The desing and control of strip cooling systems by use of advanced modelling techniques allied to practical measurements

Variable mechanical and physical properties arise in final cold coil from hot flat mills, that can degrade the performance of the product. A multi-national project, involving Arcelor Research SA, MEFOS and Corus UK, has been carried out to address this issue, by improving consistency via better control of strip temperature. Experimental measurements of velocity, pressure, flow patterns and surface heat flux were obtained for single and multiple water jet arrangements, typical of hot strip mill run-out table (ROT) cooling systems. Computational fluid dynamics (CFD) models gave simulations of cooling water flow on the strip surface, in reasonable agreement with the experimental results, and different methods of predicting heat transfer using the CFD models were demonstrated. Computation times were excessive and this places a significant limitation on the modelling of full-scale ROTs. Mathematical models gave good predictions of the steel temperature distribution, phase fraction and hardness between reheating furnace and coiler and were used to assess cross-width temperature control techniques and the causes of non-uniformity in the strip temperature profile. On the full-scale ROT, top to bottom cooling ratio was optimised to give improved strip shape, hence heat transfer uniformity. However, it was concluded that the finishing mill was the optimum place for improving strip temperature uniformity. Therefore, a system of inter-stand edge water sprays was used to reduce temperature differences from about 40°C to within 5°C. Mathematical model simulations of this were encapsulated in a statistical approach that formed the basis for a predictive model control concept for inter-stand cooling.