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EP0182656A2
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EP
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Ferrofluid seal apparatus and method
Assignee: Ferrofluidics Corp
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Filing: 1985-11-20
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Granted: —
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Expires: 2005-11-20
Abstract
Abstract A ferrofluid exclusion seal apparatus comprises an annular permanent magnet (46) and at least one pole piece (42 or 44) one end (52) of which is shaped with a step (54) to form with the surface of the shaft (50) to be sealed a sealing gap (56) for ferrofluid and radial air gaps on either side to provide a defined magnetic flux gradient across the free surface or ferrofluid in the sealing gap (56), thereby providing a ferrofluid seal which has a static pressure which does not change with time. Instead of a central step (54) the pole piece may have a side step (88) (Fig. 9) or a tapered end design (Fig. 8) providing a sealing gap (66) and radial air gaps (62) on either side.
Inventors
- 👤 Kuldip Raj
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-07 21:24
CPC Classifications
F; F16; F16J; F16J15/00; F16J15/16; F16J15/40; F16J15/43
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
196 words
A ferrofluid exclusion seal apparatus comprising an annular permanent magnet to surround a rotary shaft element to be sealed and a first pole piece element having a one end and another end, one end in a magnetic flux relationship with the permanent magnet, and the other end to extend into a close, non-contacting relationship with the surface of a shaft element to be sealed characterized in that said other end of said first pole piece element has a step-like or tapered end means to provide a first radial sealing gap between the end means and the surface of the shaft element to retain a sealing amount of ferrofluid in the sealing gap by magnetic flux, and a second radial air gap between the other end of the end means and the surface of the shaft element, the second radial air gap lying on at least one side of the first radial sealing gap, the end means providing for a magnetic flux gradient across the free surface of ferrofluid retained within the sealing gap of about 10 4 gauss/cm or less to provide a ferrofluid seal which has a static pressure which does not change with time.
Claim 2
Dependent Claim
196 words
A ferrofluid exclusion seal apparatus comprising an annular permanent magnet to surround a rotary shaft element to be sealed and a first pole piece element having a one end and another end, one end in a magnetic flux relationship with the permanent magnet, and the other end to extend into a close, non-contacting relationship with the surface of a shaft element to be sealed characterized in that said other end of said first pole piece element has a step-like or tapered end means to provide a first radial sealing gap between the end means and the surface of the shaft element to retain a sealing amount of ferrofluid in the sealing gap by magnetic flux, and a second radial air gap between the other end of the end means and the surface of the shaft element, the second radial air gap lying on at least one side of the first radial sealing gap, the end means providing for a magnetic flux gradient across the free surface of ferrofluid retained within the sealing gap of about 10 4 gauss/cm or less to provide a ferrofluid seal which has a static pressure which does not change with time.
Claim 3
Dependent Claim
37 words
The seal apparatus of claim 1 including a rotary shaft element wherein the first radial sealing gap ranges from about 2 to 8 mils and the second radial air gap ranges from about 4 to 16 mils.
Claim 4
Dependent Claim
29 words
The seal apparatus of claim 1 including a rotary shaft element wherein the second radial air gap ranges from about 2 to 3 times the first radial sealing gap.
Claim 5
Dependent Claim
38 words
The seal apparatus of claim 1 including a rotary shaft element and ferrofluid in the first radial sealing gap wherein the magnetic flux gradient across the free surfaces of the ferrofluid is less than about 10 3 gauss/cm.
Claim 6
Dependent Claim
31 words
The seal apparatus of claim 1 including the rotary shaft element and ferrofluid in the first radial sealing gap wherein the amount of ferrofluid ranges from about 40 to 60 microlitres.
Claim 7
Dependent Claim
39 words
The seal apparatus of claim 1 including a rotary shaft element and ferrofluid in the first radial sealing gap wherein the static pressure capacity of the seal apparatus ranges from about to 2 psi for the first pole piece.
Claim 8
Dependent Claim
98 words
The seal apparatus of any preceding claim which further includes a second pole piece element having a one and another end, the one end lying in a magnetic flux relationship with the opposite end of the annular permanent magnet and the other end to extend or extending into a close, non-contacting relationship with the surface of the rotary shaft element to be sealed to form a radial gap therewith, whereby ferrofluid may be or is retained in the radial gap under the second pole piece element to provide a seal with the surface of the rotary shaft element.
Claim 9
Dependent Claim
60 words
The sealing apparatus of any preceding claim wherein the end means at the other end of said first pole piece element comprises a generally side or centrally extending step element to form a first radial sealing gap and second or second and third radial air gaps at said other end on one or either side of the radial sealing gap.
Claim 10
Dependent Claim
41 words
The seal apparatus of claim 8 wherein the step element comprises a generally rectangular step element and the second or second and third radial air gaps have a radial dimension from 2 to 3 times that of the radial sealing gap.
Claim 11
Dependent Claim
50 words
The seal apparatus of claim I to 7 wherein the end means at the other end of said first pole piece element comprises a trapezoidal-like shape tapered pole piece to define a radial sealing gap and a defined tapered radial air gap on either side of the radial sealing gap.
Claim 12
Dependent Claim
54 words
The seal apparatus of claim 9 or 10 wherein the first pole piece containing the side step element comprises a compound pole piece formed of a pole piece element which defines the side step element and another pole piece element secured thereto to form the side step portion of the side step pole piece.
Claim 13
Dependent Claim
35 words
The seal apparatus of any preceding claim wherein the pole piece element ranges from about 20 to 40 mils in thickness and the annular permanent magnet ranges from about 80 to 150 mils in thickness.
Claim 14
Independent Claim
98 words
A method of sealing a rotary shaft with a seal which does not change in pressure capacity with time comprising forming a radial sealing gap and a larger adjacent radial air gap at the one end of a magnetic pole piece with the surface of the rotary shaft to be sealed and retaining within the radial sealing gap a defined quantity of a sealing amount of ferrofluid to form an O-ring ferrofluid seal and maintaining a magnetic flux gradient across the free surfaces of the ferrofluid in the radial sealing gap of about 10 4 gauss/cm or less.
Claim 15
Independent Claim
98 words
A method of sealing a rotary shaft with a seal which does not change in pressure capacity with time comprising forming a radial sealing gap and a larger adjacent radial air gap at the one end of a magnetic pole piece with the surface of the rotary shaft to be sealed and retaining within the radial sealing gap a defined quantity of a sealing amount of ferrofluid to form an O-ring ferrofluid seal and maintaining a magnetic flux gradient across the free surfaces of the ferrofluid in the radial sealing gap of about 10 4 gauss/cm or less.
Claim 16
Dependent Claim
21 words
The method of claim 13 wherein the magnetic field in the radial sealing gap ranges from about 3,000 to 11,000 gauss.
References Cited (Backward Citations)
No citation records indexed.
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