Understanding Submerged Nozzle

Classification
In the continuous casting technology, in order to improve the quality of the cast billet, there is a submerged nozzle between the tundish and the mold, its main functions are:(1) to prevent the secondary oxidation and nitriding of molten steel and the splash of molten steel;(4) It has a decisive influence on the yield and quality of cast billets.
The submerged entry nozzle is installed at the bottom of the tundish and inserted into the crystallizer. Its main forms are:
A integral immersion nozzle: this nozzle does not need to use a tundish nozzle, its shape is longer, generally more than 700mm. There are two forms, one is the built-in nozzle, which is installed from the inside to the outside of the tundish. The nozzle is an integral structure with good sealing performance. The other is the external nozzle, which is installed inward from the bottom of the tundish and has not been used in China.
B external type immersion nozzle: the form nozzle is used in conjunction with the upper nozzle of the tundish. in use, the upper end of the immersion nozzle is hung outside the bottom of the tundish through a support ring or a mechanical arm and is connected with the head of the upper nozzle, and its lower end is inserted into the crystallizer.
C quick-change submerged nozzle: this submerged nozzle is equivalent to the water outlet of sliding nozzle. it is mainly used for continuous casting of slab and wide and thick slab. it is used in conjunction with the water outlet of quick-change middle package. this form is the future development direction.
D thin slab immersion nozzle: this type of immersion nozzle is specially developed for the needs of thin slab continuous casting. its remarkable feature is that it has a flat tapping port with a thickness of 60-80mm.
The immersion nozzle has a certain porosity, also has air permeability, the outside air in the steel flow generated by the negative pressure to penetrate into the inside of the nozzle, contact with the steel to make it oxidized. Therefore, the outer surface of the long spout and the submerged entry nozzle must be coated with a layer of anti-oxidation glaze. Submerged entry nozzles of any material and construction must meet the following conditions:
(1) Ensure the flow of molten steel at normal speed;
(2) as far as possible to make the mold, the billet section of the heat flow distribution uniform;
(3) It is conducive to the rapid melting of the slag;
(4) It is conducive to the floating of inclusions without slag rolling;
(5) Avoid violent turning of the steel liquid level in the mold;
(6) easy to install.
Material
In the early stage of continuous casting, the molten quartz immersion nozzle with good thermal stability and high purity can meet the pouring of ordinary carbon steel, low manganese steel, aluminum killed steel and other steel grades. However, under the condition of high manganese steel and high alkalinity slag, the erosion is very serious. At this time, aluminum carbon immersion nozzle is widely used. The raw materials of aluminum-carbon immersion nozzle are super-grade bauxite, fused corundum or sintered corundum, etc., and graphite and anti-oxidant are added. The product has the advantages of anti-erosion and thermal shock resistance.
In order to solve the serious erosion of the slag line of the submerged nozzle and to prevent the blockage of the nozzle caused by the adhesion of alumina, a series of new submerged nozzles were developed on the basis of aluminum carbon.