Method for preparing rare earth sintered magnet

Patent metadata

Field	Value
Publication number	US-9711280-B2
Application number	US-201514678529-A
Country	US
Kind code	B2
Filing date	Apr 3, 2015
Priority date	Apr 9, 2014
Publication date	Jul 18, 2017
Grant date	Jul 18, 2017

Abstract

A rare earth sintered magnet is prepared from a corresponding alloy powder, using a mold comprising a die, an upper punch, and a lower punch which is divided into a plurality of punch segments which are independently movable within the die. The method comprises the steps of filling the mold cavity with the alloy powder when one or more selected punch segments are moved to a higher position than the remaining punch segments; moving the selected punch segments down to the position where the selected and remaining punch segments assume the normal shape of the lower punch during the compression step; compressing the alloy powder between the upper and lower punches under a magnetic field while the normal shape of the lower punch is maintained, for thereby molding a compact; and heat treating the compact.

First claim

The invention claimed is:

1. A method for preparing a rare earth sintered magnet from a corresponding alloy powder using a mold, said mold comprising a die, an upper punch having a pressure surface, and a lower punch having a pressure surface, the pressure surface of one or both of the upper and lower punches being shaped non-planar, the lower punch being divided into a plurality of punch segments which are independently movable within the die in a compression direction, provided that the pressure surface of the lower punch during a compression step has a normal shape, a cavity being defined between the die and the lower punch, said method comprising the steps of:
moving one or more selected punch segments upward such a position that their pressure surface is positioned relatively higher than the pressure surface of the remaining punch segments,
filling the cavity with the alloy powder,
moving the selected punch segments downward until they join with the remaining punch segments to assume the normal shape of the lower punch during the compression step,
compressing the alloy powder in the cavity between the upper and lower punches, while the normal shape of the pressure surface of the lower punch is maintained, under a magnetic field for uniaxial pressure molding to form a compact, and
heat treating the compact,
wherein in the step of moving the selected punch segments downward, the selected punch segments are moved down while a magnetic field is applied.

2. The method of claim 1 , further comprising, after the pressure molding step, the step of withdrawing the compact from the die by relatively moving the upper and lower punches and the die while the compact in the mold is kept under pressure by both of the upper and lower punches.

3. The method of claim 2 wherein during the step of withdrawing the compact, the pressure on the compact is increased or decreased when the upper and lower punches and the die are relatively moved.

4. The method of claim 1 wherein the top of the alloy powder is leveled during or after the filling step.

5. The method of claim 1 wherein the selected punch segments are disposed at positions where the vertical thickness of the compact is thin.

6. The method of claim 1 wherein at least a portion of the pressure surface of one or both of the upper and lower punches is a curved surface of arch or inverse arch shape.

7. The method of claim 1 wherein the pressure surface of the upper punch is a curved surface of arcuate arch shape.

8. The method of claim 7 wherein the pressure surface of the lower punch consist of a central surface section having parallel side edges and two flanks extending from the side edges of the central surface section.

9. The method of claim 8 wherein the central surface section is a horizontal surface or a curved surface of arcuate arch shape, and the flank is a horizontal surface or a curved or flat surface inclined toward the convex side of the arch.

10. The method of claim 8 wherein the selected punch segments of the lower punch are two punch segments having a pressure surface corresponding to the flanks, and the remaining is one punch segment having a pressure surface corresponding to the central surface section.

11. The method of claim 2 , further comprising, between the step of filling and the step of moving the selected punch segments downward, the steps of moving the die upward and/or the overall lower punch downward, and then resting the upper punch on top of the alloy powder.

12. The method of claim 1 wherein the lower punch is divided into two punch segments corresponding to said selected punch segments, and one punch segment corresponding to said remaining punch segment and providing the central section of the pressure surface of the lower punch.

13. The method of claim 12 wherein, in the step of withdrawing, the pressure applied to the compact, in each molding step and per compact, is 0.01 to 0.5 MPa/cm 2 of a transverse section of the die perpendicular to the pressure application direction.

14. The method of claim 1 wherein the pressure surface of the upper punch is shaped non-planar.

15. The method of claim 14 being for preparing a rare earth sintered magnet having ID shape.

16. The method of claim 14 wherein the pressure surface of the lower punch is shaped non-planar.

17. The method of claim 16 being for preparing a rare earth sintered magnet having C shape.

18. The method of claim 14 wherein the upper punch has a downward pressure surface corresponding to the upper surface of the magnet, and the lower punch has an upward pressure surface corresponding to the lower surface of the magnet.

19. The method of claim 1 wherein, in the step of heat treating, the compact is sintered in a heat treatment furnace in high vacuum or a non-oxidizing gas atmosphere at a temperature of 1,000 to 1,200° C. for 1 to 10 hours.

Assignees

• Shinetsu Chemical Co

Inventors

• Uesaka Eiji
• Kohno Osamu
• Imamura Kenji
• Umebayashi Yoshihiro
• Hashimoto Takahiro

Classifications

• B22F1/14

  Treatment of metallic powder (mixing with lubricating or binding agents or with organic material B22F1/10) · CPC title

• B22F3/004

  Filling molds with powder (feeding material to presses in general B30B15/302) · CPC title

• H01F1/0536

  sintered · CPC title

• H01F41/0266 Primary

  Moulding; Pressing (H01F41/0273 takes precedence; hard magnetic particles H01F1/06, H01F1/11) · CPC title

• C22C2202/02

  Magnetic · CPC title