In comparison, bonded fluxes are made by finely grinding the individual components of the flux,
mixing them in appropriate proportions and then adding a binder, typically potassium and/or sodium
silicate. The wet mixture is then baked at a relatively low temperature and ground to size for
packaging. The main advantage of bonded fluxes is that it is easier to add deoxidizers and ferroalloys.
On the negative side, such fluxes are prone to moisture pick up, and to local changes in composition
due to segregation or removal of fine mesh particles.
Fluxes that significantly influence the composition of the weld metal through slag/metal reactions are
termed active fluxes. Typically, these fluxes add manganese, silicon and chromium to the weld metal.
The extent of this addition increases with arc voltage, since higher arc voltage leads to increased flux
consumption (Figure 4.37). Very active fluxes may be used to deposit single or two pass welds only,
since the increase in the Si and Mn content of subsequent passes may be sufficiently large to impair
the weld metal ductility and also make it more prone to hydrogen cracking. Certain active fluxes,
termed alloy fluxes, add elements such as Ni and chromium. Such fluxes enable the welding of
weathering steels (containing chromium, nickel or copper) using carbon steel wires, and compensate
for the loss of chromium from the wire by oxidation when welding stainless steels.