JP2020009886A - Method for manufacturing sintered magnet - Google Patents

Abstract

To provide a method for manufacturing a sintered magnet, which can suppress an eddy current flowing through a mold, increase the precision of the size of the sintered magnet and suppress the cracking of the sintered magnet.SOLUTION: A method for manufacturing a sintered magnet comprises: a compacting step of compacting magnetic powder 10 by a mold 2 to form a compact 10b; an orientation step of applying a magnetic field to the compact 10b in the mold 2 to orient the magnetic powder 10 in the compact 10b; and a sintering step of sintering the compact 10b by heating after the orientation step. The mold 2 has at least a part (6) made of a resin. In the mold 2, the resin part (6) is covered with a coating film 6A. The coating film 6A has a hardness higher than that of the resin. In the compacting step, the coating film 6A is put in contact with the magnetic powder 10, and the compact 10b is sintered by heating, the relative density of which is adjusted to a value equal to or larger than 38% and under 60%, provided that the relative density of the compact 10b is 100×d/D, where D is a true density of the magnetic powder 10 and d is an apparent density of the compact 10b.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing a sintered magnet.

  Sintered magnets such as rare earth magnets, ferrite magnets, and alnico magnets are components such as motors or actuators, such as hard disk drives, hybrid vehicles, electric vehicles, magnetic resonance imaging (MRI) devices, smartphones, digital cameras, and thin TVs. It is used in various fields such as scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners, washing and drying machines, elevators and wind power generators. The size and shape required for the sintered magnet are different depending on these various uses. Therefore, in order to efficiently manufacture various types of sintered magnets, a molding method capable of easily changing the size and shape of the sintered magnet is desired.

  For example, in the production of a conventional rare earth magnet, a magnetic field is applied to the magnetic powder while pressing the magnetic powder (alloy powder containing a rare earth element) at a high pressure (for example, 50 MPa or more and 200 MPa or less). As a result, a compact is formed from the magnetic powder oriented along the magnetic field. Hereinafter, such a forming method is referred to as a “high-pressure magnetic field pressing method”. According to the high-pressure magnetic field press method, it is possible to obtain a molded body in which the magnetic powder is easily oriented and has a high residual magnetic flux density Br and excellent shape retention. A sintered body is obtained by sintering the molded body, and the sintered body is processed into a desired shape, thereby completing a sintered magnet as a magnet product.

  However, in the high-pressure magnetic field press method, since a high pressure needs to be applied to the magnetic powder in a magnetic field, a large-scale and complicated molding device is required, and the size and shape of a molding die are limited. Due to this limitation, the shape of a general molded body obtained by the high-pressure magnetic field pressing method is limited to a coarse block. Therefore, when manufacturing various types of magnet products by the conventional method, after sintering the block-shaped molded body to obtain a sintered body, the sintered body is formed according to the dimensions and shape required for the magnet product. Need to be processed. In the processing of the sintered body, since the sintered body is cut or polished, waste containing expensive elements (for example, rare earth elements) is generated. As a result, the yield rate of the magnet product is reduced. In the high-pressure magnetic field press method, the mold or the molded body is easily damaged by galling between the molds or galling between the mold and the molded body. For example, a compact obtained by a high-pressure magnetic field pressing method may have cracks.

  For the reasons described above, the manufacturing method using the conventional high-pressure magnetic field pressing method is not suitable for manufacturing a variety or a small amount of magnet products. As a molding method that replaces the high-pressure magnetic field pressing method, Patent Literature 1 below discloses a method of molding an alloy powder at a low pressure (not less than 0.98 MPa and not more than 2.0 MPa). This method of manufacturing a rare earth magnet includes a step of filling an alloy powder into a mold and pressing the alloy powder at a low pressure to form a compact (filling step), and applying a magnetic field to the compact in the mold. A step of orienting the alloy powder in the compact (orienting step) and a step of sintering the compact taken out of the mold (sintering step). And in the manufacturing method of the following patent document 1, a filling process and an orientation process are performed in another place.

WO 2016/047593 pamphlet

  When the magnetic powder is molded at a low pressure as in the molding method described in Patent Document 1, durability against a high pressure is not required for a mold, and a large-scale and complicated molding apparatus is not required. Therefore, when molding magnetic powder at low pressure, the material, dimensions and shape of the mold are not limited, and it is relatively easy to manufacture various types of sintered magnets using molds having various dimensions and shapes. Can be. In the high-pressure magnetic field pressing method, it takes a long time to form and orient the magnetic powder, but by molding the magnetic powder at a low pressure, the time required for the shaping and orientation is greatly reduced, and the productivity of the sintered magnet is reduced. improves.

  However, in the molding method described in Patent Document 1, a pulse magnetic field is applied to magnetic powder disposed in a mold made of an electric conductor such as metal or carbon. Therefore, an eddy current flows in the mold, and a reverse magnetic field is generated. When a reverse magnetic field is generated near the surface of the mold (the inner wall of the mold) in contact with the magnetic powder, the magnetic powder constituting the compact is attracted to the surface of the mold by the reverse magnetic field, and the center of the compact is thereby loosened. May be. As described above, when a compact having a non-uniform density due to a reverse magnetic field is sintered, a crack is easily generated in the obtained sintered body (sintered magnet). Also, the reverse magnetic field generated by the eddy current disturbs the orientation of the magnetic powder, and as a result, the magnetic properties of the sintered magnet may be impaired. The above problem caused by the eddy current may occur when a static magnetic field is applied to the magnetic powder disposed in the mold.

  Further, as a result of a study by the present inventors, it has been found that a rare earth magnet manufactured by using the molding method described in Patent Document 1 does not necessarily have a sufficient residual magnetic flux density Br. Further, it has been found that when a sintered magnet is manufactured using the molding method described in Patent Document 1, cracks are easily formed in the sintered magnet.

  The present inventors have succeeded in suppressing an eddy current flowing through the mold in the alignment step by using a mold formed of a resin having significantly lower electric conductivity than an electric conductor such as a metal. However, as a result of a study by the present inventors, it has been found that when a mold formed from a resin is used, the size and shape of the sintered magnet tend to deviate from design values, and cracks are easily formed in the sintered magnet.

  An object of the present invention is to provide a method for manufacturing a sintered magnet that suppresses eddy current flowing through a mold in an orientation step, improves the dimensional accuracy of the sintered magnet, and suppresses cracks in the sintered magnet. I do.

A method for manufacturing a sintered magnet according to one aspect of the present invention includes a molding step of molding a magnetic powder in a mold to form a compact, and applying a magnetic field to the compact held in the mold to form a compact. An orientation step of orienting the magnetic powder included in the mold, and after the orientation step, a sintering step of heating and sintering the molded body separated from the mold, wherein at least a part of the mold is a resin, At least a part of the resin portion is covered with the coating, and the hardness of the coating is higher than the hardness of the resin. In the molding process, the coating contacts the magnetic powder, and the true density of the magnetic powder is D [ g / cm ³ ], the bulk density of the molded body is represented as d [g / cm ³ ], the relative density of the molded body is defined as 100 · d / D [%], and the relative density is 38. The molded body adjusted to a value of not less than 60% and less than 60% is heated and sintered.

  The hardness of the coating may be higher than the hardness of the magnetic powder.

The Vickers hardness of the coating may be 150 N / mm ² or more and 8000 N / mm ² or less (150 HV or more and 8000 HV or less).

  The mold may include a lower mold, a cylindrical side mold disposed on the lower mold, and an upper mold inserted into the side mold from above the side mold, and the lower mold, the side mold, and At least the side mold of the upper mold may be formed of resin, and at least a part of the inner wall of the side mold may be covered with a coating.

  The resin may be an insulating resin.

  The pressure exerted on the magnetic powder by the mold may be adjusted to 0.049 MPa or more and 20 MPa or less.

  The magnetic powder may include a rare earth element, and the sintered magnet may be a rare earth magnet.

  The magnetic powder may be a granule.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the sintered magnet which suppresses the eddy current which flows into a type | mold in an orientation process, improves the dimensional accuracy of a sintered magnet, and suppresses a crack in a sintered magnet is provided.

FIG. 2 is a schematic perspective view of a mold (punch and die) used in a molding step. (A) in FIG. 2 and (b) in FIG. 2 are schematic views of cross sections of a mold and a magnetic powder (molded body), and show an example of a molding step.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the drawings, equivalent components are denoted by the same reference numerals. The present invention is not limited to the following embodiments. X, Y and Z shown in each figure mean three coordinate axes orthogonal to each other. The direction indicated by each coordinate axis is common to all drawings. The Z axis corresponds to the vertical direction. The XY plane corresponds to the horizontal direction.

  As one embodiment of the present invention, a method for manufacturing a rare earth magnet (sintered magnet) will be described below. The method for manufacturing a rare earth magnet according to the present embodiment includes at least a forming step, an orientation step, and a sintering step. In the molding step, the magnetic powder is molded with a mold to form a molded body. In the orientation step, a magnetic field is applied to the compact held in the mold to orient the magnetic powder contained in the compact. In the sintering step performed after the orientation step, the molded body separated from the mold is heated and sintered.

  At least a part of the mold used in the molding step is a resin. At least a part of the resin portion in the mold is covered with a coating. The hardness of the coating is higher than the hardness of the resin. In the molding step, the coating comes into contact with the magnetic powder. The hardness described below may be Vickers hardness or Mohs hardness.

The true density of the magnetic powder is represented as D [g / cm ³ ]. The bulk density of the molded body is expressed as d [g / cm ³ ]. The bulk density of the compact is a value obtained by dividing the mass of the compact by the volume of the compact. The relative density of the compact is defined as 100 · d / D [%]. A sintered body is obtained by heating and sintering the molded body whose relative density is adjusted to a value of 38% or more and less than 60%. However, the relative density of the compact is adjusted before the sintering step, and is not adjusted in the sintering step.

  Hereinafter, details of each step will be described.

