Reduzierung der Kopflunkerlänge bei großformatigen Vertikal- und Bogenstranggießanlagen durch numerische und experimentelle Untersuchungen

Hauenstein, Gian; Pfeifer, Herbert (Thesis advisor); Odenthal, Hans-Jürgen (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023

Abstract

The problem of crop-end loss and shrinkage pipe in continuous casting is becoming increasingly relevant as larger casting formats and higher casting speeds are to be achieved. As a result of density change between the liquid and solid phases of steel, the steel volume shrinks during solidification and cooling. In continuous casting, this shrinkage is noticeable as a cross-sectional shrinkage from the mold exit to those in the cold state. After stopping of the melt pouring at the end of a casting process, shrinkage is primarily manifested by an open shrinkage pipe at the strand end. The aim of the present work is to investigate and optimize crop-end loss and shrinkage pipe of bloom sections in semi-continuous and continuous casting machines. Operational trials and numerical simulations were carried out on a strand with diameter of D=1000 mm. The operational trials were performed on the continuous casting machine of Taewoong (Busan, South Korea) with a casting radius of R=18 m, a casting speed of v_c=0.12 m/min to 0.14 m/min and the steel grades 42CrMo4 and S355J2G3. The strand solidification with shrinkage pipe after regular continuous casting was calculated with the numerical simulation based on FVM with the VOF model and enthalpy porosity approach for solidification.It can be seen that the shrinkage pipe is a huge problem in these sections, reducing the output of a continuous casting machine. The strand end with the shrinkage pipe must be separated from the high-quality strand and scrapped. This loss of material reduces the output, particularly for semi-continuous casting machines. During continuous casting of blooms with a diameter of D=1000 mm, a shrinkage pipe with a length of l_Kl≈ 2000 mm is formed, which corresponds to a crop-end loss of 10 t of steel. The shrinkage pipe length depends on casting speed, cooling intensity and steel grade. The hot-top process was successfully applied in operational trials. The shrinkage pipe length l_Kl was reduced by around 25 % which corresponds to a recovered steel quantity of 3.1 t. The calculated shrinkage pipe length (with FVM) was about 5 % smaller than the experimentally determined length. This is a good agreement and validates the simulation. The hot-top process and the influence of immersion depth, wall thickness and material of the hot-top ring was investigated and optimized by numerical simulations. The most important interactions for the hot-top process in continuous casting have been demonstrated. The developed simulation model can be applied to other casting section. Ultimately, under the right conditions, the economic and ecological aspects of continuous casting machines with large-sections can be improved by implementing hot-top technology.

Institutions

• Division of Materials Science and Engineering [520000]
• Chair of High-Temperature Technology and Department for Industrial Furnaces and Heat Engineering [525110]