Inclusions in molten steel have received worldwide concern due to their serious influence on both the steel product quality and the steel production process. These inclusions may come from the deoxidation process, reoxidation by air and/or slag due to an entrainment during steel transfer, and so on. They can break up a casting process by clogging a nozzle. A good knowledge on both steel flow and inclusion behavior is really important to understand nozzle clogging, as well as to take some possible measures to alleviate clogging. In this thesis, steel flow and inclusion behavior during a teeming process were investigated by mathematical simulations with verification by pilot-plant experiments. Firstly, steel flow phenomena during a ladle teeming process were studied. Different turbulence models, including the low Reynolds number k-ɛ model and the realizable k-ɛ model both with an enhanced wall treatment (EWT) and a standard wall function (SWF), were used to simulate this process. All of these turbulence model predictions generally agreed well with the experimental results. The velocity distributions in the nozzle were also predicted by these turbulence models. A large difference of the boundary-layer velocity predicted with these two near wall treatment methods was found. At the late stage of the teeming process, the drain sink flow phenomena were studied. The combination of an inclined ladle bottom and a gradually expanding nozzle was found to be an effective way to alleviate a drain sink flow during teeming. Then, inclusion behavior during a teeming stage was studied. A Lagranian method was used to track the inclusions in steel flow and compare the behaviors of different-size inclusions. In addition, a statistical analysis was conducted by the use of a stochastic turbulence model to investigate the behaviors of different-size inclusions in different nozzle regions. Inclusions with a diameter smaller than 20μm were found to have a similar trajectory and velocity distribution in the nozzle. However, inertia force and buoyancy force were found to play an important role for the behavior of large-size inclusions or clusters. The statistical analysis results indicate that the regions close to the connection between different angled nozzle parts seem to be very sensitive for an inclusion deposition. / <p>QC 20130305</p>
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-118848 |
| Date | January 2013 |
| Creators | Ni, Peiyuan |
| Publisher | KTH, Tillämpad processmetallurgi, Stockholm |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, info:eu-repo/semantics/masterThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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