Continuous casting is the process where molten steel is solidified into a semi-finished billets, blooms, or slabs for subsequent rolling in finishing mills. In continuous casting, liquid steel is transferred in a ladle to the casting machine. When the casting operation starts, the sliding shutter at the bottom of the ladle is opened and the steel flows at a controlled rate into the tundish and from the tundish into one or more molds.
Prior to the introduction of continuous casting in the 1950s, steel was poured into stationary molds to form ingots. Since then, continuous casting has evolved to achieve improved yield, quality, productivity and cost efficiency. Casting companies are always striving for process improvements, and simulation with FLOW-3D Cast offers them the chance to do so without physical trial-and-error, which can be both costly and time-consuming.
There are numerous aspects of the tundish process that can be the subject of optimization studies, including:
- Filling of an empty tundish at beginning of the casting sequence
- Time during incoming metal from the ladle
- Ladle change (with and without grade change)
- Filling of the tundish to operating level after ladle change (with and without grade change)
- Temperature distribution development and particle behavior during operation
- End of the casting sequence (machine stopping order)
- Asymmetric flows (scrapping practice)
- Special situations such as when there is more than one mold, and one or more of the molds are not in use.
Sami Vapalahti, researcher in Metallurgy Laboratory at Helsinki University of Technology, working with Finnish steel and copper industry and VTT Industrial Systems, has been conducting investigations into various continuous casting operations. The Metallurgy Laboratory has a long history in mathematical modeling of heat transfer and materials properties for continuous casting and the industry is very interested in continued expansion of modeling capabilities because they realize how important fluid flow behavior in both the tundish and the mold is for both the quality of the final product as well as the ease of process operation and overall productivity.
Sami’s focus thus far has been on the tundish, the tasks of which are to:
- Act as a distributing reservoir between ladle and mould;
- Provide a constant and continuous flow of metal to the process;
- Separate inclusions
- Distribute homogeneous steel into the molds (i.e., with the same temperature, composition and dynamic behavior).
Some parameters to focus on for optimization studies for the tundish are:
- Tundish geometry (size, shape)
- Other tundish geometry (weirs, dams, etc.)
- Residence time distribution Ladle change parameters (e.g. level of steel, rate of filling)
Modeling Tundishes: Ladle Change
In the simulation at left, a new ladle has just been brought in to add metal to the tundish. The evolution of the temperature field is displayed. From this view, engineers estimate where the steel from the previous ladle is located, as well as its temperature. The animation shows well how the temperature of the whole tundish increases, and how the surface moves.
Modeling Tundishes: Particle Separation
This animation displays one of the most important tasks of the tundish: particle separation. When the tundish is filled up to its operating level, the velocity of the metal entering the tundish is typically three times the normal operational velocity. Simulating this process, engineers can try to estimate whether geometry changes should be made in order to help particles to climb upwards and connect to the slag layer.