fluxing

Fluxing is a process used in metallurgy, welding, brazing, soldering, and related manufacturing steps in which a flux—a chemical cleaning agent—is introduced to a metal surface or melt to promote bonding. Flux serves to remove oxides, prevent re-oxidation during heating, and improve the wetting and flow of molten metal, which helps produce a stronger, more uniform joint.

In foundry and metallurgical operations, fluxing aids in impurity removal by forming a slag that floats on the molten metal. The slag captures oxides and other inclusions, which can then be skimmed away, leaving purer metal. Flux materials vary with the metal and process and may include calcium oxide (lime), silica, borax, fluorspar, chlorides, and other compounds designed to form protective slags or modify melt chemistry.

In soldering and brazing, fluxes such as rosin-based, synthetic, or water-soluble formulations clean metal surfaces by dissolving oxides and forming a protective layer that facilitates capillary flow and joint formation. No-clean fluxes are designed to leave minimal residues, though some applications still require cleaning to prevent long-term corrosion or electrical leakage.

Application and safety considerations vary by flux type. Flux residues may be corrosive or conductive, so residues are often cleaned after soldering or brazing, especially in electronics or critical applications. Flux fumes and skin or eye exposure require appropriate ventilation and protective equipment.

The term fluxing thus covers several context-specific practices aimed at improving surface cleanliness, protecting against oxidation, and enabling effective bonding of metals across metalworking disciplines.