Service of zircon-containing nozzles for use in continuous steel casting plant

Summary During service in the casting of killed steel, zirconium containing nozzles took on a zonal structure. The least changed zone of the nozzles is scarcely distinguishable from the refractories before service. The working zones during service are saturated with oxides of iron, manganese, aluminum, silicon and titanium, and their amount is strictly related to the compositon and quantity of deoxidant.Highly refractory nozzles of ZrO₂ and made of a mixture of ZrO₂ and zircon, possessing a higher apparent porosity, acquire a larger working zone than nozzles made of zircon with clay additions.The dense working zone is more rapidly formed in nozzles made of zircon and clay. The oxides adsorbed in the pores of the refractory contribute to the tightening up of the aperture of the nozzles.Zircon nozzles with clay additions used at the Donets Steel Mill proved to have excellent wear resistance and the lowest tendency to closing up when casting low-carbon killed steels and can be recommended for permanent use in continuous steel casting plants.     

Service of zircon nozzles for continuous casting of converter steel

Conclusions In the continuous casting of converter steel without replacing the intermediate ladle between heats there is an increase in the resistance of the zircon nozzles. Wear somewhat increases with an increase in the number of heats from one to two, after which there is practically no change up to four heats.It became clear that an increase in the density of the zircon nozzles reduces their erosion.The nature of the erosion of zircon nozzles during continuous casting of converter steel does not alter, compared with the previously known character.With the use of zircon nozzles in the Red Army Silica Factory for rates 0.7 m/min, it is possible to cast without braking the jet of steel with the stopper.S. Z. Afonin, E. I. Ermolaeva, V. V. Parfenteva, V. D. Ryazantsev, and T. K. Chirkina took part in the work.Translated from Ogneupory, No. 1, pp. 20–23, January, 1968.     

Service of zircon nozzles for continuous steel casting

Conclusions The Chasov-yar Refractories Combine has introduced a technology developed by UNIIO for making zircon nozzles for continuous steel casting equipment. Zircon nozzles possess a high erosion resistance and give a more stable casting for killed and unkilled steels compared with other types of nozzle. Tightening of the nozzles when pouring killed steel depends on a number of factors (amount of reducing agent, casting temperature, chemical composition of the steel, refractory, etc.) and requires further study.T. M. Vysotskaya-Kvitko took part in the work.     

Nozzles for equipment for semicontinuous casting of stainless steels under synthetic slag

Summary The most aggressive influence is exerted by synthetic slag on aluminosilicate refractories, and the least — on zirconia and graphite-containing refractories.During the casting of steel under synthetic slag, high-alumina, zircon, and zirconia nozzles were cracked in the first minutes of operation and did not insulate the jet of metal from slag.Alumina-graphite, alumina-silicon carbide and alumina-graphite nozzles during the casting of steel did not crack, were only slightly eroded with slag and metal and provided normal working of the continuous casting plant.Alumina-graphite or alumina-graphite elongated nozzles are recommended for a unit used for the semicontinuous casting of titanium-containing steels involving synthetic slag.     

Physicochemical processes during the contact of steel with casting nozzles

Conclusions The results of physicochemical processes taking place in casting nozzles depend on the content of the steel of chemically active components and the composition of the refractory. An examination of the phase diagram of the systems forming contact zones in the nozzles enabled us to obtain a nomogram for determining the degree of erosion or tightening up of the nozzles in the intermediate ladles as a function of the composition of the refractory material and the content of aluminum in the steel being cast.In order to explain the stable feed of metal from the intermediate ladels in continuous steel casting plant in the crystallizer we recommend the casting of rimmed steel through magnesite nozzles, killed steel with a content of less than 0.01% aluminum through zircon nozzles, and containing more than 0.01% aluminum through fireclay (35–40% Al₂O₃).Translated from Ogneupory, No. 6, pp. 33–38, June, 1973.     

Service of refractories in the continuous casting of 100 ton converter heats

Conclusions Refractories for steel-casting ladles used at present in the converter shop of the Novolipetsk Factory can be used for casting 100-ton heats. However, it is necessary to increase the resistance of the ladle linings.Ladle bricks, stopper tubes, and zircon nozzles provide reliable casting of 3–4 heats in series without replacing the intermediate ladle.To provide reliable covering of the jets where necessary it is recommended that use be made of highalumina plugs for intermediate ladle stoppers.Translated from Ogneupory, No. 7, pp. 37–41, July, 1968.     

Improving the production of zircon nozzles for continuous steel-casting plant

Conclusions The use of zircon concentrate of original grain-size distribution for making nozzles reduces the dust concentration at the work sites, conferring a higher apparent density on the green briquette. The briquette can be much better pressed, which increases the output of the press. The loss of nozzles is halved.The properties of the finished goods correspond to the technical specifications. The zircon nozzles ensure four or more castings in service, instead of a single casting through a nozzle.The saving effect from using zircon concentrate of the original grain size was about 50,000 rubles per annum.Translated from Ogneupory, No.5, pp.1–4, May, 1972.     

