Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
MULTI-LAYERED SEAL STRUCTURE
FIELD OF THE INVENTION
The present invention relates to a multi-layered seal ring or other
geometric configuration that minimizes, controls or essentially eliminates
fluid
leakage over a wide range of temperatures.
BACKGROUND OF THE INVENTION
Sealing rings are used for creating a seal between a shaft or rod and
the walls of a bore or cylinder in many types of mechanical devices such as,
for example, compressors, pumps, automatic transmissions and power
steering devices.
A seal ring generally has an open annular shape and is mounted in the
circumferential groove of a shaft or rod (e.g., a piston) that is situated
within a
cylindrical housing. The normal function of the seal ring is to prevent or
control
the leakage of fluid across the ring structure from one side to the other,
while
also allowing the shaft or rod upon which it is disposed to rotate, pulsate or
reciprocate within the cylindrical housing.
Several seal ring designs having a joint are described in the industry,
wherein the joint allows the seal ring to expand or contract in response to
the
thermal expansion and/or contraction of the cylindrical member, rod or shaft
upon which they are mounted. The joints of these seal rings have a variety of
geometric configurations such as, for example, step joints, scarf joints and
butt
joints. However, thermal expansion and exposure to other forces exerted upon
the seal rings during their use causes seal rings using these types of joints
have gaps in their structure. These gaps are disadvantageous in that they
allow for the excessive leakage of fluid across their structure.
Varying degrees of leakage occur over a range of temperatures, a
factor that needs to be taken into account in fluid systems (e.g. automatic
transmissions) for proper operation. The wide range of temperatures is
observed from initial start-up through the upper portion of the operating
temperature range of the mechanical process. For example, fluids such as oil
will vary in viscosity in response to changes in temperature, and thus its
rate of
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leakage increases as its viscosity decreases, which could result in a greater
rate of leakage. Furthermore, the size of a particular material, for example a
metal shaft or rod, also varies with temperature due to thermal expansion,
wherein an increase in temperature generally results in an increase in the
size
of the joint gaps in those seal rings known in the art, which again results in
greater leakage.
The industry has taken steps to minimize or eliminate leakage, across
seal rings, however, such attempts have proven unsuccessful. By example,
the rate of leakage across known joints such as, for example, a micro-cut,
step
gap or butt gap (and others) is reduced by sizing the seal ring to have a
smaller gap at cold temperatures. However, this is problematic because as the
ring thermally expands in response to its operating temperature, a completely
closed gap may result in the ring binding in the groove or even buckle. The
binding or buckling results in premature wear and/or causes the ring to
improperly seal, wherein the rate of leakage actually increases, especially
with
the lower viscosities of higher temperature oil.
Therefore, there is a need within the industry to develop a seal ring that
eliminates leakage or only allows for minimal yet controlled amounts of
leakage across its structure over a wide range of temperatures. The present
invention provides just such a seal ring.
SUMMARY OF THE INVENTION
The present invention relates to an expandable multi-layered seal ring
design or other geometric configuration allowing for its installation onto a
shaft,
rod or other cylindrical member, wherein the present invention essentially
eliminates or allows for only minimal yet controlled leakage over a wide range
of operating temperatures.
An embodiment of the present invention relates to a multi-layered seal
ring or other geometric configuration comprising:
a.) a first annular or non-annular form having a gap or fracture
therein; and
b.) a second annular or non-annular form having a gap or fracture
therein, wherein the second annular form is contiguous with or
adjoining to the first annular form; and
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wherein the at least first and second annular forms are affixed to one
another at an affixation zone with an affixing agent.
The present invention also relates to a process for forming a multi-
layered seal ring or other geometric configuration comprising:
(i) affixing at least a first annular or non-annular form and second
annular or non-annular form to one another at an affixation zone
with an affixing agent, wherein the at least first annular or non-
annular form is contiguous with (or adjoining to) the second
annular or non-annular form.
Other alternatives, modifications and equivalents of the present
invention will be or become apparent to one with skill in the art upon
examination of the following detailed description. It is intended that all
such
additional alternatives, modifications and equivalents be included within this
description and within the scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 depicts a side view of an embodiment of the multi-layered seal
ring according to the present invention.
Figure 2 depicts an exploded side view of an embodiment of the multi-
layered seal ring according to the present invention.
