Magnetic fluid sealing device

• US 5,826,885 A
• Filed: 10/02/1996
• Issued: 10/27/1998
• Est. Priority Date: 10/02/1996
• Status: Expired due to Term

• Current Assignee: Rigaku/USA, Inc.
• Original Assignee: Rigaku/USA, Inc.
• Inventors: Helgeland, Walter
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Beres, John L.
• Application Number:
  US08/720,634
• Time in Patent Office: 755 Days
• Field of Search: 277/1, 277/80, 277/235, 277/22
• US Class Current: 277/302
• CPC Class Codes: F16J 15/162 Special parts or details relating to lubrication or cooling of the sealing itself F16J15/324, F16J15/3404, F16J15/40 take precedence
• CPC Class Codes: F16J 15/43 kept in sealing position by magnetic force

Abstract

A magnetic fluid sealing device adapted to enable rotary motion to be coupled by a shaft between an ambient high pressure environment to a high temperature, low pressure environment. Gaps in the shaft are dynamically sealed by a magnetic seal which uses a thin walled pole piece, a high power magnet and magnetic fluid. The pole piece and an extension thereof form a vacuum envelope for the remainder of the device, eliminating the need for the usual O-ring static seals.

Claims

1. A magnetic fluid sealing device comprising:

a) a housing;

b) an axially extending shaft rotatably mounted in said housing and wherein one end of the shaft is adapted to be disposed at a low pressure environment and another end at a high pressure environment;

c) a pole piece and magnets radially encircling said shaft;

d) a magnetic fluid seal enclosing said shaft for magnetic sealing of any gaps between the shaft and the pole piece;

e) a mounting means nearest the low pressure environment for mounting the device to a fixture, and wherein an integral section of the pole piece extends to the mounting means coaxially of the shaft forming with the pole piece a static vacum tight envelope between the low pressure environment and the high pressure environment, except for said gaps which are sealed by said magnetic seal.

2. The device of claim 1 wherein the housing is in thermal contact with the pole piece and forms a heat sink for the exchange of heat to the ambient atmosphere.

3. The device of claim 1, wherein the mounting means is a flange, and the section is a thin walled tubular portion of the pole piece which forms a first thermal resistance between the flange and the seal.

4. The device of claim 1 wherein a portion of the shaft adjacent the seal comprises an outer tubular member of steel and an inner core of aluminum to provide a first thermal shunt between the ends of the shaft.

5. The device of claim 1, wherein the pole piece has a thin wall section radially disposed between the shaft and the magnets, the section being sufficiently strong to support the pressure difference between the low pressure atmosphere and the high pressure atmosphere, but sufficiently thin to become magnetically saturated by the magnets.

6. The device of claim 1, wherein a first portion of the shaft nearest the low pressure environment is formed of magnetic stainless steel, and a second portion of the shaft nearest the high pressure environment is formed of solid carbon steel.

7. The device of claim 6, wherein the shaft is cantilevered from, and rotatably supported by, cross-roller bearings disposed near the high pressure environment.

8. The device of claim 3, wherein the housing is formed of two portions of aluminum, a first portion nearest the low pressure environment in thermal contact with the magnets and pole piece to provide thermal conductivity between them, and a second portion enclosing the bearings.

9. A magnetic fluid sealing device comprising:

a) a housing;

b) a shaft rotatably mounted in said housing;

c) at least two permanent magnets mounted in said housing coaxially of said shaft;

d) a pole piece disposed coaxially between said magnets with a thin walled section of the pole piece radially separating the magnets from the shaft; and

e) an integral extension of the pole piece forming, with the pole piece, a vacuum tight static envelope between a low pressure and a high pressure environment.

10. The device of claim 9, including a mounting means external to the housing nearest the low pressure environment, and wherein the pole piece extension extends to and is in thermal contact with said mounting means.

11. A method of forming a rotary shaft and a seal for the rotary shaft, the shaft being formed of first and second ends axially extending between a low pressure, high temperature atmosphere and a high pressure ambient temperature atmosphere further comprising the steps of:

a) forming a magnetic seal about an axial extension of the shaft using a pair of magnets spaced apart by a magnetic pole structure;

b) extending the magnetic pole structure coaxial to the shaft on a low pressure side thereof to form a vacum envelope radially about the shaft between the low and high pressure atmospheres.

12. The method of claim 11 including forming a portion of the shaft adjacent the seal of an outer tubular member of steel and an inner core of aluminum to provide a first thermal shunt between the ends of the shaft.

13. The method of claim 11, wherein the pole structure is formed with an integral thin wall section and radially disposing the section between the shaft and the magnets, the section being sufficiently strong to support the pressure difference between the low pressure atmosphere and the high pressure atmosphere, but sufficiently thin to become magnetically saturated by the magnets.

