Vliv granulometrické skladby ostřiva na kvalitu bentonitem pojených směsí

Abstract

The presented dissertation examines the influence of the granulometric composition and shape of silica sand grains on the quality of bentonite-bonded moulding mixtures. Six different types of washed silica sands with a high SiO₂ content from deposits in Central Europe were analyzed. The work focuses on the influence of granulometric composition, degree of sorting, grain shape, and surface on the properties of both the sand and the resulting properties of green sand moulding mixtures. The experiment is subsequently divided into two main areas of research: a detailed characterization of the silica sands used, including monitoring changes in chemical purity, surface characteristics, and linear thermal dilatation based on granulometry variation, and a partial characterization of the development of the mechanical properties of the resulting bentonite mixtures. The results show that round-grain sands with smooth surfaces exhibit lower absorbency and better moisture distribution, which enhances the mechanical properties of green sand mixtures, such as compressive strength and mixture toughness. In contrast, angular-grain sands, characterized by greater surface roughness and higher absorbency, result in lower strength characteristics. The research revealed that the granulometric composition, particularly the proportion of fine and coarse grains, significantly affects the compactability and permeability of the mixtures. Furthermore, grain shape, granulometric composition, and chemical purity of the sand significantly influence the thermal dilatation of the sands. This work confirms that the correct choice of sand, considering its shape, grain composition, and chemical purity, is crucial for optimizing the properties of bentonite-bonded mixtures for foundry purposes.