The occurrence of “blowing” on liquid-glass mixtures during curing with carbon dioxide

One of the first mentions of the use of liquid glass in foundry production are the works of A.I. Zhilin, I.N. Zavyalov in the mid-30s of the XX century. At this time, the curing of liquid glass was carried out by drying, in order to accelerate the solidification process. The introduction of chemically cured liquid glass in the foundry for the preparation of molds and rods in the USSR was started in 1948-1949, which made it possible to shorten the technological process, increase production productivity, reduce labor intensity and significantly reduce the marriage of castings. But with the positive features listed above, when blowing the mold with carbon dioxide, foundry workers faced difficulties when using the CO2-process. Such difficulties were the presence of a prig and difficult knocking out of the rods, which prevents the active introduction of the chemical hardening process. The main reason for the shortcomings in chemical curing was the overdrive of a chemical reagent, that is, carbon dioxide. The optimal and scientifically proven curing time of liquid glass is the stoichiometric ratio of the coefficients in a certain reaction equation. Excessive purging time of liquid glass mixtures during curing with carbon dioxide leads to a decrease in the strength of the shaped product. This disadvantage largely depends on the significant accumulation of low-melting sodium bicarbonate in the molding mixture, which leads to the appearance of thermal burn. One of the reasons for the occurrence of thermal burn is the appearance of sodium bicarbonate, which has a low melting point, leading to low-melting inclusions, which lead to the appearance of burn. It is possible to remove fusible bicarbonate by adding water-soluble copper salts to the separation coating.