Flux Selection

While selec a flux for any particular application the following points need to be considered

The most important technical property of fluxes is there ac ve range. This property is indicated by two temperatures : the lower one is the temperature at which flux starts to be ac ve, the upper one is the is the temperature at which the flux is exhausted and will not perform it's deoxidant and protective function.

It is good rule to choose flux in a such a way so that the lower temperature is at least 50°c lower than the solidus temperature (melt) of the brazing alloy to be used, and the upper temperature is at least 50°c higher than the liquidus temperature (flow) of the alloy. Many different type of fluxes are available, each with the different chemical composi on, ac vity temperature range and proper es, that may be used with different alloys, different range products and for different applica ons. for example when reference is made to EN 1045 FH10 or AWS TYPE FB3-A, many fluxes are given the same classifica on, yet they have different properties and characteristics.

The fact that fluxes are proprietary formula on o en causes problems if one wants to change from one Manufacturers' product to another's. Operators will say that the flux does not work as well. This could be the case, but in many cases what the operator is saying is that it works differently, or perhaps more likely that it reacts differently when heated. This is too expected, as each formula on will result in a flux with different characteris cs. What must be assessed is whether the difference is good, bad, or indifferent and whether the joints produced are of acceptable quality.

Rather than just selec ng one flux from JO FLUX® range, it could be well be worth tes ng two or three that appears to be suitable, to see which provides the best 'on-the-job 'performance.