Sand inclusion defects are surface defects of wet molding clay sand expansion, which mainly appear on the upper and side large plane surfaces of castings. When the temperature of liquid steel is high, the water in the surface layer of green molding clay sand moves into the mold, and the sand particles expand when heated. However, the temperature of each part of molding sand varies greatly, the expansion is inconsistent, and the volume change of each layer of molding sand is inconsistent, resulting in compressive stress. The water migration reduces the tensile strength of molding sand, and it is easy to form sand inclusion defects after the impact of liquid steel.
Sand inclusion defects must be removed first and then repaired by welding. On the one hand, there are many cleaning work, and even the castings are scrapped in serious cases. The measures to prevent sand inclusion defects in the production of Wet Mold clay sand cast steel process are: to ensure the quality of raw sand and clay; Control molding sand moisture; Starch additives are added to provide space for molding sand expansion and reduce expansion compressive stress; Improve the compaction uniformity of molding sand, and the compactness should not be too high; Improve the pouring position to avoid sand washing and sand inclusion defects at important parts.