Electrode coating refers to the coating layer applied on the surface of the welding core.
The coating is decomposed and melted in the welding process to form gas and slag, which play a role in mechanical protection, metallurgical treatment, and improvement of process performance.
The composition of the coating includes: minerals (such as marble, fluorspar, etc.), ferroalloys and metal powders (such as ferromanganese, ferro-titanium, etc.), organic substances (such as wood flour, starch, etc.), chemical products (such as titanium White powder, water glass, etc.).
Electrode coating is an important factor in determining the quality of the weld, and it has the following effects in the welding process.
Improve the stability of arc combustion. The uncoated electrode is not easy to ignite the arc. Even if it is ignited, it cannot burn stably.
The electrode coating generally contains substances with low ionization potentials such as potassium, sodium, calcium, etc., which can improve the stability of the arc and ensure the continuous welding process.
Protect the weld pool. During the welding process, oxygen, nitrogen and water vapor in the air penetrate into the weld seam, which will have an adverse effect on the weld seam. Not only formation of pores, but also reduce the mechanical properties of the weld, and even cause cracks. After the electrode coating is melted, a large amount of gas is generated covering the arc and the molten pool, which will reduce the interaction between the molten metal and the air. When the weld is cooled, the melted coating forms a layer of slag, which covers the surface of the weld, protects the weld metal and cools it slowly, reducing the possibility of porosity.
Ensure that the weld is deoxidized and desulfurized and phosphorus impurities. Although protection is carried out during the welding process, it is still inevitable that a small amount of oxygen will enter the molten pool to oxidize the metal and alloy elements, burn the alloy elements, and reduce the quality of the weld. Therefore, it is necessary to add a reducing agent (such as manganese, silicon, titanium, aluminum, etc.) to the electrode coating to reduce the oxides that have entered the molten pool.
Add alloying elements to the weld. Due to the high temperature effect of the arc, the alloying elements of the weld metal will be evaporated and burnt, which will reduce the mechanical properties of the weld. Therefore, it is necessary to add appropriate alloying elements to the weld through the coating to compensate for the burnt loss of the alloy elements and to ensure or improve the mechanical properties of the weld. For welding of some alloy steels, it is also necessary to infiltrate the alloy into the weld through the coating, so that the weld metal can be close to the metal composition of the base metal, and the mechanical properties can catch up with or even exceed the base metal.
Improve welding productivity. The electrode coating has the effect of increasing the droplet and reducing the spatter. The melting point of the electrode coating is slightly lower than the welding point of the core, but because the core is in the center of the arc and the temperature is higher, the core melts first, and the coating melts a little later. In this way, a short section of sheathed sleeve is formed at the end of the electrode, and the effect of the arc blowing force makes the droplet shoot directly onto the molten pool, making it beneficial to overhead welding and vertical welding. In addition, after the welding core is coated, the arc heat is more concentrated. At the same time, since the metal loss caused by spatter is reduced, the deposition coefficient is increased, and the welding productivity is also improved. In addition, the amount of dust generated during welding will also be reduced.
