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Materials  For Aluminum For Magnesium For Plastics - Plastic vs Standard - Properties of Plastics - Installation - Design Issues - Fastener Selection - Threaded Fastener Selection For Sheet Metal For Steel  General Information: infoEurope@acument.com Request a Quote: RFQEurope@acument.com Sales: salesEurope@acument.com
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Privacy Policy Acument™ Global Technologies Europe Europarc 41, rue le corbusier 94046 Créteil Cedex - France General Information: infoEurope@acument.com |
Flexural modulus is the best indicator of how a
plastic will respond to fasteners. Generally, the
lower the flexural modulus, the more the material
will flow and allow the formation of threads.
Thermoplastics with a higher flexural modulus also
allow the formation of threads, but usually require
a fastener with a low helix angle to avoid excessive
drive torque. Plastics with a high flexural modulus,
including thermosets, are too stiff for thread
forming and will require thread-cutting fasteners.
There are definite exceptions to these guidelines
which can adversely affect fastening performance.
Involve our application specialists early in the
design process to maximize joint reliability.
The stress/strain curve for thermoplastics is very
temperature dependent. Plastics expand much faster
than metals do when subjected to the same thermal
loading. Since very few joints operate at constant
temperatures, thermal expansion or contraction is
virtually universal. This will affect clamp load.
However, this is only a problem if the application
uses materials with dissimilar expansion rates and
the temperature change is significant.
Fillers and reinforcements change one or more properties of the thermoplastic. They can also
affect fastening performance. For example, impact resistant
resins tend to act
more ductile than their
flexural modulus would
indicate. Lubricants added
for molding, such as
silicone, tend to reduce
drive torque but can
negatively affect clamp load.
Again, it is important to test your application early
in the design process to ensure optimal
performance.
Under load or heat all plastics will creep, or
permanently deform. Creep will, in turn, cause a loss
in clamp load. The chart above demonstrates the loss
of clamp load, at a stable temperature, over 64 hours
for a 4.0 mm Plastite® fastener driven into acetal
resin. However, creep can be compensated for in
joint design through a variety of methods.