GB2092240A - Gasket - Google Patents

Abstract

A gasket comprises a sheet of sealing material defining a central aperture (2) and two spaced bolt holes (3, 4) on opposite sides thereof. The central region (A) of the gasket is more compressible than the material (B, B) outwardly thereof, the interface between the regions lying outwardly of the inner edge of the bolt holes. The interface, between the regions acts as a fulcrum so that when assembled between two flanged components, the flanges tend to bend convexly to improve sealing. As shown, the gasket comprises a relatively incompressible phenolic polymer (5) having recesses (6, 7) for layers (9, 10) of a more compressible polypropylene-bonded cork composition. <IMAGE>

Description

SPECIFICATION Gasket This invention relates to gaskets.

One common type of gasket used to seal joints between two conduits which terminate in flanges comprises a sheet of sealing material defining a central aperture, which registers with the conduit, and two, or more, bolt holes on opposite sides of the central aperture, which register with bolt holes in the flanges.

When such a joint is formed, bolts are passed through the holes in the flanges and the gasket and tightened to compress the gasket. As the joint is tightened, the flanges tend to bend, producing concave surfaces. The gasket is therefore compressed more tightly in the region of the bolt holes than in the central region. This can lead to leaks, especially in joints connected by only two bolts. In order to reduce bending, the flanges usually thickened, which results in a heavier and more expensive component.

According to the present invention, there is provided a gasket comprising a sheet of sealing material defining a central aperture and at least two spaced bolt boles on opposite sides of the central aperture, characterised in that the sealing material in the central region of the gasket is more compressible than the material in the regions outwardly thereof, and in that the interface between the two regions lies outwardly of the inner edge of the bolt holes.

Since the material of the gasket is more compressible inwardly of the bolt holes and the interface between the two materials lies outwardly of the inner edges of the bolt holes, the interface provides a fulcrum so that the compressive forces in the flange tend to produce convex bending of the flange which offsets the tendency to concave bending. The risk of leakage from the joint is therefore reduced. Moreover, the flanges need not be manufactured to the thickness used hitherto.

Although it is possible for the interface between the two materials of the gasket to lie wholly outwardly of the bolt holes, we have found that the best results are obtained if the interface passes through the bolt holes, and preferably through the centres thereof.

In order to provide the difference in compressibility between the two regions of the gasket, the material in the central region may be formed from a plurality of layers of different materials. With such an arrangement, one of the layers may be of the same composition as the material outwardly of the central region.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:~ Figure 1 is a plan of a gasket according to the invention, Figure 2 is an elevation thereof, and Figure 3 is a side view of a joint incorporating the gasket of Figures 1 and 2.

Referring to the drawings, a gasket 1 comprises a roughly eliiptical sheet of sealing material having a central aperture and two spaced bolt holes 3, 4 on opposite sides thereof. The gasket is composed of a layer, 5 (Fig. 2) of a relatively incompressible sealing material, such as a phenolic polymeric material of a type commonly used in the manufacture of gaskets. The central region of each face of the layer of phenolic material includes a recess, 6, 7 in each of which is positioned a layer 9, 10 of a more compressible material, in this case a polypropylene-bonded cork composition. Each of the latter layers 9, 10 is thicker than the depth of the recess in which it is positioned so that the central region A of the gasket is thicker than the regions B outwardly thereof.

This construction provides a relatively compressible central region A in the gasket, the material in the regions B, B outwardly thereof being relatively incompressible. The interface between the regions A and B extends along lines 1 1, 12 passing through the centre of each bolt hole 3, 4, which are outwardly of the inner edges 13, 14 of the bolt holes.

In use the gasket is positioned between two components 15, 16 (Figure 3) provided with flanges 17, 18 and the joint is assembled by means of bolts 19. As the bolts are tightened, the edges of the layer of phenolic materials acts as fulcrums around which the flanges 17, 18 tend to bend, as illustrated by the arrows in Figure 3. This counteracts the bending of the flange which would otherwise occur in the opposite direction as a result of tightness of the bolts, thereby keeping the two flanges flat. A good seal therefore results.

Claims

1. A gasket comprising a sheet of sealing material defining a central aperture and at least two spaced bolt holes on opposite sides of the central aperture, characterised in that the sealing material in the central region of the gasket is more compressible than the material in the regions outwardly thereof, and in that the interface between the two regions lies outwardly of the inner edge of the bolt holes.

