GB2058953A

GB2058953A - A magnetic fluid bearing

Info

Publication number: GB2058953A
Application number: GB8024332A
Authority: GB
Original assignee: Litton Systems Inc
Current assignee: Northrop Grumman Guidance and Electronics Co Inc
Priority date: 1979-07-30
Filing date: 1980-07-24
Publication date: 1981-04-15
Also published as: GB2124033B; DE3028454A1; FR2467318B1; FR2467318A1; IT1128663B; GB2058953B; JPS5642722A; IT8049355A0; GB2124033A; IL60597A0; CA1149852A

Abstract

A bearing is disclosed having a bearing member (10), with a cylindrical bore (20), and a shaft (12) in the bore, a magnetic fluid (14) being between the shaft and the bore walls. In order to retain the magnetic fluid in a simple manner, the member (10) is a permanent magnet which is magnetized with its internal magnetization radially directed relative to the axis of the bore. The shaft (12) may be of, or be covered with, ferro-magnetic material. The member (10) can conveniently be made in segments each of which is magnetized radially of the bore. <IMAGE>

Description

SPECIFICATION Ferro-fluid bearings This invention relates to ferro-fluid bearings.

In recent years, bearings have been disclosed having self-contained fluid pools. Such fluidic, low friction, self-contained bearings are made possible by the development of magnetically responsive magnetizable fluid given the name ferro-fluid by its developer, Dr. Ronald E. Rosensweig. Ferrofluid is described in Rosensweig's "Progress in Ferrohydrodynamics", Industrial Research, October, 1970, Vol. 12, No. 10, 36-40. Ferro-fluid as defined herein is a dispersion of colloidal magnetic particles in a liquid carrier. These particles tend to align themselves with applied magnetic fields. It should be noted from the description of ferro-fluid that ferrofluid need not necessarily contain iron or ferrous-type metal. It is only necessary, for a fluid to be socalled, that the fluid be magnetizable or capable of being influenced by magetic fields.The term "magnetic fluid" is used interchangeably herein with the term "ferro-fluid".

Bearings using ferro-fluid concentrate magnetic field at particular axial positions along the shaft of the bearing to produce a seal for the ferro-fluid. Typically, vanes, or the like, are used to distribute ferro-fluid on the bearing surface to maintain a sufficient fluid thickness to support or lubricate the bearing.

According to one aspect of the invention, there is provided a ferro4luid bearing comprising: a bearing structure having radially directed internal magnetization; a ferromagnetic shaft positioned within said bearing structure; and a ferro-fluid between said bearing structure and said shaft.

According to a second aspect of the invention, there is provided a ferro-fluid bearing comprising two relatively rotatable bearing members having opposed bearing surfaces defining between them an annular gap containing ferro-fluid, the bearing surface of a first of the members being defined by ferromagnetic material and the second member being magnetized radially of the axis of rotation of the bearing so that there exists at substantially all regions of its bearing surface in said gap a pole face providing magnetic lines of force in the gap which have a radial component.

A preferred embodiment is a ferro-fluid bearing which uses a magnetic sleeve as a bearing for a shaft, the magnetic sleeve being a permanent magnet which produces a magnetic field, having both radial and axial components, between the bearing and the shaft.

The axial components are directed inwardly toward the centre of the bearing, and ferrofluid is held within the bearing gap between magnet and shaft. The opposing surfaces of the shaft and bearing may be contoured or smooth at the option of the designer.

To produce the desired magnetic field configuration, the bearing sleeve is magnetized with the pole faces on the outer and inner surfaces of the sleeve instead of the usual practice of placing the poles on the ends of a cylinder. The internal magnetization of the sleeve is radially directed.

To produce a cylindrical sleeve having a high intensity magnetic field in a small volume and having the pole faces on the outer and inner surfaces, the sleeve may be made of platinum cobalt alloy or rare earth cobalt alloys such as samarium cobalt alloys. Other permanent magnet materials may be used, however, at considerably lower flux fields.

The sleeve is either prefabricated in axial slices or is cut into axial slices. The slices are each magnetized by placing them into an electromagnetic field which is poled to induce permanent magnet pole positions on the outer and inner surface of the slices. The slices are then assembled or reassembled into a cylindrical sleeve.

