Periclase carbonaceous refractories are currently used in those regions where there is extra wear on the linings of the superheating zone and of the slag wells of steel-smelting aggregates [1][2][3][4][5]. These refractories are gradually replacing the periclase-chromite and fusecast refractories used to date.In order to determine the physicochemical processes which occur in the molding of periclase carbonaceous articles, we studied the effect of the forms of binder and the carboncontaining materials on the degree of burn-off of the carbon in micrograin mixtures consisting of slntered periclase powder and carbon.Taking into account the technicoeconomic information and the fact that the properties , of the refractories must satisfy high user standards, we used a sintered periclase powder PPE-88 which meets GOST 24862--81 and different forms of carbon-containing materials (Table i).As the binding materials (10 parts by wt. added to 100 parts of the mass of dry batch) We used technical sodium polyphosphate (NaPO3)n toGOST20291--80 with a density of 1.45 g/cm3; wate~ glass grade B, Na20,SiO2-mH~O with a density of 1.35 g/cmS; and ethyl silicate E'TS-32 and ETS-40 to TU 6-02-641-76 and TU 6-02-895-78, respectively.The batches for pressing were made using a method involving the simultaneous milling of the periclase powder and carbon-containing material in a 60:40 ratio in a vibromill before passing at least 90% through a 0.06-mm mesh sieve. The specimens of cylindrical shape, 25-mm diameter and height, were pressed at 100 MPa and heat-treated at 1000~ with a 2-h dwell in a furnace with sillite heaters.After the firing we made an approximate calculation of the relative (Amre I) and absolute (dmabs) degree of burn-off of carbon in accordance with the formulas:C where mz is the mass of the specimen before firing, g; m2, mass of the specimen after firing, O g; n, mass fraction of carbon-free material:; Amrel, relative loss of mass of the carbon-free material, %; and C, mass fraction of carbon in the batch, %.The results showed (Table 2) that the greatest degree of burn-off is found in the natural crystalline graphite from the Zaval'evsk Deposits (batch 2-P).It was established that the use of sodium polyphosphate is preferable to that of water glass for reducing the burn-off of carbon.A complex thermal analysis (CTA)* of specimens was carried out in 0D-102 and 0D-103 derivatographs in air over the 20-1000~ temperature range. The rate of increase in the temperature:reference material was aluminum oxide. The portions weighed 0.3-1.0 g. The results of the thermographic studies (Tables 3 and 4) showed that the degree of burn-off of the carbon-containing materials from masses containing water glass is greater than from those *The study was carried out by E. I. Kelareva (Eastern Institute of Refractories). L. I. Brezhnev Dnepropetrovsk Metallurgical Institute. Eastern Institute of Refractories~
Before ramming (molding) of suspended structures the reinforcing, the height of which must be not more than 50% of the total lining thickness, is prepared.The configuration of the reinforcing may vary (grid, split and bent metal plates,?pins, etc.). The parts of the reinforcing are welded on in a checkerboard pattern at a distance from one another of i00-150 mm. The diameter of the bars and the thickness of the plates used for the reinforcing must be not more than 7 mm.To form the outer surface of the lining a template sheath of sheet metal or wood was prepared.With the use of a reusable sheath it is covered with machine oil before ramming the concrete for better removal of it after completion.The prepared mixture of stiff consistency is packed with air rammers with an air pressure in the lines of 0.4-0.6 MPa. The thickness of the layer of mixture before ramming (single filling) must be from 40 to 60 mm.With the use of a mixture of plastic consistency manual ramming or a vibrator is used for better packing of it and removal of the air bubbles. The depth of a single filling of the mixture is 80-100 mm.
A new process for production of corrosion-resistant steels provides for refining of the high-alloy semifinished product produced in electrical furnaces in a converter with bottom blowing. Before pouring into the converter, solid metal additions in a quantity of 10-12% of the weight of the heat are added to the semifinished product.The refining is done by blowing the metal bath with gaseous mixtures with different oxidation potentials, which leads to alternation of oxidation and reduction service conditions of the lining. To correct the slag conditions of the heat, lime and fluorspar are added to the converter bath.The gas--oxygen refining (GOR) process is conducted in a converter with a detachable bottom in the center portion of which are located "tube in tube" telescopic tuyeres for supplying gases to the molten metal.In oxidation periods I and II of the heat the metal bath is blown with oxygen with a protective (natural) gas and with a mixture of oxygen and a neutral gas, respectively, and in period III, the reducing period, with only neutral gas.The converter has the form and dimensions normal for similar 60 ton converters. Its walls are lined with fired periclase--chromite parts and the bottom with unfired periclase--carbon ones.Testing in the converter lining of periclase--chromite parts of sintered periclase powder and chromium ore showed their insufficient wear resistance (not more than 53 heats), which was responsible for the use of PShPKh parts made of expensive and scarce fused materials, periclase--chromite, chrome-alumina spinel, and periclase. Under similar service conditions PShPKh parts provide a converter life of up to 80 heats but their use has a significant influence on the economic indices of the process as the result of their high cost.During service of the lining the slag belt, the life of which limits the length of a campaign, is subjected to especially intense wear.The basic failure factors acting on the lining of a GOR converter are the high temperature of the process (up to 1700-1720~ the alternating oxidation--reduction character of the gaseous atmosphere and the molten slag, the aggressiveness of the slag, the unjustifiably long time of contact of the lining with the slag in period III, and the long interheat downtimes.With positive test results in the lining of a GOR converter of PShPKh parts the question of replacement of them with refracturies equivalent in wear resistance but less expensive made of not so scarce and expensive original materials remains a pressing one.
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