Seznam abstraktů 2023: POSTEROVÁ SEKCE A

One of the factors influencing the surface quality of castings is the resulting thermal expansion when silica sands are used. This is characterised both by its high value compared to other non-silica sands, and by its typical discontinuous behaviour, leading in many cases to defects such as veining or increased surface roughness, which further lead to increased costs of processing the castings or, in extreme cases, to scrap pieces. The amount of thermal expansion of silica sand is influenced by various factors, including granulometric composition and chemical purity. It is the SiO2 content of the sand that contributes significantly to the degree of dilation, and which can vary depending on grain size alone. Two silica sand samples from the same locality of origin with different mean grain sizes were evaluated. The granulometric composition as well as the SiO2 and impurity content were evaluated by SEM analysis and XRFS and their effect on the linear thermal expansion. The effect of grain size on the final SiO2 content was observed, with sands of the same origin with larger grains containing 1.3% more SiO2 and achieving 36.8% higher dilatation. This combination increases the susceptibility of the sand, and hence the resulting moulding mixture, to the formation of foundry defects from braked stress as veining.

To meet the increasing cleanliness requirements in conticast steel production, innovative solutions must be developed. The tundish, which serves as the final refractory-lined reactor, provides ample space to eliminate inclusions through optimization of the steel flow. The key component of the tundish is the impact pad, which determines the flow pattern of steel and is a crucial element of tundish metallurgy. To prevent the formation of dead zones and slag eyes in the slag layer surrounding the ladle shroud, the optimal steel flow within the tundish must facilitate the removal of inclusions through reactions at the steel-slag interface. Additionally, the flow must prevent excessive erosion of the tundish refractory lining. This study compares the standard impact pad with the spherical impact pad using physical modelling, evaluating the residence time and flow within the tundish at three different casting speeds.

The influence of varying thermal treatment conditions on reducing zinc and lead content from a steelmaking and blast furnace sludge was studied. The Waelz process in a laboratory rotary kiln was used for the experiments. It was found that the level of zinc and lead reduction strongly depends on used atmosphere and the reducing element used. A significant reduction of the zinc and lead content (well below 1 wt. %) was achieved at temperatures of 1000 °C and 1200 °C, respectively. A neutral atmosphere and high graphite content reduced the zinc and lead very efficiently. A nitrogen atmosphere caused the reduction of zinc and lead even without the use of an additional reducing agent; the carbon contained in the sludge was used for the reduction.

This article describes a method for processing of experimental data obtained on a physical model of an FDU (Foundry Degassing Unit). For different refining gas flow rates and rotor rotation speeds of the FDU unit, the concentration of oxygen removed was measured as a function of time. Many experiments have been carried out with different types of rotors and under various conditions. After examining the nature of the obtained data, a method was proposed to evaluate the performance of individual rotors in degassing at a particular gas flow at different rotor speeds. This method is based on the interpolation of several degassing curves in such a way that the resulting characteristics can be expressed by one parameter. This final parameter then makes it possible to quantify the effectiveness of degassing (refining ability). In this unique way, the degassing efficiency of different types of rotors can then be objectively compared. In addition, it is possible to use the thus obtained parameter to determine the expected time at which the desired drop in the concentration of the unwanted gas in the bath will occur. Attention is also paid to the possible deviation if the described approximation reduces a large amount of experimental data to a single parameter.

The preparation of the charge for steelmaking furnaces is a key area from the point of view of the quality of the produced steel. One of the most important components of the charge is the treated steel scrap (in general, you can say metal waste). Technologies such as shearing, crushing and briquetting are currently used to treat steel scrap. Among the most widespread and, at the same time, the most economical technologies for the treatment of steel scrap is the baling technology, which can be described as the pressing of steel scrap, which takes place in the direction of three axes at most and that axes are perpendicular to each other. This technology is realized by means of so-called baling presses. The design of the individual structural nodes of the baling press itself has a significant influence on the correct way of charge adjusting when using baling technology. The presented article will inform readers about the possibilities of determining selected design parameters of the baling press.

This research article introduces a methodology for studying the operational wear of experimental shaped parts of moulds for high-pressure die casting (HPDC) of zinc alloys. The study includes roughness analysis and geometric dimensioning and tolerancing (GD&T) based on a coordinate measuring machine (CMM) and 3D scanning to quantify the wear of the mould parts due to contact with the zinc alloy melt and solidifying castings during the HPDC process cycles. The research aims to improve the understanding of the mechanisms of mould wear in HPDC of zinc alloys if different types of steel grades and their production technologies are applied during a hundred thousand casting cycles. The results show roughness and geometrical changes on the surface of shaped parts of moulds made from H11steel grade conventionally, respectively additively manufactured by selective laser melting (SLM).
The results so far have shown that the shaped parts of the mould made of conventional H11 steel after 500,000 or additively manufactured H11 steels show the good shape and surface stability after 100,000 casting cycles. Until now, it has not been possible to determine the negative effect of the given HPDC process on the wear of the studied shape parts of the moulds using the above methods; the analyses will continue until their final wear. In parallel with evaluating the shape and surface of the shaped parts, these parameters are also assessed for the zinc alloy castings. However, the evaluation can't be squeezed into the required scope of this contribution. In the following research phase, also metallographic methods will be applied to study the quality parameters of both shaped mould inserts (after their wear) and castings (after different numbers of casting cycles) too. The final and tested methodology, in connection with other extensive outputs of the research and development carried out within the framework of the solved project, should be helpful for designers and manufacturers of shaped parts of moulds and for the own HPDC of zinc alloys.

