Metallic Arc Welding: Working Principle and Types of Electrodes Used

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The type of electric welding in which an arc is established between the workpiece and the filler metal electrode is known as metallic arc welding or simply metal arc welding.

The figure shows the simplified circuit diagram of metallic arc welding.

In metallic arc welding, the intense heat of the arc forms a molten pool in the metal being welded and at the same time melts the tip of the electrode. As the electric arc is maintained, filler metal from the tip of the electrode is transferred across the arc and it fuses with the molten base metal.

The electric arc in this method of welding may be created by direct current or alternating current. In the places, where normal electricity supply is not present, diesel driven generators are used for welding. The DC supply can be obtained from the electricity mains with the help of transformer and rectifier unit.

Although a transformer is widely used for AC arc welding as it is inexpensive and simple having no maintenance cost due to absence of moving parts. With AC system, the coated electrodes are used while with the DC system, bare electrodes can be used.

In metallic arc welding, to strike the electric arc, an open circuit voltage of between 60 to 80 volts is required and for maintaining the short arc 15 to 25 volts is necessary. Depending upon the class of the work to be welded, the electric current required for metallic arc welding varies from 10 to 500 Amperes.

With the DC system, the main disadvantage of the metallic arc welding is the presence of arc blow, i.e. distortion of the arc stream from the intended path due to magnetic forces of a non-uniform magnetic field. However, with the AC system, the problem of arc blow is considerably reduced.

Electrodes for Metallic Arc Welding

The electrodes which are used for metal arc welding are of three types viz −

  • Bare Electrodes

  • Dipped or Light Covered Electrodes

  • Heavy Coated Electrodes

Bare Electrodes

Bare electrodes have no coating of flux on them. The bare electrodes are not used in these days because, it was found that the weld made by the bare electrodes was considerably poor in ductility, resistance to impact and fatigue. The appearance of the weld made by the bare electrode was also not good. This poor performance of the bare electrodes is due to vaporization of important elements of the weld metal during welding process and also due to the presence of oxides and nitrides resulting from the atmospheric contamination of weld metal.

Bare electrodes are mainly used at a lower welding voltage. For the bare electrodes, the welding current ranges from 150 to 300 A, depending upon the size of the electrode used. However, with the bare electrodes, more difficulty is experienced in the stating of the arc.

Dipped or Light Covered Electrodes

Dipped or light covered electrodes are considered an improved version of the bare electrodes. In case of dipped electrodes, the electrode is lightly covered with the flux material. The dipped electrodes provide better protection against the oxidation of the weld. These electrodes require a higher welding voltage and lower welding current as compared to the bare electrode.

Heavy Coated Electrodes

In heavy coated electrodes, the electrode is heavily covered with a flux material. The flux is a material of substantial thickness and solidity that is calculated to provide protection to the electrode. In case of heavy coated electrodes, the flux coated on the core wire is composed of special element which protect both the arc and the weld metal. The appearance and the physical properties of the weld are also improved considerably.

Applications of Metallic Arc Welding

The field of application of metallic arc welding includes −

  • Welding of carbon steel.

  • Welding of high-alloy austenitic stainless steel.

  • With many precautions, this welding process can also be used for low and medium steels.

raja
Updated on 17-Mar-2022 05:25:13

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