Note: Descriptions are shown in the official language in which they were submitted.
CA 02301772 2004-12-13
SEALING RING
Field of the Invention
The invention relates to the field of seals and in particular to the field of
sealing
rings.
Background of the Invention
German Patent Application DE-OS 33 16 063 discloses a sealing ring. This
sealing
ring is intended for a machine part carrying out rotational movements and is
composed of
a support ring, which is connected with a gasket made from PTFE
(polytetrafluoroethylene) such that it is leakproof to fluids. The gasket is
bent in a
trumpet-like fashion away from the space that needs to be sealed and has
hydrodynamically acting backflow conveying members on the side facing the
shaft that
needs to be sealed. The trumpet-like bent gasket is provided with at least two
parallel
backflow conveying members which penetrate each other and which have a
different
profile depth and/or incline.
Summary of the Invention
The invention is based on the objective to further develop a sealing ring as
described
in the above cited application such that the sealing ring provides an improved
static seal
when the shaft to be sealed is standing still.
In order to fulfill the objective an annular sealing flange closed in itself
is provided
between the backflow conveying member and the dust/sealing lip. The annular
sealing
flange tightly surrounds the circumference of the shaft. This embodiment
provides the
advantage that the sealing section of the gasket has three differently
designed functional
areas on the side facing the shaft that needs to be sealed. Each of the
functional areas
solves only one task. The first surface profiling causes the medium to be
sealed to be
transported back towards the space to be sealed. The sealing flange
continuously
surrounds the shaft to be sealed and thus prevents leakage of the medium to be
sealed in
the direction of the dust/sealing lip, i.e. in the direction of the
surroundings when the shaft
is standing still. The dustlsealing lip brings about a protection of the
sealing flange and
the backflow conveying member from abrasive pollutants in the environment,
wherein the
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dust/sealing lip preferably surrounds the surface of the shaft to be sealed at
a very small
radial spacing of up to a maximum of 0.5 mm, or in special circumstances can
be in
contact with the shaft. Hence, the dust/sealing lip does not have any wear or
abrasions and
its working characteristics remain constant for a long service life.
The backflow conveying member is preferably helically shaped and in
longitudinal
section, has sawtooth-like first recesses, which are axially spaced from one
another,
wherein the first boundary area of each recess and the surface of the shaft to
be sealed
enclose a smaller angle than the second boundary area of each recess. The
first boundary
area is the area that faces the space to be sealed and the second boundary
area is the area
which faces away from the space to be sealed. As there is a plurality of
recesses, there is
correspondingly a plurality of first boundary areas and a plurality of second
boundary
areas. The sawtooth-like profile of the first surface profiling has the
advantage that the
medium to be sealed is transported back exceptionally well in direction of the
space to be
sealed during the use of the radial shaft sealing ring in accordance with the
invention. The
significantly larger volume of the sawtooth-like recesses compared to
indentations makes
them less sensitive to oil carbonation.
A second surface profiling is preferably provided on that side of the backflow
conveying member that is turned away from the shaft. The second surface
profiling is
formed in longitudinal section by substantially U-shaped, circumferentially
extending
second recesses, which are open towards that side which is turned away from
the shaft and
arranged axially spaced from one another. The sawtooth-like recesses on the
side of the
gasket facing the shaft and the U-shaped recesses on the side of the gasket
turned away
from the shaft produce a gasket which is very flexible in radial direction and
can follow
the movements of the shaft to be sealed, even if deviations from concentricity
occur.
Furthermore, the U-shaped recesses in combination with the sawtooth-like
recesses
produce a very large surface which is well suited for a rapid removal from the
gasket of the
produced friction heat generated.
The gasket is preferably made from polytetrafluoroethylene (PTFE). Thus, the
gasket is resistant to most of the media to be sealed. In addition, PTFE has a
good thermal
stability as well as good glide properties. A gasket made from PTFE is almost
free from
wear since the surface becomes glazed after a certain initial wear and thus
becomes very
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robust.
For example, injection moldable copolymers can be used, such as FEP
(perfluoroethylenepropylene), or PFA (perfluoroalcoxy copolymer), or a
thermoplastic
elastomer.
The gasket, however, can also be made from other materials.
The gasket has preferably a thickness of 0.5 to 1 mm. The working
characteristics
are particularly advantageous when the thickness is 0.6 to 0.75 mm, depending
on the
diameter of the shaft to be sealed. It is disadvantageous if the thickness of
the gasket is
smaller than 0.5 mm since the depth of the recesses has to be reduced and the
gasket
surrounds the shaft to be sealed only with a very small preload.
