The main functions of the flux include removing the oxide from the welding surface, reducing the melting point and surface tension of the solder, protecting the weld metal from the harmful gases in the surrounding atmosphere when it is liquid, and making the liquid solder have a suitable flow speed to fill the brazing joint.
Flux plays a vital role in the welding process. First of all, the flux can remove the oxide from the welding surface and prevent the reoxidation of the solder and the welding surface during welding, thus reducing the surface tension of the solder and ensuring the smooth progress of the welding process. Secondly, the melting point of the flux is usually lower than that of the solder, which means that before the solder melts, the flux has melted and is able to fully play its role as a solder aid. In addition, the flux has a high infiltration diffusion speed, which usually requires an expansion of around 90% or more to ensure even distribution of solder. The viscosity and specific gravity of the flux should also be smaller than that of the solder, in order to avoid the difficulty of infiltration diffusion and the coverage problem caused by the large viscosity. In the welding process, the flux can also prevent the welding bead splash, do not produce toxic gas and strong irritating odor, and the residue after welding is easy to remove, with no corrosion, no moisture absorption and no electrical conductivity and other characteristics. Finally, the flux is stored stably at room temperature, which ensures its applicability and reliability in different environments.
The role of flux also includes the protection of welding area, to prevent the invasion of oxygen and hydrogen in the air; Ensure weld chemical composition; Ensure stable welding process and good weld formation; Slow down the cooling rate of molten metal, reduce the defects such as slag inclusion in pores; Prevent metal splash, improve the efficiency of deposition. In addition, the flux can also play an arc stabilization, protection and chemical metallurgy role in the welding process, by improving the arc conductivity, protecting the arc and molten pool from oxidation, nitriding and evaporation of alloying elements, and removing harmful impurities (deoxygenation) and alloying, to meet the requirements of chemical composition and performance.
The use of flux mainly includes the following steps:
Ensure that the welding surface is clean : Before starting welding, it is necessary to ensure that the metal surface to be welded is clean and free of oil, dust, and oxides. This is because a clean metal surface facilitates flux adsorption and fusion .
Select the right flux : Select the right type of flux according to the characteristics of the welding material and welding requirements. Different metal materials and welding requirements may require different kinds of flux .
Apply flux : Use a brush, spraier, or other application tool to apply flux evenly to the metal surface to be welded. Make sure that the flux coverage is sufficient, leaving no gaps .
Heat the weld area : Heat the weld area to a high enough temperature to melt the flux and fuse with the metal surface. This usually requires the use of heating equipment such as flame guns, arc welding, etc. .
Add solder : When the solder area reaches the temperature where the flux melts, add solder to the heated joint, ensuring that it flows and covers the surface to be joined.
Remove excess flux : After welding is complete, remove excess flux to ensure the cleanliness of the weld area .
The use of heat release flux is slightly different, it uses the heat of chemical reaction of metal compounds as a heat source, through the overheating of molten metal direct or indirect heating work, in the special graphite mold cavity to form a certain shape, size of the fusion welding joint. With exothermy fluxes, no additional heat source is needed for heating, but the heat generated by chemical reactions completes the welding process 34.
In general, the method of flux application varies according to the specific welding requirements and the type of flux selected, but the core steps include surface preparation, flux selection and application, heating, and addition of solder and removal of excess flux. Exothermy fluxes rely on the heat generated by chemical reactions to complete the welding process, requiring no additional heat source