GB2065794A - Magnetic Bearings - Google Patents

Abstract

A permanently magnetic radial bearing comprising two permanent magnet races which are disposed coaxially one inside the other and which repel each other radially due to magnetisation of the races in the same direction, which races are disposed rotatably relative to each other, characterised by the fact that the races are magnetised axially in the same direction (3) in the preferred state of magnetisation and have different axial lengths. Preferably the inner race (2) is fixed to a rotatable shaft (4) of a gas ultracentrifuge consisting of non-magnetisable material, and the outer race (1) is attached non-movably to the housing (5). <IMAGE>

Description

SPECIFICATION Permanently Magnetic Radial Bearings and Their Use In Gas Ultracentrifuges This invention relates to permanently magnetic radial bearings comprising two permanent magnet races which are disposed coaxially one inside the other and which repel each other radially due to magnetisation of the races in the same direction, which races are disposed rotatably relative to each other.

Permanently magnetic radial bearings are known e.g. for separators running at high speed used for uranium enrichment. The separators are mounted at their upper ends by the radial bearings. These radial bearings were hitherto produced from isotropic Al-Ni-Co magnets, which consist of radially magnetised permanent magnet races disposed one above the other. The radial rigidity of such a design is however affected to a high degree by axial deflection, and thus only short separators could be mounted by such means. At high speeds of revolution, contraction occurs in the pipe of the separators due to radial expansion thereof. Due to the limitations of the known design of the magnetic hearings, this axial displacement hitherto has had to be absorbed by elaborate mechanical expedients.

The present invention provides bearings having a higher radial rigidity, which allows a greater structural length for separators supported thereby and hence an increase in the throughput quantity.

In general the races forming the bearing should be magnetically homogeneous and stress-free, and display an eccentricity 50% less than the designs existing hitherto. Further there is the requirement that with predetermined maximum axial forces at a deflection provided for in the axial direction of +7 mm the radial rigidity should not fall below a minimum value of 1000 N/m and the radial rigidity at the working point amounts to at least 2000 N/m.

The invention provides a bearing which can meet such requirements as defined in the accompanying claims.

Thus in order not to fall below minimum values of radial rigidity at a given axial deflection, the heights of the races must be different between stationary and moving bearing parts. A length ratio of about 1:2.5 is preferred as this has proved to be an optimal ratio for throughput capacity.

The invention also provides a permanently magnetisable race as defined in the accompanying Claim 1, wherein the inner race is fixed to a rotatable shaft of a gas centrifuge consisting of non-magnetisable material, and the outer race is attached non-movably to the housing of the gas centrifuge.

Due to the use of magnetic races in which direction of pressing, and magnetic preferred direction and direction of magnetisation, are identical, stress problems do not occur, so that stress-free homogeneous races can be produced.

The advantages of the bearing according to the invention are as follows:- 1) At given axial deflection, a degree of radial rigidity is obtainable which results in a decrease in imbalancing forces; 2) Absorption of axial length variation of the system in the magnetic bearing is achieved thus removing the necessity for elaborate mechanical expedients; 3) Production of stress-free races, in particular when using rare earth cobalt alloy magnets; 4) Production of the races each from one piece, whereby high magnetic homogeneity and resulting low magnetic eccentricity is obtainable; 5) Higher obtainable energy density than with radially magnetised races; 6) Economical production.

The accompanying drawing schematically illustrates one embodiment of a permanently magnetic radial bearing according to the invention.

In the drawing two permanent magnet races 1, 2 are set concentrically one inside the other and are each magnetised in an axial direction 3, which is a preferred state of magnetisation. The inner race 2 is mounted on a non-magnetisable shaft 4 and the outer race 1 with the same direction of magnetisation is mounted on a housing 5. The stable equilibrium in the axial direction can be achieved with an end journal rigid bearing.

In order to allow axial relative displacements of the permanent magnet races 1, 2 without substantial decrease in radial rigidity, the inner race 2, or the outer race 1, is constructed with an axial length greater than the other (thus providing different heights of magnetisation).

Claims

1. A permanently magnetic radial bearing comprising two permanent magnet races which are disposed coaxially one inside the other and which repel each other radially due to magnetisation of the races in the same direction, which races are disposed rotatably relative to each other, characterised by the fact that the races (1,2) are magnetised axially in the same direction in the preferred state of magnetisation (3) and have different axial lengths.

2. A bearing according to Claim 1, wherein the axial length ratio of the races (1, 2) is about 1:2.5.

3. A bearing according to Claim 1 or Claim 2, wherein the races (1, 2) consist of a rare earth/cobalt permanently magnetic alloy.

