Normally, in continuous casting plants, the molten metal produced, for example from an electric furnace, or from a converter, is subjected to a series of pouring passages between containers, prior to being cast in the ingot mould to form ingots, slabs, bars, strips and others.
A typical example is given by the application of the technology of continuous strip casting in which the steel coming from the production oven is collected in a ladle, from which it is unloaded into one or more tundishes, each of which feeds one or more melts above two cooled, counter rotating crystallising rolls, which constitute the ingot mould in which the metal solidifies and exits in the form of finished product, for example a strip, a bar or otherwise. Between the tundish and the ingot mould there can also be provided an under tundish, or another discharging device, from which the liquid metal is dosed into the ingot mould.
It is known that the quality of the final product, and also the execution of the process itself can be compromised by the contact of air with the molten metal. For example, the oxygen in the air can combine with elements dissolved in the steel forming inclusions, which deteriorate the quality of the steel, as also with dissolved oxygen itself. In case the steel is used in continuous casting, for example in a dual roller plant, the oxygen combined with the iron can produce scale which deposits on the rollers, locally altering, amongst others, the heat exchange, with serious consequences for the final product. Nitrogen can also provoke the formation of precipitates which compromise the quality of the product.
In the containers into which the molten metal passes, there is generally maintained a protective atmosphere, generally through the feeding of an inert gas, for example argon.
The various passages of the metal from one container to another are critical, with regard to the problem of possible contamination with air, bearing also in mind that the various containers must be emptied in between, both for the normal movement during the metal production operation, as for example in the case of the tundishes, and to allow for the substitution of the parts in refractory material, such as, for example the discharging sleeves or tubes through which the molten metal flows, subject to rapid wear and corrosion.
Discharging devices in the known art are not easy to operate and require delicate operations to allow the approaching of two containers for joining. Sometimes the impacts produced during the coupling damage the parts of the discharging device. Therefore, the need is felt of providing discharging devices, to interpose between the various containers in which the molten metal passes, avoiding contact between the air and the metal and allowing a rapid and precise coupling between the containers, in addition to a likewise rapid uncoupling.