GB2308869A - Gasket - Google Patents

Abstract

A gasket (10) is formed from an impermeable sheet (12). The sheet (12), preferably of stainless steel, is formed into a spiral having at least one and a half turns about a central axis (20) of the spiral. Said spiral being formed into a closed ring with said central axis (20) extending around the ring. The sheet may have a resilient layer (16) of expanded graphite and a sealing layer (18) of tin plated onto it. The spiral can be formed by supplying the sheet in the form of a tube and using a punch (28) Fig 2, with a concave annular forming surface (30) of semi-circular cross-section which engages the edge portion of the tube.

Description

GASKET This invention is concerned with a gasket adapted when clamped between two members to seal the gap between the members around a chamber or passage jointly defined by the members. Such gaskets are used, for example, for sealing between flanges at the ends of pipes. Such gaskets are often in the shape of an annular ring but may have other shapes. Accordingly, the term "ring" is used herein to include a continuous band surrounding a hole of any shape.

Many existing gaskets comprise a sheet made of metal.

For example, in one type of gasket, the metal sheet is generally planar and has a hole therethrough which corresponds to the passage or chamber. The metal sheet has resilient material, eg rubber, graphite or cork, mounted on opposite sides thereof. In such gaskets, the resilient material is not protected from fluids in the passage or chamber and may be extruded out of the sealed joint rendering the gasket ineffective. In another type of gasket, the gasket consists of a number of generally planar parallel sheets of metal, some of the sheets being embossed to form sealing ridges around holes through the sheets.

This type of gasket is somewhat complex and requires the use of stoppers to avoid the embossed ridges from being crushed. Another type of gasket consists of a metal strip which is wound into a spiral centred at the centre of the hole through the gasket. A strip of resilient material is wound into the spiral between the turns of the metal strip.

Thus, in this type of gasket, the spiral lies in the plane defined by the gasket. This type of gasket is complex to make and, in order to ensure adequate sealing, has to be quite wide.

It is an object of the present invention to provide a gasket in which the disadvantages of the above-mentioned types of gaskets are avoided.

The invention provides a gasket adapted when clamped between two members to seal the gap between the members around a chamber or passage jointly defined by the members, the gasket comprising an impermeable sheet which is formed into a spiral having at least one and a half turns about a central axis of the spiral, said spiral being formed into a closed ring with said central axis extending around the ring.

In a gasket according to the invention, the sheet can be made of springy material, eg stainless steel, and the inherent resilience of the spiral shape can be used to ensure sealing so that, in some circumstances, the use of additional resilient material can be avoided. However, where additional resilient material is required, this can be contained within the spiral thereby preventing the resilient material from being extruded out of the joint while simultaneously protecting the resilient material from fluids in the chamber or passage. Furthermore, the spiral shape allows flexure of the structure of the gasket reducing the risk of rupture due to pressure created by the resilient material. The curved surfaces which contact the members allow a smooth distribution of the clamping pressure.

While the spiral requires to have at least one and a half turns in order to operate satisfactorily, there is no reason that there should not be a greater number of turns.

It is preferred that there should be at least two and a half turns but any other number greater than one and a half is possible.

The exposed edge of the sheet, ie the outer edge of the spiral, may face radially outwardly of the ring so that fluid in the chamber or passage cannot penetrate into the interior of the spiral. However, said edge may face inwardly of the ring, eg in order to protect the resilient material from oxygen. It is often desirable that said exposed edge does not contact said members. The gap at the exposed edge of the sheet may be partially closed by bending said edge inwardly out of the spiral towards said central axis. This gap may also be closed by sealant or by securing said edge to the remainder of the spiral, eg by welding.

Where the gasket incorporates resilient material, the resilient material may form a layer laminated with said sheet so that the resilient material is wound into the spiral with the sheet. The resilient layer may be wound on to the inside of the spiral, and preferably fills the space within the spiral without leaving voids. In some cases, the layer of resilient material is discontinuous to assist coiling of the spiral. Suitable resilient materials are PTFE and graphite, eg expanded graphite.

In order to improve the sealing, particularly against rough surfaces, the gasket may also comprise sealing material, eg soft metal such as tin, which covers at least the portions of the spiral which, in the use of the gasket, engage said members. The sealing material may be provided as rings which are adhered to the metal layer of the spiral after the spiral has been formed or, alternatively, the sealing material may form a layer laminated on to said sheet so that the formation of the spiral winds the sealing material on the outside of the sheet. The sealing material layer may, in some cases, only be on that part of the spiral which, in the use of the gasket, is contacted by said members. Another possibility is for the sealing material to be provided as a tape wrapped around outside of the spiral after the spiral has been formed.

The invention also provides a method of forming a gasket according to the invention, method comprising providing said sheet in the form of a tube having an internal size substantially equal to that of the required ring, and coiling one end of the tube outwardly to form said spiral. The shape of the gasket may, if desired, be altered after formation of the spiral. In an alternative method, a gasket according to the invention may be made by forming the spiral, bending it into a ring shape, and joining ends of the spiral together, eg by twisting the spiral and inserting one end into the other.

There now follow detailed descriptions, to be read with reference to the accompanying drawings, of a gasket which is illustrative of the invention and of an illustrative method of making the illustrative gasket.

