Method for Determining the Time Constants Characterizing the Intensity of Steel Mixing in Continuous Casting Tundish

Abstract

A common method used in identification of hydrodynamics phenomena occurring in Continuous Casting (CC) device's tundish is to determine the RTD curves of time. These curves allows to determine the way of the liquid steel flowing and mixing in the tundish. These can be identified either as the result of numerical simulation or by the experiments -as the result of researching the physical models. Special problem is to objectify it while conducting physical research. It is necessary to precisely determine the time constants which characterize researched phenomena basing on the data acquired in the measured change of the concentration of the tracer in model liquid's volume. The mathematical description of determined curves is based on the approximate differential equations formulated in the theory of fluid mechanics. Solving these equations to calculate the time constants requires a special software and it is very time-consuming. To improve the process a method was created to calculate the time constants with use of automation elements. It allows to solve problems using algebraic method, which improves interpretation of the research results of physical modeling.Keywords: physical modelling, flow of fluids, RTD curves Powszechnie stosowaną metodą w identyfikacji zjawisk hydrodynamicznych, zachodzących w kadzi pośredniej urządzenia COS, jest wyznaczanie krzywych czasu rezydencji RTD. Krzywe te umożliwiają określenie sposobu przepływu i mieszania się ciekłej stali w kadzi pośredniej. Mogą one być wyznaczane zarówno metodami numerycznymi jak i w sposób eksperymentalny, jako wynik badań na modelach fizycznych. Szczególny problem stanowi ich obiektywizacja w przypadku badań fizykalnych. Konieczne jest wówczas precyzyjne wyznaczenie stałych czasowych charakteryzujących badane zjawiska na podstawie danych uzyskanych z pomiaru zmiany stężenia znacznika w objętości cieczy modelowej. Matematyczny opis wyznaczonych krzywych opiera się na złożonych równaniach różniczkowych, sformułowanych w teorii mechaniki płynów. Rozwiązywanie tych równań, w celu wyznaczenia wspomnianych stałych czasowych, wymaga specjalistycznego oprogramowania oraz jest czasochłonne. Aby usprawnić ten proces opracowano sposób wyznaczania stałych czasowych z wykorzystaniem metody elementów automatyki. Umożliwia ona rozwiązywanie problemu metodami algebraicznymi, co zdecydowanie usprawnia interpretację uzyskiwanych wyników badań modelowania fizycznego.

Study of the Influence of Intermix Conditions on Steel Cleanliness

“…Due to this being a standard Intermix evaluation methodology [12][13][14][15], the limit of the standardized composition of the main transition element is generally considered to be 0.9 at the end of the transition zone under the stricter assessment criterion (10/90). The area for achieving this limit value is shown in Tables 3 and 4, and for the standard practice in samples 5 and 6, and for the ULT practice in samples 4 and 5.…”

“…The measurement of F-curves on a physical model is used to describe the transition zone in the case of Intermix casting [10,11]. The tracer, 150 mL of an aqueous solution containing 10% KCl and 1% KMnO 4 , was dissolved in the entire volume of the tundish, and when the required level of water in the tundish corresponding to the beginning of the transition was reached, the tundish was filled with pure water, resulting in a change in the concentration of the tracer at the tundish output, which very clearly defines the beginning and the end of the transition zone under specific conditions [12][13][14][15][16]. The water flow was scaled using Froude s dimensionless number [17].…”

“…An important step, apart from the preparation of the operating tests themselves, was also the choice of the most appropriate method for evaluating the results obtained, regarding the change in chemical composition in the transient area of the slab for the given conditions. This choice was based on our previous knowledge and experience in this area of research, and consequently, the methodology of determining the dependence of the change in the so-called normalized composition by considering the mass of the cast steel in each mold from the moment the ladle was opened with a different steel grade was used [12,13].…”

Archives of Metallurgy and Materials

“…To calculate concentrations, following dependency was applied [45]: Summary presented in Fig. 9 demonstrates high compliance between the physical experiments (water model) and results from numerical calculations based on CFd.…”

“…To convert calculations on the gas flow volumetric streams from the real conditions occurring in the model into the model conditions, the Froud criterion was used [43][44][45]:…”