Introduction
Ladle scab is a major problem experienced in blast furnaces. It is most commonly seen in hot metal ladles as a coating on the lowermost part of the ladle’s insulation. It is also known as “Skull” or “Lack” and is formed due to the condensation of molten iron onto the cold surface of the insulation shell. Helping to regulate heat transfer, the thin carbon layer of ladle scab can cause a significant increase in energy costs if left unchecked.
Cause of Ladle Scab
Ladle scab is caused by the contact of liquid iron with the cold contact surfaces of a ladle or tundish during steel transfer operations. This can occur during a change of vessel from a furnace to a ladle or in the ladle itself when ladling hot steel from the refining station. In both cases, the molten-liquid iron transfers thermal energy to the contact vessels walls and surface elements, leading to the condensation of molten iron onto the cold surface of the insulation shell.
Effects of Ladle Scab
Not only undesirable, the formation of ladle scab on a ladle or tundish can be damaging to the steel being ladled. As the layer of scab is generally thin and non-reinforced, it can be easily removed. It reduces the efficiency of heat transfer as well as the integrity of the insulation system, thus creating a potential fire risk. In addition, the scab layer increases the risk of air contamination and decreases the capability of smooth steel transport, limiting the life cycle of the ladle’s performance.
Control Of Ladle Scab
In an effort to control ladle scab, there are several measures that can be taken. The use of an effective insulation system is essential for preventing the condensation of molten steel onto the cold contact surfaces of a ladle. This should be complemented by the use of well-maintained airlocks and ventilators as well as an effective thermocouple/temperature control system in order to ensure the proper functioning of the ladle’s insulation. Proper maintenance and replacement of the insulation system should also be carried out on schedule in order to reduce the formation of ladle scab over time.
Conclusion
Ladle scab is a costly problem experienced in blast furnaces. Although the formation of this layer of carbon on the cold surfaces of a ladle or tundish is generally thin, it can cause a significant increase in energy costs as well as decrease the efficiency of heat transfer. However, there are several measures that can be taken in order to reduce its formation and ensure the proper functioning of the ladle’s insulation system. These include the use of effective insulation systems, maintenance and replacement of insulation systems, properly functioning airlocks and ventilators and the use of a thermocouple/temperature control system. With the implementation of these measures, the risks associated with ladle scab can be significantly reduced.
