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

L. I. Leushina, Cand. Eng., Associate Prof., the Chair “Metallurgical technologies and equipment”
I. O. Leushin, Dr. Eng., Prof., Head of the Chair “Metallurgical technologies and equipment”, E-mail: igoleu@yandex.ru; kafmto@mail.ru
M. A. Larin, Cand. Eng., Associate Prof., the Chair “Metallurgical technologies and equipment”
S. V. Plokhov, Dr. Eng., Prof., Chair “Nanotechnologies and biotechnologies”

For reasons of economic feasibility, some domestic enterprises practice a duplex scheme for manufacturing multilayer shell molds for investment casting, which involves using expensive hydrolyzed ethyl silicate or finished binder for the internal, working, shell layers, and relatively cheap and environmentally friendly liquid glass for the outer, reinforcing layers. However, the reduced crack resistance of the outer layers of such forms often does not guarantee the stability of the quality of the obtained castings during the calcination of the shells and the subsequent pouring of the metal melt, which is especially unacceptable for the production of critical products. In this regard, enterprises are often forced to resort to an increase in the number of working layers of the shell or to the use of an energy-intensive technological scheme for casting casting molds in a support filler poured into special flasks from expensive heat-resistant material. The paper presents a solution to the problem of choosing an economical technological option to increase the crack resistance of the outer layers of the shell form on liquid glass, applicable to the conditions of the current production and not requiring significant expenditures during development. The known curing mechanisms of molding and core compositions based on liquid glass are analyzed, the conclusion is drawn that the dehydration is insufficient as the only curing mechanism for the outer layers of shells formed on the basis of a liquid binder, and the hypothesis of an increase in crack resistance of the liquid glass composition when several curing mechanisms are combined is formulated. As a working curing option for combining with dehydration, a CO₂-process was chosen, the physics and chemistry of which are discussed in detail in the article. Variants of non-deficient substances were evaluated that could play the role of a technological additive to the mold material during its manufacture at the base enterprise while simultaneously performing the most important function of the supplier of carbon dioxide. As a result, carbonate and ammonium bicarbonate were selected, the use of which allows to provide the required level of characteristics of the casting mold. A pilot test of a solution to a problem successfully confirmed its effectiveness and acceptability for existing production.

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