Note: Descriptions are shown in the official language in which they were submitted.
CA 02320647 2000-09-25
GASKET
FIELD OF THE INVENTION
The present invention is drawn to elastomeric static gaskets and specifically
to elastomeric seals with compression limiters to prevent over compression of
the
seal.
BACKGROUND OF THE INVENTION
Many sealing applications demand "thin" elastomeric static seals because of
space limitations. This requirement often dictates the use of unsupported or
homogeneous elastomeric seals. However, unsupported elastomeric seals are
difficult to install in high production conditions especially if they fit into
a shallow,
narrow groove. This is because there is a tendency for the unsupported seal to
pop
out of the groove or for the seal to twist within the groove during
installation. Either
condition can result in a leak at the joint and/or damage to the mating
component.
Other approaches include molding the seal into a groove. This solves the
seal installation problem but this approach has been found to be too expensive
for
high volume applications. Another approach is the use of an elastomeric
carrier
gasket. An elastomer is molded into a groove or around the periphery of a
metal or
plastic carrier which is 3.0mm thick to provide stiffness to the seal for ease
of
handling. This approach also has limitations in that these carriers are
typically too
thick for tight clearance applications. The thickness of the 3.0mm carrier is
unsatisfactory for multi-stack applications where overall length of the sealed
unit
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must be kept to a minimum or for sealing powertrain components with height or
length
packaging constraints.
Thus, none of the prior art designs have been found to be satisfactory for
applications with tight clearance requirements and there exists a need for a
thin gasket
with an overall compressed thickness in the order of 0.015mm to 1.75mm.
SUMMARY OF THE INVENTION
Generally speaking, the problems of the prior art are overcome with the
present
invention which broadly provides a static gasket adapted to seal between a
first
sealing surface and an opposed second sealing surface that are secured
together
such that a clamp load is applied to the static gasket by the first and second
sealing
surfaces, the static gasket comprising: a generally flat carrier member having
a
generally planar top surface facing the first sealing surface and an opposite
surface
facing the second sealing surface; a first stopper member located on the top
surface,
the first stopper member formed independently from the carrier member; a
second
stopper member on the top surface in spaced relationship to the first stopper
member,
the second stopper member formed independently from the carrier member, the
first
and second stopper members forming a cavity therebetween, and with each having
a height above the top surface; and an elastomeric seal member located in the
cavity,
the elastomeric seal member having at least one sealing bead, the sealing bead
having an apex which extends from the top surface and is greater than the
height of
the first and second stopper members, and the apex is adapted to compress to
the
height of the first and second stopper members, with the first stopper member
and the
second stopper member preventing the seal member from being over compressed
while the gasket is subjected to the clamp load from the first sealing surface
and the
second sealing surface.
These and other features of the present invention will become apparent from
the subsequent descriptions and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a planar view of the preferred embodiment of the invention;
FIG. 2 is a cross sectional view along A-A of FIG. 1;
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FIG. 3 is a cross sectional view along B-B of FIG. 1;
FIG. 4 is an enlarged view of Circle C in FIG. 2;
FIG. 5 is an enlarged view of Circle D in FIG. 3;
FIG. 6 is a cross sectional view of the elastomeric static gasket according to
the
preferred embodiment of the invention in between two opposite surfaces showing
the
elastomeric seal on the top surface of the carrier being compressed and the
elastomeric seal on the opposite surface of the carrier being in an
uncompressed
condition;
FIG. 7 is a cross sectional view of the method of making the preferred
embodiment of the gasket according to the invention; and
FIG. 8 is a cross sectional view of an alternative embodiment of the gasket of
the present invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figures 1-6 show an elastomeric static gasket according to the present
invention, designated by the numeral 100. The invention is drawn to both the
apparatus and the process for making the gasket 100. The gasket 100 seals
fluid.
The fluid may be a gas or liquid, a mixture of both, or solid particles
entrained in a
fluid such as dust in air or dirt in air. A liquid may be water, oil, fuel,
anti-freeze, air
conditioning fluid or any other similar material. The gas may be water vapor,
hydrogen, air, oxygen, nitrogen, carbon dioxide, air conditioning vapor, fuel
vapor,
lubricating vapor or any other similar material.
