Anpassning av kallvalsningsinställningarför ökad kvalitet : En kombinerad experimentoch simuleringsstudie

Sammanfattning

This thesis investigates how process data from previous production steps can be used to improve the quality outcome in cold rolling of steel strip, with a focus on minimizing the relative change in the strip cross-sectional profile. The cross-sectional profile is quantified using the crown measure C40. By studying how C40 changes through the rolling mill, the work examines how rolling affects the cross-sectional profile and how the mill settings can be adapted based on the strip’s incoming cross-sectional profile to reduce this change. The work was carried out through a combination of current-state analysis, an experimental study in production, a simulation study, and a concluding experimental validation. The current-state analysis showed that the current operating practice, in which the bending force in roll pair 3 was locked as part of an effort to standardize operation, instead causes variation to shift to other parameters that compensate for the fixed setting. The experimental study showed that strips with lower incoming crown generally resulted in a poorer quality outcome. This indicates that the current mill configuration is better suited to strips with higher incoming crown, while strips with lower crown and a more rectangular cross-sectional profile are more adversely affected. This is particularly problematic since these strips are best suited to meet the highest thickness tolerance requirements in the final product, but changes in the cross-sectional profile can reduce their ability to meet these requirements. The simulation model was designed to replicate the rolling process under the same conditions as in the actual trials. A comparison showed that the simulated C40 values agreed well with the measured values, and the model was therefore used for further analysis of the rolling process. Through simulation of a full two-level factorial experiment, the mill parameters with the greatest influence on the change in cross-sectional profile were investigated. The results showed that several parameters that vary over time contribute to this change, including incoming crown, roll bending, roll force, and work roll diameter. This suggests that a standardized operating practice, which does not account for these variations, is not sufficient to ensure a consistent and favorable quality outcome for strips with different incoming cross-sectional profiles in combination with varying process conditions. The model was then used to optimize the bending force in roll pair 3 with the aim of minimizing the relative change in cross-sectional profile. The resulting settings were evaluated through experimental validation, which indicated that the change in C40 decreased compared with the current standard setting. This shows that the quality outcome can be improved by adapting the bending force to the strip’s incoming cross-sectional profile. Overall, the work shows that process data from previous production steps can be used as a basis for a more strip-adapted process control strategy and thereby contribute to improved production processes, in this case through a better quality outcome in a cold rolling mill.