Not that the following is any recommendation to pretreatment of galvanized steel.
Do these descriptions sound about right, it has been so long I forget. Thanx. skip.
Zinc plating is electroplating where the parts are cathodic [-] drawing the zinc from [+] anodes of zinc; appling a thin smooth layer for decorative and protective uses.
Galvanizing is a system where zinc is melted onto a molten form and the parts are fluxed and dipped into the molten bath and then removed to cool. This usually applies a thicker and rougher finish of great resistance to rust.
This galvanizing [highway guard rails] is a self sacrificing finish which means that 'it'...the galvanizing self oxidizes instead of the part. Any painted coating on the galvanized work degrade, and usually chalk off.
Zinc electro plating is also a form of galvanization which is commonly called electogalvanization. Guard rails and buckets are usually hot dip galvanized to get a thicker deposit of the sacrificial zinc. Unlike tin plating, a scratch down to the steel will not cause rust until the zinc in the area is all sacrificed. In fact, the zinc will oxidize and in many cases heal over the scratch to further prevent parent metal corrosion. There is another safer process where the zinc is essentially powder coated onto a panel and then heated to bond the zinc. This doesn't weaken the metal to extent that electrogalvanizing does and is a less hazardous process that produces a finish with great tooth for paint to stick to.
skip.
Last edited by skip (12/28/2009 - 09:20 PM)
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