Over 15 million tons of cold rolled steel are produced annually in the U.S. on multi-stand rolling mills. These mills consist of a sequence of roll stacks through which steel sheet is rolled, successively reducing its thickness to the desired gauge and imparting the desired surface finish. While this is an old and seemingly simple process it is actually very complex and not well understood.

Schematic of Roll Stacks

An issue of particular concern is chatter. Rolling mill chatter is a vibration problem limiting the throughput of nearly all metal rolling operations. In addition, associated sensitivity of the system to forced vibration necessitates costly maintenance programs to minimize these forces. The root cause of the problem is a destabilizing feedback mechanism which renders the system extremely sensitive to any excitation. In the limit, the rolling process is unstable and self excited. The extension/tension relationship of the inter-stand steel sheet is a critical component of the feedback path.