A high-alumina lining for crucible-type induction furnaces

Conclusions In crucible-type induction furnaces, the durability of a lining of compound MLM-1 (Technical Specifications 14-8-119-74) is several times higher than that of a quartzite lining or a sintered lining based on corundum and kyanite-sillimanite concentrate. The compound can be recommended for crucible furnaces when melting high-grade cast iron and steel.The density of compound MKE-78 can be increased by adding up to 20% synthetic corundum No. 6 and 3–4% orthophosphoric acid solution. Its high refractoriness makes it possible to use this lining as well for melting steel with a casting temperature of 1680–1700°C Its durability in this case is at least 2 months.Translated from Ogneupory, No. 3, pp. 24–28, March, 1977.     

Development of a lining made from Karelian quartzites for crucible induction furnaces

Factors are considered that increase the service life of a lining for a crucible induction furnace. Results are provided for laboratory studies and industrial tests of Karelian quartzites of Jotnian age of the Shokshinsk formation and Jatulian age of the Metchang’yarvinsk formation. The effect of impurities is quartzites on crucible induction furnace lining wear resistance is studied. Brief characteristics of quartzites are provided. The possibility is established of using waste materials from quarry production of Shokshinsk quartzites for preparing quartzite mixes.     

Effect of Melting Temperature Regimes on Change of Interplanar Distance in Quartzite

Refractories and Industrial Ceramics - The reliability of an industrial frequency crucible (IFC) induction furnace, used in casting manufacture, depends on its lining life. For this reason...     

Effects of mixture composition on the lining stability of a crucible induction furnace

Research results are reported on the effects of components on the resistance of acid lining for the crucible induction furnace. To raise the lining resistance, one needs to eliminate components that react with the silica crucible. The extent of silicon reduction from the lining is dependent on the heating of the metal and the contents of carbon and silicon in the liquid. Increasing the carbon content and reducing the silicon concentration in the metal favor wear on the crucible. The slag components most actively influencing the resistance of the lining are magnesium and calcium oxides, which are produced on modifying cast iron, ferrous oxide, and manganese on account of reduction in the viscosity of the slag, increase in its wetting power, and penetration into the pores and unevenness in the walls of the crucible. Translated from Novye Ogneupory, No. 5, pp. 41–43, May, 2008.     

Service conditions and improvement of the lining of vacuum induction furnaces

Conclusions A study was made of the temperature conditions in the lining of 1.0 and 2.5 ton vacuum induction furnaces. It was established that after the fourth heat the temperature conditions are stabilized and the values of the temperature gradient and the temperature at different distances from the working surface of the crucible were obtained.A design of vibropacking unit was developed making it possible to accomplish uniform packing of the crucible lining simultaneously over the whole volume.The failure stresses in the lining were relieved by introducing into its composition coarse grained corundum and by packing the mass by vibration over its whole volume.Translated from Ogneupory, No. 6, pp. 29–32, June, 1982.     

Phase composition of the products of encrustation of the channels of magnetodynamic feeders for aluminum alloys

Conclusions The investigations made it possible to establish the composition of the crust and the influence on its formation of certain service factors. In operation of MDN-6A feeders encrustation of the channels has a local character. The crust is formed in one of the side vertical portions of the channel. Failure of the crucible lining, contamination of the metal with coarse nonmetallic particles, and the occurrence of local overheating in the channel influence the operating life of the channel and the feeder in general. The rate of crust formation is determined by the quality of the lining fluorophlogopite material. The presence of cracks, shrinkage porosity, and an increased quantity of free glassy substance causes acceleration of failure of the channel lining.Translated from Ogneupory, No. 3, pp. 49–52, March, 1988.     

