PROCESS FOR COATING A MAGNET FOR A ROTOR

Abstract

The invention relates to a process for coating a magnet to be inserted into a pocket of a rotor comprising the steps of providing a permanent magnet, and applying a dry powder coating comprising a prepolymer, a hardener, at least one functional filler and a blowing agent. In order to avoid premature reaction of the prepolymer, the blowing agent is a chemical blowing agent. Further, the invention relates to a permanent magnet to which a process according to the invention was applied and to a rotor comprising a permanent magnet to which a process according to the invention was applied.

Claims

1. Process for coating a magnet (10) to be inserted into a pocket (20) of a rotor comprising the steps of providing a permanent magnet (10), and applying a dry powder coating (14) comprising a prepolymer, a hardener, at least one functional filler and a blowing agent, characterized in that the blowing agent is a chemical blowing agent.

2. The process according to claim 1, characterized in that the prepolymer is an epoxide prepolymer.

3. The process according to claim 1, characterized in that the hardener is a non-latent hardener.

4. The process according to claim 1, characterized in that the dry powder coating (14) is free of elastomers.

5. The process according to claim 1, characterized in that the dry powder coating (14) is free of physical blowing agents.

6. The process according to claim 1, characterized in that the process further comprises the step of melting the dry powder coating (14) as present on the magnet as a powder coating (16) in order to form a coating (18) on the permanent magnet, preferably by applying a coating temperature (TB) of 80° C. to 120° C.

7. The process according to claim 6, characterized in that the process further comprises the step of inserting the permanent magnet (10) into a pocket (20) of a rotor.

8. The process according to claim 7, characterized in that the process further comprises the step of expanding the coating (16) on the permanent magnet (10) and hardening of the prepolymer, preferably by applying a process temperature (TP) from 180° C. to 260° C., in order to form an expanded coating (24).

9. A permanent magnet (10) to which a process according to claim 1 was applied.

10. A rotor comprising a permanent magnet (10) according to claim 9.

11. The process according to claim 2, characterized in that the hardener is a non-latent hardener.

12. The process according to claim 2, characterized in that the dry powder coating (14) is free of elastomers.

13. The process according to claim 2, characterized in that the dry powder coating (14) is free of physical blowing agents.

14. The process according to claim 2, characterized in that the process further comprises the step of melting the dry powder coating (14) as present on the magnet as a powder coating (16) in order to form a coating (18) on the permanent magnet, preferably by applying a coating temperature (TB) of 80° C. to 120° C.

15. The process according to claim 14, characterized in that the process further comprises the step of inserting the permanent magnet (10) into a pocket (20) of a rotor.

16. The process according to claim 15, characterized in that the process further comprises the step of expanding the coating (16) on the permanent magnet (10) and hardening of the prepolymer, preferably by applying a process temperature (TP) from 180° C. to 260° C., in order to form an expanded coating (24).

17. A permanent magnet (10) to which a process according to claim 16 was applied.

18. A rotor comprising a permanent magnet (10) according to claim 17.

Description

[0044] FIGS. 1A-1E are a schematic representation of the method according to the invention. Like reference numerals in the figures indicate like or analogous elements. The Figures show the manufacturing method according to the invention for a rotor of an electric machine in five schematic sub-steps.

[0045] In a first step a, a permanent magnet 10 is provided.

[0046] In a further step b, the provided permanent magnet 10 is sprayed by means of a powder coating system 12 with a dry powder coating 14, so that a uniform powder coating 16 is deposited on the surface of the permanent magnets 10.

[0047] In further step c, the powder-coated permanent magnet 10 is subjected to a coating temperature TB, so that the powder coating 16 is converted into a coating 18.

[0048] In a further step d, the now permanently coated permanent magnet 10 is inserted into the pockets 20 of a sheet stack 22, which serves as the basic body of the electric machine rotor.

[0049] In step e, the sheet stack 22 is heated together with the permanent magnet 10 to the process temperature TP, so that the coating 18 converts into an expanded coating 24. The method according to the invention employs a chemical blowing agent. In contrast to physical blowing agents, as for instance microspheres, the chemical blowing agent, upon activation, reacts for instance in such a way that a moiety is released which acts as an expanding gas and therefore also expands the coating 18 to form the expanded coating 24. In the embodiment shown in FIGS. 1A-1E, the chemical blowing agent decomposes upon heating. Activation of the chemical blowing agent and activation of the prepolymer, i.e. the polymerization reaction of the prepolymer induced by the hardner, take place essentially concomitantly. The chemical blowing agents do not prematurely react with the coating 18. Therefore, the epoxide is not consumed prematurely and, hence, remains available for filling the gaps between the permanent magnets 10 and adhering the permanent magnets 10 to the fixation pockets 20. Further, since no premature reaction of the adhesive takes place, the overall structural stability of the coated magnets 10 during transport and storage is retained.

REFERENCE SIGNS

[0050] Permanent magnet 10

[0051] Powder coating system 12

[0052] Dry powder coating 14

[0053] Powder coating 16

[0054] Coating temperature TB

[0055] Coating 18

[0056] Pockets 20

[0057] Sheet stack 22

[0058] Process temperature TP

[0059] Expanded coating 24