GB2189851A

GB2189851A - Metallic sealing rings

Info

Publication number: GB2189851A
Application number: GB08610773A
Authority: GB
Inventors: Michael John Caswell Tozer
Original assignee: Heat Transfer Technology Ltd
Current assignee: Heat Transfer Technology Ltd
Priority date: 1986-05-02
Filing date: 1986-05-02
Publication date: 1987-11-04
Also published as: GB8610773D0; CA1289158C

Abstract

A hollow metallic sealing ring is of substantially W-shaped radial cross-section and has a pair of divergent limbs (1) connected by a contiguous single loop (3) with substantially parallel sides (3a). The transition curve (2) between the sides (3a) of the loop (3) and the divergent limbs (1) is of constant radius and the free ends (1a) of the limbs are straight and substantially parallel. <IMAGE>

Description

SPECIFICATION Hollow metallic sealing ring This invention relates to hollow metallic sealing rings of the so-called low-load self-energising static kind as used for instance in pumps, motors and other apparatus to form leakproof seals between opposed, usually plane, parallel surfaces.

Conventional metallic sealing rings for this purpose are of 'C' or '0' shaped radial crosssection 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 and 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 two outer limbs, intended to engage the surfaces or flanges to 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 3575432, 3797836 and 4121843. In each of those examples the outer limbs are of sinuous configuration with curved extremities which make line contact with the surfaces or flanges to be sealed.

The present invention 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 the present invention a hollow metallic seal is of substantially Wshaped radial cross-section comprised of a pair of divergent limbs connected by a contiguous single loop with substantially parallel sides, the transition curve between the sides of said loop and the said divergent limbs being of constant radius and the free ends of said limbs being straight and substantially parallel. Preferably the radius of the curved end of the loop is considerably less than the radius of the aforesaid transition curve.

A particular and at present preferred embodiment of the invention is illustrated in the accompanying drawings, in which: Figure 1 is a plan view of the sealing ring; Figure 2 is an enlarged scale radial crosssection on line A-A of Fig. 1; and Figures 3, 3A, 3B, 3C and 30 are diagrammatic views to illustrate final stages in the formation of a sealing ring as shown in Figs.

1 and 2.

Referring now to 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 BS 2HR 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 925"C+ 10 C in a vacuum, then force cooled, and finally heat treated for 4 hours at 750"C+10" in vacuum.

As shown in Fig. 2 the ring in radial crosssection is of somewhat W-shape with two divergent limbs 1 connected by constant radius curved transitions 2 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 radius S of the curved transitions 2, whilst the free ends 1 a of the 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 10.478 inches, the axial length is 0.248 inches, the inside radius S of each transition curve 2 is .023 inches and the inside radius R is .009 inches. The length of the straight free ends 1a is .020 inches, the inside diameter at the free ends is 10.2 inches, the inside diameter at the loop 3 is 10.150 inches and the outside axial length of the loop 3 and the two curved transitions 2 is about .158 inches.

The mode of formation of the hollow metallic ring is hereafter described by reference to Figs. 3, 3A, 3B, 3C and 3D.

Fig. 3 shows in radial section a hollow metallic sealing ring substantially as disclosed in our co-pending patent application of the same date and which has been made in stages as described with reference to the drawings of that application. Two radii R1 and R3 are indicated, and as shown part of the ring formed by radius R3 is removed (Fig.

3A), whereafter the radiused part R1 is extended to a line B-B (Fig. 3B) perpendicular to the diametric plane of the ring.

A radius R2 equal to the thickness of the material of the ring is now added at line B-B and at line C-C, which is parallel thereto, to form parts DD and EE.

Finally, the two parts D are connected to one another as are the two parts E to achieve the final formation shown in Fig. 3D.

In suitable circumstances the sealing ring could be made of other metals than the one mentioned in the foregoing, such as for instance steel, stainless steel or an alloy with a high nickel content using appropriate heat treatments.

Claims

1. A hollow metallic sealing ring of substantially W-shaped radial cross-section comprised of a pair of divergent limbs connected by a contiguous single loop with substantially parallel sides, the transition curve between the sides of said loop and the said divergent limbs being of constant radius and the free ends of said limbs being straight and substantially parallel.

2. A hollow metallic sealing ring as claimed in Claim 1 in which the radius of the curved end of the loop is considerably less than the radius of the transition curve.

3. A hollow metallic sealing ring shaped substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.