In the method of manufacturing a rare earth magnet, first, a raw material alloy is cast. The casting method may be, for example, a strip casting method. The raw material alloy may be in the form of flakes or ingots. The raw material alloy contains the rare earth element R. The rare earth element R may be at least one selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. . The raw material alloy is selected from the group consisting of B, N, Fe, Co, Cu, Ni, Mn, Al, Nb, Zr, Ti, W, Mo, V, Ga, Zn, Si and Bi in addition to the rare earth element R. It may contain at least one selected element. The chemical composition of the raw material alloy may be adjusted according to the chemical composition of the main phase and the grain boundary phase of the rare earth magnet to be finally obtained. That is, the starting materials containing the above elements may be weighed and blended according to the composition of the target rare earth magnet to prepare the raw material of the raw material alloy. The rare earth magnet may be, for example, a neodymium magnet, a samarium cobalt magnet, a samarium-iron-nitrogen magnet, or a praseodymium magnet. Main phase of the rare earth magnets, for _{example, Nd 2 Fe 14 B, SmCo} 5, Sm 2 Co 17, Sm 2 Fe 17 N 3, Sm 1 Fe 7 N x, or from PrCo _5. The grain boundary phase may be, for example, a phase in which the content of the rare earth element R is higher than that of the main phase (R-rich phase). The grain boundary phase may include a transition metal rich phase, a B rich phase, an oxide phase or a carbide phase.

  A coarse powder is obtained by coarse pulverization of the raw material alloy. In the coarse pulverization, for example, the raw material alloy may be pulverized by absorbing hydrogen into the grain boundaries (R-rich phase) of the alloy. In the coarse pulverization of the raw material alloy, a mechanical pulverization method such as a disk mill, a jaw crusher, a brown mill or a stamp mill may be used. The particle size of the coarse powder obtained by the coarse pulverization may be, for example, 10 μm or more and 100 μm or less.

  Fine powder is obtained by finely pulverizing the above coarse powder. In the fine pulverization, the coarse powder may be pulverized by a jet mill, a ball mill, a vibration mill, a wet attritor, or the like. The particle size of the fine powder obtained by the fine pulverization may be, for example, 0.5 μm or more and 5 μm or less.

  Organic substances may be added to the coarse powder obtained by the coarse pulverization. An organic substance may be added to the fine powder obtained by the fine pulverization. That is, the organic matter may be mixed with the powder of the raw material alloy before or after the pulverization. The organic material functions as, for example, a lubricant. By adding the lubricant to the powder of the raw alloy, the aggregation of the powder of the raw alloy is suppressed. Further, by adding the lubricant to the powder of the raw material alloy, the friction between the mold and the powder of the raw material alloy is easily suppressed in a later step. As a result, in the orientation step, the powder of the raw material alloy is easily oriented, and scratches on the surface of the compact or the surface of the mold obtained from the powder of the raw material alloy are easily suppressed. The organic matter may be, for example, a fatty acid or a derivative of a fatty acid. Organic substances include, for example, oleamide, zinc stearate, calcium stearate, stearamide, palmitamide, pentadecylamide, myristic amide, lauric amide, capric amide, pelargonic amide, caprylic amide, enanthic acid It may be at least one selected from the group consisting of amides, caproic acid amides, valeric acid amides and butyric acid amides. The lubricant may be a powdered organic substance. The lubricant may be a liquid organic substance. An organic solvent in which a powdery lubricant is dissolved may be added to the powder of the raw material alloy.

  Hereinafter, the powder of the raw material alloy obtained by the above procedure is referred to as “magnetic powder”.

  The magnetic powder may be a granule. When the magnetic powder is a granule, the fluidity of the magnetic powder is increased, so that the variation in the density of the compact before sintering and the chipping of the sintered body may be further suppressed. In addition, since the magnetic powder is granular, it is difficult for the magnetic powder to penetrate the clearance between the punch used in the molding process and the side mold, and the inner wall of the side mold is not easily worn, so that the dimensional accuracy of the sintered magnet is improved. It is easy to suppress cracks in the sintered magnet.

  Granules can be obtained by applying a known granulation method using a powder of a raw alloy and a granule forming agent. Examples of the granulation method include rolling granulation, spray granulation, and vibration granulation. Specifically, granules can be produced by a granulation method described in Japanese Patent No. 4662046.

  Examples of the granulating agent include hydrocarbon compounds, alcohol compounds, ether compounds (including glycol ether compounds), ester compounds (including glycol ester compounds), ketone compounds, fatty acid compounds, and terpene compounds. is there. As hydrocarbon compounds, toluene, xylene, alcohol compounds, terpineol, ethanol, ether compounds, butyl cellosolve, cellosolve, carbitol, butyl carbitol, ester compounds, ethyl acetate, ketone compounds Examples include acetone (dimethyl ketone), methyl isobutyl ketone, methyl ethyl ketone, and the like. Other than these, other organic liquids such as ethylene glycol, diethylene glycol, and glycerin can be used. Further, a binder such as a polymer may be used as the granule forming agent.

  In the volume-based particle size distribution of the granules measured by a laser diffraction method, the D50 of the granules may be from 20 μm to 1000 μm.

  One example of a mold used in the molding step is shown in FIG. The procedure of the molding process using the mold shown in FIG. 1 is shown in (a) and (b) of FIG.

  The mold 2 includes a punch 4 (upper mold) and a die 3. The die 3 includes a lower die 8 and a cylindrical side die 6 disposed on the lower die 8. That is, the mold 2 includes the lower mold 8, the side mold 6 disposed on the lower mold 8, and the punch 4 inserted into the side mold 6 from above the side mold 6. The side mold 6 is separable from the lower mold 8. However, the side mold 6 and the lower mold 8 may be continuous without being separated from each other. A space corresponding to the shape and size of the compact 10b formed from the magnetic powder 10 penetrates the side die 6 in the vertical direction. The side mold 6 may be referred to as the side wall of the mold 2 (side wall of the die 3). The lower die 8 may be plate-shaped. The punch 4 has a shape that fits into the die 3 (inside the side die 6). The structure, size, and shape of the mold 2 may be changed according to the design size and shape of the molded body 10b and the sintered magnet, and are not limited.

  At least a part of the mold 2 is a resin (preferably an insulating resin). Since at least a part of the mold 2 is a resin, an eddy current flowing through the mold 2 in the alignment step is suppressed. In the present embodiment, at least the entire side die 6 among the lower die 8, the side die 6, and the punch 4 is formed of resin. Of the lower mold 8, the side mold 6, and the punch 4, only the side mold 6 may be formed of resin. However, the resin portion in the mold 2 is not limited to the side mold 6. All of the lower die 8, the side die 6, and the punch 4 may be formed from resin. Of the lower die 8, the side die 6, and the punch 4, only the lower die 8 may be formed of resin. Of the lower die 8, the side die 6, and the punch 4, only the side die 6 and the lower die 8 may be formed of resin. Of the lower die 8, the side die 6, and the punch 4, only the punch 4 may be formed from resin. Of the lower mold 8, the side mold 6, and the punch 4, only the side mold 6 and the punch 4 may be formed from resin. Of the lower die 8, the side die 6, and the punch 4, only the lower die 8 and the punch 4 may be formed of resin.

  The resin forming part or all of the mold 2 may be an insulating resin. Examples of the insulating resin constituting part or all of the mold 2 include acrylic resin, acrylonitrile-butadiene-styrene copolymer, polyethylene (such as high-density polyethylene), polyethylene terephthalate, polybutylene terephthalate, and polychlorotrifluoroethylene. , Polytetrafluoroethylene, ethyl cellulose, polypropylene, polybutene, polystyrene, acrylonitrile-styrene copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, atactic polypropylene, polymethacryl Methyl acrylate, methacrylic acid copolymer, polycarbonate, polyetheretherketone, polyetherimide, polyacetal, modified polyphenylene oxide, polyphenylene For sulfide, polyamide (polyamide 6, polyamide 46, polyamide 66, polyamide 6.66), polyimide, polyarylate, polyvinyl alcohol, epoxy resin, phenol resin, polyester resin, unsaturated polyester resin, liquid crystal polymer, paraffin wax and silicone resin It may be one or more selected from the group consisting of:

  Since the shrinkage ratio of a rare earth magnet (for example, neodymium magnet) in the sintering process is anisotropic, it is difficult to accurately predict the shape (particularly a complicated shape) of the shrinked rare earth magnet (sintered body). is there. Therefore, trial and error for adjusting the size and shape of the mold 2 is necessary for the net shape, and a resin that is easy to cut is suitable as the material of the mold 2. That is, in order to efficiently manufacture various kinds of rare earth magnets corresponding to various uses, the mold 2 made of resin is suitable. Conventional dies are difficult to process and expensive, and therefore are not suitable for producing a wide variety of rare-earth magnets for various applications.

  A filler may be contained in the resin of the mold 2. When the filler is contained in the resin, the raw material cost of the mold 2 is reduced by increasing the amount of the filler, the workability of the mold 2 is improved, and the mechanical strength of the mold 2 is improved. Fillers include, for example, calcium carbonate, talc, silica, clay, wollastonite, potassium titanate, zonotolite, gypsum fiber, aluminum borate, basic magnesium sulfate inorganic fiber, aramid fiber, glass fiber, mica, glass flake, polyoxy It may be at least one selected from the group consisting of benzoyl whiskers, balloons, hexagonal BN (boron nitride), molybdenum sulfide, and polytetrafluoroethylene powder (Teflon powder). Multiple types of fillers may be included in the resin.

  The portion of the mold 2 other than the resin is, for example, at least one selected from the group consisting of iron, silicon steel, stainless steel, permalloy, aluminum, an aluminum alloy, molybdenum, tungsten, and ceramics (eg, alumina), carbon, and glass. It may be formed. A part or the whole of the part other than the resin in the mold 2 may be covered with the coating 6A having a higher hardness than the magnetic powder 10.

  At least a part of the resin portion in the mold 2 is covered with the coating 6A, and the hardness of the coating 6A is higher than the hardness of the resin. In the case of the present embodiment, the entire inner wall of the side die 6 is covered with the coating 6A, and the hardness of the coating 6A is higher than the hardness of the resin forming the side die 6.