Preferably, the static gasket has a carrier 10, a first pair of stopper
members
20, a second pair of stopper members 40, a first elastomeric seal 60 and a
second
elastomeric seal 80. The gasket is formed with a thin carrier 10 that is less
than
1.0mm thick. The preferable thickness of the carrier, which is not to be taken
as a
limitation of the scope of the invention, is between 0.01mm to 0.75mm and
preferably it is between 0.05mm to 0.5mm. The carrier is preferably made of a
polymeric material such as Nylon , Mylar , Kapton , polybutylene terephthalate
(PBT), polyethylene naphtlate (PEN) or polyethylene terephathalite (PET).
Nylon ,
Mylar , Kapton are registered trademarks of DuPont. Alternatively, the
carrier 10
can be made of a polymer material such as polyester, polyamide, silicone,
polyimide, polyethersulphone, or a thin layer of metal such as steel, brass,
aluminum, magnesium or stainless steel, or a gas diffusion layer, a graphite
plate, a
proton exchange membrane, a layer of non-woven material, a fiber board used in
making cellulose composite gaskets, a woven fabric, a rubber coated metal
layer, a
ceramic layer, or any other material suitable for practicing the invention.
The layer of
non-woven material may be made of polyester, polyolefin, metal or ceramic or
any
other material suitable for the application. The carrier material is
preferably a
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compliant material which is stiffened by the forming of an elastomeric seal
and
stopper members that add sufficient stiffness to the gasket to facilitate
handling and
assembly. Alternatively, the carrier material may be relatively non-compliant
to
facilitate handling and assembly in the application. The ultimate choice of
compliance of the carrier material is made by taking into account the
temperature,
fluid medium to be sealed and the application constraints including geometry,
ease
of assembly and the material used in making the mating components.
As best shown in FIGS. 4, 5, and 6, the carrier 10 has a top surface 12 and
an opposite surface 18. Preferably, a first pair of stopper members 20 are
formed or
molded of a polymeric material onto the top surface 12. The pair of stopper
members 20 consists of two spaced.apart relatively flat compression limiters
or stops
22, 24, respectively. In between the stops 22, 24, respectively is a first
void or first
cavity 36. The cavity 36 that is formed between the two stops 22, 24 is a
volumetric
space (a width, a height and a length), as is well known in the art.
In between the stops 22, 24, respectively, a first rubber elastomeric seal 60
is
molded, formed, attached, disposed, applied or inserted into the cavity 36
preferably
in the form of a void-volume seal 78. A void-volume seal is one which is
formed with
the cavity or void 36 being greater than the maximum volume of the seal 60
when
compressed into the cavity 36. This permits the elastomeric seal 60 to expand
due
to swelling or temperature expansion or chemical interactions without
extruding out
of the cavity 36. The bead is preferably in the shape of a triangle with its
base
contiguous to the top surface 12 of the carrier 10. Optionally, the shape of
the seal
60 is a semicircle on a flat planar surface which is contiguous to the top
surface 12
of the carrier 10. Further optionally, any other bead configuration in the
elastomer
seal that produces an adequate sealing force, such as rectangular, square,
polygonal, semi-elliptical, semi-oval, semi-round, truncated triangular or any
other
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shape may be used as long as it prevents the migration of fluid across the
seal,
would be suitable for the application in practicing the invention. In the
uncompressed state, the seal 60 has at least one bead 62 with an apex 64 which
is
higher than the height 27, 29, respectively, of the stops 22, 24,
respectively, above
the surface 12. In the compressed state, that is when the seal 60 is clamped
against
a mating surface to seal it by a clamp load imposed on the mating surfaces,
the
bead 62 is compressed into the cavity 36. Because the seal is made of an
elastomer or rubber which is incompressible, the rubber will conform to the
volume in
the space in the cavity 36 when a clamp load is applied to the gasket 100. If
the
volume of the cavity 36 is smaller than the seal volume, the elastomer will
extrude
out of the cavity. Thus, the space in cavity 36 is designed to be 100.1% to
130% of
the volume of the seal. Preferably, the volume in space in the cavity is
between
105% to 110% of the volume of the seal. The compression on the bead 62 may be
compressed up to 80% from the apex 64 to the surface of the carrier and
preferably
from 1.5% to 75%.
