Binder-Free NaCl Cores via Core Shooting for Aluminum Gravity Casting

In metal casting, creating undercuts in components requires cores, typically made from sand–binder mixtures such as environmentally friendly sodium silicate binders. For intricate geometries like cooling channels, higher binder content is used to achieve sufficient core strength. However, removing inorganic-bound high-strength sand cores mechanically without residue remains challenging, limiting cavity complexity in thin-walled aluminum parts. This research develops an alternative process chain for aluminum gravity casting, using sodium chloride (NaCl) salt without binding agents as the core material in the core shooting process. Moist salt powder is fluidized with compressed air and injected into a mold, where crystallization - controlled by moisture content and drying - yields a stable, temperature-resistant core. After casting, the water-soluble cores are removed and can be recycled, eliminating harmful emissions and worker exposure to respirable dust. This study examines the influence of core-shooting parameters and in-mold drying on the three-point flexural strength of porous salt cores. Increasing the fine-particle fraction is found to enhance strength, and complete drying is essential. Binder-free, salt-based cores provide superior surface quality and sufficient strength for gravity casting and can be removed either dry or by washout with water. Future work will focus on strengthening the cores to meet typical sand casting standards and reducing the crystallization process time.