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Abstract

Today, foundries are facing increasing demands for greener and more economical production while maintaining or improving the quality of the castings produced. The importance and use of green sand mixtures using bentonite as a binder are thus coming to the fore once again. They have the advantage of both eliminating the chemicalization of production and also allowing the immediate use of the already used mixture, including the binder, after adjustment of the composition and mulling. In order to maintain the quality of the resulting castings, it is necessary to monitor the properties of the moulding mixture through a series of laboratory tests. It is also essential to look at the processing quality of these mixtures, i.e. the combination of good mulling quality and efficient mulling time, which is often neglected. It is the quality of mulling and the effective mulling time that help to develop the bonding properties of the bentonite, improve the properties of the mixture, determine the efficiency of the muller and possibly reduce the time and energy required for mulling. The aim of this work is to present the effect of mulling on the properties of sand-water-bentonite mixtures. The properties studied are mainly the compactability, strength characteristics, moisture content of the mixture and the order of addition of raw materials.
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Bibliography

[1] Jelínek, P. & Mikšovský, F. (1985). Contribution to the evaluation of the efficiency of uniform green moulding mixture. Slévárenství. XXXIII (7), 268-274. (in Czech)
[2] Troy, E.C. et al. (1971). A Mulling Index Applied to Sand-water-bentonite. AFS Transactions. 79, 213-224.
[3] Strobl, S.M. (1995). How to improve green sands through more effective mulling. Modern casting. 85(2), 40-43.
[4] Thambiah, T.R. & Sarkar, A.D. (1973). Effect of mulling time on the properties of greensands. Foundry Trade Journal. 1973, 683-684.
[5] Headington, F., Rothwell, M.D. & Green, R. (1998). Available clay control and mulling efficiency. AFS Transactions. 1998, 271-291.
[6] Dietert, H.W., Graham, A.L. & Schumacher, J.S. (1971). How Mulling Time Affects Sand Properties. Foundry. 1971, 42-47.
[7] Kyncl, M. (2008). Evaluation of mixers efficiency. Diploma thesis, VŠB-TU Ostrava, Fakulta metalurgie a materiálového inženýrství, Ostrava, Czech Republic. (in Czech)
[8] Jelínek, P. (2004). Binder systems of foundry moulding mixtures – chemistry of foundry binders. (1st ed.). Ostrava. ISBN: 80-239-2188-6. (in Czech)
[9] Weniger, C.E. & Volkmar, A.P. (1970) A new control tool: a graph for evaluating effectiveness of available bentonite within foundry system sand. AFS Transactions. 1970, 17-24.
[10] Kumari, A., Murari, A.K., Prasad, U. (2020). Prediction of Green Sand Moulding Properties Using Artificial Neural Network. In U. Prasad (Eds.), Advances in Science & Technology (pp. 39-52). India: Empyreal publishing house.

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Authors and Affiliations

M. Gawronová
1
ORCID: ORCID
Š. Kielar
1
P. Lichý
1
ORCID: ORCID

  1. VSB-Technical University of Ostrava, Faculty of Materials Science and Technology, Department of Metallurgical Technologies, Czech Republic
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Abstract

CM247LC alloy was manufactured by using selective laser melting (SLM) process, one of the laser powder bed fusion ­(L-PBF) methods. The hot isostatic pressing (HIP) process was additionally conducted on the SLM-built CM247LC to control its microstructures and defects. The high temperature oxidation property was investigated, and it was compared with conventional DS247LC sample (reference) prepared via the directional solidification process. The L-PBF HIP sample showed blocky-type MC carbides generated along the grain boundary with average size of about 200 nm. A semi-spherical primary γ' phase of size 0.4-1.0 μm was also observed inside the grains. Moreover, the DS247LC sample displayed a coarse eutectic γ' phase and many script-type MC carbides. Furthermore, cuboidal-type γ' with an average size of about 0.5 μm was detected. High-temperature oxidation tests were conducted at 1000°C and 1100°C for 24 hours. The results at 1100°C oxidation temperature showed that the measured oxidation weight gains for HIP and DS247LC were 1.96 mg/cm2 and 2.26 mg/cm2, respectively, indicating the superior high-temperature oxidation resistance of the L-PBF HIP sample. Based on the above results, a high-temperature oxidation mechanism of the CM247LC alloys manufactured by the SLM process and the directional solidification process has been proposed.
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Authors and Affiliations

Jung-Uk Lee
1
Young-Kyun Kim
2
ORCID: ORCID
Seong-Moon Seo
2
Kee-Ahn Lee
1
ORCID: ORCID

  1. Inha University, Department of Materials Science and Engineering, Incheon 22212, Republic of Korea
  2. Korea Institute of Materials Science, Changwon 51508, Republic of Korea
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Abstract

Relatively cold die material comes into contact with the substantially higher temperature melt during the casting cycle, causing high thermal fluctuations resulting into the cyclic change of thermal field. The presented contribution is devoted to the assessment of the impact of temperature distribution on individual zones in the die volume. The evaluated parameter is the die temperature. It was monitored at two selected locations with the 1 mm, 2 mm, 5 mm, 10 mm and 20 mm spacing from the die cavity surface to the volume of cover die and ejector die. As a comparative parameter, the melt temperature in the middle of the runner above the measuring point and the melt temperature close to the die face were monitored. Overall, the temperature was monitored in 26 evaluation points. The measurement was performed using the Magmasoft simulation software. The input settings of the casting cycle in the simulation were identical to those in real operation. It was found, that the most heavily stressed die zones by temperature were within the 20 mm from the die face. Above this distance, the heat supplied by the melt passes gradually into the entire die mass without significant temperature fluctuations. To verify the impact of the die cooling on the thermal field, a tempering system was designed to ensure different heat dissipation conditions in individual locations. At the end of the contribution, the measures proposals to reduce the high change of thermal field of dies resulting from the design of the tempering channel are presented. These proposals will be experimentally verified in the following research work.

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Authors and Affiliations

J. Majerník
M. Podařil
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Abstract

Nowadays, there are growing demands on the accuracy of production. Most of this is reflected in precise manufacturing, such as the investment casting process. Foundries are looking for causes of defects in some cases for a very long time, and it may happen that the source of defects is completely different from what was originally assumed. During the casting process there exist potential causes of defects as oxygen inclusions. This paper represents a summary of the beginnings of a wider research that will address the problems of gating systems in investment casting technology. In general, the influence of the melt flow is underestimated and the aim of the whole scientific research is to demonstrate the significant influence of laminar or turbulent flow on the resulting casting quality. Specifically, the paper deals with the analysis of the most frequent types of defects found in castings made of expensive types of materials casted in an open atmosphere and demonstration of connection with the design of gating systems in the future.
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Authors and Affiliations

O. Vrátný
A. Herman

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