic% or less. In addition, when the above-mentioned other elements are contained, it is preferable that the other elements are contained in an amount of more than 0 atomic% and 3 atomic% or less in total. Here, the balance is the total amount of T and the elements unavoidably included.

  More specifically, as the RTB-based magnet powder, trade names: MQP-C, MQP-14-12, MQP-AA14-12, MQP-14-13, MQP-AA14-13, MQP- 13-14 (manufactured by Magnequench) is preferably used. One of these RTB-based magnet powders may be used alone, or two or more thereof may be used in combination.

  In the billet forming step (ST2), as shown in FIG. 2, the RTB-based magnet powder is formed by a spark plasma sintering (SPS) apparatus to form a billet having a square prism (right prism) shape. It is manufactured (ST2-1). In addition, the obtained square pillar-shaped billet may be a cube. The molding may be performed under the condition that the form can be maintained as a billet. The molding is preferably performed by applying a pressure of, for example, 10 MPa or more and 100 MPa or less. The molding may be performed while heating, for example, to 500 ° C. or more and 800 ° C. or less.

  In the billet forming step (ST2), when the billet is placed in a cylindrical die used for the hot working step (ST3), the bottom surface of the billet forms an inner circumferential circle of the die. It is shaped to be a square having vertices at equally dividing points. If the bottom surface of the square prism-shaped billet is formed in the above size, the R-T-B permanent magnet in which the magnetic flux density on the side surface of the cylinder continuously changes along the circumferential direction after hot plastic working. Can be manufactured. In addition, having a vertex at a point that equally divides the inner circumferential circle of the die has an advantage that the waveform of the magnetic flux density on the side surface of the cylinder can be easily adjusted.

  Here, the billet is a right prism, and the space of the die is a right cylinder. For this reason, in the above billet, any transverse section (a section perpendicular to the height of the prism) is formed into a square having a vertex at a point equally dividing the inner circumferential circle of the die. Further, in the present specification, “having a vertex at a point that equally divides the inner circumference circle” means that not only does the above-mentioned equally dividing point coincide with the vertex, but also that it substantially coincides Including. Further, in the present specification, the term “right prism” includes a case where the right prism is substantially a right prism.

[Hot working process (ST3)]
In the hot working step (ST3), the square quadrangle (right prism) billet obtained in the billet forming step (ST2) is put into a cylindrical die having an opening at one end and the other end closed. A pressure is applied to the billet from the opening side, and the billet is heated to produce a columnar (rectangular) RTB-based permanent magnet from a square prism-shaped billet.

In the hot working step (ST3), specifically, a cylindrical die containing a square pillar-shaped billet is set in the SPS device. Pressure is applied to the billet from the opening side. At this time, it is preferable to apply pressure evenly to the upper surface (upper bottom surface) of the square pillar-shaped billet. The hot working is preferably performed by applying a pressure of, for example, 1 MPa or more and 90 MPa or less. The hot working is performed while heating is started at, for example, 600 ° C. or more and 700 ° C. or less after applying pressure. At the time of heating, specifically, an ON-OFF DC pulse is applied to the billet in the shape of a square prism. The current density is set, for example, to 100 A / cm ² or more and 1000 A / cm ² or less. Heating is performed from room temperature to the above-mentioned heating temperature, for example, at a heating rate of 10 ° C./min to 100 ° C./min. During hot working, it is desirable to adjust the pressure so that the hot working speed does not increase, preferably so that the hot working speed becomes constant. The hot working is also preferably performed under reduced pressure or in an argon atmosphere.

  The hot working is preferably performed from the start of the displacement to the completion of the displacement while monitoring the displacement. Usually, it is performed for 100 seconds or more and 500 seconds or less. Here, as for the displacement monitor, the displacement amount of the servomotor that is under pressure control is usually monitored.

  By the hot working step (ST3), as shown in FIG. 2, the billet in the shape of a regular quadrangular prism is plastically deformed to obtain a columnar (rectangular) RTB-based permanent magnet (ST3-1). In the hot working step (ST3), the obtained cylindrical RTB-based permanent magnet has a bottom surface of the RTB-based permanent magnet in contact with the inner circumferential circle of the cylindrical die. It has been hot worked so that When the bottom surface of the RTB-based permanent magnet is plastically deformed to the above size, the magnetic flux density on the side surface of the cylinder continuously changes along the circumferential direction. Such an RTB-based permanent magnet is suitably used for an axial gap type motor. The obtained RTB-based permanent magnet shows magnetic isotropy.

