In the continuous casting of steels, clogging of the submerged entry nozzle has long been a persistent and costly issue. Previous modelling attempts have assumed that inclusions of different types exhibit the same degree of adhesion when colliding with the nozzle wall - an assumption not borne out by evidence in the literature.
In this thesis, a dynamic clogging model is proposed which accounts for the effects of different degrees of inclusion-wall and inclusion-clog adhesion on clog formation and growth. The overall clogging model consists of several sub-models in order to account for the different physics. The melt flow and inclusion motion are modelled using an Eulerian-Lagrangian approach. The inclusion adhesion behavior is determined by the use of a stochastic model activated when an inclusion collides with a surface. A user defined sticking probability is used to determine if an inclusion sticks to a surface (Swall for wall collision or Sclog for clog collision) or instead bounces off. A macroscopic model is used to determine clog growth, where the volume of clog in a cell is tracked and used to determine when the clog grows into adjacent cells. Finally, a modified Kozeny-Carmen equation is used as a porosity model so that the presence of the clog affects and diverts the melt flow. The modified melt flow then alters subsequent inclusion deposition and clog growth.
The model is used to investigate the effects of different degrees of inclusion adhesion on inclusion deposition and clog growth. Three scenarios are examined - 1) Inclusion deposition in a pilot scale nozzle, 2) Inclusion deposition in an industrial scale slide-gate controlled nozzle and 3) Clog formation and growth in a pilot scale nozzle.
The deposition studies indicate that in a pilot scale nozzle, only a minority of inclusions ever collide with the nozzle (≈ 10%). In contrast, in the industrial scale nozzle there are far more inclusion collisions with the nozzle wall, ranging from 80% when the slide-gate is 20% open to 30% when the slide-gate is 100% open. Despite the differences in nozzle geometry and flow conditions, a similar effect on inclusion deposition is seen when Swall is varied. The effects of Swall can be divided into two regimes. When 0 ≥ Swall < 0.05 there is a sharp increase in the deposition ratio as Swall increases. When Swall > 0.05 there is a small and linear increase in the deposition ratio as Swall increases.
This pattern is also seen in the study of clog formation and growth in a pilot scale nozzle. The effects of Swall or Sclog on clog volume can be divided into two regimes. As Swall or Sclog increases, there is a large increase in clog volume, until the sticking probability increases above 1E-2, then any further increase results in only a small increase in clog volume. In comparison to literature data the model successfully simulates the location of clog formation, the initial jump in clogging factor and the clogging factor growth rate in the later stages of clogging. However, the model underestimates the overall increase in clogging factor, resulting in a clogging factor at the end of the simulation which is half of that seen in the experiment. / Thesis / Doctor of Philosophy (PhD) / One of the ongoing challenges in the continuous casting industry is the occurrence of nozzle clogging. Over time, a buildup of material occurs within the submerged entry nozzle, called a clog. The clog leads to the partial or complete blockage of the nozzle, resulting in increased production costs. Since studying this phenomena experimentally is difficult due to the high temperature and opacity of the molten steel, modelling provides a useful alternative approach. However, previous modelling efforts regarding nozzle clogging have treated all inclusions as exhibiting the same adhesion behavior.
This thesis aims to address this issue by presenting a dynamic nozzle clogging model which accounts for the effects of different degrees of inclusion adhesion. The model is used to study both inclusion deposition and clog formation. Results indicate that even a small amount of sticking probability results in a significant degree of inclusion deposition and clogging. The effect of sticking probability on clogging can be divided into two regimes, one where the clogging is very sensitive to the sticking probability and one where it is insensitive. Finally, the model was shown to run adequately even on coarser meshes (meshes with a smaller number of larger cells), indicating its utility in industrial applications, where it can be used to predict the location of clog formation and the clog growth rate.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29757 |
| Date | January 2024 |
| Creators | Mohamed Shibly, Kaamil Ur Rahman |
| Contributors | Phillion, Andre, Tullis, Stephen, Materials Science and Engineering |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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