Fluid Flow Phenomena, Inclusion Characteristics and some Heat Transfer Phenomena during Filling of an Ingot Mmold

Sammanfattning: Clean steel production requires a good understanding of theinclusion characteristics at all stages of the steelmakingprocess. So far there exist little information about theformation and evolution of inclusions during the filling ofingot molds. Therefore, this work has been undertaken with aview to increase the knowledge about the formation ofinclusions due to interactions between the steel and the moldpowder during ingot filling. A detailed study of the inclusioncharacteristics was done (i.e. total number, size distributionand chemical composition) before and during filling of theingot mold. It was found that some of the inclusions had aquite substantial size and a composition that resembled themold powder that is covering the surface of the steel as themold is filled. The existence of large and harmful macroinclusions both during the ladle treatment operation and thesubsequent mold filling was studied in another series of planttrials. Also in this investigation, inclusions that have acomposition resembling of mold powder were found in steelsamples taken during filling of the mold.Thermal diffusivity measurements of slags aiming at anincreased understanding of the phenomenas involved in the heattransfer in slags have been pursued in this work. Thermaldiffusivity data was determined in the CaO-Al2O3-SiO2slag system. This particular system was chosensince it is the building block in many metallurgical slag,including mold fluxes. The study did also include aninvestigation of the melting behavior of the mold flux used inup-hill teeming of ingots. It was concluded that very littlemold flux melts during the filling of the mold.It was foreseen early in the project that the fluid flow inthe ingot mold during filling will be one of the factors thatwill influence the formation of inclusion during mold filling.Therefore, the fluid flow was studied using both physical andmathematical modeling. The physical modeling work has beenfocused on LDA measurements of the fluid velocities in atransparent scaled down water model of an ingot mold. The thefluid velocities in the same scaled model have also beencalculated using CFD modeling. The results from the water modelstudy and the numerical experiments have been compared in orderto find a the most suitable turbulence description. Thecomparison showed that the LES turbulence description bestvalidates the experimental results. Thereafter, the design ofthe inlet nozzle of the mold was studied since it is known tobe a factor influencing the fluid flow in ingot molds duringfilling. More specifically, a study where undertaken in orderto investigate the effect of the opening angle of the inletnozzle on the fluid flow. It was found from the numericalsimulations that an angeled inlet produced less surfacedeformation and lower velocities in the horizontal direction atthe surface compared to a straight inlet nozzle during fillingof the ingot mold.Keywords:up-hill teeming, mold powder, inclusions,plant trials, thermal diffusivity, fluid flow, physicalmodeling, CFD, turbulence