  Here, the RTB-based permanent magnet is a right cylinder, and the space of the die is a right cylinder. For this reason, in the above permanent magnet, any transverse cross section (a cross section perpendicular to the height of the cylinder) is plastically deformed so as to be a circle in contact with the inner circumferential circle of the die. Further, in the present specification, the “circle in contact with the inner circumference circle” is not limited to the case where the above inner circumference circle is in contact with the above circle, but also includes the case where it is substantially touching. Further, in the present specification, the term “right cylinder” includes a case where the cylinder is substantially a right cylinder.

  It is considered that the composition of the RTB-based permanent magnet maintains the composition of the RTB-based magnet constituting the RTB-based magnet powder.

In the hot working step (ST3), the hot working speed defined by the following equation (1) is preferably 0.00310 (1 / s) or more and 0.00328 (1 / s) or less.
Hot working speed (1 / s) = (Bottom area of cylindrical R-T-B permanent magnet (mm ² )) / (Bottom area of square prism-shaped billet (mm ² )) / (Square prism-shaped Displacement time (s) from the start of displacement of the billet to the end of displacement as a cylindrical RTB-based permanent magnet) (1)

  When the hot working speed is in the above range, the degree of orientation of the c-axis on the side surface of the cylinder changes in a shape close to a sine wave along the circumferential direction, which is preferable. It is also preferable from the viewpoint of coercive force. Therefore, the magnetic flux density on the side surface of the cylinder changes in a shape close to a sine wave along the circumferential direction, which is preferable. Specifically, during one round in the circumferential direction, the shape has four peaks and four valleys. If properly magnetized, a four-pole RTB-based permanent magnet capable of realizing high output, low cogging and low torque ripple can be obtained.

[Post-processing step (ST4)]
In the post-processing step (ST4), post-processing is performed on the RTB-based permanent magnet obtained in the hot working step (ST3). For example, as shown in FIG. 2, surface treatment (ST4-1), inspection (ST4-2), and magnetization (ST4-3) are performed. Specifically, in the surface treatment, plating treatment of nickel (Ni), tin (Sn), zinc (Zn) or the like, aluminum (Al) vapor deposition, resin coating, and the like are performed.

  In the method of manufacturing an RTB-based permanent magnet according to the above-described embodiment, the magnet powder preparation step (ST1) is not limited to the above step. Other preparation steps may be performed as long as the RTB-based magnet powder having the above composition is obtained.

  In the billet forming step (ST2), the shape of the billet is not limited to a square prism. FIG. 4 is a diagram for explaining the shape of the bottom surface of the billet. The shape of the billet may be a polygonal column shape having a bottom surface as shown in FIGS. Specifically, in the method of manufacturing an RTB-based permanent magnet according to the above-described embodiment, a square prism is read as a polygonal column, and a square is read as a polygon. That is, in this embodiment, the RTB-based magnet powder (R represents a rare earth element containing Nd and / or Pr, and T represents Fe, or Fe and Co) is formed. A billet forming step of producing a polygonal column-shaped billet, and into a cylindrical die having an opening at one end and a closed end at the other end, put the polygonal column-shaped billet obtained in the billet forming step, Applying a pressure to the billet from the opening side, heating the billet, and manufacturing a cylindrical R-T-B-based permanent magnet from the polygonal pillar-shaped billet; In the billet forming step, the polygonal column-shaped billet is a polygon having a vertex at a point at which the bottom surface of the billet equally divides the inner circumferential circle of the die when the billet is put into the cylindrical die. Become In the hot working step, the cylindrical R-T-B-based permanent magnet is formed as a circle in which the bottom surface of the R-T-B-based permanent magnet is in contact with the inner circumferential circle of the cylindrical die. It is hot-worked to become.

