Safely welding galvanized steel

Galvanizing has been used to protect iron and steel from rusting for over a hundred years in places as diverse as the wire rope used for suspension cables. It is simply the coating of zinc over steel. Welding of galvanized steel is done almost exactly the same way as welding of the bare steel of the same composition; the same welding processes, volts, amps and travel speed can be used with little modification when the switch is made from uncoated steel to galvanized steel, unless the zinc coating is unusually thick. The difference between welding galvanized steel and welding uncoated steel is a result of the low vaporization temperature of the zinc coating. Zinc melts at about 900癋 and vaporizes at about 1650癋. Since steel melts at about 2,750癋 and the welding arc temperature is 15,000 to 20,000癋, the zinc that is near the weld does not stand a chance -- it's vaporized. By the time the weld pool freezes, the zinc is gone. However, there are two immediate consequences: the vaporized zinc increases the volume of welding smoke and fumes; and the zinc at and near any welds is actually burned off by the heat of the arc, removing the protective zinc coating. Galvanized steel welds The successful welding of galvanized steel is so widely accepted that there is very little recently-published mechanical property data comparing uncoated versus galvanized weld properties. The welding industry recognized fifty years ago that welds on galvanized steel and welds on uncoated steel are of comparable strength if the quality of the welds is comparable. Recent publications on welding galvanized steels deal with weld toughness, porosity control, weld appearance, restoring corrosion resistance and other issues that are much more complex than the strength of the weld. When using shield metal arc welding (SMAW), galvanized steel can be welded in the same manner as uncoated steel. When using metal inert gas (MIG) or flux cored welding, one may have to adjust the voltage slightly to control spatter, and one may have to clean the welding gun of spatter and zinc oxide deposits more frequently that when welding uncoated steel. Hobart makes a flux cored wire called "Galvacore" that some users have had good success with when welding galvanized steel. When difficulty is encountered welding galvanized steel that was not encountered during welding uncoated steel, it is usually because the welding engineer has not accounted for the volume of gas that is evolved by the vaporization of zinc during welding. The thicker the zinc coating, the more fumes are generated, and those fumes have to be able to escape easily into the atmosphere and not be forced through the liquid weld metal. Avoid filtering fumes The first line of defense in dealing with zinc oxide fumes is welder training. Welders should be taught -- even when welding uncoated materials -- to keep their heads out of the fume plume and to position themselves relative to the air flow around themselves so fumes and dust do not collect inside their welding shields. If a welder finds white dust inside his welding shield when welding galvanized products, he is not positioning himself properly. When welding galvanized products that have thin, uniform coatings and the process is gas-shielded MIG or flux core, the fumes generated are sparse and the shielding gas blows them away from the welder; this is frequently sufficient to avoid metal fume fever without further action.

"Welding of galvanized steel is done almost exactly the same way as welding of the bare steel of the same composition."

Restoring corrosion resistance The heat from welding vaporizes the protective zinc coating near the weld. Even though the remaining zinc continues to provide some protection to the zinc-free areas, the appearance is poor, and the zinc-free areas will rust when exposed to the environmenNike news