Author丨Yi Danping
Unit丨China Construction 5th Bureau 3rd Company Steel Structure Company
With the progress of modern science, new welding processes, new materials, new equipment continue to emerge, and the level of mechanization and automation continues to improve. This article will introduce the welding method of steel structure in detail according to the "Steel Structure Welding Code" GB 50661-2011. The welding methods generally used in steel structures include electrode arc welding, gas shielded arc welding, flux cored wire self-shielded welding, submerged arc welding, electroslag welding, gas-electric vertical welding, resistance welding, bolt welding and its combination.
1
Electrode arc welding
Electrode arc welding is a welding process that uses the heat generated by arc discharge as a heat source to heat, melt and fuse the electrode and weldment with each other to form a firm joint. Advantages: flexible operation, strong adaptability, wide range of applications, strong anti-risk ability, etc.; Disadvantages: high requirements for welder operation technology, low welding efficiency, not suitable for the welding of special metals, etc.
Electrode arc welding
2
Gas shielded arc welding
CO2 gas (instead of flux), welding wire, arc to melt the welding wire to form a weld, CO2 gas to protect the welded metal from contact with air. Features: fast welding speed and large melting depth; It can be welded manually or automatically; At present, the welding method is very commonly used in factories; Outdoor welding should have shelter measures to prevent pores and welding pit defects.
Gas shielded welding
3
Self-shielding welding of flux cored wire
No external gas or flux protection is required, and only the slag formed by the reaction of the wire flux core at high temperature and the gas shielded welding area are used for welding. Advantages: fast welding speed, strong wind resistance, weld qualification rate of more than 90%, beautiful weld forming, can be used for full-position welding with large welding current, etc.; Disadvantages: the manufacturing process of welding wire is complicated, the wire feeding is more difficult than the solid core welding wire during welding, the surface of the welding wire is easy to rust, and the powder is easy to absorb moisture.
4
Submerged arc welding
Submerged arc welding is a type of arc welding that burns under a layer of flux. The welding process is carried out automatically or semi-automatically, and the flux is equivalent to the coating of the electrode, which plays a more complete role in the flux process than the coating of the powder. Features: the chemical composition of the weld is relatively stable, the welded joint has good comprehensive utilization performance, it is suitable for the welding of components with large thickness, the weld forming is smooth and beautiful, and it can reduce the consumption of electric energy and metal. It is the main welding method in the production of important steel structures such as pressure vessels, pipeline manufacturing, box-type beams and columns.
Submerged arc welding
5
Electroslag welding
Electroslag welding is a method of welding by using an electric current through liquid slag and generating resistance heat as a heat source. Its types are: wire electroslag welding, plate electroslag welding, nozzle electroslag welding, electroslag welding, electroelectroslag welding, tube sheet electroslag welding, etc. Its features: suitable for large thickness welding, suitable for welding where the weld is in a vertical position.
Electroslag welding
6
Gas-electric vertical welding
Gas-electric vertical welding is a kind of MIG-shielded arc welding formed by the development of ordinary MIG/MAG welding and electroslag welding. Advantages: high productivity, low cost.
7
Resistance welding
Resistance welding is a method of combining workpieces and applying pressure through electrodes, and using the resistance thermal effect generated by current passing through the contact surface of the joint and adjacent areas to heat it to a molten or plastic state, so that it forms a metal bond. There are four main resistance welding methods, namely electric welding, seam welding, convex welding, and butt welding. Advantages: low welding cost, simple operation, high yield, no noise and harmful gases; Disadvantages: The current lack of reliable non-destructive testing methods, etc.
Seam welding
Butt welding
8
Bolt welding
Bolt welding, also known as bolt welding, is divided into arc bolt welding and energy storage bolt welding. Most of the applications in construction projects are arc bolt welding. Arc bolt welding is to put the end of the bolt in the ceramic protective cover to contact with the base metal and direct current, so that the arc is excited between the bolt and the base metal, and the heat generated by the arc melts the bolt and the base metal, and the bolt is pressed into the local melting zone of the base metal after maintaining a certain arc burning time. Energy storage bolt welding is the use of alternating current to charge the large container and discharge instantaneously between the bolt and the base metal, so as to achieve the purpose of melting the bolt end and the base metal.
Schematic of the bolt welding process
Schematic illustration of the on-site welding process of bolts