Ladle nozzle preheating is an important process before continuous casting or die casting.
The main purposes are:
Preventing cold steel from solidifying: to avoid local solidification of the molten steel when it comes into contact with the cold nozzle, which can cause blockage or unstable flow.
Reducing thermal shock damage: preheating can reduce cracks or spalling of the nozzle refractory material caused by sudden temperature changes.
Improving safety: to avoid molten steel splashing (for example, an un-preheated nozzle in contact with molten steel may cause explosive vaporization).
I. Preheating Methods
1. Gas/Natural Gas Baking
method:
Use a gas burner to directly bake the nozzle from below or the side, with a temperature of 1000–1200°C (depending on the nozzle material).
The preheating time is usually 30–60 minutes (longer for large ladles).
Advantages: Even heating, suitable for all types of nozzles.
Disadvantage: high energy consumption, attention must be paid to the alignment of the flame to avoid local overheating.
2. Electric Heating (Resistance/Induction Heating)
Method:
the nozzle is heated by a resistance wire wound around the nozzle or an induction coil, with precise temperature control (up to 1200°C or more).
Advantage: temperature can be controlled, no open flame, suitable for high cleanliness steel grades.
Disadvantage: high equipment cost, complex maintenance.
3. Preheating With Red-Hot Molten Steel (Auxiliary Baking)
Method:
A small amount of red-hot molten steel (or the remaining steel from the previous furnace) is used to quickly raise the temperature before the steel is poured.
Advantages: Saves time and is suitable for fast-paced production.
Disadvantages: Higher risk (strict operation is required to avoid molten steel splashing).
4. Combined Preheating
gas baking + electric heating: The temperature is quickly raised with gas, and then maintained with electric heating, to achieve both efficiency and stability.
