THE ADHESIVE HARDENING MECHANISM AND HYGROSCOPICITY-RESISTANT OF A-STARCH COMPOUND BINDER FOR DRY SAND MOLD (CORE)

摘要

The adhesive hardening mechanism and hygroscopicity-resistant of a-starch compound binder for dry sand mold (core) were studied by way of DSC, XRD, IR spectra analyses and SEM. It is thought that the bonding strength of molding sand is mainly depended on the strength of the adhesive membrane itself. While the binder is heated at certain temperature between 160°C -200°C for one hour, the reactions of condensation and condensation polymerization as well as esterification happen between silicon-hydroxyl groups (-SiOH) of sodium silicate, starch and sodium silicate, starch and phosphate respectively, thus, a three-dimensional skeleton mainly consisting of Si (silicon), O (oxygen) C (carbon), P (phosphorus) is formed. And kaolin grains adsorbing a layer of starch gum are well-distributed in the skeleton, therefore the binder is provided with higher low-temperature drying strength and better hygroscopicity-resistant. Because kaolin in the binder can react with sodium silicate and phosphate at high temperature separately, forming Al-O-Si three-dimensional skeleton and AIPO_4 correspondingly, the binder is also provided with higher high temperature-resistant strength.