13.4.1 Materialsof construction
Construction materials coming in contact with food (includingassociated
adhesives) must be food grade (Foodand Drug Administration(FDA) or
European Food SafetyAuthority (EFSA) approved or national equivalent).
Selectionof constructionmaterials depends greatlyuponthe dry materials,
methodof cleaning and cleaningagents to be used.The abrasive characteristics
of powders can particularlyaffectthe product contactsurfaces.
Metals
Hygienic dry materials handlingis best conducted withproduct contactsurfaces
of stainlesssteel.Suitablegradesare SS 304,304L(EN 1.4301/1.4306)and SS
316,316L(EN1.4401/1.4404). The 316 grades are moreresistantto chloride-
containing solutions, especially underwet and hot conditions.
Aluminium and aluminium alloys(coated and non-coated) mightalso be used
as dry material contact surfaceswhereonlydry cleaningis applied. However,
the abrasive characteristicsof the processed powder shallbe consideredin this
choice.Moreover, if aluminium is specifiedfroman operationalor weight
aspect,thereis a potential corrosionproblemwhena wet cleaning procedureis
applied. Carbonsteelcan also be consideredas a contact surfacein components
involving dry processingand dry cleaning operations.
Non-metals
Plastics (e.g. polycarbonate, polyetheretherketone (PEEK), polyvinylidene
fluoride(PVDF), polyacrylamide (PA)and polytetrafluoroethene(PTFE)) and
elastomers(e.g.nitrilebutylrubber (NBR),viton,ethylene propylenediene
monomer (EPDM)and siliconrubber) maybe used.Whenin contact withdry
materials theymust retaintheiroriginalsurfacecondition and conformational
properties when exposed to the processing conditions of temperature and
humidity, and also during cleaning operations.It is important to realisethat
plasticsand elastomers in particularare sensitive to abrasive powders and
therefore the contactsurfaces should be minimised as much as possible.
Glassis a hygienic material, but shouldnot be usedbecause of the risk of
breakageand subsequentdifficultyin detecting broken glass in dry materials.It is
recommendedthat the glassis replaced with another material,e.g. polycarbonate.
Non-metallicsurfaces usedin dry materialshandlingcan createelectrostatic
chargeson the material. Thiscan causesurface adhesion by smallparticles.
Electrostaticeffects duringdry materials handlingin pneumaticconveying
systems and non-metallic equipmentparts, for example, can be problematic, and
therefore specialattentionshouldbe paidto accessibilityand cleaningin such
systems.
13.4.2 Product contact surfaces
Product contact surfaces should be smooth and resistant against both dry
material contactand againstliquid chemicals usedin wet cleaning.Product
Improving the hygienic designof equipmentin handling dry materials 223