DEVELOPMENT OF THE TECHNOLOGY FOR OBTAINING ENGOBED CONSTRUCTION ARTICLES WITH THE "ANTIQUITY" EFFECT

The physical and chemical processes that occur when obtaining engobe coatings for construction ceramics with the decorative "antiquity" effect were considered, the composition of the charge, the technology of manufacturing and applying of the coatings on a ceramic product were proposed. The coatings have dark brownish-lilac color with a volumetric effect of light "variability". Engobes can be used when decorating the front ceramic bricks of single annealing with keeping at the maximum temperature of 1,070 °C. It was found that to provide a gradient volumetric decorative effect, it is recommended to introduce in the composition of engobe charge the microspheres of TPP fly ash in the amount of 3–5 %, and for the thick brown-lilac color – up to 60 % by weight of manganese ore. To ensure the necessary rheological indicators of the engobe slip and its high adhesion capacity, the fineness of grinding of charge components should be not more than 1 % by the residue on sieve No. 0063. The moisture content of the slip is 45 % and fluidity is 18 s. The mechanisms of shrinkage processes of engobe coatings and the ceramic base at different methods for application of the engobe slip on the product were established. To decrease the difference of shrinkage of the coating and ceramics, it is recommended to apply the engobe slip of the developed composition on the dried ceramic semi-finished product. After annealing at 1,070 °C, the products are of high quality with the indicator of water absorption of the coating of 5.2–5.4 % and hardness of ~5 by the Mohs scale. The obtained data can be applied in modeling of processes of engobing the products and in the development of compositions of engobe coatings. The practical value of the results consists in creating a new kind of the decorated building products, which enables increasing the market of its sales and enhancing the competitive capacit