GB2263739A - Sealing ring - Google Patents

Description

1 SEALING RING 2263739 This invention relates to sealing rings, and in

particular to sealing rings of the "low-load" kind, as used for example in valves, pumps, motors and other apparatus to form leakproof seals between opposed, usually plane, parallel surfaces.

One known form of sealing ring has a radial cross-section of C-shape with the open side of the C facing the centre of the ring. Other known seals have radial cross sections of generally similar profile. Two examples are a seal having a radial cross-section of modified parabolic form with convergent margins, as described in GB 2187805, and a further seal in which the limbs of the seal cross-section have out-turned lips, forming an n-shaped cross-section, as shown in GB 2038961. W- or M-section seals are also known The above-mentioned known seals have been very successful in numerous static sealing applications, but are not always suitable for meeting the desired shape recovery values after compression.

The present invention sets out to provide,a seal capable of solving the problems of known seals, and in 2 particular capable of a substantial degree of shape recovery after compression.

According to the present invention there is provided a sealing ring having a cross-section which comprises a first limb in its radially outermost region and a second limb in its radially innermost region, said limbs being aligned substantially in the direction in which the ring is compressed during use, the said limbs being directed in mutually opposite directions and being interconnected by an intermediate portion defining two oppositely orientated arcuate portions for contacting the surfaces to be compressed, said arcuate portions each being connected to a respective one of the said limbs.

The provision of the limbs serves to prevent this rotation of the crosssection about the intermediate portion during compression of the seal. The hoop strength in the limbs serves to restrain spreading of the ring and cause a roughly similar degree of opposed spreading in the intermediate portion within the overall cross-sectional envelope, thus serving to oppose the rotation of the intermediate portion about the cross-sectional centre.

The result of this arrangement is that it is possible to 1 3 provide a seal having a high recovery value.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a cross-section of a seal in accordance with the present invention, in position between two surfaces to be sealed, before compression; and Figure 2 shows a further embodiment of the seal according to the invention, also in position between two surfaces to be sealed, before compression.

Figures 1 and 2 show upper and lower bodies 1 and 2 to be sealed, which are, for example, pipe end or valve body flanges. The upper flange 1 has a plain surface, the lower flange 2 has a rectangular recess 4 at the end of the bore 15. A resilient sealing ring 3 is seated in the recess 4.

The sealing ring shown in Figure 1 comprises a radially outer, downwardly directed limb 6 and a radially inner, upwardly directed limb 8. The two limbs are connected by a generally S-shaped intermediate portion 10 which comprises, at its ends, two respective arcuate portions 4 12 and 14, for contacting the flanges at P and Q respectively. The portions 12, 14 extend axially beyond the ends of the limbs 6, 8 respectively. Under compression the portions 12, 14 contact the flange surfaces and the portion 10 flexes, tending to rotate about its centre.

Because of the hoop strength in the vertical limbs 6 and 8, the natural tendency of the portions 12, 14 of the seal to spread in directions BB and CC during compression is counteracted and the seal ring cross-section will tend also to spread in the opposite directions DD and EE in reaction to hoop strength of the limbs. These movements create a reaction on the intermediate portion 10 in that it tends to encourage a reduction in the intermediate portion diameter at points F and increase in the diameter of the intermediate portion in the region of G.

These flexings effectively define springs, thereby providing a seal having an unusually high recovery value. The high recovery value is particularly important in environments which are susceptible to extremes in temperature and pressure such as, for example, explosions and sudden fire.

The seal ring can be made of any suitable material, metal or non-metal, but is preferably made of high nickel alloys or other metal capable of having its spring characteristics improved by heat treatment, leading to a seal in which the regions of flexure are effectively high temperature springs of very high quality, providing a seal with very high recovery values and capable of coping with extremes of temperature and pressure arising for example from an explosion or sudden fire. Such extremes can lead to sudden leakage because of variations in expansions of fixing bolts joining the members between which the seal is placed, for example at a valve body.

As compression is increased the tip of the outer limb 6 will come into contact with the opposing meeting surface of the seal seat at R and will then become stressed as a strut. In reaction this increasing the contact pressure at P on portion 14.

The outer limb 6, has three basic functions:

(i) to assist in locating the seal in its recess; (ii) to restrain the radially outwards spreading of the seal when compressed; and 6 (iii) to increase contact pressure at point P (which is a non-self energizing contact point) when the base of the strut 6 comes into contact with its opposing mating face of the recess 4 at R.

The seal is preferably made from a high nickel alloy j order that it can be age hardened (i.e. heat treated) rather than simply work hardened. The seal can be coated with PTFE or a suitable metal such as silver, lead, nickel or gold, for example. However, the seal itself can be made from any metal which can provide suitable spring characteristics. It is also possible for the seal to be made entirely from non-metallic materials, provided that the necessary hoop strength and spring characteristics can be achieved.