  As shown in FIG. 1A and FIG. 2A, in the molding step, the side die 6 is placed on the lower die 8, and the opening (hole) on the lower surface side of the side die 6 is lowered. Close with 8. With such an arrangement, the side die 6 and the lower die 8 constitute the die 3. Subsequently, the magnetic powder 10 is supplied from the opening on the upper surface side of the side die 6 to the inside of the die 3 (a space penetrating the side die 6). Die 3 may be filled with magnetic powder 10. That is, the inside of the die 3 may be filled with the magnetic powder 10.

  As shown in FIG. 2B, in the molding step, the punch 4 is inserted into the die 3, and the magnetic powder 10 in the die 3 is pressed on the end face of the punch 4. As a result, the magnetic powder 10 is molded so as to correspond to the shape and dimensions inside the die 3, and a molded body 10b is obtained.

  If the resin portion (the inner wall of the side mold 6) of the mold 2 is not covered with the coating 6A, the magnetic powder 10 harder than the resin is applied to the surface of the mold 2 made of resin (the inner wall of the side mold 6). Rub directly. As a result, with the repetition of the molding process, the surface of the mold 2 made of resin (the inner wall of the side mold 6) wears out, and the size and shape of the mold 2 (dimension, shape and volume of the die 3) gradually increase. Change. As the size and shape of the mold 2 change, the size, bulk density, and shape of the formed body 10b formed in the forming process deviate from the designed size, bulk density, and shape. As a result, the size and shape of the sintered body obtained by sintering the molded body 10b deviate from the design dimensions and shape. In addition, scratches are formed on the surface of the mold 2 due to wear of the surface of the mold 2 made of resin. As a result, flaws may be formed on the surface of the molded body 10b that comes into contact with the surface of the mold 2. Scratches formed on the surface of the molded body 10b cause cracks in the sintered body.

  On the other hand, the portion of the mold 2 that is a resin (the inner wall of the side mold 6) is covered with the coating 6A that is harder than the resin, so that the surface of the mold 2 that is in contact with the magnetic powder 10 ( That is, the wear of the coating 6A) is suppressed, and the change in the size and shape of the mold 2 (the size, shape and volume of the die 3) due to the repetition of the molding process is suppressed. As a result, the size, bulk density, and shape of the compact 10b easily match the design size, bulk density, and shape, and the size and shape of the sintered body also easily match the design size and shape. That is, the accuracy of the size and shape of each of the molded body 10b and the sintered body is improved. In addition, by covering the resin portion (the inner wall of the side mold 6) of the mold 2 with the coating 6A harder than the resin, the surface of the mold 2 that comes into contact with the magnetic powder 10 ( That is, scratches on the surface of the coating 6A) are suppressed. As a result, scratches on the surface of the molded body 10b in contact with the surface of the mold 2 are suppressed, and cracking of the sintered body is also suppressed.

  The portion covered with the coating 6A in the mold 2 may be at least a part of the resin portion in the mold 2, and the portion covered with the coating 6A is not limited to the entire inner wall of the side mold 6. As described above, in the portion of the mold 2 covered with the coating 6A, the wear of the resin is prevented or suppressed, the accuracy of the dimensions and the shape of the molded body 10b and the sintered body is improved, and the crack in the sintered body is suppressed. Is done. For example, the end face of the punch 4 for pressing the magnetic powder 10 may be covered with the coating 6A. The surface of the lower die 8 corresponding to the bottom surface of the die 3 may be covered with the coating 6A. The entire inner wall of the side die 6, the end surface of the punch 4, and the surface of the lower die 8 may be covered with the coating 6 </ b> A. Only the portion of the inner wall of the side mold 6 facing the surface of the compact 10b after compression may be covered with the coating 6A. Part or all of the side surface of the punch 4 that rubs with the die 3 (the inner wall of the side die 6) and part or all of the inner wall of the die 3 (the side die 6) may be covered with the coating 6A. Since the side surface of the punch 4 and the inner wall of the side die 6 are covered with the coating 6A, the wear of the punch 4 and the side die 6 due to the sliding of the punch 4 and the side die 6 is suppressed. As a result, the accuracy of the size and shape of each of the molded body 10b and the sintered body is improved, and cracks in the sintered body are suppressed.

The Vickers hardness of the coating 6A is, for example, 150 N / mm ² or more and 8000 N / mm ² or less, 150 N / mm ² or more and 900 N / mm ² or less, 600 N / mm ² or more and 900 N / mm ² or less, and higher than 600 N / mm ² and 900 N / mm ^2. mm ² or less, or 620N / mm ² or less 900 N / mm ² may be less. “N / mm ² ” is a unit of Vickers hardness and is equal to “HV”. As the Vickers hardness of the coating 6A is higher, abrasion of the coating 6A itself due to friction between the coating 6A and the magnetic powder 10 is more likely to be suppressed. In addition, as the Vickers hardness of the coating 6A is higher, the wear of the resin is more easily prevented or suppressed in the portion of the mold 2 covered with the coating 6A, and the accuracy of the dimensions and shape of the molded body 10b and the sintered body is improved. It is easy to suppress cracks in the sintered body. The coating 6A having a Vickers hardness of 150 N / mm ² is, for example, a copper plating film. The coating 6A having a Vickers hardness of 8000 N / mm ² is, for example, a diamond-like carbon film.

The hardness of the coating 6A may be higher than the hardness of the magnetic powder 10. Since the hardness of the coating 6A is higher than the hardness of the magnetic powder 10, wear of the coating 6A itself due to friction between the coating 6A and the magnetic powder 10 is easily suppressed. Therefore, when the hardness of the coating 6A is higher than the hardness of the magnetic powder 10, wear of the resin is easily prevented or suppressed in the portion of the mold 2 covered with the coating 6A, and the dimensions of the molded body 10b and the sintered body In addition, the accuracy of the shape is easily improved, and cracks in the sintered body are easily suppressed. The beakers hardness of the magnetic powder 10 which is a raw material of the rare earth magnet may be, for example, 400 N / mm ² or more and 700 N / mm ² or less, and the beakers hardness of the coating 6 </ b> A may be higher than the beakers hardness of the magnetic powder 10. .

The composition of the coating 6A is not limited as long as the hardness of the coating 6A is higher than the hardness of the resin. For example, the Vickers hardness of the resin, for example, 0N / mm ² higher 150 N / mm less than ² than, or may be at higher 100 N / mm ² or less than 0N / mm ^2. The coating 6A is made of an electroless nickel plating film, an electrolytic nickel plating film, a polytetrafluoroethylene (PTFE) film, a chromium plating film, a copper plating film, an alumite film, a hard alumite film, a nickel boron plating film, an electroless nickel teflon (Ni -PTFE) plating film, nickel-cobalt alloy plating film, cast iron film, pure iron film, silicon carbide film and diamond-like carbon film. The resin portion in the mold 2 may be covered with a plurality of types of coatings 6A. The portion of the mold 2 that is a resin may be covered with a plurality of types of coatings 6A that overlap.

  According to the electroless nickel plating method, the growth rate of the nickel plating film is appropriately suppressed as compared with the electrolytic nickel plating method, so that a nickel plating film having a uniform thickness is easily obtained. The more uniform the thickness of the coating 6A, the more easily the friction between the coating 6A and the punch 4 is suppressed, and the more accurate the size and shape of the molded body 10b and the sintered body are. Easy to do. For this reason, the coating 6A is preferably an electroless nickel plating film. On the other hand, since the thickness of the electrolytic nickel plating film tends to vary, when the coating 6A is an electrolytic nickel plating film, the coating 6A facing the side surface of the punch 4 may bend. When the electrolytic nickel plating film is formed on the surface of the mold 2, a conductive film serving as a base of the electrolytic nickel plating film may be formed on the surface of the mold 2 in advance (by an electroless nickel plating method or the like).

  The coating 6A may be an annealed electroless nickel plating film. Annealing the electroless nickel plating film increases the hardness of the electroless nickel plating film. The annealing temperature may be, for example, about 100 ° C. However, the annealing of the electroless nickel plating film tends to warp the electroless nickel plating film. When the mold 2 covered with the electroless nickel plating film is annealed, the mold 2 covered with the electroless nickel plating film may warp together with the electroless nickel plating film. The warpage of the electroless nickel plating film causes friction between the electroless nickel plating film and the punch 4, and may affect the accuracy of the size and shape of the molded body 10b and the sintered body. Therefore, as the coating 6A, an unannealed electroless nickel plating film is preferable as compared with an annealed electroless nickel plating film.

  The electroless nickel plating film may include phosphorus (P). The content of phosphorus in the electroless nickel plating film may be, for example, from 1.0% by mass to 12% by mass, and preferably from 1.0% by mass to 3.0% by mass. The smaller the phosphorus content in the electroless nickel plating film, the higher the hardness of the electroless nickel plating film.

  As shown in FIG. 2A, the coating 6A covering the inner wall of the side die 6 may extend to the end surface (upper surface) of the side die 6, and an opening at the end surface of the side die 6 may be provided. It may cover the edge of the part. If the coating 6A covering the inner wall of the side die 6 does not extend to the end face (upper surface) of the side die 6, the interface (boundary line) between the inner wall of the side die 6 and the coating 6A is It is exposed at the inner wall or opening. As a result, with the insertion of the punch 4 into the side die 6 or the removal of the punch 4 from the side die 6, the coating 6A tends to peel off from the inner wall of the side die 6 starting from the interface. However, since the coating 6A covering the inner wall of the side die 6 extends to the end surface of the side die 6 and covers the edge of the opening of the side die 6, the interface between the inner wall of the side die 6 and the coating 6A (boundary line) ) Is not exposed on the inner wall of the side die 6 and the opening, and peeling of the coating 6A from the inner wall of the side die 6 is suppressed.

  When the coating 6A is a conductor, the coating 6A may be electrically grounded (via another conductor). The grounding of the coating 6A suppresses charging of the mold 2 due to friction between the punch 4 and the die 3. The suppression of the charging of the mold 2 makes it difficult for excess magnetic powder 10 to adhere and remain on the surface of the punch 4 and the inner wall of the die 3, and the mass, size, bulk density, and shape of the molded body 10b are hardly varied. When the coating 6A is a conductor, not only the inside of the die 3 (side die 6) but also a part or the entire outer surface of the die 2 is covered with the coating 6A in order to suppress charging of the mold 2. Is also good.

