Q. Describe the electro slag welding process.
OR
Describe electro slag welding process. What are the specific situations where electro slag welding process is used.
Ans. Electro slag welding: In this welding process, welding heat is produced by the molten slag, which melts the filler metal and the surfaces of the work to be welded.
Operation: Electroslag welding is initiated by starting an arc between the filler metal/electrode and the work. This arc heats the flux and melts it to form the slag. The arc is then extinguished and the slag (conductive) is maintained in molted condition by its resistance to the flow of electric current between the electrode and the work. The temperature of this molten slag pool is approx. 1650º at the surface and 1950º inside, under the surface. This much heat is sufficient to weld thick sections or joints in a single pass. Several electrodes are used for long welds so that the heat is uniformly spread.
Water-cooled shoe or dam plate fastened to the dies of the workpiece prevents the molten metal from running off. These plates also assist the solidification process by removing heat and are moved up as the weld progress.
Flux : Combination of oxides of silicon, manganese, titanium, calcium magnesium and fulspar are used as flux in this process. It shields the molten metal and clears the impurities from the molten metal.
(i) Thicker plates can be welded in single pass and economically.
(ii) Extremely high deposition rates can be achieved (10-20 kg/hr/electrode).
(iii) Flux consumption as compared to submerged arc welding is low.
(iv) No spattering and arc flashing occurs.
(v) Welding speed of about 1.5 m/hr is possible.
(i) Submerged arc welding is more economical than electroslag welding for joints below 60 mm.
(ii) It is difficult to close cylindrical welds.
(iii) Welding is carried out in vertical up position only.
(i) Heavy plates, forging and castings can be easily butt-welded.
(ii) Following alloys can be welded.
(iii) Low carbon and medium carbon steel.
(iv) High strength structural steels.
(v) Alloy steels such as stainless steel and nickel alloys.