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What are the classification methods for welding fluxes?
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Release Date:
2023-01-03
Welding flux is a granular welding consumable. During electric arc welding, it melts to form slag and gases, providing protection for the weld pool and performing metallurgical functions. In the welding process, it melts to produce slag and gases that protect the molten metal and facilitate metallurgical treatment.
The flux is composed of natural marble, quartz, fluorite, and other iron ores, as well as compounds such as polyethylene wax and fibers. Flux is primarily used in arc welding and electroslag welding. When welding various structural steels and rare metals, it must be properly matched with the corresponding welding electrodes to achieve satisfactory weld quality.
There are numerous ways to classify fluxes, including classification based on primary application, manufacturing method, composition, and metallurgical performance in arc welding, as well as classification according to the flux’s pH level and particle size. Regardless of the classification method used, each approach highlights only a specific aspect of the flux’s characteristics and cannot encompass all of its properties. Common classification methods include:
1. Neutralizing Flux A neutralizing flux is one in which the composition of the deposited metal after welding does not differ significantly from that of the electrode. Such fluxes are used in multi-pass welding and are particularly suitable for welding base metals with thicknesses exceeding 25 mm. Neutralizing fluxes have the following characteristics:
a. The flux contains virtually no metal oxides such as SiO2, MnO, or FeO.
b. The flux has virtually no chemical effect on the weld metal.
c. When welding base metals that have severe surface oxidation, porosity and weld cracks may also occur.
2. Active Flux Active flux refers to a flux that contains small amounts of Mn and Si deoxidizers. It can enhance resistance to porosity and cracking. Active flux has the following characteristics:
a. Due to the presence of deoxidizers, the Mn and Si content in the weld metal will vary with changes in arc voltage. Increased Mn and Si levels enhance the strength of the weld metal but reduce its fracture toughness. Therefore, during multi-pass welding, arc voltage must be strictly controlled.
b. Active flux exhibits strong resistance to porosity.
3. Alloy Fluxes: Alloy fluxes contain a relatively high proportion of alloying elements to facilitate the bonding of alloy constituents; most alloy fluxes are calcined fluxes. They are primarily used in the electric arc welding of low-alloy steels and for wear-resistant surfacing.
4. Smelting Flux: Smelting flux is prepared by uniformly mixing raw mineral materials according to specified proportions, heating the mixture to approximately 1,300°C, melting and thoroughly blending it, then rapidly quenching it in water for granulation. The resulting granules are subsequently dried, crushed, screened, and packaged for final use.
In China, the designation of smelting fluxes begins with “HJ,” where the subsequent digits indicate the MnO content, the second digit specifies the SiO2 and CaF2 contents, and the third digit denotes different grades within the same flux type.
5. The calcined flux is first dry-mixed according to the specified proportions, then wet-mixed with a cementing agent (sodium silicate), followed by granulation. The resulting granules are then fed into a drying unit for solidification and drying, and finally calcined at temperatures above 500°C.
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