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Abstract

Submitted work deals with the analysis of reoxidation processes for aluminium alloys. Due to the aluminium high affinity to the oxygen, the oxidation and consequently reoxidation will occur. Paper focuses on the gating system design in order to suppress and minimize reoxidation processes. Design of the gating system is considered as one of the most important aspect, which can reduce the presence of reoxidation products - bifilms. The main reason for the reoxidation occurrence is turbulence during filling of the mold. By correctly designing the individual parts of gating system, it is possible to minimize turbulence and to ensure a smooth process of the mold filling. The aim of the work is an innovative approach in the construction of gating system by using unconventional elements, such as a naturally pressurized system or vortex elements. The aim is also to clarify the phenomenon during the gating system filling by visualization with the aid of ProCAST numerical simulation software. ProCAST can calculate different indicators which allow to better quantify the filling pattern.

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Authors and Affiliations

A. Remišová
M. Brůna
ORCID: ORCID
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Abstract

The melt cleaning is an important aspect in the production of high-quality aluminum castings. Specifically inclusions within the melt and an excessively high hydrogen content lead to defects and undesired porosity in the castings. Although it is possible to reduce the amount of hydrogen and oxidic inclusions by purge gas treatment and the use of melting salts, it is impossible to remove oxides (bifilms) created during filling of gating system. Paper deals with the effects of melt quality and the placement of a filter in the filling system on Al-7%Si-Mg alloy mechanical properties. Three different filters were used: (a) rectangular ceramic pressed filter with 3 mm thickness (b) cubical pressed ceramic filter with thickness 10 mm (c) cubical pressed ceramic filter with thickness 22 mm. The results showed that the highest tensile strength values were obtained from the filter with thickness of 22 mm. Numerical simulation analysis of the filling process showed that velocity reduction by filter is the major phenomenon affecting the mechanical properties. Another evaluated aspect during experiments was capability of filters to retain old bifilms. For this purpose multiply remelted alloy was prepared and analyzed. Results showed that filter efficiency increases with decreasing melt quality as a result of possibility to retain “old” bifilms better than small and thin “new” bifilms.

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Authors and Affiliations

M. Bruna
A. Remišová
A. Sládek
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Abstract

Submitted work deals with the possibilities of reducing reoxidation by improved gating system design. The result of the reoxidation is the of furled oxide layers – bifilms. During experimental works, non-pressurized and naturally pressurized gating systems designs were introduced and evaluated. Mechanical properties, fracture area, hot tearing index, bifilm index and EDX analysis were used during evaluation. Paper aim is also to clarify the reoxidation phenomenon by visualization with the aid of ProCAST numerical simulation software. Achieved results clearly confirmed the positive effect of the naturally pressurized gating system, main emphasis needs to focus on finding the proper way to reduce the melt velocity. By using vortex element extension at the end of the runner was achieved positive results in term of reoxidation suppression.
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Authors and Affiliations

M. Brůna
1
ORCID: ORCID
M. Galčík
1
A. Sládek
1
D. Martinec
1

  1. University of Žilina, Faculty of Mechanical Engineering, Department of Technological Engineering, Univerzitná 8215/1, 010 26 Žilina, Slovakia
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Abstract

The naturally pressurized gating system was used for reoxidation suppression during aluminium alloy casting. A naturally pressurized gating system appears to be a suitable solution to reduce reoxidation processes, which was proven by our previous works. The disadvantage of this system is that without inserting deceleration elements, the melt velocity is supercritical. Therefore, the aim of paper is to find a proper way to reduce the melt velocity, which is the main parameter affecting the scale of reoxidation processes. For the purpose of the melt velocity reduction, labyrinth filters, foam filters and flat filters effect on the melt velocity and the number of oxides were investigated by numerical simulation software in the first stage of the experiment. After simulations observation, the effect of filters on the mechanical properties was investigated by experimental casts. The simulations and experimental casts proved that filters had a positive effect on the melt velocity reduction and it was associated with increased mechanical properties of castings. The best results were achieved by the foam filter.
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Bibliography

