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What is the effect of the electrode polarity in SA (Submerged Arc) welding?

 

The deepest penetration is usually obtained with the direct current electrode positive (DCEP) polarity which also gives the best surface appearance, bead shape and resistance to porosity. Direct current electrode negative (DCEN) polarity gives an increased burnoff rate and decreased penetration as maximum heat is developed at the tip of the electrode instead of at the surface of the plate. For this reason, DCEN polarity is often used for surfacing or cladding and for other applications where high deposition rates are required, with minimum dilution from the parent material. The flux/wire consumption ratio is less with DCEN polarity than with DCEP so transfer of alloying elements from the flux is reduced.

In changing from DCEP to DCEN polarity, some increase in arc voltage may be necessary to obtain a comparable bead shape. Alternating current requires a voltage about halfway between DCEP and DCEN polarity and is particularly useful when arc blow is a problem. It is often used in tandem arc systems in which DCEP is used on the leading electrode and AC on the trailing electrode in order to minimise magnetic interaction between the two arcs.

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