Improvement in throughput and product quality of continuous annealing lines by extended models and advanced control

To avoid wrinkling and to improve the guiding of strip processed in continuous annealing lines, the incoming strip flatness, thermal crown alignment of rolls and the guide roll actuator range must be enhanced. This project focused on a determination of allowable incoming strip flatness deviation, control of roll profile by measurements plus local heating/cooling, and lateral strip flow by roll profile plus control of roll axis alignment. Calculations of the interaction between intrinsic flatness of the strip and crown roll buckling related to the folding risk were carried out on a small strip size and confirmed by high-scale pilot plant experiments. Flatness defects such as long centres drastically decrease the critical tension of folding. The risk of lateral strip instability was assessed by a roll temperature model, a thermal roll profile model, the superposition of both profiles and a conclusion about the lateral strip flow effect, which is explained by a concave curvature of the roll due to a thermal expansion at the strip edges. A roll temperature monitoring system for control purposes, using high temperature optical fibres, was developed and tested successfully in an industrial line. The choice between a thermal actuator utilising a gas of the same nature as the furnace gas or the use of a liquid for cooling still has to be decided. A roll inclination actuator that exploits the effect of the roll alignment on the lateral strip flow was designed, constructed and tested successfully at the CRM pilot plant. It can be easily implemented in furnace rolls and works on the principle of a roller bearing adjusted by a motor-driven eccenter.