During the welding process

The electrode coating serves the following functions during the welding process:

I. Improving the stability of arc combustion.

Bare welding rods without a coating are difficult to ignite an arc. Even if ignited, the arc cannot burn stably.

II. Protecting the weld pool.

During welding, oxygen, nitrogen, and water vapor from the air penetrate the weld, which can have adverse effects on the weld. This not only forms pores but also reduces the mechanical properties of the weld and can even lead to cracks. When the electrode coating melts, the large amount of gas produced envelops the arc and the weld pool, reducing the interaction between the molten metal and the air. As the weld cools, the molten coating forms a layer of slag that covers the weld surface, protecting the weld metal and allowing it to cool slowly, reducing the possibility of pore formation.

III. Ensuring deoxidation and removal of sulfur and phosphorus impurities from the weld.

Although protection is provided during welding, a small amount of oxygen inevitably enters the weld pool, causing oxidation of the metal and alloy elements, burning off alloy elements, and reducing weld quality. Therefore, reducing agents (such as manganese, silicon, titanium, and aluminum) are added to the electrode coating to reduce the oxides that have entered the weld pool.

IV. Supplementing alloy elements to the weld.

Due to the high temperature of the arc, the alloy elements in the weld metal are vaporized and burned off, reducing the mechanical properties of the weld. Therefore, it is necessary to add appropriate alloy elements to the weld through the coating to compensate for the loss of alloy elements and ensure or improve the mechanical properties of the weld. For welding some alloy steels, it is also necessary to introduce alloys into the weld through the coating so that the weld metal composition is close to that of the base metal, and the mechanical properties can match or even exceed those of the base metal.

V. Improving welding productivity and reducing spatter.

The electrode coating has the effect of increasing the molten droplet size and reducing spatter. The melting point of the electrode coating is slightly lower than that of the welding core,

but because the welding core is in the central area of ​​the arc, where the temperature is higher, the welding core melts first, and the coating melts slightly later. At the same time, because the metal loss caused by spatter is reduced, the deposition coefficient is increased, thus improving welding productivity.