Search

CN-115280441-B - Method for producing rare earth sintered magnet and wet molding apparatus

CN115280441BCN 115280441 BCN115280441 BCN 115280441BCN-115280441-B

Abstract

A method for producing a rare earth sintered magnet, comprising a step of producing a molded body by compression molding a slurry containing an alloy powder containing a rare earth element and a dispersion medium using a wet molding device, and a step of sintering the molded body, wherein when the slurry is injected into a space in which a cavity of the wet molding device is formed, the slurry is pressed without applying a magnetic field, and the dispersion medium contained in the slurry is started to be discharged from the space.

Inventors

  • TSUKUDA TAKASHI

Assignees

  • 日立金属株式会社

Dates

Publication Date
20260505
Application Date
20210311
Priority Date
20200326

Claims (14)

  1. 1. A method for producing a rare earth sintered magnet, comprising supplying a slurry containing an alloy powder containing a rare earth element and a dispersion medium into a space of a mold, press-molding the supplied slurry to obtain a molded body, and sintering the molded body, characterized by comprising: When the slurry is supplied into the space of the mold, the space is temporarily or intermittently covered with a non-magnetic cover that does not absorb the dispersion medium without applying a transverse magnetic field, Moving the non-magnetic cover from a position covering the space before applying the transverse magnetic field to the space, A filter cloth is arranged on the space of the die, When the dispersion medium is discharged from the space of the die, the application of a transverse magnetic field in a direction orthogonal to the pressing direction is started before the discharge.
  2. 2. The method for producing a rare earth sintered magnet according to claim 1, wherein: the size of the molded article is 90mm or more in length, 90mm or more in width and 90mm or more in height.
  3. 3. The method for producing a rare earth sintered magnet according to claim 1 or 2, comprising: a1 st dividing step of dividing the molded body into 10 or more molded body pieces by cutting the molded body, and And a sintered body material producing step of producing a plurality of sintered body materials by sintering the plurality of molded body pieces, respectively, after the 1 st dividing step.
  4. 4. The method for producing a rare earth sintered magnet according to claim 3, comprising: And a2 nd dividing step of dividing the sintered body raw material into 100 or more sintered body pieces by cutting each of the plurality of sintered body raw materials after the sintered body raw material producing step.
  5. 5. The method for producing a rare earth sintered magnet according to claim 1 or 2, characterized by: A gap is formed between the means for press forming the slurry and the upper surface of the slurry before the application of the transverse magnetic field is started.
  6. 6. A method for producing a rare earth sintered magnet, comprising: A step of preparing a wet molding apparatus including a die having a through hole, a lower punch that moves up and down relative to the die in a state in which at least a tip end is inserted into the through hole, and an upper punch that moves up and down relative to the lower punch, wherein the upper punch has a lower end provided with a plurality of discharge holes through which a liquid passes, and a cavity is formed in the through hole by an upper end of the lower punch and the lower end of the upper punch, and a volume of the cavity can be reduced by reducing a space between the upper end of the lower punch and the lower end of the upper punch; A step of preparing a slurry containing an alloy powder containing a rare earth element and a dispersion medium; Forming a space from an inner wall of the through hole and the upper end of the lower punch in the wet forming apparatus, injecting the slurry into the space, and filling the space with the slurry; A step of closing the space with the lower end of the upper punch to form the cavity filled with the slurry; a step of reducing the interval between the lower end of the upper punch and the upper end of the lower punch while applying a transverse magnetic field in a direction perpendicular to the direction in which the lower punch moves up and down with respect to the cavity, and discharging the dispersion medium contained in the slurry through the plurality of discharge holes in the upper punch, thereby producing a molded body of the alloy powder, and A step of sintering the molded article, When the slurry is injected into the space, the space is temporarily or intermittently covered with a non-magnetic cover that does not absorb the dispersion medium without applying a magnetic field to the space, After the injection of the slurry is completed and before the removal of the non-magnetic cover, an air gap is formed between the underside of the upper punch and the slurry, or between the optionally used filter cloth and the slurry, The non-magnetic cover is moved from a position covering the space before the transverse magnetic field is applied to the cavity.
  7. 7. The method for producing a rare earth sintered magnet according to claim 6, wherein: In the step of manufacturing the molded body of the alloy powder while reducing the interval between the lower end of the upper punch and the upper end of the lower punch, a filter cloth or a filter is disposed between the slurry in the cavity and the lower end of the upper punch.
  8. 8. The method for producing a rare earth sintered magnet according to claim 6 or 7, wherein: The method includes a step of moving the non-magnetic cover from a position covering the space after filling the space with the slurry, and relatively lowering the lower punch with respect to the die at least before starting application of the transverse magnetic field, thereby forming a gap between the slurry and at least one of the lower end of the upper punch and the filter cloth.
  9. 9. The method for producing a rare earth sintered magnet according to claim 8, wherein: The size of the gap is 2mm or more and 4mm or less.
  10. 10. The method for producing a rare earth sintered magnet according to claim 6 or 7, wherein: after filling the space with the slurry, moving the non-magnetic cover from a position covering the space, The application of the transverse magnetic field is started before the discharge of the dispersion medium contained in the slurry through the plurality of discharge holes in the upper punch is started.
  11. 11. The method for producing a rare earth sintered magnet according to claim 6 or 7, wherein: the method includes a step of temporarily connecting the inside of the space to the outside by moving the non-magnetic cover up and down when the slurry is injected into the space.
  12. 12. The method for producing a rare earth sintered magnet according to claim 6 or 7, wherein: The concentration of the alloy powder in the slurry at the time of injection is 75 to 88 mass%.
  13. 13. A wet molding apparatus for producing a molded body of a rare earth alloy powder, comprising: a die having a through hole; a lower punch that moves up and down relative to the die with at least a tip end inserted into the through hole; an upper punch which moves up and down relative to the lower punch and has a lower end provided with a plurality of discharge holes for passing a liquid therethrough, and An electromagnetic coil for applying a transverse magnetic field in a direction perpendicular to a direction in which the lower punch moves up and down relative to the lower punch to the inside of the through hole of the die, The die has an injection port for injecting a slurry containing the rare earth alloy powder into a space formed by an inner wall of the through hole and an upper end of the lower punch, The wet molding apparatus further includes a non-magnetic cover that does not absorb the dispersion medium, and temporarily or intermittently covers the space when the slurry is injected into the space, After the injection of the slurry is completed and before the removal of the non-magnetic cover, an air gap is formed between the underside of the upper punch and the slurry, or between the optionally used filter cloth and the slurry.
  14. 14. A wet forming apparatus as claimed in claim 13, wherein: the wet forming device comprises a control device for controlling the actions of the upper punch, the lower punch, the die, the electromagnetic coil and the non-magnetic cover, The control device performs the following steps: forming the space by the inner wall of the through hole and the upper end of the lower punch in the wet forming device, injecting the slurry into the space, and filling the space with the slurry; A step of closing the space by the lower end of the upper punch to form a cavity filled with the slurry, and A step of reducing a distance between the lower end of the upper punch and the upper end of the lower punch in a state where the transverse magnetic field in a direction perpendicular to a direction in which the lower punch moves up and down with respect to the cavity is applied, discharging a dispersion medium contained in the slurry through the plurality of discharge holes in the upper punch, thereby producing a molded body of the rare earth alloy powder, When the slurry is injected into the space, a magnetic field is not applied to the space, and the space is temporarily or intermittently covered with the non-magnetic cover, The non-magnetic cover is moved from a position covering the space before the transverse magnetic field is applied to the cavity.

