Also known as ESW, electroslag welding is a method where a primary arc is used at first to heat the slag and is then smothered by the conductive slag. The heat is then generated by the slag resisting the electricity passing between the consumed electrode and the work. It is usually used to weld steel in a vertical position and was used widely in the Soviet Union in the 1940’s. This is not an arc welding process however, though an arc is briefly ignited in the beginning stages. Past this, there is not arc involved in the procedure. The thickness limit for this welding process reaches up to 30″. Extreme heat helps to gain this type of penetration, and multiple electrodes can be used to speed up this process. In the 1970’s, electroslag welding became a popular choice for welding metals that were very thick. These applications include parts for bridges, buildings, ships, and pressure vessels.
The positive side of electroslag welding is that very thick metals can be joined and multiple electrodes can be used to complete a weld in a single pass. The heat is held in the weld longer and gas bubbles are allowed to escape from the weld pool before it cools. The entire process is automatic and once it starts it does not stop until the weld is complete. For large or thick pieces of stock, electroslag welding is the quickest way to join the pieces together. There is very little work that needs to be done to prepare the joints prior to welding and the distortion of the metal is relatively low. The drawbacks come from the fact that the system is very complicated and only works on flat or vertical joints. Also some of the instruments used in this procedure have to be cooled with a constant water supply.