Calculation of Mechanical and Thermal Influences During Coiling of Hot Strip

Coiled steel strip is the final product from flat hot rolling processes. With increasing demand for higher quality of hot rolled strips, especially the evolution of strip flatness during and after coiling becomes a crucial aspect. The main impacts on the flatness properties of hot rolled strips result from residual stresses and “eigen-strains” induced by the last hot rolling passes, by strip cooling at the run-out table, and finally, by the mechanical and thermal conditions during and after the coiling process itself. In this paper, a mathematical model is presented, which takes into account the mechanical and thermal effects on hot rolled strip during and after the coiling process. To improve the prediction quality of the underlying process, a customized self-developed 3D finite-element model has been developed and programmed in C++, leading to a software prototype, which is highly superior to commercial FEM-packages with respect to calculation time and storage capacities. The model is based on a dynamic implicit total Lagrangian formulation. All relevant devices directly interacting with the strip, such as pinch rolls, coiler rolls and mandrel are incorporated in the calculation model. Well known and established methods in the solid-shell theory, like the EAS- and ANS-method, were applied to prevent the occurrence of locking phenomena resulting from low order interpolation functions. Selected benchmark tests were performed to evaluate the accuracy of these novel solid-shell elements in comparison to the results attained by the FEM-package ABAQUS©. The results obtained so far agree very satisfactorily. A further important topic is the contact and friction algorithm, where Coulomb’s friction law is applied. The accurate and reliable determination of the contact between strip and interacting devices as well as the aspect of self-contact was treated by applying a sophisticated two dimensional contact search algorithm.