한국주조공학회

The effect of sodium gluconic acid on the collapsability of the sodium silicate type CO_2 mold was studied. The bending strength was saturated with gassing CO_2 for 60 sec. under 1kg/cm^2 and with the flow rate of 10L/min. It was decreased with aging after having been fully hardened. The retained strength was reduced in the heating temperature range of 100~1,100℃ and the retained strength peak near the heating temperature of 100℃ was removed by the effect of the sodium gluconic acid. Silica gel, Na_2CO_3 and dehydrated sodium silicates were formed from the binder of sodium silicate with the addition of sodium gluconic acid at the heating temperature of 100℃. Na_4SiO_4 was formed by the reaction of Na_2O, from decomposed Na_2CO_3, with the dehydrated sodium silicate at 500℃. The crystobalite type of SiO_2 was formed at 900℃. The sodium gluconic acid had no effect on the bending strength at around 1,100℃ due to the combustion loss of it.