Non-ageing permanent magnet from an alloy powder and method for the production thereof
View Patent ↗A method for the production of pressed permanent magnets comprises the following steps: A mixture of at least one magnetic powder and a thermosetting binder is provided and pressed to produce a moulded body. In order to obtain a permanent and particularly reliable protection against oxidation and corrosion, the moulded body is impregnated with an acid and solvent mixture in an impregnating bath before the cure of the thermosetting binder, whereby the entire surface of the permanent magnet is coated with a reaction layer [FIG. 1].
1. A method for the production of a permanent magnet, comprising:
providing a mixture of at least one magnetic powder and a thermosetting binder;
pressing the mixture to produce a porous moulded body;
impregnating the porous moulded body in an impregnating bath with a solution containing an acid to produce an impregnated moulded body;
curing the thermosetting binder to produce a cured impregnated moulded body permanent magnet after said impregnating.
2. The method according to claim 1 , wherein the solution containing an acid comprises phosphoric acid.
3. The method according to claim 1 , wherein the impregnating bath comprises 2 to 6 percent by weight of 85%-phosphoric acid, 1 to 2 percent by weight of distilled water and rest alcohol.
4. The method according to claim 1 , wherein the impregnating comprises retaining the moulded body in the impregnating bath for a retention time of at least 15 minutes.
5. The method according to claim 1 , wherein the impregnating further comprises subjecting the moulded body to a vacuum, or to a positive pressure, or both.
6. The method according to claim 1 , wherein the at least one magnetic powder comprises a metal or alloy powder.
7. The method according to claim 6 , wherein the at least one magnetic powder comprises a hard magnetic alloy powder.
8. The method according to claim 7 , wherein the magnetic powder comprises an alloy powder of neodymium, iron and boron containing the hard magnetic phase Nd 2 Fe 14 B.
9. The method according to claim 7 , wherein the magnetic powder comprises an alloy powder of samarium and cobalt containing the hard magnetic phase Sm 2 Co 17 or Sm 1 Co 5 .
10. The method according to claim 1 , wherein the magnetic powder has an average particle size d, such that 50 μm≦d≦150 μm.
11. The method according to claim 1 , further comprising applying a coating to the particles of the magnetic powder.
12. The method according to claim 5 , wherein the impregnating further comprises subjecting the porous moulded body to a positive pressure after the application of the vacuum.
13. The method according to claim 1 , wherein the pressing of the mixture comprises pressing the mixture at room temperature at a pressure of 6 t/cm 2 or more to produce a moulded body.
14. The method according to claim 1 , further comprising exposing the mixture to a magnetic field during the pressing process.
15. The method according to claim 1 , wherein the curing comprises exposing the moulded body to the presence of air at a temperature of at least 120° C.
16. The method according to claim 1 , further comprising impregnating the moulded body with an epoxy resin in a second impregnation that follows the impregnation of the moulded body with the phosphoric acid and solvent mixture.
17. The method according to claim 16 , further comprising drying the moulded body between its impregnation with the phosphoric acid and solvent mixture and the second impregnation step.
18. The method according to claim 1 , wherein the solution containing an acid further comprises a plastic material or other organic components, or both.
19. The method according to claim 1 , wherein the solution containing an acid further comprises inorganic components.
20. A pressed, porous permanent magnet made from a rare earth alloy powder and a thermosetting binder, wherein the surface of the permanent magnet which forms an interface with ambient atmosphere is coated with a protective layer formed by reaction with an acid.
21. The pressed, porous permanent magnet according to claim 20 , wherein the protective layer comprises phosphate.
22. The pressed, porous permanent magnet according to claim 20 , wherein the protective layer comprises molybdate.
23. The pressed, porous permanent magnet according to claim 20 , wherein the protective layer comprises tungstate.
24. The pressed, porous permanent magnet according to claim 20 , wherein the protective layer comprises vanadate.
25. The pressed, porous permanent magnet according to claim 20 , wherein the protective layer comprises titanate.
26. The pressed, porous permanent magnet according to claim 20 , wherein the rare earth alloy powder comprises a powder of neodymium, iron and boron containing a hard magnetic phase with the composition Nd 2 Fe 14 B produced in accordance with a hydrogenation disproportionation desorption recombination (HDDR) process.
27. The pressed, porous permanent magnet according to claim 20 , wherein the rare earth alloy powder comprises a powder of samarium and cobalt containing a hard magnetic phase with the composition Sm 2 Co 17 or Sm 1 Co 5 .
28. The pressed, porous permanent magnet produced according to the method of claim 1 .