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ОРИГИНАЛ ПЕРЕВОД Колесник Е. В.
Steel flow optimization in five - standart tundish
(Pindor,J.- Michalek, K.-Cieslar, M.-Bednaru)
The research of steel flow in five strand asymmetric tundish of CCM No.1 has been carried out using
cold physical modeling. The model of tundish has been on the been made on the scale 1:5 and then has
been studied the character of flow and then has been studied the character of flow and residence times
for “the basik operational case”. We have studied also the change of this flow during some emergency
cases (deflection of shroud nozzle, closure of some casting strand). We have also evaluated the incline
of impact pad and the influence of dam installation with the aim to suggest the placement, with the aim
to suggest the placement, with under operational conditions for increasing the quality of steel.
The fluid visualization in model was made by injection of the ladle shroud. For the objective evaluation
of residence times we have used the method of measuring changes of measuring changes of conductivity of liquid
in critical points of tundish after injecting KCI solution. On the best of model study results we have suggested
final configurations of inner tundish arrangement, with the location of dams in the inner area of tundish
separating impact place from other areas of tundish.
The suggested layout equalized the residence limes of all nozzles, especially in relation to nozzle No,1,
which is in the greatest distance from impact area. We have'also eliminated short circuit (low towards the nozzles
No.3 and No.4 and decreased dead volume, which existed in the area above nozzle No.1.
Putting this arrangement into practice substantially decreased heat number with regulation lost in the
beginning or during of casting from 12,4 to 3,6 %, which is relative decrease more than 70 %. This version of
inner arrangement is used in TZ, a.s. as a standard for more than 6 years.
In the setting of five-strand tundish in TZ, a.s we have tested the
possibility of steel filtration both by foam and channel ceramic filters. These filters were mounted into
vertical baffle in the tundish. We have tested filters based on Al2O3 -SiO2. ZrO2-SiO2. Our hitherto results
are unsatisfactory, the filters gradually degraded during casting of sequences and after casting we have found
out, that the filters are eroded. It seems, that foam filters based on pure ZrO2 stabilized by MgO are suitable
for (his type of usage. We are going to use filters made by company FOSECO.
Important and perspective tool for further increasing cleanliness of continuously cast steel is using baffles
and inert gas bubbling by porous blocks. One particular difficulty for introduction of this technology into
practice is the necessity to optimize the place of gas entry into steel. It is also necessary to optimize rate
of inert gas flow so that the maximal efficiency of non-metallic inclusion elimination ,would be achieved and at
the same time preserve the optimal steel flow character, which also has great influence on steel quality.
On the basis of the facts mentioned above we have decided to evaluate the utility value and efficiency of
this technology. We have made extensive research by means of physical modelling. On the basis of model research
results we have suggested specific operating arrangement of multi-holes baffles and porous blocks with defined
porosity for bubbling of argon for the whole tundish. The baffles with bubbling elements were located between the
impact pad and casting strands No.3 and No.4. We have suggested also reduced version to be able to compare the
influence of this technology on steel quality with the usual operating results. Multi-holes baffle and argon
bubbling were located between impact pad and casting strand No.4, the other side was left unchanged in the
original configuration commonly used for casting- see.
At first, the refractory beam with inbuilt circle porous blocks was used for argon bubbling.
Later we have used refractory pad with porous longitudinal beam. Then we have used monolithic multi-holes
baffle with longitudinal porous beam. The prerequisite for design of porous beam was the required rate of
argon flow from 5 to 10 l.min-1, These beams have undirected porosity and are made from materials based on AI2O3.
We have cast more than 60 heats of steel grade TZ C70K (tire cord steel) with the above mentioned
version of tundish inner arrangement with the use of multi-holes baffle and argon bubbling.
The assessment of this technology influence on steel cleanliness has been made for wire rod. The
method BEKAERT GA-03-02 was used for evaluation of amount and size of undeformable inclusions with the
use of number of penalty points. We have focused on the undeformable inclusions because these inclusions
are in steel grade TZ C70K one of the main causes of eventual fragile fracture during drawing and exploitation
under cyclical and dynamical stress.