In the drawings: Figure 1 is a perspective view showing the illustrative gasket with half of the gasket cut away to show the construction, Figure 1 also including an enlargement of a portion of the sheet forming the illustrative gasket; and Figures 2 and 3 are diagrammatic representations of successive stages of the illustrative method.

The illustrative gasket 10 is adapted when clamped between two members (not shown) to seal the gap between the members around a chamber or passage jointly defined by the members. In this case, the gasket 10 is annular and adapted to seal around a passage of circular transverse cross-section.

The gasket 10 is formed from an impermeable sheet 12 whose construction can be seen from the enlarged view in Figure 1. The sheet 12 comprises an impermeable layer 14 made of metal, specifically stainless steel which is 0.2mm in thickness. The sheet 12 also comprises a resilient layer 16 which is laminated on to one side of the layer 14 and a sealing material layer 18 which is laminated on to the other side of the layer 14. The layer 16 is made of expanded graphite which is 0.7mm thick and the sealing layer 18 is 0.2mm thick and made of soft material, in this case tin which is plated on to the layer 14.

The sheet 12 is formed into a spiral having two and a half turns about a central axis 20 of the spiral. A first edge 22 of the sheet 12 is in the middle of the spiral and an opposite edge 24 of the sheet 12 is exposed at the outside of the spiral. As a result of the formation of the spiral, the layer 18 of sealing material is exposed on the outside surface of the outer turn of the spiral and the layer 16 of resilient material is contained within the spiral except for the edge of the layer 16 at the exposed edge 24 of the sheet. If desired, the edge 24 can be bent inwards towards the axis 20 to further protect the layer 16.

The spiral formed by the sheet 12 is formed into a closed ring with the central axis 20 of the spiral extending circumferentially around the ring.

The gasket 10 is made by the illustrative method illustrated by Figures 2 and 3. Firstly, in the illustrative method, the sheet 12 is provided in the form of a tube 26 having an internal shape and size equal to that of the ring formed by the gasket 10. In the tube 26, the layer 16 forms a cylindrical inner surface of the tube while the layer 18 forms a cylindrical outer surface of the tube.

In the illustrative method, an end portion of the tube 26 terminating at the edge 22 of the sheet 12 is coiled outwardly to form the spiral. The first turn of the spiral is formed by the punch 28 shown in Figure 2 which turns the edge 22 outwardly. The punch 28 has a cylindrical portion which fits within the tube 26 and a concave annular forming surface 30 of semi-circular cross-section which engages the edge portion of the tube 26 adjacent to the edge 22 and guides it into the outwardly curved shape required. Once the edge 22 has been turned through 1800, the hoop tension in the layer 14 draws the edge back towards its original diameter so that continued movement of the punch 28 causes the end of the tube to continue to make a complete turn.

Once one turn of the spiral has been formed, the spiral can no longer be accommodated by the surface 30 of the punch 28, and the punch 28 is withdrawn and replaced by the punch 32 shown in Figure 3. The punch 32 has a cylindrical portion which fits into the tube 26 and a 90" curved forming surface which guides the sheet 12 at the transition between the tube 26 and the spiral. The punch 32 is used to form the remaining one and a half turns of the spiral.

When a spiral with a sufficient number of turns has been formed by the operation of the punches 28 and 32, the remainder of the tube 26 is cut away from the spiral, thereby forming the edge 24 and completing the gasket 10.

The remaining portion of the tube 26 can be used to make a further gasket. In a variation of the illustrative method, the tube 26 can have a length selected to exactly form one gasket, thereby avoiding the cutting operation.

When the illustrative gasket 10 is in use, the spiral formed by the sheet 12 is compressed between the members.

This causes the resilient material 16 and the metal layer 14 (due to natural resilience caused by its spiral shape) to provide sealing forces. The sealing material layer 18 is deformed into any roughness of the members, thereby improving the seal. The resilient material of the layer 16 is unlikely to be extruded out of the joint since it is contained within the spiral and is protected from the fluids in the chamber or passage around which the gasket 10 seals.

Claims (8)

1 A gasket adapted when clamped between two members to seal the gap between the members around a chamber or passage jointly defined by the members, the gasket comprising an impermeable sheet which is formed into a spiral having at least one and a half turns about a central axis of the spiral, said spiral being formed into a closed ring with said central axis extending around the ring.

2 A gasket according to Claim 1, wherein said spiral has at least two and a half turns.

3 A gasket according to either one of Claims 1 and 2, wherein the exposed edge of said sheet faces radially outwardly of said ring.

4 A gasket according to any one of Claims 1 to 3, wherein the gasket also comprises a layer of resilient material laminated on to said sheet.

5 A gasket according to any one of Claims 1 to 4, wherein the gasket also comprises sealing material which covers at least the portions of the spiral which, in the use of the gasket, engage said members.

6 A gasket according to Claim 5, wherein the sealing material forms a layer laminated on to said sheet.

7 A gasket substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

8 A method of making a gasket according to any one of Claims 1 to 7, the method comprising providing said sheet in the form of a tube having an internal size substantially equal to that of the required ring, and coiling one end of the tube outwardly to form said spiral.