Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal for a pipe – conduit – or cable
Reexamination Certificate
2001-05-24
2002-09-10
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal for a pipe, conduit, or cable
C277S614000, C277S644000, C277S647000, C277S314000
Reexamination Certificate
active
06446978
ABSTRACT:
FIELD OF INVENTION
The invention relates to a resilient seal. The invention pertains to pressure-energized resilient seals generally suitable for high pressure, high temperature gas applications in which virtually hermetic sealing may be accomplished, combined with the ability to maintain sealing efficiency while mating sealing members undergo separating deflections. Seals according to the present invention can be made so as to be suitable for sealing liquid/gas fuel rocket motor nozzles and cases, jet engine component interfaces, nuclear pressure vessels and high vacuum systems.
BACKGROUND OF INVENTION
Resilient metallic sealing rings of C-shaped cross-section are widely known and used in numerous applications where relatively low leakage rates are allowable. To obtain a hermetic seal in vacuum and high pressure gas applications, however, it has heretofore been the common practice to reinforce the sealing force developed by the seal upon compression by the use of additional components, such as internal helically-wound toroidal “garter” springs (see U.S. Pat. No. 2,819,920) reverse facing concentric layers (see U.S. Pat. No. 4,218,067) or “resilience control members” (see U.S. Pat. No. 4,946,174).
FIGS. 2A and 2B
depict a prior art C-shaped seals
1
and
2
. Compression of the cross section of these seals induces meridional bending stresses reaching a maximum value on the axis of symmetry of the cross-section, indicated by the line labeled A. As compression increases from initial contact to a nominal 20% of the seal free or original height, where the maximum sealing contact force consistent with safe operation is obtained, the area of the cross-section in which the stress has surpassed the yield stress gradually extends until it approaches a fully-soaked condition over nearly the entire cross-sectional area at line A. Because only a small area of the cross-section, if any, at line A remains in an elastic state, the degree of springback obtained when the compression force is removed is reduced. A different shape of C-seal is shown in U.S. Pat. No. 3,879,043, which discloses a C-shaped seal having inwardly turned ends. However, the shape of these ends make them subject to crushing, also causing a reduction in springback.
One commonly used reinforced C-shaped seal is that which employs a helically-wound, toroidal “garter” spring nested inside the C-shaped cross-section of the sealing ring. An advantage of this arrangement is that it reinforces the sealing contact stress, thereby reducing leakage by increasing deformation of the seal material or coating at the sealing interfaces. A disadvantage is that in high pressure applications, the stiffness of the toroidal spring must be sufficient to overcome the stiffness of the C-shaped shell, which in turn must be thick enough to resist severe deformation and rupture by the pressure to be contained. The result is a seal with very little more springback than the plain C-shaped seal which it replaces and one which undergoes severe and debilitating stress relaxation—reducing both sealing force and springback—especially at elevated operating temperatures.
The importance of springback and the maintenance of sealing load are paramount in elevated temperature sealing of relatively flexible pressure containment structures such as rocket motors and jet engines. At operating pressures and temperatures, the joints sealed by resilient metallic seals usually experience a widening of the distance between their sealing faces, due to the effects of pressure forces and a reduction in the modulii of elasticity of their materials. Pressure-energization of segmental toroidal shell sealing elements provides partial recovery of their pre-compressed (pre-installed) dimensions, thereby tending to maintain the required sealing force. In many cases, however, this is insufficient to expand the seal cross-section beyond its natural springback recovery to ensure continued sealing as separation increases.
SUMMARY OF INVENTION
In the background description above, it has been demonstrated that a need exists for low-leakage sealing rings with improved springback. The present invention addresses this need, in the form of a one-piece, integral sealing ring, with improved springback and sealing efficiency.
In one aspect, the invention provides a sealing ring, comprising an annular curved region having a generally C-shaped cross section and a pair of annular leg regions. A first bend connects one of said leg regions to the curved region, and a second bend connects the other of the leg regions to the curved region. Each said leg region has a free end and extends generally radially inward towards the inside of the C-shaped cross section.
In another aspect, the invention provides a sealing ring, comprising an annular curved region having a generally C-shaped cross section and a pair of annular leg regions extending from the C-shaped cross section generally radially inwards towards the inside of the C-shaped cross section. When the seal is compressed, an internal stress area exists in each leg region which has a stress greater than a maximum stress present in the curved region.
In yet another aspect, the invention provides a sealing ring, comprising an annular curved region having a generally C-shaped cross section, and a pair of generally frustro-conical spring members extending inwardly from said curved region. The spring members are adapted to contact each other and to provide a restoring force when the sealing ring is compressed.
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Halling Horace P.
Porter Paul L.
Baker & Hostetler LLP
Jetseal, Inc.
Knight Anthony
Peavey Enoch
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