  As shown in FIGS. 4A, 4B, and 4D, the bottom surface of the billet is not limited to a regular polygon having vertices at points equally dividing the inner circumferential circle of the die. For example, as shown in FIGS. 4C and 4E, the bottom surface of the billet is a polygon having a vertex at a point that equally divides the inner circumference of the die, and equally divides the inner circumference of the die. It may be a polygon having vertices between the points to be formed. Here, a vertex such as a triangle may be an odd polygon. Even when the vertices are odd polygons, a permanent magnet applicable to an axial gap type motor can be obtained by appropriately performing magnetization.

  Further, the method of manufacturing an RTB-based permanent magnet according to the embodiment includes an RTB-based magnet powder (R represents a rare earth element containing Nd and / or Pr, and T represents Fe or Fe and Co are represented by a billet forming step of forming a polygonal column-shaped billet, and a cylindrical die having an opening at one end and a closed end at the other end. The above-mentioned polygonal column-shaped billet is put, pressure is applied to the billet from the opening side, and the billet is heated to produce a columnar RTB-based permanent magnet from the polygonal column-shaped billet. The billet forming step, the polygonal column-shaped billet is formed so that the bottom surface of the billet is polygonal, and the cylindrical R-T is formed in the hot working step. -B system permanent Stone may be in the form of embodiment which is hot worked to a bottom surface of the the R-T-B-based permanent magnet is circular. In the hot working step, it is preferable to apply pressure along the height direction of the billet. Also in this case, it is considered that the degree of orientation of the axis of easy magnetization changes in the obtained cylindrical RTB-based permanent magnet in accordance with the amount of plastic deformation. Further, in the obtained columnar RTB-based permanent magnet, the magnetic flux density on the side surface of the column continuously changes along the circumferential direction according to the degree of orientation of the axis of easy magnetization.

  In the billet forming step (ST2), the billet may be formed by a device other than the SPS device. Other devices may be used as long as a billet that can hold the shape can be obtained.

  In the hot working step (ST3), hot working may be performed by an apparatus other than the SPS apparatus. Other devices may be used as long as the above-mentioned RTB-based permanent magnet is obtained by plastic deformation. From the viewpoint of rapid heating, an SPS device is preferably used. The hot working step (ST3) is not limited to the case where heating is started after applying pressure. The application of pressure and the heating may be started at the same time, or the application of pressure after the start of heating may be used.

<RTB Permanent Magnet According to Embodiment>
The RTB-based permanent magnet according to the embodiment is a column-shaped RTB-based permanent magnet (R represents a rare earth element containing Nd and / or Pr, and T represents Fe, or Fe and Co.). The composition of the RTB-based permanent magnet is the same as that described in the method of manufacturing the RTB-based permanent magnet according to the embodiment. This RTB-based permanent magnet shows magnetic isotropy.

  In the RTB-based permanent magnet according to the embodiment, the magnetic flux density on the side surface of the cylinder changes continuously along the circumferential direction. This corresponds to the fact that the degree of orientation of the c-axis continuously changes along the circumferential direction on the side surface of the cylinder.

  The RTB-based permanent magnet according to the embodiment includes flat crystal grains, and the size of the crystal grains is 200 nm or more and 500 nm or less. The size of the crystal grains can be observed using a scanning electron microscope. It is considered that the portion where the flat crystal grains are stacked has a large degree of c-axis orientation.

  In addition, the RTB-based permanent magnet is often obtained as a sintered magnet by a powder metallurgy manufacturing method. In this sintered magnet, the crystal grains are usually in a crushed shape of 1 μm or more and 2 μm or less.

  In the RTB-based permanent magnet according to the embodiment, it is preferable that the magnetic flux density on the side surface of the cylinder changes in a sinusoidal shape along the circumferential direction. This case corresponds to the fact that the degree of orientation of the c-axis changes in a sine wave shape along the circumferential direction. In addition, it is preferable to have a shape having four peaks and four valleys during one round in the circumferential direction. If properly magnetized, a four-pole RTB-based permanent magnet capable of realizing high output, low cogging and low torque ripple can be obtained.

  The RTB-based permanent magnet according to the embodiment has a shape other than a shape having four peaks and four valleys while the magnetic flux density on the side surface of the cylinder makes one round along the circumferential direction. Good. A shape having three peaks and three valleys, a shape having six peaks and six valleys, a shape having eight peaks and eight valleys, and the like may be used.

