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COATED ELECTRODES

Types of electrodes

The function of the core rod is to provide electricity to the arc and to melt and become weld deposit. The coating consisting of metals, minerals and organic substances have several functions:

Ionisation

Air is a non conductor. By adding ionising elements that evaporates during welding we create a plasma cloud where the current can travel.

For AC welding this

function is essential in order to perform welding.

3.01

Crater Formation

Elements in coating

that makes the melting boundary of the coating to be behind that of the core rod. The arc is in this way concentrated to one spot directly under the electrode tip.

Metal Transfer The transfer of metal globules from the electrode tip to the molten pool is made possible by a combination of elements in the coating "exploding" the droplets over and the current that performs a "pinch" effect.

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Alloying Elements In the arc the temperature reaches 7000 °C. Many of the elements might evaporate and will have to be compensated for by putting alloying elements into the coating.

AIR

AIR

Gas Shield

The shielding ingredients in the coating is to provide a dense smoke shield preventing Oxygen and Nitrogen from reaching the pool / arc area Slag Formation Slag forming elements are part of the electrode coating and they are there in order to: 1) Protect crater and globules against oxygen during the droplet transfer,

2) Clean the

weld pool by combining itself with impurities and bring them to the surface before solidification, 3) Give the weld a slow cooling rate, 4) Form the weld: Welding is a small scale casting operation and requires a mould. The slag is the mould.