The construction of a department for the production of purer baddeleyite--cortmdum refractories, viz., grade BKCh, which are used in the production of optical and electrovacuum glass was completed in 1973. The construction plans were based on a design project prepared by the All-Uniun Institute of Refractories (AIR). The department was started up, the production trials were carried out, and the production technology of BKCh refractories was developed and introduced by the AIR jointly with the Podolsk Refractories Plant. * The work was carried out with account taken of the experience gained in the production of fusion-cast corundum and baddeleyite--corundum refractories [1; 2, pp. 35-116; 3, pp. 40-43].The starting materials for the production of the refractory are zirconia of grade , commercial alumina of grade GA85 (GOST 6912--64), a pure grade of silica , and a pure grade of sodium carbonate (GOST 83-63). According to the specifications the content of coloring oxides in the starting materials for the production of BKCh refractories should not exceed 0.05% for TiOp, 0.0i% for (CuO + NiO), 0.001% for CaO, and 0.07% for (Fe203 + Mn203 + Cr203).On their delivery at the Plant all starting materials for the baddeleyite--eorundum refractories were systematically subjected to spectral analysist to determine their content of coloring impurities (Table 1)

No abstract

Apparent density is used as the main characteristic of the cast refractories of the bad ~ deleyite-corundum composition. This parameter makes it possible to evaluate the corrosion resistance objectively. It depends on the actual density of the material and on the ratio of the porous (shelly) and the dense portions of the beam [I, 2].In order to facilitate the production of optical glass, the Podolsk Refractories Factory is manufacturing products corresponding to the BKCh-33 and BKCh-34 grades and having an apparent density not less than 3.4 and 3.6 g/cm 3, respectively [3]. The experience gained during the service of these products showed that the formation of striae* (spills) and bubbles becomes very intense when the central porous zone (cavity) of the beam comes into contact with the glass mass. This zone is characterized by a high concentration of a glassy phase, pores~ and gas liberating impurities.In order to eliminate the shrinkage cavity from the body of the beam and to improve the absolute density of the products, we produced experimental castings using a cylindrical riser.A cylindrical feeder head was made from sand using a special tooling designed for forming circular sand components (Fig. i). During the first stage of the experiments, for the No. 2 products measuring 600 x 400 • 250 mm, we used a head having an internal diameter of 395 mm, a height of 340-630 mm, and a gate opening (diameter) of 230-395 mm.We selected the BKCh-38 charge composition that exhibits a distinct gradual solidification characteristics and makes it possible to eliminate the shrinkage cavities effectively from the beam. The optimum proportion of the parameters (dimensions) of the mold and the casting were established for increasing the apparent density of the castings up to a value not less than 3.9 g/cm 3. Subsequent separation of the riser was carried out by diamond cutting. Table 1 shows the results of the first series of our experimental studies. # Fig. I. Tooling for shaping circular sand components~ *Striae is a term used to indicate the inhomogeneous regions of a glass mass. In the present situation~ it is a result of the reaction between the glass mass and the refractory.iV. V. Kolomeitsev, V. A. Korostelev, N. S. Logacheva, V. P. Shishkin, and V. A. Zamkov (PZO!) participated in these studies.

The Podolsk Refractories Factory (PZOI) produces baddeleyite--corundum refractories according to for the working zones of glass furnaces.Studies [2][3][4] showed that during the service of these refractories carbon monoxide, carbonic acid, and nitrogen separate in the glass, since the content of carbon and its oxides in the articles comes within the range 0.02-0.10%* [I].Contamination of refractories by undesirable carbon impurities is a result of the reaction of graphitic electrodes and oxides of the melt in refractory batch in the reducing conditions of electric-arc melting.In this case the carbon of the electrodes enters the melt as a result of direct transfer under the action of plasma jets, erosion, and oxidation of electrodes.Furthermore, the melt is contaminated by carbon during burning-in of the furnace with coke which occurs during single-shift working at PZOI.According to data in [3], a reducing atmosphere in the melt contributes to nitrogen absorption by bakor melt because of the formation of compounds such as nitrides and nitrocarbides of aluminum, zirconium, and silicon.In order to create oxidizing conditions and reduce the content in the articles of gasproducing impurities, experiments were done on the electric furnaces OKB 2126A in shop No. 4 of the factory using the plasma-arc method of melting.The tests were done with double-shift operation of the furnace.Before the start of the experimental meltings we created a double-shift store of sand blocks for assembling the molds, installed special electrodes with increased resistance, impregnated with borate solutions according to the technology of the Chelyabinsk Electrometallurgical Combine [5]; and furthermore the melting tank was insulated around the perimeter with shrinkage-head tiles and split blocks to avoid burnthrough in the lining.Burning-in of the furnace was done with ground coke in amounts of 40 kg. Melting was done with ordinary batch (articles grade BKCh-33).In the first shift the furnace was burnt-in, the melt was cleaned to remove coke, and the casting of ordinary articles was carried out.The experimental articles were cast in the second shift and the batch was melted with different electrical cycles.

Mortar mixtures are normally used to construct tanks in glass furnaces in order to seal the gaps at the joints between the wall and bottom structures, and also in building the bottom plates. In addition to common technical requirements, the refractory mortars for glass furnaces need to have but the minimum amount of coloring impurities.Investigations were therefore made to develop a technology for producing refractory mortar suitable for laying tanks with BKCh [1] refractories.The use of Soviet-made refractories containing zircon concentrate and technical alumina [2] is based on high-temperature reaction in the dissociation of zircon, and in this the separating silica is bonded with the alumina, forming mullite: 2ZrO 2 9 SiO2+3Al2Os-+2ZrO2+ 3A1203 9 2SiO 2.The same reaction occurs during the firing up to 1800~ of zircon--mullite material.The main drawback of such mortars is the presence of coloring impurities in the glass --oxides of iron, titanium, and chromium, added to the mortar in the form of clay and other binders to increase the sintering rate and the overall glass resistance of the lining.The present authors developed a mortar with a rapid sintering rate, a plasticity, and a corrosion resistance, meeting the demands of high purity in the glass being turned out.The base of the mortar consisted of a body with 54% by weight zircon. To increase the plasticity we added vibromilled alumina, milled DN-1 clay, and Prosyanovsk kaolin. The organic binder consisted of water solutions of sulfite lye, methyl cellulose, and calcium carboxymethyl cellulose. Best results were obtained by adding methyl cellulose.Since the main components of the mortar are zircon and alumina, the developed composition was given the description MTsG.