Calculation of thermal stress affecting strip flatness change during run-out table cooling in hot steel strip rolling

Abstract

To fulfill further reducing production costs at the meantime enhancing product quality is always one of the objectives pursued by steel enterprises and researches. With increasing demand on higher quality of hot rolled strip shape, strip flatness change developed during cooling on the run-out table has received significant attention and should be considered in online strip shape control model. Non-uniformity of transverse temperature distribution in strip is the ultimate reason for the occurring of strip flatness defect after hot rolled flat strip is cooled to room temperature. Based on the large amount of thermal image field measurements on strip surface, transverse temperature distribution rules of strip were concluded. A FE model was established to analyze the thermal stresses developed during the cooling of hot rolled strip on the run-out table using finite element program ABAQUS. Analysis results demonstrate that temperature drop within strip edge region will make strip flatness develop to the trend of edge wave and are verified by the actual strip flatness observation on skin pass rolling line. This viewpoint agrees well with the actual production condition. One compensation control strategy, named slight center wave rolling, is proposed based on the FE analysis work. The main idea is that steel strip is rolled with slight center wave at the exit of the last stand of finishing mill to compensate the flatness change trend of edge wave during the cooling.