The welding core is the metal core of the electrode. In order to ensure the quality of the weld, there are strict regulations on the content of various metal elements in the weld core. In particular, there are strict restrictions on harmful impurities (such as sulfur and phosphorus), and the quality of the weld core metal should be better than that of the base metal. Arc welding cannot be carried out on a smooth rod without a coating. This is because the arc stability is very poor, splashing is very large, and the weld is not well formed. After long-term practice, it is gradually found that the performance of the electrode is greatly improved by coating the welding core with some mineral raw materials (i.e. electrode coating). (1) Ensure stable arc combustion, so that the welding process is normal. (2) Using the gas produced after the drug skin reaction, protect the arc and the molten pool, prevent the harmful gases in the air (such as nitrogen, oxygen, etc.) from invading the molten pool, such as these gases will cause cracks and pores in the welding material, so that the welding can not achieve the ideal effect. (3) After the drug skin is melted, slag is formed, which covers the weld surface to protect the weld metal, make the weld metal slowly cool, help the gas escape, prevent the generation of pores, and improve the structure and performance of the weld. (4) After melting, various metallurgical reactions will be carried out, such as deoxygenation, sulfur removal, phosphorus removal, etc., so as to improve weld quality and reduce alloying element burning loss.