The tundish is the last metallurgical vessel through which molten metal flows before solidifying in the continuous casting mold. Proper design, lining, and operation of a tundish ensure less interaction with refractories, slag, and atmosphere which helps to produce steel of desired composition and quality.
Tundish shell: It represents the outer bone of the tundish. This is made up of high-performance manganese steel, which can withstand high temperatures (m.p -1500 oC approx). It has 25 mm to 30 mm in thickness. The tundish shell structure is tapered from top to bottom which basically serves two purposes: one is to provide downward vertical momentum to molten steel for continuously casting and the other is to facilitate easy de-skulling.
Evaporation holes in the Shell:- Tundish shell has holes for the easy escape of the evaporated water during the time of drying. The absence of steam coming out of the holes represent completely dried out tundish.
S-S anchors with plastic caps:- Stainless steel anchors can withstand high temperature and has low thermal expansion. It is far better than mild steel anchors. The main purpose of the S-S anchors is to hold the ceramic fibre board and permanent lining of the tundish. Plastic caps fitted on the tip of s-s anchors minimize the crack formation in the backup lining, compensate for the expansion of the anchors and reduce the stress burden when expansion occurs at high temperatures. Anchors are placed at a horizontal distance of 250 mm and a vertical distance of 300 mm from each other.
Ceramic fibre board: – It is an alumino-silicate ceramic material that has high porosity and low thermal conductivity. It is used mainly as an insulation material to prevent an abnormal increase of the tundish shell temperature and also prevents heat loss from the tundish pool. Holes are made in the fiberboard at a particular measured distance for the indentation of anchors to take place.
Permanent refractory lining:- Low cement castables (LC-70) is generally preferable. In most cases monolithic, alternatively, bricks can also be used. Normally monolithic permanent linings are used because of the absence of space between bricks and better service performance. Monolithic linings can be applied as either thixotropic mixes, thickened by vibration, or free-flowing castables. Thus 70% alumina-based vibratable castables are used. Anchors are welded to the tundish shell to keep the lining intact. A thickness of about 140 mm and 180 mm permanent lining is applied on the wall and the bottom respectively. A newly made permanent lining has to be carefully dried and a proper drying pattern is to be followed for better results.
Well block: It is a PCPF material, made from low cement castable base materials. It is used before the application of working lining for proper fixing and centering of SEN. After placing the well block into the tundish hole, the gap between the lining and well block is covered by ramming mass with 2% water which is meant to restrict well block movement and fill the micro gaps present in the permanent lining of the tundish.