The use of a combined lining in copper production converters

Conclusions Strengthening of the above-the-tuyere zone of converter linings with fused periclasechromite refractories in combination with chromite-periclase heat-resistant refractories provides more uniform wear over the whole surface of the lining.With the use of a combined lining the life of a converter lining is at least as long or longer than the life of a lining with the use of only PKhP fused periclase-chromite refractories.The use of scientifically based heat-up conditions and converter operation taking into consideration the specific plant conditions may significantly increase the effect from the use of highly resistant refractories.As the result of use of combined linings in copper melting converters a 35–49% increase in converter life has been obtained.Translated from Ogneupory, No. 5, pp. 46–49, May, 1986.     

Calculation of the liquid phase in the Al2O3-B2O3-SiO2 system for the composition of commercial quartzite powders

Conclusions A calculation of the percent liquid phase from the phase diagram Al₂O₃-B₂O₃-SiO₂ showed that quartzite powders containing 97.5% or less SiO₂ are unsuitable as lining for crucible, especially at the reheating temperature of cast iron (1550°C), owing to the possible melting of about 30% of the working zone of the lining, the migration of the melt into the colder zones, and the consequent increase in the rate of sintering.The erosion of a crucible in service depends on the percent and viscosity of the liquid phase being formed. The viscosity of the boroaluminosilicate melts forming in the Al₂O₃-B₂O₃-Si₂ system at 1550°C is high so that their activity relative to the substance in the solid state is insignificant and the sintering effect is inhibited.However, owing to the nonequilibrium course of the process mainly low-temperature liquid phases are formed and then overheated. The B₂O₃ content of these phases is high (up to 18.3%) so that their fluidity is high; Since the erosion rate of the lining depends on the action of these melts the quartzite powders used for the lining of induction furnaces should contain not more than 1.1% Al₂O₃ and not more than 1% B₂O₃.Translated from Ogneupory, No. 6, pp. 68–70, June, 1978.     

The nature of the destruction and method of increasing the resistance of electric furnace linings

Conclusions During service, abundant saturation of the lining by components of the melting region is observed. The amount of silicates in the slag belt reaches 40–60% and in the high-lying lining — 10–15%.In regard to composition of the silicate bond in the working zones the lining is divided in height into two zones: the slag belt and the high-lying part. In the slag belt the bond is composed chiefly of cuspidine and fluorite; in the high-lying part — of dicalcium silicate and glass.Formation in the silicate bond of cuspidine and fluorite is due to the high rate of wear of the lining of the slag belt.In refractories of high density there is a smaller zone impregnated with reagents of the melting region, and so there is less wear during service.Further increase in the life of the lining can be obtained by using refractories with a minimum porosity in the slag belt and opposite the hot-phase arc; such refractories include fusion-cast blocks.     

Interaction between CA6-MA crucible and molten wrought Ni-based superalloys

The interfacial behavior between CaAl₁₂O₁₉-MgAl₂O₄ spinel (CA₆-MA) crucible and molten wrought Ni-based superalloys during the vacuum induction melting process have been comprehensively investigated, with Al₂O₃ crucible included for comparison. Experimental and theoretical results suggest that CA₆-MA crucible exhibits higher thermodynamic stability and poor wettability to the superalloy melt. Benefited from these merits, the superalloy ingot with cleaner surfaces and more metallic luster is obtained in the CA₆-MA crucible. Furthermore, the total oxygen content in the superalloy ingots obtained from CA₆-MA crucible is 17.9 ppm, which is considerably lower than that from Al₂O₃ crucible (29.7 ppm). These results indicate that CA₆-MA crucible can be a promising candidate for melting wrought Ni-based superalloys.     

Life of refractories in service in a furnace for melting in a molten bath

Conclusions As the result of laboratory and production tests it was established that the periclase-chromite refractories produced from fused material show the greatest life in the lining of furnaces for melting in a molten bath.A method of production of fused chromite-periclase used for the production of fused periclase-chromite refactories to Technical Specification (TU) 14-8-368-81 was developed.A design of combined lining of a furnace for melting in a molten bath with the use of highly resistant refractories was developed.Translated from Ogneupory, No. 1, pp. 56–60, January, 1986.     

