Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal for a pipe – conduit – or cable
Patent
1996-06-20
1998-05-12
DePumpo, Daniel G.
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal for a pipe, conduit, or cable
277627, 277650, 264127, 264234, F16J 1500
Patent
active
057495866
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a porous polytetrafluoroethylene gasket and a method of making the gasket. The gasket is particularly suitable for use in the joint areas of sanitary piping such as the piping used in equipment for manufacturing medicines, foods and other products where sanitary conditions are required.
BACKGROUND OF THE INVENTION
The joint structure of sanitary piping is generally constituted such that coupling ferrules, or confronting piping end flanges, are connected or pressed together by a clamp band with the gasket being pressed between the ferrules or flanges. The specifications for joint structures including such gaskets for sanitary piping are prescribed by the International Standardization Organization in ISO-2852.
Known gaskets for sanitary piping include, generally, annular gaskets made of silicone rubber or other rubber, or annular gaskets made of polytetrafluoroethylene (PTFE), having annular protrusions projecting concentrically from both faces of the gaskets. The protrusions engage with annular recesses formed on the confronting surfaces of the ferrules so as to position the gasket relative to the ferrules.
However, rubber gaskets are not suited to sanitary piping where a high degree of cleanliness is required because plasticizers are likely to exude from the rubber over long periods of use. Furthermore, according to recent practice, the sanitary piping is subjected to steam sterilization treatment more frequently, and the steam sterilization treatment temperature tends to be higher. When steam sterilization treatment is done frequently in high temperature conditions, the rubber gasket deteriorates in a relatively short period of time. The deterioration leads to a lowering of elasticity (the gasket becomes stiff), the formation of cracks, surface peeling, and a drop off the sealing function. Thus, the rubber gasket has disadvantages with respect to cleanliness and durability, and is not well suited for use as a gasket for sanitary piping.
Owing to the properties of polytetrafluoroethylene, a polytetrafluoroethylene gasket does not have the disadvantages associated with a rubber gasket. However, a gasket made of polytetrafluoroethylene is stiff and is hence inferior in flexibility, affinity and resilience or restoration. Therefore, to exhibit a specific sealing function, an extremely large tightening torque is needed. Frequent retightening is necessary, and it is difficult to recover the sealing function by repeated retightening.
As a means for solving the problems associated with gaskets made of silicone rubber or polytetrafluoroethylene, it has recently been proposed that an annular gasket for sanitary piping (hereinafter called "conventional gasket") be composed of porous polytetrafluoroethylene. This gasket is made of polytetrafluoroethylene made porous by drawing (for example, see Japanese Laid-open Patent No. 5-99343).
Porous polytetrafluoroethylene is a soft material hence a gasket made of this material possesses an excellent flexibility, affinity and restoration not obtained in the usual polytetrafluoroethylene gasket, while maintaining the intrinsic properties of polytetrafluoroethylene such as durability, cleanliness, and resistance to chemicals, and may be used satisfactorily in severe sealing conditions in sanitary piping.
In the conventional gasket, since it is made of porous material, the sealed fluid may permeate from the inner circumferential parts of the gasket which are in direct contact with the sealed fluid, thereby causing so-called osmotic leak. Such osmotic leak is not significant when the sealed fluid is liquid, but is a serious problem when the gasket is used as a gas seal or vacuum seal.
To reduce osmotic leak, the forming density of the gasket may be increased but increasing the forming density has its own limit, and it is impossible to prevent osmotic leak completely. Furthermore, when the forming density is heightened more than necessary, the intrinsic properties (flexibility, etc) of the porous polytetrafluoroethylene a
REFERENCES:
patent: 2951721 (1960-09-01), Asp
patent: 4106782 (1978-08-01), Hyde et al.
patent: 4176434 (1979-12-01), Cromwell et al.
Abe Makoto
Akai Tetsuya
Miyoshi Takeshi
Tanimura Tosiyasu
Wada Katsuo
DePumpo Daniel G.
Nippon Pillar Packing Co. Ltd.
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