Advanced Coil Cooling Model Incorporating Layering and Interface Effects of Strip Windings

Understanding the hot rolled coil cooling behavior is critical to coil yard design, storage, delivery scheduling and improvement of product properties such as mechanical performance, surface quality, shape, and profile. The layering and interfacial conditions between strip windings strongly affect the coil cooling but these effects have not been clearly addressed due to the complexity of investigation and modelling. Existing models have the common difficulty to measure or calculate the contact pressure between coil layers required for determining the thermal conductivity in the coil radial direction. Understanding these effects becomes increasingly important as advanced thin slab casting and rolling technologies like endless strip production enable the production of ultrathin endless hot rolled coil (eHRC) strips down to 0.6 mm. In this work, a novel method is developed to calculate the radial thermal conductivity and a heat transfer model based on finite difference method is further proposed. The model prediction demonstrates good agreement with experimental results. The influences of strip thickness and initial air gap on coil cooling are revealed and analyzed using the model. It was found that coils with thinner strips exhibit significantly faster surface cooling rates during the early stage of cooling. As cooling progresses, a transition in the cooling rate is observed, and by the later stage of cooling, differences in cooling rate among different strip thicknesses become negligible. The impact of these cooling behaviors on surface oxidation was discussed, indicating that thinner strip coils are likely to form thinner oxide scales on the outer surface.