Figure 3 depicts a side view of an embodiment of the multi-layered seal
ring positioned on a rod or shaft.
Figure 4 depicts a side view of an embodiment of the multi-layered seal
ring having a fracture therein.
DETAILED DESCRIPTION
Where a range of numerical values is recited herein, unless otherwise
stated, the range is intended to include the endpoints thereof, and all
integers
and fractions within the range. It is not intended that the scope of the
invention
be limited to the specific values recited when defining a range. Moreover, all
ranges set forth herein are intended to include not only the particular ranges
specifically described, but also any combination of values therein, including
the
minimum and maximum values recited.
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The multi-layered seal rings according to the present invention can be
used in a variety of applications including static, reciprocating and rotating
applications to perform a sealing function. The multi-layered seal rings are
used in applications where fluids in the form of a liquid or gas are isolated,
such that the fluid exerts pressure against the seal ring thereby creating a
sealed surface.
The present invention relates to an expandable multi-layered seal ring
design or other geometric configuration thereby allowing its installation onto
a
shaft, rod or other cylindrical member, and then once in position, provide a
seal as though it were a continuous solid ring. Furthermore, the present
invention provides for a multi-layered seal ring that essentially eliminates
or
allows for only minimal yet controlled leakage over a wide range of operating
temperatures. More specifically, as shown in FIGS. 1-3, an embodiment of the
present invention relates to a multi-layered seal ring (1 ) comprising:
a.) a first annular form (2) having a gap (4) therein; and
b.) a second annular form (3) having a gap(4) therein, wherein the
second annular form is contiguous with or adjoining to the first
annular form;
wherein the at least first and second annular forms are affixed to one
another at an affixation zone (5) with an affixing agent (6).
The design of the present invention contemplates the use of multiple
annular or non-annular forms, wherein at least two individual annular or non-
annular forms are connected to one another. For ease of description, an
embodiment utilizing two annular forms is set forth herein. Preferably, when
only two annular forms are utilized each singular annular form has a thickness
that is about one-half as thick as a typical equivalent seal ring.
The at least first and second annular forms of the multi-layered seal ring
according to the present invention may generally have a wide range of
diameters and still confer its particular advantages.
The at least first (2) and second (3) annular forms according to the
present invention may be comprised of any material capable of providing the
necessary sealing function while being able to withstand the forces and
temperatures generated in the environment in which it is used, for example,
metals such as cast iron, flexible elastomers and various polymers.
Preferably,
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the at least first (2) and second (3) annular forms are comprised of polymeric
materials, where the first (2) and second (3) annular forms may comprise
either the same polymer or different polymers.
A preferred embodiment of the multi-layered seal ring (1) comprises a
high performance polymer. More preferably, the present invention comprises a
synthetic high performance polymer that is temperature resistant, has a high
melting point, has high compressive strength, is not brittle, has a low
coefficient of thermal expansion and a low coefficient of friction.
Other physical properties are also important in a seal ring such as, for
example, tensile strength, modulus and elongation. Although metal seal rings
tend to have better tensile strength and modulus, elongation is higher in
polymers. It has been found that for rings of the present invention, tensile
strength should be in the range of about 9000 to about 18000 psi (62.1 x 103
to
124.1 x 103 kPa), elongation in the range of about 2.5% to about 10%, and
tensile modulus in the range of about 310,000 to about 750,000 psi (2.14 x 106
to 5.17 x 10 kPa). One of ordinary skill in the art would understand that
these
are merely preferred ranges, but are not limiting. A wide variety of polymers
are suitable for use in the multi-layered seal rings (1) in the present
invention.
Those that are particularly suitable are polyimide, polyamide, polyester,
polyether ether ketone (PEEK), polyamide imide (PAI), polyether imide,
polyether ketone ketone (PEKK), polyether ketone (PEK), polyphenylene
sulfide, polybenzimidazole, and thermoplastic polyimide (TPI),
polytetrafluoroethylene (PTFE), and liquid crystal polymer (LCP).
If the polymer is a polyimide, it is preferred that it be prepared from at
least one diamine and at least one anhydride. Preferred diamines include m-
phenylene diamine (MPD), p-phenylene diamine (PPD), oxydianiline (ODA),
methylene dianiline (MDA), and toluene diamine (TDA). Preferred anhydrides
include benzophenone tetracarboxylic dianhydride (BTDA), biphenyl
dianhydride (BPDA), trimellitic anhydride (TMA), pyromellitic dianhydride
(PMDA), malefic anhydride (MA), and nadic anhydride (NA).
