The coating applied on the surface of the welding core is called the drug skin.The coating of electrode plays an important role in welding process.If the use of no coating of bare electrode welding, in the welding process, the oxygen and nitrogen in the air will be a large number of molten metal, the metal iron and beneficial elements carbon, silicon, manganese and other oxides and nitride forms a variety of oxides and nitride, and residual in the weld, resulting in weld slag or crack.The gas into the weld pool may cause a large number of pores in the weld, which can greatly reduce the mechanical properties (strength, impact value, etc.) of the weld and make the weld brittle.In addition, the use of bare electrode welding, arc is very unstable, serious spatter, weld formation is poor.People in the practice of the process found that if the outside of the bare electrode coated with a layer of various minerals, such as the composition of the coating, can make the arc combustion stability, weld quality is improved, this kind of electrode is called the coated electrode.With the continuous development of industrial technology, people have created the high quality thick coated electrode which is widely used now.