Chemically hardened sands offer a large choice of moulding and coring processes by the use of organic and mineral compounds. The use of these binders requires a knowledge of associated risks, to obtain a reduced residual resistance (in order to facilitate the discharging and the unstopping of the parts) and for the success of the products. The aim of this study was to rationalise the utilisation conditions of sodium silicate moulded sands, with additives, hardened by carbon dioxide. This should minimize the eventual defects in the cast parts. Sand resistance is very important right after the casting; it makes more difficult the tasks of discharging and unstopping. The need to incorporate organic matter to the sands becomes a necessity. The role of the organic matter is to reduce the sand resistance. The use of silicate binder requires the identification of the mechanism of the mixture hardening by carbon dioxide. It also calls for a knowledge of the gel structure formation, and of the influence of certain parameters on the properties. The experimental part is concerned with a comparative study of the behaviour of these sands in the foundry. The factors influencing this behaviour are: grain size, carbon dioxide blowing-in time, binder rates, adjuvant ratios and mixing time, etc... A thermographic study was carried out in order to perform the experimental work in real conditions. The obtained results have led to the determination of the optimal values of the above-mentioned parameters. This allows to obtain the smallest residual resistance, hence to improve the discharging and unstopping processes. This approach is clearly exhaustive and shows all possible interactions of the adjuvants with sodium silicate and the considered sands.
