| Seam Welding
Because the galvanized coating has a lower surface contact
resistance than bare steel, welding conditions for galvanized sheet
will differ somewhat from those used for welding hot rolled or cold
rolled sheet. Generally, higher electrode forces and higher
welding currents and/or longer weld-cycle times are required to
produce the same fused-zone area in galvanized sheet as achieved
with uncoated sheet.
Zinc pickup on the electrodes during seam welding can cause
fairly rapid electrode wear. To minimize zinc pickup, the
electrodes should be kept as cool as possible by utilizing water
cooling and controlling the rate of welding.
For all galvanized products, extremely high welding current is
to be avoided, because excessive heating tends to cause expulsion
of the zinc coating under the electrodes. The optimum setting
of the welding parameters must be determined by trial and are
dependent on the specific application and sheet characteristics
such as thickness or coating weight.
Seam welding of galvanized steel sheet can be considered to be
continuous spot welding; the guidelines for spot welding should be
followed for seam welding. To produce acceptable welds, the
procedures used for cold rolled sheet should be modified toward
slightly narrower electrode width, higher electrode force, higher
welding current and slightly lower welding speed.
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