Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal for a pipe – conduit – or cable
Reexamination Certificate
1999-02-04
2003-05-20
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal for a pipe, conduit, or cable
C277S591000, C277S592000, C277S600000, C277S627000, C277S652000
Reexamination Certificate
active
06565099
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a flat gasket including at least one inner eyelet or at least one outer eyelet or at least one inner and one outer eyelet, as well as a gasket body. In each case the inner eyelet is positioned at a transition to each cavity to be sealed by the gasket. The gasket body having the at least one eyelet is formed of a pressure-resistant core which has long-term resistance to temperatures of at least 150° C. and a covering that is present on both flat outer sides of the core.
Flat gaskets are used in industry in order to seal spaces, such as pipelines, containers, reaction spaces, etc. containing fluid products, at locations at which such spaces have at least one transition to another structural or functional part of a technical assembly to which they belong and which is materially separated from the spaces. It is their function, where there are pressure differences between an interior of the container and a space outside the container to prevent an escape of fluids from such a container or system of containers or an unwanted penetration of fluids into the container or system of containers, as far as possible.
Moreover, even in the absence of pressure differences, exchanges of materials between the interior of the container and the exterior of the container as a result of diffusion should be prevented as far as possible. For economic reasons, for reasons of public health and because of the necessity for environmental protection, the demands placed on the efficiency and especially on the impermeability of flat gaskets have steadily increased in recent times and that process continues. If leakage limiting values in the vicinity of 0.01 mg/(m s) were adequate in the past, nowadays values of 0.0001 mg/(m s) are under discussion for the field of mineral oil processing. As a rule, such high requirements for impermeability can no longer be met by conventional single-material or single-layered flat gaskets. Sealing systems built up from several layers of different materials are also known. U.S. Pat. No. 5,128,209 describes a gasket material formed of layers of a fluoropolymer, graphite foils and metal foils, wherein the layers are bonded to one another by an adhesive. The object of developing that gasket material was to make a gasket which would be easy to handle and have a high spring back capacity. The criterion of impermeability was of secondary importance in that case. The layers of the fluoropolymer are formed of material which is porous and therefore permeable to fluids. They impart a greater stability, toughness and tensile strength and an improved ease of handling to that component of the composite formed of the graphite foils and the fluoropolymer foils. A great disadvantage of that gasket material is the permeability of the fluoropolymer foils to fluids combined with the presence of adhesives as bonding agents between the layers. The fluoropolymer foils contribute virtually nothing to the impermeability of the overall system, which has an adverse effect, especially in the case of gaskets for high and very high impermeability requirements. The adhesives can be a weak point, especially in the case of gaskets subjected to high pressures or stresses. That is because the layers of the laminate can slide on the adhesives, which can ultimately lead to the non-functioning of the gasket or, particularly in combination with more elevated temperatures, the adhesive layer can develop fine cracks which impair the sealing action. German Utility Model G 92 08 943.7 discloses packing rings for packed glands. The rings are formed of layers of graphite foils and of metal foils and have an at least partial covering of a foil of polytetrafluoroethylene as a diffusion barrier. The polytetrafluoroethylene foils can also be sintered onto the graphite rings. However, the mechanisms which bring about the sealing in gland packings are not readily transferable to flat gaskets. A gland packing is completely enclosed in its packing seat and is pressed against walls of the packing space surrounding it by tightening the packing seat. Unlike the case of flat gaskets, flow processes of the packing ring are provided for in that case and can only go as far as the space surrounding it allows. The metal rings disposed in the packing serve primarily as diffusion barriers between the graphite layers. The graphite layers have free diffusion paths in all directions. In flat gaskets the conditions are different. They are not completely enclosed and can have no, or only a very limited, tendency to flow where there is stressing of the sealing surfaces such as, for example, flanges, forming a boundary to them above and below. Fine channels and diffusion paths which pass horizontally through such gaskets control the leakage rate of those gaskets. Such diffusion paths are virtually absent in gaskets which have a core constructed only of plastics materials or of metal. However, gaskets of that type cannot meet the technical sealing demands placed on them, or only inadequately do so. In gaskets containing a pure plastics core, the plastics core flows under pressure and lacks an adequate spring back capacity. In gaskets containing a pure metal core, the metal core does not flow but it has no spring back capacity at all from the aspect of sealing technology and consequently does not have a reliable long-term sealing action. Other materials have therefore been used as gasket cores in order to surmount those difficulties. For example, such materials may be plastics having a certain elasticity, or special rubbers, for instance nitrile-butadiene rubber, which on one hand have been reinforced with fillers and by incorporating reinforcing fibers such as aramid fibers or carbon fibers, and on the other hand have been made flow-resistant or creep-resistant, or else inorganic materials such as, for example, graphite foils or graphite laminates. However, gasket cores of that type also have diffusion channels, as has been demonstrated, for instance, in Published European Patent Application 0 676 570 A1 by the example of graphite foil gaskets. In summary, it can be stated that the known flat gaskets do not completely meet the requirements of modern sealing technology with regard to impermeability and compressive strength and are in need of improvement.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a gasket with an eyelet, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which provides a flat gasket having high compressive strength, that is suitable for long-term temperature stability of at least 150° C. and through the use of which improved leakage values, that is of less than 0.01 mg/(m.s), are achieved. With the foregoing and other objects in view there is provided, in accordance with the invention, a flat gasket for sealing at least one cavity, comprising a gasket body including a pressure-resistant core having long-term resistance to temperatures of at least 150° C. and two flat outer sides, and coverings each completely covering a respective one of the flat outer sides, the coverings made of a gas-tight foil of an organic polymer having a long-term temperature resistance of at least 150° C.; and at least an inner eyelet or at least an outer eyelet or at least one inner and one outer eyelet or eyelet sheet, positioned at a transition between the gasket body and the at least one cavity and enclosing the gas-tight foil of the gasket body with a gas-tight joining.
Besides their low permeability to fluids, the polymer foils covering the core of the gasket body have yet another important property. Due to their good flow performance under pressure, they adapt themselves extremely well to the unevennesses and damage which are present on the surfaces to which they are sealed and thus also effect an excellent sealing against them. If they are used in a sufficiently low thickness in this case, their tendency to creep, which per se is disadvantageous for gaskets, and their low
Mederle Otto
Öttinger Oswin
Greenberg Laurence A.
Locher Ralph E.
Peavey E
SGL Carbon AG
Stemer Werner H.
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