Development and Application of a Finishing Mill Off-Line Temperature and Roll Force Model

An off-line model was developed and used to improve an on-line model for a Finishing Mill (FM) operation set-up in a Hot Strip Mill (HSM). The off-line model estimated the temperature and roll force of the steel hot band which passed through the holding table and FM. The hot band temperature was estimated using the finite difference method. The steel specific heat and thermal conductivity were functions of not only temperature but also chemistry of steel. The heat transfer coefficient of water flowing on the hot strip surface in FM was expressed as a function of temperature. A semi-empirical equation was used to calculate temperature increase due to strip rolling deformation. Equations were also applied to calculate heat transfer coefficients by water jet descaling, bottom roller and strip contact, air velocity and radiation. The estimate for roll force was improved by modifying both the roll force modification equation (called Qp equation), and the deformation resistance equation. The new Qp equation included parameters such as reduction, aspect ratio of the deformation zone, inter-stand looper tensions, and steel deformation resistance. The deformation resistance equation was a function of strip temperature, chemical composition, strain, strain rate, and residual strain. The residual strain was found existing only for the Cb- and Ti-containing steels. The deformation resistance equation was derived using the strip temperature (estimated by the off-line model) and measured operation data (which included roll force and roll speed). A comparison was made between the off-line model estimation and mill measurements for temperature and roll force. The derived deformation resistance equation was tested in the plant on-line model. The roll force estimated by the on-line model, before and after modification of both the deformation resistance equation and the roll force Qp modification equation, was also compared with the measurements.