Estudo da caracterização dos constituintes utilizados para o sistema de moldagem em areia a verde aplicados ao processo de fundição

Abstract

The purpose of this research was the characterization study of the components applied in the green sand molding system, evaluating the importance of the properties control of these materials when submitted the molding and to the casting process. The compostion of the green sand is a mixture of new sand, commonly silica sand, bentonite (acting like a bonding agent), coal dust (additive for better surface qualities) and water. The materials applied were a 66 AFS new sand, 55 AFS reclaimed sand, sodic bentonite, Cardiff Coal Dust and distilled water. Appropriate mixers are used to promote the coesion in the grains of the silica sand, bentonite and coal dust, providing important properties to the system, such as plasticity, consistency, compactability, permeability and mechanical strenght. These properties have dependence with the granulometric distribution of silica sand, the bentonite swelling and the umidity content. The phases of the mold building totally depends of these green sand properties, that is subjected to deterioration process when silica grains are exposed to the melted metal directly on the green sand surface, making sand reclamation. The oolitization process (sinterization of the clay materials and fines in the sand surface) occurs when the molten metal is verted on the mold, promoting the sand reclamation process, carring on some loss of properties, such as compactability, mechanical strenght, that might be restored by a new addition of bentonite and coal dust. However, the addition level of additives to the green sand is higher than to the original pattern because the higher the ooliltization, the higher the consumption of additives process to promote the same level of properties like compactability and permeability before a new exposition to the casting. The oolitization rate is increased and when reached, the viability of adding new additives is prejudicated, turning the sand of reclaim in a solid waste that promotes environmental impacts, that is the biggest problem of this process.