[1] Campbell, J. (2015). Complete Casting Handbook. (2nd ed.). Oxford: Elsevier Ltd.
[2] Dobosz, St.M., Grabarczyk, A., Major-Gabrys, K. & Jakubski, J. (2015). Influence of quartz sand quality on bending strength and thermal deformation of moulding sands with synthetic binders. Archives of Foundry Engineering. 15(2), 9-12. ISSN (1897-3310)
[3] Lakoma, R., Camek, L., Lichý, P., Kroupová, I., Radkovský, F. & Obzina, T. (2021). Some possibilities of using statistical methods while solving poor quality production. Archives of Foundry Engineering. 21(1), 18-22. DOI: 10.24425/afe.2021.136073
[4] Baghani, A., Kheirabi, A., Bahmani, A. & Khalilpour, H. (2012). Removal of double oxide film defects by ceramic foam filters. Journal of Materials Engineering and Performance. 21(7), 1352-1362. DOI: 10.1007/s11665-011-9991-3
[5] Jezierski, J., Dojka, R. & Janerka, K. (2018). Optimizing the Gating System for Steel Castings. Metals. 8(266), 1-13. DOI: 10.3390/met804026
[6] Pastirčák, R. & Ščury, J. (2016). Effect of technological parameters on microstructure in alloy AlCu4Ti using squeeze casting technology. The application of experimental and numerical methods in fluid mechanics and energy. ISBN 978-0-7354-1402-0.
[7] Gyarmati, G., Fegyverneki, G., Mende, T. & Tokár, M. 2019. Characterization of the double oxide film content of liquid aluminum alloys by computed tomography. Materials Characterization. 157, 109925.
[8] Remišová, A. & Brůna, M. (2019). Analysis of reoxidation processes with aid of computer simulation. Archives of Foundry Engineering. 19(4), 55-60.
[9] Brůna, M., Galčík, M., Sládek, A. & Martinec, D. (2021). Possibilities of bifilm amount reduction in Al castings by gating system design optimization. Archives of Metallurgy and Materials. 66(2), 549-559. ISSN 1733-3490

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Authors and Affiliations

M. Bruna
1
ORCID: ORCID
M. Galčík
1

  1. University of Žilina, Slovakia
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Abstract

One of the main reason for decreased internal homogeneity of aluminium alloy castings is reoxidation. The resulting products of reoxidation are doubled oxides, so called "bifilms". Submitted paper deals with optimization of gating system design in order to reduce reoxidation processes taking place in mold cavity. Experimental work compares and evaluates three gating systems designs based on non-pressurized and naturally pressurized principles. Unconventional spin trap extension of runner was used in third design. Among the evaluated aspects were: mechanical properties, hot tearing index, visual inspection of average porosity amount, numerical simulation of velocity, turbulence and oxide amount. Paper aim is also to clarify the reoxidation phenomenon by visualization with the aid of ProCAST numerical simulation software. Results of mechanical properties and hot tear index clearly confirmed the positive effect of the naturally pressurized gating system with applied element for velocity reduction.
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Bibliography

[1] Svoboda, J.M., Monroe, R.W., Bates, C.E. & Griffin, J. (1987). TAFS. 95, 187-202.
[2] Campbell, J. (2006). Entrainment defects. Materials Science and Technology. 22(2), 127-145. ISSN 0267-0836. https://doi.org/10.1179/174328406X74248.
[3] Campbell, J. (1993). Invisible Macrodefects in castings. Journal de Physique Archives. 03(C7), 861-872. https://doi.org/10.1051/jp4:19937135.
[4] Dojka, R. Jezierski, J. & Campbell, J. (2018) Optimized gating system for steel castings. Journal of Materials Engineering and Performance. 10. DOI: 10.1007/s11665-018-3497-1.
[5] Sladek, A., Patek, M. & Mician, M. (2017). Behavior of steel branch connections during fatigue loading‎. Archives of Metallurgy and Materials. 62 (3), 1597-1601‏.
[6] Brůna, M., Bolibruchová, D. & Pastirčák, R. (2017). Archives of Foundry Engineering. 17, 23-26. https://doi.org/10.1515/afe-2017-0084.
[7] Lin, S., Aliravci, C. & Pekguleryuz, N.I.O. (2007). Hot-tear susceptibility of aluminum wrought alloys and the effect of grain refining. Materials Science and Engineering. A Sci. 38A, 1056-1068. https://doi.org/10.1007/s11661-007-9132-7.
[8] Campbell, J. (2006). An overview of the effects of bifilms on the structure and properties of cast alloys. Metallurgical and Materials Transaction B. 37, 857-863. https://doi.org/ 10.1007/BF0273500.

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Authors and Affiliations

M. Bruna
1
ORCID: ORCID
M. Galčík
1

  1. Department of Technological Engineering, University of Zilina, Univerzitna 1, 010 26 Zilina, Slovakia

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