This process is often seen as the 'magic solution' but!
I was involved in an engineering exercise on Sydney's famous bridge (
for those considering a visit 'down under' make sure you go 'up and
over' as walks are available to the top of the bridge arch every day)
The specification called for powder coating of the steelwork. No Coater
was able to give me an Australian Standard or warranty that their
product provided. Finally I located the manager of a large corrosion
protection company who said;
powder coating was developed in the architectural field for aluminium
due to its basic corrosion resistance ( not does not corrode) and nice
surface finish. Basically it acts as a condom to exclude the atmosphere
but when torn or broken through it offers no protection and in the case
of steel it can trap the water and iron oxide quickly forms and as rust
grows to seven times the volume of non rusted steel it quickly breaks
out and looks very unsightly offering no protection. His solution as to
the application of powder coating was; grind the powder very fine ( a
special order) to avoid air gaps and porosity of the powder coating
product. Prior to application grit blast the surface and apply a paint
type primer, then an undercoat these two providing best protection and
THEN apply the nice looking powder colour of your choice.
Industry will always prefer a zinc rich primer undercoat that has a
chemical sacrificial protection of the metal surface. This can then have
nice colour finishes to complete the job and provide a suitable image
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