Basic knowledge of flux cored wire arc welding

What is flux-cored arc welding?

Flux-cored wire arc welding is a welding method that uses the arc between flux-cored wire and workpiece to heat, and its English name is simply FCAW. Under the action of arc heat, welding wire metal and workpiece are connected by melting, forming a weld pool, arc forward after the crystallization of the weld pool tail.

What is flux-cored wire? What are the characteristics of the cartridge?

Flux-cored welding wire is a kind of welding wire made by rolling thin steel strip into steel pipe or special-shaped steel pipe, filling the pipe with certain components of powder, and drawing. The composition of the powder core is similar to that of the electrode coating, which is mainly composed of arc stabilizing agent, slag forming agent, gas forming agent, alloying agent, deoxidizing agent, etc.

What is the role of the flux in the flux-cored wire?

The role of the flux is similar to that of the electrode coating, and there are mainly the following kinds.

① Protective effect of some components in the welding flux decomposition, some melting! The decomposition of welding flux releases gas, which provides some or most protection. The molten flux forms a molten slag, which covers the surface of the droplet and the molten pool, and the liquid metal protects it.

② Arc stabilizer in arc stabilizer cartridge can stabilize arc and reduce spatter rate.

③ Alloying action Some of the alloy elements in the core can alloyed the weld.

④ Deoxidation alloy elements of slag can react with liquid metals. Improve the composition of weld metal, improve its mechanical properties.

In addition, the covered slag can also reduce the cooling rate of the molten pool, prolong the existence time of the molten pool, which is beneficial to reduce the content of harmful gas in the weld and prevent porosity.

What kinds of flux cored arc welding are there?

There are two types of flux cored wire arc welding (FCAW-G) and self-protection welding (FCAW-S), depending on whether external shielding gas is used or not.

The gas shielded welding of flux-cored wire usually uses carbon dioxide or carbon dioxide plus argon as the shielding gas, and the flux in the wire contains little gassing agent. This method is similar to the general gas shielded welding. Self-protective welding does not need external protective gas. There are a large number of gasifier in the flux, and the gas and slag decomposed by the gasifier are used for protection.

What are the advantages of flux-cored arc welding?

Flux-cored arc welding has the following advantages.

(1) High welding productivity high melting efficiency (up to 85%~90%), fast melting speed; For flat welding, the coating speed is 1.5 times that of manual arc welding, and for other welding positions, it is 3-5 times that of manual arc welding.

② Small splash, weld forming good drug core added arc stabilizer, so arc stability, small splash, good weld forming. Because the molten pool is covered with molten slag, the weld surface shape is significantly better than that of carbon dioxide welding.

(3) High welding quality Because of the slag gas combined protection, it can more effectively prevent harmful gas from entering the welding zone. In addition, the existence time of molten pool is long, which is conducive to gas precipitation, so the weld has low hydrogen content and good porosity resistance.

(4) Strong adaptability only need to adjust the composition of the solder wire cored, it can meet the requirements of different steels on the weld composition.

What are the disadvantages of flux-cored arc welding?

The shortcomings of flux-cored arc welding are as follows.

Compared with gas shielded welding, the cost of welding wire is higher and the manufacturing process is complex.

② Wire feeding is difficult, it is necessary to use a wire feeding machine whose clamping pressure can be adjusted accurately.

③ The cartridge is easy to absorb moisture, so it is necessary to keep the welding wire strictly.

④ Slag removal is needed after welding.

⑤ More smoke and harmful gases are generated in the welding process, so ventilation should be strengthened.

What protective gas is usually used in flux-cored arc welding? What are the characteristics of each?

Flux cored wire arc welding usually uses pure carbon dioxide gas or carbon dioxide and argon gas as a shielding gas. The gas type needs to be selected according to the flux-cored wire used.

Argon is easily ionized, so it is easy to achieve ejection transition in argon arc. When the argon content of gas mixture is not less than 75%, the flux cored wire arc welding can achieve stable jet transition. With the decrease of argon content, the penetration depth increases, but the arc stability decreases and the spatter rate increases. Therefore, the optimal gas mixture is 75%Ar+25%CO2. In addition, Ar+2%O2 can also be used for gas mixture.

When pure CO2 gas is selected, it will decompose under the action of arc heat and produce a large number of oxygen atoms, which will oxidize manganese, silicon and other elements in the molten pool, leading to the burning of alloying elements. Therefore, welding wire with high manganese and silicon content should be used.