Arc Shielding:

The arc shielding action, shown in Figure 4, is basically the same for all electrodes, but the particular method of shielding and the volume of slag generated differ from type to type. The bulk of the covering materials on some of the electrodes is converted to gas by the heat of the arc, and just a small amount of slag is generated. This type of electrode depends largely on a gaseous shield to avoid atmospheric contamination. Weld metal from such electrodes might be identified by the incomplete or light layer of slag that covers the bead.

For electrodes at the other extreme, the bulk of the covering is changed to slag by the heat of the arc, and just a small volume of shielding gas is generated. The tiny globules of metal being transferred across the arc are completely coated with a thin film of molten slag. This molten slag floats to the surface of the weld puddle because it is lighter than the metal. The slag solidifies after the weld metal has been solidified. Welds made with these electrodes are recognized by the heavy slag deposits that totally cover the weld beads. Between these extremes is a broad variety of electrode types, each with a different combination of slag and gas shielding.

Variations in the amount of gas and slag shielding also effect the welding characteristics of covered electrodes. Electrodes, which generate a heavy slag may carry high amperage and provide high deposition rates, by making them ideal for heavy weldments in the flat position. Electrodes, which generate a light slag layer are utilized with lower amperage and provide lower deposition rates. These electrodes generated a smaller weld pool and are appropriate for making welds in all positions. Due to the differences in their welding characteristics, usually one type of covered electrode will be best suitable for a given application.