Process for producing self-assembled rare earth-iron bonded magnet and motor utilizing the same
View Patent ↗The present invention provides a method for manufacturing a self-organized rare earth-iron bonded magnet, including: a first step of covering a rare earth-iron magnet powder with oligomer or prepolymer in which one molecule includes at least two or more reactive ground substances to provide a surface-treated magnet powder; a second step of melting and kneading stretchable polymer and the surface-treated magnet powder to coarsely crush the resultant material to provide a granule; a third step of dry blending the granule with hardener to provide a compound; a fourth step of compressing the compound under temperature conditions by which the oligomer or prepolymer, the polymer, and the hardener are caused to melt and to flow to provide a green compact; a fifth step of causing the green compact to be a self-organized rare earth-iron bonded magnet by reacting the oligomer or prepolymer, and polymer with the hardener; and a sixth step of stretching the bonded magnet to transform the shape to any of a circular-shape or a circular arc-like shape.
1. A method for manufacturing a rare earth-iron bonded magnet comprising:
a first step of covering a rare earth-iron magnet powder with oligomer or prepolymer to provide a surface-treated magnet powder, wherein the oligomer or prepolymer has a functional group for fixing the rare earth-iron magnet powder;
a second step of melting a stretchable polymer and kneading the melted stretchable polymer with the surface-treated magnet powder at a temperature equal to or higher than a melting point of the polymer to coarsely crush a resultant material to provide a granule;
a third step of dry blending an additive and a hardener with the granule to provide a compound;
a fourth step of compressing the compound under conditions in which the oligomer or prepolymer, the polymer, and the hardener are heated to melt and to flow at a temperature equal to or higher than the melting points of the oligomer or prepolymer, the polymer, and the hardener to provide a green compact; and
a fifth step of stretching the rare earth-iron bonded magnet to transform the shape to any of a circular-shape or a circular arc-like shape.
2. The method according to claim 1 , wherein a compression pressure in the fourth step is 50 MPa or less.
3. The method according to claim 1 , wherein the second step simultaneously melts the stretchable polymer and kneads the melted stretchable polymer and the surface-treated magnet powder together with a lubricant to coarsely crush the resultant material to provide the granule.
4. The method according to claim 3 , wherein the lubricant is pentaerythritol C17 triester and is added to in an amount of 3 to 15 parts by weight to the polymer of 100 parts by weight.
5. The method according to claim 3 , wherein the fourth step heats the compound with a temperature equal to or higher than melting points of the oligomer or prepolymer, the stretchable polymer, the hardener, and the lubricant to compress the compound with a pressure of 15 to 50 MPa to provide the green compact.
6. The method according to claim 1 , wherein the rare earth-iron magnet powders have magnetically-anisotropic polycrystalline aggregate-type Nd 2 Fe 14 B powders having an average particle diameter of 50 μm or more and magnetically-anisotropic single domain particle-type Sm 2 Fe 17 N 3 fine powders having an average particle diameter of 3 μm or less.
7. The method according to claim 6 , wherein the rare earth-iron magnet powders include the single domain particle-type Sm 2 Fe 17 N 3 fine powders with a proportion of 40% weight or more.
8. The method according to claim 1 , wherein the oligomer or prepolymer includes at least one type of epoxy compound that has an oxirane ring and that has a melting point in a range from 70 to 100° C.
9. The method according to claim 1 , wherein the stretchable polymer is polyamide resin having a melting point in a range from 80 to 150° C.
10. The method according to claim 1 , wherein the hardener is a powdery latent hardener consisting of hydantoin derivative.
11. The method according to claim 1 , wherein the third step dry-blends the, the hardener and the granule together with catalyst as an additive agent.
12. The method according to claim 1 , wherein the compound includes the rare earth-iron magnet powders in an amount of 95 weight percent or more.
13. The method according to claim 5 , wherein the fourth step heats the compound filled in a forming die cavity to subsequently subject the compound to a compression molding under an orientation magnetic field of 1 MA/m or more and with a pressure of 25 to 50 MPa.
14. The method according to claim 13 , wherein the application of the orientation magnetic field is performed with the green compact having a relative density or 50% or less.
15. The method according to claim 13 , wherein the green compact has a plate-like shape having a thickness of 1.5 mm or less that is obtained by subjecting the rare earth-iron magnet powders to a compression molding while orientating the rare earth-iron magnet powders in the thickness direction with a parallel magnetic field of 1 MA/m or more that is parallel to a plane of the green compact so that the green compact is anisotropic in a direction perpendicular to the plane.
16. The method according to claim 13 , wherein the green compact has a plate-like shape having a thickness of 1.5 mm or less that is obtained by subjecting the rare earth-iron magnet powders to a compression molding while orientating the rare earth-iron magnet powders in the thickness direction with a transverse magnetic field of 1 MA/m or more that is transverse to a plane of the green compact so that the green compact is anisotropic in an in-plane direction.
17. The method according to claim 1 , wherein the fourth step manufactures the green compact with a compression forming die composed of nonmagnetic material having a plurality of cavities.
18. The method according to claim 17 , wherein the compression forming die is made of nonmagnetic material.
19. The method according to claim 1 , wherein the green compact has a relative density of 98% or more.
20. The method according to claim 1 , wherein the compressing and heating by the fourth step provide the rare earth-iron bonded magnet with a relative density of 98% or more.
21. The method according to claim 1 , wherein the fifth step stretches the rare earth-iron bonded magnet by rolling the rare earth-iron bonded magnet to transform the shape to a circular shape.
22. The method according to claim 1 , wherein the fifth step stretches the rare earth-iron bonded magnet by stamping the rare earth-iron bonded magnet to transform the shape to a circular arc-like shape.
23. The method according to claim 21 wherein the rare earth-iron bonded magnet has the maximum energy product at 20° C. of 120 kJ/m 3 or more when being magnetized at 1.2 MA/m.
24. The method according to claim 21 , wherein the rare earth-iron bonded magnet has the maximum energy product at 20° C. of 160 kJ/m 3 or more when being magnetized at 2.0 MA/m.
25. A motor including the circular, and rare earth-iron bonded magnet obtained by the manufacture method according to claim 21 .
26. A motor including the circular, and rare earth-iron bonded magnet obtained by the manufacture method according to claim 22 .
27. A motor having a magnetic field system that consists of the rare earth-iron bonded magnet anisotropic in a direction perpendicular to the plane according to claim 15 .
28. The method according to claim 22 , wherein the rare earth-iron bonded magnet has the maximum energy product at 20° C. of 120 kJ/m 3 or more when being magnetized at 1.2 MA/m.
29. The method according to claim 22 , wherein the rare earth-iron bonded magnet has the maximum energy product at 20° C. of 160 kJ/m 3 or more when being magnetized at 2.0 MA/m.
30. A motor having a magnetic field system that consists of the rare earth-iron bonded magnet anisotropic in the in-plane direction according to claim 16 .