The electrode is composed of a metal core and coating consists of two parts, the main role is as the core electrode and filler metal; coating is the main function of the arc stability, protection, deoxidization, alloying and improve welding process.
　　Basic principles of electrode selection:
　　1) equal strength principle, that is, to choose the electrode with the same strength grade as base metal. Generally used for welding low carbon steel and low alloy steel.
　　2) the principle of the same composition is to select the electrode with the same or similar chemical composition as the base metal. Generally used for welding heat-resistant steel, stainless steel and other metal materials.
　　3) the principle of crack resistance should be chosen for the basic electrode with good crack resistance, so as to avoid cracks in the joint during welding and use. Generally used for welding structure with large rigidity, complex shape and dynamic load in use.
　　4) the principle of anti porosity is limited by the welding process conditions, such as the oil and rust in the joints of butt welding parts, so the acid electrode with strong anti porosity ability should be selected to avoid the gas remaining in the weld during the welding process and form pores.
　　5) low cost principle, in the premise of meeting the use requirements, as far as possible to choose good process performance, low cost and high efficiency of welding rod