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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.

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