A new binder system for preparing high strength inorganic molds in precision casting

A new composite binder system has been developed to improve the strength and to decrease the processing time of inorganic binder mold for precision casting, as functions of dipping time and binder composition. The new binder system was prepared by mixing tetraethyl orthosilicate and polydimethyl siloxane as silicate precursors, and sodium methoxide as the precursor of sodium oxide. Samples of molds coated with an organic binder were dipped into the prepared binder systems, and then heat treated at 1000 °C for a period of 1 h. The fracture strength was markedly enhanced in the new binder systems owing to the increase in reaction depth, independent of the dipping time, whereas the fracture strength of the conventional binder system was not increased, even after a dipping time of 2 h. The new binder system containing 7.6 wt% PDMS showed the highest nominal strength of 8 MPa. When PDMS was used as the silicate precursor in the new binder system, the high glassification efficiency of silicate led to the higher fracture strength, resulting from the lack of hydrolysis and condensation reactions of PDMS. The fracture strength could be controlled by changing the molecular structure of binder and the binder composition.