Early Stages of the Aluminothermic Process: Insights into Separation and Mould Filling

The aluminothermic (AT) process utilises a self-propagating high-temperature synthesis (SHS) type reaction for producing primarily thermite steel and alumina slag at high temperatures during the welding of rails. In this work, an investigation on the early stages of the aluminothermic process, the separation of AT reaction products and mould filling has been carried out, using both experimental and computational methods to predict the time duration of a complete separation and to obtain a better understanding of the internal multiphase flow within the crucible and mould. The decomposition of AT reaction products after the combustion and the subsequent mould filling by thermite steel and alumina slag have been simulated numerically, using a diffusive phase field and volume-of-fluid model. However, to minimize numerical errors on the input parameters of the high- temperature multiphase flow, a careful review on transport properties has been made. Missing data, e.g. the contact angle of thermite steel on waterglass-bonded mould and crucible wall material has been investigated experimentally. Being further necessary for the prediction of the separation time of AT reaction products in compacted thermite, results on the propagation front velocity show a decreasing trend with increasing initial compact temperature. Further, the combustion front velocity is used for a subsequent analysis of the separation time, which is obtained from the phase distribution of thermite steel, alumina slag and intermetallic compounds, using a combustion front quenching (CFQ) methodology. Moreover, geometric modifications on the crucible and mould have been developed for a reduction in changeover time, as well as an optimized multiphase flow field. Their performance during crucible discharge and mould filling has been verified numerically. Furthermore, alumina slag inclusions have been tracked within the mould using a volume-of-fluid approach with their final positions being verified through an authentic welding.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

TU Bergakademie Freiberg

Year

2019

Author dc:creator

• Weiß, Sebastian

Contributors dc:contributor

• Hantusch, Jan
• Groß, Ulrich
• Schwarze, Rüdiger

• thermite
• phase-field
• volume-of-fluid
• multiphase flow
• combustion front quenching
• Thermit
• Phasenfeld
• Mehrphasenströmung
• VOF
• CFQ