  The RTB-based permanent magnet according to the embodiment is obtained by the above-described manufacturing method. By appropriately changing the shape of the billet, the hot working speed, and the like, an RTB-based permanent magnet having a desired magnetic flux density can be obtained. Note that the composition of the RTB-based permanent magnet according to the embodiment is such that the composition of the RTB-based magnet constituting the RTB-based magnet powder used in the production is maintained. Conceivable.

  Hereinafter, the above embodiment will be described in more detail based on an example performed to clarify the effects of the above embodiment. The above embodiment is not limited by the following examples and comparative examples. FIGS. 5, 6 and 7 are diagrams for explaining the embodiment.

[Example 1]
An isotropic Nd-Fe-B-based magnet powder (MQP-C: manufactured by Magnequench) was hot-pressed to produce a square pillar-shaped billet 1 (FIG. 6). Specifically, the hot press was performed by heating from room temperature to 700 ° C. while applying pressure at 30 MPa. As shown in Table 1 (FIG. 5), the billet 1 was a square prism having a length of 7.07 mm, a width of 7.07 mm, and a height of 10.42 mm, and weighed 3.99 g. Table 1 (FIG. 5) also shows the cross-sectional area (S), volume (V), density (D), and relative density (RD) of the billet 1.
As shown in FIG. 7, a billet 1 was placed in a hollow cylindrical die 2. The die 2 was set in the SPS device. Next, the billet 1 (the bottom surface of the square) was pressed at 90.0 MPa from the axial direction by a punch. Then, while being pressurized, it was electrically heated from room temperature to 700 ° C. The amount of displacement of the billet 1 was monitored during pressurization and energization. The time when the displacement began to be seen was defined as the start of hot working, and the time when the displacement was no longer seen and ended when the hot working was completed. The time from the start of hot working to the end of hot working (hot working time) was 120.00 s (Table 1 (FIG. 5)). After the hot plastic working, the sintered magnet obtained from the SPS device was taken out. Due to the hot plastic working, the billet 1 composed of the Nd-Fe-B-based magnet powder was a cylindrical Nd-Fe-B-based permanent magnet. The columnar Nd—Fe—B permanent magnet had the physical properties shown in Table 1 (FIG. 5).
This cylindrical Nd-Fe-B-based permanent magnet was magnetized in the axial direction (the height direction of the cylinder).

[Example 2]
An isotropic Nd-Fe-B-based magnet powder (MQP-C: manufactured by Magnequench) was hot-pressed to produce a square pillar-shaped billet 1 (FIG. 6). The hot press was specifically performed by heating from room temperature to 600 ° C. while applying a pressure of 30 MPa. As shown in Table 1 (FIG. 5), the billet 1 was a square prism having a length of 7.14 mm, a width of 7.14 mm, and a height of 13.39 mm, and weighed 4.00 g. Table 1 (FIG. 5) also shows the cross-sectional area (S), volume (V), density (D), and relative density (RD) of the billet 1.
As shown in FIG. 7, a billet 1 was placed in a hollow cylindrical die 2. The die 2 was set in the SPS device. Next, the billet 1 (square bottom surface) was pressed at 50.0 MPa from the axial direction with a punch. Next, while being pressurized, it was electrically heated from room temperature to 680 ° C. The amount of displacement of the billet 1 was monitored during pressurization and energization. The time when the displacement began to be seen was defined as the start of hot working, and the time when the displacement was no longer seen and ended when the hot working was completed. The time from the start of hot working to the end of hot working (hot working time) was 174.00 s (Table 1 (FIG. 5)). After the hot plastic working, the sintered magnet obtained from the SPS device was taken out. Due to the hot plastic working, the billet 1 composed of the Nd-Fe-B-based magnet powder was a cylindrical Nd-Fe-B-based permanent magnet. The columnar Nd—Fe—B permanent magnet had the physical properties shown in Table 1 (FIG. 5).
This cylindrical Nd-Fe-B-based permanent magnet was magnetized in the axial direction (the height direction of the cylinder).

