It is necessary to use large and intricate (highly complex) products in a number of thermal units of ferrous metallurgy and other fields of industry.Fused mullite is one of the most promising materials for obtaining products possessing a long service life under load at high temperatures [i].This paper presents the results of our studies on the production technology of largesized intricate products (in particular, the blocks of the air belts of shaft furnaces intended for metallization of pellets). The technology is based on the vibrocasting (vibrational casting) method that facilitates mechanization of the forming process and obtaining uniform properties throughout the volume of the product [2].In this study, fused mullite was used as a granular constituent of the charge and as a finely dispersed (milled) binder obtained by vibrational milling.For the purpose of comparison, alumina was also used as a finely milled binder. Table 1 shows the chemical composition of the raw materials.Fused mullite contained 7.12% glass phase and 92.88% mullite in the form of long prismatic crystals.The GKZh-II hydrophobizing agent and sodium tripoliphosphate Na~P3Ozo [2] were used as additives facilitating vibrational movement of the body.In order to increase the strength of the dried products, we tried out additions of sulfite yeast mash (s.y.m) and bentonite. Gypsum molds were used both in laboratory investigations and industrial tests.The properties of the laboratory specimens are given in Table 2. For the charges containing a finely milled binder in the form of fused mullite the GKZh-II hydrophobizing agent is a better thinning medium; it permits one to obtain bodies having a lower moisture content as compared to the bodies containing sodium tripoliphosphate.The additions of sulfite yeast mash and bentonite make it possible to increase the strength of the dried specimens significantly; however, bentonite additions make it necessary to increase the moisture content of the body and the duration of holding the specimens in the mold and the bodies containing s.y.m adhere to the molds. TABLE i. Chemical Composition of Raw Materials Material Weight content, % SiO= TiO2 AI20= Fe~O= MgO CaO Na~O K=O Fused mullite 21,85 Absent 77,99 0,07 Trace Trace 0,II Trace PMLP-3 GK alumina 0,19 0,02 99,44 0,08 0,02 0,04 0,26 --
The progress of technology and the intensification of thermal processes are requir'mg a constant improvement in the quality of refractories production, an expansion of the range of types, and the creation of new high-efficiency materials. One of the progressive types of refractories for lining thermal plants comprises fibrous heat-insulating materials, which have low specific heat, negligible thermal conductivity, exceptional heat resistance, lightness, elasticity, and springiness. The use of fibrous materials enables us to reduce the heat consumption of thermal processes, the quantity of heat stored in linings, the times of heating and cooling the furnaces, and the weight of the linings. Considering the economic importance of the production and applications of heat-insulating materials, we are beginning the publication of a series of articles on "Fibrous Heat-insulation Materials."
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