14. The method of claim 11, including the step of forming a first portion of the shaft nearest the low pressure atmosphere of magnetic stainless steel, and forming a second portion of the shaft nearest the high pressure of solid carbon steel.

15. The method of claim 11, wherein a housing formed of two portions of aluminum is provided to house the shaft and seal, and wherein a first portion of the housing nearest the low pressure atmosphere is placed in thermal contact with the magnets and pole structure to provide a heat sink for thermal conduction from the high temperature atmosphere to the low temperature atmosphere, and a second portion encloses bearings which support the shaft.

16. A method of forming a seal for a rotary shaft having first and second ends and axially extending between a low pressure, high temperature atmosphere and a high pressure ambient temperature atmosphere comprising the steps of:

a) forming a magnetic seal about radial gaps provided between the shaft using magnetic energy provided by magnets axially spaced apart by a magnetic pole structure and coaxial to said shaft;

b) extending the magnetic pole structure coaxial to the shaft on a low pressure side thereof to form a vacum envelope radially about the shaft between the low and high pressure atmospheres; and

c) forming the shaft in sections, one of which is adjacent the magnetic seal and includes a core of aluminum.

17. The method of claim 16, wherein the pole structure is formed with a thin wall section and radially disposing the section between the shaft and the magnets, the section being sufficiently strong to support the pressure difference between the low pressure atmosphere and the high pressure atmosphere, but sufficiently thin to become magnetically saturated by the magnets.

18. A magnetic fluid sealing device comprising:

a) a housing adapted to be disposed between a low pressure environment and a high pressure environment;

b) an axially extending shaft rotatably mounted in said housing and wherein one end of the shaft is adapted to be disposed at the low pressure environment and another end at the high pressure environment;

c) a pole piece and magnets radially encircling said shaft;

d) a magnetic fluid seal enclosing said shaft for magnetic sealing of any gaps between the shaft and the pole piece; and

e) a flange nearest the low pressure environment for mounting the device to a fixture, and wherein a section of the pole piece extends to the mounting means coaxially of the shaft forming with the pole piece a static vacuum tight envelope between the low pressure environment and the high pressure environment, except for said gaps which are sealed by said magnetic seal;

and wherein the section is a thin walled tubular portion of the pole piece which forms a first thermal resistance between the flange and the seal; and

wherein the housing is formed of two portions of aluminum, a first portion nearest the low pressure environment in thermal contact with the magnets and pole piece and a second enclosing the bearings; and

including an intermediate shaft portion extending from the first portion of the housing to the flange and having a tubular core of thermally insulated material.

19. The device of claim 18, wherein the tubular section of the pole piece extends outside the housing coaxial to the intermediate shaft portion.

20. A magnetic fluid sealing device comprising:

a) a housing adapted to be disposed between a low pressure environment and a high pressure environment;

b) a shaft rotatably mounted in said housing;

c) at least two permanent magnets mounted in said housing coaxially of each other and said shaft;

d) a pole piece disposed coaxially between said magnets with a thin walled section of the pole piece radially separating the magnets from the shaft;

e) an extension of the pole piece forming, with the pole piece, a vacuum tight static envelope between the low and high pressure environment; and

f) a mounting means external to the housing nearest the low pressure environment, and wherein the pole piece extension extends to and is in thermal contact with said mounting means;

and wherein the shaft is formed of four sections, a first section closest to the low pressure environment of magnetic metal, a second section axially adjacent the first section having a high thermally insulative axially extending interior, a third section radially adjacent the magnets having a high thermally conductive axially extending interior and a fourth section having a solid core of highly thermally conductive metal extending beyond the housing into the high pressure environment.

21. A method of forming a seal for a rotary shaft having first and second ends and axially extending between a low pressure, high temperature atmosphere and a high pressure ambient temperature atmosphere comprising the steps of:

a) forming a magnetic seal about an axial extension of the shaft using a pair of magnets spaced apart by a magnetic pole structure;

b) extending the magnetic pole structure coaxial to the shaft on a low pressure side thereof to form a vacum envelope radially about the shaft between the low and high pressure atmospheres;

and wherein a housing formed of two portions of aluminum is provided to house the shaft and seal, and wherein a first portion of the housing nearest the low pressure atmosphere is placed in thermal contact with the magnets and pole structure, and a second portion encloses bearings which support the shaft, including forming an intermediate shaft portion extending from the first portion of the housing to a flange with a tubular core of thermally insulated material.

22. The method of claim 21, including extending a tubular section of the pole structure outside the housing coaxial to the intermediate shaft portion.