An acceleration of the steelcasting processes makes it necessary to increase the handling capacity of the casting bays of the open-hearth and converter shops. A promising solution of the problem consists of a change to high-speed top teeming.Since 1973 capped open-hearth steel and killed steel have been cast at the Krivorozhstal' Plant through nozzles with a channel diameter of i00 mm at an average mold-filling speed of 3.8 m/min.It was decided to investigate the feasibility of casting at a higher linear speed with a view to reducing the total casting time and improving the quality of the rolled products.To this end, it was necessary to design pouring devices of a larger diameter and to develop a method of producing them. The first stage of the work resulted in the design of a nozzle with a channel diameter of 120 mm which made it possible to use SP-14 stoppers according to GOST 5500-64.The main interest centered on high-speed casting from large ladles (330-480 tons); according to the thickness of the bottom lining of these ladles, the height of the nozzles should be 400-450 mm.The production of such nozzles by pressure-molding from semidry compositions on existing equipment would be difficult because on most presses the working stroke is not long enough in addition to which the considerable height of the nozzle may be the source of significant differences in the vertical density (even in bilateral pressing) and the high molding pressure may result in overpressure cracks and the premature failure of the expensive, complex mold.The feasibility was investigated therefore of producing these nozzles by pressure molding accompanied by vibration.The efficiency of this method was demonstrated in earlier experiments at the All-Union Institute of Refractories with corundum, silicon carbide, zircon, and other difficult to mold compositions which showed that it can be used for the manufacture of large products of complex configuration.The tests were carried out with laboratory specimens (diam., 71.2; height, 65 mm) on an experimental vibropressure molding installation at a vibration frequency of 50 Hz, a disturbing force of 2200 kgf, a clamping force of 1-2 kgf/cm =, and a process time of 20, 30, 45, and 60 sec.The tests were carried out with individual grain-size fractions of magnesite powder and with the composition used by the ~gnezit Combine and the Panteleimonovsk Plant for the production of steelcasting nozzles. The grain-size distribution of the compositions used in the tests is given in Table i.In view of the lack of data about the action of the metal jet at a high casting speed on the surface of the nozzle channel with account taken of the structural characteristics of the layers in contact with the mold elements, it was assumed that a grain-size distribution which gives a maximum density in vibromolding is not necessarily the best in terms of durab$1-ity in service. The aim of the experiments with a varied grain-size distribution was to determine not only the composition which would give the maximum apparent de...
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