  The thickness of the coating 6A is not particularly limited, but may be, for example, 3 μm or more and 50 μm or less, or 3 μm or more and 30 μm or less. As the coating 6A is thinner, the resin covered by the coating 6A is more likely to be exposed due to wear of the coating 6A with the repetition of the molding process. As the coating 6A is thicker, the cost for forming the coating 6A and manufacturing the mold 2 increases, but the durability of the coating 6A does not always improve.

  As long as the relative positional relationship between the lower die 8, the side die 6, and the punch 4 shown in FIG. 1 is maintained, in the forming process, the lower die 8, the side die 6, and the punch 4 are inclined with respect to the vertical direction. May be. In other words, as long as the punch 4 is located on the side mold 6 and the side mold 6 is located on the lower mold 8, in the molding process, the entire mold 2 may be inclined with respect to the vertical direction. . For example, in the forming step, the angle formed by the entire mold 2 with respect to the vertical direction (Z-axis direction) may be 0 degrees or more and 45 degrees or less.

  In an orientation step described later, a magnetic field is applied to the compact 10b held by the punch 4 and the die 3 to orient the magnetic powder 10 contained in the compact 10b. When one punch 4 is used from the molding step to the orientation step, it is preferable that at least a part of the punch is an insulating resin, and it is more preferable that the entire punch 4 is an insulating resin. In the orientation step, when the formed body 10b is held by the die 3 and a punch (second punch) different from the punch 4, it is preferable that at least a part of the second punch is an insulating resin. More preferably, the entirety of the punch is made of an insulating resin.

  As shown in FIG. 1, the side mold 6 may be seamless. That is, the side mold 6 may be seamless. If the side mold 6 has a joint (for example, if the side mold 6 can be disassembled into a plurality of members), the magnetic powder 10 is moved from the joint (gap) of the side mold 6 to the mold 2 in the molding step or the orientation step. May leak out of the room. As a result, the shape retention of the molded body 10b is impaired, and for example, burrs may be formed on the molded body 10b. When the side mold 6 is separated from the molded body 10b by disassembling the side mold 6 into a plurality of members, a force may erroneously act on the molded body 10b, and the molded body 10b may be damaged. If the magnetic powder 10 leaks out of the mold 2 from the joint of the side mold 6, the size, bulk density and shape of the compact 10b vary, and the size, shape and characteristics of the finally obtained sintered body also vary. There is also. These problems are easily suppressed by using the side mold 6 having no seams.

  In the forming step, the relative density (100 · d / D) of the formed body 10b may be adjusted to 38% or more and less than 60%. When the relative density is 38% or more, the molded body 10b tends to have sufficient mechanical strength, and the molded body is unlikely to be damaged in a subsequent step following the molding step. When the relative density is less than 60%, the magnetic powder 10 constituting the molded body 10b is easily rotated freely in the orientation step, and easily oriented along the magnetic field. As a result, the residual magnetic flux density Br of the finally obtained rare earth magnet tends to increase.

In the molding step, the pressure of the mold 2 on the magnetic powder 10 may be adjusted to more than 0.049 MPa 20 MPa or less (0.5 kgf / cm ² or more 200 kgf / cm ² or less). When the molding pressure is within the above range, the relative density of the molded body 10b immediately after the molding step is easily adjusted to 38% or more and less than 60%. The pressure may be, for example, a pressure exerted on the magnetic powder 10 by the end face of the punch 4. Thus, by forming the compact 10b from the magnetic powder 10 at a lower pressure than the conventional high-pressure magnetic field press method, the friction between the mold 2 and the compact 10b is easily suppressed, and the mold 2 or the compact 10b is damaged. (For example, cracks in the molded body 10b) are easily suppressed. If the pressure is too high, the mold 2 bends, and it is difficult to secure the capacity of the target cavity, and it is difficult to obtain the density of the target molded body 10b. In the conventional high-pressure magnetic field pressing method, it was necessary to simultaneously perform molding and orientation of the magnetic powder under high pressure. On the other hand, in the present embodiment, since it is not necessary to perform molding and orientation at the same time, the orientation step can be performed after the molding step. By separating the molding step from the orientation step, a smaller and less expensive device (for example, a press molding device and a magnetic field applying device) can be used for each step. The molding step and the orientation step may be performed substantially simultaneously.

  In the orientation step, a magnetic field is applied to the compact 10b held in the mold 2 to orient the magnetic powder 10 constituting the compact 10b in the mold 2 along the magnetic field. The magnetic field applied to the molded body 10b may be at least one of a pulse magnetic field and a static magnetic field. For example, the molded body 10b held in the mold 2 is arranged together with the mold 2 inside an air-core coil (solenoid coil), and a current (AC) is caused to flow through the air-core coil to form the molded body 2 in the mold 2. A pulse magnetic field may be applied to the body 10b. A pulse magnetic field may be applied to the molded body 10b in the mold 2 by flowing an electric current through the double coil or the Helmholtz coil. A double coil is a magnetic field generator in which two coils are arranged so as to have the same central axis. By using a double coil or a Helmholtz coil, a more uniform pulsed magnetic field can be applied to the molded body 10b than when using an air-core coil. As a result, the orientation of the magnetic powder 10 in the molded body 10b is easily improved, and the magnetic properties of the finally obtained rare earth magnet (sintered body) are easily improved. A pulsed magnetic field may be applied to the molded body 10b in the mold 2 using a magnetized yoke. The intensity of the pulse magnetic field applied to the molded body 10b in the mold 2 may be, for example, 796 kA / m or more and 5173 kA / m or less (10 kOe or more and 65 kOe or less). After the orientation step, the molded body 10b may be demagnetized. The strength of the magnetic field applied to the molded body 10b in the mold 2 is not necessarily limited to the above range. The strength of the static magnetic field applied to the molded body 10b may be, for example, about 796 kA / m or more and 2388 kA / m or less (10 kOe or more and 30 kOe or less).

  The pulse magnetic field has a higher magnetic field strength than the static magnetic field frequently used in the conventional high-pressure magnetic field press method, and is applied to the compact 10b in a short time. Therefore, preferably, by the orientation step using a pulsed magnetic field, a compact 10b having a high degree of orientation is obtained in a shorter time than in the case of using a static magnetic field, and as a result, a rare earth magnet having a high residual magnetic flux density is manufactured. . However, if a pulse magnetic field is applied to the molded body 10b held in the mold 2 made of an electric conductor (for example, a metal), the magnetic field acting on the mold 2 is greater than when a static magnetic field is applied. Since the intensity of the current rapidly changes in a short time, an eddy current easily flows through the mold 2 by electromagnetic induction, and a reverse magnetic field is easily generated. However, when part or all of the mold 2 is formed of a resin (insulating resin), an eddy current hardly flows in the mold 2 and a reverse magnetic field hardly occurs. Therefore, the phenomenon that the magnetic powder 10 constituting the molded body 10b is attracted to the surface of the mold 2 by the reverse magnetic field is suppressed. As a result, the density of the compact 10b is likely to be uniform, and cracks are less likely to occur in the sintered body (rare earth magnet) in the sintering step. In addition, by suppressing the eddy current and the reverse magnetic field in the orientation step, the orientation of the magnetic powder 10 is improved, and as a result, the magnetic properties of the rare earth magnet are also improved. Further, when part or all of the mold 2 is formed of a resin (insulating resin), the temperature rise of the mold 2 due to eddy current loss is suppressed in the alignment step, and the mold 2 itself is instantaneously added to the mold 2 itself. Impact (magnetic force) hardly acts. As a result, the mold 2 is less likely to be consumed.

  If a pulse magnetic field is applied to the molded body 10b held in the mold, the saturation magnetic flux density of the metal (for example, iron) constituting the mold is limited. Is lower than the intensity of the pulsed magnetic field outside the mold. On the other hand, when the mold 2 is formed from a resin, a strong pulsed magnetic field can be applied to the molded body 10b in the mold 2, and the orientation of the magnetic powder 10 is improved.

  As the contact area between the portion where the eddy current flows in the mold 2 and the molded body 10b is larger, cracks in the sintered body due to the eddy current and deterioration of magnetic properties are more likely to occur. Among the lower die 8, the side die 6, and the punch 4, the contact area between the side die 6 and the molded body 10b is larger than the contact area between the lower die 8, the punch 4, and the molded body 10b. Therefore, of the lower die 8, the side die 6, and the punch 4, the side die 6 having a large area in contact with the molded body 10b is formed of resin, so that the generation of the eddy current and the reverse magnetic field in the side die 6 is effective. , And cracking of the rare-earth magnet and deterioration of magnetic properties caused by the eddy current and the reverse magnetic field are easily suppressed.

  As described above, the position of the portion formed of the resin in the mold 2 is not limited. The portion of the mold 2 that needs to suppress eddy currents may be formed of resin according to the size and shape of the mold 2 or the direction of the magnetic field. For example, an eddy current and a reverse magnetic field are likely to occur in a part of the mold 2 where a circuit that circulates in the direction of the magnetic field for orienting the magnetic powder 10 is formed. That is, when the penetrating portion of the side mold 6 (the inner wall of the side mold 6) is parallel to the direction of the magnetic field, an eddy current and a reverse magnetic field are easily generated. Therefore, in the case where the side mold 6, which is a part of the mold 2 that forms a circuit that circulates in the direction of the magnetic field for orienting the magnetic powder 10, is formed of resin, the eddy current and the reverse magnetic field are easily suppressed.

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

  In the above-described molding step, the mass of the magnetic powder 10 molded in the mold 2 may be measured together with the mass of the mold 2 while supplying the magnetic powder 10 into the mold 2. When measuring the mass of the magnetic powder 10 molded in the mold 2 and the mass of the mold 2 at the same time, the heavier the mass of the mold 2 is, the lower the accuracy of the balance is, and the more the mass of the magnetic powder 10 itself is measured. Accuracy also decreases. However, by using the mold 2 made of a resin having a specific gravity lower than that of the conventional magnetic powder 10, the mass of the magnetic powder 10 can be measured with high accuracy together with the mass of the mold 2 itself.