[Example 3]
An isotropic Nd-Fe-B-based magnet powder (MQP-C: manufactured by Magnequench) was hot-pressed to produce a square pillar-shaped billet 1 (FIG. 6). Specifically, the hot press was performed by heating from room temperature to 700 ° C. while applying pressure at 30 MPa. As shown in Table 1 (FIG. 5), the billet 1 was a square prism having a length of 7.07 mm, a width of 7.07 mm, and a height of 10.35 mm, and weighed 3.99 g. Table 1 (FIG. 5) also shows the cross-sectional area (S), volume (V), density (D), and relative density (RD) of the billet 1.
As shown in FIG. 7, a billet 1 was placed in a hollow cylindrical die 2. The die 2 was set in the SPS device. Next, the billet 1 (square bottom surface) was pressed at 30.0 MPa from the axial direction with a punch. Next, while being pressurized, it was electrically heated from room temperature to 680 ° C. The amount of displacement of the billet 1 was monitored during pressurization and energization. The time when the displacement began to be seen was defined as the start of hot working, and the time when the displacement was no longer seen and ended when the hot working was completed. The time from the start of hot working to the end of hot working (hot working time) was 395.00 s (Table 1 (FIG. 5)). After the hot plastic working, the sintered magnet obtained from the SPS device was taken out. Due to the hot plastic working, the billet 1 composed of the Nd-Fe-B-based magnet powder was a cylindrical Nd-Fe-B-based permanent magnet. The columnar Nd—Fe—B permanent magnet had the physical properties shown in Table 1 (FIG. 5).
This cylindrical Nd-Fe-B-based permanent magnet was magnetized in the axial direction (the height direction of the cylinder).

[Example 4]
An isotropic Nd-Fe-B-based magnet powder (MQP-C: manufactured by Magnequench) was hot-pressed to produce a square pillar-shaped billet 1 (FIG. 6). The hot press was specifically performed by heating from room temperature to 600 ° C. while applying a pressure of 30 MPa. As shown in Table 1 (FIG. 5), the billet 1 was a square prism having a length of 7.14 mm, a width of 7.14 mm, and a height of 13.39 mm, and weighed 4.00 g. Table 1 (FIG. 5) also shows the cross-sectional area (S), volume (V), density (D), and relative density (RD) of the billet 1.
As shown in FIG. 7, a billet 1 was placed in a hollow cylindrical die 2. The die 2 was set in the SPS device. Next, the billet 1 (square bottom surface) was pressed at 20.0 MPa from the axial direction with a punch. Next, while being pressurized, it was electrically heated from room temperature to 680 ° C. The amount of displacement of the billet 1 was monitored during pressurization and energization. The time when the displacement began to be seen was defined as the start of hot working, and the time when the displacement was no longer seen and ended when the hot working was completed. The time from the start of hot working to the end of hot working (hot working time) was 468.00 s (Table 1 (FIG. 5)). After the hot plastic working, the sintered magnet obtained from the SPS device was taken out. Due to the hot plastic working, the billet 1 composed of the Nd-Fe-B-based magnet powder was a cylindrical Nd-Fe-B-based permanent magnet. The columnar Nd—Fe—B permanent magnet had the physical properties shown in Table 1 (FIG. 5).
This cylindrical Nd-Fe-B-based permanent magnet was magnetized in the axial direction (the height direction of the cylinder).

[Example 5]
An isotropic Nd-Fe-B-based magnet powder (MQP-C: manufactured by Magnequench) was hot-pressed to produce a square pillar-shaped billet 1 (FIG. 6). The hot press was specifically performed by heating from room temperature to 600 ° C. while applying a pressure of 30 MPa. As shown in Table 1 (FIG. 5), the billet 1 was a square prism having a length of 7.14 mm, a width of 7.14 mm, and a height of 13.42 mm, and weighed 3.99 g. Table 1 (FIG. 5) also shows the cross-sectional area (S), volume (V), density (D), and relative density (RD) of the billet 1.
As shown in FIG. 7, a billet 1 was placed in a hollow cylindrical die 2. The die 2 was set in the SPS device. Then, the billet 1 (square bottom surface) was pressed at 10.0 MPa from the axial direction with a punch. Next, while being pressurized, it was electrically heated from room temperature to 680 ° C. The amount of displacement of the billet 1 was monitored during pressurization and energization. The time when the displacement began to be seen was defined as the start of hot working, and the time when the displacement was no longer seen and ended when the hot working was completed. The time from the start of hot working to the end of hot working (hot working time) was 495.00 s (Table 1 (FIG. 5)). After the hot plastic working, the sintered magnet obtained from the SPS device was taken out. Due to the hot plastic working, the billet 1 composed of the Nd-Fe-B-based magnet powder was a cylindrical Nd-Fe-B-based permanent magnet. The columnar Nd—Fe—B permanent magnet had the physical properties shown in Table 1 (FIG. 5).
This cylindrical Nd-Fe-B-based permanent magnet was magnetized in the axial direction (the height direction of the cylinder).

