Evaluation of possibility of using a complex technological additive to reduce the residual strength of sand-liquid glass mixtures used for production of steel castings

The formation of residual strength of sand-liquid glass mixtures under the conditions of interaction of sodium silicate films with a complex technological additive after calcination of standard cylindrical samples at a temperature of 800 °C was studied, which allows to estimate the knockout of casting molds and rods used to obtain large-sized steel castings. Refractory molding clay (GOST 3226–93), metallurgical dust (hazard class IV according to FCCW), formed during the cleaning of gases exhausted from arc steel-smelting furnaces, and spent coffee grounds (hazard class V according to FCCW), which is a waste resulting from grinding coffee beans and subsequent extraction during its preparation in coffee machines, were used as components of the technological additive. The latter is a new material for foundry production, the share of the organic component in which, depending on the coffee variety and region of cultivation, according to a preliminary information and analytical review and determination of the elemental composition of spent coffee grounds by X-ray fluorescence analysis on an EDX-8000 spectrometer, is 98–99 %. The stability of the composition and the available raw material base of this waste, caused by the domestic popularization of coffee, accompanying the growth of its consumption, as well as the lack of a system for its centralized processing and disposal, allow to consider spent coffee grounds as one of the softening components in the compositions of molding and core mixtures. As a result of determining the physical and mechanical properties, a positive effect of the complex additive on the formation of the raw and residual strength of the studied sand-liquid glass mixtures was established due to an increase in adhesive bonds in the “quartz sand - technological additive - liquid glass” system in a wet state and a violation of the integrity of the binder films after calcining the rods at a temperature characteristic of heating the mixture under conditions of large-sized steel casting due to thermal destruction of the organic component of the spent coffee grounds and a shift in the temperature peak of the second maximum of the mixture`s residual strength to the region of higher temperatures, arising from the chemical interaction of sodium silicates and iron oxide, which is a part of the metallurgical dust.The research was carried out at the expense of the funds of the development program of VSTU “Priority 2030”, within the framework of scientific project No. 8/647-24.