Engineering plastics – The Manual - F.wood-supply.dk

Chemical stress
If a component comes into contact with chemicals, its resistance
to the substances in question must be considered
in the light of the application conditions. Decisive factors
here are:
ˌˌContact temperature
ˌˌContact time
ˌˌConcentration
It should be noted that the substances should be considered
not only in the light of their application but also during
processing (cooling lubricants etc.). In addition, in the
case of substance mixtures, it should be borne in mind that
these can behave completely differently in relation to a material
than the individual substances alone.
Tribological stress
If the case in consideration is a sliding-friction application,
then on principle good sliding properties and abrasion
characteristics are required. However, these variables usually
depend directly on the other application conditions. In
addition, the sliding system as such plays a key role.
ˌˌApplication temperature
ˌˌSliding speed
ˌˌCompression
ˌˌSliding partner
ˌˌSurface properties
In principle it is only conditionally possible to assess the
general suitability of a material in respect of its sliding friction
abrasion behaviour, as the interaction of all occurring
parameters can only be assessed in detail by conducting a
practical test.
Required approvals / Physiological harmlessness
The application conditions frequently provide a clue to the
necessary approvals and certifications. As the relevant approvals
are often dependent on the raw material used, a
prior detailed clarification of the necessary certifications is
required.
ˌˌFood (FDA, 10/2011, NSF 51 …)
ˌˌMedicine (ISO 10993, USP class VI, …)
ˌˌDrinking water (KTW, NSF 61, …)
ˌˌAerospace (ABS, ABD, …)
Electrical requirements
When electrical requirements exist, the key issue is generally
whether an electrically dissipating / conducting or electrically
insulating material is required. In order to avoid
static charges, for example when producing electronic components,
dissipating or conductive materials are required.
This also applies in the case of ATEX applications (ATmosphere
EXplosive). In contrast, in the case of components
required to demonstrate high dielectric strength, good insulating
materials are required.
Optical requirements
Frequently optical requirements are imposed on a component.
This can range from simple colouration, for example
to reflect a corporate design, to transparent components for
viewing windows through to colour coding (e.g. blue in
food-related applications) for optical detection.
Requirements imposed on fire behaviour
In many fields such as aerospace engineering, railways and
so on, stringent demands are made on fire protection, in
order to guarantee the safety of an application. Here, a material
is frequently required to be self-extinguishing. Wideranging
different sector-specific approvals exist with which
the material / component is required to comply.
Requirements imposed on radiation / weather resistance
If components are used for instance for outdoor applications,
in radiology or in applications involving exposure to
high-energy radiation such as power stations, the materials
used require suitable radiation resistance. Decisive to the
material selection are the exposure dosage and the relevant
application conditions.
How is the component intended to be produced?
The material selection is also dependent on the planned
processing method. It should be known in advance, for instance,
whether the component will be produced using a
machining process, by injection moulding, direct forming
or a similar process.
Non-standard specifications
Alongside the requirements listed here, there may be a
wide range of additional framework conditions, specifications
or approvals to which a material must comply in a
certain application. The relevant points must be separately
tested and determined.
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