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The adhesion and cohesion properties of a Gun,re composition applied on a downward-facing surface, e.g., the roof lining of metallurgical furnaces, should be satisfactory not only in the application process but also during the heat treatment of the Gun,re layer, i.e., over a wide temperature range.The present authors have developed Gun,re compositions with a binder which not only improves the initial adhesion of the Gun,re mix but subsequently improves the adhesion and cohesion properties by virtue of the formation of a liquid phase at temperatures below 1000~ i.e., before the formation of a ceramic bond between the surface and the coating. The binder consists of a i/i mixture of sodium polyphosphate and sodium silicate solution.It is well known that in the initial stage of the gun,ring process the particles of the composition are retained on the surface by the molecular interaction at the points of contact [i]. Owing to its high viscosiy and good wetting power relative to the basic filler {2], the sodium silicate solution improves the cohesion of the particles and their adhesion to the coated surface, more especially during the application process when the temperature of the coating is not high.Heating the layer produces a liquid phase as a result of the melting of the phosphates (at 600-700=C). The presence of the liquid phase between the solid particles results in the formation of capillary forces which increase the force of cohesion of the particles by 2-3 orders compared with the molecular forces [3, pp. 20-33] and thereby h@ip the Gun, re to adhere to the lining surface and to give the coating the necessary initial firmness.The influence of the binder on the degree of cohesion between the coating and a refractory was investigated in laboratory conditions together with the physicomechanical properties of the coating. The refractory constituent was prepared in a ball mill by simultaneously grinding chromite ore (49.88% Cr=Os, 19.37% MgO, 12.62% Fe=Os, 5.60% SiO=, 8.67% Al=Os, and 0.87% CaO) and magnesite powder (86.43% MgO, 4.23% CaO, 3.65% SiO=, 2.15% Fe=O, , and 1.30% Cold adhesion stren~h, l~f/cm z, All-Union Institute of Refractories.

Investigations have been made to ascertain the feasibility of using dust, trapped during roasting of kaolin to chamotte, to make aluminosilicate guniting compounds. It was postulated that incorporation of highly dispersed dust into the charge would increase the density of the gunite coating and that the carbon introduced into its composition would reduce the wettability of the coating by metal and slags.The initial refractory materials for this investigation were ShKN-2 kaolin chamotte, Pologi kaolin, and dust collected by electrostatic precipitators and cyclones downstream of the furnace, during roasting of kaolin. Table 1 shows the chemical composition of the initial materials. The binder was sodium water glass (density 1.2 g/cm~ with ratio SiO2/Na20 = 2. The initial components were separately ground in a ball mill with metal balls. After grinding the kaolin chamotte contained 5?o of the + 2 mm fraction, 45?o of the 2-0.5 nun fraction, and 50% of the 0.5-0.09 mm one; the grain size of the kaolin and the dust particles was less than 0.09 ram.Using mechanical mixing, from the initial materials we obtain five guniting compounds containing 90?o of kaolin chamotte and 107o of kaolin, without dust and containing from 10 to 40% of dust (above 100%). The amount of binder introduced was 10% (above 100%).From the resulting guniting compounds, under a pressure of 100 kgf/cm 2 we molded cylindrical specimens (diameter and height 25 mm) and roasted them at 1600~176 i 8 9 10 . 1t 2, Fig. I. Diagram of gunlting sector: 1) ladle; 2) rotating arm; 3) manipulator; 4) pulverizer; 5) control disk; 6) guniting machine; 7) feed hopper; 8) belt conveyer; 9) tank with bubbler; 10) vessel for binder; 11) bin for powder. The guniting powder is fed to the bin from the working platform of the furnace.All-Union Institute of Refractories. Zaporozhe Refractory Factory. Zaporozhstal' Factory.

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