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Preparation and Evaluation of Properties of Cast Metallic Foams with Regular Inner Structure

Lichý P., Elbel T., Kroupová I., Radkovský F.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 3

1643--1646

EN

Lately we encounter still more new applications of metallic foams, as well as possible methods of their manufacture. These metallic materials have specific properties, such as large rigidity at low density, in some cases high thermal conductivity, capability to absorb energy, etc. The work is focused on the preparation of these materials using conventional casting technology, which ensures rapid and economically feasible method for production of shaped components. In the experimental part we studied conditions of casting of metallic foams with a regular structure made of ferrous and non-ferrous alloys. For thus obtained castings we evaluated the achieved microstructure and mechanical properties, which determine the possible use of these materials. The samples were subjected to compression tests, by which we investigated deformation behaviour of selected materials and determined the value of energy absorption.

2

Expert System for Analysis of Casting Defects - ESVOD

Elbel T., Králová Y., Hampl J.

Archives of Foundry Engineering

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2015

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Vol. 15, iss. 1

17--20

EN

The powerful tool for defect analysis is an expert system. It is a computer programme based on the knowledge of experts for solving the quality of castings. We present the expert system developed in the VSB-Technical University of Ostrava called ‘ESWOD’. The ESWOD programme consists of three separate modules: identification, diagnosis /causes and prevention/ remedy. The identification of casting defects in the actual form of the system is based on their visual aspect.

3

Proposal of Method of Removal of Mould Material from the Fine Structure of Metallic Foams used as Filters

Kroupová I., Bednářová V., Elbel T., Radkovský F.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 2

727--730

EN

Metallic foams are materials that are subject of an ongoing research with the broad applicability in many different areas (e.g. automotive industry, building industry, medicine, etc.). These metal materials contain in their structure artificially created pores. These pores give them specific properties, such as: large rigidity at low density, high thermal conductivity, capability to absorb energy, etc. Since the discovery of porous metallic materials numerous methods of production have been developed. The aim of the paper is to introduce effective casting methods of manufacturing of metallic foams, namely cast metal filters from the aluminum alloy. Research deals with investment casting with use of pattern made of polymeric foam, which is used for production of metallic foam with open pores. The main disadvantage of this procedure consists in removing the mould material without damaging the fine structure of the cast filter. Plaster is used as the mould material and the most important result of this paper is the presentation of the effective procedure of plaster removal from the porous structure of cast filters.

PL

Piany metalowe są przedmiotem wielu badań gdyż znajdują szerokie zastosowanie w wielu dziedzinach np. produkcji samochodów. budownictwie czy w medycynie. W swojej strukturze zawierają sztucznie wytworzone pory, zapewniające uzyskanie specyficznych właściwości jak duża wytrzymałość, niewielka gęstość, wysokie przewodnictwo cieplne zdolność do absorpcji energii itp. Od czasu wynalezienia porowatych materiałów metalowych opracowano wiele metod ich wytwarzania. Celem opracowania jest wprowadzenie efektywnych metod odlewniczych produkcji pian metalowych, szczególnie ze stopów glinu. Studium zajmuje się precyzyjną metodą odlewania przy zastosowaniu modelu wykonanego z piany polimerowej stosowanej w produkcji piany z otwartymi porami. Główna niedogodność metody polega na trudności usuwania materiału formierskiego, bez naruszenia delikatnej struktury odlewanego filtra. Jako materiał formierski stosuje się gips i najważniejszym wynikiem pracy jest przedstawienie efektywnej procedury usuwania gipsu z porowatej struktury odlanego filtra.

4

Thermodynamic analysis of cast irons solidification with various types of graphite

Elbel T., Hampl J.

Archives of Foundry Engineering

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2012

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Vol. 12, iss. 4

157-165

EN

The contribution summarises the results of oxygen activity determinations, which were measured and registered continuously in castings from cast irons with various types of graphite. The results were used to find the relationship between two variables: natural logarithm of oxygen activities and reverse value of thermodynamic temperature 1 /T. Obtained regression lines were used to calculate oxygen activity at different temperatures, to calculate Gibbs free energy \deltaG at the different temperatures and to calculate the single \deltaG value for significant temperature of the graphite solidification. The results were processed by a statistical analysis of data files for the different types of graphite with flake, vermicular and spheroidal graphite. Each material has its proper typical oxygen activities range and individual temperature function of Gibbs free energy for analysing and governing casting quality.

5

Casting routes for porous metals production

Lichý P., Bednarova V., Elbel T.

