Research On Characteristics Of Moisture Absorption And Moisture Resistance Of Sodium Silicate Sand

Sodium silicate sand is considered to be the mould sand that is most likely to realize green casting. In order to achieve the goal, it must be completely solved the problems including the bad collapsibility and difficult reclamation for the sodium silicate used sand. The research and practice results showed that the best way to resolve the above problems is to minimize the adding quantity of sodium silicate binder. After many years hardworking, researchers have found effective methods to reduce the adding quantity of sodium silicate binder, e.g. using new technology of sodium silicate sand hardened by microwave heating and new types modified sodium silicate binder, etc., but when adding quantity of sodium silicate becomes low the sodium silicate sand strength is very sensitive to the environment humidity. The sodium silicate sand strength would significantly drop because of strong moisture absorption in high humidity environment.In this thesis, it was tested systematically that the moisture absorption disciplinarian of some typical sodium silicate sand processes includes CO2 hardening process, powder hardening process, ester hardening process and microwave heating hardening process. The moisture absorption properties of these sand samples were compared and analyzed. The results shown that the moisture absorbability of sodium silicate sand hardened by microwave heating is consumedly stronger than the ones hardened by ester, CO2 or powder, so the sodium silicate sand hardened by microwave heating has the strongest moisture absorbability. In this thesis, it was analyzed that why the difference in moisture absorbability of the above four typical sands was generated based on the hardening mechanism, micro-morphology and film composition, and it was expounded that how the sand strength was established during hardening process and the strength was lossed after absorbing moisture.Aiming at the sodium silicate sand hardened by microwave heating, and combining the common problems of sodium silicate sand process, it was analyzed the factors influence the moisture absorbability of sodium silicate sand hardened by microwave heating. Some measures were proposed to improve moisture resistance. The moisture resistance measures include using modified sodium silicate binder and shielded humidity foundry coating. The results showed that the strength of sodium silicate sand sample, which established during microwave heating hardening process, was increased about 25% when sodium silicate is modified by PVA. The strength of modified sodium silicate sand samples placed in the environment with relative humidity 95% to 98% for 48 hours is double to the ordinary sodium silicate sand samples placed in the same humidity. Applying alcohol-based foundry coating, the strength of sand sample placed in the environment with relative humidity 87% to 90% for 48 hours is enhanced more about 88% than the strength of ordinary sodium silicate sand sample placed in the same humidity. The problem of strong moisture absorbability is the common problem of sodium silicate sand. It is also the most difficult problem of practical application sodium silicate sand hardened by microwave heating. In this thesis, the research results of moisture absorbability and moisture resistance of sodium silicate sand hardened by microwave heating have laid foundation for solving the problems of moisture absorbability of sodium silicate sand, and it also has an important promoting effect on practical application of sodium silicate sand hardened by microwave heating.