Papers by Author: Zenon Ignaszak

Abstract: High-temperature heat shock is caused by pouring a liquid alloy (cast iron in this case) into cavity of a wet sand mould. In the mould material, thermal-chemical-physical phenomena of very high intensity occur. These phenomena are important in metal alloys casting only insofar as they influence quality of a casting (dynamics od solidification and casting’s structure, gas and shrinkage defects). This quality can be forecasted using simulation codes dedicated for the foundry branch. The most important phenomena are subject of hard and/or soft modeling. Heat transfer from a casting to a mould is related to simultaneous mass transfer. This coupling of phenomena is differently interpreted by creators of simulation codes and introduced to algorithms solved numerically. The paper presents an example of simplified modeling of phenomena of thermal influence of a wet mould sand on solidification of a test cast iron casting, with use of selected foundry simulation codes.

Abstract: The problem described in the paper concerns the thermo-physical properties of the green mould material to which the cast iron is most often poured. The study includes the experiment of pouring the cast iron plate into green bentonite-sand mould. The temperature fields of casting and in different zones of the mould were recorded. The goal of the study was to determine the substitute thermo-physical properties of mould sand containing the over-moisture zone by means of simulation tests (inverse problem). An originality of the related research is an attempt to take into account the effects of the global thermal phenomena occurring in the quartz sand bonded by bentonite-water binder, by application of the substitute thermal coefficients without using the coupled modeling. In the simulation tests in order to achieve the effect of rapid heating of the mould (below temperatures 100 °C) by poured cast iron (T>1300 °C), the function of the latent heat source and the modified values of substitute thermal conductivity and substitute specific heat of the molding sand were used. In order to facilitate the solution, the mould was divided into zones, in which different starting humidity of molding sand was assumed.

Abstract: The problem presented in the paper concerns physical properties of porous multi-component mould material, into which a liquid metal is poured. The aim of the study was to determine the distribution of moisture in an intensively heated porous sand mould. In the past, several measuring methods have been developed, consisting in water evaporation out of a test sample (at a given time moment , the selected position coordinates of a sample), to determine the accumulated amount of water in the sample, which is a percentage of moisture content. The study described in the paper includes experiments of heating a green sand sample. Moisture distribution in a moisture transfer zone of the sample (temperature of the molding sand is approx. 100°C) was determined. In order to determine the moisture distribution, an original method was used. This method allows interfere in various layers of material of predetermined thickness, parallel to the surface of the mould in contact with a heat source. The classical measurement method (gravimetric method) was used for determining the moisture content of each layer.

Abstract: The paper describes influence of the structure type and its parameters on the mechanical properties of cast products (not subjected to plastic forming), made out of Al-Si-X alloys. The special attention has been focused on the dendritic structure parameters: dendritic arms spacing of the first order (DAS 1) and the second order (DAS 2). The results of investigations of mechanical properties of the test castings made using three basic casting technologies: gravity sand casting (GSC), gravity die casting (GDC) and high pressure die casting (HPDC), are presented. All the castings were made out of the same AlSi9Cu3 alloy. The test castings (adherent samples and separately cast samples) were subjected to a static tensile test and their mechanical properties were determined. In the next stage, the samples fractures and zones near the fractures (metallographic specimen) were subjected to visual testing, penetrating testing PT and metallographic microscopic tests. The microstructure, including the size of the DAS 2, was determined. Evaluation of the porosity state was also undertaken. A customer casting was also manufactured and subjected to the metallographic, tomographic (CT) and strength tests. The castings solidification simulation tests were performed for all the three casting technologies (GSC, GDC and HPDC) using the Nova Flow &Solid system. The results were used for estimation of the correlation between the cooling rate of the particular casting solidifying in the above mentioned mould types and for the DAS size. The coupled influence of the structure parameters on the mechanical properties, regarding the occurrence of porosity, was also analyzed.

Abstract: The problem concerns the thermo-physical properties of the mould material to which the liquid metal is poured (foundry industry). In the foundry processes the sand mould fulfils an auxiliary role only as technological tool, but its physical and technological properties determine the quality of the casting. The study includes the iron plate casting experiments poured in multi-component porous sand mould. The temperature fields of casting and in different zones of the mould were recorded. The determining of the thermo-physical properties of mould sand in over-moisture zone using simulation tests in Procast system was the goal of our study. An originality of the related research is an attempt to take into account the effects of the global thermal phenomena occurring in the quartz sand bonded by bentonite-water binder, using the apparent thermal coefficients. The majority of foundry simulation systems are not capable to modeling the phase transformation of water into vapor, vapor transport and its condensation in porous media (mould). In these cases the application of apparent coefficients is an effective way.

