Pouring molten steel into a high-tech and expensive continuous casting machine is no easy process and requires a variety of steps. This is because the steel, which is a combination of iron and a small amount of carbon, needs to be as pure and as homogenous as possible in order to achieve the desired grade.
In the continuous casting process, the steel is melted in a furnace at temperatures of up to 2,500F and then poured into a small tundish, which acts as the intermediate vessel between the steel’s molten form, and its entry into the moulds of the continuous caster.
The tundish is a crucial part of the continuous casting process and is responsible for maintaining the correct level of temperature and alloy composition of the steel. The steel is slowly poured into the tundish and allowed to flow through a system of holes and runners, where it is then fed continuously into the multiple moulds of the caster.
Beyond setting up the correct environment prior to pouring, the steel must also be monitored and tested while it is being cast and the tundish technician ensures that the minimum levels of impurities and alloy composition remain within the desired range.
It is not possible to pour boiling steel into a continuous caster, as the burnout of the tundish level would be immense and this is why the steel must be cooled back down to a pourable temperature. This is achieved by using a DC power source to generate an electromagnetic field which induces eddy currents against the steel’s evaporation. This has the dual effect of reducing the boiling temperature of the steel and also enabling more uniform cooling - a process known as electroslag remelting.
The molten steel is then transferred to either a ladle, sometimes referred to as a heat treatment furnace, or a tundish furnace for reheating and homogenisation prior to entering the tundish. Once the steel reaches the tundish it is rapidly cooled, stirring and agitation are used to ensure a homogenous product.
The steel is then poured into the moulds of the continuous caster, this part of the process known as continuous casting also allows for the flow of nitrogen in order to reduce the amount of oxygen taken up by the steel and thus prevent the formation of oxide inclusions.
The caster is then operated in a manner to ensure the correct steel tensile strength and form. This involves altering the filling, solidification and stretching rates of the steel within the caster in order to obtain the desired product.
Throughout the entire casting process, the tundish is a vital component of the caster and acts as the first stage of the cooling process to make the steel more pourable, as well as allowing for several treatments like heating, stirring and nitrogen introduction prior to pouring.
As a result of all these steps, the steel has then been cooled, reheated and homogenised within the tundish and poured into the caster in order to obtain its desired form and grade.
The whole process above highlights why it is not possible to pour boiling steel into a continuous caster and also gives an insight into why a tundish is a crucial component of a caster. Without the tundish, the steel would be unable to achieve the desired grade and form.
