Magnetic bearing and rotary machine comprising such a bearing

Abstract

A magnetic bearing comprising a stator magnetic circuit secured to a stationary support device, the stator magnetic circuit comprising at least one coil and a ferromagnetic body placed in a protective annular support, the protective annular support leaving uncovered a surface of the ferromagnetic body and a surface of the at least one coil. The bearing also comprises at least one annular plug placed on the surface of the at least one coil which is left uncovered by the protective annular support, and the annular plug and the surface of the ferromagnetic body which is left uncovered by the protective annular support are coated by a protective layer.

Claims

1. A magnetic bearing for a rotary machine having a rotor with an armature, the bearing comprising: a stator magnetic circuit secured to a stationary support device, the stator magnetic circuit comprising at least one coil and a ferromagnetic body placed in a protective annular support, the protective annular support leaving uncovered a surface of the ferromagnetic body and a surface of the at least one coil; and at least one annular plug disposed within the ferromagnetic body, the at least one annular plug covering the uncovered surface of the at least one coil; wherein the at least one annular plug and the surface of the ferromagnetic body are re-machined to obtain a flat surface, wherein the annular plug and the surface of the ferromagnetic body which are left uncovered by the protective annular support and the protective annular support are covered by a protective coating, and wherein the flat surface of the ferromagnetic body and the annular plug covered by the protective coating are uncovered and configured to face the armature of the rotor.

2. The bearing according to claim 1, wherein the protective coating comprises nickel.

3. The bearing according to claim 2, wherein the coating is formed by electroless-nickel plating.

4. The bearing according to claim 3, wherein the at least one annular plug comprises magnetic material selected from the group consisting of ferromagnetic material, magnetic stainless steel, and nickel base alloy.

5. The bearing according to claim 3, further comprising a rotor armature in the form of a disk secured to the rotor, and wherein the stator magnetic circuit is facing the rotor armature.

6. The bearing according to claim 5, wherein the rotor and the rotor armature are, in use, in contact with at least one of a fluid and a gaseous atmosphere, that is at least one of corrosive, acidic, and carrying particles.

7. The bearing according to claim 6, wherein the at least one annular plug is brazed to the at least one coil.

8. The bearing according to claim 7, wherein the at least one annular plug has a U section with a radial web and two axial flanges.

9. The bearing according to claim 2, wherein the coating comprises nickel and phosphorus.

10. The bearing according to claim 1, wherein the at least one annular plug comprises magnetic material selected from the group consisting of ferromagnetic material, magnetic stainless steel, and nickel base alloy.

11. The bearing according to claim 1, wherein the bearing is an axial magnetic bearing.

12. The bearing according to claim 1, further comprising a rotor armature in the form of a disk secured to the rotor, and wherein the stator magnetic circuit is facing the rotor armature.

13. The bearing according to claim 12, wherein the rotor and the rotor armature are, in use, in contact with at least one of a fluid and a gaseous atmosphere, that is at least one of corrosive, acidic, and carrying particles.

14. The bearing according to claim 1, wherein the at least one annular plug is brazed to the at least one coil.

15. The bearing according to claim 1, wherein the at least one annular plug has a U-shaped cross section with a radial web and two axial flanges.

16. The bearing according to claim 1, wherein the annular plug has a thickness greater than a thickness of the protective annular support.

17. The bearing according to claim 1, wherein a thickness of the protective coating ranges from about 1 nm to about 10 m.

18. A rotary machine, comprising: a rotor including an armature; and a bearing comprising: a stator magnetic circuit secured to a stationary support device, the stator magnetic circuit comprising at least one coil and a ferromagnetic body placed in a protective annular support, the protective annular support leaving uncovered a surface of the ferromagnetic body and a surface of the at least one coil; and at least one annular plug disposed within the ferromagnetic body, the at least one annular plug covering the uncovered surface of the at least one coil; wherein the at least one annular plug and the surface of the ferromagnetic body are re-machined to obtain a flat surface, wherein the annular plug and the surface of the ferromagnetic body which are left uncovered by the protective annular support and the protective annular support are covered by a protective coating, and wherein the flat surface of the ferromagnetic body and the annular plug covered by the protective coating are uncovered and facing the armature of the rotor.

19. A method for manufacturing a bearing comprising a stator magnetic circuit secured to a stationary support device, the stator magnetic circuit comprising at least one coil and a ferromagnetic body placed in a protective annular support, the protective annular support leaving uncovered a surface of the ferromagnetic body and a surface of the at least one coil, the method comprising: a) welding at least one annular plug to the at least one coil and/or to the ferromagnetic body; b) re-machining the at least one annular plug and the surface of the ferromagnetic body which is left uncovered by the protective annular support to obtain a flat surface; and c) coating the at least one annular plug, the protective annular support, and the surface of the ferromagnetic body which is left uncovered by the protective annular support with a protective layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics used appear on reading the following description of a particular embodiment of the invention given as a non limiting example and with reference to the accompanying drawings, in which:

(2) FIG. 1 is an axial section view on line I-I of FIG. 2, showing a magnetic bearing according to an exemplary embodiment; and

(3) FIG. 2 is a radial section view on line II-II of FIG. 1.

