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Tech Tips
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Home » Products » Rubber-Edged Composites » Select-a-Seal » Tech Tips
Select-a-Seal is the first gasket technology to offer a polymer edge on a
compressible carrier structure. This invention (covered in our patent
applications) is dramatically different from O-rings or rubber-edged metal
gaskets because compression of the polymer is not fixed over time.
Traditional rubber sealing systems must limit compression to avoid cracking
and cold-flow of the rubber. Select-a-Seal controls these potential failure
modes through its polymer formulation and the use of a carrier that can
"relax" over time to "transfer" sealing stress to the polymer edge.
Compressive Stress Relaxation vs. Energy Transfer
Compressive Stress Relaxation (CSR) is a phenomenon that occurs in
polymers that are compressed by a fixed amount and held there. For
example, a rubber edge molded gasket has a metal carrier that is 0.060
inches thick and a rubber edge that is 0.080 inches tall. When the gasket is
installed in the joint, the rubber edge is compressed from 0.080 inches to
0.060 inches and held there for the rest of the life of the joint. Initially, this
compression produces a certain amount of sealing force on the surfaces of
the polymer bead, but over time that sealing force diminishes. This is
primarily due to heat and fluid exposure effects on the rubber.
Energy Transfer is a phenomenon that occurs in polymers that are
compressed by a certain initial amount, and subsequently compressed more
as they stress-relax. This can only occur in a situation where a polymer's
compression is being controlled by some other compressible member rather
than a metal carrier. Select-a-Seal uses a compressible, fiber-reinforced
carrier with a polymer edge bonded to it. Using a similar example as above,
a fiber carrier that is 0.030 inches thick has a polymer edge that is 0.040
inches tall bonded to it. When the gasket is installed in the joint, both carrier
and edge compress to 0.028 inches. Over time, as the polymer edge stress
relaxes, the fiber carrier also relaxes, and both members are further
compressed to 0.026 inches. Thus, the relaxation of the carrier actually
improves polymer edge compression in Select-a-Seal gaskets over time. The
energy transfer maintains sealing stress on the polymer edge for long-term
sealing performance.
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