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ABSTRACT
This article explains the basics of rolling mills and roll pass design using results from thermal and mechanical modeling. It is mostly restricted to a 2D vision and to flat products. The reader is referred to the documentation for the very important 3D aspects and for long products. The slab method is used to describe the effects of roll diameter, thickness reduction or strip tensions on stresses, roll load and torque, and thus clarifies technological choices for different rolling mills in relation to the characteristics of their products. The finite element method is needed to study heterogeneities and their thermal or metallurgical consequences, the generation of residual stresses and the measures taken to keep the related defects under control.
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Pierre MONTMITONNET: CNRS Research Director - Center de Mise en Forme des Matériaux (CEMEF), UMR CNRS 7635, MINES ParisTech, PSL, Sophia-Antipolis, France
INTRODUCTION
Rolling mills are extremely diverse. The reason for this is that the rolled products themselves form very different families in terms of geometry (long and flat products, tubes, rings, etc.), dimensions (from thick sheet for shipbuilding to thin aluminum foil for food use), metals and alloys used (few are not rolled), and temperatures of course (cold rolling, hot rolling, and the hot of aluminum is not the same as the hot of steel). This leads to a diversity of stresses, temperature ranges and precision requirements, all of which call for very different tools and machines.
Beyond these differences, the behavior of all these rolled products and the behavior of rolling mills follow immutable laws: those of plastic deformation of metals, those of elastic deformation of structures and those of heat transfer. The ambition of this text is to highlight the common features of all rolling operations conferred by these universal laws, while showing how these physical laws, each responding in their own way to the size and time scales present in rolling mills, lead to highly typified behaviors.
We therefore focus exclusively on the mechanical and thermal aspects of rolling flat products, as these are simpler to analyze and therefore more instructive. We compare them with practical experience, and show how various types of model enable us to move from a general view of the process to a more intimate look at the behavior of this complex system. The aim is to explain why a particular type of stand is chosen for a given rolling operation, how the interweaving of economic considerations and technical arguments leads to the design of a different range for different metals, and how these choices then condition product quality. Over and above the immediate technical aspects, we make the choice of a model adapted to a given objective more concrete. Ultimately, the aim is to highlight the current state of theoretical knowledge and modeling methods used to advance rolling processes.
A glossary, a table of symbols and a table of indices are presented at the end of the article.
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KEYWORDS
rolling | metal forming | mechanical modelling and applications
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Bibliography
Software tools
Rolling mill modeling can be addressed by most of the major structural calculation codes on the market. In addition, the main metallurgical companies concerned have developed dedicated software, such as MT, UBM or FEM, which may or may not be stationary, but which are of course not available on a self-service basis.
Events
The International Rolling Conferences (IRC), which take place every 3 years, are the main meeting place for those interested in rolling, but rolling modeling is regularly covered at all conferences dealing with metal fabrication processes: NUMIFORM, ESAFORM Metal Forming, AMPT...
Laboratoires
Most research into rolling and its modeling is carried out in the laboratories of metallurgical companies. In France, the main public laboratories working on rolling models and the problems they are used to study are few and far between. Without wishing to be exhaustive, we would like to mention the following (in alphabetical order):
CEMEF – Centre de Mise en Forme des Matériaux, MINES ParisTech....
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