Front End Curvature(FEC) is one of defects that occurs in rolling process and has influence on the quality of the product as well as productivity. When FEC occurs upward from normal pass line, strip cannot normally enter within roll gap in the next stand. Moreover, the FEC of downward direction leads to damage on roller table or work rolls.
This phenomenon is resulted from asymmetric rolling factor, which is caused by various rolling conditions such as difference of the roll diameter and roll speed, initial thickness of strip, draft ratio, friction condition, temperature distribution and entrance angle of the strip.
Even though the looper is particularly essential part of finishing mill to control tension of the strip between each roll stand, operation of the looper varies the entrance angle of strip, which also affects the FEC. Therefore, it is significantly important to investigate the effect of the entrance angle of the strip on the occurrence of FEC.
The purpose of this study is to predict the FEC in hot strip finishing mills and to prevent the FEC by controlling the rolling condition. Theoretical model based on the slab method is developed to predict the FEC by taking entrance angle of strip, friction condition and back tension into account. To verify the validity of the developed theoretical model, theoretical curvature value is compared to the result of FEA and consequently, it shows that the results calculated by theoretical model are good agreement with those calculated by FEA.
Furthermore, the curvature control model based on geometrical and mathematical approaches that can reduce the curvature by control of roll speed ratio between upper and lower rolls is suggested. To verify the proposed curvature control model, FEA is performed. And it is shown that the FEC can be considerably reduced by using the suggested model. Therefore, the proposed control model to reduce the FEC in hot strip finishing mill can be used to improve the quality of rolled product.