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1

Two numerical models of a slab caster

Štetina J., Mauder T., Kavicka F., Franek Z., Sekanina B.

Prace Instytutu Metalurgii Żelaza

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2009

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T. 61, nr 5

131-136

EN

Optimization and control of production of steel slabs on real casters, with the aim of achieving the maximum possible savings and product quality, is unthinkable without perfect knowledge of the course of solidification and cooling, which must be known with the aid of an on-line model of the transient temperature field of the concasting in real time. The on-line model is the basis for establishing the prediction system. An application server with its own database is established for acquiring the data files from three sources – from the steelworks information system, from the on-line model of the temperature field and the data on the quality of the final products (i.e. sheet-steel) from the rolling mill information system. A data warehouse is created of which the data will be processed statistically. Recommended limit values of the deciding parameters are established. Based on these limit values and the current state of the caster displayed on the computer screen in the control room, a new system is be designed for the control and correction of its operation. In the final step, a system for comprehensive prediction is established first. This system includes only really occurring defects. It must also be possible to enter new defects, including a definition of their cause/origin. Modern mathematical & statistical methods and artificial intelligence methods, based on knowledge acquisition from data, are used to predict defects.

2

Numerical model of heterogeneity of the ductile cast-iron

Stransky K., Kavicka F., Dobrovska J., Stetina J., Sekanina B.

Prace Instytutu Metalurgii Żelaza

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2009

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T. 61, nr 5

137-141

EN

An original three-dimensional (3D) model of solidification is used to describe the process of solidification and cooling of massive 500×1000×500 mm cast-iron castings. The castings are cast in sand moulds. The calculated mode of the kinetics of the temperature field of the casting is verified during casting with temperature measurements in selected points. The sizes and positions (xi, yi, zi, where i = 1,2,3 is the number of samples taken) of the experimental samples are exactly defined and corresponding with the decreasing rate of solidification. The experimental samples – 15 mm in diameter and 12 mm high – are metallographically analysed and also in terms of heterogeneity of the chemical composition. The coordinates xi, yi, zi characterise approximately – within an accuracy of +/- 5 mm – the centres of the samples. Successively, the local solidification time (i.e. the time the specified position of the casting, defined by the coordinates xi, yi, zi, remains within the temperature range between the liquidus and solidus) is also calculated using the 3D model. The following dependences are later determined according to the experimental and calculated data: the average size of the graphite spheroids rg, graphite cells Rb and the average distances among the particles of graphite Lg – always as a function of the local solidification time [xi, yi, zi]. Furthermore, it has been found out that the given basic characteristics of the structure of the cast iron rg, Rb and Lg are directly proportional to the logarithm of the local solidification time. The original spatial model of solidification can therefore be used in its first approximation for the assessment of the pouring structure of massive cast-iron castings.

3

A concast billet caster and electromagnetic stirring of the melt

Stransky K., Kavicka F., Sekanina B., Stetina J., Dobrovska J., Stransky L.

Prace Instytutu Metalurgii Żelaza

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2009

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T. 61, nr 5

142-145

EN

Electromagnetic stirring (EMS) suppresses the growth of columnar crystals of billets and reduces the tendency to cracking during casting and at low temperatures. A caster was used for the testing of two induction stirrers – one on the actual mould and the other beneath the mould – to determine the effect of EMS on the formation of the structure of non-alloy steel. As part of these tests, certain parts of the billets had been cast without the use of stirrers and other parts underwent alternate switching on and off of the stirrers for as many as nine combinations of modes. Samples were taken from the sections of these billets, fine-ground and etched in order to make the dendritic structure visible. The mode with the highest effi ciency was when both stirrers ran simultaneously. The growth of the columnar crystals, which pointed inward, was limited to 1/4 -to- 1/3 of the length of the case when there was no stirring. Experimental research was also confronted with results acquired from the application of the models of the temperature field and chemical heterogeneity and the physical-similarity theory. Statistical monitoring of the quality of concast billets has proven that stirring significantly reduces the occurrence of defects – in this case cracks.

4

Numerical model for the calculation of the temperature field of a concast billet

Stetina J., Kavicka F., Sekanina B., Bazan J., Dobrovska J.