  In the orientation step, a magnetic field may be applied to the magnetic powder 10 while pressing the magnetic powder 10 of the die 3 with the punch 4. That is, the molded body 10b in the mold 2 may be compressed also in the orientation step. The pressure exerted on the molded body 10b by the mold 2 in the orientation step may be adjusted to 0.049 MPa or more and 20 MPa or less for the above-described reason.

The relative density (100 · d / D) of the molded body 10b that has undergone the molding step and the orientation step may be adjusted to 38% or more and less than 60%. The bulk density d of the molding process and the molded body 10b having passed through the orientation process (sintering step prior to the molded body 10b) is, for example, 2.85 g / cm ³ or more 4.40 g / cm ³ or less, 3.00 g / cm ³ or more 4.40 g / cm ³ or less, preferably 3.20 g / cm ³ or more 4.20 g / cm ³ or less, more preferably have been adjusted to 3.40 g / cm ³ or more 4.00 g / cm ³ or less.

  In the separation step, at least a part of the mold 2 is separated from the molded body 10b. For example, in the separating step, the molded body 10b may be placed on the lower mold 8 by separating and removing the punch 4 and the side mold 6 from the molded body 10b. For example, the side die 6 may be moved upward while the position of the punch 4 in the vertical direction (Z-axis direction) is fixed. As a result, the punch 4 inserted into the side die 6 penetrates the side die 6, and the end face of the punch 4 pushes the molded body 10b below the side die 6. That is, the molded body 10b held in the side die 6 is pulled out from the lower surface of the side die 6. However, the molded body 10b held in the side die 6 may be extracted from the upper surface of the side die 6. In the separation step, the side mold 6 and the punch 4 holding the molded body 10b are separated from the lower mold 8, and the side mold 6 and the punch 4 holding the molded body 10b are placed on a heating step tray. Good. Then, the side die 6 and the punch 4 may be separated from the molded body 10b, and the molded body 10b may be placed on the heating step tray. The side mold 6 may be capable of being disassembled and assembled. In the separation step, the punch 4 and the side mold 6 may be detached from the molded body 10b by disassembling the side mold 6.

  Following the separation step, the following heating step may be performed. However, the heating step is not essential.

  In the heating step, the molded body 10b may be heated to adjust the temperature of the molded body 10b to 200 ° C or more and 450 ° C or less. In the heating step, the temperature of the molded body 10b may be adjusted to 200 ° C to 400 ° C, or 200 ° C to 350 ° C. In the molding step, the pressure applied to the magnetic powder 10 is lower than that of the conventional high-pressure magnetic field pressing method, so that the magnetic powder 10 is hard to be compacted and the obtained molded body 10b is easily broken. However, the mechanical strength and the shape retention of the molded body 10b are easily improved by the heating step.

  In the heating step, when the temperature of the molded body 10b becomes 200 ° C. or higher, the molded body 10b starts to solidify, and the shape retention of the molded body 10b is improved. In other words, when the temperature of the molded body 10b is equal to or higher than 200 ° C., the mechanical strength of the molded body 10b is improved. Since the shape retention of the molded body 10b is improved, the molded body 10b is less likely to be damaged during transportation of the molded body 10b or handling of the molded body 10b in a later step. For example, when the compact 10b is gripped by a transport chuck or the like and arranged on a sintering tray, the compact 10b is unlikely to collapse. As a result, defects of the finally obtained rare earth magnet are suppressed.

  If the temperature of the molded body 10b exceeds 450 ° C. in the heating step, a crack is easily formed in the molded body 10b in the sintering step performed after the heating step. The cause of the crack formation is unknown. For example, cracks may be formed in the molded body 10b by causing hydrogen remaining in the molded body 10b to blow out of the molded body 10b as a gas due to a rapid temperature rise of the molded body in the heating step. However, by adjusting the temperature of the compact to 450 ° C. or less in the heating step, cracks in the compact 10b in the sintering step are suppressed. As a result, cracks in the finally obtained rare earth magnet are also easily suppressed. In addition, since the temperature of the compact 10b is adjusted to 450 ° C. or lower in the heating step, the time required for raising or cooling the compact 10b is suppressed, and the productivity of the rare earth magnet is improved. Further, since the temperature of the molded body 10b in the heating step is 450 ° C. or lower, which is lower than a general sintering temperature, even if the molded body 10b is heated together with a part (for example, a lower mold) of the mold 2, Deterioration or a chemical reaction between the molded body 10b and the mold 2 hardly occurs. Therefore, it is possible to use even the mold 2 composed of a composition (resin) that does not necessarily have high heat resistance.

  The mechanism by which the temperature of the molded body 10b is adjusted to 200 ° C or more and 450 ° C or less to improve the shape retention of the molded body 10b is not clear. For example, the lubricant added to the magnetic powder 10 may become carbon in the heating step, and the metal particles constituting the magnetic powder 10 may be bound via carbon. As a result, the shape retention of the molded body 10b may be improved. If the temperature of the compact 10b exceeds 450 ° C. in the heating step, there is a possibility that carbide of a metal constituting the magnetic powder 10 is generated or metal particles are directly sintered. On the other hand, when the temperature of the molded body 10b is adjusted to 200 ° C. or more and 450 ° C. or less, metal carbide is not necessarily generated, and the metal particles do not necessarily directly sinter.

  The time for maintaining the temperature of the molded body 10b at 200 ° C. or more and 450 ° C. or less in the heating step is not particularly limited, and may be appropriately adjusted according to the size and shape of the molded body 10b.

  In the heating step, the molded body 10b may be heated by irradiating the molded body 10b with infrared rays. By directly heating the molded body 10b by irradiation of infrared rays (that is, radiant heat), the time required for raising the temperature of the molded body 10b is shortened as compared with the case of heating by conduction or convection, and production efficiency and energy efficiency are increased. However, in the heating step, the molded body 10b may be heated by heat conduction or convection in the heating furnace. The wavelength of the infrared ray may be, for example, 0.75 μm or more and 1000 μm or less, preferably 0.75 μm or more and 30 μm or less. The infrared light may be at least one selected from the group consisting of near infrared light, short wavelength infrared light, middle wavelength infrared light, long wavelength infrared light (thermal infrared light), and far infrared light. Near infrared rays among the above infrared rays are relatively easily absorbed by metal. Therefore, when irradiating near-infrared rays to the molded body 10b, the temperature of the metal (magnetic powder 10) is easily increased in a short time. On the other hand, far infrared rays among the above infrared rays are relatively easily absorbed by an organic substance and are easily reflected by a metal (magnetic powder 10). Therefore, when irradiating the molded body with far-infrared rays, the above-described lubricant is easily heated selectively, and the molded body 10b is easily cured by the above-described mechanism caused by the lubricant. When irradiating the molded body 10b with infrared rays, for example, an infrared heater (such as a ceramic heater) or an infrared lamp may be used.

  When the molded body 10b separated from part or all of the mold 2 is heated in the heating step, deterioration of the mold 2 due to heating (for example, deformation, hardening or wear of the mold) is easily suppressed, and the molded body 10b and the mold 2 Is also easily suppressed. When heating the molded body 10b separated from part or all of the mold 2, it is difficult for the mold 2 to insulate heat, and the molded body 10b is easily heated. As a result, the shape retention of the molded body 10b is improved. When the molded body 10b separated from part or all of the mold 2 is heated, the possibility that the mold 2 chemically reacts with the molded body 10b is low. Therefore, the mold 2 is not necessarily required to have heat resistance, and the material of the mold 2 is not easily limited. Therefore, it is easy to select an inexpensive material that can be easily processed into a desired size and shape as a raw material of the mold 2. If the compact 10b and all of the mold 2 are heated collectively in the heating step, stress acts on the compact 10b due to the difference in the coefficient of thermal expansion between the compact 10b and the mold 2. The molded body 10b is easily deformed or broken. Further, when the molded body 10b and all of the mold 2 are heated collectively in the heating step, the volume and the heat capacity of the whole object to be heated are large. As a result, the number of compacts to be heated collectively is limited, the time required for the heating step is increased, energy is wasted, and the productivity of the rare earth magnet is reduced.

  In the heating step, for example, the molded body 10b placed on the lower mold may be heated. In the heating step, the compact 10b placed on the heating step tray may be heated. In the heating step, the molded body 10b may be heated in an inert gas or vacuum to suppress oxidation of the molded body 10b. The inert gas may be a rare gas such as argon.

  In the heating step, after adjusting the temperature of the molded body 10b to 200 ° C or more and 450 ° C or less, the molded body 10b may be cooled to 100 ° C or less. When the surface of the chuck used for transporting the molded body 10b after the heating step is made of resin, by cooling the 10b, a chemical reaction between the surface of the chuck and the molded body 10b is suppressed, and the deterioration of the chuck and the molded body Contamination on the 10b surface is suppressed. The cooling method may be, for example, natural cooling.

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

As described above, the true density of the magnetic powder 10 is represented as D [g / cm ³ ]. The bulk density of the molded body 10b is expressed as d [g / cm ³ ]. The relative density of the compact 10b is defined as 100 · d / D [%]. In the sintering step, the molded body 10b whose relative density (100 · d / D) has been adjusted to a value of 38% or more and less than 60% is heated and sintered. That is, before the sintering step, the relative density of the molded body 10b is adjusted within a range of 38% or more and less than 60%. When the above heating step is performed before the sintering step, before the heating step, the relative density of the molded body 10b is adjusted within a range of 38% or more and less than 60%. The true density D of the magnetic powder 10 is substantially equal to the density of the finally obtained sintered body (sintered magnet). The true density D of the magnetic powder 10 is not particularly limited because it depends on the composition of the magnetic powder. For example, the true density D of the magnetic powder 10 may be 4.0 g / cm ³ or more and 8.0 g / cm ³ or less. The bulk density d (density of the molded body 10b immediately before the sintering step) of the molded body 10b to be sintered in the sintering step is, for example, 2.85 g / cm ³ or more and 4.40 g / cm ³ or less, 3.00 g / cm. ³ to 4.40 g / cm ³ or less, 3.20 g / cm ³ or more 4.20 g / cm ³ or less, 3.40 g / cm ³ or more 4.00 g / cm ³ or less, or 3.70 g / cm ³ or more 4. It may be adjusted to 10 g / cm ³ or less. The “density” described below implies both the relative density (100 · d / D) and the bulk density (d) of the molded body 10b.