This article presents technological issues related to operation of self-baking electrodes in a six-electrodes submerged arc furnaces during the process of smelting high-grade silicon alloys with iron and other elements by carbothermal reduction, carried out in Re Alloys ferroalloys plant.
Particular attention is paid to technological problems related to the use of Søderberg electrodes during start-ups of electric furnaces after shutdowns.
The impact of furnace shutdowns and start-ups on thermal conditions disturbance of electrode sintering process, formation of micro-cracks, and thus deterioration of mechanical strength of the electrode leading to increased risk of breaking, is presented.
Actual examples of electrode breaking during SAF start-up, causes of breakings and possible ways to avoid them are described in the article.

The basic procedure of secondary metallurgy is blowing liquid steel with inert gases. This treatment is applied in the ladle at the ladle furnace station. The main task of the injected gas is to homogenize the liquid steel both in terms of temperature and chemistry, and to capture and transfer non-metallic inclusions (NMIs) to the slag phase. NMIs have a significant impact on the quality of the steel produced. Their genesis may be related to the processes of steel deoxidation and desulphurisation, capture of slag particles by the liquid metal moving under it, and destruction of the refractory lining. In addition to the fact that NMIs are undesirable in the final product, their presence can cause causing disturbances in the subsequent stages of the production process. The effectiveness of the liquid steel blowing process in the ladle depends on many factors. The main of them is the energy of the injected gas stream, under the influence of which the hydrodynamic conditions for mixing liquid steel in the ladle are formed. As well as the size and number of gas bubbles that flow out, which determine the efficiency of refining liquid steel with NMIs.
The article presents the results of tests carried out on a laboratory stand equipped with a physical water model of a ladle. The research was aimed at determining the importance of the size of the active surface of the porous plug used when blowing argon into the ladle to the above-mentioned factors. The criteria for evaluating the effectiveness of the liquid steel blowing process were the minimum time of complete mixing of the model liquid in the ladle model and the degree of gas dispersion in the volume of the model liquid. The minimum mixing time was determined on the basis of the determined RTD curves, and the degree of gas dispersion in the liquid was determined on the basis of visualization tests.

Achieving a balance between strength, toughness and technological properties of cast iron requires knowledge of the relationships between local and macroscopic failure processes. High toughness is conditional upon the substantial dissipation of deformation energy during crack propagation and the initiation of ductile failure. In spheroidal graphite cast iron, toughness depends on the size distribution of these particles, their volume fraction, and the strength of the ferritic matrix/particle phase boundary. The proposed model of fracture surface formation shows how nucleation deformation depends on the local characteristics of the cast iron, graphite particle size, and the strength and energy of the phase boundary. Local fracture deformation during cavity coalescence is most strongly affected by the geometric characteristics of the structure, the spatial distribution of particles, their volume fraction in the matrix, and also the strengthening characteristics of the matrix. The model of fracture surface formation was successfully tested on commercially produced ferritic spheroidal graphite cast iron. The criterion of deformation energy equilibrium was used to predict nucleation deformation and deformation during cavity coalescence. The model can be applied in designing optimized graphite particle size distribution and developing optimized technological parameters for cast iron production.

This article is aimed at obtaining new and unique knowledge in the field of additively manufactured shaped parts of molds within their operational application in high-pressure casting of aluminum alloy castings. Part of the work is the mapping of the service life of conventional and additively produced shapes parts of molds. The evaluation of operational experiments was focused on mapping the life cycle by the help of 3D measurements and contactless scanning. Within the text, attention is also paid to the implementation of a multidisciplinary approach related to quality control, material and metallographic analysis to verify the application possibilities of additively manufactured shaped parts of molds in the operating conditions of a Die-casting foundry.

AISI H13 is commonly used for tooling, requiring higher wear resistance, thermal fatigue resistance or hot toughness. Such examples include forging dies, plastic moulds, hot shear blades, high-pressure die casting, and extrusion dies. Thus, thermal conductivity is one of the more important factors for hot work tools. Typically, the work cycle of a hot work tool designed for forging consists of four main phases: the forging stroke, with which the die imparts its shape onto the part, a brief pause while the die is reset to its original position, a lubrication phase, and a post lubrication dwell phase. During the forging phase, a significant amount of heat is transferred to the die while it is in contact with the part. This heat must then be dispelled for the part to return to a working temperature. While somewhat different, other hot work processes mentioned above are similar in that the hot work tool gets heated to a high temperature due to the contact with the object of deformation. The process of additive manufacturing (AM) promises better, more efficient tool production with features like conforming cooling channels, which would reduce the thermal fatigue of tools, prolonging tool life. However, the powder bed fusion (PBF) method creates a columnar microstructure, which has a detrimental effect on the thermal conductivity of H13 tool steel. Our investigation focused on the beneficial effect of heat treatment, specifically annealing at different temperatures, on the thermal conductivity of AM-produced H13 parts.

The main topic discussed in this work is the reduction of hydrogen content in high grades of steel for the production of seamless pipes using processes of secondary metallurgy and vacuum degassing. The aim of the thesis is the statistical analysis of operational data with a follow-up to the preparation of a statistical model for calculating the final hydrogen content in steel after processing in a vacuum. The preparation of the model consisted in the analysis of operating conditions from available production datas, statistical evaluation of individual input parameters and their mutual dependence and impact on melt processing. From the results of the analytical part, the necessary inputs for the preparation of a prediction model were obtained, which enables the simulation of the resulting values of the final hydrogen content in the melting on the key´s input parameters defined by the analysis. The result of the predictive statistical model is the approximate expected final hydrogen content, including the values of the other variables that enter into the process.