Karel Stransky

The Numerical And Experimental Investigation Of A Concasting Process

Solidification and cooling of a continuously cast steel slab and simultaneously heating of a mould is from the viewpoint of thermokinetics, a very complicated problem of non-stationary heat and mass transfer. This process is described by the Fourier-Kirchhoff equation, in a mould by the Fourier equation. The solving of such a problem is impossible without numerical models of the temperature field, not only of the concasting itself, while it is being processed through the caster, but of the mould as well. A three-dimensional (3D) numerical model of the temperature field of a solidifying concasting has been used. This model is able to simulate the temperature field of a concasting machine (caster) as a whole, or any of its parts. It is also able to solve current thermokinetic problems both globally and in detail. Simultaneously, together with the numerical computation, the experimental research and measuring have to take place. The experimental investigation was focused mainly on the temperature in the tundish, the temperatures of the walls of the mould and the surface temperatures within tertiary cooling zone (measured by means of thermocouples), on the surface temperatures of the slab under the mould (measured by means of pyrometers) and the metallurgical length of the concast slab using radio-isotope methods. The cooling intensity of individual cooling jets had to be conducted on the experimental laboratory device. Each jet had been measured separately on the hot plate-model, on which the hot surface of the slab, which is cooled by a moving jet, can be modeled. The temperatures measured beneath the surface of the modeling plate by means of thermocouples are converted to cooling intensities using an inverse task, which, in turn, are converted to the courses of the heat transfer coefficients using an expanded numerical model. This laboratory facilities is also capable of measuring the effect of radiation, which is dependent not only on the surface temperature but also on the actual quality of the surface. Experimental research and measuring have to take place not only to confront it with the numerical model, but also to make it more accurate throughout the course of the process. The similarity of the results attained from the computed and from the experimentally measured temperature field of the steel slab is very satisfactory.

Industrial Application Of Two Numerical Models In Concasting Technology

This paper deals with the causes of a transversal crack in a steel slab with a 1300x145 mm cross-section by means of two numerical models. Samples were taken from and around the crack in order to analyze the concentration, as well as the chemical heterogeneity y of the constituent elements and impurities. Simultaneously, the concentration of elements at the surface of the crack was measured after the crack was opened. The heterogeneity of elements was analyzed by the JEOL JXA 8600/KEVEX device. The measurement results were processed using mathematical statistics. The chemical heterogeneity of elements in the steel matrix around the crack, and at the crack surface, had been evaluated with the help of heterogeneity y parameters, i.e. the arithmetic mean of concentration, the standard deviation of concentration and the index of heterogeneity of the analyzed elements. The results proved that there was an internal crack initiating immediately below the solidus temperature and consecutively propagating.

The Optimization Of Concasting Using Two Numerical Models

Solidification and cooling of a continuously cast steel slab and the simultaneous heating of the crystallizer is. f~om the viewpoint of thermokinetics, a very complicated problem of transient heat and mass transfer. The solving of such a problem is impossible without a numerical model of the temperature field-not only for the slab while it is being processed through the entire concasting machine (CCM) but for the crystallizer as well. An original (one of two) three-dimensional (3D) numerical model of the temperature field of a concasting had been used. This model is able to simulate the temperature field of a CCM-either as a whole, or any of its parts. The experimental research and data acquisition have to take place simultaneously with the numerical computation, not only to be confronted with the numerical model, but also to make it more accurate in the course of the process. In order to apply the second original numerical model-a model of dendritic segregation of elements-it is necessary to analyze the heterogeneity of samples of the constituent elements and impurities in characteristic places of the solidifying slab. The samples are taken from places, which provide information on the distribution of elements under both standard and extreme conditions for solidification, where the mean solidification (crystallization) rate is known for points between the solidus and liquidus curves. Using this method, it is possible to forecast the occurrence of the critical points of a slab from the viewpoint of its susceptibility to crack and fissure. Verification of technological impacts of optimization resulting from both models is conducted on a real industrial CClM.

