Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
2001-04-12
2004-07-27
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C277S559000
Reexamination Certificate
active
06767016
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to seals that interact with lubricant during rotation of a relatively rotatable surface to wedge a film of lubricant into the interface between the seal and the relatively rotatable surface to reduce wear. More specifically, the present invention concerns the provision of static and dynamic sealing lips in a hydrodynamic seal that controls interfacial contact pressure within the dynamic sealing interface for efficient hydrodynamic lubrication and environmental exclusion while permitting relatively high initial compression and relatively low torque.
FIG. 1
of this specification represents a commercial embodiment of the prior art of U.S. Pat. No. 4,610,319, and
FIG. 1A
represents a commercial embodiment of the prior art of U.S. Pat. No. 5,678,829. These figures are discussed herein to enhance the readers' understanding of the distinction between prior art hydrodynamic seals and the present invention. The lubrication and exclusion principles of
FIG. 1
are also used in the prior art seals of U.S. Pat. Nos. 5,230,520, 5,738,358, 5,873,576, 6,036,192, 6,109,618 and 6,120,036, which are commonly assigned herewith. The aforementioned patents pertain to various seal products of Kalsi Engineering, Inc. of Sugar Land, Tex. that are known in the industry by the registered trademark “Kalsi Seals”, and are employed in diverse rotary applications to provide lubricant retention and contaminant exclusion in harsh environments.
Referring now to
FIG. 1
, the seal incorporates a seal body
18
that is solid and generally ring-like, and defines a lubricant end
20
and an environment end
22
. The seal incorporates a dynamic sealing lip
24
defining a dynamic sealing surface
26
and also defining a exclusionary geometry
28
which may be abrupt, and which is for providing environmental exclusion.
The dynamic sealing lip
24
has an angulated flank
30
having intersection with the seal body at lip termination point
32
. Angulated flank
30
is non-circular, and forms a wave pattern about the circumference of the seal, causing dynamic sealing surface
26
to vary in width.
Hydrodynamic inlet radius
38
is a longitudinally oriented radius that is the same size everywhere around the circumference of the seal, and is tangent to dynamic sealing surface
26
and angulated flank
30
. Since hydrodynamic inlet radius
38
is tangent to angulated flank
30
, it also varies in position about the circumference of the seal in a wavy manner. Angulated flank
30
defines a flank angle
40
that remains constant about the circumference of the seal. The tangency location
42
between hydrodynamic inlet radius
38
and dynamic sealing surface
26
is illustrated with a dashed line.
When installed, the seal is located within a housing groove and compressed against a relatively rotatable surface to establish sealing contact therewith, and is used to retain a lubricant and to exclude an environment. When relative rotation occurs, the seal remains stationary with respect to the housing groove, maintaining a static sealing relationship therewith, while the interface between the dynamic sealing lip
24
and the mating relatively rotatable surface becomes a dynamic sealing interface. The lubricant side of dynamic sealing lip
24
develops a converging relationship with the relatively rotatable surface a result of the compressed shape of hydrodynamic inlet radius
38
.
In response to relative rotation between the seal and the relatively rotatable surface, the dynamic sealing lip
24
generates a hydrodynamic wedging action that introduces a lubricant film between dynamic sealing lip
24
and the relatively rotatable surface.
The compression of the seal against a relatively rotatable surface results in compressive interfacial contact pressure that is determined primarily by the modulus of the material the seal is made from, the amount of compression, and the shape of the seal. The magnitude and distribution of the interfacial contact pressure is one of the most important factors relating to hydrodynamic and exclusionary performance of the seal.
The prior art seals are best suited for applications where the pressure of the lubricant is higher than the pressure of the environment. Owing to the complimentary shapes of the seal environment end
22
and the mating environment-side gland wall, the seal is well supported by the environment-side gland wall in a manner that resists distortion and extrusion of the seal when the pressure of the lubricant is higher than the pressure of environment.
If the pressure of the environment is substantially higher than the pressure of the lubricant, the resulting differential pressure-induced hydrostatic force can severely distort body
18
, hydrodynamic inlet radius
38
and exclusionary geometry
28
. The hydrostatic force presses body
18
against the lubricant-side gland wall, and can cause body
18
to twist and deform such that angulated flank
30
and hydrodynamic inlet radius
38
are substantially flattened against the relatively rotatable surface. Such distortion and flatting can inhibit or eliminate the intended hydrodynamic lubrication, resulting in premature seal wear because the gently converging relationship between dynamic sealing lip
24
and the relatively rotatable surface (which is necessary for hydrodynamic lubrication) can be eliminated. Such distortion can also cause exclusionary geometry
28
to distort to a non-circular configuration and may also cause portions of dynamic sealing surface
26
to lift away from the relatively rotatable surface, producing a low convergence angle between dynamic sealing surface
26
and the relatively rotatable surface on the environment edge, and causing the exclusionary geometry
28
to become non-circular and skewed relative to rotational velocity V. Such distorted geometry is eminently suitable for the generation of a hydrodynamic wedging action in response to relative rotation of the relatively rotatable surface. Such wedging action can force environmental contaminants into the sealing interface and cause rapid wear.
To effectively exclude a highly pressurized environment, one must use a pair of oppositely-facing prior art hydrodynamic seals; one to serve as a partition between the lubricant and the environment, and the other to retain the lubricant, which must be maintained at a pressure equal to or higher than the environment. This scheme ensures that neither seal is exposed to a high differential pressure acting from the wrong side, but requires a mechanism to maintain the lubricant pressure at or above the environment pressure. For example, see the sealed chambers of the artificial lift pump rod seal cartridge of U.S. Pat. No. 5,823,541, and see the first pressure stage of the drilling swivel of U.S. Pat. No. 6,007,105.
Many applications, such as the oilfield drilling swivel, the progressing cavity artificial lift pump, centrifugal pumps, and rotary mining equipment would benefit significantly from a hydrodynamic rotary seal having the ability to operate under conditions where the environment pressure is higher than the lubricant pressure. The resulting assemblies would avoid the complexity and expense associated with using pairs of seals having lubricant pressurization there-between.
In the absence of lubricant pressure, the compressed shape of the environment end
22
becomes increasingly concave with increasing compression because the compression is concentrated at one end of the seal. This reduces interfacial contact pressure near exclusionary geometry
28
and detracts from its exclusionary performance. In the presence of differential pressure acting from the lubricant side of the seal, the environment end
22
is pressed flat against the wall of the housing groove, which increases the interfacial contact pressure near exclusionary geometry
28
and improves exclusionary performance.
Although such seals perform well in many applications, there are others where increased lubricant film thickness is desired to provide lower torque and heat gen
Dietle Lannie
Gobeli Jeffrey D.
Kalsi Manmohan S.
Andrews & Kurth LLP
Jackson James L.
Knight Anthony
Patel Vishal
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