Research On Mathematical Model For Solidification Heat-transfer And Dynamic Control Of Secondary Cooling In Continuous Casting Of Round Billet

The secondary cooling technique plays a very important position during continuous casting. It influences the themal state of casting billet, then affects the formation of solidification structure. The disadvantages such as internal crack, center crack, segregation and strand drum, have association with irrelevancy secondary cooling process. A secondary cooling system should have proper caster structures and operating parameters, to satisfy the requirements of metallurgical criteria and uniform cooling.A two dimensional heat-transfer mathematical model in continuous casting of round billet was established according to a newly built cater in a steel plant in this paper. The model was solved by the changeable space FDM. The effective spraying water coefficient was determined according to the actual spray condition of round billet. The differences of circumferential cooling condition were considered, by changing the water flow density distribution tested on the plate to the distribution of water flow density for round billet.The software of secondary cooling simulation in round billet continuous casting (SSRBCC version1.0) was developed by Visual Basic, which has friendly interface, simple operation, strong interactive ability and functions of simulation of casting process, iterative calculation of cooling water, water formula regression and data post-processing.By simulation with the SSRBCC software and combination with the requirements of metallurgical criteria, the round billlet caster structures and operating parameters were designed auxiliary. The design of transition region and nozzle arrangement in the circumferential direction were analyzed. The proper secondary cooling system of steel 37Mn2 was confirmed by combination of the steel high temperature properties test and iterative calculation of cooling water by iterative adjustment were determined. After that, the influences of superheat, casting speed and cooling intensity on solidification of round billet (including billet temperature, liquid core length and all clotting time) were analyzed to explore the solidification law of round billet.For the non-steady process with changeable speed and casting temperature, a dynamic spray model for round billet was developed, with the function of real-time tracking (including fixed length blank tracking and fixed time interval tracking). In the model, the actual casting speed was replaced by the virtual casting speed of each zone, obtained by tracking as the parameter of water distribution and the influence of superheat on cooling water was considered. Comparing with the static spray control, the thermal state of billet was more stable to improve the quality and decrease the formation of crack by the dynamic spray control which adopted the virtual casting speed as the parameter of water distribution.By tracking the actual production after commissioning of caster, we found that the measured strand surface temperature was proper, gently decreased, the strand quality was controlled well, especially the cracks. The results show that the secondary cooling structure of the casting machine and the operating parameters are reasonably designed.