GB2072277A - Gaskets - Google Patents

Abstract

A gasket comprises an elastomer coated (2) inner sealing ring (1) and a plain metal outer guide ring (7), each ring being a substantially flat annulus. The inner ring preferably has its radially outermost edge (5) profiled (6) to engage a mating profile on the radially innermost edge of the outer ring. The coating may be ribbed (3). <IMAGE>

Description

SPECIFICATION Improvements in and relating to gaskets This invention relates to flat, annular gaskets of the kind which can be clamped between pipe flanges to form a seal therebetween.

Such gaskets are well-known and suffer from the disadvantage that it is relatively easy to under, or over-compress the gasket material, which is usually relatively soft and deformable.

Our copending application of even date discloses and claims an elastomer coated inner ring for use with a spiral wound gasket. However, the use of such a combination is not appropriate for some low pressure joints where there is not enough bolt head to compress the spiral wound component to form a seal. Also, where the pipe flanges are completely coated with a protective resin layer, a spiral wound gasket is liable to cut into, or through the coating, making it difficult to re-form a good seal if the joint ever has to be broken.

The present invention provides a gasket comprising an elastomer coated inner sealing ring and a plain metal outer guide ring.

The word ring in this present context has its usual significance and means a substantially flat annulus. Because the outer ring is of plain metal, it can be used to provide control over the total, inuse compression of the elastomer coating on the inner ring. The resultant joint is strong and unlikely to damage the protective coating on the flanges.

Preferably the elastomer material on at least one of the flat faces of the inner sealing ring incorporates a sealing profile, for example, in the form of a series of concentric ridges of V-shaped section with the apex of the V projecting away from the plane of the ring. In this preferred configuration, the inner ring resembles the traditional serrated gasket machined from solid metal, but its mode of use is entirely different, because the profiled elastomer faces do not cut into the flanges to be joined. The use of a profiled surface also allows for some displacement of elastomer material on compression.

It has been found that the use of a gasket according to the invention can provide a seal, effective to minimize the risk of leakage through to the outer guide ring. It also serves to protect the flange coating material from mechanical damage.

In particular the action of bolting-up the joint does not tend to crack or cut into an epoxy or other resinous coating in the way that a conventional spiral wound gasket would do.

However, as is made clear in the aforesaid copending application, the use of a spiral wound gasket with partly coated flanges and in a relatively high pressure joint, is perfectly acceptable, because in such a case, the coated inner sealing ring protects the vulnerable part of the flange, whilst the spiral wound component provides the seal.

It will be appreciated that it is not simply a matter of coating a standard inner ring with elastomer. It is necessary to allow for the thickness of the elastomer material by making the inner ring thinner than usual. However, it may not be necessary to machine the radially-outer most edge of the inner ring to engage the inner circumference of the outer guide ring. The appropriate edge profile can be supplied by moulding it in situ from the elastomer material so that the coated inner ring will be retained in the outer ring, for ease of handling. In general terms the combination of the elastomer coating and the inner ring will be somewhat thicker than the outer guide ring, provided that the elastomer profile allows for displacement of the elastomer, rather than for its extrusion from the joint.

Because the core portion of the inner ring is effectively encapsulated, it is not necessary to make it from an expensive metal or alloy and indeed, it is not even essential to make it from metal, provided that it has sufficient hardness and rigidity, of course. It therefore may be significantly cheaper than a conventional inner ring, particularly one formed, say, wholly from a fluoroelastomer material or from an expensive alloy. For many applications, the elastomer material can be a chemically-resistant rubber such as neoprene, although it may occasionally be necessary to use a fluoroelastomer. Even if it is necessary to do this only the inner ring will be affected of course; the cost of the rest of the joint will not be altered.

In order that the invention be better understood, one embodiment of it will now be described by way of example with reference to the accompanying drawing in which the sole figure is a cross-sectional side view through a gasket in accordance with the invention.