Preferred polyimides include those prepared from the following
combinations of anhydride and diamine: BTDA-MPD, MA-MDA, BTDA-MDA-
NA, TMA-MPD & TMA-ODA, BPDA-ODA, BPDA-MPD, BPDA-PPD, BTDA-4,
4'-diaminobenzophenone, and BTDA-bis(P-phenoxy)-p, p'-biphenyl. An
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especially satisfactory polyimide useful in the seal ring of present invention
is
that prepared from pyrometillitic dianhydride and 4,4'-oxydianiline (PMDA-
ODA). Even more preferably, the multi-layered seal ring comprises a
commercially available polyimide such as, for example, VESPEL~
Thermoplastic material (available from E.I. du Pont de Nemours and
Company, Wilmington, DE).
The polyimide compositions can also contain a blend of at least one
polyimide with at least one other polymer which is melt processible at a
temperature of less than about 400°C and is selected from polyamide and
polyester resin and may be present in a concentration of from about 45 to 79.9
weight percent. Melt processible is used in its conventional sense, that the
polymer can be processed in an extrusion apparatus at the indicated
temperatures without substantial degradation of the polymer.
A wide variety of polyamides and/or polyesters can be used in the
present invention and/or can be blended with polyimides. For example,
polyamides, which can be used, include nylon 6, nylon 6,6, nylon 610 and
nylon 612. Polyesters, which can be used, include polybutylene terepthalate
and polyethylene terepthalate.
A fusible or melt processible polyamide or polyester can additionally be,
in the form of a liquid crystal polymer (LCP). LCP's are generally polyesters,
including, but not limited to polyesteramides and polyesterimdes. LCP's are
described by Jackson et al., for example, in US Pat. Nos. 4, 169,933,
4,242,496 and 4,238,600, as well as in "Liquid Crystal Polymers: VI Liquid
Crystalline Polyesters of Substituted Hydroquinones."
The polymers of the multi-layered seal ring (1 ) of the present invention
can further include other additives, fillers and dry lubricants, which do not
depreciate the overall characteristics of the finished seal rings, as would be
evident to those skilled in the art. For example, the incorporation of
graphite
into the composition can extend the range of its utility as a wear resistant
material. Another beneficial additive is carbon fiber, for the purpose of
reducing coefficient of thermal expansion. Various inorganic fillers are known
to reduce the coefficient of friction and improve wear resistance. The filler
used should not prevent the fracturing of the seal ring in the present
invention.
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Alternatively, as noted above, the multi-layered seal ring (1) according
to the present invention may be comprised of various combinations of
polymers, wherein each individual annular form comprises a different polymer.
For example, the polymers may be chosen based on their performance and
use in varying applications, wherein the wear side of a two-layered ring may
comprise a first polymer that provides high wear and low friction
characteristics, while the adjoining annular form comprises a more ductile
polymer providing for better sealing against a stationary surface. When
combinations of polymers are utilized it is preferred to use those polymers
having similar thermal expansion rates, preferably within 10% of one another.
The present invention preferably relates to a multi-layered seal ring (1)
since rotating equipment frequently draws a substantially circular path.
However, a variety of other multi-layered geometric configurations including,
but not limited to, multi-layered elliptical sealing structures may be
utilized in
more specialized applications.
Preferably the individual annular forms according to the present
invention have a square or rectangular cross-sectional configuration, however
other cross sectional configurations such as, for example, chamfered corners
may be used. The chamfer may be an angle or have an inside radius.
The at least first (2) and second (3) annular forms of the present
invention have a gap (4) in their structures, which allows the adjoining rings
to
slide in relation to one another. Thus the gap (4) acts as a "joint" or point
of
expansion during installation of the present invention for installation
purposes.
The gaps (4) formed in the multiple annular forms of the present invention are
preferably direct formed gaps. As shown in FIGS. 1-3, each individual annular
~
form has a gap (4) through the entirety of its thickness thereby forming a
pair
of ends having opposing faces (4a, 4b) that are substantially parallel to one
another and have smooth faces. Additionally, the gap's opposing faces (4a,
4b) are preferably substantially perpendicular to the major axis or plane of
the
particular individual annular form.
