Papers by Author: Dag Mortensen

Abstract: Wire rod is produced by hot-rolling a bar of metal coming from a wheel/belt continuous casting process. This kind of process, e.g. Properzi, is an elaborate process in which the molten metal is poured in a cooled rotating mould formed by the groove of a wheel and closed by a belt. In order to better understand the heat transfer phenomenon and solidified bar characteristics, depending on process parameters a three dimensional thermo-mechanical model has been developed. The model, based on the finite-element method, calculates the heat transfer coefficient of the air gap at the metal-mould interface as a function of the size of the gap determined by the bar contraction and wheel and belt thermal deformations. The air gap formation due to metal shrinkage and mould deformation is the main factor which determines the heat extraction. Wheel temperature measurements with thermocouple and belt temperature measurements with an infrared system were carried out to verify model results. Attempts were also made to measure a liquid pool profile using doping with copper rich alloy. The model shows the effect of the casting temperature and the rotation speed on the air gap formation and resulting temperature and stress fields. The model can be applied to issues such as maximising wheel and belt life and minimising solidification defects.

Abstract: A coupled heat and fluid flow, stresses and deformation modelling tool including macrosegregation and inter-dendritic flows have been developed for various semi-continuous or batch casting processes in use by the light metal industries. Results from the mechanical calculation are back-coupled to the thermal boundary conditions regarding size of contact zones and air-gaps and thereby enabling automatic calculation of gap dependent heat transfer coefficients, which is very useful for the industrial use of the tool. Examples from the application of the model on direct chill castings are made, as well as on twin roll, wheel and belt and chain conveyor casting. Comparison with measurements and other process data are done. The finite element method is used for the modelling tool including dynamic treatment of elements in moving parts of the calculation domains. In continuous casting there are frequently interfaces where the metal slides against the equipment, and although the grid across such surfaces does not match they are still coupled implicitly in Alsim. This adds an ability to model complex processes involving stresses and deformations in mechanical coupled moving parts and it alleviates the time consuming process of producing the initial finite element grids for the geometries. In order to handle solidification phenomena like hot-tearing, macrosegregation and exudation local adaptive grid refinement is necessary, as well as parallelization of the code, to achieve acceptable accuracies. How these numerical challenges are handled in the model is described.

Abstract: A simplified numerical model for the solid state phase transformation from Al6(Mn,Fe) to α-Al(Mn,Fe)Si phase in 3xxx alloys has been constructed. In this model, the phase transformation is assumed to be initiated by the heterogeneous nucleation of α-Al(Mn,Fe)Si dispersoids at the interface between Al6(Mn,Fe) particle and matrix and the growth of the α- Al(Mn,Fe)Si phase into the Al6(Mn,Fe) particle is controlled by the diffusion of Si from the matrix. The model has been implemented into a numerical homogenization model. The simulation results show that the implementation of the phase transformation model improves much the prediction results of the homogenization model on the evolution of solid solution level of alloying elements and the volume fraction evolution of dispersoids in 3xxx alloys during homogenization.