Closed loop automatic shape and residual stress control during levelling

The aim of this project was to provide closed loop control of the levelling operation to improve flatness performance and consistency. Trials on an advanced plate leveller evaluated the performance of existing levelling strategies for flatness and residual stress control. This revealed that the strategies available were capable of delivering a flat plate while correcting a poor residual stress (RS) distribution. New levelling strategies for high-strength and thick plates were developed. Pilot tension levelling facilities were used to investigate the significant parameters that control the strip flatness. A regression analysis of these results identified that the dominant factor influencing the strip shape was the work roll shape, although its effect can be modified by adjustment of the other levelling parameters such as strip tension. The equations developed could be adapted to produce leveller set-up algorithms and adaptations to improve the flatness of the length of the coil. Online measurement of RS would be a significant advancement in the production of stress-free material. Difficulties of RS measurement using the 3MA technique arose due to the sensitivity of the process to the variation of principal stress direction, stand-off distance and the localised area of measurement. It was considered that the use of the 3MA sensor in automated devices for determination of stress distributions online is not currently viable. A new NDT system for online measurement of residual stress utilising dynamic magnetostriction (DM) parameters was developed to complement the existing 3MA parameters. It was shown that the DM technique is less sensitive to the parameters that reduced the accuracy of the 3MA parameters.