12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

Today, steel producers find in their portfolio many kind of steels, including the new high strength steels, each with their specific heat cycle. Adding to this the final customer specifications, and on the top of it the requirements of various sizes, the coil schedule faced day-by-day on production level stretches into an extensive mix. A modern galvanizing line must be a flexible tool able to cope with continuous changeover of the process conditions. Controlling a continuous galvanizing furnace requires to master the physical behaviour of its components. On vertical annealing furnaces, the processed strip is deflected by rolls at each pass and between the process sections. During operation, repetitive contacts between the transported strip and the furnace rolls take place. The unceasing changes in the annealing process linked to the variability of the production schedule, leads to recurrent thermal exchange between the strip and the rolls. The heat transfer by contact between the strip and the rolls is very effective and take place in short time. However, the rolls have a big thermal inertia with long time constant, hence the need for a roll model. In the roll models used in mathematical applications for furnace control we find for example radial models, which consider the roll size in the heat transfer. These models showed themselves to be too simple in relation to the physical behaviour. Today, an angular and multilayer roll model considering the heat exchange along the contact between the strip and the rolls, as well as the heat transfer through the roll thickness is implemented in Drever's Mathematical Model for continuous control of galvanizing furnaces and lines. The implementation of an angular and multilayer roll model provides another dimension to higher level functionalities of process control. When used along the furnace transition management, advanced control with process forecast is achieved. Industrial results will be presented.