Hybrid modelling of the continuous casting of steel

To prevent surface defects and to increase the quality of the product, a controlled cooling is necessary. In order to unsure a constant heat dissipation surface-temperature above the “Leidenfrost-temperature” and therefore a stable vapor layer on the slab is a prerequisite. This condition has some dependencies, like the surface temperature and condition, the spray properties regarding the size and velocity of the water droplets and the water distribution, which itself varies with the operating parameters. Additionally, a sustainable use of cooling water and air also helps to reduce the costs and the environmental impact of steel production. To investigate on the impact of nozzle types and operating parameters The Nozzle Measuring Stand at the Chair of Ferrous Metallurgy was established. Following parameters can be adjusted to investigate their influence on cooling intensity:

• Water flow rate V_(H2O) / water pressure p_(H2O)
• Air flow rate V_(AIR) / air pressure p_(AIR)
• Sample velocity v (< 6 m/min)
• Surface start temperature T_Start (<1200 °C)
• Distance nozzle – surface N_z
• In case of two nozzles: Distance nozzle – nozzle N_x

Regarding the gained data a distinction between the water distribution “WD” (or water impact density “WID”) and the heat transfer coefficient “HTC” can be made. For the measurement of the WD seven measuring grids are used for collection the water from the strays in a defined period of time. Via a photo-optical analysis using all measuring grids as a depth value a 3D-Simulation of the spray pattern in milliliters per minutes can be generated. Furthermore, it is also possible to measure the HTC with a moving pre-heated specimen. Trough the heat drop caused by the water spray the surface temperature and the HTC of the sample can be calculated with an inverse heat conduction model. As an outcome of the measurements data triples were generated, because the WID, the HTC and the temperature on the surface are corresponding. For an implementation in an in-house-developed simulations software called “m²CAST” regression models are used as a statistical prediction method for the forecast of the time- and location- dependent HTC for the solidification modelling.