Abstract: The porosity (void caused by technological reasons) in engineering materials always decrease their mechanical characteristics and usually affects the deterioration of the functional mechanical characteristics of the finished products. In the castings the porosity resulting from the specific casting processes phenomena occurs inevitably in the matrix structure. The paper shows this problem in relation to the High-Pressure-Die-Casting (HPDC) technology of Al-Si alloy. The analysis of the experimental results and the results from virtualization of HPDC process allowed to assess the effectiveness of this mixed scenario and improve the quality predictions probability for HPDC, with particular consideration of shrinkage and gas porosities. The problem of the tolerance (admissibility) of porosity occurrence in castings and the castings made of liquid Al-Si alloy to which the gas (hydrogen) was introduced intentionally are signalized.

Abstract: This paper highlights permanent development of process virtualization in the mechanical engineering industry, especially in the area of foundry. Virtualization is increasingly developed on the stage of product design and materials technologies optimization. Simultaneously, increasing expectations of design and process engineers regarding the practical effectiveness of applied simulation systems is observed. To enhance the knowledge in the scope of modelling and simulation in the foundry processes, one should be acquainted with the hard modelling based on physical-mathematical formula and also the soft modelling, burdened with simplifications resulting from both knowledge level on description of particular phenomena and level of theirs complexity. The trends observed in modelling of foundry processes and expectations of users compared with creators upgraded propositions new, additional modules based mostly on poorly tested theory are discussed. In such cases, each new module should be tested on sensitivity of additional parameters, which appear in these new modules. If needed and possible, these tests ought to be related to validation of the whole complex model containing such new modules. The purpose is to obtain simulation tools allowing the most possible realistic prognosis of the casting structure, including indication, with the highest possible probability, places in the casting that are endangered with the possibility of a gas and shrinkage porosity formation. These problems with elements of model validation are presented in the paper.

Abstract: The problem concerns the structure and properties heterogeneity of cast products, on the example of the Al-Si (A356) alloy. The trends of usage of this knowledge by constructors of that kind of products are described in this paper. It is well known that soundness of cast products is a postulate formulated by designers and users of machines and devices, where castings are among important parts. It is often forgotten though, that perfect soundness (density) of the cast material in ready for use parts simply does not exist. The gas and shrinkage porosities, present in semi-finished casting products, obtained from a liquid state of an alloy is the result of phenomena occurring during multiphase metallic system crystallization. Still, general introduction of the tolerance of damage rule requires knowledge about casting technology, inspection of the state of discontinuity of casting structure. The use of coupled experimental researches (including NDT non-destructive testing and local mechanical properties of castings) and simulation tests (Procast, ANSYS) have shown how the properties gradient influences on the safety factor distribution in the casting subjected by chosen load.

Abstract: The paper presents the complexity of the thermo-mechanical phenomena in multi-component porous material during thermal shock and heat transfer, including identification of its behavior by Hot Distortion Plus^® test, elastic/plastic interpretation and modelling using Comsol system on the example of granular material (quartz sand bonded by selected resins used for mould production in foundry industry).

Abstract: Discontinuities in cast products, obtained from a liquid state of an alloy, are the result of phenomena occurring during multiphase system crystallization. On the one hand, compacted defects as a shrinkage pipe are relatively easy to eliminate. On the other hand, it is known that presence of fine shrinkage and gas porosity is unavoidable. Detectability of these dispersed discontinuities depends on type of inspection method applied. Structure, including intensity and location of porosity zones, is dependent on the type of the alloy, casting configuration and conception of technological solution, related with control of velocity of the heat extraction to the mould. Thus, mechanical properties in the volume of a casting are not homogenous and are strongly reduced only in the zones of porosity. However, in strength calculations of cast products, this obvious fact is not taken into consideration. The rule of material homogeneity is applied instead, along with drastic increase of factor of safety. The paper indicates benefits of precise determination of limits of porosity zones located in the casting, using the NTD methods (for example, Phased Array ultrasonic tomography). Coordinates of porosity zones in 3D, introduced into CAD geometry and assigned with different properties allow to estimate the actual state of stress and strain of real object using FEM methods (systems like Ansys, Comsol). Load justified by operating conditions and application of tolerance of damage rule, with simultaneous reference to the limited state of stress according to LOV (Loss of Volume) and LEFM (Linear Elastic Fracture Mechanics) methods should find their place in design procedures of cast products, which will allow for better use of material and reduction of weight of the casting. This approach, named Tolerance of damage concerning the castings is the motto of this paper.