The relatively flat surfaces 26, 28, respectively, of the polymeric stops 22,
24
respectively will compress somewhat under load. At the same time, the faces or
sides 23, 25 respectively, of the stops 22, 24 respectively, are designed not
to bulge
substantially by careful selection of shape factor of the stops 22, 24
respectively,
and their material properties. The sides 23, 25, respectively, are preferably
sloping
away from the top surfaces 26, 28 respectively. Optionally, they may be
substantially
perpendicular to the top surfaces 26, 28 and are designated as 23', 25',
respectively.
The stops 22, 24 respectively, are preferably made of the same material as the
seal
but the stops may be made of a higher durometer elastomer than the elastomer
bead 62, or optionally, made of polymers such as thermoplastic, thermoset
plastic or
thermoplastic elastomers or, further optionally, made of suitable layers of
metal,
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ceramic or composite fiber board. The elastomer bead 62 must be more compliant
than the stops 22, 24, respectively. When the gasket is subjected to a clamp
load,
the seal 60, by being more compliant, will create a high line sealing pressure
at the
apex 64 of the bead 62 which prevents the migration of fluid past it without
requiring
a correspondingly high sealing force (load) against the entire mating surface
of the
component which is to be sealed. This is desirable in certain applications
such as
fuel cells where a seal pressing against a brittle component such as graphite
bipolar
plate can create high stress in the plate and can cause the plate to crack. A
seal can
crack a mating plate if the sealing force exceeds the plate's material
strength
capability.
As stated earlier, preferably, the stops, 22, 24, respectively, and the
elastomeric bead 60 are formed of the same polymeric material. Alternatively,
the
stops 22, 24, respectively, may be made of a different polymer than the
material
used to form the elastomeric bead 60, such as silicone, fluorosilicone, butyl,
natural
rubber, fluorocarbon, ethylene-acrylate, polyacrylate, fluoropolymer,
isoprene,
epichlorohydrin, EPDM, nitrile, hydrogenated nitrile (HNBR), TPE or any other
polymer which is suitable for practicing the invention. The preferred polymers
used
in forming the elastomer seal 60 and stops 22, 24, respectively are reaction
cured.
Reaction cured elastomers include addition ion, catalytic, ultraviolet, infra-
red
radiation, condensation and free radial cure. In using conventional reaction
cured
elastomers, a primer coat or adhesive may be applied to the carrier to enhance
the
bond of the elastomer to the carrier. The primer coat may be silane based or a
phenolic resin. Silane based and phenolic resin primers are well known in the
art
and are used extensively with elastomers. Examples of silane based primers
are:
General Electric Company of Waterford, NY, Product No. SS4155; Dow Chemical
Company of Midland, MI, Product No. 3-6060; Rohm & Hass of Philadelphia, PA,
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CA 02320647 2000-09-25
Thixon Product Number 304 and Lord Corporation, of Erie, PA, Chemlock
Products Numbers 607 and 608. Rohm & Haas also produces Solvent Based
Product Numbers 2000, 05N-2, P15, 300, 715, 720 and Thixon Water Based
Products Numbers 2500, 7002, 7010, 7011 and 7015. Other primer coats are well
known in the art. Thixon is a registered trademark of Rohm & Hass.
Optionally,
the elastomers may be self bonding which eliminates the need to apply a primer
coat
or adhesive to enhance bonding of the elastomer to the surface of the carrier
10.
Examples of self bonding silicone elastomers are available from Wacker
Silicones of
Adrian, MI, Product Serial Nos. LR 3070, LR 3071, LR 3072, and LR 3073. Self
bonding silicone elastomers are made by ShinEtsu of Tokyo, Japan and General
Electric Co. Other self bonding elastomers include nitrile, HNBR, EPDM, butyl,
fluorocarbon, ethylene acrylate, fluoropolymers, fluorosilicone, isoprene, and
epichlorohydrin.
