Improving the thermal-shock resistance of corundum ceramic

Conclusions We have studied the effect of coarse-grained additives of electrocorundum, sintered mullite, SiC, and electrosmelted ZrO₂ on the thermal-shock resistance of a corundum ceramic obtained from a mixture of technical alumina and glass-forming oxides. New ceramic materials have been obtained with a higher thermal-shock resistance, a lower open porosity, and adequate strength. The materials can be used in the manufacture of articles to be operated under conditions of stringent thermal loading.Translated from Ogneupory, No. 2, pp. 44–48, February, 1982.     

Improving the thermal-shock resistance of siliceous refractories

Conclusion The thermal-shock resistance of siliceous specimens with additions, measured by the water-heat cycling method, as a rule, is increased with increase in the content of the additives from 5 to 30%, and is maximal for a content of 30% chromite-periclase. The crack resistance, determined by the air-heat cycling method is characterized by a maximum ¯R_T factor for each type of additive with a content of 15–20%. The maximum ¯R_T value is shown by specimens containing 20% chromite periclase.The maximum thermal-shock resistance of the specimens, without additives and with additions of silciding filling scrap, chrome-ore fractions <0.5 and 0.09 mm, clay, and chromitepericlase relate to each other respectively as follows: 11.82.52.83.55, and the crack resistance as 10.44.63.82.98.1. The number 2.9 obtained with specimens containing clay apparently is not maximal, since the clay content was limited to 15% for the reasons stated.Clay additives increase the thermal-shock resistance of the dinas [3], but markedly redice the temperature of initial softening under load and the mechanical strength. Therefore, thermal-shock resistant dinas with clay additions can be used only in special working conditions.The most promising of the compositions studied is one with an addition of chromite-periclase scrap. This helps to create a porous, microcracked structure which increases the thermal-shock resistance by five times (water-heat cycle tests) and the crack resistance by more than eight times (air-heat cycle method) compared with the ordinary dinas.The optimum content of chromite-periclase scrap, to obtain siliceous refractories with the maximum thermal shock resistance, is 15–20%. However, considering the reduced refractoriness under load noted with this (respectively to 1480 and 1370 deg C) we recommend that the additive be limited to 10%.Translated from Ogneupory, No. 4, pp. 9–11, April, 1991.     

Improved quality zircon nozzles for continuous steelcasting

Conclusions An incorrect drying schedule is the main source of internal cracks in zircon nozzles. Cracking can be prevented either by drying the nozzles by an extended schedule (8 days at 30°C, 2 days at 50°C, and 1 or 2 days at 110°C) or by using ACPB instead of s. s.l. and drying the nozzles by a shorter schedule.Translated from Ogneupory, No. 5, pp. 15–19, May, 1977.     

Study of the thermal-shock resistance of ultralightweight refractories

Conclusions A complex investigation was carried out into the thermal shock resistance of ultralightweight refractories ShUB-0.4, ShLB-0.6, and ShLBDS-0.4. Using calculations and experimental techniques and specimens in the form of plates and standard bricks we established the criterion values for thermal shock resistance. It was shown that the refractory ShLBDS-0.4 is the most thermally shock resistant product of those investigated.Translated from Ogneupory, No. 7, pp. 32–35, July, 1973.     

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.     

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.     

High thermal-shock resistance of aluminum nitride ceramics

Conclusions The possibility of significantly improving the thermal-shock resistance of an A1N ceramic has been established. This is done by using compounds of a coarser grain composition and by adding Y₂O₃ and SiO₂ additives.The physicomechanical, electrophysical, and dielectric properties and the thermal-shock resistance of the newly developed ceramic have been determined. This ceramic can be taken as a promising material for high temperature electrical insulation purposes.Translated from Ogneupory, No. 3, pp. 50–53, March, 1980.     

Statistical methods of determining the thermal-shock resistance of refractories

Conclusions A statistical analysis of the test results for the thermal-shock resistance of a large batch of specimens of zirconium dioxide established that there is satisfactory correspondence between the experimental data and the exponential distribution of Weibull. The appreciable spread in the thermal-shock resistance criteria R for brittle refractory materials should be considered as regular, and therefore to obtain reliable calculation characteristics for thermal-shock resistance it is necessary to treat the test results statistically.It is proposed that one of the causes of variation in the thermal-shock resistance criterion R is the slight (unavoidable even within the limits of a single batch of specimens) change in the density of the material.Translated from Ogneupory, No. 2, pp. 53–56, February, 1971.