A Numerical Model of the Crystallization of Pure Aluminium

The model was originally designed to confirm and enhance the capabilities of experimental research in the crystallization of pure aluminium (99.99% Al), specifically to determine the zone of the occurrence of columnar and equiaxed crystals and the positions of the transition interface. The character of primary crystallization was investigated on a simple cylindrical sample, crystallizing in a cast-iron mould pre-heated to various temperatures. The experimental research comprised the measurement of temperatures using thermocouples, the evaluation of the experimentally acquired temperature gradients G, and the shift rate of the phase transition interface R. The numerical model had been developed to expand the limited experimental capabilities of the evaluation of G and R to every point of the longitudinal section, based on the investigation of the 3D transient temperature field within the system comprising the casting, the mould and ambient. This enabled the prediction of the character of the crystallization in greater detail.Copyright

Two Numerical Models for Optimization of the Foundry Technology of the Ceramics EUCOR

Corundo-baddeleyit material — EUCOR — is a heat- and wear-resistant material even at extreme temperatures. This article introduces a numerical model of solidification and cooling of this material in a non-metallic mould. The model is capable of determining the total solidification time of the casting and also the place of the casting which solidifies last. Furthermore, it is possible to calculate the temperature gradient in any point and time, and also determine the local solidification time and the solidification interval of any point. The local solidification time is one of the input parameters for the cooperating model of chemical heterogeneity. This second model and its application on samples of EUCOR prove that the applied method of measurement of chemical heterogeneity provides detailed quantitative information on the material structure and makes it possible to analyse the solidification process. The analysis of this process entails statistical processing of the results of the measurements of the heterogeneity of the components of EUCOR and performs correlation of individual components during solidification. The crystallisation process seems to be very complicated, where the macro- and microscopic segregations differ significantly. The verification of both numerical models was conducted on a real cast 350 × 200 × 400 mm block.Copyright

Two Numerical Models for Prediction of an Industrial Concasting Process

This paper introduces the application of two three-dimensional (3D) numerical models of the temperature field of a caster. The first model simulates the temperature field of a caster—either as a whole, or any of its parts. Experimental research and data acquisition take place simultaneously with the numerical computation in order to enhance the numerical model and to perfect it in the course of the process. In order to apply the second original numerical model—a model of dendritic segregation of elements—it is necessary to analyze the heterogeneity of samples of the constituent elements and impurities in characteristic places of the solidifying slab. The samples are taken from places, which provide information on the distribution of elements under both standard and extreme conditions for solidification, where the mean solidification (crystallization) rate is known for points between the solidus and liquidus curves. Using this method, it is possible to forecast the occurrence of the critical points of a slab from the viewpoint of its susceptibility to crack and fissure. Verification of the technological impact of optimization, resulting from both models, is conducted on a real industrial caster.Copyright

Numerical Optimization of the Method of Cooling of a Massive Casting of Ductile Cast‐Iron

An original application of ANSYS simulating the forming of the temperature field of a massive casting from ductile cast-iron during the application various methods of its cooling using steel chills. The numerical model managed to optimize more than one method of cooling but, in addition to that, provided serious results for the successive model of structural and chemical heterogeneity, and so it also contributes to influencing the as solidified microstructure. The file containing the acquired results from both models, as well as from their organic unification, brings new and, simultaneously, remarkable findings of causal relationships between the structural and chemical heterogeneity and the local solidification time in any point of the casting. Therefore the determined relations enable the prediction of the local density of the spheroids of graphite in dependence on the local solidification time. The calculated temperature field of a two-ton (500 × 500 × 1000) mm casting of ductile cast-iron with various methods of cooling has successfully been compared with temperatures obtained experimentally. This has created a tool for the optimization of the microstructure with an even distribution of the spheroids of graphite in such a way so as to minimize the occurrence of degenerated shapes of graphite, which happens to be one of the conditions for achieving good mechanical properties of castings of ductile cast-iron.

