Lenka Řeháčková

Experimental verification of hematite ingot mould heat capacity and its direct utilisation in simulation of casting process

Heat capacity of alloys (metals) is one of the crucial thermophysical parameters used for process behaviour prediction in many applications. Heat capacity is an input variable for many thermodynamical (e.g. Thermocalc, Pandat, MTData, …) and kinetic programs (e.g. IDS-Solidification analysis package, …). The dependences of heat capacity on common variables (temperature, pressure, ...) are also commonly used as the input data in software packages (e.g. ProCast, Magmasoft, ANSYS Fluent, …) that are applicable in the field of applied research for simulations of technological processes. It follows from the above that the heat capacities of materials, alloys in our case, play a very important role in the field of basic and applied research. Generally speaking, experimental data can be found in the literature, but corresponding (needed) data for the given alloy can very seldom be found or can differ from the tabulated ones. The knowledge of proper values of heat capacities of alloys at the corresponding temperature can be substantially used for addition to and thus towards the precision of the existing database and simulation software. This study presents the values of Cp measured for the hematite ingot mould and comparison of the measured data with the Cp values obtained using the software CompuTherm with respect to simulation of technological casting process.

Registration of rheological properties of liquids by electromagnetic levitation

The presented paper is focused on possibilities of research of rheological properties of liquids with use of the device based on the principle of electromagnetic levitation. The device works on the principle of damping of the levitated body vibrations by the liquid. Levitation is ensured by feedback control of the magnetic field using an optical barrier. Vibrations are excited by controlled interruptions of electromagnetic field. Thanks to this principle it is possible to investigate the liquid of non-Newtonian character, as well as liquids susceptible to clinging on spindles of rotational viscometers. The equipment was calibrated using silicate oil standards and its performance was compared with commercially used models of viscometers Anton Paar FRS1600 (viscosity range 3 mPa s–20 Pa s, precision 0.5%, temperature range 300–1600°C) and Brookfield DV-III Ultra (viscosity range 1.4 mPa s–20 Pa s, precision 1%, temperature range 100–1600°C).

On Mathematical Modelling of the Diffusion Characteristics in the close Vicinity of Two Steels Welded Joint

This paper deals with the quantitative evaluation of temperature and time effect on the concentration distribution of the substitutive elements in the vicinity of the welded joint. The calculations were performed for the weld of two different steels. The measurement of the concentration profiles of the elements in the weld was evaluated by the numerical optimalisation methods using the 2nd Fick’s law. The output of calculations defines quantitatively two terms: diffusion and penetration layers.

Assessment of Heterogeneity of Welded Joint of Two Different Metals by Modeling of Diffusion of Substitution Elements

The paper presents original methodology for assessment of heterogeneity of welded joint by measurement of concentration profiles of substitution elements in three straight lines in a plane perpendicular to the weld interface. The weld joint is formed by low-alloyed CrNiMoV steel and low-alloy silicon steel. Three concentration profiles are evaluated by modeling of diffusion based on solution of the 2nd Fick’s law. Primary goal of evaluation consists in assessment of chemical heterogeneity in the narrow area on both sides of the weld joint on the basis of their mutual position. Experimental data are optimized by original adaptation of the Levenberg–Marquardt’s algorithm of non-linear regression. Modeling comprises also determination of diffusivities and graphical representation of their temperature dependencies. The paper deals with diffusion of silicon as an example of many other investigated elements.

On Mathematical Modelling of Substitution Elements Diffusion in the Neighbourhood of Welded Joint of Steels

This paper deals with new approach of measurement of the concentration profiles, concerning the redistribution of substitution elements in close vicinity of welded joint of two different steels. These concentrations have been measured in three straight lines in a plane perpendicular to the weld interface. The concentration profiles have been evaluated from experimental data by modelling of diffusion based on 2nd Fick’s law. Original computation program for nonlinear regression was evolved based on Levenberg - Marquardt`s algorithm for evaluation of diffusivities and other quantities. Three groups of measured data enable variations in methodology of their processing. If each group is processed individually then the possible differences in mutual position of concentration profiles offers the view on chemical heterogeneity of welded joint.