Speaker
Description
Process stability during continuous casting is an essential criterion to produce high-quality slabs. The meniscus is the most sensitive zone of the whole strand, as the initial strand shell is generated there. Unsteady bulging of the strand shell between two rollers is inducing feedback on the mold level position due to the liquid core of the strand. During unsteady bulging, heavy mold level fluctuations can build up and lead to surface defects and casting instabilities. Peritectic steels, which develop a rippled shell in the mold, are known for that effect. In addition, soft steels with creeping material behavior such as ultra-low carbon steels, silicon steels, and ferritic stainless steels show unsteady bulging.
The roller geometry of the casting machine has a high impact on the unsteady bulging affinity, as consecutive identical pitches lead to the superposition of the pumping effect. A new software tool has been developed in order to simulate the unsteady bulging effect and the generated level fluctuations. Therefore, a coupled simulation model combines solidification, shell transport, mechanical bulging, strand pumping, and mold level control. This tool offers new options to design the strand guide with an optimum distribution of the roller pitches in order to reduce unsteady bulging affinity. Each new caster built by Primetals Technologies has an optimized strand containment configuration in order to minimize mold level instabilities related to unsteady bulging.