Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
2000-04-26
2002-05-07
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C277S549000, C277S559000, C277S584000
Reexamination Certificate
active
06382634
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to hydrodynamically lubricating seals having a hydrodynamic geometry which interacts 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 thereby provide for cooling and wear resistance of the seal and to significantly extend the service life thereof. More specifically, the present invention concerns the provision of a dynamic sealing lip geometry in a hydrodynamic seal which enhances lubricant retention and environmental exclusion of the seal and maintains interfacial contact pressure within the dynamic sealing interface for efficient hydrodynamic lubrication.
2. Description of the Prior Art
The prior-art hydrodynamically lubricated compression—type rotary shaft seals disclosed in U.S. Pat. No. 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 products of Kalsi Engineering, Inc. of Sugar Land, Tex.
FIGS. 1A through 1C
of this specification represent the prior art of U.S. Pat. No. 4,610,319 and 5,230,520 which is discussed herein to enhance the reader's understanding of the distinction between prior art hydrodynamic seals and the present invention.
Referring now to the prior art of
FIGS. 1A and 1B
, there are shown radially uncompressed cross-sectional shapes of the prior art seals, which are known in the industry respectively as “Style A” and “Style B” Kalsi Seals. The seal of
FIG. 1A
is representative of the commercial embodiment of the technology described in U.S. Pat. No. 4,610,319 and the seal of
FIG. 1B
is representative of the commercial embodiment of the technology described in U.S. Pat. No. 5,230,520.
Seal
1
A and
1
B incorporate a seal body
4
which is solid (ungrooved) and generally ring—like. Both seal
1
A and seal
1
B are designed to be installed in a housing groove which holds the seal in compression against a relatively rotatable surface. Seals
1
A and
1
B provide a predetermined compression range over a finite axial width.
The difference between the seals
1
A and
1
B is that the static sealing surface
6
of seal
1
A is a cylindrical surface of the seal body
4
, while the static sealing surface
6
of seal
1
B is formed by a static sealing lip
8
projecting from the seal body
4
. Seal
1
B is a product improvement over seal
1
A which improves interfacial contact pressure and twist resistance per the teachings of U.S. Pat. No. 5,230,520 by providing an approximation of compressive symmetry.
Seal body
4
of seals
1
A and
1
B each define a first seal body end
10
for facing a lubricant and an second body end
12
for facing an environment. Seals
1
A and
1
B each incorporate a dynamic sealing lip
14
defining a dynamic sealing surface
16
which has an non-hydrodynamic circular edge
18
which may be abrupt, and which is for environmental exclusion per the teachings of U.S. Pat. No. 4,610,319.
The dynamic sealing lip
14
of seals
1
A and
1
B have an angulated flank
20
having intersection with the seal body at lip termination point
21
. Angulated flank
20
is non-circular, and varies about the circumference of the seal in a wave pattern.
Angulated flank
20
defines a flank angle
60
which is tangent to hydrodynamic inlet hydrodynamic inlet curve
52
. Flank angle
60
and dynamic sealing surface
16
have theoretical intersection at theoretical intersection
22
. In seals
1
A and
1
B, angulated flank
20
takes the form of a straight line in the longitudinal cross-sectional view of the seal, as shown, and theoretical intersection
22
is blended by a hydrodynamic inlet curve
52
which is typically a 0.072 inch radius. Theoretical intersection
22
varies in distance from non-hydrodynamic circular edge
18
by a distance represented at the minimum location by minimum dimension
24
, and represented at the average location by average dimension
25
, and represented at the maximum location by maximum dimension
26
. The minimum dimension
24
is known in the industry as the “low point of the wave”. By virtue of the waviness of angulated flank
20
, the dynamic sealing surface
16
has a wavy edge for hydrodynamic wedging of lubricant into the compressed dynamic sealing interface between dynamic sealing lip
14
and the mating relatively rotatable surface, per the teachings of U.S. Pat. No. 4,610,319.
In keeping with American drafting third angle projection conventional representation, theoretcial intersection
22
is represented by a line even though the intersection is blended by a radius. (For a discussion of this general blended intersection illustration practice see paragraph 7.36 and FIG. 7.44(
b
) on page 213 of the classic drafting textbook “Technical Drawing”, 10th edition (Prentice-Hall, Upper Saddle River, N.J.: 1997).
One liability of the prior art seals
1
A and
1
B is that, in keeping with conventional hydrodynamic seal design wisdom, minimum dimension
24
has purposely been kept relatively small throughout the entire Kalsi Seals Style A and Style B product line, to help insure (
1
) that the entire width of dynamic sealing surface
16
is adequately lubricated by said hydrodynamic wedging of lubricant, and (
2
) to help maintain a low running torque to minimize heat generation.
Wear damage caused by environmental abrasives, and extrusion damaged caused by high differential pressure, acts axially on the dynamic sealing surface
16
, starting at non-hydrodynamic circular edge
18
and progressively working toward theoretical intersection
22
. Once the wear damage has progressed to minimum dimension
24
, the seal no longer blocks the lubricant leakage path, and ceases to function effectively as a seal, thereby permitting intermixing of the lubricant and the environment.
Referring now to the prior art illustration of
FIG. 1C
there is shown a cross-sectional view of a rotary shaft sealing assembly showing the installed condition of the prior art seal of
FIG. 1B
when the pressure of the lubricant
34
is higher than the pressure of the environment
36
.
FIG. 1C
is shown at the minimum dimension
24
between theoretical intersection
22
and non-hydrodynamic circular edge
18
. The rotary shaft sealing assembly includes a housing
28
in close proximity to a relatively rotatable surface
30
. The housing
28
defines an internal seal installation groove
32
within which is located a ring shaped prior art hydrodynamic seal of the styles discussed in conjunction with FIG.
1
B. The prior art seal is compressed between the groove peripheral wall
38
and the relatively rotatable surface
30
, resulting in compressive stresses, as determined by finite element analysis, over the region between second seal body end
12
and curved compressive region boundary
33
. The compressed region has a compressed region width
35
. The interfacial contact pressure at the dynamic sealing interface is determined by the modulus of the seal material, the amount of compression, and the compressed region width
35
of the compressed region of the seal between second seal body end
12
and curved compressive region boundary
33
.
The hydrodynamic seal is used to separate the lubricant
34
from the environment
36
. When a condition of elevated lubricant pressure exists, the hydrostatic force resulting from the lubricant pressure acting over the area between the groove peripheral wall
38
and the relatively rotatable surface
30
drives the seal against the second groove wall
46
, as shown by FIG.
1
C. The non-hydrodynamic circular edge
18
is located at the extreme end of the seal. Since the shape of the second seal body end
12
of the seal is of the same general shape as the second groove wall
46
, the second seal body end
12
of the seal is generally well supported against the lubricant pressure at all locations except clearance gap
40
which exists between the housing
28
and relatively rotatable surface
30
.
Dietle Lannie L.
Kalsi Manmohan S.
Andrews & Kurth Mayor, Day, Caldwell & Keeton, LLP
Jackson James L.
Kalsi Engineering, Inc.
Knight Anthony
Peavey Enoch
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