GB1594309A - Alminar graphite sealing tape - Google Patents

Description

(54) LAMINAR GRAPHITE SEALING TAPE (71) We, SIGRI ELEKTROGRAPHIT GESELLSCHAFT MIT BESCHRANKLER HAFTUNG, a German Company, of 8901 Meitingen bei Augsburg, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a sealing tape for use with flat seals formed of flexible laminar graphite sheet structures.

It is known from German Patent No.

66,804 that laminar graphite sheet structures and other flexible forms of graphite can be produced by dipping natural graphite flakes into a liquid oxidising agent and subsequently heating the flakes for a few seconds to a temperature of around 1000"C. During this treatment, the individual graphite particles expand to a considerable extent and a mass of them may be compacted to form flexible sheet-form structure, for example a thin film or thicker forms hereinafter referred to as laminar sheet structure, without the addition of a special binder, for example by rolling or stamping. Flexible graphite is impermeable to liquids and gases, is temperatureresistant and is unaffected by most substances, except for a few strongly oxidising acids.

Laminar graphite sheet structures are selflubricating and even when compacted by weak forces, have appropriate fluid tightness.

The bulk density of laminar graphite sheet structures used for seals is preferably from 0 5 to 1 5 g/cc, corresponding to a linear compressibility coefficient of from 4 x 10-3 to 2 x 10-5 cm2/N.

Flat seals, for example for flanged joints, may be formed from laminar graphite sheet structures applied in the form of tapes to the annular surfaces of the joints of which sealing is required. The difference in diameter between the inner and outer edges of the annular surfaces may be compensated for by increasingly stretching or pulling the tape in the tangential direction. Since the low tensile strength of the laminar graphite parallel to the surfaces of the tape permits only limited deformation, this procedure is only suitable for flat seals having a very large radius of curvature. To improve the flexibility of tapes it is known from German Patent No. 1,253,130 that laminar graphite tapes can be stamped with linear grooves or provided with other depressions in the surface of the tape.However, stampings of any type involve a local reduction in the thickness of the tape and an increase in its density can lead to the formation of cracks and rib-like compression zones which complicate the formation of efficient flat seals.

According to this invention, there is provided a sealing tape formed of a flexible laminar graphite sheet structure and for use in the production of a flat seal, the tape having a uniform thickness and being formed with undulations which reduce its overall length by at least 5%.

A laminar graphite tape embodying this invention is suitable for use in the production of annular flat seals because it can be adapted even to small radii of curvature without any cracks or unfavourable compression zones being formed in the laminate.

The reduction in length of tapes embodying this invention from a flat configuration may be varied in accordance with the amplitude and frequency of the undulations and is preferably proportional to the difference in diameter determined by the particular dimensions of the seal, so that when a tape embodying this invention is applied to the sealing surface in a curved configuration, only the undulations are smoothed and there is no reduction in the thickness of the tape and formation of cracks or rib-like compression zones. A particular advantage of the undulating tapes is their high flexibility so that application of even low tensile stresses is sufficient for complete adaptation to annular sealing surfaces of small radius to be obtained.

It is preferred that the undulations extend transversely of the longitudinal axis of the tape. In order to avoid mechanical weakening, the undulations should have a constant radius of curvature and the radius of curvature preferably amounts to at least 0.5 times the thickness of the tape. The amplitude of the undulations preferably amounts to from 0 5 to 5 times the thickness of the tape.

Sealing tapes embodying this invention are particularly suitable for use as flange seals which are exposed to thermal and/or corrosive stressing. Since the tapes equalise irregularities in the sealing surfaces, there is generally no need for these surfaces to be precision-machined. The handling properties of the sealing tapes may be improved by coating at least one contact surface with an adhesive, the adhesive layer preferably being lined with parting paper or with a plastics film.

For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made by way of example only, to the accompanying drawings, wherein: Figure 1 is a perspective view of a sealing tape embodying this invention; and Figure 2 is a perspective view of part of a flattened tape embodying this invention.

