Product Description
During welding, a substance that can melt to form slag and gas, and protect and
metallurgically treat the molten metal. Submerged arc welding flux is used. For needle
welding, there are: brazing flux and soft soldering flux. Flux is also called flux, and the
definition should be very broad, including molten salt, organic matter, active gas, metal
vapor, etc., that is, except for the base material and the solder, it generally refers to all
substances used to reduce the interfacial tension between the base material and the solder.
The wettability of the solder and the base material is certainly closely related to the nature
of the solder, but it is much less important than the role of the flux.
Functions of flux The functions of flux can be divided into three parts:
1. Remove oxides on the welding surface, reduce the melting point and surface tension
of the solder, and reach the brazing temperature as soon as possible.
2. Protect the weld metal from harmful gases in the surrounding atmosphere when it is
in liquid state. 3. Make the liquid solder have a suitable flow speed to fill the brazing seam.
The melting point of the flux should be 10-30ºC lower than the melting point of the
solder. In special cases, the melting point of the flux can also be higher than that of the
solder. If the melting point of the flux is too low, it will melt too early, and the flux
components will evaporate, react with the base material, etc., and the flux will lose its
activity when the solder melts. The choice of flux usually depends on the nature of the oxide
film. For alkaline oxide films such as Fe, Ni, Cu, etc., acidic brazing flux containing boric
anhydride (B2O3) is often used. For acidic oxide films such as cast iron oxide films with high
SiO2, alkaline brazing flux containing Na2CO3 is often used to generate fusible Na2SIO3 and
enter the slag. Some fluoride gases are also often used as fluxes. They react evenly and
leave no residue after welding. BF3 is often mixed with N2 to braze stainless steel at high
temperatures. The flux used for brazing below 450ºC is called soft flux. There are two types
of soft solder. One is water-soluble, usually composed of hydrochloride and phosphate single
or sogar salt aqueous solution, which is highly active and corrosive and needs to be cleaned
after welding. The other is water-insoluble organic flux, usually based on rosin or artificial
resin, with organic acid, organic amine or its HCl or HBr salt added to improve the film
removal ability and activity.
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