Results are presented for a laboratory study of the substance composition of a periclase-carbon torcrete mix for restoring a converter lining, comparative methods for testing a torcrete mix under laboratory conditions, and the main production parameters for a torcrete mix under existing production conditions. Industrial tests are performed in the converter section of the OAO MMK oxygen-converter workshop. The life of a torcrete layer is two melts.Semidry torcreting relates to a number of efficient technologies for servicing the lining of a steel-pouring unit during operation. In the oxygen-converter workshop (OCW) of OAO MMK for hot repair of the most worn zones of a converter lining, i.e. the pouring and tilting cradles, trunion zones, torcrete mixes of periclase-carbon composition are used. Since OAO MMK has a natural raw material base for producing refractories of basic composition, specialists of the technical services studies the possibility of preparing torcrete mixes for restoring a converter lining under actual production conditions, i.e., in the workshop of magnesia-dolomite refractories (MDRC) of OOO Ogneupor.In developing torcrete mix compositions under laboratory conditions the refractory filler used was periclase powder or composite material, consisting of fuzed periclase grains, bonded with flaky graphite by a synthetic resin. In order to improve the production and operating properties a combined binder was added to the composition of the torcrete mix, consisting of sodium polyphosphate and carbon-containing components (coal tar high-temperature pitch, SFP phenolic resin binder, Carbores), and special additions (silicate materials, bentonite, magnesium sulphate). Alongside the choice of these binder materials and additions the grain size composition of the torcrete mix was refined.In the first research stage a study was made of the adhesion properties of the compositions developed for degree of mix sticking with the refractory surface. Tests were carried out on plates with a cross section of 100´100 mm 2 , cut from periclase-carbon refractory. Plates were held at 1200°C in a laboratory furnace for 1 h, and then the torcrete mix moistened with water was applied to them. After settling, a visual estimate was made of the degree of adhesion of torcrete layer with the plate surface. For comparison a control mix adopted was series produced composition torcrete mix PUTMK-3 produced by NPO VOSTIO-Ural used in the OCW.From the results of the first stage of studying 22 developed compositions ten were selected exhibiting a high degree of adhesion with the refractory. Compositions with weak adhesive properties were excluded from further study. It should be noted that all of the composition selected contain sodium polyphosphate. In the first stage of laboratory studies a comparative estimate was made of the quality indices of laboratory specimens manufactured from torcrete mixes of control and test compositions in a laboratory hydraulic press under a pressure of 40 MPa. After pressing specimens were heat treated...
Results of a study of the effect of antioxidant additives, i.e., metallic aluminum and titanium diboride, on the quality parameters of periclase-carbon ladle refractories are presented. Laboratory studies have shown that the addition of the studied antioxidants into the batch increases the strength and lowers the porosity of the specimens. The size of the decarburized layer due to the addition of metallic aluminum and titanium diboride is virtually the same, but the use of TiB 2 adds additional strength to the decarburized and transition layers of the specimens. It is recommended that pilot tests be performed for joint introduction of the additives.A study of the mechanism of fracture of periclase-carbon refractories in contact with molten slag and metal has shown that decarburization of the functional zone affects the wear of the refractories considerably. Above 500°C the carbon component (graphite and the carbon binder) of the refractory oxidizes (burns out) and this process continues to the maximum service temperature [1]. This causes softening of the articles at 500 -900°C and increases their porosity. When the entire carbon is oxidized, the surface layer of the refractory is slagged, the periclase powder dissolves, and the contact products are washed out.In order to protect the carbon from oxidation the refractory composition is enriched with antioxidant additives in the form of fine powder, the amount of which is optimized for every kind of article; as a rule, the content of antioxidants does not exceed 5% [2]. These additives are oxidized by oxygen and by the iron oxides of the slag more rapidly, and this lowers the rate of carbon oxidation. Despite the limited proportion of antioxidant additives in the batch the former affect the properties of the refractory (oxidation, thermomechanical properties, corrosion, phase composition, etc.) quite substantially. The lining of the slag-line area of steel teeming ladles at the shop of magnesia-dolomite refractories of the "Ogneupor" Company is produced from refractories with metallic aluminum added as an antioxidant. In order to optimize the composition of the periclase-carbon articles the Company searches for more efficient additives capable of improving the oxidation resistance and raising the stability of the lining in the slag-line area. Analysis of published data shows that boron-bearing compounds possess higher activity than aluminum when heated in an air atmosphere [3]. The compounds include titanium diboride, boron carbide, magnesium diboride, boron nitride, etc. The antioxidant action of these additives is explainable by oxidation at a temperature exceeding 1300°C that yields a melt of magnesium borate (3MgO·B 3 O 3 ) and gaseous products of the reaction of oxidation of the borates (B 3 O 3 , gaseous Mg, etc.). The appearance of liquid phase promotes lowering of the open porosity and thus prevents the diffusion of oxygen into the refractory. The gases formed lower the oxygen pressure in the pores of the refractory, prevent oxidation of the graphite, diffus...
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