Alternatively, in place of gaps, the present invention utilizes individual
forms that have been fractured as shown in Figure 4. Each individual annular
form is completely fractured (12), through the entirety of its thickness
thereby
forming a pair of ends having opposing faces (11a, 11b) that are substantially
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parallel to one another. The fracture's opposing faces (11 a, 11 b) or the
fracture line is preferably substantially perpendicular to the major axis or
plane
of the particular individual annular form. Generally, the fracture's opposing
end
faces are rough, and mesh together when the faces are forced into contact,
which may further aid in the prevention of leakage.
As is generally known to those of ordinary skill in the art, the multi-
layered seal ring (1) becomes heated during the rotational or reciprocating
movement of the shaft, rod or other cylindrical member, causing the multi-
layered seal ring to thermally expand when the multi-layered seal ring is at
operating conditions. For that reason, the opposing end faces (4a, 4b or 11a,
11b) may not necessarily make contact until the operating conditions are
reached. It is preferred that the gap (4) or fracture (12) is open at cold
temperatures and closed at peak operating temperatures, which minimizes the
leakage by the first ring.
The width of the gap (4) is not critical, however its size should not be so
large such that when a multi-layered seal ring (1) is formed there is no
overlap
of the at least first (2) and second (3) annular or non-annular forms.
Preferably,
the gap width is only a small fraction of the overall circumference
measurement of the particular annular form. Additionally, the gap width is
generally in linear relation to the diameter of the particular annular form,
wherein if the diameter of the individual annular form is doubled, the width
of
the gap likewise doubles.
Along with temperature, fluid pressure is another operating condition,
which affects the multi-layered seal rings' ability to perform the sealing
function. When operating pressure is achieved on the pressurized side of the
multi-layered seal ring (1) and the operating temperature is achieved, the
opposing faces (4a, 4b and 11a, 11b) come together, thereby closing the gap
(4) or fracture (12) that was created for installation of the seal ring and
whereby the gap or fracture (12) does not become a point of leakage,
therefore a single multi-layered seal ring is all that is required to perform
the
sealing function.
As may be expected, undesirable leakage of fluids across the multi-
layered seal ring (1) would be evidence that it is not functioning properly.
As
mentioned above, in some instances complete removal of leakage is not
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possible, and in fact, controlled leakage of only minimal amount of fluids is
preferred. For example, a controlled leakage may be used for lubrication or
heat removal for a bearing or bushing on the non-pressured side such as in a
transmission. When the multi-layered seal ring is installed on a shaft or rod
used in a bore or cylinder and upon pressurization, a properly functioning
multi-layered seal ring will prevent, or at least minimize, leakage of fluids.
In a
cylinder having a pressurized side upstream of the installed multi-layered
seal
ring and a non-pressurized side downstream of the seal ring generally
functions by isolating the pressurized side from the non-pressurized side.
Moreover, the path of any leaking fluids is typically through the gap (4)
or fracture (12) in the first annular form (2), then by way of the interface
between the adjoining annular forms until reaching the gap (4) or fracture
(12)
in the second annular form (3). The length of this pathway between the gaps
(4) or fractures (12) of the adjoining annular forms is important in the
reduction
of the leakage. Therefore the longer the pathway, the better the corresponding
reduction in fluid leakage. Accordingly, the gap (4) or fracture (12) may be
positioned anywhere along the individual annular forms, as long as these gaps
(4) or fractures (12) are not in alignment with one another when the multi-
layered seal ring is formed. The gaps (4) or fractures (12) in the multi-
layered
seal ring may be positioned in close proximity with one another for ease of
assembling on a shaft, rod or other cylindrical member (7), thereby shortening
the leakage pathway; however there will be an increase in the leakage volume.
It is preferred that the gaps (4) or fractures (12) are substantially opposite
one
another, more preferably about 180 degrees apart, thereby eliminating or
minimizing the amount of leakage.
The advantages conferred by the gaps or fracture (12) in the multi-
layered seal ring (1) of the present invention are negated when the individual
annular forms rotate relative to one another, resulting in alignment of the
gaps
(4) or fracture (12) on the shaft, rod or other cylindrical member (7).
