Proceedings of the 7th World Congress on Mechanical, Chemical, and Material Engineering (MCM'21)
Prague, Czech Republic Virtual Conference – August, 2021
Paper No. HTFF 139
DOI: 10.11159/htff21.139

Numerical Modelling and Simulation of the Aluminothermic Welding ofRails: Heat Transfer and Solid-Liquid Phase Change
Ravi Govindram Kewalramani1, Ingo Riehl1, Jan Hantusch2, Joerg Keichel3, Martin Niederkrueger4,Tobias Fieback1
1

Chair of Technical Thermodynamics, TU Bergakademie Freiberg
Gustav-Zeuner-Str. 7, 09599 Freiberg/Saxony, Germany
Ravi.Kewalramani@ttd.tu-freiberg.de; Ingo.Riehl@ttd.tu-freiberg.de; Tobias.Fieback@ttd.tu-freiberg.de
2
Technology Innovation Center, Goldschmidt Holding GmbH,Am Schenkberg 20, 04349 Leipzig, Germany
Jan.Hantusch@goldschmidt.com
3
Elektro-Thermit GmbH & Co. KG.
Chemiestr. 24, 06132 Halle (Saale), Germany
Joerg.Keichel@goldschmidt.com
4
Goldschmidt Holding GmbH
Hugo-Licht-Str. 3, 04109 Leipzig, Germany
Martin.Niederkrueger@goldschmidt.com

Extended Abstract
The aluminothermic (AT) welding, a.k.a. THERMIT® welding or thermite welding (TW), is well known for its
simplicity, robustness, portability and economic usage for joining and repairing of rails. It has been successfully used all
around the world for over a century. It is, in principle, a casting process in which the molten metal from the crucible is settled
in a preheated mould and then allowed to solidify. For an efficient and high-quality weld, the knowledge of each stage
involved during welding, such as preheating, thermite reaction, mould filling (pouring), cooling (solidification) process, issignificant.
The present work numerically investigates the thermal conditions involved during the preheating and cooling stages ofthe AT welding process along with solid-liquid phase change. The steel-slag system is considered as two immiscible fluids
and has been modelled using the Volume of Fluid (VOF) method [1, 2]. The enthalpy-porosity technique [3] has been
employed to predict the temporal and spatial evolution of the solid-liquid phase front and to enforce the velocity field in thesolid region to zero. The complete multi-physics model is developed and implemented in the open-source Finite VolumeMethod (FVM) based Computational Fluid Dynamics (CFD) software, OpenFOAM®, and has been rigorously validated in
our previous work [4].
A typical THERMIT® SkV-ELITE L25 mould assembly for a 60E1 rail profile has been investigated, here SkV(German: Schnellschweißverfahren mit kurzer Vorwärmung) means rapid welding process with short preheating and ELITE
is a type of mould used for the AT welding of rails. Taking advantage of two symmetry planes, only one-fourth of thecomputational domain is considered for the simulation. To predict the temperature distribution in the rail at the end of thepreheating stage, simulations are carried out by prescribing a predefined heat flux profile on the rail end inside the mould.
The heat flux profile is calculated using the temperature measurements in the rail obtained from experiments as discussed byChen et al. [5]. For simplicity, the mould filling simulation is not performed. Instead, it is assumed that the mould is alreadyfilled with a constant molten metal temperature of 2473 K. Furthermore, the heat transfer between the mould and the molten
metal is neglected (i.e., the insulated boundary condition is imposed on the mould walls).
At the beginning of the cooling stage, as the hot molten metal is in direct contact with the rail surface inside the mould,
the primary heat flux inside the mould goes through the relatively cold rail. The density of the molten metal close to the rail
surface increases and results in buoyancy-driven thermal convection. As time progresses, the temperature gradients in themolten metal decrease due to the heat loss through the rail, thereby weakening the velocity field in the molten metal.

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The solid-liquid phase front inside the mould progresses from the rail end towards the weld centre and from rail baseto rail head, such that the temporal and spatial evolution of the solid-liquid phase front results in a V-shaped solidification.
Finally, the simulation results are qualitatively compared with experiments conducted at Goldschmidt Holding GmbH.
The predicted temperature profiles in the rail during preheating and cooling stage, fusion zone (FZ) and heat-affected zone(HAZ) have shown a good agreement with experiments.
Keywords: Aluminothermic welding, Buoyancy-driven flow, CFD, Multiphase, OpenFOAM®, Rail joining, Solid-liquid
phase change, Thermal convection.

References[1] C. W. Hirt and B. D. Nichols, “Volume of Fluid (VOF) Method for the Dynamics of Free Boundaries,” Journal ofComputational Physics, vol. 39, pp. 201-225, 1981.
[2] H. Rusche, “Computational fluid dynamics of dispersed two-phase flows at high phase fractions,” Ph.D. dissertation,
University of London, 2002.
[3] V. R. Voller and C. Prakash, “A fixed grid numerical modelling methodology for convection-diffusion mushy region
phase change problems,” International Journal of Heat and Mass Transfer, vol. 30(8), pp. 1709-1719, 1987.
[4] R. G. Kewalramani, S. Pose, I. Riehl and T. Fieback, “Solid-Liquid Phase Change in the Presence of Gas Phase:
Numerical Modeling and Validation,” Journal of Fluid Flow, Heat and Mass Transfer, vol. 7, pp. 1-11, 2020.
[5] Y. Chen, F. V. Lawrence, C. P. L. Barkan, and J. A. Dantzig, “Heat transfer modelling of rail thermite welding,”
Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, vol. 220, pp. 207217, 2006.

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