  As the pressure exerted on the compact 10b (magnetic powder 10) by the mold 2 in the compacting step and the orientation step is lower, the density of the compact 10b immediately before the sintering step tends to be lower. Further, as the pressure exerted by the mold 2 on the molded body 10b (magnetic powder 10) in the molding step and the orientation step is lower, the magnetic powder 10 constituting the molded body 10b is more easily rotated and easily oriented along the magnetic field. As a result, the residual magnetic flux density of the finally obtained rare earth magnet tends to increase. Therefore, it can be said that the lower the density of the compact 10b immediately before the sintering step, the more easily the residual magnetic flux density of the rare earth magnet increases. However, if the pressure exerted on the compact 10b (magnetic powder 10) by the mold 2 in the molding step and the orientation step is too low, the shape retention (mechanical strength) of the compact 10b is insufficient. On the other hand, as the pressure applied to the compact 10b (the magnetic powder 10) during the period from the compacting step to the sintering step is higher, the density of the compact 10b immediately before the sintering step is higher, and the shape retention of the compact 10b ( High mechanical strength). As a result, cracks in the finally obtained rare earth magnet are easily suppressed. Therefore, it can be said that the higher the density of the compact 10b immediately before the sintering step, the more easily the cracks in the rare earth magnet are suppressed. However, when the pressure exerted by the mold 2 on the compact 10b (magnetic powder 10) in the molding step and the orientation step is too high, cracks are easily formed in the compact 10b due to springback, and the rare-earth magnet obtained from the compact 10b Cracks remain in the Note that the springback is a phenomenon in which the compact 10b expands when the pressure is released after the magnetic powder 10 is pressed and formed. As described above, the density of the compact 10b immediately before the sintering step is correlated with the residual magnetic flux density and the crack of the rare earth magnet. By adjusting the density of the compact 10b immediately before the sintering step to be within the above range, the residual magnetic flux density of the rare earth magnet is easily increased, and cracks in the rare earth magnet are suppressed. Since the residual magnetic flux density of the rare earth magnet is easily increased and the cracks in the rare earth magnet are easily suppressed, the relative density (100 · d / D) of the molded body 10b heated in the sintering step is 40% or more and less than 60%. 42% or more and less than 60%, 45% or more and less than 60%, 40% or more and 59% or less, 42% or more and 59% or less, 45% or more and 59% or less, 45% or more and less than 56%, 45% or more and less than 55%, Alternatively, it may be 45% or more and 54% or less.

  In the sintering step, the compact 10b placed on the lower mold may be transferred onto a sintering tray. In the sintering step, the compact 10b placed for the heating step may be transferred onto a sintering tray. Since the shape retention of the molded body 10b is improved in the heating step, when the molded body 10b is gripped by the transport chuck and arranged on the sintering tray, breakage of the molded body 10b is suppressed.

  In the sintering step, the plurality of compacts 10b may be placed on a sintering tray, and the plurality of compacts 10b placed on the sintering tray may be heated collectively. By arranging a large number of compacts 10b at a narrow interval on a sintering tray and heating the large number of compacts 10b collectively, the productivity of the rare earth magnet is improved.

  The composition of the tray for sintering may be any composition that does not easily react with the compact 10b during sintering and does not easily generate substances that contaminate the compact 10b. For example, the sintering tray may be made of molybdenum or a molybdenum alloy.

  The sintering temperature may be, for example, 900 ° C. or more and 1200 ° C. or less. The sintering time may be, for example, 0.1 hours or more and 100 hours or less. The sintering step may be repeated. In the sintering step, the compact 10b may be heated in an inert gas or vacuum. The inert gas may be a rare gas such as argon.

  The sintered body may be subjected to an aging treatment. In the aging treatment, the sintered body may be heat-treated at, for example, 450 ° C. or more and 950 ° C. or less. In the aging treatment, the sintered body may be heat-treated for, for example, 0.1 hours or more and 100 hours or less. The aging treatment may be performed in an inert gas or vacuum. The aging treatment may be composed of a multi-stage heat treatment at different temperatures.

  The sintered body may be cut or polished. A protective layer may be formed on the surface of the sintered body. The protective layer may be, for example, a resin layer or an inorganic layer (for example, a metal layer or an oxide layer). The method for forming the protective layer may be, for example, a plating method, a coating method, a vapor deposition polymerization method, a gas phase method, or a chemical conversion treatment method. The sintered body may be magnetized.

  By the above manufacturing method, a sintered magnet (a rare earth magnet) is completed.

  The size and shape of the sintered magnet vary depending on the use of the sintered magnet, and are not particularly limited. The shape of the sintered magnet may be, for example, a rectangular parallelepiped, a cube, a polygonal column, a segment, a fan, a rectangle, a plate, a sphere, a disk, a column, a ring, or a capsule. The cross-sectional shape of the sintered magnet may be, for example, polygonal, chordal, arcuate, or circular.

  The preferred embodiment of the present invention has been described above, but the present invention is not necessarily limited to the above-described embodiment.

For example, the sintered magnet manufactured in the present invention is not limited to the rare earth magnet described above. The sintered magnet may be one type selected from the group consisting of a rare earth magnet, a ferrite magnet, and an alnico magnet. Therefore, the magnetic powder that is the raw material of the sintered magnet is not limited to the above-described metal powder (alloy powder) containing a rare earth element. The magnetic powder may be one selected from the group consisting of a metal powder containing a rare earth element, a ferrite powder, and an alnico alloy powder (an alloy powder containing Al, Ni and Co). When manufacturing a ferrite magnet, the Vickers hardness of the coating 6A may be higher than the Vickers hardness of the ferrite powder (ferrite particles). The beakers hardness of the ferrite powder is, for example, about 550 N / mm ² . When manufacturing an Alnico magnet, the Vickers hardness of the coating 6A may be higher than the Vickers hardness of the Alnico alloy powder. The beakers hardness of the Alnico alloy powder) is, for example, about 650 N / mm ² . Regardless of whether a ferrite magnet or an alnico magnet is manufactured, similarly to the case of manufacturing a rare-earth magnet, the green body whose relative density is adjusted to a value of 38% or more and less than 60% is heated and sintered. Tie. The temperature of the compact in the sintering step may be appropriately adjusted according to the composition of the magnetic powder constituting the compact.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
[Production of rare earth magnet]
According to the strip casting method, the composition was Nd ₂₉ Dy ₁ Fe _bal. To produce a flake-like alloy is B _1. After occlusion of hydrogen in the alloy, the alloy was dehydrogenated at 600 ° C. for 1 hour to obtain a coarse powder. Oleic acid amide (lubricant) was added to the coarse powder. Subsequently, the coarse powder was pulverized by a jet mill in an inert gas to obtain a magnetic powder (a metal powder containing a rare earth element). The true density D of the magnetic powder was 7.5 g / cm ³ . The Vickers hardness of the magnetic powder was 600 N / mm ² (600 HV). The particle diameter D50 of the magnetic powder was adjusted to 4 μm. The content of oxygen in the magnetic powder was 1000 mass ppm or less. The content of nitrogen in the magnetic powder was 800 mass ppm or less. The content of carbon in the magnetic powder was 1000 mass ppm or less.

  In the molding step, the magnetic powder to which oleic acid amide was added was supplied into a mold to form a molded body. The details of the molding step were as follows.

  As shown in (a) and (b) in FIGS. 1 and 2, the mold 2 includes a rectangular lower mold 8, a rectangular parallelepiped side mold 6 disposed on the lower mold 8, and a side mold 6. And a punch 4 arranged on the mold 6. The punch 4 and the lower mold 8 were formed from aluminum. The side mold 6 was formed from an acrylonitrile-butadiene-styrene copolymer (ABS resin). A rectangular parallelepiped space penetrated vertically in the center of the side mold 6. That is, the side mold 6 was cylindrical. The entire inner wall of the side mold 6 was covered with a coating 6A shown in Table 1 below. "P: 3 mass%" described in Table 1 below means the phosphorus content (unit: mass%) in the coating 6A. The Vickers hardness HV of the coating 6A was a value shown in Table 1 below. The punch 4 had a shape fitting into the side mold 6. In the molding step, the side mold 6 was placed on the lower mold 8, and the opening on the lower surface side of the side mold 6 was closed with the lower mold 8. The side die 6 and the lower die 8 in this state correspond to the die 3. The space surrounded by the side mold 6 and the lower mold 8 was a rectangular parallelepiped, and the dimensions of this space (the volume of the die 3) were A × H × B = 12 mm × 75 mm × 8 mm. The design dimensions (target values of the dimensions) of the molded body obtained in the molding step were: vertical side a × height b × horizontal side c = 12 mm × 12 mm × 8 mm.

  In the molding step, the magnetic powder 10 having a predetermined mass was filled into the side mold 6 from the opening on the upper surface side of the side mold 6. By vibrating the entire side mold 6 and lower mold 8 holding the magnetic powder 10, the magnetic powder 10 in the die 3 was leveled. Subsequently, the magnetic powder 10 in the die 3 was made denser by tapping. After tapping, the punch 4 was inserted into the side mold 6, and the magnetic powder 10 in the die 3 was compressed at the end face of the punch 4. In the molding step, the pressure exerted on the magnetic powder 10 in the die 3 by the punch 4 was adjusted to a value shown in Table 1 below. In the following, the pressure exerted by the punch 4 on the magnetic powder 10 in the die 3 in the molding step is referred to as “molding pressure” or “MP” (Molding Pressure).

