What Is Welding Flux and 5 Types of It Explained

What is welding flux?

Welding flux is granular welding material.

When welding, it can melt to form slag and gas — a substance that protects the molten metal and plays a role in metallurgical treatment.

What Is Welding Flux and 5 Types of It Explained 1

Flux composition

The welding flux is composed of marble, quartz, fluorite and other minerals, titanium dioxide, cellulose and other chemicals.

Welding flux is mainly used for submerged arc welding and electroslag welding.

Related reading: Types of welding

When it is used to weld various steels and non-ferrous metals, it must be used reasonably with the corresponding welding wire to obtain satisfactory welds.

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Types of welding flux

There are many classification methods for welding flux, including usage, manufacturing method, chemical composition, welding metallurgical properties, etc., as well as the pH and particle size of the flux.

No matter which classification method is used, it only reflects the characteristics of the welding flux from one aspect and cannot include all the characteristics of the welding flux.

Common classification methods include:

1. Neutral welding flux

Neutral welding flux refers to the flux that has no obvious change in the chemical composition of the deposited metal and the chemical composition of the welding wire after welding.

Neutral welding flux is used for multi pass welding, especially for the base metal with a welding thickness greater than 25 mm.

Neutral welding flux has the following characteristics:

a. The flux basically contains no oxides such as SiO2, MnO and FeO.

b. The flux has no oxidation effect on the weld metal.

c. Porosity and weld bead crack will be produced when welding seriously oxidized base metal.

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2. Active welding flux

Active welding flux refers to the flux added with a small amount of Mn, Si deoxidizer.

It can improve the anti porosity and anti crack ability.

Active welding flux has the following characteristics:

a. Due to the presence of deoxidizer, Mn and Si in the deposited metal will change with the change of arc voltage.

The increase of Mn and Si will increase the strength of the deposited metal and reduce the impact toughness.

Therefore, the arc voltage should be strictly controlled during multi pass welding.

b. Active welding flux has strong anti porosity ability.

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3. Alloy welding flux

Alloy welding flux is added with more alloy components for transition alloy elements. Most alloy  welding fluxes are sintered fluxes.

Alloy welding flux is mainly used for welding of low alloy steel and wear-resistant surfacing.

4. Melting welding flux

Melting welding flux is to mix raw materials of various minerals in a given proportion, heat them to above 1300 ℃, melt and stir them evenly, and then take them out of the furnace, and then quench them in water to make them granulated.

Then it is dried, crushed, sieved and packaged for use.

The brand of domestic melting welding flux is represented by “HJ”.

The first digit after it represents the content of MnO, the second digit represents the content of SiO2 and CaF2, and the third digit represents different brands of the same type of welding flux.

5. Sintered welding flux

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After batching according to the given proportion, dry mixing is carried out, and then the binder (water glass) is added for wet mixing, and then granulation is carried out.

Then it is sent to the drying furnace for curing and drying, and finally sintered at about 500 degrees.

The brand of domestic sintered welding flux is represented by “SJ”, the first digit after it represents the slag system, and the second and third digits represent different brands of the same slag system flux.

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