To reduce this source of buildup, the use of calcium-bearing compounds such as fluorspar, calcium carbide or limestone will also contribute to the buildup as these cause an erosion of either the refractory in the molten metal transfer equipment or the channel furnace uppercase refractory.
The presence of sulfides, whether inherent to the molten metal or as a by-product of any treatment step, will influence the buildup. Typically, oxy-sulfides have been known to float within the molten metal.
The first step in solving a clogging problem is to identify and minimize the use of buildup constituents, all sources including steel scrap which must be used in the production of ductile base iron, deserve careful scrutiny.
One approach to minimizing throat clogging may be periodic superheating of inductor channels to help control certain buildup applications.
Carbon additions in the form of silicon carbide, or carbon pick-up from introducing a "green" wood pole into the throat, may reduce the amount of silica in the buildup and create a carbon boil.
Alternative measures to consider for reducing inductor buildup may include the following: * Consider switching refractories from a magnesia base to an alumina/mullite forming mix.
This will not prevent buildup from occuring, but will allow for extended inductor operating times.
PHOTO : Cathodoluminescence (CL) micrograph of a buildup showing a large crystal of corundum (dk red to black), bladed crystals of hibonite or [Ca.sub.6] (dk green) crystallized on corundum.
PHOTO : CL micrograph of spinel + melilite-rich buildup showing zoned isometric common spinel crystals (green) in a melilite (blue) matrix.
PHOTO : CL micrograph of a buildup sample showing anorthite (yellow), corundum (red) and hercynite (black) crystals.
PHOTO : CL micrograph of MgO-Si[O.sub.2] rich buildup showing fosterite (red to orange) and spinel (green) crystals.
PHOTO : MgO rich buildup showing internally zoned periclase crystals with a minor amount of oldhamite (yellow).(25x)