Referring to Figure 1, there is shown a sealing tape 1 of flexible laminar graphite which has a constant thickness and whose length is reduced by the presence of undulations therein. The reduction in length amounts to at least 5% and is achieved by selecting a suitable amplitude and frequency of the undulations. The undulations have a constant radius of curvature which is at least 0 5 times greater than the thickness of the tape.

In Figure 2, the sealing tape 1 is applied to a sealing surface 2 of a flange 3 and adapted to the curvature of the sealing surface. The undulations are substantially smoothed in the vicinity of the outer edge and slightly compressed in the vicinity of the inner edge.

When the seal is tightened, a linear density gradient is formed in the radial direction, the density remaining constant in the tangential direction, so that a particularly favourable cross-sectional tightness of seal is obtained.

WHAT WE CLAIM IS:- 1. A sealing tape formed of a flexible laminar graphite sheet structure and for use in the production of a flat seal, the tape having a uniform thickness and being formed with undulations which reduce its overall length by at least 5%.

2. A sealing tape as claimed in claim 1, in which the undulations extend transversely of the longitudinal axis of the tape.

3. A sealing tape as claimed in claim 1 or 2, wherein the undulations have a constant radius of curvature.

4. A sealing tape as claimed in any one of claims 1 to 3, wherein the radius of curvature of the undulations amounts to at least 0.5 times the thickness of the tape.

5. A sealing tape as claimed in any one of claims 1 to 4, wherein the amplitude of the undulations amounts to from 0 5 to 5 times the thickness of the tape.

6. A sealing tape as claimed in any one of claims 1 to 5, wherein the graphite sheet structure has a bulk density of from 0-5 to 1.5 g/cc.

7. A sealing tape formed of a flexible laminar graphite sheet structure, substantially as hereinbefore described, with reference to and as shown in the accompanying drawing.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. the undulations preferably amounts to from 0 5 to 5 times the thickness of the tape. Sealing tapes embodying this invention are particularly suitable for use as flange seals which are exposed to thermal and/or corrosive stressing. Since the tapes equalise irregularities in the sealing surfaces, there is generally no need for these surfaces to be precision-machined. The handling properties of the sealing tapes may be improved by coating at least one contact surface with an adhesive, the adhesive layer preferably being lined with parting paper or with a plastics film. For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made by way of example only, to the accompanying drawings, wherein: Figure 1 is a perspective view of a sealing tape embodying this invention; and Figure 2 is a perspective view of part of a flattened tape embodying this invention. Referring to Figure 1, there is shown a sealing tape 1 of flexible laminar graphite which has a constant thickness and whose length is reduced by the presence of undulations therein. The reduction in length amounts to at least 5% and is achieved by selecting a suitable amplitude and frequency of the undulations. The undulations have a constant radius of curvature which is at least 0 5 times greater than the thickness of the tape. In Figure 2, the sealing tape 1 is applied to a sealing surface 2 of a flange 3 and adapted to the curvature of the sealing surface. The undulations are substantially smoothed in the vicinity of the outer edge and slightly compressed in the vicinity of the inner edge. When the seal is tightened, a linear density gradient is formed in the radial direction, the density remaining constant in the tangential direction, so that a particularly favourable cross-sectional tightness of seal is obtained. WHAT WE CLAIM IS:-

1. A sealing tape formed of a flexible laminar graphite sheet structure and for use in the production of a flat seal, the tape having a uniform thickness and being formed with undulations which reduce its overall length by at least 5%.

2. A sealing tape as claimed in claim 1, in which the undulations extend transversely of the longitudinal axis of the tape.

3. A sealing tape as claimed in claim 1 or 2, wherein the undulations have a constant radius of curvature.

4. A sealing tape as claimed in any one of claims 1 to 3, wherein the radius of curvature of the undulations amounts to at least 0.5 times the thickness of the tape.

5. A sealing tape as claimed in any one of claims 1 to 4, wherein the amplitude of the undulations amounts to from 0 5 to 5 times the thickness of the tape.

6. A sealing tape as claimed in any one of claims 1 to 5, wherein the graphite sheet structure has a bulk density of from 0-5 to 1.5 g/cc.

7. A sealing tape formed of a flexible laminar graphite sheet structure, substantially as hereinbefore described, with reference to and as shown in the accompanying drawing.