[Comparative Example 1]
In Example 1, the steps up to the production of the billet were performed.

[Evaluation]
(Hot working speed)
The hot working speed (1 / s) was obtained from the following equation (1). Table 1 (FIG. 5) shows the hot working speed (1 / s) obtained for Examples 1 to 5.
Hot working speed (1 / s) = (Bottom area of cylindrical R-T-B permanent magnet (mm ² )) / (Bottom area of square prism-shaped billet (mm ² )) / (Square prism-shaped Displacement time (s) from the start of displacement of the billet to the end of displacement as a cylindrical RTB-based permanent magnet) (1)
“(Bottom area of cylindrical RTB-based permanent magnet (mm ² )) / (Bottom area of square pillar-shaped billet (mm ² ))” is shown in Table 1 (FIG. 5). Same as the degree of processing. "(Displacement time (s) from the start of the displacement of the square prism-shaped billet to the end of the displacement as a cylindrical RTB-based permanent magnet)" is the above-described hot working start time. It is the same as the time from the time to the end of hot working (the hot working time shown in Table 1 (FIG. 5)).

(Magnetic flux density)
The surface magnetic flux density of the cylindrical Nd-Fe-B permanent magnet magnetized in the axial direction was measured. In this specification, the surface magnetic flux density is a magnetic flux density measured along a circumferential direction on a side surface of a cylinder. Specifically, the outer peripheral edge (radius r = 4 to 5 mm) of the cylinder was measured at 360 ° along the circumferential direction.
With respect to the cylindrical Nd-Fe-B-based permanent magnet (after magnetization) obtained in Example 5, the magnetic flux density was also measured at the center (radius r = 0 to 1 mm) of the magnet.
Here, in the measurement of the magnetic flux density, since the thickness of the measuring element is less than 1 mm, the magnetic flux density can be measured in the range of the thickness of the measuring element (that is, less than 1 mm). Therefore, the surface magnetic flux density is a value measured in a range of less than 1 mm from the surface, and the magnetic flux density at the center is a value measured in a range of less than 1 mm from the center.

(Coercive force and demagnetization curve)
The coercive force and demagnetization curve of a columnar Nd—Fe—B permanent magnet were determined using a BH tracer. Table 1 (FIG. 5) shows the coercive force determined for Examples 1 to 5. The coercive force was also measured for the billet of Comparative Example 1.

(result)
8 and 9 are diagrams showing the measurement results of the surface magnetic flux density of the RTB-based permanent magnet (after magnetization) manufactured in the example. In order to obtain a more preferable quadrupole sinusoidal waveform, the hot working speed of the fourth embodiment is desirably equal to or lower than that. It is considered that the reason why the hot working speed is related to the appearance of the sinusoidal waveform is that the hot working speed and the degree of orientation disorder are proportional. If the orientation disorder is large, it becomes difficult to mechanically control the degree of hot working. Therefore, the hot working speed of the fourth embodiment is desirably lower than that.

  FIG. 10 is a diagram showing the measurement results of the magnetic flux density of the RTB-based permanent magnet (after magnetization) manufactured in Example 5. At the center, the value of the surface magnetic flux density does not change due to rotation. On the other hand, at the outer peripheral edge, there is a difference in the surface magnetic flux density depending on the amount of plastic deformation caused by hot plastic working. That is, a sinusoidal surface magnetic flux density waveform is obtained. This is because, when a billet having a square cross section is subjected to hot plastic working, the amount of plastic deformation at the four vertices is small, and the amount of plastic deformation at the four sides is large, resulting in a difference in the degree of anisotropic deformation. it is conceivable that. The amount of plastic deformation at the center of the four sides is the largest, and the degree of anisotropy is also the largest. The amount of plastic deformation decreases as approaching the four apexes, and the degree of anisotropy also decreases. As a result, a substantially four-pole sinusoidal surface magnetic flux density waveform is obtained. It is considered that the disorder of the orientation can be further suppressed by adjusting the conditions such as the hot working speed.

