GB2124033A

GB2124033A - Permanent magnet

Info

Publication number: GB2124033A
Application number: GB08229706A
Authority: GB
Inventors: George J Hoffman
Original assignee: Litton Systems Inc
Current assignee: Northrop Grumman Guidance and Electronics Co Inc
Priority date: 1979-07-30
Filing date: 1982-10-18
Publication date: 1984-02-08
Also published as: GB2058953B; GB2058953A; DE3028454A1; FR2467318B1; IT1128663B; JPS5642722A; FR2467318A1; GB2124033B; IT8049355A0; CA1149852A; IL60597A0

Abstract

There is disclosed a permanent magnet 10 having a cylindrical bore 20. The permanent magnet is composed of a plurality of axial slices 10a to 10h which have radially directed contact faces and which are magnetised individually & assembled in such a way that the outer surface of the permanent magnet is of one polarity and the inner surface, which forms the entire inner surface of the cylindrical bore 20, is of an opposite polarity. <IMAGE>

Description

1

GB 2124033A 1

SPECIFICATION Permanent magnet

5 This invention relates to a permanent magnet comprising a permanent magnetic structure having a circularly cylindrical bore therethrough.

According to one aspect of the invention 10 there is provided a permanent magnet comprising a permanent magnetic structure having a circularly cylindrical bore therethrough, said bore having an axis of symmetry, and in which:

15 the structure is divided circumferentially of said bore into a plurality of substantially contacting circumferential portions each having an inner surface which forms a part of the cylindrical surface of said bore;

20 and all of said portions are magnetised along their entire length and throughout the entire inner surfaces thereof with their internal magnetisations identically poled in a radial direction relative to said axis to cause substan-25 tially the entire surface of said bore to become identically poled magnetic pole faces of said portions.

According to a further aspect of the invention there is provided a process for fabricating 30 a permanent magnet structure having a circularly cylindrical bore having the same polarity of internal magnetisation, along the entire lengths and around the entire circumference of said bore, directed radially relative to the 35 axis of said bore to produce the same pole face over substantially the entire surface of the bore and comprising:

fabricating slices of said structure having radially directed contact surfaces; 40 magnetising each slice by placing it in an electromagnetic field which is directed perpendicular to the surface of the portion of the bore on that slice, with the polarity the same for each slice;

45 and assembling the magnetised slices into contact on their radially directed surfaces to form said structure.

For a better understanding of the invention, and to show how the same may be carried 50 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 ferro-fluid bearing incorporating a permanent mag-55 net structure according to the invention;

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 60 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 cylin-65 der.

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 70 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 12 and a space containing ferro-fluid 14 therebetween. 75 The ferro-fluid 14 serves as a lubricant between the shaft 12 and the surface 18 (Fig. 3) of the bore 20.

The structure 10 and shaft 12 may rotate relative to each other, but it is not important 80 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 16 and the inner surface 18 thereof (Fig. 3). Such polarity configura-85 tion 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 90 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, 95 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 100 ends of the bore 20. To reduce power loss due to viscous damping, the diameter of the shaft 12 optionally may be reduced near the centre of the bore 20 in the region 22.

To magnetize cylindrical member 10, the 105 member 10 is axially sliced into slices 10a, 10b, 10c, 10d, 10e, 10f, 10g, 10h, and disassembled for magnetizing. Alternatively, the slices 10a, 10b, 10c, 10d, 10e, 10f, 10g and 10h, may be fabricated into the shape 110 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, 10b, 10c, 10d, 10e, 10f, 10g, 10h have been magnetized, they are assembled or 115 reassembled into the cylinder shown in Figs. 1 and 2.

To magnetize the slices they are placed in the field of an electromagnet which induces a permanent magnetism into the slice 10a with 120 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 125 energized, for example, from a DC energy source 32.

The described bearing, because of its radially directed internal magnetization, is a simplified bearing which adequately confines the 130 ferro-fluid without leaking.

2

GB2124033A 2

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 5 limited by that description alone, but only together with the accompanying claims.

The preferred materials from which the slices of the permanent magnet structure (bearing structure 10) are made are platinum 10 cobalt alloy or rare earth cobalt alloys such as samarium cobalt alloys.

Claims

1. A permanent magnet comprising a per-15 manent magnetic structure having a circularly cylindrical bore therethrough, said bore having an axis of symmetry, and in which:

the structure is divided circumferentially of said bore into a plurality of substantially con-20 tacting circumferential portions each having an inner surface which forms a part of the cylindrical surface of said bore;

and all of said portions are magnetised along their entire length and throughout the 25 entire inner surfaces thereof with their internal magnetisations identically poled in a radial direction relative to said axis to cause substantially the entire surface of said bore to become identically poled magnetic pole faces of said 30 portions.

2. A permanent magnet according to claim 1, in which the portions of said structure are divided substantially by planes defined by radii from said axis and by said axis.

35

3. A permanent magnet according to claim 1 or 2, in which the outer surface of said magnetic structure is substantially circularly cylindrical.

4. A permanent magnet according to 40 claim 3, in which said outer and inner surfaces are substantially concentric about said axis, and the internal magnetisations of said portions are identically poled and radial of said axis to cause the entire inner cylindrical

45 surface of said structure to be a different polarity magnetic pole piece of said magnet than the magnetic polarity of said outer cylindrical surface.

5. A permanent magnet according to any 50 one of claims 1 to 4, in which the portions of said structure are made of platinum cobalt alloy, rare earth cobalt alloys, or samarium cobalt alloys.

6. A process for fabricating a permanent magnet structure having a circularly cylindri-85 cal bore having the same polarity of internal magnetisation, along the entire length and around the entire circumference of said bore, directed radially relative to the axis of said bore to produce the same pole face over 90 substantially the entire surface of the bore and comprising:

fabricating slices of said structure having radially directed contact surfaces;

magnetising each slice by placing it in an 95 electromagnetic field which is directed perpendicular to the surface of the portion of the bore on that slice, with the polarity the same for each slice;

and assembling the magnetised slices into 100 contact on their radially directed surfaces to form said structure.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd.—1984.

Published at The Patent Office, 25 Southampton Buildings,

London, WC2A 1AY, from which copies may be obtained.

6. A process for fabricating a permanent 55 magnet structure having a circularly cylindrical bore having the same polarity of internal magnetisation, along the entire lengths and around the entire circumference of said bore, directed radially relative to the axis of said

60 bore to produce the same pole face over substantially the entire surface of the bore and comprising:

fabricating slices of said structure having radially directed contact surfaces; 65 magnetising each slice by placing it in an electromagnetic field which is directed perpendicular to the surface of the portion of the bore on that slice, with the polarity the same for each slice;

70 and assembling the magnetised slices into contact on their radially directed surfaces to form said structure.

7. A process according to claim 6, in which the slices are formed by slicing the

75 bearing structure along planes defined by radii and the axis of the bore.

8. A process according to claim 6, in which the slices are formed individually by casting, forging or powder metallurgy tech-

80 niques.

CLAIMS (27 Jul 1983)