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Electroslag Welding (ESW)

ELECTROSLAG WELDING

The Process :-

Electroslag welding (ESW) is a process that melts and joins metals by heating them with a pool of molten slag held between the metals and continuously feeding a filler wire electrode into it, as shown in Figure. The weld pool is covered with molten slag and moves upward as welding progresses. A pair of water-cooled copper shoes, one in the front of the workpiece and one behind it, keeps the weld pool and the molten slag from breaking out. Similar to SAW, the molten slag in ESW protects the weld metal from air and refines it. Strictly speaking, however, ESW is not an arc welding process, because the arc exists only during the initiation period of the process, that is, when the arc heats up the flux and melts it. The arc is then extinguished, and the resistance heating generated by the electric current passing through the slag keeps it molten. In order to make heating more uniform, the electrode is often oscillated, especially when welding thicker sections. Figure 1.23 is the transverse
cross section of an electroslag weld in a steel 7 cm thick (13).Typical examples of the application of ESW include the welding of ship hulls, storage tanks, and bridges.



Advantages and Disadvantages :-

Electroslag welding can have extremely high deposition rates, but only one single pass is required no matter how thick the workpiece is. Unlike SAW or other arc welding processes, there is no angular distortion in ESW because the weld is symmetrical with respect to its axis. However, the heat input is very high and the weld quality can be rather poor, including low toughness caused by the coarse grains in the fusion zone and the heat-affected zone. Electroslag welding is restricted to vertical position welding because of the very large pools of the molten metal and slag. Figure summarizes the deposition rates of the arc welding processes discussed so far. As shown, the deposition rate increases in the order of GTAW, SMAWGMAW and FCAW, SAW, and ESW. The deposition rate can be much increased by adding iron powder in SAW or using more than one wire in SAW,, ESW, and GMAW .

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