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Preliminary Plastics Selection - p3

A Quick Guide to Plastics Selection

PP Hood Cover

Polypropylene Hood Cover

Approach (read this first)

 

Criteria -

 

Cost & Availability

Operating Temperatures

Transparency Needs

Impact and Toughness

Abrasion & Wear Issues

Strength

Environmental Resistance

 

References

Impact and Toughness

Rapid material fracture due to impact conditions may be a concern in many plastic component designs. Components may be incidentally impacted by dropping, transportation, accident etc, or they may be impacted by design. Material toughness will contribute to resistance to failure but several other factors including part geometry, working temperature and environment and processing factors will also be significant.

 

B&B, table 6-8 lists some factors affecting part toughness.

 

Polymers variously reported for their good toughness -

 

Polypropylene PE

Polyethylene PE

 

PTFE

 

Toughened PVC

High Impact PS

ABS

 

Acetal POM

Nylon PA

Polycarbonate PC

PC/ABS Blends

 

...and under High Performance Plastics

 

Polyphenylene Oxide Blends - PPO/PA, /ABS etc

possible PEEK (but depends on info source!)

 

It is interesting to note that many of these are the cheaper general purpose plastics, with some engineering polymers (POM, PA, PC etc). High Performance plastics are not well represented.

 

Strong, table 7.1 includes impact data for some engineering platics.

B&B, table 6-4 shows impact data for a range of polymers.

 

NB B&B report that particle fillers & fibre reinforcements can reduce toughness, this isn't the case for some composite materials - check the particular polymer grade you are interested in!

 

 

 

Abrasion Resistance

 

Generally the abrasion resistance of plastics when compared to other engineering materials is not great. Alternative materials with or without surface coatings might be used where high levels of abrasion resistance are required in a design. However plastics parts may see abrasive contacts eg carrying cases, exposed shells or housings, and some plastics will be better at resisting damage than others.

 

B&B, figure 9-14 gives wear volumes under sand abrasion for a range of polymeric materials. It suggests that two materials are most often associated with abrasion resistance -

 

Polyurethane PUR

and UHMWPE

 

PUR is also used as an abrasion resistant coating on, for example, floors.

 

Nylons and Acetals are commonly used in plastic bearing and gearing applications and these are subjected to surface contact and wear effects.

 

Strong suggests that Polypropylene PP is a better material with regard to abrasion resistance than the Polyethylenes PE.

 

 


 

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