Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGR WND OF THE INVENTION
m is invention relates to shaft seals and particularly to such
seals having hydrodynamic characteristics.
~ ny types of shaft seals are known in the prior art and many
such seals include ribs or ridges angularly displaced so as to provide
a pumping action to return errant fluid, which may have passed the seal
because of imperfections in the shaft, to the fluid side of the seal.
Most such prior art devices have a resilient sealing portion which is
formed by molding. Mblding is a comparatively expensive operation and
not well suited to certain otherwise desirable materials particularly
polytetrafluoroethylene.
~ It has also been proposed to form hydrodyn~mic shaft seals utilizing
a plurality of differently formed "washers" of materials such as
polytetrafluoroethylene, the washers being stacked axlally along the
shaft and each of the washers perfonming a separate function to
o~
provide an overall seal. An example of such a seal is found in U.S.
Patent 3,801,114. While being somewhat more amenable to construction
with materials such as polytetrafluoroethylene than the prior art
molded seals such a seal is nevertheless relatively complicated.
It is an object of the present invention to provide a seal which
can be readily made from materials such as polytetrafluoroethylene.
It is another object of this invention to provide such a seal
which utilizes a minim~m number of parts and is therefore simple and
inexpensive to manufacture.
It is a further object of this invention to provide such a seal
having excellent hydrodynamic pumping characteristics.
SUMM~RY OF THE INVENTION
The above and other objects are provided by the seal of the pre-
sent invention which includes an annular housing of metal or the like
which clampingly engages and supports a single annular sealing member
of polytetrafluoroethylene or the like. The sealing member, prior to
its insertion on the shaft, is planar and includes an interior wall
which is at right angles to the plane of the seal. The interior wall,
when viewed perpendicular to the plane of the unstressed sealing member,
is scalloped. When placed on the shaft, the seal, and more particl11arly
the sealing member thereof, engages the shaft in a correspondingly
scalloped manner; i.e., at greater and lesser axially positions from
a base line such positions being determined by the relative dimensions
of the shaft and seal and by the magnitude of the scallops on the un-
stressed seal member. The seal engages the shaft at one edge of thesealing member, i.e., at the intersection of one flat face thereof
and the scalloped interior each part of which is normal to the adjacent
portion of the flat face. The scalloped face is oriented in the direction
so as to force the fluid against which it is sealing and it is at a
~ t3~
varying angle with respect to the shaft providing thereby a scraping
effect which provides a very efficient hydrodynamic pumping action.
BRIEF DESCRIPTION OF THE ~RAWINGS
In the drawings:
Fig. 1 is a plan view of a preferred embodiment of the invention
showing, in the top half thereof, the seal as it appears in use on a
shaft and, on the bottom half thereof the seal as it appears in its
initial unstressed condition;
Fig. 2 is a cross-sectional view of the seal and shaft taken in
the direction of the arraws 2-2 of Figure 1 and showing the in use
configuration of that portion of the sealing member at the maxim~m
diameter thereof; and
Fig. 3 is a cross-sectional view taken in the direction of the
arrows 3-3 in Figure 1 and showin~ the in use configuration of that
portion of the sealing member having the minimum diameter.
DESCRI~LlON OF THE PREFERRED EMBODIMENTS
Figures 2 and 3 show the seal of the present invention in its
in use position on Shaft S. The seal comprises a housing of relatively
rigid material such as metals which clampingly engages the seal member
10. The housing can and preferably does include an inner '~"-shaped
member 11 and an outer '~"-shaped member 12 between which are sandwiched
the seal member 10. An annular elastomeric resilient material in the
form of washer 13 is preferably provided in face-to-face contact with
the seal member 10 compressed between the halves of the casing to pro-
vide limited yieldability and thereby enhance the integrity of the clampedjoint. The seal is formed by inserting the elastomeric ring 13 and
sealing member 10 followed by the inner '~"-shaped member 11 within the
outer '~"-shaped member 12 and then deforming the outer~ "-shaped
member in~ardly at 14 to secure the structure together. The seal 10
3~iOO
i5 preferably made of polytetraflouroethylene although other plastic
or rubber materials suitable to the particular application such as
Neoprene can be used.
m e sealing member 10 is shown in its unstressed condition in the
lower half of Figure 1. As will be seen the inner wall (15 in Figures
2 and 3) of the sealing member 10 is perpendicular to the axially
spaced flat faces thereof and is scalloped when viewed perpendicular
to the plane of the sealing member, i.e., as seen in Figure 1. The
scalloping is such that the unstressed sealing member has an opening
with a maximum radius Rl and a minimum radius R2. The radius increases
in a generally uniform fashion fram a minimum R2 to a maximum Rl several
times in progressing around the seal. m e number of "cycles" (i.e., the
number of times the radius progresses fram a minimum to a maximum and
back to a mini~um) preferably increases as the overall seal size increases.
Preferably there are about one to two cycles per inch of seal diameter.
In a seal of very small diameter, for instance one inch (2.54 cm.), a
single or double cycle could successfully be used. For larger seals up
to approximately six inches (15.25 cm.) between about six and about
twelve cycles are preferably used.
A variety of scalloped geometries can be used. In one preferred
embodiment, not illustrated, the scallops are sinusodial; i.e., the
radius is defined by the equation R=Ro+ K sin (N~) where Ro is the
average radius, K is a constant related to the amplitude of the
excursions fram the average radius, N is the number of scallops or
"cycles" around the seal lip and ~ is the angular position around
the seal fram an arbitrary zero point.
In another preferred embodiment and as illustrated, the scallops
can be generated as circular arcs having a center located between the
center of the seal and the sealing portion thereof with a radius R3
less than the average radius of the seal and preferably in the range
3fi()0
of 75% - 90% the such average diameter.
As will be appreciated the amplitude of the radial excursions of
the seal lip and the average diameter of the seal lip relative to the
diameter of the shaft will both affect the in/use angles between the
interior face 15 of the seal member and the shaft S. Preferably this
angle increases from a n~rLu~un Ql shown in Figure 2 and associated
with the noucu~un interior diameter of the seal member 10, of between
45 and 80 degrees and a maxLmum angle Q2' shown in Figure 3 and
associated with a mininn~n interior diameter of the seal nember 10,
of a n~uui~lm of 90 degrees.
The seal member 10 is displaced axially by a minimum distance A
which is preferably at least equal to the radial clearance B between
the radially innermost portion of the casing m~mbers and the shaft.
In addition, the magnitude of the amplitude of the scallops will be
such that the axial position of the sealing edge between its mnlLi~um
displacement A and the maxinnlm displacement C (see Figure 3) will be
between about .030 and .120 inches.
It has been found in a seal according to the present invention
that it is very simple to construct and provides a very efficient
hydrodynamic pumping action. The foregoing description of the pre-
ferred embodi~Ents is considered illustrative and not limiting.
Many i ~ entions within the spirit and scope of the following claims
will occur to those skilled in the art.
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