15.6.2 Plastics
Plasticsmay,in somecases,haveadvantagesoverstainlesssteel, suchas lower
cost and weight,as well as betterchemicalresistance.For cablesupports the use
of plastics is not recommended due to EMCrequirementsand potential build-up
of static electricity.
The selectedplastic should comply withthe following regulations:
∑ USACodeof FederalRegulationsof the FDA(CFR 21, parts170±199latest
edition);
∑ Germanlist of constituents(BGVV).
In principle,plasticsnot in directcontact withproduct and not in the contact
area do not require specialapproval. Theyshould be easyto cleanand resistant
to the chemicals and temperaturesoccurring withinits immediate installed
environment.
Whenselecting a typeof plastic,cleanability is an importantfactor. The
plastics listed in Table 15.3 may be used for construction. The use of
poly(tetrafluoroethene)(PTFE)or Teflon requiresthe particular applicationto
be reviewedcarefullysincepracticalexperience has shown that PTFEcan be
verydifficult to clean.
Wherereasonably practicable,avoidusing glass-reinforced plastic(GRP)
products as it is known that components of GRPcan react withcertainwetting
agentsin detergents. Thiscan be observedby the fact that the material turns
black. Of more concernis the riskof small pieces of material becoming
dislodged and findingtheirwayinto the product.
15.6.3 Elastomers
Whenthe use of rubber is required, e.g. for seals,gaskets and jointrings, the
recommendedchoicesare (in random order,the preferenceswill dependon the
areaof application)givenin Table15.4.Rubbersthat are not in directcontact
withproductand not in the contactareain principle do not require special
approval. However, theyshouldbe easyto cleanand resistant to the chemicals
and temperaturesoccurring withintheirimmediate installedenvironment.
Table15.3 Preferredplastics
∑ Polyvinylchlorideunplasticised(PVC)
∑ Polycarbonate(PC)
∑ *Polypropylene(PP)
∑ Acetalcopolymer
∑ High-densitypolyethylene(HMWPE)
∑ Halar(coating)(ECTFE)
∑ Polyoxymethylene(POM)
- Mostfrequentlyused.
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