Valve Gaskets of Exfoliated Graphite
Exfoliated graphite is manufactured by the thermal exfoliation of graphite intercalation compounds and then calendered into flexible foil and laminated without an additional binder. The material thus produced possesses extraordinary physical and chemical properties that render it particularly suitable for gaskets. Some of theses properties are:
* High impermeability to gases and liquids, irrespective of temperature and time.
* Resistance to extremes of temperature, ranging from -200℃(-330℉) to 500℃(930℉) in oxidizing atmosphere and up to 3,000℃(5430℉) in reducing or inert atmosphere.
* High resistance to most reagents, for example, inorganic or organic acids and bases, solvents, and hot oils and waxes. (Exceptions are strongly oxidizing compounds such as concentrated nitric acid, highly concentrated sulfuric acid, chromium(VI)-permanganate solutions, chloric acid, and molten alkaline and alkaline earth metals)
* Graphite gaskets with an initial density of 1.0 will conform readily to irregularities of flange faces, even at relatively low surface pressures. As the gasket is compressed further during assembly, the resilience increases sharply, with the result that the seal behaves dynamically. This behavior remains constant from the lowest temperature to more than 3,000℃(5430℉). Thus graphite gaskets absorb pressure and temperature load changes, as well as vibrations occurring in the flange.
* The ability of graphite gaskets to conform relatively easily to surface irregularities makes these gaskets particularly suitable for sensitive flanges such as enamel, glass, and graphite flanges.
* Large gaskets and those of complicated shape can be constructed simply from combined segments that overlap. The lapped joints do not constitute weak points.
* Graphite can be used without misgiving in the food industry.
Common gasket constructions include:
* Plain graphite gaskets
* Graphite gaskets with steel sheet inserts
* Graphite gaskets with steel sheet inserts and inner or inner and outer edge cladding
* Grooved metal gaskets with graphite facings
* Spiral wound gaskets
Because of the graphite structure, plain graphite gaskets are sensitive to breakage and surface damage. For this reason, graphite gaskets with steel inserts and spiral wound gaskets are commonly preferred. There are, however, applications where the unrestrained flexibility of the plain graphite gasket facilitates sealing.
没有评论:
发表评论