timerequired in orderto achievea set standard of cleaning increases withan
increase in the surface roughness orRa value. Thesymbol Ra standsfor
roughness average and is given in micrometres (m). Thistermis internationally
adoptedand is quoted as the mainparameterto specifysurfaceroughness (for
definition ofRa, see ISO 468).
It is recommended that the surfaceroughness,Ra, for conduits, trunkings,
enclosures and suchlike for installation in hygienicproduction areasshould not
exceed2.5m. For all equipmentand materials that are to be usedin a hygienic
production area, it is importantto keepin mindthat the highertheRavalue, the
longerit willtaketo cleanthe equipment to achieve the same standard of
cleaning.
15.6.6 Use of constructionmaterials
Beloware somegeneraldos and don'ts in the use of construction materials.
Do:
∑ use a foodstandard silicon sealantto preventcreating soil;
∑ use nitrileor siliconerubber in environments withedible oils and fats;
∑ use materials having aRavalueas low as practicable in orderto minimise
cleaning time.
Don't:
∑ use nickel platedbrasscableglandswhen there is a chance of directproduct
contact;
∑ use GRPproducts sincepiecesmightbecomedetached(dueto wettingagents
in detergents) and end up as foreign bodiesin the product;
∑ use ethylene propylenediene monomer (EPDM)rubbers in environments
withedibleoils and fats.
15.7 Futuretrends
Therewillbe less electricalwiring/cablingin the future.It is expected that
wireless transfer of databetween instrumentationand controlequipment will
replace field buses and control wiring/cabling. Low-energy sensors and
actuators will end up battery supplied or energisedby the process flow.Energy
cablingto motorswill still be necessary,but probably projectedas an energy
ring, with local switching or converting due to further innovation of
semiconductors. It soundsfuturistic,but when youcompare this withthe
development of the mobile phone....
Improvingthe hygienicdesignof electricalequipment 261