A novel potential ceramic material for melting Ti6Al4V alloy: A solid solution of BaZrO3 and CaZrO3

Vacuum induction melting technology is a promising low-cost method for producing high-quality titanium alloy. The key challenge lies in the development of ceramic crucibles with excellent chemical stability for titanium alloy corrosion. In this work, (Ba_1−x,Ca_x)ZrO₃ ceramic was designed and synthesised via pressureless sintering of a mixture of BaZrO₃ and CaZrO₃ powders. X-ray diffraction and scanning electron microscopy analyses showed that a new phase, Ba_0.8Ca_0.2ZrO₃, was formed after heat treatment at 1700 °C. Vacuum induction melting experiments of the Ti6Al4V alloy were carried out using a Ba_0.8Ca_0.2ZrO₃ crucible. Compared with the original BaZrO₃ crucible and CaZrO₃ crucible, the erosion layer of the Ba_0.8Ca_0.2ZrO₃ crucible was significantly reduced by approximately 85∼92.5%. The interface between the crucible and the alloy was clearly visible, and there was no obvious element diffusion between the alloy and the material. This shows that Ba_0.8Ca_0.2ZrO₃ is highly promising as a crucible material for melting Ti6Al4V alloys.     

结晶器保护渣熔化速度测定方法的研究

通过分析结晶器保护渣熔化速度测定方法的国内外现状 ,提出用坩埚法测定的方法。与灰熔点仪法和GX -高温物性测试仪法进行对比研究 ,表明在测定结果的稳定性和代表性方面 ,坩埚法是目前结晶器保护渣熔化速度测定的合适方法。     

Oxidation–Reduction Equilibrium in Copper Phosphate Glass Melted in Air

Copper phosphate glasses with 40, 50, and 60 mol% CuO in batch were melted in air at 1000°, 1100°, and 1200°C using quartz or alumina crucibles, and the [Cu²⁺]/[Cu_total] ratio variations with melting time were measured. Glasses were oxidized during melting and reached equilibrium [Cu²⁺]/[Cu_total] ratios which were independent of melting temperature and identical for the 40 and 50 mol% CuO content glasses. Structural considerations seemed to have determined oxidation-reduction equilibrium rather than an equilibrium redox reaction. Also, the effects of crucible type on the oxidation-reduction balance were examined. It was found that a quartz crucible is more inert and has less effect on the oxidation-reduction equilibrium of glass than an alumina crucible. Crucible contamination and phosphorus vaporization were found to diminish as the CuO content in the batch was increased.     

INFLUENCE OF BATCH MIXING TIME AND BATCH GRAIN SIZE ON HOMOGENEITY OF A SODA-LIME-SILICA GLASS*

Density-spread determinations were made on a series of melts of a soda-lime-silica glass employing batches compounded from raw materials varying in particle size from 20- to 60-mesh to minus 200-mesh, which had been mixed by tumbling for one, ten, or thirty minutes. The two melting techniques employed were (1) melting for sixteen hours in a stationary platinum crucible at 1400°C. under conditions of even temperature distribution and consequently a minimum of convection mixing and (2) melting for four hours at 1400°C. in a rotating tilted crucible; this condition was intended to simulate convection mixing Under the experimental conditions employed, it was found that (1) batch mixing time has relatively little effect on the homogenizing rate, (2) homogenization increases rapidly with decrease in grain size, and (3) in all cases the 4-hour melting treatment with moderate mixing gives better homogeneity than sixteen hours melting time in a stationary crucible, this effect increasing with decrease in grain size. No significant difference in glass homogeneity resulted from three different methods of mixing, namely, tumbling, ball milling, and mixing in a muller-type mixer, although the homogenizing influence imposed probably was sufficient to mask any differences in uniformity of mixing that might have existed.     

