Welding is the process of joining two separate objects together using energy. The welding method can not only join metal materials such as steel, aluminum, copper, titanium, etc.;
It can also bond non-metals such as plastics and ceramics;
It can even resolve the connection between metal and non-metal, which we collectively call engineering welding.
A structure fabricated by welding is called a welded structure, also known as an engineering weldment.
According to the object and application, it can be roughly divided into four types: building welded structure, tank and container welded structure, pipeline welded structure, and conductive welding structure. The building steel structure we call includes these four types of structural welding.
Steel is chosen as the structural material, and most of them are ordinary carbon steel and low alloy structural steel. Main welding methods: manual arc welding, shielded gas welding, self-shielded arc welding, submerged arc welding, stud welding. , spot welding, welding, etc.
(1) Manual arc welding
The welding method based on the heat of the arc is called arc welding. Manual arc welding is a type of arc welding that uses manually operated electrodes for welding. This is the most commonly used method in the welding of structural steel structures.
The principle of manual arc welding, as shown in fig. 7-1, the electrode and the work piece are two electrodes that generate an arc, and the arc generates a lot of heat to melt the electrode and the weld joint.
The end of the electrode melts to form a drop that passes into the base metal of the molten weld and melts to form a molten pool and undergoes a series of complex physical and metallurgical reactions. As the arc moves, the liquid melt gradually cools and crystallizes, forming a weld.
Under the action of high temperature, the cold-applied coating on the steel core of the welding wire melts into slag and coats the metal surface of the molten bath, not only protecting the metal of the high-temperature bath from chemical reactions with harmful oxygen and nitrogen in the air. It can also participate in the chemical reaction of the molten bath and penetrate into the alloy, etc., and form a mold slag shell on the surface of the cooled and solidified metal.
(2) Gas shielded arc welding
Also known as gas consumable arc welding, the welding wire and weldment are used as two poles, and the heat of the arc is generated between the two poles to melt the welding wire and base metal of the weld, and at the weld point. At the same time, the shielding gas is directed into the welding area to creategive an arc and melt. The welding wire, the molten pool and the surrounding base metal are separated from the surrounding air, the welding wire is automatically fed, continuously melted by the action of the arc, and fused with the molten base metal to form the weld metal.
Welding) can be divided into CO2 shielded arc welding due to the difference in shielding gas. This is the most widely used welding method at present. It is characterized by the use of large current and thin welding wire.high.
(3) Self-protective arc welding
Self-shielded arc welding was once called gasless gas-shielded arc welding. Compared to gas-shielded arc welding, it has better wind resistance: at wind speeds of up to 10 m/s, welds without porosity and with excellent mechanical properties can be obtained. Thanks to automatic welding, the welding efficiency is extremely high. The welding torch is lightweight and does not require a gas cylinder, so the operation is very convenient, but the cost of the welding wire is higher than CO2 welding.
(4) Submerged arc welding
Submerged arc welding is a type of arc welding in which the arc burns under a layer of molten granular flux. Bare welding wire continuously fed into the molten pool is not only a metal electrode, but also a filling material. The arc burns under a layer of flux, melting the welding wire and base metal to form a molten pool.
The molten flux turns into a slag that coats the surface of the bath of molten metal and separates the high temperature bath metal from the air. The resulting flux slag plays not only a protective role, but also participates in metallurgical reactions with molten metal, thereby affecting the chemical composition of the weld metal.
(5) Narrow gap welding
This method uses the existing special technology of gas shielded welding, and the cross-sectional area of the groove of the welded joint is smaller than that of manual arc welding or gas shielded welding. This is the characteristic of this method. .
Narrow gap welding can be performed in flat welding, horizontal welding and vertical welding positions. Horizontal welding is suitable for column joints in engineering site, flat welding and vertical welding are suitable for box column corner joints in factories and welding. columns and beams.
(6) Stud welding
Stud welding is a method of passing welding current between a stud and a base metal to heat and bond parts that are in contact with each other. It is mainly used for welding connectors and concrete anchors. It is also widely used. .Armature for installation of heat and sound insulation.
(7) Spot welding
First of all, the spot welding mentioned here is different from the spot welding used to assemble building steel structure components by joining. Spot welding is widely used in the automotive industry and household appliances, and spot welding is also used for complex joints in steel structures.