  The above molding process was repeated 1510 times. The mass of the magnetic powder used in each molding step was constant. In each forming step, the forming pressure MP exerted on the magnetic powder 10 in the die 3 by the punch 4 was also constant. The stroke (movement amount and movement range) of the punch 4 in each molding step was also constant. After 1510 molding steps, the side mold 6 was disassembled, and the maximum depth D1510 of the coating 6A covering the inner wall of the side mold 6 was measured. For the measurement, a surface profile measuring device (F-RM-S014) manufactured by Tokyo Seimitsu Co., Ltd. was used. D1510 of the coating 6A of Example 1 is shown in Table 1 below. As D1510 is larger, the coating 6A is more worn.

  Using another unused mold 2 which is completely the same as the above-described mold 2, the above-described molding step was repeated 7510 times to produce 7510 molded bodies. The mass of the magnetic powder used in each molding step was constant. In each forming step, the forming pressure MP exerted on the magnetic powder 10 in the die 3 by the punch 4 was also constant. The stroke (movement amount and movement range) of the punch 4 in each molding step was also constant. Hereinafter, the ten molded bodies obtained in the first to tenth molding steps of the 7510 molding steps are referred to as “molded bodies 10”. Hereinafter, ten molded bodies obtained in the 1501 to 1510th molding steps of the 7510 molding steps are referred to as “molded bodies 1510”. Hereinafter, the ten molded bodies obtained in the 7501 to 7510 molding steps of the 7510 molding steps are referred to as “molded bodies 7510”.

The dimensions of each of the ten compacts 10 were measured with a micrometer. Then, the bulk density of each molded body 10 was calculated from the volume and mass of each molded body 10. Further, the average value d1_10 of the bulk density of the ten molded bodies 10 was calculated. The average value d1_10 of the bulk density of the molded body 10 of Example 1 immediately after the molding step was adjusted to a value shown in Table 2 below. From the average value d1_10 of the bulk density of the molded body 10 and the true density D (7.5 g / cm ³ ) of the magnetic powder, the average of the relative density (100 · (d1_10) / D) of the molded body 10 immediately after the molding step is obtained. Values were calculated. Hereinafter, the average value of the relative density of the molded body 10 immediately after the molding step is described as “RD1_10”. RD1_10 of Example 1 was adjusted to the values shown in Table 2 below. The bulk density d0 of the designed compact 10 was calculated from the design dimensions (12 mm × 12 mm × 8 mm) of the above-described compact and the mass of the magnetic powder used to produce each compact 10. Δd1_10, which is the absolute value of 100 · {(d1_10) −d0} / d0, was calculated. Δd1_10 of the first embodiment is shown in Table 2 below.

  The average value d1_1510 of the bulk density of the molded body 1510 immediately after the molding step was calculated in the same manner as in the case of the molded body 10. The average value d1_1510 of the bulk density of the molded body 1510 of Example 1 was adjusted to a value shown in Table 2 below. The average value of the relative density (100 · (d1 — 1510) / D) of the molded body 1510 immediately after the molding step was calculated in the same manner as in the case of the molded body 10. Hereinafter, the average value of the relative density of the molded body 1510 immediately after the molding step is expressed as “RD1 — 1510”. RD1_1510 of Example 1 was adjusted to the values shown in Table 2 below. Δd1_1510, which is an absolute value of 100 · {(d1_1510) −d0} / d0, was calculated in the same manner as in the case of the molded body 10. Table 1 below shows Δd1_1510 of the first embodiment.

  The average value d1_7510 of the bulk density of the molded body 7510 immediately after the molding step was calculated in the same manner as in the case of the molded body 10. The average value d1_7510 of the bulk density of the molded body 7510 of Example 1 immediately after the molding step was adjusted to the value shown in Table 2 below. The average value of the relative density (100 · (d1 — 7510) / D) of the molded body 7510 immediately after the molding step was calculated in the same manner as in the case of the molded body 10. Hereinafter, the average value of the relative density of the molded body 1510 immediately after the molding step is expressed as “RD1 — 7510”. RD1_71510 in Example 1 was adjusted to the values shown in Table 2 below. Δd1_7510, which is the absolute value of 100 · {(d1_7510) −d0} / d0, was calculated in the same manner as in the case of the molded body 10. Δd1_7510 of the first embodiment is shown in Table 2 below.

  After the 7510 molding steps, the side mold 6 was disassembled, and the maximum depth D7510 of the coating 6A covering the inner wall of the side mold 6 was measured. For the measurement, a surface profile measuring device (F-RM-S014) manufactured by Tokyo Seimitsu Co., Ltd. was used. The D7510 of the coating 6A of Example 1 is shown in Table 1 below. As D7510 is larger, coating 6A is more worn.

  The following steps were performed using the molded body 10, the molded body 1510, and the molded body 7510 (a total of 30 molded bodies).

  In the orientation step following the molding step, a magnetic field generator equipped with an AC power supply was used. The magnetic field generator had an air core coil and a capacitor. Both the inductance L of the air core coil and the capacitance C of the capacitor are freely variable, and according to the magnetic field generator, a pulsed magnetic field having a desired AC decay waveform could be generated.

  In the orientation step, the molded body held in the mold was placed in an air-core coil, and the mold was fixed with a jig. Then, a pulse magnetic field that attenuated while reversing with the passage of time was applied to the molded body in the mold. By applying this pulse magnetic field (attenuating alternating magnetic field), the individual magnetic powders constituting the compact were oriented and demagnetized. In the orientation step, the intensity of the first wave (maximum magnetic field) of the pulse magnetic field was adjusted to 6.1 T, and the cycle of the first wave was adjusted to 9 milliseconds.

After the orientation step, the upper mold and the side mold were separated from the molded body. The dimensions of each of the ten compacts 10 were measured with a micrometer. Then, the bulk density of each molded body 10 was calculated from the volume and mass of each molded body 10. Further, the average value d2_10 of the bulk density of the ten molded bodies 10 was calculated. Immediately after the orientation step (before the heating step), the average value d2_10 of the bulk density of the molded body 10 of Example 1 was adjusted to the value shown in Table 3 below. From the average value d2_10 of the bulk density of the compact and the true density D (7.5 g / cm ³ ) of the magnetic powder, the average value of the relative density (100 · (d2_10) / D) of the compact 10 immediately after the orientation step Was calculated. Hereinafter, the average value of the relative density of the molded body 10 immediately after the orientation step (before the heating step) is referred to as “RD2_10”. RD2_10 of Example 1 was adjusted to the values shown in Table 3 below. The bulk density d0_10 of the designed compact 10 was calculated from the design dimensions (12 mm × 12 mm × 8 mm) of the above-described compact and the mass of the magnetic powder used to produce each compact 10. Δd2_10, which is the absolute value of {100 · (d2_10) -d0} / d0, was calculated. Table 3 below shows Δd2_10 of the first embodiment.

  The average value d2_1510 of the bulk density of the molded body 1510 immediately after the orientation step (before the heating step) was calculated in the same manner as in the case of the molded body 10. The average value d2_1510 of the bulk density of the molded body 1510 of Example 1 was adjusted to the value shown in Table 3 below. The average value of the relative density (100 · (d2 — 1510) / D) of the compact 1510 immediately after the orientation step (before the heating step) was calculated in the same manner as in the case of the compact 10. Hereinafter, the average value of the relative density of the molded body 1510 immediately after the orientation step (before the heating step) is described as “RD2 — 1510”. RD2_1510 of Example 1 was adjusted to the values shown in Table 3 below. Δd2_1510, which is the absolute value of 100 · {(d2_1510) −d0} / d0, was calculated in the same manner as in the case of the molded body 10. Table 3 below shows Δd2 — 1510 of the first embodiment.

  The average value d2_7510 of the bulk density of the molded body 7510 immediately after the orientation step (before the heating step) was calculated in the same manner as in the case of the molded body 10. The average value d2_7510 of the bulk density of the molded body 7510 of Example 1 was adjusted to a value shown in Table 3 below. The average value of the relative density (100 · (d2 — 7510) / D) of the molded body 7510 immediately after the orientation step (before the heating step) was calculated in the same manner as in the case of the molded body 10. Hereinafter, the average value of the relative density of the molded body 1510 immediately after the orientation step (before the heating step) is described as “RD2 — 7510”. RD2_71510 in Example 1 was adjusted to the values shown in Table 3 below. Δd2_7510, which is the absolute value of 100 · {(d2_7510) −d0} / d0, was calculated in the same manner as in the case of the molded body 10. Table 3 below shows Δd2 — 7510 of the first embodiment.

  After the orientation step, the following heating step was performed.

  In the heating step, the compact placed on the lower mold was heated together with the lower mold in a heating furnace at 600 ° C. for 10 minutes. The rate of temperature rise from room temperature to 600 ° C. in the heating furnace was 10 ° C./sec. The atmosphere in the heating furnace was argon gas.

  The heated compact was separated from the lower mold, and the compact was placed on a sintering tray. The sintering tray was composed of molybdenum.

  In the sintering step, the compact on the sintering tray was sintered in a vacuum atmosphere. The sintering temperature (maximum temperature) was adjusted to 1100 ° C. The sintering time was adjusted to 4 hours. Following the sintering step, an aging treatment was performed. In the aging treatment, the sintered body was heated at 900 ° C. (maximum temperature) for 1 hour. Subsequently, the sintered body was heated at 500 ° C. (maximum temperature) for 1 hour.

  Through the above steps, 30 rare earth magnets were produced.

