High temperatures challenge many gasket materials. Nitrile gaskets will go up to about 95oC, silicone gaskets to 200oC and PTFE to 260oC, but what if you need to go higher? One option is to go with a metal gasket. A better one is to ask about graphite. Graphite seals and gaskets retain their properties at temperatures as high as 450oC, and have some other very useful sealing characteristics.
Properties of graphite
Graphite is a form of carbon where the atoms are arranged in layers or sheets. That lets them slide over one another easily, which translates to a slippery feel when rubbed between finger and thumb. (It’s also what lets a “lead” pencil write – graphite actually rubs off onto the paper.)
This slipperiness or low coefficient of friction is useful in gasketing or sealing. As mating surfaces are brought together graphite allows some slip. That accommodates any rotation or sideways movement as the clamping load goes on without damaging the sealing material. Used as a dynamic or shaft seal the low friction properties of graphite minimize energy losses and heat build-up while maintaining an effective barrier.
Graphite is also a very soft material, (which might seem odd when you consider it’s a cousin of diamond,) but that lets it flow into surface irregularities, which is what provides the sealing function.
Like PTFE, graphite is quite inert. It resists attack from most corrosive chemicals, even at high temperatures, and likewise doesn’t contaminate them.
Graphite seals and gaskets
It’s possible to buy graphite for use as a gasket or seal. It’s also used as a coating for some metal gaskets, (Kammprofile gaskets are an example,) where it provides excellent sealing performance along with temperature and chemical resistance. If you’re looking for gasket material for a high temperature application, ask Hennig Gasket if graphite seals might be right for you.