Jacketed active magnetic bearing

1. A jacketed active magnetic bearing for a rotary machine having a rotor in contact with a process gas and placed in a leaktight enclosure, the magnetic bearing comprising a bearing armature of laminated magnetic material secured to the rotor and placed inside said leaktight enclosure, a bearing stator made up of electromagnet windings associated with a yoke of laminated magnetic material that presents end pole pieces disposed at a short distance from said bearing armature but without making contact therewith, the bearing stator being disposed outside said leaktight enclosure, at least one position detector of the electromagnetic type comprising a detecter armature of laminated magnetic material mounted on the rotor inside the leaktight enclosure and a detector stator comprising electromagnet windings associated with a yoke of laminated magnetic material, the detector stator being disposed outside said leaktight enclosure, and electronic control circuits connected to said bearing electromagnet windings and to said detector electromagnet windings,

wherein the bearing stator is protected by a first jacket of magnetic anti-corrosion material which constitutes a portion of said leaktight enclosure and is secured to said bearing stator, wherein the detector stator is protected by a second jacket of non-magnetic anti-corrosion material that constitutes a portion of said leaktight enclosure and that is secured to said detector stator, wherein the first jacket is made of magnetic stainless steel of the 17/4 PH type, and wherein the second jacket is made of one of the materials constituted by a non-magnetic stainless steel of the AISI 304, 304L, 316, or 316L type, of Inconel, or of a superalloy.

2. An active magnetic bearing according to claim 1 , wherein the first and second jackets present thickness lying in the range 0.3 mm to 0.5 mm.

3. An active magnetic bearing according to claim 1 , wherein the first jacket is welded on a first leaktight housing containing the bearing stator and the second jacket is welded on a second leaktight housing containing the detector stator.

4. An active magnetic bearing according to claim 3 , wherein the first leaktight housing containing the bearing stator and the second leaktight housing containing the detector stator are interconnected in leaktight manner in a zone that is remote from the first and second jackets.

5. An active magnetic bearing according to claim 3 , wherein the first and second leaktight housings are filled with a potting compound.

6. An active magnetic bearing according to claim 1 , wherein the bearing armature and the detector armature are made of thin magnetic laminations made of material identical to that of the first jacket.

7. An active magnetic bearing according to claim 1 , wherein the bearing armature and the detector armature are made of silicon iron laminations covered in an anti-corrosion protection layer of the nickel, chromium, or ceramic type.

8. An active magnetic bearing according to claim 1 , constituting a radial bearing.

9. An active magnetic bearing according to claim 1 , constituting an axial bearing.

10. An active magnetic bearing according to claim 1 , wherein the position detector of the inductive type is fed with a carrier at a frequency lying in the range 20 kHz to 40 kHz.

11. An active magnetic bearing according to claim 1 , wherein an airgap of the magnetic bearing situated between the first jacket and the bearing armature lies in the range 0.3 mm to 0.5 mm.