Decisive quality characteristics of produced cold strip include the transverse gauge profile over the length of the strip, the flatness of the strip, and the residual stresses in the strip. The most uniform thickness possible over the width of the strip is of particular importance for downstream processing into slit or narrow strip, while good flatness and low residual stresses are a precondition for all the downstream processing stages and subsequent products. These quality characteristics are strongly correlated and depend on the properties of the in-put strip and on the corresponding process-related effects and disturbances during rolling.
 
To realise adequate strip flatness and, at the same time, minimum residual stresses in the strip at tandem cold rolling mills, a strategy of utilising the strip-length-related information concerning the transverse gauge profile of the input hot strip, gained after hot rolling or at the pickling line, is being pursued with a view to dynamically controlling available actuating vari-ables, compensating for particular disturbance variables occurring during rolling (e.g. changes in rolling force), and installing a modern (model predictive) closed-loop flatness con-trol system.

An (online) observer provides estimates for process variables not measured between the mill stands. A higher coordination level allows for mutual influences and ensures an optimum distribution of the positioning and control element actions and compliance with size restric-tions. The combination of these control measures creates a coordinating closed-loop flatness control system for complete tandem cold rolling mills.
Initial testing of a prototype at a tandem cold rolling mill in Germany has yielded promising results, with the consequence that this system is now to be installed industrially (under SIMATIC).