Wear on periclase and corundum tiles in sliding steel casting gates

Abstract

At the present time approximately half of the steel smelted in the USSR is cast through a sliding gate. The high cost and the stringent specifications for the tiles for steel-casting gates has made it necessary to study the wear on these gates in some depth. This problem has already been considered in a few publications [1][2][3][4].The wear on the tiles in the sliding steel-casting gates was determined after the co~monest grades of steel had been cast on MNLZ and in molds. The state of the tiles after casting was evaluated by visual inspection of the dismantled gate. Petrographic studies of the longitudinal section of the chosen specimens were made. It is important that, for this purpose, gates were chosen only after normal casting of melts with the consequent coating of "metal" which would eliminate any contact between the tile and slag.The main features of the service conditions of various parts of the tile have been noted in [5]. A summary of the observations on the character of the wear of the tiles indicates that it differs slightly for the steel cast on MNLZ and in molds in the case of the upper and lower tiles. A diagram of the zones of greatest wear is shown in Fig. 1. The extent of the worn zone on the sliding surface of the tiles is due to the design of the gate; the diameter of the casting channel, the magnitude of the "path" with the jet covered over [6]. When the steel is cast from a steel-casting bucket in molds, the work of the gate consists mainly of covering the channel and when the casting is done on MNLZ, in choking the jet and these differences cause the different wear profiles on the moveable tile for these two cases. The eyternal appearance of the longitudinal section of the tile after casting is shown in Fig. 2.Contact between the melt and the refractory causes the surface of the refractory to heat up to 1600~ in 15-30 sec. Continuous contact between the melt and the bearing region of the sliding surface of the lower tile when casting is done into molds causes gradual heating but for most of the casting, the temperature differences in the surface layer are >-400~ [7]. On the basis of theoretical calculations it has been shown that the thermal-shock resistance of refractory materials can be compared in specimens of the same shape; this is widely used in practical laboratory work and characterizes the thermal-shock resistance, e.g., by the ultimate strength or the ultimate temperature differences [8]. Practical experience shows that the mazimum value of the temperature difference which can be withstood without the destruction of periclase refractories is Fig. 1. Diagram of the wear of tiles in sliding steel-casting gates: A) upper stationary tile; B) lower moveable tile when casting is into a mold; C) lower moveable tile with casting on MNL Z.All-Union Institute of Refractories.