3Fluxes can be further classified as active or neutral:ACTIVE FLUXES are those fluxes that will cause a substantial change in the weld metal chemistry whenwelding voltage (and consequently, the amount of flux fused) is changed. Active fluxes generally add largeamounts of manganese and silicon to the weld metal and cause the weld strength to increase. If an activeflux is used for multipass welding, excessive manganese and silicon build-up can occur, causing the weld tobe brittle and crack prone. Active fluxes should be limited in the number of passes, especially over rust andmill scale.nWhen an active flux is used for multipass welding, the voltage must be carefully controlled to avoidexcessive build-up of manganese and silicon. Active fluxes should not be used to multipass weld platesmore than 1" (25 mm) thick.NEUTRAL FLUXES are fluxes that will not cause a significant change in the weld metal chemistry evenwith variations of welding voltages. Neutral fluxes will not significantly affect the strength of the weld metalregardless of the welding voltage used or the number of passes. As a rule neutral fluxes should be specifiedfor multipass welding.
![]()
