The Master’s thesis was conducted under the project FR-TI1/070 “Optimalization of heavy steel casting manufacture” in cooperation with ŽĎAS a. s. foundry. It evaluates rate of conchoidal fracture in samples extracted from experimental castings. The testing bar for the static tensile test were extracted from thermal axis of casting. The research part describes ways of deoxidating the liquid metal and usage of separate deoxidating chemical parts, followed by summary of research knowledge on conchoidal fractures. In the practical part, the process of sample evaluation is described. The conchoidal fracture, the surface of which was evaluated on the fracture surfaces, influences mechanical qualities of cast steel. Simultaneously, impacts of metallurgical factors on rate of conchoidal fracture were examined

This diploma thesis is focusing on possibilities of influencing casting’s structure of nickel superalloy Inconel 713LC by force effects caused by vibration and rotation during crystallization. In this research were cast three test castings of turbine wheels with different solidification conditions that have affected the size and distribution of the grains. The aim was to compare the different microstructure and macrostructure of castings and then compare the dependence of grain refinement on mechanical properties. Changes in the structure were analyzed by means of light and electron microscopy methods after the fracture of test bars.

This master thesis deals with structural design of pendulum for single toggle jaw crusher DC 110x70 and consists of several main parts. The first part focuses on the processing of mineral materials, especially on the process of mechanical uncoupling. The second part compares main characteristics of single toggle and double toggle jaw crushers. The third part deals with the structural nodes for the crusher DC 110x70. Another part is consisted of two variants for the pendulum construction with a comparison of the advantages and disadvantages. For the selected variant is carried out the stress control using Finite element method (FEM) in the program I-DEAS. The last part focuses on the positioning an exit slit for designed pendulum.

This master thesis will cover the possibility of using directed gassing of Al-Si alloys in a high pressure die casting foundry. As a control gas, rotary degasser with gaseous 20 % H2 in N2 as a medium was used. Castings were casted via high pressure die casting machine. The aim of this research is to compare internal defect such as porosity or shrinkage of a casts made from degassed and control gassed melt.

The goal of this thesis is to examine a possible influence of the water soluble cores on the microstructure of commonly used aluminum alloys AlSi7Mg and AlSi10Mg in the lost wax technology. This thesis only deals with the changes of the eutecticum on the contact surface between the metal and the core and its surroundings where interactions can appear between the core based on the alkali salts NaCl and KCl and the alloy modified by sodium or strontium. The experimental part investigates the influence of the alkali salts on the modification additives and the modification of the structure itself.

The thesis focuses on the process of production of castings in the company ŽĎAS, a.s. and its methods for implementing customer's requirements. The goal was to create a Work Flow diagram of technical preparation of production based on the company's internal directives. The next step was to compare it with the actual situation represented by a case job and to make a conclusion. The customer's requirements for the case production order included increased level of control and purchasing weld-on parts. The incorporation process for these requirements was not described by the original Work Flow and was the subject of its new revision. For its better practical application the Study contains business and organizational structures of ŽĎAS, a.s.

ZELNÍČKOVÁ Marta: Optimizing of heat treatment of casting produced by SEED method. This work deals with designing optimum heat treatment method for casting alloy AlSi7Mg0,3, cast by SEED. Different temperature and times are tested in regimes of heat treatment, mechanical properties are determined with dependence of on the heat treatment method and optimal temperature regime is determined from the detected values.

Continuous casting is an important process to transform molten metal into solid. Arrays of spray nozzles are used along the process to remove heat from the slab letting it solidify. Efficient and uniform heat removal without slab cracking is desired during steel continuous casting, and air-mist sprays could help to achieve this goal.Air-mist nozzles are one of the important keys for determining the quality of steel as well as energy consumption for pumping the water. Based on industrial data, it is estimated that a 1% reduction in scrapped production due to casting related defects can result in annual savings of 40.53 million dollars in the U.S. Computational simulations studies can minimize defects in steel such as cracks, inclusions, macro-segregations, porosity, and others, which are closely related to the heat transfer between water droplets and hot slab surface.<div><br></div><div>Conducting multiple spray experiments in order to find optimum operating conditions might be impractical and expensive in some cases. Thus, Computational Fluid Dynamics (CFD) simulation is aimed to be used for simulating the air-mist spray process. Because it is a challenging process due to strong air and water interaction, then numerical models have been developed to simulate water droplets. The first model involves air and water phases which then are transformed in single-phase water droplets. To do so, a Volume of Fraction (VOF) to the Discrete Phase Model (DPM) is used.<br></div><div><br></div><div>VOF-TO-DPM transition model involves the primary and secondary breakup which occurs in the water atomization process, starting with a single water core, followed by a smaller compact mass of water known as lumps or ligaments due to the interaction of air, and finally converted into water droplets.The second model is using the Nukiyama-Tanasawa function size distribution which injects water droplets based on defined size range and velocity profile. A validation of droplet size and velocity against experimental data has been accomplished. The models can avoid acquiring expensive equipment in order to understand nozzle spray performance, and droplets generated. Quality, water droplet velocity, size, energy, and water consumption are the core of the current study. Last but not least, the methodology for this model can be used in any other air-mist nozzle design.<br></div>

