Defeitos de fundição em ferro fundido cinzento: investigação de causas e alternativas de mitigação

Abstract

Green sand casting is a process through which parts of varying size, weight, and geometry are produced by pouring molten metal into the internal cavity of a non-permanent mold, composed primarily of a mixture of sand, clay, and water, followed by solidification. This process is widely used for the manufacturing of cast iron parts, and the control of each stage of the casting process is essential to avoid defects that may lead to the rejection of the casting. This study aimed to analyze defects found in engine brake manifolds made of gray cast iron, which are considered vehicle safety components, manufactured using green sand molding, with an emphasis on investigating the causes and proposing mitigation measures. For this purpose, analyses of chemical composition and hardness were conducted, along with optical and scanning electron microscopy, as well as characterization of the molding sand. Based on the results obtained, the hypothesis was raised that the defect found in the manifolds, which led to the rejection of these components, is a slag inclusion, caused by a combination of factors such as excessive sand compactability and low permeability; possible misplacement of the ceramic filter; and geometric conditions of the part that favored impurity retention. Considering this hypothesis, alternatives to minimize the occurrence of inclusions include adjustments to sand compaction and proper positioning of the ceramic filter.