WHAT ARE THE FUNCTIONS OF THE ELECTRODE COATING?

The functions of the coating are governed by three groups which are:

1. Electrical Function.
2. Metallurgical Function.
3. Physical Function

Electrical Function: It supplies arc ignition and maintains it easily during welding execution; this is achieved by the decomposition of certain chemical elements as they burn in the arc. In turn, they generate an ionized gas atmosphere that conducts electricity.

The Electrical group allows the use of Alternating Current. When using this type of electrical current, the arc strikes and extinguishes 120 times per second. Under these circumstances the arc becomes very unstable due to the cooling of the gaseous column surrounding it (Cycle).

Certain elements in some types of electrodes require a relatively low temperature to remain in an ionized state, which is the way they facilitate the periodic re-striking of the arc, thus resolving the instability problem.

Metallurgical Function. It replaces certain elements of the metal that partially volatilize due to the high temperature of the electric arc. These replacement elements are contained within the coating in such a proportion that, although part of them also volatilize, the remainder is incorporated into the molten metal.

The metallurgical group of the coating improves the mechanical properties of the fusion zone. This is achieved through the action of elements that contribute alloying materials included within the coating. These materials can improve the mechanical properties in two ways: 

1. They act as denitriding, deoxidizing, and desulfurizing agents, which are elements that are detrimental to weld metal quality.
2. They contribute alloying elements that improve and enhance the quality of the deposited or fused metal. For example, an electrode with a mild steel core can produce a hard or stainless deposit through the action of the coating.

This property can contribute to increasing the filler metal deposition in the following way: in certain types of electrodes, the coating incorporates a metallic element in powder form (Fe powder) iron of a chemical composition similar to that of the core, which melts in the arc and joins the molten metal coming from the core, thereby increasing the amount of deposited material and consequently the deposition rate.

Physical Function. This coating group protects the molten metal from harmful gases in the air, such as oxygen and hydrogen.

Oxygen and hydrogen from the air, when combined with the molten metal, form oxides and nitrides, causing the metal to become brittle and porous, with a consequent reduction in mechanical properties.

Certain components of the coating, when burned in the electric arc, form a protective atmosphere that prevents air from coming into direct contact with the molten metal.

Some elements of the coating melt to form a slag that completely surrounds the molten metal droplets during their transfer from the tip of the electrode to the base metal, thus achieving their full protection.

As the deposit is made, the slag mixes with the molten metal and collects its impurities, causing them to float to the surface of the weld bead where the slag finally solidifies.

The solid slag forms a layer over the deposit, which at the same time protects the hot metal from the harmful effects of air and slows down cooling, thereby preventing the metal from hardening or hardening excessively.

This physical group of the coating directs the arc force and the molten metal in the desired direction; this is achieved because the coating tends to melt more slowly than the metallic core, forming a kind of nozzle that guides the direction of the electric arc and directs the molten metal droplets.