Therefore,
the at least first (2) and second annular (3) forms are affixed to one another
at
an affixation zone (5) using an affixing agent (6) to prevent the rotation
relative
to one another, as shown in FIGS. 2 and 4.
The affixing agent (6) may be any method known in the art such as, for
example, an adhesive; pinning using a dowel, or annular forms molded or
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manufactured where one annular form has a projection, while an adjoining
annular form has a recess capable of accepting the projection (e.g. a
male/female configuration). Affixing the individual forms of the multi-layered
seal ring (1 ) allows them to retain the ability to slide relative to one
another for
the purpose of expansion for installation of the multi-layered ring, while not
rotating relative to one another.
Dowels used in the present invention must be made from a strong
material capable of be formed into small cross sectional pins. The dowel must
be of a size that it is stiff enough to withstand its insertion into the
respective
holes in the individual annular forms as well as being capable of withstanding
the pressures, forces and thermal requirements of the fluid system, while not
degrading the integrity of the individual annular forms of the multi-layered
seal
ring (1). Furthermore, the dowel must also be made from inert materials or
those chemically compatible with both the annular forms and the fluid system
in which it is to be used. Suitable dowels for use in the present invention
include those made from small gauge wire, fiberglass, carbon fiber, stainless
steel, copper, aluminum, glass, polymers etc. Preferably, the dowel diameter
is
no more than 50% of the wall thickness of the individual annular forms, more
preferably no more than 20% of the wall thickness.
Typically the dowels are of a size that when pressed into place they
maintain their positioning, however, maintaining them in position may be
supplemented by the use of adhesives, such as those described below for
affixing the annular forms to one another. Furthermore, a groove such as, for
example, a ring groove found in some shafts, rods or other cylindrical
members with which the annular forms are utilized also assists in preventing
the dowel from working its way out of position. In positioning the dowel there
needs to be sufficient penetration into each annular form such that the dowel
holds the annular forms in contact with one another and prevents the rotation
of the annular forms relative to one another, but should not extend beyond the
non-adjoining planar surface of the annular form perpendicular to the end
surface of the dowel.
Adhesives utilized in the present invention should not weaken (e.g.
chemically degrade) the annular forms, and such adhesives may be applied
manually or using any method known in the art for such applications. The
to
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portion of the multi-layered seal ring (1) where the individual annular forms
are
affixed to one another is the affixation zone (5), which is generally a small
area
in relation to the overall circumference of the multi-layered seal ring.
Typically
with the use of adhesives, the size (or width) of the affixation zone is kept
as
small as possible where it is kept as close to the circumferential mid-point
of
the annular forms between the gaps (4) or fractures (12), while still being
able
to affix the individual annular or non-annular forms to one another. Any
applied
adhesive should not extrude from between the adjoining annular forms, so
care must be taken in the amount applied. Over-application of an adhesive
may interfere with the sealing capabilities of the multi-layered structure and
could also break-off and become a contaminant to the rest of the fluid system.
Generally, when determining the positioning of the affixation zone, it is
located at the mid-point of the centerline between the gaps (4) or fractures
(12). Preferably, the affixation zone is located 90 degrees from the location
of
the gaps (4) or fractures, when such gaps (4) or fractures (12) are 180
degrees
apart.
Suitable adhesives for use in the present invention are well known to
those skilled in the art, and are typically chemically inert and have a
temperature rating appropriate for the particular application in which they
are
to be utilized. Suitable adhesives are also commercially available such as,
for
example, Loctite~, available from the Henkel Loctite Corporation, Rocky Hill
CT.
The individual annular forms according to the present invention may be
produced by various methods known in the art such, for example, injection
molding, extrusion molding, compaction formed and the like.
The methods for making the individual at least first (2) and second (3)
annular forms having a fracture (12) according to the present invention are
well
known in the art, including but not limited to that set forth in Attorney
Docket
AD7059 (E.I. Dupont de Nemours and Company).
The present invention also relates to a process for forming a multi-
layered seal ring according to the present invention, the process comprising
affixing at least a first annular form having a gap or fracture therein and
second
annular form having a gap or fracture therein to one another at an affixation
zone with an affixing agent, wherein the at least first annular form is
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contiguous with (or adjoining to) the second annular form. The above-noted
process may also be utilized for affixing non-annular forms to form multi-
layered seal structures.
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