Roller Levelling Of Eliminating Flatness Defects And Its Application

Sheet metal often presents shape defects after rolling, such as waves, curl, camber and residual stress. Roller levelling is the last straightening process in the cut-to-length line, eliminating these shape defects by an alternating elastic-plastic bending of the sheet with a decline of bending intensity. At present, the study of eliminating waves by roller levelling is limited to adjusting the convexity of the rollers qualitatively and lack of an effective model to represent the relationship between convexity of the rollers and waves. Even if the study of curl and residual stress is relatively in-depth, the curvature coupling between adjacent bending is not fully considered. This paper tries to solve these problems and the details are as bellow:The reviews of roller levelling, roller leveler and the flatness defects of sheet metal are given in the first chapter. The shortage of present study on roller levelling is discussed. In addition, the main content and the architecture of this article are also presented.In the second chapter, the expression of rollers with convexity based on beam-membrane method in the FEM model is introduced. The beam-membrane method, which expresses the mechanical properties by beam elements while using membrane elements to express the contact properties, can express the bending characteristic of rollers effectively. The effective roller levelling model to eliminate wave defects is built and the relationship between convexity of the rollers and the residual waves after roller levelling is analyzed.In the third chapter, the fundamental of eliminating curl by roller levelling is presented. The roller levelling model to eliminate curl defects based on coupling curvature integration is proposed. The model is composed of two parts:geometric model and moment-curvature model. The geometric model is built based on curvature integration and the moment-curvature model takes into account the curvature coupling between adjacent bending. The evolution of curvature, flatness curve of sheet and the plastic ratio during roller levelling is analyzed. The intermesh has a deep influence on residual curl after roller levelling. There are countless combinations of inlet intermesh and outlet intermesh that can make the residual curl be zero. The residual curl is sensitive to inlet intermesh while not sensitive to outlet intermesh.In the fourth chapter, the evaluation criterion of residual stress is introduced and the evolution of residual stress during roller levelling is analyzed on the base of the coupling curvature integration model proposed in the previous chapter. Roller levelling can not only eliminate the initial residual stress, but also cause new inner stress in the sheet. The evolution model of residual stress is built and the effects of intermesh and plastic ratio on residual stress are presented. The result indicates that the initial residual stress decreases while the inner stress introduced by roller levelling increases with the increasing inlet intermesh.In the fifth chapter, the roller levelling technology proposed in the previous three chapters are applied to the design of roller set. The design details of structure parameters, process parameters and mechanical parameters are presented. The roller leveler designed based on these technology substitutes for the imported one.The sixth chapter summarizes the roller levelling technology to eliminate waves, curl and residual stress proposed in this dissertation. Besides, the research prospects of the future work are put forward.