Gaskets
Gasketing has developed from the early days of copper, leather and basic
cork to non-asbestos materials, silicones and a variety of metals.
Engines operate under conditions where the gaskets must be able to cope with the high-pressure sealing and be able to handle the differential rates of expansion and contraction between flanges.
The gasket selection requires examination of three basic elements, namely
The medium being sealed
Temperature and pressure influences
The construction of the flange where the gasket will be fitted
Determining the material which can be used to best effect, must ensure that what is being sealed will not cause gasket degradation and be able to conform to flange
irregularities without physical distortions of the flange.
Details of some of the gasket materials available to perform these functions will be the subject of future news reports.
Corkrubber and Rubber
Used for sealing oils, air and water at low bolt loads. Cork has a good resistance
to oil at 80 - 100C and is resistant to the effects of climate. Many applications
ranging from gearboxes, inspection covers to water piping gaskets use rubber
or corkrubber
Corkrubber offers many of the advantages of rubber compounds, along with
the added benefit of controlled compressibility and recovery. The addition of
cork granules to the compound helps to decrease the amount of flow or creep
that occurs in compounds that are only made with rubber. This also creates a
better distribution of load when compression occurs between bolt spans
Non-Asbestos Composites
With the demand for ever increasing pressures and temperatures, asbestos
jointing has been replaced by non-asbestos composites and can be used for
high temperatures and pressures. The material covers a wide spectrum of
specifications and is used throughout industry.
Non-asbestos materials are used for steam, water and other non-aggressive
media, such as oils and fuel.
Engineering Papers
Providing good service are the engineering papers used where high flange loads
are available, but low pressure is evident i.e. gear boxes. Engineering papers
composed of cellulose or vegetable fibre give excellent service. They are
recommended for general engineering, where resistance to oils and fuels is
required and are normally used on machined flanges.
Ideal Storage Conditions
A dry atmosphere. Some materials (particularly cellulose based) are hygroscopic and consequently are dimensionally unstable in damp conditions.
20C or below. The rate of oxidation is directly related to the ambient temperature and above 20C some materials will harden over a period of time. Lower temperatures (e.g. frosts) will not normally harm gaskets. Avoid localised heat such as steam pipes or radiators.
In the dark. Ultra-violet light in the sun?s rays can attack some gasket materials and cause cracking and embrittlement.
Away from any electrical discharge. Some electrical equipment (e.g. arc-welding) can create ozone gas, which has a serious effect on many polymers.
Flat. The gasket will give its best performance if stored flat instead of rolled, folded or hung on hooks.
Avoid oil contamination (particularly important for graphite gaskets)
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