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Gasket material Fills the space
between two objects, generally to prevent leakage between the two
objects while under compression. Gasket material saves money by allowing less
precise mating surfaces on machine parts which can use gasket
material to
fill irregularities. Gaskets are commonly produced by cutting from
sheet gasket materials, such as gasket paper (beater addition), Non-asbestos,
Rubber, EPDM, Nitrile, Buna, Neoprene, Flexible Graphite, Grafoil, Aflas, Kalrez, Viton, Silicone, Metal,
Mica, Felt or a plastic polymer such as Teflon®
(PTFE), Peek, Urethane, or Ethylene Propylene (EP). In the
past, the gasket material selected for specific applications may contain have contained
asbestos.
Today's sealing products manufacturer's in the United
States no longer produce or offer any asbestos containing products.
Gasket materials containing asbestos have been claimed to have
caused Asbestosis. Of course it would take the grinding of gasket
material to release the fibers and then the breathing in of those
fibers....possible but in the real world this would be rare. Wetting
or oiling a gasket before grinding for removal greatly reduces any
risk (not grinding is even better). Asbestos gasket material
is still used in most of the rest of the world and is a very
effective low cost material.
It is usually desirable that the gasket be made from a
material that is compressible such that it tightly
fills the space it is designed for, including any slight
irregularities. The most common misconception when selecting a
gasket materials thickness is to choose a gasket material that is
too thick. The thicker the material the more likely the material
being contained can weep through the pores of the gasket material
itself. This is a greater issue with some materials than others.
A rule of thumb is to have the material thick enough to compensate
for any surface face irregularities and to permit some compression.
The required compression for your gasket material will depend many
factors including:
1)Surface area
2)Pressure being sealed
3)Size of bolts (assuming bolts are being used)
4)Number of bolts
5)Condition of the bolts
6)Lubrication on the bolts
All must be considered when determining torque. Torque data
must be determined using all of the above and should be provided by
an engineer. In most cases unless your gasket is a standard
ANSI or API flange using Ring or Full Face gaskets torque data will
be difficult to come by (due to staffing and the fear of law suits). In most cases the old tighten it
tight enough to stop any leaks but not too tight as to completely
crush the gasket is generally accepted.
Over compression of gasket
material is a common
problem with metal gaskets which have mechanically designed recovery
built into the gasket. Over compression removes the gasket
materials
ability to recover. This is also true of expanded PTFE (Teflon
®), once over compressed it will
have no recovery and therefore will not longer adapt to maintain a
seal. The common strategy of "The more compressive load
exerted on the gasket, the longer it will last" is generally true of
elastomeric materials since elastomers (rubbers) are not
compressible but deflect compression. Many materials such as
non-asbestos compressed gasket materials and beater addition (ie;
Armstrong) materials contain elastomers in the mix of material they
are produced from, making them difficult to over compress.
One of the more desirable properties of an effective gasket
material in
industrial applications is the ability to withstand
high compressive loads. Most industrial gasket applications involve
bolts exerting compression well into the 14 MPa (2000 psi) range or higher.
This is why Non-asbestos gasket materials are so widely used in industrial
gasket material applications.
Ph: 714-593-9780
Fax: 714-593-9701
E-Mail:
sales@americansealandpacking.com
Call American Seal
& Packing for your gasket material requirements.
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