The seal is, in relative terms, a "low-load" seal, but, it is only 50% self-energizing. This is because, during use, internal pressure from the bore builds up between the limb 8 and the intermediate portion 10, thus forcing arcuate portion 12 into contact with recess 4 at point 2, serving to encourage sealing action, this pressure build up does not occur between the intermediate portion 10 and limb 6, thus arcuate portion 14 does not form a self-energising seal with flange 1.

7 The illustrated seal is used for sealing against internal pressure. To seal against external pressure, the seal cross-section should be rotated through 180', that is to say, the radially innermost limb should be directed downwardly and the radially outermost limb directed upwardly, so that fluid pressure can enter the space between the outer limb 6 and the intermediate portion 10.

In the second embodiment, as shown in Figure 2, it can be seen that the inner limb 8 has been extended so that it can come to rest against the face 1 during compression. This could be desirable to, for example, prevent the void between the limb 8 and the intermediate portion 10 being filled with foreign matter or to prevent turbulence in the flow of fluid. However, if the inner limb 8 is to be extended in this manner, it could well be necessary to provide apertures 16 in the inner limb, in order to maintain a pressure balance on either side of the limb 8, and to facilitate a self-energising sealing action.

Generally, in order to reduce the risk of seal distortion, it will be necessary to increase metal thickness and size of section in proportion to the diameter of the seal and its operating pressure.

8 Exiinles Two seals were tested, each having an initial uncompressed radial cross- sectional width and overall axial thickness (A) = 2.5mm, and internal diameter = 26.5mm. The length of the limbs 6,8 was less than the overall axial thickness (A) before compression by an amount equal to 55% of the expected degree of compression for limb 8 and 45% for limb 6. The seals were produced from a high nickel alloy known as Nimonic 80A (trade mark of Inco Alloys), 0.3 mm thick; one set was only work-hardened, the other age-hardened. The seals were tested for their ability to recover after being compressed by 20% of their overall thickness. The results were as follows:

Work Hardened Before ComDression 2.54mm Acre Hardened Before ComDression 2.54mm Co=ressed 2.03mm ComDressed 2.03mm Af ter Com-oression 2.21mm Af ter Comi:)ression 2.335mm % Recovgry 35% % Recovery 60% 9 The age hardened seals were then silver plated to a depth of 0.02mm all over and pressure tested to 1000 psi with nitrogen, when they sealed perfectly, when the pressure was increased to 1250 psi, perfect sealing was still achieved.

Generally, the seals are produced by a series of pressing operations. However, if desired, it is possible to produce the seals by machining from solid material.

Many modifications will suggest themselves to a person skilled in the art upon making reference to the foregoing description, which is given by way of example only and is not intended to limit the scope of the invention in any way.

For example, whereas the illustrated seal has a Z-like cross-section, the number of intermediate portions and curved contact portions may be increased for example to a W or M-shaped cross-section or even further.

Claims (10)

1. A sealing ring having a cross-section which comprises a first limb in a radially outer region and a second limb in a radially inner region, the said limbs being (i) aligned generally in the direction in which the ring is compressed during use, (ii) directed in mutually opposite directions and (iii) interconnected by an intermediate portion defining two oppositely orientated arcuate portions; the said arcuate portions each being connected to a respective one of the said limbs.

2. A sealing ring according to claim 1, comprising a generally straight intermediate portion situated between the two arcuate portions.

3. A sealing ring according to claim 2, wherein the intermediate portion is aligned generally parallel with the said limbs.

4. A sealing ring according to any preceding claim, wherein the said first limb is of such a length that, during normal compression of the ring by two surfaces between which a sealing action is to be effected, the tip of the first limb comes into contact with the adjacent compressing surface.

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5. A sealing ring according to any preceding claim, wherein the said second limb is of such a length that, during normal compression of the ring by two surfaces between which a sealing action is to be effected, the tip of the second limb does not come into contact with the adjacent compressing surface.

6. A sealing ring according to any one of claims 1 to 4, wherein the said second limb is of such a length that, during normal compression of the ring by two surfaces between which a sealing action is to be effected, the tip of the second limb comes into contact with the adjacent compressing surface.

7. A sealing ring according to claim 6, wherein at least one aperture is provided in the second limb.

8. A sealing ring according.to any preceding claim made from a high nickel alloy.

9. A sealing ring according to any preceding claim comprising a coating selected from the group consisting of PTFE, silver, lead, nickel and gold.

10. A sealing ring substantially as herein described, with reference to Figure 1 or 2 of the accompanying drawings.