Nizhniy Novgorod State Technical University (Nizhniy Novgorod, Russia):

I. O. Leushin, Dr. Eng., Prof., Head of the chair “Metallurgical equipment and technologies”, e-mail: igoleu@yandex.ru
L. I. Leushina, Cand Eng., Associate Prof., e-mail: kafmto@mail.ru
O. S. Koshelev, Dr. Eng., Prof., Chair “Machine-building technological complexes”

Drying of the shell after the application of the next layer of slurry and refractory covering material to the model is one of the limiting operations of the technological process for the production of castings for removable (melted, burned, gasified) models. The article presents a critical analysis of some known solutions of the problem of reducing the duration of layer-by-layer drying of the suspension and coating applied to the model block. An alternative providing introduction of a small amount of alum into the composition of applied refractory coating material is proposed. The hydrophilicity of alum along with the acceleration of the drying process in the open air allows to provide in a short period of time gelatination, thereby preventing washing of the applied layer from being washed off during subsequent immersion in the slurry of the refractory filler in the binder solution. At the same time, the coacervation effect is quickly achieved and fixed upon contact of the dusting with the suspension, thereby reducing the necessary drying time and improving the environmental friendliness of the process. The chemical nature of the binder does not change, which preserves its adhesive ability and, as a result, provides high strength properties of the shell material. At the same time, the probability of swelling of the previous layer is minimized when it is wetted by the next layer, leading to buckling and swelling of the shell. As a result, a high level of manufacturability of the ceramic shells is ensured and a minimum of casting defects due to the shape fault is consequently achieved. The sequence of manufacturing operations in the basic technology of manufacture of shell moulds for casting on removable models does not change, additional equipment is not required, additional personnel is not involved. Innovative technology has been successfully tested under current production conditions and recommended for use.

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