1. Improve the electric conductivity in the arc region to improve the arc ignition and stabilization of the arc.
2. Formation of slag, which;
(a) Influences size of droplet.
(b) Protects the droplet during transfer and molten weld pool from atmospheric gases.
(c) Protects solidified hot metal from atmospheric gases.
(d) Reduces the cooling rate of weld seam.
3. Formation of shielding gas to protect molten metal (The coating give off inert gases as CO2 under arc heat, which shields the molten metal pool and protects it from the atmosphere oxygen,Hydrogen and Nitrogen pick- up,thus reducing contamination of the weld.)
4. Provide deoxidizers like Si and Mn in form of FeSi and FeMn.
5. Alloying with certain elements such as Cr, Ni, Mo to improve weld metal properties.
6. Improve deposition rate with addition of iron powder in coating since the thermal losses to the atmosphere from the electro tip are reduced.
One of the major concerns with the coated electrodes is the moisture pick-up by the coating. This moisture, when it enters the puddle, dissociates into oxygen and hydrogen with the hydrogen being absorbed by the liquid metal and subsequently relesed during solidification, causing porosity. Normally, some additives are added to the coating to reduce the moisture pick-up from the damp atmosphere. But they do not ensure complete safety from the moisture pick-up. The electrodes should be picked out of the oven only when welding is to be done. They should not be out of the oven for more than 30 min to 4 hours depending upon the moisture picking time of a particular coating
Nice one
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