Guniting concretes have been widely used in recent years to line firing plants.The main bonding component of aluminosilicate guniting concretes i& alumina or high-alumina cement.According to All-Union State Standard (GOST) 969-77, alumina cement grades 400 and 500 is prepared from blast-furnace slag; the cement mainly satisfies the requirements set for it in relation to binding properties and strength.The high-alumina cement VTs-75 made from ironsmelting slag in accordance with the Technical Specifications (TU) 21-20-25-76 has unstable binding properties and strength due to the conditions under which it is made.In the clinker from ferrosmelting slags supplied in the form of lumps measuring <50 mm, there is a large amount of inert components: calcium hexaaluminate (up to 35%); Mg(AI, Cr) 204 spinels (up to 5%); metallic chromium; etc.The presence of these components has a bad effect on the quality of the VTs-75 cement and lowers the strength of the concrete based on it.When samples were taken before the off-loading of the clinker, it was established that there were six types of clinker (A-F) which differed in their external appearance and their chemical and mineral compositions. In the clinker supplied for the manufacture of VTs-75 cement, varieties A (up to 10%), B (up to 40%), C (up to 20%), D (up to 15%), and E (up to 10%) are shown in Table i.It was established that the VTs-75 cements obtained from clinker with volume fractions of varieties A, D, and E of more than 15% and of Fof morethan 5%in thetotal mass and also the concretes based on them (Fig. i, period of manufacture 4-7) have a reduced strength.The strength of the guniting concrete based on alumina cement increases during the period of manufacture of the lining; the strength of the guniting concrete made from highalumina cement depends on the variety of the clinker and is less stable because of the variations in the concentration of inert components in the high-alumina cement.To evaluate the stability of the properties of the guniting-concrete mixtures we analyzed the mineral composition of the clinker supplied to produce the cement in accordance with the criterion of workability when manufacturing guniting concrete linings. The compositions of the guniting concrete mixtures are given in Table 2.To improve the working properties* of the guniting mixture based on high-alumina cement we added 3% refractory clay to the composition. The criterion of workability in this case is the index used to evaluate the properties of guniting-conerete mixtures and was determined from a comparison between the results of chemical and petrographic analyses of the mineral composition of the clinker and the strength, adhesion, and porosity of the guniting-concrete coatings.

At present guniting is widely used in the repair and preparation of the linings of thermal equipment with the use of chamotte guniting compounds containing aluminocalcium cements [1][2][3][4]. The necessary properties of the gunited concrete coatings are determined by the operating parameters of the guniting machine, including the pressure of compressed air in the dry aereated mixture hose, the pressure in the moistener hose, and the distance from the nozzle to the surface to which the coating is being applied.It is known [5, 6] that the pressure of the compressed air and the distance from the nozzle to the surface being gunited determine the pressure of the stream of compound on the surface, upon which depends the density and strength of the layer of gunited concrete coating and also the amount of spring-back.The moisture of the gunited compound is regulated by the pressure of the moistener. A high moisture content leads to slipping or runoff of the compound from the surface while the compound held to the surface forms a gunited cement coating with high porosity and low strength. Low moisture content produces increased dust formation, an increase in losses of compound with the spring-back, and a reduction in the strength of the layer of gunited concrete coating.The basic requirements for linings of gunited concrete in thermal equipment are high strength and low porosity [7, 8], which determined the necessity of searching for the guniting parameters in mass preparation of the linings of new thermal equipment. For a solution of this problem experimental guniting was done on a stand equipped with an SB-67A guniting machine and a tank with a VK-5/24A-U2 peripheral pump.For the guniting a dry mixture* of 25% cement and 75% type AShA chamotte powder of class No. 4 according to All-UnionState Standard (GOST) 23037-78 was prepared. The temperatures of the hardener (water), the air, and the lining were constant (20~ Cement of two types was used, type 500 alumina to GOST 969-77 and VTs-75 high alumina to Technical Specification (TU) 21-20-25-76.In guniting the coefficient of adherence, the ratio of the weight of the compound adhering to the surface (the layer of gunited coating) to the weight of the original compound, was investigated. After preparation of the samples (cutting out) from the layer of gunited concrete, a moist hold for 72 h, and drying at II0~ for 5-8 h their compressive strength was determined according to and the open porosity to GOST 2409-80.About 70 tests were made and 57 groups of values of the guniting parameters and the properties of the gunited coating (adhesion, strength, and porosity) according to the task formulated were obtained. From the results obtained the original data was set up for calculation on a Mir-I computer of the optimum guniting parameters. For this the guniting parameters were adopted as the independent variables (Table i). The boundaries of variation of the independent variables were determined experimentally and the level of variation by analysis of the parameters of guniting,...

