Use of tundish metering nozzle

The tundish metering nozzle is one of the refractory materials for billet continuous casting, and it plays the role of controlling the flow of molten steel. The molten steel flows into the mold through the tundish metering nozzle at a constant speed and stably, which is a necessary condition to ensure the normal operation of continuous casting. As a flow control element, the metering nozzle should have good anti-scour and anti-erosion capabilities. During use, the inner diameter should not expand too quickly. Once the expansion size of the zirconia tundish  metering nozzle exceeds the allowable range of the mold pulling speed, it means the sizing The nozzle has been seriously damaged and cannot be used any longer. The expansion of the tundish  metering nozzle has become a bottleneck problem in the study of improving the life of the tundish.

Zirconia has good thermal stability, low thermal conductivity, and stable chemical properties, and has good stability to most acids, alkalis and alkali melts, glass melts and molten metals, so zirconia materials are high temperature insulation materials. Ideal for thermal and structural materials. It was used to melt glass and smelt steel as early as the 1970s. In the early stage of continuous casting development, due to the short continuous casting time, ordinary zirconium metering nozzle products made of zircon and zirconia can meet the production needs, and the zirconia content is 72%-85%; With the development of casting technology, the continuous casting time is more than 500min. Due to the reaction and decomposition of zircon with some metal oxides in molten steel and steel slag, the phenomenon of diameter expansion, bursting and peeling of ordinary metering nozzle is caused. Ordinary zircon metering nozzle can no longer meet the needs of continuous pouring, and the zirconia metering nozzle with better corrosion resistance must be used. The zirconia content is about 93%-95%. The zirconia metering nozzle has good erosion resistance and excellent thermal shock stability. , which can meet the needs of multi-furnace continuous casting, improve continuous casting efficiency, and reduce production costs. At present, the material with the best corrosion resistance among functional refractory materials for continuous casting is zirconia.

During the use of the zirconia metering nozzle, as the inclusions in the steel slag and molten steel penetrate into the pores at high temperature and react with the impurities and stabilizers in the metering nozzle, the tight bond between the zirconia particles is destroyed, and the stable phase is destroyed. The transition from the high temperature phase to the low temperature phase occurs due to the reduction of the stabilizer. The volume expansion caused by the phase transformation weakens the bond between the particles, which leads to the rupture between the particles in the zirconia metering nozzle, and the molten steel enters the nozzle. The diameter keeps increasing. The expansion of the inner diameter of the nozzle will lead to an increase in the flow of molten steel flowing into the mold through the nozzle, and the pulling speed of the slab will also increase accordingly, which will easily cause the slab to break and stop pouring, affecting the normal production process.