DETAILED DESCRIPTION

(4) The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale.

(5) FIGS. 1 and 2 show an exemplary embodiment of an axial magnetic bearing 1 of the present invention, for a rotary machine. The magnetic bearing 1 comprises a stator armature 2 and a rotor armature 3 in the form of a disk secured to a rotary shaft 4 of the rotary machine.

(6) The stator armature 2 comprises a stator magnetic circuit 5 including, in conventional manner, one or more annular coils 6 and a ferromagnetic body 7. The ferromagnetic body 7 may be massive or it may be laminated locally. The stator magnetic circuit 5 is placed in a metallic protective annular support 8 that is itself secured to a stationary support device 9.

(7) The stator magnetic circuit 5 is placed facing the rotor armature 3. The stator magnetic circuit 5 and its protective annular support 8 define an airgap relative to the rotor armature 3. In some embodiments, the airgap may lie in the range of 0.4 mm to 1.5 mm, and in some embodiment in the range of 0.4 mm to 1.2 mm.

(8) The protective annular support 8 of the stator magnetic circuit 5 has a U section with a radial web 10 and inner and outer axial flanges 11 and 12. The length of the flanges 11 and 12 in the direction of the axis of the rotary shaft 4 is at least equal to the height of the ferromagnetic body 7 of the stator magnetic circuit 5. Therefore, the protective annular support 8 leaves uncovered a surface of the ferromagnetic body 7, in particular the surface of the ferromagnetic body 7 facing the rotor armature 3, and a surface of the one or more annular coils 6, in particular the surface of the one or more annular coils 6 facing the rotor armature 3.

(9) The magnetic bearing 1 also comprises one or more annular plugs 13. The annular plugs 13 have a U section with a radial web 14 and inner and outer axial flanges 15 and 16. The annular plugs 13 are welded to the ferromagnetic body 7 by their flanges 15 and 16. The annular plugs 13 may also be brazed to the coils 6 by the use of low temperature brazing material. The annular plugs 13 are placed on the surface of the one or more coils 6 which is left uncovered by the protective annular support 8.

(10) The annular plugs 13 may comprise magnetic material, for instance magnetic stainless steel, nickel base alloy such as Inconel or, in an embodiment, ferromagnetic material such as carbon and low alloy steels. In particular, as the plugs are coated by a protective layer to be protected against corrosion, it is no more necessary to use materials with high properties against corrosion: the material of the plugs 13 is chosen according to its magnetic properties and its mechanical properties.

(11) Moreover, as the surface of the ferromagnetic body 7 which is left uncovered by the protective annular support 8 and the external surface of the radial web 14 of the annular plugs 13 may be re-machined to get a surface with an improved flatness, the annular plugs 13 may have a thickness similar to or greater than the one of the protective annular support 8, in order to avoid any deformation of the annular plugs 13 under pressure.

(12) The magnetic bearing 1 also comprises a protective layer 17. The aim of the protective layer 17 is to protect the stator magnetic circuit 5 against corrosion. The protective layer 17 is present on the surface of the ferromagnetic body 7 left uncovered by the protective annular support 8, and the external surface of the web 14 of the annular plugs 13. In other words, the protective layer 17 covers the surface of the stator armature 2 facing the rotor armature 3. The protective layer 17 may also cover the external surface of the flanges 11, 12 of the protective annular support 8.

(13) In some embodiments, the thickness of the protective layer 17 may be in the range of 1 nm to 1 mm, and in an embodiment in the range of 100 nm to 10 m.

(14) In some embodiments, the protective layer 17 may be a layer of nickel. The layer of nickel may be formed by electroless-nickel plating. The layer of nickel may comprise nickel and phosphorus.

(15) Thanks to the use of the annular plugs 13 and of the protective layer 17, it is possible to get a protection of the stator magnetic circuit 5 against corrosion, while keeping an airgap between the stator magnetic circuit 5 and the rotor armature 3 smaller than in the magnetic bearings of the prior art. In particular, when the annular plugs 13 comprise ferromagnetic material, the airgap is the sum of the distance between the protective layer 17 and the rotor armature 3, and of the thickness of the protective layer 17.

(16) Moreover, thanks to the re-machining of the surface of the ferromagnetic body 7 together with the surface of the radial web of the annular plugs 13, and thanks to the coating by the protective layer, it is possible to get a surface with a high flatness facing the rotor armature 3, and then to reduce the airgap.

(17) The above description is made with reference to an axial type magnetic bearing. However, it can be applied in like manner to a magnetic bearing of radial type or to a magnetic bearing of conical type combining the functions of a radial bearing and of an axial bearing.