  FIG. 11 is a diagram showing measurement results of demagnetization curves of the RTB-based permanent magnets manufactured in the examples. FIG. 12 is a diagram illustrating the relationship between the hot working time and the coercive force of the RTB-based permanent magnet manufactured in the example. FIG. 11 shows that the lower the hot working speed is, the smaller the coercive force is. This is presumably because the longer the heat application time, the more grain growth occurs and the fine structure in the magnet is disturbed. Since the hot working time is almost equal to the heat application time, it is considered that the longer the hot working time, the smaller the coercive force. FIG. 12 shows the correlation. Since the coercive force is an index indicating the heat resistance of the magnet, it is difficult to sacrifice it. Therefore, it is desirable to set the hot working speed of the fifth embodiment or higher.

  In Table 1 (FIG. 5), “after diapset” is the physical properties of the columnar Nd—Fe—B permanent magnet. The length is the length of one side (vertical and horizontal lengths) of the square serving as the bottom surface in the billet 1, and the diameter of the circle serving as the bottom surface after diap setting. In addition, in the columns of “start of hot working” and “end of hot working”, the numerical value of the length [mm] indicates a displacement value displayed on the monitor. “Hot working amount” is a value obtained from a difference between displacement values at the end of hot working and at the start of hot working.

1 billet 2 dice

Claims (5)

A billet for producing a polygonal column-shaped billet by molding an RTB-based magnet powder (R represents a rare earth element containing Nd and / or Pr, and T represents Fe or Fe and Co). Molding process,
Into a cylindrical die having an opening at one end and the other end closed, put the polygonal column-shaped billet obtained in the billet forming step, and apply pressure to the billet from the opening side, A hot working step of heating the billet to produce a cylindrical RTB-based permanent magnet from the polygonal billet ;
A magnetizing step of magnetizing the columnar RTB-based permanent magnet obtained in the hot working step in a height direction of the columnar RTB-based permanent magnet;
Including
In the billet forming step, the polygonal pillar-shaped billet is formed such that the bottom surface of the billet is polygonal,
In the hot working step, the columnar RTB-based permanent magnet is hot-worked such that the bottom surface of the RTB-based permanent magnet is circular, and the plasticity of the hot working is reduced. Depending on the amount of deformation, the degree of orientation of the axis of easy magnetization of the RTB-based magnet powder occurs in the direction in which the pressure is applied,
A method for producing an RTB-based permanent magnet. In the billet forming step, the polygonal pillar-shaped billet is a square having a vertex at a point where the bottom of the billet equally divides an inner circumferential circle of the die when the billet is put in the cylindrical die. Molded to become
In the hot working step, the column-shaped RTB-based permanent magnet is configured such that a bottom surface of the RTB-based permanent magnet is a circle that is in contact with an inner circumferential circle of the cylindrical die. Hot worked,
A method for producing an RTB-based permanent magnet according to claim 1. The hot working speed determined by the following equation (1) is 0.00310 (1 / s) or more and 0.00328 (1 / s) or less.
A method for producing an RTB-based permanent magnet according to claim 2.
Hot working speed (1 / s) = (Bottom area of cylindrical RTB-based permanent magnet (mm ² )) / (Bottom area of polygonal billet (mm ² )) / (Polygonal billet) Displacement time (s) from the start of the displacement until the end of the displacement as a cylindrical RTB-based permanent magnet (1) A column-shaped RTB-based permanent magnet (R represents a rare earth element containing Nd and / or Pr, and T represents Fe, or Fe and Co);
The magnetic flux density on the side of the cylinder changes continuously along the circumferential direction,
Including flat crystal grains, wherein the size of the crystal grains is 200 nm or more and 500 nm or less;
RTB-based permanent magnet. The magnetic flux density on the side surface of the cylinder changes in a sine wave shape along the circumferential direction,
The RTB-based permanent magnet according to claim 4.