Archives of Foundry Engineering

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2012

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Vol. 12, iss. 1

71-74

EN

The last decade has seen growing interest in professional public about applications of porous metallic materials. Porous metals represent a new type of materials with low densities, large specific surface, and novel physical and mechanical properties, characterized by low density and large specific surface. They are very suitable for specific applications due to good combination of physical and mechanical properties such as high specific strength and high energy absorption capability. Since the discovery of metal foams have been developed many methods and techniques of production in liquid, solid and gas phases. Condition for the use of metal foams - advanced materials with unique usability features, are inexpensive ways to manage their production. Mastering of production of metallic foams with defined structure and properties using gravity casting into sand or metallic foundry moulds will contribute to an expansion of the assortment produced in foundries by completely new type of material, which has unique service properties thanks to its structure, and which fulfils the current demanding ecological requirements. The aim of research conducted at the department of metallurgy and foundry of VSB-Technical University Ostrava is to verify the possibilities of production of metallic foams by conventional foundry processes, to study the process conditions and physical and mechanical properties of metal foam produced. Two procedures are used to create porous metal structures: Infiltration of liquid metal into the mold cavity filled with precursors or preforms and two stage investment casting.

6

Study of pinholes genesis in iron castings

Elbel T., Hampl J., Senkypl M.

Archives of Foundry Engineering

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2011

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Vol. 11, iss. 1

21-26

EN

Purpose: The study concerns the formation of pinholes in castings formed by reaction between a green foundry mould and lamellar graphite cast iron. Great numbers of works have been aimed at clarifying the causes of pinholes formation in iron castings. In spite of this there exists no united opinion on the pinholes formation (genesis) and the authors of this contribution having studied this phenomenon in compacted graphite and spheroidal graphite iron castings were also aimed at lamellar graphite cast iron and they applied for it their knowledge gained in study of reoxidation processes during casting of ferrous alloys. Methodology: Experiments were done on castings of stepped bars moulded in green bentonite mixtures with s graduated moisture and with use of two types of carbonaceous matters. Metal was melted in a 100 kg induction furnace from the same charge. Inoculation was done in a ladle after pouring out from the furnace. Aluminium was dosed in the ladle in some cases and the inoculator kind was changed too. Results: Pinholes were present on castings as small flat pits; on horizontal surfaces sooner singly, on casting edges in clusters. The formation of pinholes wasn't caused by high moisture of moulds but the defect was sensitive to aluminium content in metal. In castings with high aluminium content > 0.01 % the pinholes were present in great numbers, and namely both under low, and also high moistures of moulding mixtures. In melts with low content of Al < 0.01 % the pinholes occurred less extensively only. Practical implications: Conclusions from literature about influence of Al on pinholes occurrence were confirmed in such a way. Study of the defect morphology has shown that the question is a oxidation reaction type of pinholes caused by oxidation of the residual melt between dendrites with formation of CO.

7

Geometrical modulus of a casting and its influence on solidification process

Havlicek F., Elbel T.

Archives of Foundry Engineering

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2011

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Vol. 11, iss. 4

170-176

EN

Object: The work analyses the importance of the known criterion for evaluating the controlled solidification of castings, so called geometrical modulus defined by N. Chvorinov as the first one. Geometrical modulus influences the solidification process. The modulus has such specificity that during the process of casting formation it is not a constant but its initial value decreases with the solidification progress because the remaining melt volume can decrease faster than its cooling surface. Methodology: The modulus is determined by a simple calculation from the ratio of the casting volume after pouring the metal in the mould to the cooled mould surface. The solidified metal volume and the cooled surface too are changed during solidification. That calculation is much more complicated. Results were checked up experimentally by measuring the temperatures in the cross-section of heavy steel castings during cooling them. Results: The given experimental results have completed the original theoretical calculations by Chvorinov and recent researches done with use of numerical calculations. The contribution explains how the geometrical modulus together with the thermal process in the casting causes the higher solidification rate in the axial part of the casting cross-section and shortening of solidification time. Practical implications: Change of the geometrical modulus negatively affects the casting internal quality. Melt feeding by capillary filtration in the dendritic network in the casting central part decreases and in such a way the shrinkage porosity volume increases. State of stress character in the casting is changed too and it increases.

8

On modelling of the effect of oxygen on graphite morphology and properties of modified cast irons

Hampl J., Elbel T.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 4

55--60

EN

Oxygen in graphitic cast irons substantially influences crystallization. The paper deals with results of experimental works concerning the influence of oxygen activities (ao) and total oxygen content OOX in cast irons, treated (modified) with master alloys NiMg and FeSiMg, on structural and mechanical properties of modified cast iron. The results show that in castings treated by Mg with subsequent inoculation FeSi strong reduction of total oxygen content in cast iron is observed. It corresponds to increasing residual content of Mg in castings and to the increase of tensile strength. The graphite morphology is connected with oxygen activity and total oxygen content in cast iron too. This decrease changes the morphology of graphite from flake to vermicular and spheroidal morphology. Increase of ultimate tensile strength of modified cast irons in consequence of greater amount of added Mg and consequently higher values of Mgres too were observed what correlates with decreasing oxygen content in cast iron. This trend expressed by linear dependencies is valid for all melts.

