Computer simulation has become a common way to analyze systems that are too complicated to be treated in a formulaic way. A model is created that represents an abstraction of the real system. By defining boundary conditions or varying parameters, the behavior of the model can be calculated with the help of numerical methods. The results can then be used to draw conclusions about the problem and its solution.
Among other things, the Chair of Metallurgy has set itself the task of researching the wear mechanisms of refractory building materials.
In addition to finite element simulations to determine the thermomechanical behavior of refractory building materials and fact-sage simulations for thermochemical calculations, flow simulations (Computational Fluid Dynamics - CFD) are also carried out.
Refractory building materials are mainly used for the lining of aggregates for high-temperature processes, i.e. the refractory lining is exposed to slag and melting at high temperatures. The chemical wear of the refractory material caused by contact with molten substances is influenced by the flow conditions.
At the Chair of Metallurgy, CFD simulations are used to investigate the influence of flows on wear. From the knowledge of the flow behavior, it is possible to draw conclusions about the transfer of matter by analogies in the transport equations.
The example below shows the simulation of the flow conditions in a crucible filled with liquid slag, in which a refractory sample rotates to investigate its wear (finger test). To verify the simulation results, Particle Image Velocimetry (PIV) is used, which enables visualization and quantification of the flow in a suitable test setup at room temperature. The simulation result is compared to such a flow visualization in the following figure.
Materials used in rock metallurgy often have a heterogeneous structure of different grain fractions. These include building materials such as concretes, mortars and binders, as well as ceramic products such as refractory building materials. Therefore, DEM (Discrete Element Method) approaches are also used, a numerical calculation method that can be used to calculate the movement of particles. The coupling of CFD (Computational Fluid Dynamics) and DEM (Discrete Element Method) enables a detailed analysis of flow processes in systems with solid particles. While CFD calculates the continuum flow of gases, liquids, or melts, DEM models the discrete behavior of individual grains, including collisions, friction, and abrasion. By coupling both methods, interactions between fluid and particles – such as force transfer, particle transport or erosion mechanisms – can be realistically reproduced. This is particularly valuable for heterogeneous materials, where microstructure and particle movement have a decisive influence on flow, stress and wear.
The figure below shows the simulated erosion of grains of a model substance due to the prevailing flow.
The cost-effective use of building materials is becoming increasingly important and optimisation measures are constantly in demand. This applies both to the field of structural applications and to refractory materials. Computer methods are used to predict the behavior of these building materials under the respective boundary conditions. The prognosis of the thermomechanical behaviour of refractory building materials is a focus of work at the Chair of Mineral Metallurgy.
Refractory building materials are used primarily where it is necessary to protect the steel structure of industrial plants from high process temperatures. Such systems are widespread and can be found in the metal-producing industry, the glass industry as well as in the building materials and chemical industries. Due to this use, refractory products reach temperatures of more than 1500°C in use. Due to the existing thermal expansions and the limited expansion possibilities, tensions occur in the inlining. These mechanical stresses represent a potential for damage and can accelerate the wear of the refractory material or cause production losses.
By selecting the materials appropriately, optimising geometries or adjusting process parameters, the behaviour of the lining can be improved or the mechanical loads reduced. For this purpose, simulations are carried out at the Chair of Metallurgy with the help of finite element methods (FEM). In order to be able to clarify the cause of damage, it is necessary to take nonlinear material behavior such as cracking into account in the simulations.
For example, the premature wear in the floor/wall transition area of an LD converter, as used for steel production, can be explained (see figure). Due to the thermal expansion of the converter floor and the wall, the stone layers in the transition zone are subjected to bending stress. In the right part of the figure, the stresses in the transition zone parallel to the stone layers are shown as a contour plot. Red areas are zones in which tensile stresses occur parallel to the stone layers, in the yellow areas compressive stresses occur. This flexural tensile load leads to crack formation at right angles to the stone layers, which can lead to the breaking out of larger lining parts.
Source
D. Gruber, K. Andreev, H. Harmuth: Optimisation of the Lining Design of a BOF Converter by Finite Element Simulations. Steel Research int. 75 (7), 455-461, 2004
der Kristallisation einer Gießschlacke.
Die Pfeile kennzeichnen die Cuspidinkristalle [2]
The work of the Chair of Ceramics is particularly concerned with the investigation of the structure of casting slags and casting powders as well as their melting behavior and crystallization. For this purpose, both original casting powders and materials from the company (casting slags, slag wreaths) are examined.
The methods used are:
- Reflected light and scanning electron microscopy on cast powder samples, slag samples and samples after step annealing
- Heating table microscopy: Examination of powder samples, grinding and slag samples at temperatures up to 1500°C
- X-ray diffractometric examinations
- Differential thermal analysis and thermogravimetry
- Investigations according to the Double Hot Thermocouple Technique (DHTT): In particular, the crystallization behavior of a slag sample is observed as a function of the temperature gradient.
- High-temperature viscometry
The characterisation of the casting powders carried out using the above-mentioned methods allows conclusions to be drawn about their operating behaviour and the selection of casting powders.
References
[1] I. Marschall, H. Harmuth: "Investigation of the slag rim growth in the continuous casting process", SCANMET III- 3rd International Conference on Process Development in Iron and Steelmaking, 8-11 June 2008, Luleå, Sweden
[2] N. Gruber, H. Harmuth: "Hot stage microscopy for in situ observations of the melting and crystallisation behaviour of mould powders", SCANMET III- 3rd International Conference on Process Development in Iron and Steelmaking, 8-11 June 2008, Luleå, Sweden
Contact: Nathalie Gruber, Irmtraud Marschall
The demand for climate-friendly, recyclable, CO₂-reduced building materials is growing rapidly in view of the climate crisis, resource scarcity and stricter regulations (e.g. life cycle balances, circular economy). The construction sector is a major contributor to global emissions; the lever over materials with a low CO2 footprint, long service life and high recyclability is correspondingly large. Against this background, the Chair of Mineral Metallurgy is researching the optimisation of sustainable insulation materials based on mineral foam.
Mineral foam is a porous, mineral insulation material that is produced from resource-efficient components such as sand, lime and cement-bound systems through a drifting and foaming process. It is non-flammable, permeable to diffusion and capillary-active, which makes it particularly safe and robust in terms of building physics. Compared to many synthetic alternatives, an all-mineral matrix offers advantages in fire protection, ageing resistance and potential recyclability. In addition, the material proximity to mineral building products will enable better integration into cycles in the future – from the use of secondary raw materials to high-quality recycling at the end of life.
Our research focus is on low-CO₂ formulation development and optimization. We integrate CO₂-reduced binders and explore the influence of other additives without sacrificing thermal performance or compressive strength. The key levers are a deep understanding of the interaction of the raw materials, the control of foam stability and a stable, not too narrow process window for further processing.
In a project cooperation with Miralis GmbH, we are bundling scientific and industrial expertise in order to transfer the developed mineral foam systems to an industrial scale. Together, we work on the scale-up steps from recipe optimization to continuous foam generation and shaping to drying and quality assurance. In doing so, we are testing the use of secondary raw materials to further reduce the carbon footprint and evaluating alternative formulation components to ensure supplier independence.
The goal is a high-performance, industrially scalable and recyclable mineral foam with a significantly reduced CO₂ footprint – an insulation material that meets the technical requirements of modern building envelopes and at the same time accelerates the transformation towards a sustainable, resource-saving construction industry. The cooperation with Miralis GmbH enables rapid validation on a pilot and pre-series scale and creates the basis for a rapid market launch.
Contact: Christina Atzenhofer