[Evaluation of rare earth magnets]
<Dimensional accuracy of rare earth magnets>
The dimensions (vertical side a ′ × height b ′ × horizontal side c ′) of each of the ten rare earth magnets produced from the molded body 10 were measured with a micrometer. The following values were calculated based on the measured values. Hereinafter, the ten rare earth magnets manufactured from the molded body 10 are referred to as “rare earth magnets 10”.
Average value of vertical side a ′ of rare earth magnet 10 = a′10
Average value of height b 'of rare earth magnet 10 = b'10
Average value of horizontal side c ′ of rare earth magnet 10 = c′10

The dimensions (vertical side a ′ × height b ′ × horizontal side c ′) of each of the ten rare earth magnets produced from the molded body 1510 were measured with a micrometer. The following values were calculated based on the measured values. Hereinafter, the ten rare earth magnets manufactured from the molded body 1510 are referred to as “rare earth magnets 1510”.
Average value of vertical side a ′ of rare earth magnet 1510 = a′1510
Average value of height b ′ of rare earth magnet 1510 = b′1510
Average value of horizontal side c ′ of rare earth magnet 1510 = c′1510

The following Δa1510, Δb1510, and Δc1510 were calculated.
Δa1510 = a′1510−a′10
Δb1510 = b′1510−b′10
Δc1510 = c′1510−c′10

When the absolute value of each of Δa1510, Δb1510, and Δc1510 is less than 50 μm, “A” is described in the column of ΔS1510 in Tables 3 and 6 below.
When at least one of the absolute values of Δa1510, Δb1510, and Δc1510 is 50 μm or more, and all of the absolute values of Δa1510, Δb1510, and Δc1510 are all less than 150 μm, ΔS1510 of Tables 3 and 6 below is used. In the column, "B" is described.
When at least one of the absolute values of Δa1510, Δb1510, and Δc1510 is 150 μm or more, “C” is described in the column of ΔS1510 in Tables 3 and 6 below.

  The smaller the absolute value of each of Δa1510, Δb1510, and Δc1510, the higher the dimensional accuracy of the rare earth magnet. ΔS1510 is preferably A or B, and most preferably A.

The dimensions (vertical side a ′ × height b ′ × horizontal side c ′) of each of the ten rare earth magnets produced from the molded body 7510 were measured with a micrometer. The following values were calculated based on the measured values. Hereinafter, the ten rare earth magnets manufactured from the molded body 7510 are referred to as “rare earth magnets 7510”.
Average value of vertical side a ′ of rare earth magnet 7510 = a′7510
Average value of height b ′ of rare earth magnet 7510 = b′7510
Average value of horizontal side c ′ of rare earth magnet 7510 = c′7510

The following Δa7510, Δb7510 and Δc7510 were calculated.
Δa7510 = a'7510-a'10
Δb7510 = b′7510−b′10
Δc7510 = c′7510−c′10

When the absolute value of each of Δa7510, Δb7510, and Δc7510 is less than 50 μm, “A” is described in the column of ΔS7510 in Tables 3 and 6 below.
When at least one of the absolute values of Δa7510, Δb7510 and Δc7510 is 50 μm or more, and all of the absolute values of Δa7510, Δb7510 and Δc7510 are all less than 150 μm, ΔS7510 of Tables 3 and 6 below is used. In the column, "B" is described.
When at least one of the absolute values of Δa7510, Δb7510, and Δc7510 is 150 μm or more, “C” is described in the column of ΔS7510 in Tables 3 and 6 below.

  The smaller the absolute value of each of Δa7510, Δb7510 and Δc7510, the higher the dimensional accuracy of the rare earth magnet. ΔS7510 is preferably A or B, and most preferably A.

<Cracks in rare earth magnets>
By visually observing the ten rare earth magnets 1510, it was examined whether or not each rare earth magnet had a crack. The occurrence rate Rc_1510 of the cracks of the rare-earth magnet 1510 of Example 1 is shown in Table 3 below. The crack occurrence rate is a percentage of the number n of the rare-earth magnets 1510 having cracks among the ten rare-earth magnets 1510, and is expressed as (n / 10) × 100 = 10n. The crack occurrence rate Rc_7510 of the rare-earth magnet 7510 of Example 1 was calculated in the same manner as Rc_1510. Rc_7510 is shown in Table 3 below.

(Examples 2 to 20, and Comparative Examples 1 to 4)
In Examples 2 to 11f and Comparative Examples 3 and 4, an electroless nickel plating film shown in Table 1 below was used as the coating 6A. In Examples 12 to 20, a coating 6A shown in Table 4 below was used instead of the electroless nickel plating film. The side mold 6 of Comparative Example 1 was formed of an acrylic resin and did not have the coating 6A. The side mold 6 of Comparative Example 2 was formed from an ABS resin and did not have the coating 6A. D1510 of each of Comparative Examples 1 and 2 is not the maximum depth of the coating 6A but the maximum depth of the inner wall itself of the side mold 6 made of resin.

The same magnetic powder as in Example 1 was used as the magnetic powder of Example 8A. However, in the case of Example 8, 6.0 parts by mass of terpineol (granule forming agent) was added to 100 parts by mass of the magnetic powder, and these were kneaded in a mortar. The obtained kneaded material was screened with a sieve to obtain granules having a particle size of 100 to 300 µm. The organic solvent was removed from the granules by drying the granules at 55 ° C. in a vacuum atmosphere of 10 ⁻² Torr. The granules prepared by the above method were used in the molding step of Example 8A.

  In Examples 2 to 20 and Comparative Examples 1 to 3, the molding pressure MP was adjusted to the values shown in Tables 1 and 4 below. As a result, d1_10, RD1_10, d2_10, RD2_10, d1_1510, RD1_1510, d2_1510, RD2_1510, d1_7510, RD1_7510, d2_7510, and RD2_7510 of Examples 2 to 20 and Comparative Examples 1 to 3, respectively, are shown in Tables 2 and 3 below. 5 and Table 6. The values of Δd1_10, Δd1_1510, Δd1_7510, Δd2_10, Δd2_1510, and Δd2_7510 of Examples 2 to 20 and Comparative Examples 1 to 3 were the values described in Tables 2, 3, 5, and 6, respectively.

  In Comparative Example 4, the molding pressure MP was adjusted to the value shown in Table 1 below. As a result, d1_10, RD1_10, d1_1510, RD1_1510, d1_7510, and RD1_7510 of Comparative Examples 4 to 3 were adjusted to the values shown in Tables 2 and 3 below. Δd1_10, Δd1_1510, and Δd1_7510 of Comparative Example 4 were the values shown in Table 2 below. In Comparative Example 4, the compact was not heated at 600 ° C. between the orientation step and the sintering step. In Comparative Example 4, after the orientation step, the molded body was transferred from the above mold to another rubber mold. A rubber mold containing the molded body was placed in water, and the molded body in the rubber mold was isotropically compressed by water pressure. As described above, in Comparative Example 4, cold isostatic pressing was performed instead of heating at 600 ° C. After cold isostatic pressing, the compact was separated from the rubber mold and placed on a sintering tray. D2_10, RD2_10, d2_1510, RD2_1510, d2_7510, and RD2_7510 in Comparative Example 4 are values measured immediately after the cold isostatic pressing (before the sintering step). Table 3 below shows d2_10, RD2_10, d2_1510, RD2_1510, d2_7510, and RD2_7510 of Comparative Example 4.

  Except for the above, molded articles and rare earth magnets of Examples 2 to 20 and Comparative Examples 1 to 4 were produced in the same manner as in Example 1. In the same manner as in Example 1, the rare earth magnets of Examples 2 to 20 and Comparative Examples 1 to 4 were evaluated. The results of Examples 2 to 20 and Comparative Examples 1 to 4 are shown in Tables 1 to 6 below.

  In Comparative Examples 1 and 2, the inner wall of the side mold 6 was significantly worn before the number of repetitions of the molding process reached 7,500. Therefore, D7510 of each of Comparative Examples 1 and 2 was not measured, and ΔS7510 of each of Comparative Examples 1 and 2 was not evaluated.

  Since the bulk density of the molded body immediately after the molding step of Comparative Example 3 was extremely low, the molded body was very brittle. As a result, the molded body was easily damaged with handling of the molded body after the molding step of Comparative Example 3. Therefore, in Comparative Example 3, ΔS1510 and ΔS7510 were not evaluated.

  In the case of Comparative Example 4, it is presumed that the water pressure in the CIP was too high and cracks occurred in the sintered body due to springback occurring in the molded body.

  According to the method for manufacturing a sintered magnet according to the present invention, it is possible to produce various types of sintered magnets according to various uses such as a hard disk drive, a hybrid vehicle, and an electric vehicle. Even if the amount is small, it is possible to suppress the manufacturing cost.

  2 ... mold, 3 ... die, 4 ... punch, 6 ... tubular side mold, 6A ... coating, 8 ... lower mold, 10 ... magnetic powder, 10b ... molded body.

Claims (8)

Molding a magnetic powder in a mold to form a molded body,
Applying a magnetic field to the compact held in the mold, an orientation step of orienting the magnetic powder contained in the compact,
After the orientation step, a sintering step of heating and sintering the molded body separated from the mold,
With
At least a part of the mold is a resin,
At least a part of the resin portion in the mold is covered with a coating,
The hardness of the coating is higher than the hardness of the resin,
In the molding step, the coating contacts the magnetic powder,
The true density of the magnetic powder is represented as D [g / cm ³ ],
The bulk density of the molded body is expressed as d [g / cm ³ ],
The relative density of the molded body is defined as 100 · d / D [%],
Heating and sintering the molded body whose relative density is adjusted to a value of 38% or more and less than 60%,
Manufacturing method of sintered magnet. The hardness of the coating is higher than the hardness of the magnetic powder,
A method for manufacturing the sintered magnet according to claim 1. Vickers hardness of the coating is 150 N / mm ² or more and 8000 N / mm ² or less.
A method for producing the sintered magnet according to claim 1. The mold includes a lower mold, a cylindrical side mold disposed on the lower mold, and an upper mold inserted into the side mold from above the side mold,
Among the lower mold, the side mold, and the upper mold, at least the side mold is formed from the resin,
At least a part of the inner wall of the side mold is covered with the coating,
A method for producing the sintered magnet according to claim 1. The resin is an insulating resin,
A method for producing the sintered magnet according to claim 1. The pressure exerted on the magnetic powder by the mold is adjusted to 0.049 MPa or more and 20 MPa or less,
A method for producing the sintered magnet according to any one of claims 1 to 5. The magnetic powder contains a rare earth element,
The sintered magnet is a rare earth magnet,
A method for producing the sintered magnet according to any one of claims 1 to 6. The magnetic powder is a granule,
A method for producing the sintered magnet according to any one of claims 1 to 7.

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