Research on the Relationship between Sodium Bicarbonate Content and “Over-gassing” in the Core Making Process of CO2 Hardening Sodium Silicate Sand

In this paper, we first defined and theoretically analyzed the “over-gassing” mechanism of CO2 hardening sodium silicate sand. “Over-gassing” is a term adopted to express the excess of CO2 agent beyond what is required to adequately cure the core that leads to the potential increase in NaHCO3. The final strength loss rate of CO2 sodium silicate sand is higher than 20%. As indicated by this paper, the sodium bicarbonate content of the sand sample increased with the increase in the storage time of “over-gassing” hardened sand sample, and the content was more higher on the sand sample surface. We investigated the effect of blowing process on the sodium bicarbonate content and bonding strength of sodium silicate sand. Furthermore, the composite blowing process could effectively increase the tensile strength of the sand sample, decrease the sodium bicarbonate content of the sand sample, and facilitate the prevention of “over-gassing”.