Effect of the Composition of Hybrid Sands on the Change in Thermal Expansion

Abstract

In the foundry industry, silica sands are the most commonly used type of sands for the production of sand foundry moulds using various types of binders. Their greatest disadvantage is their significant volume changes at elevated temperatures, which are associated with the formation of many foundry defects from stress, such as veining, and thus have a direct influence on the final quality of the casting. In the case of non-silica sands and synthetic sands, the volume stability is more pronounced, but this is accompanied by a higher purchase price. Therefore, a combination of silica sand and synthetic sand CERABEADS is considered in order to influence and reduce the thermal expansion. The hybrid mixtures of sands, and their most suitable ratios, were evaluated in detail using sieve analysis, log W and cumulative curve of granularity. It was found that the addition of 50% CERABEADS achieves a 32.2% reduction in dilatation but may increase the risk of higher stresses. The measurements showed a significant effect of the granulometric composition of the sand on the resulting thermal expansion, where the choice of grain size and sorting can achieve a significant reduction in dilatation with a small addition of CERABEADS.

Differences in Characteristic Properties of Silica Sands from Neighbouring Deposits

“…On the other hand, the value of The grain arrangement probability criterion log W for the Grudzeń Las sample was 2.5% lower than that of the Biala Góra sample, indicating a more monofraction sorting characteristic of the Grudzeń Las sand. Generally, the sand becomes more monofraction as the log W approaches 0, and vice versa [21]. The log W result in the case of Grudzeń Las sand means that the sand was more sharply sorted and contained more grains in fewer fractions than in the case of Biala Góra sand.…”

Variability in the Distinctive Features of Silica Sands in Central Europe

“…However, technologically more significant is the transformation from β-SiO 2 to α-SiO 2 , occurring at lower temperatures, around 573 • C, accompanied by a sharp increase in volume of up to approximately 3.9% [11]. This transformation is reversible and is significantly affected by grain size (smaller particles resulted in higher dilatation) and chemical composition (sample with a SiO 2 content higher by 1.1% achieved 19.8% more dilatation compared with a sample with less SiO 2 ), as suggested by some studies [31][32][33].…”

“…In the case of samples SH 35, SE 22, and BK 23, they were rounded-grain sands with a smooth grain surface, as evident from Figures 3a and 4e,f. Rounded grains interlock well under load, forming assemblies with minimal pore content and point contact with adjacent grains [32]. The absence of pores between grains and cracks or otherwise irregular surfaces in samples SH 35, SE 22, and BK 23 made these samples more susceptible to higher expansion because there was no space to compensate for grain expansion, thus preventing a certain natural relaxation of this expansion.…”