What role does welding rod coating play in the welding process?

The electrode coating refers to the coating layer applied to the surface of the welding core. The coating decomposes and melts during the welding process to form gas and slag, which plays a role in mechanical protection, metallurgical treatment, and improvement of process performance. The components of the coating include: minerals (such as marble, fluorite, etc.), ferroalloys and metal powders (such as ferromanganese, ferrotitanium, etc.), organic matter (such as wood powder, starch, etc.), and chemical products (such as titanium dioxide, water glass, etc.). The electrode coating is an important factor in determining the quality of the weld. It has the following functions during the welding process:

1. Improve the stability of arc burning. It is not easy for a bare welding rod without a coating to ignite the arc. Even if it is ignited, it cannot burn stably. The electrode coating generally contains substances with low ionization potential such as potassium, sodium, and calcium, which can improve the stability of the arc and ensure the continuous welding process.

2. Protect the welding pool. During the welding process, oxygen, nitrogen and water vapor in the air penetrate into the weld, which will have an adverse effect on the weld. Not only will pores be formed, but it will also reduce the mechanical properties of the weld and even cause cracks. After the electrode coating melts, a large amount of gas is generated to cover the arc and the molten pool, which will reduce the interaction between the molten metal and the air. When the weld cools, the melted coating forms a layer of slag, which covers the surface of the weld, protects the weld metal and makes it cool slowly, reducing the possibility of pores.

3. Ensure the deoxidation of the weld and the removal of sulfur and phosphorus impurities. Although protection is carried out during the welding process, it is inevitable that a small amount of oxygen enters the molten pool, oxidizing the metal and alloy elements, burning the alloy elements, and reducing 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.

4. Supplement alloy elements for the weld. Due to the high temperature of the arc, the alloy elements of the weld metal will be evaporated and burned, which will reduce 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 burning of the alloy elements and ensure or improve the mechanical properties of the weld. For the 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 composition of the parent metal, and the mechanical properties can catch up with or even exceed the base metal.

5. Improve welding productivity and reduce spatter. The coating of the welding rod has the effect of increasing the molten droplet and reducing spatter. The melting point of the welding rod coating is slightly lower than the welding point of the welding core, but because the welding core is in the center of the arc and the temperature is higher, the welding core melts first and the coating melts a little later. In this way, a short section of the coating sleeve is formed at the end of the welding rod, and the effect of the arc blowing force makes the molten droplet directly shoot onto the molten pool, which is conducive to overhead welding and vertical welding. In addition, after the welding core is coated with the coating, the arc heat is more concentrated. At the same time, since the metal loss caused by spatter is reduced and the deposition coefficient is increased, the welding productivity is also improved. In addition, the amount of dust generated during welding will also be reduced.