Welding types and methods:
1.Electrode arc welding:
Principle——The arc welding method of welding with manual welding rod. The stable burning arc established between the welding rod and the weldment is used to melt the welding rod and the weldment to obtain a firm welded joint. It belongs to gas-slag joint protection.
Main features-flexible operation; low assembly requirements to be welded; wide range of weldable metal materials; low welding productivity; strong dependence on weld quality (depending on the welder's operating skills and on-site performance).
Application-widely used in shipbuilding, boilers and pressure vessels, machinery manufacturing, building structures, chemical equipment and other manufacturing and maintenance industries. Suitable for welding of various metal materials, various thicknesses, and various structural shapes (in the above-mentioned industries).
2. Submerged arc welding (automatic welding):
Principle-The arc burns under the flux layer. The heat generated by the arc burning between the welding wire and the weldment is used to melt the welding wire, flux and the base material (weldwork) to form a weld. Belongs to slag protection.
Main features-high welding productivity; good weld quality; low welding cost; good labor conditions; difficult to weld in space; high quality requirements for weldment assembly; not suitable for welding thin plates (when welding current is less than 100A, arc stability Bad) and short welds.
Application-widely used in shipbuilding, boilers, bridges, hoisting machinery and metallurgical machinery manufacturing. Submerged arc welding can be used for all weldments whose welds can be kept in a horizontal position or whose inclination angle is not large. The thickness of the board must be greater than 5 mm (to prevent burn through). Welding carbon structural steel, low-alloy structural steel, stainless steel, heat-resistant steel, composite steel, etc.
3. Carbon dioxide gas shielded welding (automatic or semi-automatic welding):
Principle: A molten electrode arc welding method using carbon dioxide as a shielding gas. It is gas protection. Main features-high welding productivity; low welding cost; small welding distortion (arc heating concentration); high welding quality; simple operation; high spatter rate; difficult to weld with AC power; poor wind resistance; cannot weld easily oxidized colored metal.
4. MIG/MAG welding (Melting extremely inert gas/active gas shielded welding):
Principle of MIG welding-an arc welding method using inert gas as shielding gas and welding wire as melting electrode. The shielding gas is usually argon or helium or their mixture. MIG uses inert gas, MAG adds a small amount of active gas, such as oxygen, carbon dioxide, etc. to the inert gas.
5. TIG welding (tungsten inert gas shielded welding)
Principle——Under the protection of inert gas, the base metal and filler wire are melted by the arc heat generated between the tungsten electrode and the weldment (or without filler wire) to form a welding seam. The electrode does not melt during welding.
6. Plasma arc welding
Principle-With the help of the restraining effect of the water-cooled nozzle on the arc, a high-energy-density plasma arc welding method is obtained.
Precautions for welding:
1. The length of the arc
The length of the arc is related to the type of electrode coating and the thickness of the coating. However, short arcs should be adopted as much as possible, especially low-hydrogen electrodes. Long arcs may cause blowholes. The short arc can prevent harmful gases such as O2 and N2 in the atmosphere from invading the weld metal, forming oxides and other undesirable impurities and affecting the quality of the weld.
2. Welding speed
The appropriate welding speed is based on the corresponding changes in conditions such as the diameter of the electrode, the type of coating, the welding current, the heat capacity of the welded object, and the beginning of the structure, which cannot be specified in the standard. Keep the proper welding speed, the molten slag can cover the molten pool well. Make the various impurities and gases in the molten pool have sufficient time to float out to avoid the formation of slag and pores in the weld. When the welding speed is too fast, the shrinkage stress will increase when the welding part cools, causing cracks in the welding seam.
3.Key points of welding wire selection
The selection of welding wire should be based on comprehensive considerations such as the type of steel to be welded, the quality requirements of the welded parts, the welding construction conditions (plate thickness, groove shape, welding position, welding conditions, post-weld heat treatment and welding operation waiting), cost and other comprehensive considerations.