Inclusion Removal and Inclusion Flotation technique from Tundish
The fluid flow pattern in the tundish has been studied with the help of physical and mathematical models. Development of mathematical models for studying fluid flow pattern in tundishes, to study inclusion removal and inclusion flotation have helped us to understand the functional role of the steel making tundish in the continuous casting process and its significance in producing clean steel casting are described as below:
(a) Tundish is an intermediate link between ladle and mold of continuous casting. Incoming melt discharges from the outlet at the same rate and at the required temperature.
(b) Tundish consists of an inlet, outlet, weir, and dam. Flow control devices affect the inclusion flotation inside the tundish.
(c) Incoming liquid steel stream coming out of the ladle is prevented from coming in contact with air with the help of a long nozzle immersed into the steel melt in the tundish commonly known as the refractory shroud.
(d) The significance of the long nozzle into the tundish reduces slag in the steel melt.
(e) Flow control devices in the tundish increase the mean residence time and help in removing the inclusion particle.
Effect of Height and Position of Dams on Inclusion Removal in a Tundish.
Numerical investigation of the inclusion removal process in a tundish has been carried out for bare tundish as well as for tundish with dams of different heights and at different locations. Two geometrical parameters such as dimensionless heights (ratio of dam height to tundish height) and dimensionless distance (ration of the distance of dam from inlet to tundish half-length) have been varied to see its effect on the inclusion removal rate in a tundish. It was observed that the inclusion removal tendency increases with the use of dams as compared to the bare tundish. It was also found that at a particular position of the dams, inclusion removal tendency increases with an increase in dam heights. However, it was found that for a particular combination of dam heights, as the dams were moved closer to the outlets (with an increase of dimensionless distance) the inclusion removal tendency was seen to decrease. Especially, when the dams are moved closer to the outlets, the presence of recirculation zone near the far outlet region is expected to increase the tendency of inclusions passing through the far outlet and hence it reduces the inclusion removal. After the study, it was found that the maximum difference of the number of inclusion particles from all the outlets was observedincase of the dimensionless heights of the near, middle and far dams being 0.52, 0.44 and 0.35 and dimensionless distances of these dams from the inlet being 0.09, .32 and 0.66 respectively.
A Mathematical modeling study of Inclusion Removal from Liquid Steel by Gas Bubbling in Casting Tundish.
The nonmetallic inclusion removal mechanism by argon bubbling effects in a continuous casting tundish operation is analyzed analytically and by the help of mathematical simulation involving a great number of variables. After analyzing the alumina inclusion removal rate by bubble attachment and by bubble fluid dynamics effects the following conclusions can be drawn.
(Where db represents the diameter of inclusions, TI represents total inclusions and RE represents removal rate of inclusions).
(1) The results show that the film rupture between the inclusion and the bubble is easier by the formation of a hole and this mechanism has a dependency on the inclusion type.
(2) The results show higher TI values. The work demonstrates that the model used to calculate TI is important and therefore smaller attachment limits are obtained. At the same time, higher values of TI lead to a smaller percentage of the alumina inclusion collection probability.
(3) The removal rate RE shows that it depends on other variables. Those variables show an indirect effect on RE, which represents the controlling variable on the inclusion removal by bubble attachment.
(4) The results obtained depict that very small bubble diameter is required to achieve acceptable RE percentages.But in the real process, this consideration is almost impossible to get, and the real bubble diameters come around 10 mm which results in a very inefficient inclusion removal process in the tundish by the process of bubble attachment.
Inclusion Removal in Tundish with the help of A Physical Model
Under the experimental conditions investigated with the physical model, the following observations and conclusions can be made:
1) The gas curtain acts as a filter or barrier and promotes an upward flow of liquid favoring separation and removal of inclusions. This effect is more pronounced with the increased proximity of the gas curtain to the ceramic nozzle.
2) It was found that taking into account all combinations of flow, position, and dimensions of the porous plug, a reduction of the piston flow fraction resulted in comparison to a tundish without a gas injection system.
3) Larger porous plug sizes and larger particle sizes resulted in better flotation and separation.
4) Basic porous blocks seem to be more effective than the acid ones. The reason can be attributed to the pore structure and consequent
resulting size of bubbles.
5) Bubbling of gas around the strand is also beneficial to the inclusion removal. However, the efficiency is 25% lower than the one obtained
with the porous block.
6) The results of the proposed simplified mathematical model for inclusion removal by bubbling are in reasonable conformity with the experimental results.