Im Rahmen des Symposiums gaben Vertreter weltweit agierender Konzerne, wie Audi AG, voestalpine Gießerei Linz, Alstom AG und SITEC GmbH Einblick in ihre Forschungs­aktivitäten im Bereich Mobilität, Energietechnik, Medizintechnik und Sondermaschinenbau. Die schweißtechnischen Institute der Universitäten Aachen, Braunschweig, Clausthal, Dresden, Magdeburg und Graz gaben einen Überblick über universitäre Forschungs­aktivitäten.

<p><a>Direct chill (DC) casting is the main production method for wrought aluminum alloys. In this semi-continuous process, significant heat is extracted through a narrow, solidified shell by impinging water jets. A combination of rapid cooling and inoculation of the liquid metal with heterogenous nucleation sites (grain refiner) produces the proper conditions for equiaxed solidification. As equiaxed grains nucleate and grow in the slurry, they are transported by natural convection until their eventual coalescence into a rigid mush. The preferential accumulation of these solute-depleted grains in localized regions of the casting can lead to long range composition differences known as macrosegregation. Because macrosegregation cannot be mitigated by subsequent processing, it is critical to understand and prevent its development during casting. </a></p> <p>Numerical models are often used to gain insight into the interplay of the different transport phenomena that cause macrosegregation. The formation of mobile equiaxed grains creates a multiphase system with many moving interfaces, causing several modeling challenges. In principle, a model could be formulated in terms of local instantaneous variables describing the evolution of these interfaces, however the associated computational cost prohibits its extension to the length scale of industrial castings. For this reason, macroscopic transport equations are mathematically formulated using volume averaging methods. Two different volume-averaged model formulations can be distinguished in the solidification literature. The first approach is the multiphase formulation, which solves separate sets of governing equations for each phase that are coupled using microscale interfacial balances. While this approach retains closure models to describe the behavior of the sub-grid interfaces, these interfacial models introduce significant uncertainty that is propagated through the model. The second approach is the mixture formulation, which solves a single set of governing equations for the mixture and utilizes more pragmatic closure relationships. While this approach significantly reduces the complexity and computational cost of the model, previous formulations have oversimplified the microscale transport. Recognizing the advantages and disadvantages of both formulations, a mixture model is rigorously derived, retaining appropriate relationships for the grain structure and microsegregation behavior in equiaxed solidification </p> <p>Implementation of this model into a 3-D finite volume method (FVM) code using a co-located grid is discussed along with appropriate treatment of the discontinuous body forces and phase mass fluxes across the interface between the slurry and rigid mush. More specifically, body forces in the momentum equation are treated at the face-centers of a control volume to prevent erroneous velocity oscillations near this interface, and a diffuse phase flux method is proposed to reduce the sensitivity of composition predictions to the numerical grid. The proposed methods are verified across a wide range of conditions present in equiaxed solidification. </p> <p>This model is then used to investigate the role of grain motion on macrosegregation development in equiaxed solidification, specifically in horizontal and vertical DC casting. In horizontal DC casting, the casting axis is perpendicular to gravity and there is a tendency for grains to accumulate along the bottom of the ingot. Feeding liquid metal through a constrained inlet near the bottom suspends grains in the slurry, both reducing the overall macrosegregation and improving the macrosegregation symmetry in the ingot. In vertical DC casting, the casting axis is parallel to gravity and there is a tendency for grains to accumulate in the center of the ingot. It is determined by a combination of simulations in the current work and previous experimental results that a strong localized jet at the centerline can suspend grains in the slurry and reduce negative centerline segregation. The change in segregation is attributed to a combination of reducing the accumulation of solute-depleted grains near the centerline and thinning the rigid mush where solidification shrinkage pulls enriched liquid away from the centerline. The strong localized jet also causes significant refinement and homogenization of the grain structure, which improves the mechanical properties of the ingot. These studies indicate that it is beneficial for DC casting practices to move towards agitated or stirred melts, and away from conventional practices which promote thermal stratification and localized accumulation of equiaxed grains.</p>