The shaft may be completely or partially ferro-magnetic. In a typical embodiment, the shaft may have a thin layer of ferromagnetic material on its outer surface. The ferromagnetic material of the shaft enhances the operation by the increase in magnetic field intensity within the region between the shaft and bearing.

According to a third aspect of the invention, there is provided a permanent magnet, suitable for the second bearing member according to the second aspect, the magnet comprising a ferromagnetic structure having a circularly cylindrical bore therethrough and being divided circumferentially of said bore into a plurality of circumferential segments each having an inner surface which is a circumferential segment of the cylindrical surface of said bore, each said segment having been magnetized with an internal magnetization in 3 radial direction relative to said axis to cause said circumferential segments of said bore to be identically poled magnetic pole faces of said segments.

According to a fourth aspect of the invention, there is provided a process of fabricating a permanent magnet according to the third aspect, comprising: fabricating segments of a cylindrical structure having an axial bore; magnetizing each segment by placing it in an electromagnetic field which is directed perpendicularly to that surface of the segment which is to form a part of said bore; and assembling said magnetized segments into said cylindrical structure with said surfaces of the segments defining said bore.

According to a fifth aspect, there is provided a process of fabricating a circularly cylindrical, magnetized, bearing structure having a circularly cylindrical bore which is adapted to receive a shaft comprising: slicing the bearing structure in planes defined by radii and the axis of said bore; magnetizing each slice by placing it in an electromagnetic field which is directed perpendicular to the surface of that portion of the bearing bore which is on that slice; and reassembling said magnetized slices into said bearing structure.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 is a perspective view of a ferrofluid bearing; Figure 2 is an end view of the bearing of Fig. 1; Figure 3 is a sectional view taken on the line 3-3 in Fig. 2 and showing the magnetic field; and Figure 4 is a perspective view of an electromagnet magnetizing an axial slice of a cylindrical sleeve to produce pole faces on the inner and outer surface of an assembled cylinder.

The figures illustrate a ferro-fluid bearing having a permanent magnet bearing structure 10 which in this example has a generally circularly cylindrical shape. The bearing is not limited, however, to a circular shape. The structure 10 is shown as a right circular cylinder having a coaxial right circular cylindrical- bore therein receiving a shaft 1 2 and a space containing ferro-fluid 14 therebetween.

The ferro-fluid 14 serves as a lubricant between the shaft 1 2 and the surface 1 8 (Fig.

3) of the bore 20.

The structure 10 and shaft 1 2 may rotate relative to each other, but it is not important which rotates. Both may rotate if desired.

The structure 10 is magnetized with a polarity configuration wherein the pole faces are on the outer surface 1 6 and the inner surface 1 8 thereof (Fig 3). Such polarity configuration produces a magnetic field having both radial and axial components within the ferro-fluid 14, and the axial components are directed toward the centre of the bearing bore 20. The magnetic field is indicated at 24 in Fig. 30.

The magnetic field holds the ferro-fluid 14 within the bore 20.

The shaft 12 may be of ferromagnetic material which enhances the magnetic field intensity in the ferro-fluid 14. It need not, however, be of such ferromagnetic material. In one preferred embodiment, only the surface of the shaft is covered with ferromagnetic material.

Most of the bearing support occurs near the ends of the bore 20. To reduce power loss due to viscous damping, the diameter of the shaft 1 2 optionally may be reduced near the centre of the bore 20 in the region 22.

To magnetize cylindrical member 10, the member 10 is axially sliced into slices 1 Oa, 10b, 10c, lOd, 10e, 10f, 10g, 10h, and disassembled for magnetizing. Alternatively, the slices 10a, 10b, 1 or, 1 Od, 1 owe, 1 Of, 1 0g, and 1 Oh, may be fabricated into the shape shown in Fig. 4. For example, the slices may be cast or forged, or they may be made by powder metallurgy techniques.After the slices 10a, lOb, 1 or, 10d, 10e, 1 Of, 109, 10h have been magnetized, they are assembled or reassembled into the cylinder shown in Fig. 1 and 2.

