Electrode arc welding
Electrode arc welding is a method of welding by manual manipulation of the electrode, so the quality of the weld depends on the operating technology of the welder, which requires the welder to master higher operating skills. According to the requirements for electrode arc welding in the standard, when the diameter of the electrode increases by more than 1mm, the welding electrode is changed from low hydrogen type to non-low hydrogen type, the tensile strength grade (steel number) of the welding electrode (wire) is changed, the groove shape is changed beyond the regulations, the groove size is changed beyond the allowable deviation, the thickness of the plate is changed beyond the specified range of application, the padded is changed to no padded, and the diameter of the welding electrode is changed from low hydrogen type to low hydrogen type. Clean welding root is changed to not clear welding root, the minimum preheating temperature specified decreases by more than Celsius, the temperature between the top layer increases by more than 50 degrees Celsius, when the heat input is limited, the heat input value increases by more than 10%, change the welding position, the above changes need to be re-evaluated welding process.
Submerged arc welding (automatic welding)
Submerged arc welding (including submerged arc surfacing and electroslag surfacing) is a welding method in which the arc is burned under the flux layer. Its inherent advantages of stable welding quality, high welding productivity, no arc light and less smoke make it become the main welding method in the production of pressure vessels, pipe section manufacturing, box beam column and other important steel structures.
In recent years, although there have been many new welding methods with high efficiency and high quality, the application field of submerged arc welding is still not affected. From the point of view of the proportion of the weight of fused metal in various fusion welding methods, submerged arc welding accounts for about 10% and has changed little over the years.
Carbon dioxide gas welding (automatic or semi-automatic welding)
Carbon dioxide gas welding is one of the welding methods, is based on carbon dioxide gas as a protective gas, welding method. In the application of simple operation, suitable for automatic welding and all-round welding. No wind during welding, suitable for indoor operation.
MIG/MAG welding (inert gas welding/reactive gas welding)
Principle of MIG welding -- an arc welding method using inert gas as protection gas and welding wire as melting electrode. The shielding gas is usually argon or helium or a combination thereof. MIG uses an inert gas, and MAG adds a small amount of active gas, such as oxygen and carbon dioxide gas, to the inert gas.
TIG welding (tungsten inert gas welding)
Principle -- Under the protection of inert gas, the welding method is to use the arc generated between the tungsten pole and the weldment to melt the base metal and the filler wire (or not) to form a weld. Electromelting is extremely low during welding.
The length of arc is related to the type of coating and the thickness of coating. But all should be taken as short arc as possible, especially low hydrogen electrode. Long arcing may cause air holes. The short arc can prevent the harmful gases such as O2 and N2 from invading the weld metal, forming bad impurities such as oxides and affecting the quality of the weld.
The appropriate welding speed is based on the diameter of the electrode, the type of coating, welding current, the heat capacity of the welded material, the beginning of the structure and other conditions have their corresponding changes, can not be made standard provisions. Keep the proper welding speed, the slag can cover the molten pool well. The various impurities and gases in the molten pool have sufficient time to emerge, to avoid the formation of slag inclusion and porosity of the weld. If the rod speed is too fast in welding, the shrinkage stress will increase when the welding part is cooled, causing cracks in the weld.
The main points of welding wire selection
The selection of welding wire should be based on the type of steel to be welded, quality requirements of welding parts, welding construction conditions (plate thickness, groove shape, welding position, welding conditions, post-welding heat treatment and welding operation, etc.), cost and other comprehensive considerations.
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