Hot Galvanized Steel

http://www.webelements.com/webelements/elements/text/Zn/heat.html gives the melting and boiling temperatures. On rising temperature in air it will probably oxidise well before it boils, producing smoke. The presence of Zinc tends to cause errors in the crystal lattices of steels thereby weakening them, which is why welding galvanised steel is verboten, quite apart from the potential health consequences to the operative in so doing.

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Air Control Pollution Rochester ... but the permissible exposure limit for occupational exposure to zinc oxide in the United States is 5.0 mg/m^sup 3^ respirable dust. www.control-s.org/air-control-pollution-rochester.html

Others might. Happy reading!

Cheers, that'll do!

I don't have any documented source, but I have a vague recollection it is around 600 deg. F. The zinc coating of galv steel collects oxides from day one, and I understand this is the "smoke" seen, not the zinc boiling off.

BTW, I have seen welded galv stee frequently, and the materials coated with a zinc-rich primer. Could one of you explain the weakening of the base steel that occurs during welding?

Both are correct. Zinc starts oxidizing from day one after galvanizing. In humid or wet environments this causes "white rust" which is a visual defect and no way damages the integreity of the zinc coating. The smoke you see at 600 is oxide, the zinc coating will not melt until ~740. Also welding of two galvanized peices of steel does not hurt the steel structure. Galvanizing actually makes a more impact resistant and durable peice of steel in addition to the corrosion protection. The zinc galvanizes in 3 layers, layers one and two are actually a chemical combanation of the zinc and iron. Now that everyone has had a lesson in galvanizing any other relevant information can be found and www.galvanizeit.org which is the American Galvanizers Association.

Thanks!