SIMULATION AND CONTROL OF HEAT-TRANSFER IN CONTINUOUS-CASTING OF STEEL

The aim of the present study was to develop numerical models and methods by which the strand thermal state could be better controlled. Another purpose was to get a new understanding of the heat extraction from the strand surface and thereby to learn to control the strand cooling better. Different kinds of models were developed: (1) The steady state heat transfer model for calculation of strand temperature field and shell thickness, (2) the steady state optimization model for calculating the optimum secondary cooling pattern so that given metallurgical criteria and technological constraints are met, (3) two real-time heat transfer models for on-line calculation of strand temperature field and shell thickness, (4) two control models, called Casim and Dyncool, for the strand cooling and shell growth, and (5) a model which calculates the thermophysical material properties of carbon and low-alloyed steels, taking into account the temperature, the cooling rate, and the composition. The first control model, Casim, is based on data tables established in advance by the steady state heat transfer model. The second one, Dyncool, is based on the real-time heat transfer model. The purpose of these models is to retain the selected temperature pattern along the strand in spite of variations in casting parameters. Another possible mode is to operate with a constant length of liquid core. Characteristics of the models developed and their industrial applications are discussed in this thesis.