The concern of the public about environmental issues will ensure that the emissions from automotive engines continue to be the subject of scrutiny. A factor likely to be of increasing interest in the future is the degree of seal achieved at the exhaust manifold.
The current trend for exhaust sealing is to use a sheet metal gasket with surface stress raising corrugations to form sealing regions. Such gaskets sometimes have strategically located coatings of filled elastomer or of exfoliated graphite. In all cases there are limitations with these styles of gaskets.
There is now a new form of sealing material that is available that has a structure similar to that of the very familiar exfoliated graphite but which, unlike graphite, does not oxidise and is therefore very appropriate for automotive exhaust applications.
The new material is based upon two forms of exfoliated vermiculite. Vermiculite is a sheet silicate mineral closely related to mica that has all of the thermal and chemical resistance for which mica is noted. But, unlike mica, vermiculite is capable of exfoliation or separation of the individual, very thin, sheets, which combine to form the naturally occurring flakes of vermiculite. One of the exfoliated forms is the familiar thermally exfoliated vermiculite and the other is the chemically exfoliated form of vermiculite.