Hearth--The hearth floor, ramps and charging sills must be resistant to molten metal penetration, chemical flux
attack and take the physical abuse during charging and cleaning.
Major sources include absorption from the atmosphere, products of fossil fuel decomposition (hydrocarbons), adherent condensation on dirty tools, chemical flux
materials and alloy additives.
On aluminum bronzes, phosphorus bronzes and some red brasses, crushed glass or proprietary chemical flux
covers were used.
Although chemical flux
may cause considerable damage to exposed refractory, it can be helpful in some instances, but patience is required because flux response is not always immediate and over application is almost always self-defeating.
Differences in chemical fluxes
found in cores from Sites 417 and 418, drilled only 500 meters apart, show that the composition of the uppermost crust may be quite heterogeneous.