Some properties of fine-grained mixtures of ZrSiO4-ZrO2

Conclusions The effect of additions of ZrO₂ in monoclinic and cubic modifications and also of Zr(OH)₄ on the swelling, thermal-shock resistance, and glass-resistance of high-density, zircon refractories has been studied.It is shown that the most effective addition for lowering the additional growth of the refractory almost fivefold was a mixture consisting of 9.5% monoclinic ZrO₂ and 0.5% Zr(OH)₄. This additive also increases significantly the thermal-shock resistance of the zircon refractories and the glass resistance as a result of the lower decomposition of ZrSiO₄, and the higher concentration of ZrO₂ in the contact zone. The density and electrical resistivity of the refractory is maintained at a high level.Translated from Ogneupory, No. 8, pp. 48–53, August, 1982.     

Life of refractories at semi-continuous casting plant

Conclusions High-alumina, zircon, chamotte-kaolin, zirconia, and clay-graphite end nozzles were tested in a semi-continuous casting plant during the pouring of stainless steel in the pouring device, and SP-25 high-alumina and zircon nozzles were tested in the intermediate ladle.For use we recommend the high-alumina nozzles which are considerably cheaper than the zirconia ones.Zircon and high-alumina SP-25 nozzles do not erode when steel is poured from the intermediate ladle, they do not close up and can provide a stream of metal without splatter.     

Submersible Ladle Nozzles for Continuous Casting Machines: State of the Art and Prospects of Development

The state of the art in the technology, properties, and uses of submersible quartz and corundum-graphite nozzles for continuum steel casting is considered. Corundum-graphite nozzles display a low heat resistance, increased air permeability and, moreover, are environmentally hazardous. The existing methods for updating corundum-graphite nozzles fail to settle the question of channel clogging in casting rimmed steel and other types of steel. Quartz nozzles fabricated by conventional technologies are devoid of these shortcomings; however, they have a shorter life because of the chemical interaction of alloying steel components and their oxides with SiO₂. Comparative tests on submersible quartz nozzles differing in structure and chemical and phase composition showed the emerging potential for new technologies and approaches in the production and uses of updated quartz glass-based nozzles for casting common and low-alloy steels. For casting common steels, updated submersible quartz nozzles are developed with a warranty endurance, under slab CCM operating conditions, of 720 tons (in terms of steel cast) against the rated life of 1200 tons. For low-alloy steels, modified submersible quartz nozzles are recommended with a warranty endurance of 360 tons (in terms of steel cast) against the rated life of 540 tons.     

Relationship between phase changes and engineering properties of materials based on the ZrO2-CeO2 system

Conclusions Complete stabilization of ZrO₂ is obtained by adding 20% (mol) CeO₂ at 1700°C with a 3-h soak, and cooling for 10 h.Using the tendency of a solid solution of ZrO₂-CeO₂ to partial decomposition when slowly cooled after firing at high temperatures, it is possible to obtain a zircon refractory with a high thermal-shock resistance, by arranging uniform redistribution of the decomposition product in the structure of the articles that is, monoclinic solid solution.The poor recrystallation capacity of presynthesized tetragonal solid solution does not guarantee the production of a more perfect microstructure in the product obtained from its combined firing with mono-clinic ZrO₂, which is one of the main causes for the low thermal-shock resistance of zircon products of this type.Translated from Ogneupory, No. 5, pp. 40–43, May, 1968.     

Sintering and properties of zircon ceramic with glass-forming additives

Conclusions The sintering and properties of a ceramic based on zircon with additions corresponding to eutectic mixtures of three-component glasses have been studied.The sintering of zircon with glassy additives is determined by the amount of the decomposed zircon and glass phase which forms in the specimen.It is shown that the most intense sintering and the greatest increase in the strength of zircon ceramic is produced by the addition of a calcium aluminosilicate glass.The relationship between the ultimate bend strength and the thermal-shock resistance of the zircon ceramic with glass additions, on the one hand, and the amount of glass phase formed in the specimens, on the other, has been established.Translated from Ogneupory, No. 4, pp. 47–52, April, 1979.     

Composite nozzles for casting boiling steel in continuous steel-casting units

Conclusions A technology was devised for the manufacture of composite nozzles for casting boiling steel in continuous steel-casting units. The composite nozzle consists of porous chamotte nozzle (holder) and a high-alumina, magnesite or zircon liner (working part).The composite nozzles with high-alumina liners showed greater durability than other liners during the tests.     

