Magnetic bearing having permanent magnet assemblies with repulsive bearing surfaces
The magnetic bearings make use of magnet assemblies with a high magnetic field gradient. The magnet assemblies use two permanent magnets with opposite polarization in a Kittel open domain structure. The basic factor of magnetic separation is the magnetic force, which acts on a particle of the substance and which is proportional to the magnetic susceptibility of the substance, the value of the magnetic induction B and the value of the gradient ∇B of the applied magnetic field. Therefore, increasing the sensitivity and selectivity of magnetic separation will require use of the highest possible values of magnetic induction B and magnetic field gradient ∇B, or their united factor—the product B∇B. The magnetic assembly have repulsive magnetic systems each having two juxtaposed permanent magnets 2, 4 with opposite magnetization in the form of a Kittel open domain structure. In such an system, near the edges of the faces of the joining magnets, a strong magnetic stray field appears and the value of the product B∇B reaches 10 11 mT 2 /m. To concentrate the magnetic stray field shields 6 are provided on top of the two magnets 2,4 with a gap 8 between the shields at the joint of the two magnets 2, 4 forming zones of high magnetic field gradient 14 with increased magnitude for the product B∇B.
1. A magnetic bearing comprising:
first and second bearing surfaces;
at least one magnet assembly on each bearing surface, wherein each magnet assembly includes:
two permanent magnets located side-by-side with oppositely oriented magnetic field polarities and end surfaces of opposite polarities next to one another, wherein the magnetic anisotropy of the magnets exceeds the magnetic inductance of the material of the magnets; and
a shield on a first end of the adjacent permanent magnets, the shield comprising a non-retentive material covering adjacent end surfaces of the two permanent magnets with a gap along a joining line between the two permanent magnets to form a zone of high-gradient magnetic field above the joining line;
wherein the magnet assembly on the first bearing surface provides a magnetic field opposed to the magnetic field of the magnet assembly on the second bearing surface, and
wherein the magnetic bearing is arranged such that the first and second bearing surfaces are magnetically repelled from one another in mechanical equilibrium.
2. The magnetic bearing as claimed in claim 1 , wherein the magnet bearing comprises a plurality of magnet assemblies.
3. The magnetic bearing as claimed in claim 1 , wherein the two bearing surfaces are in close proximity to one another.
4. The magnetic bearing as claimed in claim 1 , wherein the separation between the two bearing surfaces at the locations of the opposed magnet assemblies is less than 0.5 mm, preferably less than 0.4 mm and more preferably less than 0.2 mm.
5. The magnetic bearing as claimed in claim 1 , wherein the bearing surfaces are cylindrical, with cylindrical magnet assemblies providing repelling forces to support a shaft while stationary and/or during rotation.
6. The magnetic bearing as claimed in claim 5 , wherein the magnet bearing comprises a shaft supported for sliding movement by an arrangement of magnet assemblies along the length of tubular bearing surfaces.
7. The magnetic bearing as claimed in claim 6 , wherein a joining line of the magnet assembly on the first bearing surface is aligned with, in parallel with and directly opposes a joining line of the magnet assembly on the second bearing surface.
8. The magnetic bearing as claimed in claim 7 , wherein the bearing also comprises a restraining mechanism to ensure that the two joining lines remain aligned.
9. The magnetic bearing as claimed in claim 7 , wherein the joining lines are parallel and the centre of the magnetic field of the magnet assembly on the first bearing surface is offset by a small amount from the centre of the magnetic field of the magnet assembly on the second bearing surface.
10. A method of manufacture of a magnetic bearing comprising:
providing first and second bearing surfaces with at least one magnet assembly on each bearing surface, wherein each magnet assembly includes:
two permanent magnets located side-by-side with oppositely oriented magnetic field polarities and end surfaces of opposite polarities next to one another, wherein the magnetic anisotropy of the magnets exceeds the magnetic inductance of the material of the magnets; and
a shield on a first end of the adjacent permanent magnets, the shield comprising a non-retentive material covering adjacent end surfaces of the two permanent magnets with a gap along a joining line between the two permanent magnets to form a zone of high-gradient magnetic field above the joining line; and
locating the first bearing surface and/or the magnet assembly thereof relative to the second bearing surface and/or the magnet assembly thereof such that the magnet assembly on the first bearing surface provides a magnetic field opposed to the magnetic field of the magnet assembly on the second bearing surface, and the first and second bearing surfaces are magnetically repelled from one another in mechanical equilibrium.
11. The method as claimed in claim 10 , wherein the magnet bearing comprises a plurality of magnet assemblies.
12. The method as claimed in claim 10 , wherein the two bearing surfaces are located in close proximity to one another.
13. The method as claimed in claim 10 , wherein the separation between the two bearing surfaces at the locations of the opposed magnet assemblies is less than 0.5 mm, preferably less than 0.4 mm and more preferably less than 0.2 mm.
14. The method as claimed in claim 10 , wherein the bearing surfaces are cylindrical, with cylindrical magnet assemblies providing repelling forces to support a shaft while stationary and/or during rotation.
15. The method as claimed in claim 14 , wherein the magnet bearing comprises a shaft supported for sliding movement by an arrangement of magnet assemblies along the length of tubular bearing surfaces.
16. The method as claimed in claim 15 , wherein a joining line of the magnet assembly on the first bearing surface is aligned with, in parallel with and directly opposes a joining line of the magnet assembly on the second bearing surface.
17. The method as claimed in claim 16 , comprising providing the bearing with a restraining mechanism to ensure that the two joining lines remain aligned.
18. The method as claimed in claim 15 , wherein the joining lines are parallel and the centre of the magnetic field of the magnet assembly on the first bearing surface is offset by a small amount from the centre of the magnetic field of the magnet assembly on the second bearing surface.