The methods of welding copper (generally called industrial pure copper) are gas welding, manual carbon arc welding, manual arc welding and manual argon arc welding, and automatic welding can be used in large structure. Gas welding of 1. copper The most commonly used welded copper joints are butt joints, lap joints and T-joints as few as possible. Two kinds of wire can be used in gas welding, one is the wire containing deoxidizing elements, such as S201 and S202, the other is the common purple copper wire and the cutting strip of the parent material, and the gas flux 301 is used as the flux. Neutral flame should be used when welding copper. Manual arc welding of 2. copper In manual arc welding, the copper electrode is 107, and the welding core is copper (T2, T3). The edge of the welding place should be cleaned before welding. When the thickness of the weldment is greater than 4 mm, it must be preheated before welding, and the preheating temperature is generally about 400~500 C. When welding with copper 107 electrode, DC power should be adopted. Short arc should be used when welding, and the electrode should not be swinging horizontally. The linear movement of the welding rod can improve the forming of the weld. The step back welding method should be adopted for long weld. The welding speed should be as fast as possible. During the multilayer welding, slag must be thoroughly removed. Welding should be carried out in a well ventilated place to prevent copper poisoning. After welding, use flat head hammer to strike weld, eliminate stress and improve weld quality. Manual argon arc welding of 3. copper In the process of manual argon arc welding of copper, the wire used is S201 (special copper wire) and S202, and also copper wire, such as T2. Before welding, the welding edge of the workpiece and oxide film, oil and other dirt on the surface of the welding wire must be cleaned up so as to avoid blowholes and slag inclusion. The cleaning methods include mechanical cleaning and chemical cleaning. When the thickness of the butt joint plate is less than 3 mm, it does not open the groove; when the plate thickness is 3~10 mm, the V groove is opened and the angle of the slope is 60~70; when the plate thickness is more than 10 mm, the X groove is opened and the angle of the slope is 60~70; in order to avoid unweld, it generally does not leave the blunt side. According to plate thickness and groove size, the gap of butt joint is selected from 0.5 to 1.5 mm. The manual argon arc welding of copper is usually made by direct current connection, that is, tungsten electrode is connected to the negative electrode. In order to eliminate porosity and ensure reliable fusion and penetration, the welding speed must be increased, the argon consumption should be reduced, and the weldments should be preheated. When the plate thickness is less than 3 mm, the preheating temperature is 150~300 C; when the plate thickness is greater than 3 mm, the preheating temperature is 350~500 C. The preheating temperature should not be too high, otherwise the mechanical properties of the welded joint will be reduced. There are also carbon arc welding of copper. Carbon arc welding electrodes have carbon electrodes and graphite electrodes. The wire used for carbon arc welding of copper is also the same as that used for gas welding. It can also be used as cutting bar for parent material, which can be used as flux for gas welding of copper, such as gas agent 301.