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Arc Welding
Contact nowWhen using covered electrodes, the electrode selection should be based on the thickness of metal and the position that will be used when welding galvanized steel. The E-XX12 or 13 will be used for welding thinner material, the E-XX10 or 11 will be used for welding galvanized pipe and for welding hot-dipped galvanized parts of heavier thickness. The low-hydrogen electrodes can also be used on heavier thicknesses.
The welding technique should utilize slow travel speed to permit degassing of the molten metal. The electrode should point forward to force the zinc vapor ahead of the arc. The quality of welds will be equal to those of bare metal, assuming the weldability of the steel is equal.
The gas metal arc welding process is becoming more widely used for joining galvanized steel. For the thinner gauges the fine-wire short-circuiting method is recommended. In this case, the technique would be similar to that used for bare metal. The shielding gas can be 100% CO2 or the 75% argon and 25% CO2 mixture. The selection is dependent primarily on the material thickness and position of welding.
For certain applications, the argon-oxygen mixture is used. The amount of spatter produced when welding galvanized steel is slightly greater than when welding bare steel. The flux-cored arc welding process can be used as easily as gas metal arc welding for galvanized steel. It is recommended for the heavy gauges and on hot-dipped galvanized parts. The highly deoxidized type of welding electrode should be used.
The gas tungsten arc welding process is not popular for welding galvanized steel, since it is one of the slower welding processes and does cause a larger area of zinc adjacent to the weld to be destroyed. In addition, the volatilized zinc is apt to contaminate the tungsten electrode and require frequent redressing of the electrode.
In an effort to overcome this, extra high gas flow rates are sometimes used, which can be expensive. Other techniques may be used as well. If a filler rod is used it may be of either the highly deoxidized steel type or of the bronze type previously mentioned. In this case the arc is played on the filler rod and zinc contamination of the tungsten electrode is avoided.
The carbon arc welding process has been widely used for welding galvanized steel. Both the single carbon torch and twin carbon torch can be used. The twin carbon torch is used as a source of heat much the same as the oxyacetylene flame; however, when the single carbon is used the carbon can be played on the filler rod and extremely high rates of speed can be accomplished. Normally in this situation the filler rod, Type RBCuZn-A (60% Cu-40% Zn). By directing the arc on the filler rod it melts and sufficient heat is produced in the base metal for fusion but not sufficient to destroy the zinc coating. This process and technique is widely used in the sheet metal duct work industry.
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