However, a gasket thickness of more than 1 mm would be disadvantageous, since
the gasket would closely surround the shaft with too high a preload, causing a
very high
dissipation.
In case the gasket is made from PTFE, the sawtooth-like andlor U-shaped
recesses
are preferably embossed into the gasket without any material removal. In
injection
moldable copolymers, the recesses are provided in the injection mold. By
avoiding
machining methods in the production of the recesses, the advantage arises that
the gasket
withholds a very high number of stress cycles without suffering damages even
when
deviations from concentricity of the shaft to be sealed occur, because notch
effects in the
area of the recesses are significantly reduced as in comparison to machining
methods.
The sawtooth-like recesses and the U-shaped recesses are staggered on their
respective sides. On one hand, such an arrangement brings about an
approximately
corresponding material strength along an axial extension of the gasket and,
undesirable
material accumulations are circumvented which would be disadvantageous from a
manufacturing point of view and also with respect to working characteristics.
On the other
hand, the joints are located between the sawtooth-like recesses such that the
geometrical
dimensions of the sawtooth-like recesses remain the same to a large degree
when the
gasket is used for sealing a shaft that is running out of round.
The ratio of the radial depth of the U-shaped recesses to the radial depth of
the
sawtooth-like recesses can range from 1 to 4.5 and is preferably chosen to be
3. Such a
ratio provides an excellent compromise between a good flexibility of the
gasket in a radial
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direction for balancing deviations from concentricity of the shaft, a good
sealing of the
medium to be sealed for a long lifetime, and a large surface area for cooling
the gasket and
removing friction heat.
The sealing flange is preferably of substantially square in longitudinal
section shape.
The axial extent, or axial distance, between axially adjacent second boundary
areas
corresponds preferably and substantially to the axial extent, or axial size,
of the sealing
flange and the axial extent, or axial size, of the dust/sealing lip. Such an
embodiment has
the advantage that the axial width of the sealing ring can be optimally
minimized.
In accordance with a preferred embodiment of the invention a mounting portion
is
provided which is connected to the support ring via an intermediate layer
composed of an
elastomeric material. A linkage between the mounting portion and the
intermediate layer
is realized for example, by vulcanizing the two parts together. From an
economical point
of view it is favourable to produce the intermediate layer in the course of a
direct molding
procedure while simultaneously connecting it with the support ring and the
gasket through
vulcanizing.
In accordance with another embodiment of the invention the possibility exists
that
the mounting portion and the support ring are directly fastened to each other
via a
tensioning member made from a very hard material. This has the advantage that
the
production of such a sealing ring is particularly easy and hence economical.
The support
ring and the tensioning element can both be made from a metallic material, for
example.
A separation of the components of the sealing ring following its use is
especially simple
because of the non-positive and/or positive connection of the holding section
between the
support ring and the tensioning member. The single components can be recycled
by type.
In accordance with a further embodiment of the invention a fleece disk is
provided in
case large amounts of dirt are present in the environment.
Brief Description of the Drawings
Exemplary embodiments of the invention will now be described in accordance
with
the drawings in which:
Fig. 1 and Fig. lA show a first embodiment of a sealing ring in accordance
with the
invention with Fig. lA showing the sealing ring in extended position;
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Fig. 2 shows a second embodiment of the sealing ring in accordance with the
invention including a first surface profiling having first recesses on the
side of the sealing
section which faces the shaft;
Fig. 3 shows a third embodiment of the sealing ring in accordance with the
invention having a support ring made from a polymeric material;
Fig. 4 shows a fourth embodiment of the sealing ring in accordance with the
invention including a tensioning member for fastening the gasket on the
support ring; and
Fig. 5 shows a further embodiment of the sealing ring in accordance with the
invention having a fleece disk for surrounding the shaft such that it is
sealed of from dirt.
Detailed Description of the Invention
Each of the drawings presented in Figs. 1 to 5 explains one embodiment of the
invention in more detail.
Figs. 1 to 5 each show an embodiment of a sealing ring in accordance with the
invention that is basically composed of a gasket 1 and a support ring 4 with
Fig. 1 A
showing the sealing ring in extended position. The gasket 1, as shown in
accordance with
the embodiments of the invention presented herein, is made from PTFE and has a
mounting portion 2 and a sealing section 3. The mounting portion 2 is
connected with a
support ring 4.
The sealing section 3 is functionally divided into three parts and is bent
towards
the space to be sealed 5 in an assembled state. The sealing section 3 has a
first surface
profiling 7 on the side facing the shaft 6 which causes a reconveyance of the
medium to be
sealed in the direction of the space to be sealed S during a rotation of the
shaft 6. The
conveying action of the medium to be sealed is caused by the backflow
conveying member
8.