In the figure, an inner ring comprises a flat steel annulus 1 encapsulated in neoprene rubber 2. The opposed flat faces of the ring are profiled by the encapsulation to incorporate a series of V-shaped ribs 3. The inner edge 4 of the ring has a substantially uniform coating of rubber on it; in use it forms the bore of the pipe joint, of course.

The outer edge 5 has a moulded rubber "nose" 6, which is shaped to engage a corresponding recess in the inner edge of an outer guide ring 7. The moulded nose could equally well be formed by machining the annulus 1 before applying the rubber to it, of course.

Because the rubber ribs 3 can be displaced sideways into the associated grooves, the opposed faces of the inner sealing ring are much softer than they would otherwise be and even when bolted up between two pipe flanges, there is little or no risk of the protective coating on the flanges being damaged. This is particularly valuable where the flanges (and pipe bore) are coated with a chemically-resistant material such as an epoxy resin. The relatively soft rubber deforms to make a seal against the resin layer, without cutting into it and exposing the pipe metal to possible corrosion by the fluid in the pipe. The seal also protects the outer guide ring and the encapsulated steel annulus 1 at the same time.

The outer guide ring limits the total compression of the joint and makes the final assembly extremely strong, without risk of damage to the seal developed between the inner ring and the flanges. Unlike a conventional soft gasket joint, the elastomer material is supported and protected from overcompression and stress due to the weight of the pipework. The outer guide ring also serves to accurately locate the inner sealing ring relative to the pipe bore and to the clamping bolts.

In horizontal pipework this is extremely important to the making of satisfactory joints. It also makes assembly much easier.

Claims (8)

1. A gasket comprising an elastomer coated inner sealing ring and a plain metal outer guide ring.

2. A gasket according to claim 1 wherein the inner ring is in the form of an annulus having two opposed substantially flat faces on at least one of which the elastomer coating material is formed into a sealing profile.

3. A gasket according to claim 2 wherein said profile is constituted by a series of concentric ridges of V shaped cross-section.

4. A gasket according to any preceding claim wherein the radially-outermost edge of the inner ring is shaped to engage the inner circumference of the outer guide ring.

5. A gasket according to claim 4 wherein said shaping is constituted by an edge portion integrally moulded from the elastomer material.

6. A gasket according to claim 4 wherein said shaping is provided by profiling the edge of the inner ring prior to applying a substantially uniform coating of elastomer material thereto.

7. A gasket according to any preceding claim wherein the elastomer coating material is neoprene rubber.

8. A gasket substantially as hereinbefore described with reference to and as illustrated by the accompanying drawing.

8. A gasket according to any of claims 1 to 6 inclusive wherein the elastomer coating material is a fluoroelastomer.

9. A gasket substantially as hereinbefore described with reference to and as illustrated by the accompanying drawing.

New claims or amendments to claims filed on 15 December, 1980.

Superseded claims 1 to 9 inclusive.

New or amended claims

1. A gasket comprising an elastomer coated inner sealing ring and a plain metal outer guide ring, the inner ring being in the form of an annulus having two opposed substantially flat faces, on at least one of which the elastomer coating material is formed into a sealing profile.

2. A gasket according to claim 1 wherein said profile is constituted by a series of concentric ridges of V-shaped cross-section.

3. A gasket according to claim 1 or claim 2 wherein the radially-outermost edge of the inner ring is shaped to engage the inner circumference of the outer guide ring.

4. A gasket according to claim 3 wherein said shaping is constituted by an edge portion integrally moulded from the elastomer material.

5. A gasket according to claim 3 wherein said shaping is provided by profiling the edge of the inner ring prior to applying a substantially uniform coating of elastomer material thereto.

6. A gasket according to any preceding claim wherein the elastomer coating material is neoprene rubber.

7. A gasket according to any of claims 1 to 5 inclusive wherein the elastomer coating material is a fluoroelastomer.