Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to hollow metallic sealing
rings of the so-called low-load self-energising static
kind as used for instance i;n pumps, motors and other
apparatus to form leakproof seals between opposed,
usually plane, parallel surEaces.
Conventional metallic sealing rings for this purpose
are of 'C' or '0' shaped radial cross-section but these
have a major disadvantage in that they have a high
spring rate and for many applications when the seal must
have a large diameter the resultant compressive loads
required are extremely high and not suited to the
relatively weak flanges such as are used, for example,
on aero engines.
Difficulties also arise when the gap to be sealed
between surfaces or flanges is relatively large as
happens with certain engines because of the need to
cater for the manufacturing tolerances in assembly of
the various parts of the engine which determine the
relative position of the flanges. Further, this
accumulated tolerance is compounded by differential
expansion of the flanges both longitudinally and
radially. There is therefore constant movement as the
engine temperature varies from cold to hot an~
sealing contact points are not of constant diameter.
The sealing ring must accordingly be sufficiently
resilient to cope with large amounts of radial and axial
expansion and contraction.
To this end, various forms of sealing ring which, in
radial section, are of concertina or bellows-shaped
profile have been proposed and comprise t~o outer limbs,
intended to engage the surfaces or flanges ~o be seated
connected by one or more contiguous loops. Typical
examples of such metallic sealing rings are those which
are disclosed in U.S.A. Patent Specifications 3575~32
3797836 and 4l2la43. In each of those examples the
outer limbs are of sinuous configura~ion with curved
extremities which make line contact with the surfa~es or
flanges to be sealed.
The present in~ention has been devised with the
object of providing a sealing ring which has a superior
performance compared with the sealing rings which have
been hitherto proposed and/or used.
In accordance with ~he present invention a hollow
metallic sealing ring is comprised in radial
cross-section of a pair of outwaLdly convex limbs which
extend from the ends of a loop formation having at least
one contiguous straight sided loop, the limbs, from
their junctions with the ends of the loop formation,
being of increasing radius towards their free ends which
are straight and substantially parallel.
',. ' -
L5~3
Preferably the radius of the curved end of the loop is
considerably less than the minimum radius of the
aforesaid outwardly convex limbs. Also where there is
more than one loop~individual loops may be of different
width.
Some particular and at present preferred embodiments
of the invention are illustrated in the accompanying
drawings, in which:-
Fig. l is a plan view of a single loop sealing ring;
and
Fig. 2 is an enlarged scale radial cross-section on
line A-A of Fig. l;
Figs. 3, 3A, 3B and 3C are diagrammatic viaws to
illustrate four stages in the formation of a particular
sealing ring;
Figs. 4, 4A, 4B and 4C similarly illustrate stages
in ~he formation of a sealing ring with alternative limb
and central loop radii:
Figs. 5, 5A, 5B, 5C and 5D similarly illustrate
changes in the loop length and straight limb part length
of a sealing ring: and
Figs. 6, 7, 8 and 9 are cross-sections of four
different plural loop embodiments of the invention.
Referring firstly to Figs. l and 2 of the drawings,
the hollow metallic sealing ring therein shown is
intended for a turbine gas path aircraft engine and is
made of a metal alloy known as NIMONIC 80A Specification
12~5~1
BS 2~R 201 of thickness .008 ~ .001 inches which is
formed as a circular arc with it's two ends subsequently
welded together. The ring is heat treated firstly for 1
hour at 925C ~ 10C in a vacuum, then foEce cooled, and
finally heat treated for 4 hours at 750C ~ 10' in
vacuum.
As shown in Fig. 2 the ring in radial cross-6ection
is of somewhat W-shape ~ith two outwardly convex limbs 1
connected to a central loop 3 of which the sides 3a are
parallel and relatively close together. The radius R of
the central part of the loop is significantly less than
the transition radius S between the sides 3a and the
limbs 1, whilst the free ends la of ~he limbs 1 which
engage the surfaces or flanges to be sealed are
straight, substantially parallel, and lightly lapped and
polished.
Typically the outside diameter of the ring is 10.~78
inches, the axial length is 0.248 inches, the inside
radius S is .023 inches and the inside radius R is .009
inches. The length of the straight free ends la is .020
inches, the inside diameter at the free ends is ~0.2
inches, the inside diameter at the loop 3 is 10.1~0
inches and the distance between the centres of radius S
is .088 inches. The nominal radius T is .126 inches.
In the stages of ring formation illustrated in Figs.
3 to 3C inclusive?D is equivalent to the width of the
space to ~e f illed by a sealing ring which in this
3L2~3~iS~
instance is made of metal such as steel, stainless
steel, or an alloy with a high nickel content using
appropriate heat treatments. The thickness T of the
metal may in this instance be .3 mm (.~12 inches). Fig.
3A shows the width D notionally divided into four egual
parts D/4 defining centres of radius lines O, K and L.
Fig. 3A shows respective radii R3 and R4 where:
R3 = D/2 - T and
R4 = D/9 - T/2
Fig. 3B shows an added radius Rl where:
Rl = R4 = D/8 - T/2
In Fig. 3C, J is a line drawn tangential to the
centre of the central loop perpendicular to lines O, K
and L and 3D shows the addition of straight sections to
the limbs as far as this line J.
Due to large variations in the size and shape of the
recesses which are to be occupied by these rings, it is
necessary on occasions to vary the relative dimensions
of their constituent parts.
Stages in variation of ~he limb and loop radii are
for example shown in Figs. 4 to 4C.
Firstly radius R4 is reduced in order to reduce the
loop width Z. Then the radius Rl is reduced and the
centre is positioned so ~hat the part formed by radius
Rl joins the reduced width loop and also still joins the
part formed by radius R3. Finally, the straight part of
the limb is reduced to the line J.
.,
~ 2~
The mode of achieving variations in loop and
straight limb part is shown in Figs. 5 to 5D.
Firstly the centre for radius R4 is moved from line
B to line E (Fig. 5A), a distance which is equal to
twice the metal thickness i.e. 2T. Also the straight
part of each limb can be extended from line F (Fig. 5)
to line G (Fig. 5B) that is to say by an amount of 2T.
The transition from Yig. 5 to Fig. 5C shows how the
centLe for radius R4 can be moved from line B to line F
where the distance between lines B and F is 2T.
Finally the transition from Fig. 5 to Fig. 5D shows
how the length of the flat part of the links can be
reduced from line F to line H a decrease of T (the
material thickness).
It is to be understood that any of the changes
depicted between Figs. 3 to 5 inclusive can be made
independently of the others or a combination of such
changes can be made.
Fig. 6 shows a plural loop version of the sealing
ring illustrated in Fig. 5 by the addition of an extra
convolution to provide two loops of equal width with two
radii Rl, two radii R3, two radii R4 and one radius R5,
the distance between the two loops being the same as the
internal width of each loop. The loops have the same
length as the outer limbs.
5~
Fig. 7 shows a plural loop sealing ring similar to
that which is shown in Fig. 7 except that, as a result
of a change in the position of radius R4. the loops are
elongated beyond the outer limbs.
Fig. 8 shows a variation of the sealing ring shown
in Fig. 6 wherein by an increase in radius R5 there is
an increased bridging dimension Z between the loops
which in this embodiment also are the same length as the
outer limbs.
Finally, Fig. 9 shows a two loop sealing ring
wherein, as a result of the movement of the centres of
radii, Rl, R4 and R5 the loops or convolutions have
non-parallel sides.
A
