Arc welding
Welding coated steel sheets

In arc welding, the main difficulty lies in the lower melting and evaporation temperatures of zinc compared with those of steel.

The diagram at 12 shows what happens in a weld. The example deals with clinch or lap welding – the most demanding – because the vaporous zinc cannot escape.

The temperature difference is such (steel melts at 1,550°C and Zn vaporizes at 906°C) that when the arc passes through and in front of it, the coating disappears and vaporizes.

As a result, it passes into the arc plasma and has two more...