Effective long-term sealing with foam rubber is a function of
compression set and stress relaxation. Learn why these material properties
matter, and how to select the right sponge profiles for custom gaskets under
compressive loads. Then, download the Sealing Essentials Guide.
Foam rubber gaskets provide reliable
sealing, cushioning, and insulation in a variety of applications. Products
designers and technical buyers can choose sponge profiles made from many
different types of foam, and compound selection can be a complex task. In
addition to material properties and compliance with industry or regulatory standards,
there are many other factors to consider. For example, long-term sealing under
constant compression is required for some industrial applications.
Let's take a look at two material
properties, compression set and stress relaxation, which you may need to consider
carefully when choosing foam rubber gaskets for compressive loads. We'll also look
at some common foam rubber materials. Elasto Proxy isn't a rubber compounder,
but we want you to understand how the rubber that's used in the sponge profiles
you ask us to custom-fabricate can affect long-term sealing performance. We
keep hundreds of foam rubber profiles in stock, but which one is right for you?
Compression Set
Compression set or C-set
resistance describes the ability of a rubber material to return to its original
thickness after a compressive load, such as from pushing or pressing, is
released. Most elastomers will not regain all of their initial thickness after a
constant load is released, however. If the rubber loses only a small percentage
of its initial thickness, the material is said to have good compression set
resistance. Conversely, elastomers that lose much of their initial thickness are
said to have poor C-set resistance.
For material buyers and gasket
designers, it's important to understand how time and temperature affect C-set.
To simulate accelerated aging, rubber compounders test materials at both an
elevated temperature and room temperature. Typically, the elevated temperature
is 70° C, a threshold that's higher than room temperature (23°C), but one that
doesn't exceed the upper service temperature for the foam rubber. By
considering C-set in terms of time and temperature, you can choose the
right compound for your gasket.
Some silicone foams and urethane
foams have good compression set when subjected to standard test conditions of
50% compression for 22 hours at 23° C and at 70° C. By contrast, a neoprene/EPDM blend may have a
poor C-set at room temperature and a worse C-set at 70° C. In this case,
blending two materials does not create a compound with superior compression
resistance. Individually though, both neoprene foam and EPDM foam have better
compression set resistance than a neoprene/EPDM blend.
Stress Relaxation
Stress relaxation also helps to determine
a foam gasket's long-term sealing effectiveness. Also known as force
relaxation, stress relaxation describes a foam rubber's tendency to lose force
deflection over time while under continuous loads. As a rule, most of a
material's stress relaxation occurs during the first few hours of compression.
Afterwards, higher-performing materials lose less force over time. Test
conditions for stress relaxation typically involve 25% material compression
over 60 hours.
Let's consider the stress
relaxation curves for some common types of foam rubber use in sponge profiles.
EPDM foam retains approximately half of its initial force after compression,
and then loses another 20% over the next 10 hours. After that, there isn't much
more change with EPDM foam. By contrast, vinyl nitride foam has steep initial
losses and then gradually loses more force deflection over time. Neoprene/EDPM
blends drop precipitously in the first 10 hours, and then decrease gradually
thereafter.
Solve Your Sealing
Challenges
Sealing challenges are complex and no two
applications are the same. Do you need foam rubber gaskets for constant
compressive loads? How well do you understand all of the application
requirements? Plus, what about seal geometry, industry standards, and vendor
selection? They're all important to consider, too. To make the right decisions,
you need a resource you can trust from a partner with experience. Download
Elasto Proxy's Sealing Essentials e-book today.
| 