Cooling of a Massive Casting of Ductile Cast-Iron and Its Numerical Optimization

The numerical models of the temperature field of solidifying castings often observe two main goals: directed solidification and optimization of the technology. These goals can be achieved only if the deciding factors which either characterize the process or accompany it are analysed and their influence controlled. An original application of ANSYS, based on the numerical finite-element method, is applied. The numerical model simulated the forming of the temperature field of a two-ton 500×500×1000 mm casting from ductile cast-iron during the application of various methods of its cooling using steel chills. This model managed to optimize more than one method of cooling but, in addition to that, provided results for the successive model of structural and chemical heterogeneity, and so it also contributes to influencing the pouring structure. The file containing the acquired results from both models, as well as from their organic unification, brings new and, simultaneously, remarkable findings of causal relationships between the structural and chemical heterogeneity and the local solidification time in any point of the casting. This has established a tool for the optimization of the structure with an even distribution of the spheroids of graphite in such a way so as to minimize the occurrence of degenerated shapes of graphite, which is one of the conditions for achieving good mechanical properties of castings of ductile cast-iron.© 2009 ASME

The temperature field of a gravitationally cast ductile-cast-iron roller and its chemical and structural heterogeneity

The quality of the working rollers from ductile-cast-iron used for rolling rails is determined by the chemical and structural composition of the material of the rollers and the production technology. The requirements of the quality cannot be ensured without perfect knowledge of the course of solidification, cooling and heat treatment of the cast rollers as well as the kinetics of the temperature field of the casting and mould. An original application of ANSYS simulated the forming of the temperature field of the entire system. In the experimental investigation of temperature field, an original methodology for the measurement of the distribution of temperatures and heat flows in the roller-mould system had been developed and verified in the operation. The kinetics of the solidification has a measurable and non-negligible influence on the chemical and structural heterogeneity of the investigated type of ductile-cast-iron. Tying on to the results of the model of the temperature field of the cast rollers, an original methodology was developed for the measurement of chemical microheterogeneity. The structure of this cast-iron is created by a great amount of the transition form of graphite and small amount of globular graphite and also lamellar graphite and cementite, whereas the structure of the metal matrix is perlitic. The chemical and structural heterogeneity of the cast roller is therefore a significant function of the method of melting, modification and inoculation and the successive procedures of risering, casting and crystallization after cooling.

Numerical Models of Crystallization and Its Direction for Metal and Ceramic Materials in Technical Application

Structure of metallic and also majority of ceramic alloys is one of the factors, which significantly influence their physical and mechanical properties. Formation of structure is strongly affected by production technology, casting and solidification of these alloys. Solidification is a critical factor in the materials industry, e.g. (Chvorinov, 1954). Solute segregation either on the macroor micro-scale is sometimes the cause of unacceptable products due to poor mechanical properties of the resulting non-equilibrium phases. In the areas of more important solute segregation there occurs weakening of bonds between atoms and mechanical properties of material degrade. Heterogeneity of distribution of components is a function of solubility in solid and liquid phases. During solidification a solute can concentrate in inter-dendritic areas above the value of its maximum solubility in solid phase. Solute diffusion in solid phase is a limiting factor for this process, since diffusion coefficient in solid phase is lower by three up to five orders than in the melt (Smrha, 1983). When analysing solidification of these alloys so far no unified theoretical model was created, which would describe this complex heterogeneous process as a whole. During the last fifty years many approaches with more or less limiting assumptions were developed. Solidification models and simulations have been carried out for both macroscopic and microscopic scales. The most elaborate numerical models can predict micro-segregation with comparatively high precision. The main limiting factor of all existing mathematical micro-segregation models consists in lack of available thermodynamic and kinetic data, especially for systems of higher orders. There is also little experimental data to check the models (Kraft & Chang, 1997).