Correct Answer - Option 2 : To increase arc stability
Explanation:
Bare electrode:
- These are the bare electrode, which is not coated with any fluxing material.
- Bare electrodes are in the form of wire.
- During welding operation an arc is struck between the workpiece and the electrode wire, then the electrode is melted down into the weld.
- When the molten metal electrode and workpiece are exposed to the atmosphere of the oxygen and nitrogen, they form their oxides and nitrides and cause the formation of some non-metallic constituent, which reduces the strength and ductility of the deposited weld.
- The bare electrodes are usually employed for automatic and semi-automatic welding.
- With the bare electrode, the welding can be done satisfactorily with DC supply only if the electrode be connected to the negative terminal of the supply.
Coated Electrode:
Depending upon the thickness of flux coating, the coated electrode may be classified into:
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Lightly coated electrode - These electrodes are coated with a thin layer up to less than 1 mm. This coating usually consists of Lime mixed with soluble glass which serves as a binder. The main purpose of using the light coating layer on the electrode is to increase the arc stability. So they are called as stabilizing electrode.
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Heavily coated electrode - These electrodes have a coating layer with heavy thickness. The materials commonly used for coating the electrodes are titanium oxide, ferromanganese, silica, flour, asbestos clay, calcium carbonate etc.
Advantages of coated electrode:
- Arc is stabilized due to flux compounds of sodium and potassium.
- The weld metal can be protected from the oxidising action of the oxygen and the nitrifying action of the nitrogen due to the gas shielding envelope.
- The impurities present on the surface being welded are fluxed away.
- The electrode coating increases deposition efficiency and weld metal deposition rate through iron powder and ferroalloy addition.
- The welding operation becomes faster due to the increased welding rate.
- The coated electrode helps to deoxidize and refine the weld metal.
Solution:
The main purpose of using the light coating layer on the electrode is to increase arc stability.
