Pony ladle nonswirl nozzles for billet continuous casting machines with a small mold cross section

Abstract

One of the important questions in organization of pouring of steel into a billet continuous casting machine with a small cross section mold is selection of the material and design of the pony ladle nonswirl nozzle providing a stable rate of pouring of the metal for a long time (up to 5 h of continuous operation).A stable pouring rate is a necessary condition for obtaining high-quality cast billets and failure-free operation of the equipment.For example, with a pouring rate of less than 1.7 m/min clogging of the channel with molten metal occurs while with pouring of the steel at a rate of more than 2.5 m/min the metal billet leaving the zone of secondary cooling does not have a completely solidifed axial portion.Providing a constant pouring rate is also complex as the result of the relationship to many production parameters.Under otherwise equal conditions the pouring rate of steel depends upon the dimensions of the nozzle channel.Forpouring into small cross section molds nonswirl nozzles with a channel diameter from 14 to 15.5 mm are used and therefore insignificant clogging or erosion of the channel leads to significant changes in pouring rate. Tests have shown that the use of nozzles with a channel diameter of 14 mm is most desirable since with the use of them the pouring rate stabilizes and is 1.8-2.0 m/min.The first domestic nonswirl nozzles for pouring of steel into small cross section molds were produced at Krasnoarmeisk Dinas Plant and were introduced under the conditions of the Melt Shop of Belorussian Metallurgical Plant in 1985 in place of Didier-Werke parts.Billets with a cross section of 125 x 125 mm up to 12 m long of killed constructional and low-alloy types of steels are cast on two curved six-strand continuous billet casting machines of the plant. The pouring is done through a 10-ton pony ladle by the "heat on heat" method in a series of three heats (average weight of a single heat 102 tons).The nozzle unit of the pony ladle consists of a zirconic composition nonswirl nozzle and an aluminosilicate funnel.The space between the nozzle unit and the reinforcing lining of the bottom is filled with corundum or quartz-clay compound.A feature of pouring of steel in the continuous billet casting machines of Beiorussian Metallurgical Plant is the free flow of the stream from the pony ladle into the open pool of metal in the mold without protection from secondary oxidation.The rate of flow of the stream is controlled by controlling the level of filling of the ladle and also by supplying gaseous oxygen for cleaning out the channel with a decrease in the pouring rate below the allowable.The absence of a stopper and controlling mechanism imposes increased requirements for the nonswirl nozzle under the action of the molten metal and the gmseous oxygen.Investigations of Didier-Werke and nonswirl nozzles showed that they consist primarily of baddeleyite and zircon (Fig. I). The chemical analysis of the nonswirl nozzles in wt.% is 23 SiO2, 0.90 CaO, 0.42 AI20 B, 0.40 Pe2Os, 0.44 MgO, 73.6 ZrO2, and 2-6 Y203, the op...