No abstract

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.

No abstract

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.

At the Krivorozhstal' Factory the life,of the brick lining of the 150-ton steel-teeming ladles of the converter shQp is 19.O meltings, ~and that of the 330-ton ladles of the openhearth shop is 22.4~eltings.The specific consumption of ladle brick is fairly high (6.0-6.5 kg/ton of steel).Guniting is a promising and relatively easy way of enhancing the resistance of the ladle lining, reducing the consumption of ladle brick.Work on guniting of the steel-teeming ladle linings has been performed at this factory since 1974.In the open-hearth shop, the ladles are gunited by hand by means of an SB-67 (BM-60) guniter.In 1975, there was put into service in No. 2 converter shop a machine for mechanized guniting of the lining of 150-ton steel-teeming ladles [i], and 1977 saw the introduction of a machine which permitted guniting not only of the lateral surfaces of the ladle but also the bottom.The trend of the work on guniting has been selection of masses exhibiting operational stability, and refinement of the guniting procedure.It was established If] that guniting masses based on Chasov-Yar semiloamy sand, quartzite, and ordinary chamotte (A1203 content less than 32%) exhibit enhanced wear during service.Furthermore, when guniting is performed with quartzite masses, the personnel must be protected from the effect of finely dispersed silica particles.Despite the fact that masses based on Chasov-Yar sand are readily available and cheap, they have not been widely used, for the following reasons.To increase the life of a steelteeming ladle lining by from three to five meltings, we must deposit a gunite layer 110-120 mm thick [i]. However, layers of this thickness often slide during deposition, and their quality is poor.If the layer is thinner, to attain the above increase in the service life we must enhance the guniting frequency; this is not always possible, because it entails a reduction ~in the number of ladles in service. Chasov-Yar sands are nonuniform in both chemical composition and quality; this also reduces the life of gunned layers based on them.Chamotte masses are the most suitable for guniting.The quality of the guniting masses is improved by enhancing their aluminum oxide content [i, 2].