Influence of Temperature on the Mechanical Strength of No-Bake Sand Molds Bonded with Alkaline Phenolic Ester-Cured Resin

Abstract Sand molds bonded with alkaline phenolic resins and ester-type hardeners are widely used in no-bake foundry processes due to their suitable mechanical performance and relatively low gas evolution. However, the combined effects of curing temperature and resin–hardener reactivity on mold strength remain insufficiently investigated. This study evaluates the influence of temperature on the mechanical performance and processing behavior of nine commercial resin–hardener formulations under conditions representative of foundry environments. Sand molds containing 1.35 wt.% resin (based on sand mass) and 25 wt.% hardener (based on resin mass) were produced and evaluated at 15, 25, and 35 °C. Tensile strength and bench life results were statistically analyzed to determine the effects and interactions among resin, hardener, and temperature. Significant interactions demonstrated that temperature does not affect all formulations uniformly, while no significant overall correlation was observed between bench life and final mechanical strength. R1 showed inadequate strength at 15 °C regardless of the hardener, whereas R2 combined with C2 achieved the best overall performance, particularly at 25 °C. In contrast, R3 exhibited higher 24 h strength at lower temperatures, and some formulations continued to develop strength up to 48 h, indicating slower curing kinetics. These findings demonstrate that faster curing does not necessarily result in higher final strength and that resin–hardener selection should consider formulation reactivity and processing temperature. The results provide practical criteria for selecting no-bake alkaline phenolic systems under seasonal or operational temperature variations, contributing to more reliable mold production and greater flexibility in industrial formulation selection.