The data helped SDI maximize throughput without causing breakouts or surface imperfections. Armco Inc. and other steelmakers have found that casters can be more susceptible to breakouts when moving from a starter flux to a working flux. Both the starter flux and the working flux develop stable thermal profiles in Armco's tests, says Ronald J. O'Malley, the company's principal process engineer for casting. But during a transition period when the caster moves from the starter flux to the working flux, the thermal profile of the steel might not be as stable. The time of instability varies by the grade and type of steel.
Some flux combinations cause virtually no change.
Other combinations might cause the temperature to fluctuate for as much as 30 minutes. To prevent this, some steelmakers use more stable, specially designed intermediate fluxes, says Kishen Koul, president and chief operating officer of Natco Intl. These types of transitional powders might not be as sensitive to temperature fluctuations experienced while changing a submerged-entry nozzle on a caster or ramping up and down operations for other reasons. Steelmakers also have gravitated toward granulated mold fluxes because they have better flowability than traditional mold powders. Natco produces a spray-dried mold powder that controls the particle size so that there's less variation and fewer fines.