Description

Method for producing rare earth sintered magnet and wet molding apparatus Technical Field The present invention relates to a method for producing a rare earth sintered magnet and a wet molding apparatus. Background In recent years, rare earth sintered magnets have been in high demand, and R-T-B sintered magnets (R is at least one of rare earth elements, T is mainly iron, and B is boron) are known as magnets having the highest performance, and are used for various motors such as Voice Coil Motors (VCM) of hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), motors for industrial equipment, and home appliances. The R-T-B sintered magnet is mainly composed of a main phase containing an R 2T14 B compound and a grain boundary phase located at a grain boundary portion of the main phase. The R 2T14 B compound as the main phase is a ferromagnetic material having high saturation magnetization and an anisotropic magnetic field. The grain boundary phase has a low-melting point R-rich phase in which the rare earth element (R) is concentrated and which is non-magnetic. As a method for improving the magnetic characteristics of R-T-B sintered magnets, (1) miniaturization of R 2T14 B phase, (2) improvement of the degree of orientation of R 2T14 B phase, (3) reduction of oxygen content, and (4) improvement of the ratio of R 2T14 B phase are known. In the production of rare earth sintered magnets such as R-T-B sintered magnets, for example, an ingot obtained by casting a molten metal or other raw material into a mold, or an alloy powder having a predetermined particle diameter obtained by pulverizing a raw material alloy casting material having a desired composition such as a sheet obtained by a tape casting method is used, and after the alloy powder is compressed in an orientation magnetic field to produce a powder compact (compact), the powder compact is sintered to produce a rare earth sintered magnet. Wherein, if the powder particles oxidize during pulverization and molding, the improvement of magnetic properties is hindered. However, there are 2 methods, dry and wet, among molding methods for producing a powder molded body, and a wet molding method is disclosed in patent document 1. It is considered that this wet molding method can suppress oxidation of powder particles, and therefore, it is less likely to inhibit improvement of magnetic properties than a dry molding method. Prior art literature patent literature Patent document 1 Japanese patent laid-open No. 8-88133 Disclosure of Invention Problems to be solved by the invention In the wet molding method disclosed in patent document 1, a slurry containing rare earth alloy powder is injected under pressure into a cavity (space) of a mold, but it has been found from the study of the present inventors that even in such a case, "density deviation of a powder molded body" and disturbance of orientation "produced by compression in an orientation magnetic field are liable to occur. The former "density deviation of the powder compact" may cause cracking or crazing at the time of taking out or later sintering of the powder compact. In addition, the latter "disturbance of orientation" may have a possibility of lowering magnetic characteristics. In particular, since the degree of density deviation and disturbance of orientation of the powder compact varies depending on the relationship between the pressing direction and the direction of the magnetic field when the slurry is pressurized and injected into the cavity of the mold, the state of the slurry in the cavity of the mold, and the like, it is difficult to stably produce the required high magnetic characteristics. The present invention provides a method for producing a rare earth sintered magnet and a wet forming apparatus which can solve the above problems. Means for solving the problems In the method for producing a rare earth sintered magnet according to the present invention, in a non-limiting embodiment, a slurry containing an alloy powder containing a rare earth element and a dispersion medium is supplied into a space of a die, and a molded body obtained by press molding the supplied slurry is sintered, wherein when the slurry is supplied into the space of the die, a magnetic field is not applied, and when the dispersion medium is discharged from the space of the die, a transverse magnetic field in a direction orthogonal to a pressing direction is applied before the discharge. In one embodiment, the molded article has a length of 90mm or more, a width of 90mm or more, and a height of 90mm or more. In one embodiment, the method includes a1 st dividing step of dividing the molded body into 10 or more molded body pieces by cutting the molded body, and a sintered body raw material producing step of producing a plurality of sintered body raw materials by sintering the plurality of molded body pieces, respectively, after the 1 st dividing step. In one embodiment, the method comprises: And a2 nd dividing step of