Mathematical and physical modelling of a single-belt casting process.

摘要

The quality of the strip produced in a near-net-shape casting process is strongly linked to the metal feeding system. An alternative metal delivery system was proposed and a comprehensive mathematical model, including heat transfer, fluid flow and stress studies was used as a tool to perform this task. This model included three-dimensional flows with fully coupled momentum and heat transfer. Turbulence effects as deduced from the standard kappa- 3 equations, macroscopic solidification, as well as flow through porous media were also modeled. A further simple model for stress was employed to calculate the displacements and the stress distribution throughout the forming strip.; Besides the mathematical model, an experimental apparatus was developed, reproducing as closely as possible the type of metal-substrate contact occurring in a single-belt caster. Casting of thin strips at high speeds was achieved and a parametric study was carried out.; The standard extended nozzle configuration did not provide a smooth flow in the reservoir. Recirculation zones besides a nonuniform delivery of the metal to the belt were observed. Divergences in the solid fractions between the center and the edges of the strips were found to increase with increasing turbulence at the exit gap. The values of the morphology constant C and the overall heat transfer coefficient h were considered the most important inputs of the model. Furthermore, modelling turbulence through a kappa- 3 model proved to be critical for this particular configuration.; The adoption of a flow modifier within the extended nozzle eliminated the recirculation zone in the reservoir and yielded a smoother flow to the belt. Such improvements in the flow distribution were decisive to ensure more uniform solidification along the width of the strip.; In early solidification, the strip was found to displace inwardly, due to the cooling and contraction of the solid shell. Tensile stresses were calculated at the cooling surface, whereas compressive stresses were found in the middle of the strip.; Interfacial heat fluxes and heat transfer coefficients measured on the strip casting simulator were highly dependent on the contact metal-substrate-coating. Values of q and h varied threefold for the various coatings and levels of roughness investigated. Correlations were derived to predict peak heat fluxes and the evolution of q after the peak, for the various coatings. A relationship was observed between the peak heat transfer coefficient and the total solidification time. (Abstract shortened by UMI.)