PARAMETERS INFLUENCING WET TENSILE STRENGTH OF MOULDING MIXTURE

摘要

Scabbing occurs when pouring large size castings, resulting in presence of scabs in castings. Pouring of molten metal exerts following influences on the mould: mechanical influences, chemical and heat influences. Heat introduction dries the mould, so that at the top of the mould cavity we have temperature approximately equal to temperature of the molten metal, which varies depending on the height of the mould. Water content in the mould evaporates and condensate in the mould zone called wet tensile zone, where temperature reaches 100°C. Consequently we get reduction of mould mixture strength, scabbing, falling and creation of sand scabs on the casting. Numerous variables affect this phenomenon of scabbing, whereby our paper undertakes to examine only a few of them, such as: moisture percentage, bentonit content, medium size of quartz sand and mould compression strength.