The effect of additives on the properties of phosphate-bonded corundum refractories

Conclusions The composition was developed for a corundum refractory, the characteristics (other than the chemical and mineral compositions) and metal resistance of which are on the level of those of an imported tested refractory.A phosphate binder reduces the porosity and increases the strength, thermal-shock resistance, and metal resistance of corundum brick.Added zircon and kyanite-sillimanite concentrates and ZrO₂, whether stabilized with yttrium oxide or unstabilized, affect the metal resistance of the refractory adversely but added B₂O₃ does not.Translated from Ogneupory, No. 3, pp. 41–46, March, 1977.     

Effect of additives on the thermal-shock resistance of corundum-zircon refractories

Conclusions It is established that the addition of 0.1–1.0% of Bi₂O₃ increases 2–7 and 1.5-fold, respectively, the resistance of a material to the nucleation and spread of destructive cracks; CoO₂ in amounts up to 0.1% has virtually no effect on the total thermal-shock resistance but increases threefold the resistance to the nucleation of destructive cracks.The addition of SnO₂ produces a slight decrease in both the number of heat cycles withstood before the appearance of the first visible crack and in the total thermal-shock resistance of the specimens before total destruction.It is established that the favorable effect of the Bi₂O₃ additive can be reduced to the fact that it melts, forming a thin film of melt on the surface of the corundum and zircon grains; this facilitates the formation of denser structures and, after evaporation, the formation of fine discontinuous microcracks.Translated from Ogneupory, No. 6, pp. 39–42, June, 1981.     

STANDARD THERMAL-SHOCK TEST FOR PORCELAIN ENAMELED UTENSILS*

The equipment and method used in testing porcelain enameled utensils for thermal-shock resistance is described. Test results are given which show that increased enamel thickness and decreased metal thickness decrease the thermal-shock resistance of enameled ware. The mechanics of thermal-shock failures is discussed. This study is one of a series sponsored by the Enameled Utensil Manufacturers' Council.     

Stability of Refractories in Hydrogen-Fluorine Flames

The flame resistance of six refractories of commercial purity was measured in the well-mixed stoichiometric portion and in the unmixed fluorine-rich portion of a hydrogen-fluorine diffusion flame. Graphite, silicon carbide, zircon, alumina, zirconia, and magnesia are decreasingly resistant to the test flame in the order indicated. The rate of ablation is about three times more rapid and the average surface temperatures are 130° to 745° C. higher where the flame is fluorine-rich. Graphite and silicon carbide are suggested for use in HF flames because of their good thermal-shock resistance and relative chemical inertness to the flame. Consideration of the ablation chemistry indicates that zircon dissociates and then, like graphite, silicon carbide, and zirconia, ablates by flame-solid reaction, whereas alumina and magnesia form liquids which flow from the impingement area.     

Properties of refractories with ZrO2 and SIO2 added in different concentrations and by different means

Conclusions It has been established that the addition to corundum of 15–20% of a stoichiometric mixture of baddeleyite and quartz sand in both an unmilled and milled form increases by almost 1.5-fold (in relation to number of heat changes) the thermal-shock resistance of the refractory by comparison with a refractory containing 7.5–20% zircon.The addition of Novoselitsk kaolin is not effective. It has a bad effect on the characteristics of the corundum-zircon refractories.Translated from Ogneupory, No. 5, pp. 40–43, May, 1981.     

Making complex products by slip casting using vibration and vacuum treatment

Conclusions A method developed for slip casting using wicks, vibration, and vacuum yields articles with orientated apertures (perforated blocks) with a cross section of up to 50%, and with an aperture diameter of 0.75–5 mm and a small ratio of pitch to diameter.Vibration helps to obtain dense thick-walled products of complex shape with granular fillers by the slip casting method, whose thermal-shock resistance is higher than that of cast products made from finely dispersed bodies. The use of vibration and vacuum processing in preparing articles from modified corundum yields an apparent density of 3.94 g/cm³ (98.7% of the theoretical density).Translated from Ogneupory, No. 6, pp. 10–15, June, 1973.     

Production and properties of highly porous zircon materials

Conclusions We proposed, using zircon as an example, the principle of forming pores of two types — cellular and capillary — for obtaining highly porous (up to 90%) ceramics. It consists of a combination of the foam method and the introduction of removeable foamed polystyrene. At the stage of forming and drying the system is distinguished by a high volume constancy, uniformity of properties, and the possibility of carrying out rapid drying.On the basis of a zircon suspension as the bond and crushed zircon foamed ceramics as the filler we obtained a highly porous ceramic concrete with a porosity of 50–70% and a compressive strength of 12–24 MPa.A marked influence on the properties of the resulting materials is exerted by the microcracks formed as a result of the removal of the expanded polystyrene (PPS) in the foamed ceramic, and the presence of uncompensated shrinkage in the ceramic concrete. With an increase in the value of the uncompensated shrinkage from 0 to 7%, the thermal-shock resistance of the ceramic concretes is increased 1.3 times and the thermal conductivity is reduced by a factor of 1.25.Translated from Ogneupory, No. 7, pp. 20–25, July, 1984.