The height of the first and second members 22, 24, respectively, is preferably
substantially the same. However, if the compressive load on the first member
is
higher than on the second member, it may be desirable to make the compressed
height of the first stopper member different than the compressed height of the
second stopper member. This difference in compressed height of the first
stopper
member 22 and the compressed height of the second stopper member 24 does not
affect the inventive concept so long as the volume in the cavity 36 is not
less than
100.1% of the maximum volume of the seal.
The gasket 100 heretofore has been described in the context of the
construction of the seal 60 and a first pair of stopper members 20 on the top
surface
12 of the carrier 10. Similarly, the bottom surface 18 of the carrier 10
preferably has
a mirror-like construction similar to that described for the top surface 12.
Thus, a
second seal 80 and a second pair of stopper members 40 are formed or molded
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onto the opposite surface 18. The stopper members 40 include stops 42, 44,
respectively, which are spaced apart to form a second cavity or void 56.
Preferably,
the stops 42, 44, respectively, have sides 43, 45, respectively, which are
substantially perpendicular to the carrier 10, and heights 47, 49
respectively, which
extend above the bottom surface 18. Alternatively, the sides are sloping (not
shown)
or slightly tapered. The second elastomeric seal 80 has at least one bead 82
which
has an apex 84 to form a void-volume seal 98. Thus, the bottom portion of the
gasket 100 has a mirror-like construction as to the top portion and the seal
80 and
stops 42, 44, respectively, function in a similar manner to that described for
the seal
60, stops 22, 24, respectively, and top surface 12 of the carrier 10.
As stated earlier, the preferred construction of the gasket is a mirror image
construction (that is the configuration on the one side of the carrier is
identical to the
opposite side) so that when the gasket 100 is compressed or clamped between
mating surfaces such as one surface 2 and an opposite surface 4, the reactive
forces are similar on each side of the carrier 10. This balances the forces on
the
carrier 10 and permits the use of "thin" carriers. The top half portion of
Figure 6
shows the stopper members 20 in an uncompressed state while stopper members
40 in the lower half of Figure 6 are in a compressed state. Additionally, this
construction minimizes the formation of bending stresses in mating brittle
materials
which can cause cracks or breaking of such brittle materials. The overall
compressed thickness of the gasket 100 is preferably in the range of 0.015mm
to
1.75mm.
Where the construction of the seals or stops is not identical on each side of
the carrier, a somewhat thicker or less compliant carrier member may be
required to
accommodate the reactive forces. However, the function of the stopper members
as
compression limiters or stops is still to limit the compressed height of the
seal and in
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a construction which has the seal between a pair of stops, the stops also
function to
prevent the seal from extruding out of the cavity. Thus, the function of the
stopper
members remains the same as previously described.
In the preferred construction, the stopper members 20, 40, respectively are
made of an elastomer and sized with a shape factor along with the elastomer's
material properties, such as Durometer number, so as to limit the bulging of
the
faces 23, 25, respectively as a compressive load is applied to the stopper
members
20, 40, respectively. Shape factor is defined as the ratio of the area of one
loaded
elastomeric face divided by the total area of the elastomer which is free to
bulge, as
defined in the American Chemical Society, Rubber Division, of Akron, OH,
Intermediate Rubber Course, Edited 1985, which is incorporated herein by
reference. Bulging is a term used in elastomeric technology to denote the
distortion
of the unloaded side faces of an elastomeric member in response to a load
applied
on the top elastomeric face of the member. The range of shape factors in
practicing
the invention is between 0.1 to 100, more preferably it is between 0.15 to 10
and,
most preferably, the range is 0.2 to 1Ø
In making the elastomeric static gasket 100, the carrier 10 is clamped
between one mold half 6 and the other mold half 8 of a conventional molding
machine as shown in Figure 7. If a conventional elastomer is used, then an
adhesive coat is applied to the surface of the carrier prior to molding prior
to
receiving the elastomer. If a self-bonding elastomer is used, it may not be
necessary to use a separate adhesive coating on the surface of the carrier.
