Paweł Popielarski

Problem of Acceptability of Internal Porosity in Semi-Finished Cast Product as New Trend "Tolerance of Damage" Present in Modern Design Office

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.

Sensitivity Tests of Simulation Models Used in Chosen Calculation Codes on Uncertainty of Thermo-Mechanical Parameters during Virtual Mechanical Stress Estimation for Ferrous Alloy Castings

Simulation systems used for many years in foundry industry such as MAGMASOFT, NovaFlow&Solid and ProCAST, contain thermo-mechanical modules permitting the estimation of mechanical stresses and hot tears appearing in casting during its cooling. It is also known that these modules are rarely used because of the very limited thermo-mechanical database especially for ceramic materials such as foundry sand moulds. These technologies – castings pouring in non-permanent sand moulds, particularly iron alloys are most often applied in foundry. In our study the method of evaluating the algorithms quality applied in thermo-mechanical phenomena models based on parameters sensitivity testing from the proper database of the simulation system was used [1]. The comparative analyses of both experimental and virtual results were realized (by stress estimation). The methodology of experimental research was similar to that described where gray cast iron castings of stress bars (grid) were casted in sand mould bonded by organic resins.

Estimation of Coupled Thermo-Physical and Thermo-Mechanical Properties of Porous Thermolabile Ceramic Material Using Hot Distortion Plus® Test

In the paper the thermo-mechanical phenomena which occur in thermal shocked thermolabile porous ceramic material were described. Such materials are applied in foundry industry for mould making and they are characterized the low thermal stability losing its strength above 400°C. In [3] the usefulness of Hot Distortion Plus® to estimate the thermo-physical parameters (apparent thermal conductivity, heat capacity) was discussed. These parameters are necessary in data base of simulation codes which permit to simulate the phenomena in casting-mould system. The aim of these tests is to predict the mould material phenomena influence on castings quality. Parameters applied in these thermo-mechanical models (Youngs modulus, Poissons ratio, Yield stress) and their variations with temperature are not really known for thermal unstable mould material. There is no adapted method in literature and description of such total investigations of both parameters groups: thermo-physical and thermo-mechanical. The authors method called Hot Distortion Plus® consists in acquisition of temperature curves of heated sample of material and correlation with curves of their dilatation. Following the simulation using inverse solution method to reproduce the measured parameters with experiment was applied. The tests were carried out for the new quartz sand bonded by resin (approx. 1%). The specimens (dimensions 114 × 25 × 6mm) from binder-sand mixture were made using special core-box.

Problems of heat source modeling in iso-exothermic materials used as riser sleeves in foundry

The modeling of heat transfer in materials containing exothermic components must take into consideration the presence of heat sources in the Fourier–Kirchhoff equation. The aim of this investigation was the identification of real and effective thermophysical parameters of the insulating–exothermic materials used as riser sleeves containing these exothermic heat sources. The experiments of steel pouring into the mould, containing different insulating and exothermic sleeves were carried out, using thermocouples measurement systems (thermal analysis of casting–mould system). Then the thermophysical coefficients of these materials were calculated using inverse problem solution. The worked time–dependent formula of exothermic reaction heat (heating yield in W/m3) was called heat source function. The paper presents the basis and the practical expression of heat source by different functions, its justification and the results of simulations using these functions. The numerical system Calcosoft and its Inverse Solution procedure were applied.

Effective Modelling of Phenomena in Over-Moisture Zone Existing in Porous Sand Mould Subjected to Thermal Shock

The problem concerns the thermo-physical properties of the porous ceramic material called mould to which the liquid metal is poured (in 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 in casting and in different zones of the mould were recorded. The determining of the thermo-physical properties of mould sand containing the over-moisture zone using simulation tests by Procast and NovaFlow & Solid foundry systems was the goal of this 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 (substitute) thermal coefficients. The majority of foundry simulation systems are not capable to modelling the phase transformation of water into vapour, vapour transport and its condensation in porous media (called green sand moulds). In these cases the application of heat and mass transfer substitute coefficients during modelling/simulation is an interesting effective way.

Sensitivity of Models Applied in Selected Simulation Systems with Respect to Database Quality for Resolving of Casting Problems

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.

Mechanical Properties Gradient Existing in Real Castings Taken into Account during Design of Cast Components

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.

Heat Transfer during Hot Distortion Test of Ceramic Porous Material Bonded by Various Resins

The problems of thermomechanical phenomena, which occur in low stability – porous ceramic material (LS-PCM) submitted to thermal shock, are discussed. The authors tried to answer the question concerning the usefulness of Hot Distortion tests (HD) for estimation of parameters necessary in data base of simulation codes, which permit to simulate the phenomena in casting-mould system. These parameters should be accessible as temperature function, especially in high temperature range of LS-PCM used as mold heating using poured casting. The new methodology and equipment, based on British Cast Iron Association (BCIRA) method, allowed to study LS-PCM specimen feature called Hot Distortion method. In this paper the modified HD methodology, are shown. The modified apparatus DMA includes two thermal sources (electric and gaseous) used to 114 x 25 x 6 mm and 120 x 22 x 22 mm sample heating were tested and analyzed. The measurement and recording of chosen parameters, i.e. deformation (distortion) during heating and variability of surface temperature fields in heated sample, by use of pyrometer and thermal camera are presented. The virtual volume temperature field in heating sample was simulated. The comparative analysis of both, experimental and virtual results are realized. This permitted also to estimate the substitute thermo-physical coefficients using inverse solution by try & error method for predefined boundary conditions on bottom and upper specimen surfaces.

Application of Simplified Inverse Solution to Estimate the Thermo-Physical Parameters of Granular Porous Materials Bonded by Different Resins

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).

Problem of the Variability of Substitute Thermo-Physical Properties for Heat Transfer Modelling in Iso- and Iso-Exo Porous Materials

In foundry technology the modeling of heat transfer in materials containing exothermic components must take into consideration the presence of heat sources in the Fourier–Kirchhoff equation. The aim of this investigation was the identification of real and effective thermophysical parameters of the insulating and insulating –exothermic materials used as riser sleeves containing these exothermic heat sources. The experiments of liquid steel or cast iron pouring into the mould, containing different insulating and exothermic sleeves were carried out, using thermocouples meas-urement systems (thermal analysis of casting–mould system). Then the thermo-physical coefficients of these materials were calculated using inverse problem solution. The numerical system Calcosoft and its Inverse Solution procedure were applied.