Prace Instytutu Metalurgii Żelaza

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2006

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T. 58, nr 4

102-104

EN

Solidification and cooling of a continuously cast steel billet is a very complicated problem of transient heat and mass transfer. The solving of such a problem is impossible without numerical model of the temperature field, not only of the concasting itself, while it is being processed through the caster but of the mold as well. This process is described by the Fourier-Kirchhoff equation. An original 3-D numerical off-line model of the temperature field of a caster has been developed. It has graphical input and output - automatic generation of the net and plotting of temperature fields in the form of color iso-therms and iso-zones, and temperature-time curves for any point of the system being investigated. This numerical model is capable of simulating the temperature field of a caster as a whole, or any of its parts. Experimental research and data acquisition have to be conducted simultaneously with the numerical computation - not only to confront it with the actual numerical model, but also to make it more accurate throughout the process. After computation, it is possible to obtain the temperatures at each - node of the network, and at each time of the process. The utilization of the numerical model of solidification and cooling of a concasting plays an indispensable role in practice. The potential change of technology - on the basis of computation - is constantly guided by the effort to optimize, i.e. to maximize the quality of the process.

PL

Krzepnięcie i chłodzenie wlewków ciągłych o przekroju kwadratowym stanowi bardzo złożony problem, jeżeli chodzi o wymianę ciepła i przenikanie masy. Rozwiązanie takiego problemu jest niemożliwe bez posiadania numerycznego modelu obliczania rozkładu temperatury nie tylko w trakcie procesu odlewania ciągłego, gdy pasmo stali przechodzi przez urządzenie do odlewania, ale również w samym krystalizatorze. Ten proces opisuje równanie Fouriera-Kirchkoffa. Opracowano autorski trójwymiarowy model numeryczny do obliczania w trybie off-line rozkładu temperatury w urządzeniu do odlewania. Posiada on graficzne wejście i wyjście - automatyczne tworzenie sieci i nanoszenie rozkładów temperatury w postaci kolorowych izoterm i izostref oraz tworzenie krzywych zależności temperatury od czasu dla każdego punktu badanego układu. Ten model numeryczny może symulować rozkład temperatury urządzenia do odlewania w całości lub dla dowolnej jego części. Wraz z obliczeniami numerycznymi należy jednocześnie przeprowadzić badania eksperymentalne oraz pobieranie danych - nie tylko po to, aby je skonfrontować z rzeczywistym modelem numerycznym, ale również w celu zapewnienia większej dokładności obliczeń w trakcie całego procesu. Po wykonaniu obliczeń możliwe jest uzyskanie temperatur dla każdego węzła sieci w dowolnym momencie procesu. Zastosowanie modelu numerycznego krzepnięcia i chłodzenia wlewków ciągłych w praktyce staje się niezbędne. Potencjalna zmiana technologii - na podstawie obliczeń - nieustannie wiąże się z działaniami mającymi na celu zoptymalizowanie, t j. zmaksymalizowanie jakości procesu.

5

Zagadnienia związane z przepływem stali przez filtry ceramiczne

Stransky K., Bazan J., Buzek Z., Dobrovska J., Kavicka F.

Hutnik, Wiadomości Hutnicze

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2006

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Vol. 73, nr 11

486-490

PL

Znaczenie filtracji ciekłych metali filtrami ceramicznymi. Wielkości hydrauliczne przy przepływie cieczy przez filtr. Równanie Bernoulliego i jego zastosowanie w opisie filtracji ciekłych metali. Zjawiska fizyczne związane z przepływem cieczy przez kapilarę. Prawo Hagena-Poiseuilla i Darcy’ego. Charakterystyka przepływu laminarnego i turbulentnego. Bezwymiarowe kryteria charakteryzujące przepływ ciekłych metali przez filtr ceramiczny i podstawowe mechanizmy filtracji ciekłych metali.

EN

Importance of metal melts filtration by ceramic filters. Hydraulic conditions at melt flow through filter. Bernouilli equation and its use for description of metal melts filtration. Physical regularities of melt flow in capillary. Hagen-Poiseuille law and Darcy’s law. Characteristics of laminar flow. Attributes of turbulent flow. Dimensionless criteria characterized melt flow through ceramic filter. Principal mechanisms of metal melts filtration.