The
uncured polymer or elastomer material is dispensed into the cavity through a
hole in
the mold so that the elastomer flows into the space between the carrier 10 and
into
the cavity halves 6, 8, respectively, so as not to deform the carrier. The
polymeric or
elastomeric material is heated in order to enhance flow into the cavity. The
CA 02320647 2000-09-25
polymeric material is at a sufficient temperature so as to cure the polymer to
form
elastomeric sealing members 60, 80, respectively and the first stopper member
20
and second stopper member 40. Alternatively, a polymer material may be
deposited,
injected, transferred, formed in place, applied by roll coating or screen
printed onto
the top surfaces 12 and bottom surface 18 of the carrier 10 to form the
elastomeric
sealing members 60, 80, respectively. Those skilled in the art will recognize
that
there may be certain applications where only one elastomeric sealing member
need
be formed on the carrier 10 and thus an elastomeric sealing member 60 is
formed
on only the top surface 12 of the carrier. In this configuration of the gasket
100, a
pressure sensitive adhesive may optionally be applied to the opposite side 12
of the
carrier 10 to aid in assembly of the gasket to one mating surface and bond to
it so as
to seal against the one mating surface. Alternatively, the first and second
stopper
members are formed of other polymers or a layer of metal, ceramic or composite
fiber board, as described earlier. '
An alternate embodiment of the present invention is shown in FIG. 8 and the
gasket is designated by the numeral 200. Where the elements are the same as in
gasket 100, the numerals remain the same.
The gasket 200 includes a thin carrier 10, a first stopper member 120, a
second stopper member 130 and a first sealing member 160, a second sealing
member 170, a third sealing member 180 and a fourth sealing member 190. The
carrier 10 has a top- surface 12 and an opposite surface 10. The first stopper
member 120 is formed on the top surface 12 and the second stopper member 130
is
formed on the opposite surface 18. The first sealing member 160 is on the top
surface 12 and adjacent to one side of the first stopper member 120. The
second
sealing member 170 is on the top surface 12 and adjacent to the other side of
the
first stopper member 120. The third sealing member 180 is on the bottom
surface
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18 and adjacent to one side of the second stopper member 130. The fourth
sealing
member 190 is on the bottom surface 18 and adjacent to the other side of the
second stopper member 130. Preferably, the first stopper member 120 is
opposite
the second stopper member 130 and the first and second sealing elements 160,
170, respectively, are opposite the third and fourth sealing elements 180,
190,
respectively. The sealing elements 160, 170, 180 and 190, respectively, are
preferably made of elastomeric materials as previously discussed for seal 60
and
seal 80 in the preferred embodiment. Likewise, the first stopper member 120
and
the second stopper member 130 are preferably made of the same materials as
discussed for the first pair of stopper members 20 and the second pair of
stopper
members 40 in the preferred embodiment. Optionally, the first stopper member
120
and the second stopper member 130 may be made of plastic, metal, ceramic or
composite fiber board as discussed earlier in the preferred embodiment.
In this alternative embodiment, the first stopper member 120 functions as a
compression limiter to prevent over compression of the first sealing member
160 and
the second sealing member 170 on the one side of the carrier 10. Similarly,
the
second stopper member 130 functions as a compression limiter to prevent over
compression of the third sealing member 180 and the fourth sealing member 190
on
the other side of the carrier 10.
In all other aspects, the stopper members 120, 130, respectively, function
similarly to the stopper members 20, 40, respectively except that the stoppers
120,
130, respectively do not form a cavity since only one stopper per side of
carrier 10 is
provided.
The width of the stopper members 120, 130, respectively, is designed to
accommodate the sealing load exerted by the mating component (not shown) which
is being sealed. The stopper members 120, 130, respectively by absorbing most
of
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the clamp load exerted by the mating component, prevent the over compression
of
the sealing members 160, 170 ,180 and 190, respectively, so that the sealing
members maintain a high line sealing force against the mating component to
prevent
the migration of fluid across the seal.
In addition to the previously described applications, the gasket according to
the present invention has use in other applications such as in water pumps,
front
covers, cam covers, throttle bodies, carburetors, rocker covers, fuel valves,
flexible
printed circuits, air conditioning units, intake manifolds, water outlet
connectors,
thermostat housings, oil pans, and between two mating flanges where the
thickness
of the gasket must be minimized because of application restrictions.
While the invention has been described with a preferred and alternative
embodiments, it is not intended to limit the scope of the invention to the
embodiments disclosed but to embrace all variations within the scope of the
appended claims.
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