电焊（Electric welding）.docVIP

电焊（Electric welding） 3. welding workshop Welding is by heating, pressurizing, or the use of both, so that the two workpiece to produce inter atomic bonding process and connection. Welding is widely used, both for metals and for metals. Welding workshop mainly includes: manual arc welding, submerged arc welding, CO2 gas shielded arc welding and argon arc welding. (1) welding process Welding process is a complete set of technical regulations in welding process. Including welding methods, pre welding preparation, welding materials, welding equipment, welding sequence, welding operation, process parameters and post welding heat treatment, etc.. Different welding methods have different welding process. The welding process is mainly determined by the material, grade, chemical composition, structure type and welding performance requirements of the weldment. First of all, according to specific conditions to determine welding methods, and then formulate welding process parameters. Preheat Preheating is beneficial to reduce the maximum hardness of the heat affected zone of medium carbon steel and prevent cold crack. This is the main measure of welding medium carbon steel. Preheating can also improve the plasticity of joints and reduce the residual stress after welding. Usually, the preheating temperature of 35 and 45 steel is 150~250 degrees C, the carbon content is higher, or the thickness of the steel is large and the crack tendency is large, the preheating temperature can be increased to 250~400 DEG C. If the weldment is too large and the whole preheating is difficult, local preheating can be carried out, and the heating range of the local preheating is 150 to 200mm on both sides of the welding joint. Electrode condition Preferential use of alkaline welding rod. Groove form As the welding groove welding type into U. If it is a casting defect, the shape of the groove shall be smooth, with the aim of reducing the ratio of the base metal into the weld metal to reduce carbon c