9

Chvorinov’s rule and determination of coefficient of heat accumulation of moulds with non-quartz base sands

Jelinek P., Elbel T.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 4

77--82

EN

Application of the „Chvorinov’s rule“ for calculation of the total time of casting solidification made also possible to determine chilling effect of foundry moulds (coefficient of heat accumulation of the mould, bf) with use of mixtures with new kinds of non-quartz base sands (Magnesite, Chromite, Olivine, Dunite, Kerphalit). Processes by several authors (G. Halbart, A. I. Vejnik, G. A. Anisovich) were used for mathematical treatment of measurement results and determination of bf. The highest values were achieved for magnesite moulds followed by chromite ones; the lowest values, approximately half-ones, represented the Dunite moulds. At the same time the results made possible to determine „the Chvorinov’s mean solidification constants“ (k) that are in direct proportional dependence on bf and indirect proportional to solidification time (τ1).

10

Behaviour of oxygen in cast irons

Elbel T., Senberger J., Zadera A., Hampl J.

Archives of Materials Science and Engineering

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2008

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Vol. 33, nr 2

111-116

EN

Purpose: Cast irons are the basic structural material and they form 75% of the world production of castings. The crystallization of cast iron and the formation of graphite are a complex process influencing by oxygen. The aim of our study is to identify the role of oxygen in Fe-C-Si melts. Design/methodology/approach: Continuous comparison of changes in metal composition and oxygen activity during melting, pouring, and solidification of experimental castings, using metallographic methods and microanalysis. Determination of total oxygen content in cast iron by the high temperature extraction method. Findings: Oxygen activity in graphitic cast irons is determined during manufacture of liquid metal and its pouring mainly by carbon and silicon activities. Silicon deoxidates cast irons at lower temperatures, at higher temperatures this function is taken over by carbon. Logarithmic dependences of oxygen activity on temperature for individual graphite forms (lamellar, vermicular, and spheroidal ones) have been obtained. Determination of total oxygen content in cast iron on the other hand gives valuable information for controlling surface and internal quality of cast irons. Practical implications: Possibility of control the cast iron structure and graphitization during crystallization by monitoring the oxygen content with an indirect method of oxygen activity measurement in the melt before metal pouring the mould. Originality/value: The used method gives reproducible results which are comparable under different conditions of metal melting and pouring. Obtained knowledge extends the understanding in the field of cast irons crystallization by less known influence of oxygen.

11

Influence of aluminium on the formation of pinholes in cast irons

Elbel T., Hampl J., Vladik R., Koukal R.

Archives of Foundry Engineering

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2008

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Vol. 8, iss. 2

27-32

EN

Purpose: This study concerns the formation of pinholes in castings by reaction between cast iron with compacted graphite and green sand mould. Methodology: Experiments were done on bar castings moulded in green bentonite mixtures without carbonaceous matters. Moulding sand moisture and aluminium content in the melt were purposely changed. Metal was melted in a 100 kg furnace by remelting the uniform charge of return material. Metal was inoculated all at once in a ladle and modified in a reaction chamber in a mould or as sandwich method in a pouring ladle. Findings: The formation of pinholes was not caused by high moisture of the mould but this defect was sensible to aluminium content in metal. In castings with high aluminium content > 0.2 % the pinholes occurred in high numbers, and namely under low and also high moistures [> 4 %]. In previous melts with aluminium contents < 0.02 % defects occurred in small range. Practical implications: Thus the conclusions known from literature about the influence of Al on pinholes occurrence in cast irons were confirmed. Oxygen activity in metal during its flowing and cooling in the mould was also measured but this quantity was not changed too in dependence on pinholes content. Morphological analyses near the defect have indicated that it is a physical type of pinholes caused by hydrogen. Originality: A number of works were aimed at explanation of causes of pinholes formation in lamellar graphite iron castings and spheroidal graphite ones. But this defect is formed in castings from compacted graphite cast iron too and the research was aimed just to this material. The contribution is in such a way an exceptional one.

12

State of the art of metal reoxidation study of iron castings

Elbel T., Senberger J., Zadera A., Vladik R.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 11

649-652

EN

Purpose: Metal reoxidation causes a number of iron castings defects, particularly when pouring them in greensand moulds. One of them is pinholes the occurrence of which is explained by several hypotheses. One of possible causes is reoxidation processes in the foundry mould cavity. During its flowing in the gating system and in the mould cavity the liquid metal gets into contact with oxygen from air and water vapour. Secondary oxidation of elements takes place in sequence of their affinity to oxygen. Design/methodology/approach: Therefore the authors were aimed at cast irons. Besides indirect methods the reoxidation was researched mainly by direct measurement of oxygen activity during filling of a mould up to solidus temperature. Findings: The use of oxygen activity measurement for direct study of changes caused by reoxidation processes is limited and that it is more suitable for study of the influence of different factors on cast iron crystallization and graphite morphology. Practical implications: Obtained results have confirmed that oxygen activity measurement can serve to the casting quality control. But it is little sensitive for explanation of processes running in a cavity during metal casting. Originality/value: Continuous monitoring of oxygen activity changes in a foundry mould is an original solution since other authors have done their measurements only in a furnace with disposable sensors.