Specific fracture energy and de-agglomeration rate of silicate-bonded foundry sand cores

Abstract

Inorganic binder systems have found increasing applications, driven by environmental and legal regulatory requirements. As a consequence of their thermal stability, the mechanical core removal process is challenging and not fully predictable, owing to a lack of mechanical fracture energy data. In the present work, the wedge splitting test method was utilised to determine the specific fracture energy of sand cores, which was related to the strength and de-agglomeration rate results from the core samples before and after thermal exposure. Silica sand (quartz) and a synthetic sintered mullite, bonded with a water glass binder, were investigated. Following thermal exposure up to 400 °C, mullite-based cores retained a high strength without apparent bonding damage, an increased brittleness, and lower specific fracture energy. Following the same thermal exposure, quartz sand samples show decreased strength, Young’s modulus and brittleness, but retained a high specific fracture energy. The characteristic differences were caused by micro-cracks in the intergranular silicate bonds. Overall, an inverse relationship between the specific fracture energy and the de-agglomeration rate was found. In contrast to non-cast reference samples, shrinkage strain and thermal loading influences from the casting process resulted in much higher de-agglomeration rates for the cast-in samples. In summary, the wedge splitting test data provided relevant improvements for the description of de-agglomeration mechanics. Future research should cover the effects of brittleness and mechanical load intensity.