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Preliminary Plastics Selection - p2

A Quick Guide to Plastics Selection

 

ABS Injection Moulded Panel

ABS Panel

Approach (read this first)

 

Criteria -

 

Cost & Availability

Operating Temperatures

Transparency Needs

Impact and Toughness

Abrasion & Wear Issues

Strength

Environmental Resistance

 

References

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.


 

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