When metals are heated in contact with atmosphere air, the oxygen of air which made
oxide formation, which causes poor quality welding, low weld strength. In many cases
make welding impossible. Due to this reason it is required to add a weldingflux
to the weld area. This being a substance capable of dissolving the oxide formation.
The welding flux is lighter than the molten metal and thus the molten metal and flux
together dissolved the oxide. These are floats on top as a slag, which may removed
by chipping or filing or grinding after cooling it. During ordinary grade of mild
steel welding it (welding flux) is not
required and joint can be made successfully which is exceptional case in welding
Nothing advantage is obtained when using more than the minimum amount of welding
flux for good welding joint. An excessive amount of flux is wasteful and makes it
more difficult to make a clean weld.
Welding flux composition
For the ferrous metal welding the flux should be borax, sodium silicate, sodium carbonate,
sodium bicarbonate, it gives best result. The borax forms compounds with the iron
oxide, when the carbonate is the cleanser and it promotes fluidity of the molten
For removing the cuprous oxide during copper and its alloy welding which is very
effective for the mixture of sodium and potassium borates, carbonates, chlorides,
sulphates and boric acid.
For the welding of aluminum and its alloy, its flux should be chosen very carefully
which must be capable of dealing with the oxide of aluminum known as alumina. During
aluminum welding the alumina forms very easily and has an extremely high melting
temperature which is near about 20000C. Generally aluminum welding fluxes used mixture
of alkaline fluorides, chlorides and bisulphates. These mixture of fluxes melt at
a temperature just bellow the melting point of aluminum and dissolved away the whole
For the magnesium alloy welding the same type of fluxes used for the aluminum.
Welding flux cleaning
In the practical field all the fluxes are chemically very effective therefore they
are strongly corrosive. If it does not cleaning proper way it may be damage the valuable
job or reduce the job life. It may be necessary to remove the fluxes from the weld
repeatedly with a hot water or steam. Another way to removing the fluxes with pickling
bath and do not keep any negligence with this cleaning. Any traces of fluxes left
in or near the weld are possible sources of corrosion, which may caused failure the
weld. Thus proper cleaning the flux which increased the job life.