No abstract

Roll wear in a hot strip mill (HSM) is a detrimental process, which progressively worsens the rolls. This necessitates replacement of the rolls after rolling a number of strips. Roll wear adversely affects the strip shape and the performance of a mill. It is important, therefore, to quantify roll wear during the rolling process. The present paper proposes a wear model for prediction of the wear profile of the rolls at the finishing stands of a hot strip mill. Initially, a roll force model was developed to calculate the roll force at each stand by considering various factors such as the strip thickness and width, mean flow stress (MFS), and roll diameter for each pass. The roll force calculated by the model was subsequently integrated with the roll wear model for calculation of the wear along the roll barrel. The effects of the continuous variable crown (CVC) profile of the roll and roll shift were also included in the wear calculation. The wear profile predicted by this model was validated experimentally in the plant. Predicted values match closely with those obtained from experiment. The model has the potential to be used as an efficient online method to predict the wear profile within a reasonable computational time.

Predictive models are required to provide the bending set point for bending for the flatness control devices at rolling stands of finishing mill of Hot Strip Mill (HSM). A simple model for roll stack deflection at the finishing mill has been illustrated where a modified Misaka's equation has been used to obtain mean flow-stress. Investigation has been performed to understand the effect of width of roll on roll stack deflection. The bending on the deflection has been found to have a positive effect to reduce the amount of the stack deflection. The results from the sensitivity analysis of the roll width on roll deflection are also described.

Rolling of thin gauge hot rolled (HR) coils demands stringent flatness tolerance. Thin HR coils ((3 mm) are rolled towards the end of any rolling campaign. The profile and flatness of the strip depend on the profile of the loaded roll gap in the mill stands. There are five key factors that influence the loaded roll gap: initial roll surface profile, roll thermal expansion, wear of roll, deflection of roll stack and shifting of work rolls. This paper deals with all these factors individually for the formulation of an objective function in order to minimise the flatness error. The shifting and bending of rolls are the controllable parameters that require optimising. This has been accomplished using a genetic algorithm (GA) optimisation technique. List of symbolsA cross sectional area of roll, m 2 a 0 , a 1 , a 2 coefficients of third order polynomial B work roll bending, kN c strip crown, m c p specific heat of work roll, J kg -1 K -1 D work roll diameter, m d continuous variable crown (CVC) shifting, m E Young's modulus, GPa e node at roll surface G modulus of rigidity, GPa h strip thickness, m I moment of inertia, kg m 2 i stand number k thermal conductivity of work roll, W m -1 K -1 L exit strip length, m Dl difference between the strip wavelengths in the middle and its edge, m l strip wavelength, m l9 contact length, m M bending moment, N m m coil position in a schedule n total number of coils in a schedule P roll separating force, MN p penalty function : q heat generation, W m -3 R rolling reduction, % r distance along the radial direction, m Dr step size in radial direction, m S shearing force, N T temperature, K DT temperature change in the Dr for the total time t time, s w strip width, m y strip thickness at a particular position across width, m z distance along the axial direction, m r density of work roll, kg m -3 a T coefficient of thermal expansion, K -1 a, b, c empirical constants w objective function

The work rolls in the finishing stands of any hot strip mill (HSM) experiences thermal shock owing to changes in temperature from initial boundary conditions. The thermal expansion owing to the change of temperature is a major contributing factor to the final shape or the profile of the strip generated at different stands of finishing stands of the HSM. A mathematical model has been developed for the prediction of temperature profile for the surface and the inner depth of the roll in the finishing stand of a HSM. The numerical result from the model calculates the temperature profile in each stand of six finishing stands of the HSM and the corresponding thermal expansion at different stands. The temperature profile and the thermal expansion of the work rolls for a complete rolling schedule have been found from this model. The measurement of the thermal expansion has been found to match closely with the calculated one.