One of the factors influencing the surface quality of castings is the resulting thermal expansion when silica sands are used. This is characterised both by its high value compared to other non-silica sands, and by its typical discontinuous behaviour, leading in many cases to defects such as veining or increased surface roughness, which further lead to increased costs of processing the castings or, in extreme cases, to scrap pieces. The amount of thermal expansion of silica sand is influenced by various factors, including granulometric composition and chemical purity. It is the SiO2 content of the sand that contributes significantly to the degree of dilation, and which can vary depending on grain size alone. Two silica sand samples from the same locality of origin with different mean grain sizes were evaluated. The granulometric composition as well as the SiO2 and impurity content were evaluated by SEM analysis and XRFS and their effect on the linear thermal expansion. The effect of grain size on the final SiO2 content was observed, with sands of the same origin with larger grains containing 1.3% more SiO2 and achieving 36.8% higher dilatation. This combination increases the susceptibility of the sand, and hence the resulting moulding mixture, to the formation of foundry defects from braked stress as veining.Keywords: Silica sand, linear thermal expansion, chemical purity, SEM analysis, foundry defects
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