Mechanism of Sintered Layers Formation in Green Sand Molds Using Artificial Sands

Most cast products are produced using sand molds, including green sand, organically bonded, inorganically bonded, and special molds. Silica sand is the most widely used material for manufacturing sand molds; however, its utilization presents several challenges, such as pneumoconiosis, risk limited recyclability, and casting defects. Therefore, replacing silica sand with artificial sand is essential. While artificial sand has effectively replaced silica sand in organically bonded molds, achieving a comparable substitution in green sand molds, which are the most widely used, remains difficult. This difficulty arises because, during casting, sintering at the bonding sites between artificial sand particles leads to the formation of sintered layers on green sand molds. These sintered layers are extremely hard to remove, thereby hindering green sand recyclability. This study aims to elucidate the unclear mechanism of sintered layer formation to help its prevent. Artificial sands for casting include mullite-based and alumina-based types. In mullite-based artificial sand, reactions are expected between the artificial sand and bentonite and between molten cast iron and bentonite. In alumina-based artificial sand, reactions are assumed among the artificial sand, bentonite, and molten cast iron, as well as between molten cast iron and bentonite. K2O, a component of artificial sand, acts as a flux that promotes these reactions. Hence, the formation of sintered layers can be suppressed by reducing the K2O content in artificial sand.