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

Material chosen
Criteria for material selection
When looking for a suitable plastic, the application conditions
involved determine the material selection. For this
reason, different specific framework conditions must be
known and assessed, for example the planned purpose, the
fields of application and further-reaching details relating to
the characteristics and application conditions. With the aid
of this information, qualified experts can compare the requirements
to technical values and make an assessment.
On the basis of defined criteria, in this way it is possible to
continuously limit the choice of suitable materials.
However, the selection can only be a recommendation,
which cannot replace practical testing.
2. Thermal
stress
1. Industry
Application
12. Non-standard
specifications
3. Mechanical
stress
11. Process
technology
part
4. Tribological
stress
Material selection
5. Chemical
stress
9. Fire
10. Radiation/ behaviour
Weather resistance
6. Required
certifications /
Physiological
harmlessness
7. Electrical
requirements
8. Optical
behaviour
Field of application / sector of industry
When the question of the application or sector of industry
arises, this often significantly limits the material selection,
as for different sectors generally speaking only special materials
can be considered, for example due to the required
approvals. Examples of this are the medical and food technology
sectors. In the medical technology sector, generally
only those materials are admissible which come with approval
for direct bodily contact.
This means that the materials must be biocompatible. In
the field of food technology, by contrast, approvals in compliance
with FDA and also European standards (e.g.
10/2011/EC, 1935/2004/EC) are required.
Consequently, for these industries only materials which
comply with requirements of the approvals can be considered.
Thermal stress
Thermal stress is another key criterion restricting the selection
of material. The temperatures transferred to the materials
as a result of the application conditions must be taken
into account here. Alongside the action of heat transferred
from the outside, system-related heat created by factors
such as friction must also be taken into consideration. Particularly
characteristic temperatures are:
ˌˌLong-term service temperature
ˌˌShort-term maximum service temperature
ˌˌNegative service temperature
ˌˌGlass transition temperature
ˌˌThermal dimensional stability
ˌˌCoefficient of linear thermal expansion
Fundamental questions relating to the choice of material
Fundamental questions relating to the choice of material
Generally speaking, thought must first be given to which
type of material is preferred for the relevant application.
This begs a number of different questions:
ˌˌIs plastic generally speaking an option
for this application?
ˌˌWhy plastic? Weight savings, improved
characteristics in use?
ˌˌWhat was used previously?
ˌˌIf a different material was used, what
is the reason for changing?
ˌˌWhy did the previous material not work?
ˌˌWhat problems occurred?
Mechanical stress
To allow the suitability of a material to be assessed in terms
of exposure to mechanical stress levels, the most detailed
possible information about the envisaged stress must be
available. In most cases, it is very helpful to obtain a sketch
of the component with information relating to the mechanical
stress. Particularly decisive factors here are:
ˌˌThe type of stress (static, dynamic)
ˌˌLevel of occurring forces
ˌˌPoint and direction of force application
ˌˌThermal stress during the application of force
ˌˌTime sequence
ˌˌSpeed where applicable
ˌˌAdmissible compression and elongation
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