Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
2000-04-26
2002-12-17
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C277S551000, C277S560000, C277S559000
Reexamination Certificate
active
06494462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to rotary seals for establishing sealing between a structure and a relatively rotatable surface for lubricant retention and environment exclusion. More particularly the present invention relates to resilient rotary shaft seals having geometry for manipulating interfacial contact pressure within the dynamic sealing interface to interact with lubricant during rotation of a relatively rotatable surface for the purpose of enhancing lubricant film thickness across the sealing interface and for causing lubricant movement toward the environment for ensuring adequate lubrication of the entire dynamic sealing surface to extend the service life thereof, and having geometry that provides for resistance to becoming skewed or twisted within the seal groove, thereby minimizing skew-induced wear caused by impingement of abrasive contaminants present in the environment.
2. Description of the Prior Art
The prior-art hydrodynamically lubricated rotary seal designs of U.S. Pat. Nos. 4,610,319, 5,230,520, 5,678,829, 5,738,358, 5,873,576 and 6,036,192 are known in the industry by the registered trademark “Kalsi Seals”, and pertain to seals that are typically used to partition a lubricant from an environment and hydrodynamically lubricate the dynamic sealing interface in response to rotation of a mating shaft.
Commercial seals are presently being manufactured and sold under U.S. Pat. Nos. 4,610,319, 5,230,520, 5,678,829, 5,738,358, all of which employ a dynamic sealing lip defining a dynamic sealing surface. The dynamic sealing lip has angulated hydrodynamic waves on its lubricant side for hydrodynamically wedging lubricant into the dynamic sealing interface, and has an abrupt exclusion edge on its environment side for excluding the environment, per the teachings of U.S. Pat. No. 4,610,319. The waves cause the dynamic sealing lip to have a variable thickness, being thinnest at the low point of the waves, and being thickest at the high point of the waves.
The lubricant film in the dynamic sealing interface is thin, and not uniform in thickness across the width of the dynamic sealing interface. The resulting lubrication of the dynamic sealing surface is uneven, and surface asperity contact and resulting rubbing wear sometimes occurs between the dynamic sealing surface and the shaft. The greatest film thickness occurs toward the lubricant side of the dynamic sealing interface, and the least occurs toward the environment side.
The angulated hydrodynamic waves cause the lubricant-side edge of the dynamic sealing surface to have a series of waves; this edge is sometimes called the wavy hydrodynamic edge. Film thickness and resulting lubrication of the dynamic sealing surface is greatest in the region of the waves because a large portion of the lubricant wedged into the dynamic sealing interface at the leading edges of the waves simply leaks out at the trailing edges, and only a much smaller portion travels toward the abrupt exclusion edge. As a result, the environment-side of the dynamic sealing surface is less well lubricated than the lubricant side, and more prone to wear and overheating.
If the lubricant is at higher pressure than the environment, the seal begins to bulge or protrude in to the extrusion gap between the seal housing and the shaft due to bending, shear and other stresses in the dynamic sealing lip caused by the pressure; this phenomenon is called “extrusion” by the seal industry. These stresses are highest at the thinnest points of the dynamic sealing lip; i.e. the low point of the waves.
Extrusion can lead to damage known as “nibbling” or “extrusion damage”, which is caused by cyclic stressing of the material protruding into the extrusion gap, causing it to fatigue and break away from the sealing element. The cyclic stress is typically caused by dynamic fluctuations in the size of the extrusion gap due to lateral shaft motion, causing high variations in the compression of any protruding material.
Localized extrusion damage promotes abrasive ingestion, and can also partially interrupt the hydrodynamic film causing the seal to run hotter and suffer premature compression set and surface embrittlement. Extrusion damage, and wear damage caused by environmental abrasives, can progressively destroy the dynamic sealing surface, beginning at the abrupt exclusion edge and progressively working toward the low point of the waves. Once the damage reaches the low point of the waves, the seal no longer blocks the leakage path, and fails.
Because the dynamic sealing lip has variable thickness, the seals have less than perfect compressive stability and can become locally twisted and skewed, especially when the pressure of the lubricant and the environment is substantially balanced. U.S. Pat. Nos. 5,230,520, 5,873,576 and 6,036,192 are directed at improving compressed stability.
The seal is radially compressed when installed, which also causes circumferential compression, which is effectively increased by thermal expansion. Since the seal circumference is relatively long compared to the seal cross-section, circumferential compression can cause buckling in a manner similar to the classic textbook example of a long, slender structural column under compressive loading. (Lubricant pressure can be used to prevent buckling.) Twisting related to lip width variation can help to initiate such buckling, which can cause the abrupt exclusion edge to acquire a skewed position. This can promote abrasive wear, particularly if the lubricant end of the seal is twisted toward the shaft at the location of skew, causing interfacial contact pressure to increase near the wavy hydrodynamic edge and decrease near the abrupt exclusion edge, which diminishes hydrodynamic lubrication and environmental exclusion.
Since there is more material at the thickest point of the dynamic sealing lip, when one attempts to axially constrain prior art seals to help control skew-induced wear, part of the differential thermal expansion between the seal and the housing is relieved circumferentially, causing material displacement from the thickest point of the lip to the thinnest point of the lip, thereby diminishing hydrodynamic lubrication. Elevated environment pressure can worsen the problem, apparently by causing higher contact pressure near the wavy hydrodynamic edge.
Testing has shown that prior art seals perform better when the lubricant pressure is higher than the environment pressure. When the environment pressure is higher than the lubricant pressure, the prior art dynamic sealing lip deforms unevenly due to its varying width, causing the environment-side edge to become non-circular and more prone to abrasion by the environment.
U.S. Pat. No. 6,036,192, which has not yet been commercialized, discloses a skew and twist resistant rotary seal assembly comprising a structure having a circular seal groove having first and second spaced seal groove walls and a relatively rotatable surface, combined with a circular body of sealing material being located within said circular seal groove and having a part thereof projecting from said circular seal groove, with at least one circular dynamic sealing projection extending from said circular body of sealing material and having sealing engagement with said relatively rotatable surface; and a plurality of bearing elements projecting from said circular body of sealing material and being circumferentially distributed about said circular body of sealing material and having bearing engagement with said relatively rotatable surface.
The present invention builds on the technology disclosed in U.S. Pat. No. 6,036,192 to provide the “plurality of bearing elements” described therein with a configuration for providing elevated contact pressure zones of skewed configuration to improve lubricant distribution across the dynamic sealing interface.
SUMMARY OF THE INVENTION
The present invention is a resilient, generally ring shaped hydrodynamic rotary seal for partitioning a lubricant from an environment, and for hydrodynamically l
Andrews & Kurth LLP
Jackson James L.
Kalsi Engineering, Inc.
Knight Anthony
Peavey Enoch E
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