Operating Temperatures
Polymers are much more significantly affected by
temperature than, for example, steel. Low temperatures can cause
embrittlement and loss of toughness, high temperatures can cause
deterioration of mechanical properties (strength, stiffness etc) or
dimensional instabilities (creep, stress relaxation). Temperature
changes may also cause thermal expansion or contraction which can be a
problem in joints made with other materials.
Temperature issues can be a particular problem for
structurally loaded plastic components.
What is the working temperature range for your
application? Remember to consider accidental or incidental exposure eg
product left in a freezing car or left in direct sunlight.
In the references -
Strong, table 7.1 shows use temperatures for
Engineering
plastics.
B&B, table 6-6 shows a relative temperature index for a
range of plastics which can be used to obtain a relative rating between
plastics.
CC&F, table 10.3 shows heat deflection temperatures.
In general working temperatures above the normal ambient
range may give problems for some
Commodity plastics. Several
Engineering plastics are
reaching maximum use temperatures around the 80-90 °C mark, others
(including some High
Performance) can go
higher but the range of choice starts to reduce.
Check the references for characteristics of the polymers
you m might be interested in.
Transparency Needs
Do you wish to be able to see through the polymer? If so
the choice of suitable plastics are reduced. In general amorphous rather
than crystalline thermoplastics are reported as being more suitable
although there are exceptions.
Candidates would be -
Polystyrene PS
Acrylics PMMA (eg Perspex)
Polyesters PET (these are
crystalline)
Polycarbonates PC
Polysulphones PSO (PES
slightly less so)
Note that adding fillers to the polymers will
significantly impact on transparency.
Strong, table 7.1 gives some indication of transparency
is some Engineering plastics.
Tangram Technology report that transparent grades of PVC
are available, so we should add
Polyvinylchloride PVC
to the list of candidates.
