Volgograd State Technical University, Volgograd, Russia:
N. A. Kidalov, Dr. Eng., Prof., Head of the Dept. of Machinery and Technology of Foundry (MTF)
N. V. Belova, Lecturer, Dept. of MTF
A. A. Belov, Cand. Eng., Lecturer, Dept. of MTF, e-mail: aa-belov@bk.ru
A. S. Adamova, Cand. Eng., Associate Prof., Dept. of MTF

The second part of the work is devoted to the study of the effect of the destruction of a combined carbon-containing additive on the softening of sand mixtures with a liquid glass binder in order to improve the knockout of casting cores from steel castings. The combined carboncontaining additive proposed in the first part of this work was introduced into the composition of the sand mixture with a sodium liquid glass binder. From the prepared mixtures, prototypes were made to determine the residual strength after calcination at temperatures corresponding to the heating of casting molds and cores when interacting with liquid steel. Next, the fractures of the samples after calcination at specified temperatures were selected to study the effect of the destruction of the additive on the formation of the sodium silicate film structure on the refractory quartz filler surface using scanning electron microscopy. It has been established that in order to ensure an effective reduction in the residual strength of the liquid-glass mixture after it is heated to the melting temperature of sodium silicate, it is necessary to form a discontinuous structure of the binder film by creating conditions that promote the continuous process of sodium silicate carbonization during the destruction of the carbon-containing additive. Pilot testing of the proposed composition of the mixture for the manufacture of foundry cores of steel casting was carried out. It is shown that casting cores from the mixture with the combined carbon-containing additive have improved knockout, while the destruction of the additive does not significantly affect the deterioration of the castings surface quality and the depth of the decarburized layer.

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