Generally most galvanizing and powder coating companies will have a pre-treatment that removes lose surface contamination, light oils etc, although there are situations where even the best system will not remove the worst.
It is inert up to about 900 degrees Centigrade: it is resistant to acids: it cannot be dissolved in water or even removed by steam: Silicon is very difficult to see.
If silicon is present on the surface of material before galvanizing or powder coating then pre-treatment or acid pickling will not eliminate it and the resulting galvanized or powder coat finish will be flawed.
Powder coated surfaces will be contaminated with what are known as “Fish eyes”, small craters in the surface. Galvanizing will be incomplete in areas of contamination, as molten zinc cannot reach the base metal.
Grease, heavy oils, cutting fluids, welding slag will not be removed by powder coating pre-treatment systems or acid pickling before galvanizing. The results will be the same as those described for silicon contamination.
Welding of greasy metal will result in a baked on layer of grease that is very difficult to remove, this will act as a barrier to formation of the zinc surface.
Shot blasting of greasy material will result in an inferior surface finish.
Avoiding Silicon and grease contamination.
- DO NOT use silicon containing maintenance lubricants.
- DO NOT use silicon containing anti-spatter spray.
- REMOVE GREASE from the area around the weld point before welding.
- REMOVE GREASE from material to be shot blast.
- REMOVE weld slag.
- REMOVE INK AND PAINT marks.
- DO NOT use high tack tapes directly on material.
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