To magnetize the slices they are placed in the field of an electromagnet which induces a permanent magnetism into the slice 1 Oa with the pole faces on the inner and outer surfaces 28 and 29. The electromagnet 30 is shown with one coil turn, but obviously it may include many more turns to produce the required field intensity. The electromagnet 30 is energized, for example, for a DC energy source 32.

The described bearing, because of its radially directed internal magnetization, is a simplified bearing which adequately confines the ferro-fluid without leaking.

Although a description of a typical bearing and a corresponding fabrication process are shown in the Figures and described above, it is not intended that the invention shall be limited by that description alone, but only together with the accompanying claims.

Claims

1. A ferro-fluid bearing comprising: a bearing structure having radially directed internal magnetization; a ferromagnetic shaft positioned within said bearing structure; and a ferro-liquid between said bearing structure and said shaft.

2. A ferro-fluid bearing comprising two relatively rotatable bearing members having opposed bearing surfaces defining between them an annular gap containing ferro-fluid, the bearing surface of a first of the member being defined by ferromagnetic material and the second member being magnetized radially of the axis of rotation of the bearing so that there exists at substantially all regions of its bearing surface in said gap a pole face providing magnetic lines of force in the gap which have a radial component.

3. A bearing according to claim 2, wherein the first member is a shaft extending with the second member.

4. A bearing according to claim 2 or 3, wherein the second member is a bearing structure of annular cross-section and having radially directed magnetization.

5. A bearing according to claim 4 in which said bearing structure is in the shape of a right circular cylinder having a right circular cylindrical bore.

6. A bearing according to claim 4 or 5, in which said bearing structure is magnetized with one of the pole faces on the radially outer surface of said structure and the other pole face on the radially inner surface of said structure.

7. A bearing according to claim 4, 5 or 6, wherein the second member is composed of a plurality of axially extending segments each having a surface portion constituting part of the bearing surface of the second member.

8. A bearing according to any one of claims 2 to 7, wherein the second member is of permanently magnetized material.

9. A bearing according to claim 8, in which said second member is fabricated of platinum cobalt alloy.

1 0. A bearing according to claim 8, in which said second member is fabricated of rare earth cobalt alloys.

11. A bearing according to claim 10, in which said second member is fabricated of samarium cobalt alloys.

1 2. A permanent magnet, suitable as the second bearing member of a bearing according to any one of claims 2 to 11, the magnet comprising a ferromagnetic structure having a circularly cylindrical bore therethrough and being divided circumferentially of said bore into a plurality of circumferential segments each having an inner surface which is a circumferential segment of the cylindrical surface of said bore, each said segment having been magnetized with an internal magnetization in a radial direction relative to said axis to cause said circumferential segments of said bore to be identically poled magnetic pole faces of said segments.

1 3. A permanent magnet according to claim 12, wherein said structure is divided between said segments substantially in radial planes containing the axis of the bore.

1 4. A permanent magnet according to claim 1 2 or 13, wherein the outer surface of said ferromagnetic structure is circularly cylindrical.

15. A permanent magnet according to claim 1 2, 1 3 or 14, wherein the radially outer and inner surfaces of the structure are concentric about the axis of the bore, and the internal magnetization of each of said segments is radial of said axis to cause said inner and outer cylindrical surfaces of said structure to be the pole faces of said magnet.

1 6. A process of fabricating a permanent magnet according to claim 1 2 comprising: fabricating segments of a cylindrical structure having an axial bore; magnetizing each segment by placing it in an electromagnetic field which is directed perpendicularly to that surface of the segment which is to form a part of said bore; and assembling said magnetized segments into said cylindrical structure with said surfaces of the segments defining said bore.

1 7. A process of fabricating a circularly cylindrical, magnetized, bearing structure having a circularly cylindrical bore which is adapted to receive a shaft comprising: slicing the bearing structure in planes defined by radii and the axis of said bore: magnetizing each slice by placing it in an electromagnetic field which is directed perpendicular to the surface of that portion of the bearing bore which is on that slice; and reassembling said magnetized slices into said bearing structure.

18. A ferro-fluid bearing substantially as hereinbefore described with reference to the accompanying drawing.

19. A permanent magnet-bearing structure substantially as hereinbefore described with reference to the accompanying drawing.

20. A process of fabricating the bearing structure of claim 19, substantially as hereinbefore described with reference to the accompanying drawing.