can be further classified as active or neutral: ACTIVE
FLUXES are those fluxes that will cause
a substantial change in the weld metal chemistry when
welding voltage (and consequently, the
amount of flux fused) is changed. Active fluxes generally add large
amounts of manganese and silicon to
the weld metal and cause the weld strength to increase. If an active
flux is used for multipass welding,
excessive manganese and silicon build-up can occur, causing the weld to
be brittle and crack prone. Active fluxes
should be limited in the number of passes, especially over rust and
mill scale. n
When an active flux is used for multipass
welding, the voltage must be carefully controlled to avoid
excessive build-up of manganese and
silicon. Active fluxes should not be used to multipass weld plates
more than 1" (25 mm) thick.
NEUTRAL FLUXES are
fluxes that will not cause a significant change in the weld metal chemistry even
with variations of welding voltages.
Neutral fluxes will not significantly affect the strength of the weld metal
regardless of the welding voltage used
or the number of passes. As a rule neutral fluxes should be specified
for multipass welding.