ELECTRO SLAG WELDING
This process is similar to the electro gas welding process designed for making butt welding in the vertical position in one single pass and the plate thickness can vary from 12.5 mm to 500 mm. The welding heat is provided by a small quantity of flux which is converted into a conductive molten slag by its resistance to the electric current passing between the continuously fed wire or wires (upto three wires for 500 mm plates) and the parent plates. The hot molten slag melts the filler wire and the joint surfaces and also shields the weld pool which moves up along full cross section of the joint as welding progresses. There is no arc and welding is quiet and spatter free. A pair of water cooled copper shoes fitted on either side of the joint retaining the molten metal and slag pool and acts as a mould to cool and shape the weld surfaces. The copper shoes move automatically along upward as welding progresses. Many years ago, the process was employed for welding of boiler drums and thick plates in India and Russia. Now it has become obsolete.