Strip tracking control using novel insights into the differential rolling process

Steel strips suffer from lateral shift when being rolled in a rolling mill, especially at the head and tail ends. That results in strip pinches with costly downtime and damage to the work rolls and the strip itself. The lateral shift can be reduced by levelling the gauge control cylinders in response to shift measurements and differential roll force measurements. Designing such controllers gave rise to the desire for analytical relations that describe the shifting process. Novel insights have been revealed, which include the differential material modulus, the differential mill modulus and the ratio to apportion the effect of levelling to entry and exit strip speed changes. The insights have resulted in compact analytical process models that have been used to implement strip tracking controllers safely and sensibly, and to schedule control gains based on actual process parameters. Focus has been on hot strip mills.