Mechanism of wear of electric arc steel melting furnace wall linings and means of increasing their life

Conclusions The walls of electric arc steel melting furnaces and especially the region of the slag belt operate under very severe conditions. Together with physicochemical factors the life of the lining is also determined by the design of the refractory shell of the working space of the furnace and the ratio of its primary dimensions.A method of increasing the wall refractory lining life as the result of rational construction in the design of new and reconstruction of existing furnaces was proposed.In the form of a discussion.Translated from Ogneupory, No. 2, pp. 51–53, February, 1988.     

X-ray imaging of a high-temperature furnace applied to glass melting

The dynamics of soda-lime-silica glass grain melting is investigated experimentally using a nonintrusive technique. A cylindrical alumina crucible is filled with glass cullet and placed into a furnace illuminated by an X-ray source. This glass granular bed is gradually heated up to 1100°C, leading to its melting and the generation of a size-distributed population of bubbles rising in the molten glass. An image processing algorithm of X-ray images of the cullet bed during melting allows the characterization of bubbles size distribution in the crucible as well as their velocity. The introduction of tin dioxide μ-particles in the glass matrix before melting enhances the texture of the images and makes possible the determination of the bubble-induced molten glass velocity field by an optical flow technique. The bubble size distribution can be fitted by a log-normal law, suggesting that it is closely related to the initial size distribution in the cullet bed. The liquid motion induced by the bubbles in Stokes' regime is strongly affected by the flow confinement and the determination of bubble rising velocity along its trajectory unveils the existence of local tiny temperature fluctuations in the crucible. Overall, the measuring techniques developed in this work seem to be very promising for the improvement of models and optimization of industrial glass furnaces.     

Obtaining high-purity fused refractory oxides

Conclusions Using yttrium oxide and aluminum oxide as examples we demonstrated the possibility of successfully using the induction heating method in a cold crucible for obtaining fused refractory materials possessing a high purity. The contamination of the charge by the crucible material during melting does not exceed 10^–3%.Translated from Ogneupory, No. 7, pp. 26–29, July, 1973.     

Service of mullite-corundum refractories in the center portion of the roof of high-power electric arc furnaces

Conclusions Type MKS domestic mullite-corundum parts to Technical Standard 14-8-140-75 have been introduced for the center portion of the water cooled roof of high-power arc steel melting furnaces at Belorussian Metallurgical Plant. The length of the roof campaign reached 180–220 heats without intermediate repairs, which is 25% longer than the life of imported refractories.The design of the center portion of the roof without a hole for charging of loose materials provides with the forms and dimensions of the parts used a symmetric lining and uniform distribution in it of the thermomechanical loads, which provides uniform wear of the lining and eliminates deformation of it during service of furnaces.On the basis of investigation of samples of the imported and domestic mullite-corundum roof parts after service it was established that wear of the lining occurs by fusion as the result of interaction of the refractories with the melting dust at 1660–1710°C.Different relative rates of chemical transformation and fusion of the mineral phases of the refractories were revealed. Mullite interacts with the melting reactants and fuses most intensely. In connection with this its content in mullite-corundum roof parts must not exceed 15–20%.Translated from Ogneupory, No. 1, pp. 56–60, January, 1987.     

Processing of vacuum heat-treated MgO-densified silicon nitride crucible for molten cast iron handling

Silicon nitride with 3% MgO powder mix is uniaxially and cold isostatically pressed to form a green Si₃N₄ crucible. Liquid phase sintering was applied to the green Si₃N₄ crucible at 1600 °C for 30 min under the nitrogen atmosphere. Intergranular Mg–Si–O–N glass remained between the silicon nitride grains which reacted with the molten metal during melting. This grain boundary glass was removed by vacuum heat treatment at 1575 °C for 5 h. The vacuum heat treated crucible was used to melt cast iron to examine reactions between the molten metal and Si₃N₄ ceramic crucible. EDX spectra across the Si₃N₄–cast iron interface and XRD for silicon nitride sample after cast-iron melting side surface analysis were carried out. Optical microscopy and SEM image analysis were made to examine the interaction between Si₃N₄ crucible and cast iron melt. Surprisingly, no reaction was observed between the vacuum heat treated crucible and melted cast iron.