Refractories and Industrial Ceramics Vol. 52, No. 4, November, 2011 V. A. Bezlepkin Translated from Novye Ogneupory, No. 7, pp. 22, July 2011. Original article submitted March 28, 2011. Studies on ways of obtaining lengthy corundum pipe are discussed. The technical characteristics of the articles that have been produced are presented. Keywords: OAO Polikor, corundum pipe, jackets for thermocouples, sag Purely corundum articles in the form of pipes or jackets for thermocouples are widely used in modern technology. Nevertheless, the question of fabricating thin-walled (from 2 to 4 mm) lengthy (from 1000 to 1500 mm) corundum pipe with sag not greater than 0.2 mm per meter of length is still a question of definite importance. A number of different meth- ods of molding such pipe are known, above all, the tradi- tional method of extrusion, then vibratory casting, quasi-iso- static, gas-flame, and detonation methods. The method of Fig. 1. quasi-isostatic molding is currently the most common, though it requires the use of expensive water gauges. The present goal has been achieved at OAO Polikor through the use of the method of plasma-jet spraying, which Next, billets that have been produced by spraying of a simultaneously combines two technological operations – 60 – 100 m corundum fraction are roasted in open air for molding and sintering. In a number of cases, therefore, arti- the purpose of selecting a temperature for the production of cles that have been produced by means of plasma-jet spray- articles with given porosity. The dependence of the porosity ing according to the “casting skin” technology may be used of the articles on roasting temperature is shown in the ac- without any additional treatment. However, if the customer companying chart. requires articles with low porosity, in such cases the articles Roasting temperature, °C . . . 1580 1650 1730 must be subjected to additional roasting either in an air atmo- Open porosity, %........ 12.5 ± 0.2 11.3 ± 0.2 7.5 ± 0.2 sphere or in a vacuum. The conditions of molding of pipe are selected on an UPU-8M plasmotron. Corundum powder with Corundum jackets measuring 40 32 1000 mm (cf. dimensions of the granules from 20 to 120 m are selected as Fig. 1) and possessing the following characteristics have the initial material. By spraying powders of three fractions been fabricated at OAO Polikor on the basis of these results: (20 – 60, 60 – 100, and 60 – 120 m), we were able to estab- content of basic substance, greater than 99%; open porosity, lish that the 60 – 100 m fraction is the optimal fraction 12.0%; sag, 0.2 mm. The latter characteristic could be from the point of view of density of the billet produced. The achieved due to 1.5% shrinkage of the article following dependence of the porosity of the billet on the dimension of roasting at 1650°C. On the basis of the experience gained at the corundum fraction is presented in the accompanying OAO Polikor the recommended working temperature of such chart. jackets must not exceed 1750°C both in open air and in a .... 20 – 60 60 – 100 60 – 120 Corundum fraction, m vacuum. Open porosity, % ....... 16.1 ± 0.2 13.2 ± 0.2 17.6 ± 0.2 The new technology is now being used at the enterprise for small-lot production of pipe and jackets. Full-scale pro- duction will become feasible once the demand for these arti- OAO Polikor, Kineshma, Russia. cles grows on the market. 1083-48771105204-0247 © 2011 Springer Science+Business Media, Inc.
Refractories and Industrial Ceramics – Springer Journals
Published: Dec 6, 2011
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