At the NorthMining-BeneficiationCombine (NlVIBC) pellets are roasted in two imported machines (service life more than 6 years) and two home-produced OK-306 machines (service life more than 3 years). Their design features are shown in Fig. 1, together with the sites at which samples of slag and the liping were taken. The pellet-roasting regimes are characterized by the mean temperatures and pressures over the zones of the roasting machines (Fig. 2).During these investigations we observed "inverting" of the cone, leading to a temperature rise in the branch pipes of the return flow manifold and to fusion of the lining. .C:ooUng , Gas-ai~ chamber numbers H) above pellet layer; 1) in gas--air chambers; 2) above pellet layer; 3) total pressure.All-Union Institute of Refractories. North Min|ng-Beneflciation Combine. Translated from Ogneupory, No. 10, pp. 33-40, October, 1979. 0034-3102/79/0910-0621 $07.50 9 1980 Plenum Publishing Corporation 621 The following m a t e r i a l s a r e used for the lining of the home-produced machines: high-alumina MKO-72 and MLO-62 artifacts, ShB-1 chamotte brick for laying the roasting, recuperation, and I cooling zones; VGL-1.3, ShLB-1.3, and SkLB-0.4 heat-insulating brick, kaolin wool, and heat-insulating gunite concrete, developed by the E a s t e r n Institute of R e f r a c t o r i e s (30% of M500 alumina cement, 30% of chamotte filler, and 40% of chrysotile asbestos of 7-450 brand); the t e m p e r a t u r e of the lining during use reaches 1000~The concrete is used for gtmiting the forward flow manifold and the branch pipes to the precombustion c h a m b e r s . Heatinsulating m a t e r i a l s constitute up to 50?o of the lining volume.To investigate the physicochemical effect on the r e f r a c t o r y lining we determined the g r a i n -s i z e and chemical compositions of the dust and gases. The g a s e s (the combustion products of natural gas of the Shebelinsk deposit) contained 0~ CO, 0.2-0.6% CO2, and 19.75-20.8% 0 2. The dust content of the g a s e s was 1.31 k g / m S ; the m o i s t u r e content was 10 g / m 3 (under n o r m a l conditions).The m e a n -s i z e composition of the dust (broken pellets) was as follows: 1.1% of the --2/~m fraction, 18.2% 5-10/~m, 23.8% 10-20t~m, 21.50/o 20-40/~m, 8.7% 40-60/zm, 4.2% 6 0 -8 0~m , 2.6% 80-100/~m, 4.1% t o r y . The s t r u c t u r e of the slag is c h a r a c t e r i z e d by i s o m e t r i chematite grains, the size of which ranges f r o m 0.02 to 0.08 ram, and a vitreous substance (Fig. 4). Table i shows the phase composition of the mullite--corundum brick with slag.The l e a s t -a l t e r e d zone is yellowish, dense, and uniform. Microscopic examination r e v e a l s s e c t o r s of mullite and corundum aggregates and a porous binder. The mullite aggregates consist of dense intergrowths of c r y s t a l s ; the corundum aggregates a r e l e s s dense. The vitreous substance is distributed in the binder fairly uniformly, but predominant filling of the p o r e s is observed.The intermediate zone is m a c r ...

No abstract

No abstract