2. A gasket according to claim 1 wherein the material in the central region of the gasket comprises a plurality of layers of material.

3. A gasket according to claim 2 wherein one of the layers of the material between the bolt holes is of the same composition as the material outwardly thereof.

4. A gasket substantially as hereinbefore described and as illustrated in the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Gasket This invention relates to gaskets. One common type of gasket used to seal joints between two conduits which terminate in flanges comprises a sheet of sealing material defining a central aperture, which registers with the conduit, and two, or more, bolt holes on opposite sides of the central aperture, which register with bolt holes in the flanges. When such a joint is formed, bolts are passed through the holes in the flanges and the gasket and tightened to compress the gasket. As the joint is tightened, the flanges tend to bend, producing concave surfaces. The gasket is therefore compressed more tightly in the region of the bolt holes than in the central region. This can lead to leaks, especially in joints connected by only two bolts. In order to reduce bending, the flanges usually thickened, which results in a heavier and more expensive component. According to the present invention, there is provided a gasket comprising a sheet of sealing material defining a central aperture and at least two spaced bolt boles on opposite sides of the central aperture, characterised in that the sealing material in the central region of the gasket is more compressible than the material in the regions outwardly thereof, and in that the interface between the two regions lies outwardly of the inner edge of the bolt holes. Since the material of the gasket is more compressible inwardly of the bolt holes and the interface between the two materials lies outwardly of the inner edges of the bolt holes, the interface provides a fulcrum so that the compressive forces in the flange tend to produce convex bending of the flange which offsets the tendency to concave bending. The risk of leakage from the joint is therefore reduced. Moreover, the flanges need not be manufactured to the thickness used hitherto. Although it is possible for the interface between the two materials of the gasket to lie wholly outwardly of the bolt holes, we have found that the best results are obtained if the interface passes through the bolt holes, and preferably through the centres thereof. In order to provide the difference in compressibility between the two regions of the gasket, the material in the central region may be formed from a plurality of layers of different materials. With such an arrangement, one of the layers may be of the same composition as the material outwardly of the central region. A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:~ Figure 1 is a plan of a gasket according to the invention, Figure 2 is an elevation thereof, and Figure 3 is a side view of a joint incorporating the gasket of Figures 1 and 2. Referring to the drawings, a gasket 1 comprises a roughly eliiptical sheet of sealing material having a central aperture and two spaced bolt holes 3, 4 on opposite sides thereof. The gasket is composed of a layer, 5 (Fig. 2) of a relatively incompressible sealing material, such as a phenolic polymeric material of a type commonly used in the manufacture of gaskets. The central region of each face of the layer of phenolic material includes a recess, 6, 7 in each of which is positioned a layer 9, 10 of a more compressible material, in this case a polypropylene-bonded cork composition. Each of the latter layers 9, 10 is thicker than the depth of the recess in which it is positioned so that the central region A of the gasket is thicker than the regions B outwardly thereof. This construction provides a relatively compressible central region A in the gasket, the material in the regions B, B outwardly thereof being relatively incompressible. The interface between the regions A and B extends along lines 1 1, 12 passing through the centre of each bolt hole 3, 4, which are outwardly of the inner edges 13, 14 of the bolt holes. In use the gasket is positioned between two components 15, 16 (Figure 3) provided with flanges 17, 18 and the joint is assembled by means of bolts 19. As the bolts are tightened, the edges of the layer of phenolic materials acts as fulcrums around which the flanges 17, 18 tend to bend, as illustrated by the arrows in Figure 3. This counteracts the bending of the flange which would otherwise occur in the opposite direction as a result of tightness of the bolts, thereby keeping the two flanges flat. A good seal therefore results. Claims

1. A gasket comprising a sheet of sealing material defining a central aperture and at least two spaced bolt holes on opposite sides of the central aperture, characterised in that the sealing material in the central region of the gasket is more compressible than the material in the regions outwardly thereof, and in that the interface between the two regions lies outwardly of the inner edge of the bolt holes.

2. A gasket according to claim 1 wherein the material in the central region of the gasket comprises a plurality of layers of material.

3. A gasket according to claim 2 wherein one of the layers of the material between the bolt holes is of the same composition as the material outwardly thereof.

4. A gasket substantially as hereinbefore described and as illustrated in the drawings.