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US 4,357,024 AGranted
Ferrofluid rotary-shaft seal apparatus and method
AssigneeFerrofluidics Corporation
InventorKuldip Raj
Life of this patent
Estimating the term…
Abstract
A ferrofluid rotary-shaft seal apparatus of extended seal life particularly adapted for use as an exclusion seal with a computer-disc-drive spindle, which seal apparatus comprises: an annular permanent magnet; first and second pole pieces, one end of each pole piece extending into a close, noncontacting relationship with the surface of the shaft, to form a gap width between the one end of the pole piece and the surface of the shaft; and ferrofluid in the gap widths to form a ferrofluid O-ring seal, whereby, in operation, the ferrofluid, under the thinner pole piece, evaporates and forms an air gap, while the ferrofluid at the wider gap width provides extended seal life.
Claims18
A ferrofluid-seal rotary-shaft system having an extended ferrofluid-seal life, which system comprises in combination:
- (a) a magnetically permeable, rotary-shaft element;
- and
- (b) a single-stage ferrofluid rotary-seal apparatus which comprises
- (i) an annular permanent magnet surrounding the shaft element and having poles of opposite polarity,
- (ii) first and second annular, magnetically permeable, pole-piece elements, the pole-piece elements at the one end in a magnetic fluid relationship with the permanent magnet, to form a closed, magnetic flux loop between the permanent magnet, the pole pieces and the shaft element, with the other end of the first and second pole pieces extending into a close, annular, noncontacting relationship with the shaft element, to form a radial gap between the other end of the first and second pole-piece elements and the surface of the shaft element,
- (iii) the first and second pole pieces further characterized by a generally L-shaped, sectional configuration, with a projection from the other end of the first and second pole pieces, the projection of the first and second pole pieces extending toward each other, to form an interstage gap therebetween,
- (iv) the first and second pole pieces further defining a ring-like air cavity between the first and second L-shaped pole pieces, the ring-like air cavity extending about the shaft element, and
- (v) a defined quantity of ferrofluid disposed and retained by magnetic flux both in the interstage gap and the adjacent radial gaps at the other end of the pole pieces, to form a single-stage, O-ring ferrofluidic seal about the shaft element, with the cavity substantially free of excess ferrofluid, whereby during operation the seal apparatus will operate sequentially as a single-stage seal, a two-O-ring seal under each radial gap, and a single-stage seal under one radial gap before seal failure,
- thereby providing a ferrofluid-seal-shaft system having an extended ferrofluid-seal life.
6 more elements
A ferrofluid-seal rotary-shaft system having an extended ferrofluid-seal life, which system comprises in combination:
- (a) a magnetically permeable, computer-disc-drive-spindle, rotary-shaft element;
- and
- (b) a single-stage ferrofluid rotary-seal apparatus which comprises
- (i) an annular permanent magnet surrounding the shaft element and having poles of opposite polarity,
- (ii) first and second annular, magnetically permeable, pole-piece elements, the pole-piece elements at the one end in a magnetic flux relationship with the permanent magnet, to form a closed, magnetic flux loop between the permanent magnet, the pole pieces and the shaft element, with the other end of the first and second pole pieces being an essentially flat surface and extending into a close, annular, noncontacting relationship with the shaft element, to form a radial gap between the other end of the first and second pole-piece elements and the surface of the shaft element,
- (iii) the first and second pole pieces further characterized by a generally L-shaped, sectional configuration, with a projection from the other end of the first and second pole pieces, the end of the projection being essentially a flat, generally parallel surface, the projection of the first and second pole pieces extending toward each other, to form an interstage gap therebetween,
- (iv) the first and second pole pieces further defining a ring-like air cavity between the first and second L-shaped pole pieces, the ring-like air cavity extending about the shaft element, and
- (v) a defined quantity of ferrofluid disposed and retained by magnetic flux both in the interstage gap and the adjacent radial gaps at the other end of the pole pieces, to form a single-stage, O-ring ferrofluidic seal about the shaft element, with the cavity substantially free of excess ferrofluid, whereby during operation the seal apparatus will operate sequentially as a single-stage seal, a two-O-ring seal under each radial gap, and a single-stage seal under one radial gap before seal failure,
- thereby providing a ferrofluid-seal-shaft system having an extended ferrofluid-seal life.
6 more elements
In a method for extending the ferrofluid-seal life of a ferrofluid-seal rotary-shaft system for sealing a magnetically permeable, rotary-shaft element, which method comprises:
- (a) surrounding the rotary-shaft element with an annular permanent magnet and having poles of opposite polarity at each end;
- (b) surrounding the rotary shaft with first and second magnetically permeable pole-piece elements having a one end and another end, the one end of the pole-piece elements in a magnetic flux relationship to the one and other ends of the permanent magnet;
- (c) extending the other end of each of the pole-piece elements into a close, noncontacting relationship with the surface of the rotary-shaft element, to form first and second radial gaps therebetween of defined width;
- and
- (d) retaining magnetically in the first and second gaps a ferrofluid, to form at least two liquid O-ring seals on the surface of the rotary-shaft element, the improvement which comprises
- (i) providing first and second pole pieces having projections at each end extending generally axially to the rotary-shaft element, the projections extending toward each other, to form an interstage gap therebetween, the pole pieces forming a generally empty air cavity therebetween, and
- (ii) retaining magnetically, in both the interstage gap and the adjacent radial gaps, a sealing amount of a ferrofluid, to form a single-stage, O-ring seal about the surface of the shaft element.
4 more elements
In a method for extending the ferrofluid-seal life of a ferrofluid-seal rotary-shaft system for sealing a magnetically permeable, rotary-shaft element, which method comprises:
- (a) surrounding the rotary-shaft element with an annular permanent magnet and having poles of opposite polarity at each end;
- (b) surrounding the rotary shaft with first and second magnetically permeable pole-piece elements having a one end and another end, the one end of the pole-piece elements in a magnetic flux relationship to the one and other ends of the permanent magnet;
- (c) extending the other end of each of the pole-piece elements into a close, noncontacting relationship with the surface of the rotary-shaft element, to form first and second radial gaps therebetween of defined width;
- and
- (d) retaining magnetically in the first and second gaps a ferrofluid, to form at least two liquid O-ring seals on the surface of the rotary-shaft element, the improvement which comprises
- (i) providing first and second pole pieces having a generally L-shaped, cross-sectional configuration and having projections at each end extending generally axially to the rotary-shaft element, the projections extending toward each other and the ends of the projections of each pole piece being flat and parallel to each other, to form an interstage gap therebetween which ranges from 10 to 30 mils, the other end of the magnetic pole pieces forming the radial gap being generally flat and parallel to the surface of the rotary-shaft element, the pole pieces forming a generally empty air cavity therebetween, and
- (ii) retaining magnetically, in both the interstage gap and the adjacent radial gaps, a sealing amount of a ferrofluid, to form a single-stage, O-ring seal about the surface of the shaft element.
4 more elements
Dependencies are inferred from the claim text.