The submerged arc welding process uses filler
metal in the form of wire or strip, and a non-metallic flux.
The Flux has a decisive effect on the result of welding operations.
It's influence on the melting characteristics and various other
physical properties such as viscosity, surface tension, density,
thermal expansion, and conductivity in turn has a considerable bearing
on the appearance of the bead surface and
the slag removability.
Another major consideration here is the influence which the flux
through the metallurgical reaction on the chemical composition,
and thus also on the mechanical properties of the deposit.
Depending on the manufacturing process used, a distinction can be
drawn between flux types as follows:
Agglomerated fluxes (identifying code B=bonded)
Produced by agglomeration followed by drying in the rotary kiln.
Highly reactive, low piled density, easy slag removal, admits alloying
additions, but sensitive to moisture and abrasion.
According to their basicity, welding fluxes may be subdivided into
neutral, and basic fluxes.
When B is less than 1, the flux is termed "acid" which
means it contains more acid than basic constituents. When B is between
1 and 1.2, the flux is neutral; in excess of this ratio the flux
is basic. It is termed highly basic when B is above 2.
According to their main constituents,
fluxes are termed manganese silicate (MS) types, containing mainly
MnO and SiO ; calcium silicate (CS) types containing mainly CaO,
MgO and SiO; aluminate rutile (AR) types, containing mainly Al2,O3
and TiO2, aluminate basic types (AB), containing mainly Al2,O3+CaO+MgO,
and fluoride basic (FB) types, containing mainly CaO, MgO and CaF2.
Each flux type has different specific properties; a flux of the
manganese silicate (FMS) type e.g. is insensitive and universally
applicable agglomerated flux of the fluoride basic type (BFB) produces
cracking resistant welds with high impact strength.