Investigation into processing changes at the hot mill coiler entry and when coiling to improve visual and latent shape in the final cold coil

There is increasing demand for direct-supply hot rolled coil to be to the required flatness, without crossbow or longbow, and with minimal residual stress. In practice, strip leaving the finishing mill can be measured without flatness deviations and assumed to be stress free. However, the cold coil can fail to meet flatness standards and residual stress requirements. The project aim was to understand, through a combination of theoretical models and practical testing, the evolution of flatness and residual stresses in the strip from exiting the hot finishing mill through to the final cold coil. Investigations (Corus, Mefos, BFI) were both practical and theoretical, on the processing changes through to the hot mill coiler, then including coiling, to try and establish the fundamental cause and effect relationships. Samples were supplied to ISQ for the measurement of latent residual stresses. Theoretical levelling system solutions (VAI) were developed for the correction of flatness and stress deviations. In summary, Corus found that, between measuring the flatness at exiting the finishing mill and subsequently at the coilers, there was an overall improvement in flatness. Mefos concluded that it is difficult to draw general conclusions since the final flatness is the result of many interacting factors. The BFI theoretical analysis was carried out for a range of conditions, which showed how flatness could evolve. ISQ carried out a comprehensive comparison of techniques for measuring residual stress. The VAI theoretical approach developed various solutions to hot levelling of the strip, in the area of the coilers.