A sealing flange 10 is arranged on the side of the first surface profiling 7
which
axially faces away from the space to be sealed. The sealing flange 10
continuously
sealingly surrounds the shaft 6 to be sealed. Thus, even if the shaft stands
still, an
excellent static sealing is provided.
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A dust/sealing lip 9 is arranged on the side of the sealing flange 10 which
faces
away from the space to be sealed 5. The dust/sealing lip 9 together with the
surface of the
shaft to be sealed 6 are defining a sealing gap 20 of small radial height.
The bend of the sealing section 3 away from the space to be sealed is
particularly
advantageous from an assembly point of view, since the installation of the
sealing ring on
a previously assembled shaft neither requires an assembly sleeve nor a prior
deformation
of the sealing section. Hence, the use of a sealing ring as described
heretofore is
particularly advantageous for use as a crankshaft seal on the side of the
flywheel and/or as
a camshaft seal.
Fig. 1 shows a first embodiment of the gasket. The backflow conveying member 8
is helically shaped and in longitudinal section has sawtooth-like first
recesses 11. The
sawtooth-like first recesses 11 are designed such that a first boundary area
12 facing the
space to be sealed encloses a smaller angle 13 with the surface to be sealed
of the shaft 6
than the second boundary area 15 that is turned away from the space to be
sealed 5.
Axially neighbouring second boundary areas are shown in Figs. lA, 3 and 4 as 1
S.1 and
15.2. The smaller angle 13 is preferably 15° to 75° while the
larger angle 14 is
approximately 90°.
The sawtooth-like recesses 11 are only present in the area of the sealing
section 3
and are arranged in an alternating fashion, i.e. staggered, with the U-shaped
second
recesses 17. The ratio of the radial depth of the U-shaped second recesses 17
to the radial
depth of the sawtooth-like first recesses 11 is 3 in this embodiment. Such a
ratio ensures
a good flexibility of the gasket in a radial direction to balance deviations
from
concentricity of the shaft. Furthermore, such a profile provides a large
surface for cooling
of the gasket and for dissipating friction heat.
This embodiment shows the mounting portion 2 connected with the support ring 4
via an intermediate layer 18, which is made from an elastomeric material.
The sealing ring presented here has aside from good working characteristics
small
dimensions in axial direction.
Fig. 2 shows a second embodiment of the sealing ring in accordance with the
invention. The sealing ring presented here is basically different from the
sealing ring
presented in Fig. 1 in that a first surface profiling 7 having first recesses
11 is only
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provided on the side of the sealing section 3 that faces the shaft 6.
The support ring 4 is arranged relatively to the gasket 1 and designed such
that the
gasket 1 becomes centered in its mounting space through the support ring 4.
The connection of the gasket 1 and the support ring 4 is realized also, in
this
example, through an intermediate layer 18 made of an elastomeric material.
This
intermediate layer 18 completely surrounds the radial leg 21.
Fig. 3 shows a third embodiment which is different from the embodiments
described heretofore in accordance with Figs. 1 and 2 in that the support ring
4 is not made
of metallic material but of polymeric material. The support ring 4 is
preferably coated
with a sealing lacquer 22 on an outer circumferential side for sealing it in a
housing not
shown herein.
The sealing section 3 obliquely extends from the support ring 4 towards the
shaft 6,
which positively influences the radial pressing onto the shaft 6.
Fig. 4 shows a fourth embodiment of the invention which is essentially
different
from the embodiment presented in Figs. 1 to 3 in that the fastening of the
gasket 1 of the
support ring 4 is different. In the fourth embodiment, the support ring 4 is
shown to be
substantially L-shaped, wherein the axial side 23 has a recess 25 on the end
24 facing away
from the space to be sealed. The tensioning member 19 form fittingly snaps
into the recess
25. The tensioning member 19 presses the mounting portion 2 under an axial
preload onto
the radial side 21 of the support ring 4.
Fig. 5 shows a further embodiment which is basically differentiated from the
above
described embodiments in that a fleece disk 26 is provided on the side facing
away from
the space to be sealed. The fleece disk 26 surrounds the shaft 6 such that it
is sealed from
dirt. As is shown in Fig. 5, the fleece disk cooperates with the sealing
flange for sealing
the shaft from dirt.
The above-described embodiments of the invention are intended to be examples
of
the present invention and numerous modifications, variations, and adaptations
may be
made to the particular embodiments of the invention without departing from the
scope and
spirit of the invention, which is defined in the claims.
