Hot rolling is an essential industrial process in the production of sheet steel. In the hot strip mill process in the iron and steel industry, reheated slabs are rolled to the required strip thickness and width at the roughing and finishing mill. In the finishing mill the strip thickness reduces while the strip passes through each of the 7 stands by controlling the gauge. Between each two stands there is a looper which is a motor driven arm. The function of the looper is to keep the strip at a reference tension. Looper and tension control are important in hot strip mills because they affect the strip quality. In addition, it is important to properly recognize interactions between sub-divisions and the rolling stands. Looper is one of the important parts in the finishing mill process that should be investigated more. Moreover studies about important parameters, sources of disturbance, effects on the product and related control systems with looper have been carried out. Then dynamic equations for rolling stands and looper system is provided. These equations have been obtained comprehensively and accurately that have provided the proper grounds for simulations. An innovative sliding mode controller for looper and tension control in hot strip finishing mills was developed based on approximately linearized model. A finishing mill performs a set of operations in a hot strip rolling mill, and a complex unit including many processes and control loops. A dynamic model of hot strip rolling with looper system has been developed. The model has two main sub-models, the stand elastic model and the strip rolling plastic model. Roll surface flattening, and the material strain rate hardening are the main sources of the nonlinearities in the mill and the rolling process sub-models respectively. All simulations were performed by MATLAB software. The Simulink tool of the MATLAB software was employed to simulating the interactions of the sub-models. Results are compared with the available experimental records by Mobarake Steel Complex (MSC). Empirical and simulation figures are verified together and performance of program is approved. Besides, new results have been obtained by simulation. Specifically the effect of thickness on the rolling force and looper response is presented. Looper response for different rolling speeds and strip thicknesses has been studied. Furthermore the effect of strip tension variations on thickness created by looper has been presented. The results have also shown that the roll load decreases with increasing interstand tension. Based on this simulation technique, valuable information can be easily obtained for possible improvements on rolling processes in the future. As well as analytical solutions might be compared with numerical solutions obtained from finite element simulation, which is left as a future work. Keywords: Hot strip finishing mill, Looper dynamic, Looper control, Interstand tension, Simulation
