The Influence of Core Box Temperature, Modified Water Glass, and Strength Enhancer on the Properties of Carbon Dioxide Hardened Water Glass Binder Sand
摘要
This paper presents a novel water glass sand core-making process for cast aluminum alloys, characterized by low core box temperatures (≤ 100 °C) and enabling carbon dioxide gas hardening at ambient temperatures. The resulting sand cores exhibit comprehensive properties suitable for aluminum casting production. The effects of different core box temperatures on the strength and gel microstructure of CO2-cured water glass sand were investigated. Results indicate that at 85 °C, the tensile strength of water glass sand cores is significantly higher than that achieved at room temperature. Subsequently, the adhesive was modified, and the optimal ratio of adhesive components was determined through orthogonal experiments, resulting in instant, 4 and 24-hour tensile strengths of 0.52, 1.02, and 1.05 MPa, respectively. To further improve the strength and collapsibility of sand cores, the influence of different strength enhancer on the strength performance of sand cores was studied, and the optimal ratio of strength enhancer was identified through orthogonal experiments. The instant tensile strength of the prepared samples was 0.88 MPa, the 4-hour tensile strength was 1.32 MPa, the 24-hour tensile strength was 1.28 MPa, and the high-temperature residual strength (750 °C × 15 min) was 0.01 MPa. Finally, SEM observations revealed that composite modified binders obtained at the optimal temperature exhibited superior gel microstructure quality. This improvement is attributed to the formation of a more uniform, non-lamellar silica gel at the appropriate temperature. Additionally, accelerated moisture loss during sand mold hardening enhances binder strength. Foundry trials further demonstrated that the novel water glass core-making process yields superior surface quality for cast aluminum alloys compared to the traditional water glass sand core-making method.