4. A bearing according to any of Claims 1 to 3, wherein the inner race (2) is fixed to a rotatable shaft (4) of a gas ultracentrifuge consisting of non-magnetisabie material, and the outer race is attached non-movably to the housing (5).

5. A permanently magnetic radial bearing substantially as hereinbefore described and illustrated in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Permanently Magnetic Radial Bearings and Their Use In Gas Ultracentrifuges This invention relates to permanently magnetic radial bearings comprising two permanent magnet races which are disposed coaxially one inside the other and which repel each other radially due to magnetisation of the races in the same direction, which races are disposed rotatably relative to each other. Permanently magnetic radial bearings are known e.g. for separators running at high speed used for uranium enrichment. The separators are mounted at their upper ends by the radial bearings. These radial bearings were hitherto produced from isotropic Al-Ni-Co magnets, which consist of radially magnetised permanent magnet races disposed one above the other. The radial rigidity of such a design is however affected to a high degree by axial deflection, and thus only short separators could be mounted by such means. At high speeds of revolution, contraction occurs in the pipe of the separators due to radial expansion thereof. Due to the limitations of the known design of the magnetic hearings, this axial displacement hitherto has had to be absorbed by elaborate mechanical expedients. The present invention provides bearings having a higher radial rigidity, which allows a greater structural length for separators supported thereby and hence an increase in the throughput quantity. In general the races forming the bearing should be magnetically homogeneous and stress-free, and display an eccentricity 50% less than the designs existing hitherto. Further there is the requirement that with predetermined maximum axial forces at a deflection provided for in the axial direction of +7 mm the radial rigidity should not fall below a minimum value of 1000 N/m and the radial rigidity at the working point amounts to at least 2000 N/m. The invention provides a bearing which can meet such requirements as defined in the accompanying claims. Thus in order not to fall below minimum values of radial rigidity at a given axial deflection, the heights of the races must be different between stationary and moving bearing parts. A length ratio of about 1:2.5 is preferred as this has proved to be an optimal ratio for throughput capacity. The invention also provides a permanently magnetisable race as defined in the accompanying Claim 1, wherein the inner race is fixed to a rotatable shaft of a gas centrifuge consisting of non-magnetisable material, and the outer race is attached non-movably to the housing of the gas centrifuge. Due to the use of magnetic races in which direction of pressing, and magnetic preferred direction and direction of magnetisation, are identical, stress problems do not occur, so that stress-free homogeneous races can be produced. The advantages of the bearing according to the invention are as follows:-

1) At given axial deflection, a degree of radial rigidity is obtainable which results in a decrease in imbalancing forces;

2) Absorption of axial length variation of the system in the magnetic bearing is achieved thus removing the necessity for elaborate mechanical expedients;

3) Production of stress-free races, in particular when using rare earth cobalt alloy magnets;

4) Production of the races each from one piece, whereby high magnetic homogeneity and resulting low magnetic eccentricity is obtainable;

5. A permanently magnetic radial bearing substantially as hereinbefore described and illustrated in the accompanying drawing.

5) Higher obtainable energy density than with radially magnetised races;

6) Economical production.

The accompanying drawing schematically illustrates one embodiment of a permanently magnetic radial bearing according to the invention.

In the drawing two permanent magnet races 1, 2 are set concentrically one inside the other and are each magnetised in an axial direction 3, which is a preferred state of magnetisation. The inner race 2 is mounted on a non-magnetisable shaft 4 and the outer race 1 with the same direction of magnetisation is mounted on a housing 5. The stable equilibrium in the axial direction can be achieved with an end journal rigid bearing.

In order to allow axial relative displacements of the permanent magnet races 1, 2 without substantial decrease in radial rigidity, the inner race 2, or the outer race 1, is constructed with an axial length greater than the other (thus providing different heights of magnetisation).

Claims

1. A permanently magnetic radial bearing comprising two permanent magnet races which are disposed coaxially one inside the other and which repel each other radially due to magnetisation of the races in the same direction, which races are disposed rotatably relative to each other, characterised by the fact that the races (1,2) are magnetised axially in the same direction in the preferred state of magnetisation (3) and have different axial lengths.

2. A bearing according to Claim 1, wherein the axial length ratio of the races (1, 2) is about 1:2.5.

3. A bearing according to Claim 1 or Claim 2, wherein the races (1, 2) consist of a rare earth/cobalt permanently magnetic alloy.

4. A bearing according to any of Claims 1 to 3, wherein the inner race (2) is fixed to a rotatable shaft (4) of a gas ultracentrifuge consisting of non-magnetisabie material, and the outer race is attached non-movably to the housing (5).