This article describes the setting, working principle and development status of ladle sliding nozzle.
Key words: ladle; sliding nozzle; refractory material; functionality; development
Slide nozzle setting
During the process of molten steel from ladle to tundish and from tundish to mold, it is necessary to ensure the compactness and concentration of the steel flow and minimize the contact between the molten steel and the atmosphere to reduce oxidation. The sliding nozzle system, that is, the flow steel system (collectively referred to as the flow control system) that combines the upper nozzle, the slide plate and the lower nozzle (submerged long nozzle), realizes the sealed steel flow and minimizes the risk of secondary oxidation of molten steel. With the development of continuous casting technology and secondary refining technology, the sliding nozzle system has become more and more important in the modern iron and steel smelting process, becoming an indispensable part of smelting.
How the sliding nozzle works
The world’s first sliding nozzle device was successfully tested on the ladle in Benteler, West Germany in 1961. It was officially put into production in 1964 and officially put into use in the late 1960s. At present, the sliding nozzle system is widely used in ladle, tundish and converter slag at home and abroad. According to different purposes, it can be divided into ladle sliding nozzle and tundish sliding nozzle. There are many types of sliding gates, but the working principle is similar. The structure of the sliding nozzle is divided into two parts: mechanical device and drive. In the mechanical device part, functional refractory materials are used as mechanical parts, and these functional refractory materials include: seat bricks, nozzles and slide plates, as shown in Figure 1.
Fig. 1 Installation diagram of functional refractory parts of sliding nozzle
The sliding nozzle mechanism is a mechanism that controls the steel flow through the relative staggered position of two open slide plates (ie, the upper slide plate and the lower slide plate). The upper water port and the upper slide plate are fixed in the mechanism, and the lower plate and the lower water port are installed in the sliding device. The schematic diagram of the control principle of the sliding nozzle mechanism is shown in Figure 2. When the upper and lower betting holes overlap during the movement, the molten steel in the ladle can flow out through the upper nozzle, upper slide, lower plate and lower nozzle for pouring operation, as shown in Figure 2(a); when the upper and lower betting holes are staggered , the gate is closed and the pouring operation stops, as shown in Figure 2(b). The sliding device is connected with the hydraulic cylinder through the connecting rod, and moves left and right with the help of the driving force of the hydraulic cylinder.
Figure 2 The working principle of the sliding nozzle mechanism
The key functional refractory component in the sliding nozzle system-sliding plate
In the cast steel flow control system, the slide plate is a key component that determines the service life. Skateboards need to withstand physical erosion and chemical erosion of high-temperature molten steel, intense and transient thermal shock and mechanical wear during use, and the conditions of use are extremely harsh. At the same time, in order to realize the free opening and closing of the steel flow, strict requirements are required on the smoothness of the sliding surface of the slide plate and the size of the plate shape. The safety of the slide plate is one of the key factors for the normal operation of continuous casting production, so the slide plate must have the characteristics of high strength, wear resistance, corrosion resistance and good thermal shock stability. Skateboard is one of the most demanding conditions of use among the components of the sliding nozzle, and it is also the one that bears the greatest risk. It is required to be foolproof during use.
Current status of skateboard refractory design
At present, aluminum-carbon and aluminum-zirconium-carbon slide plates are mainly used in China (the carbon content is generally 8%-12%), which can basically meet the needs of ordinary steel continuous casting. However, when the carbon-containing slide plate is heated, carbon oxidation occurs, and the carbon loss behavior will cause the slide plate to react with slag, reaming, grinding, erosion, steel infiltration, etc., and finally manifests as flow steel hole destruction and surface corrosion. Moreover, the carbon-containing slide plate will increase the carbon content of the molten steel when casting clean steel. Since the development of the iron and steel industry, the birth of clean steel smelting technology requires that the carbon content in steel must be reduced to an extremely low level, and the slide must be developed in the direction of low carbon or no carbonization. Compared with skateboards with high carbon content, the development of low-carbon or carbon-free skateboards needs to solve the problems of anti-slag erosion and thermal shock resistance.
Metal-Oxide No Burn Low Carbon Skateboard
In recent years, metal composite non-burning skateboard materials have used metal as a raw material to obtain skateboard materials with unique microstructure and properties, and opened up a new method for developing high-performance skateboard materials. The process principle is shown in Figure 3: The inorganic non-metallic phase is the main body, followed by the metal phase. Using the plastic forming of the metal, the metal is liquefied or softened during sintering or high-temperature use, filling the pores, and improving the density and toughness of the product; the metal phase on the working surface of the slide plate and The atmosphere or the surrounding components undergo chemical reactions to generate non-oxide reinforcing phases in situ to improve the high-temperature strength, thermal shock resistance and erosion resistance of the slide. Non-oxide has the same excellent non-wetting properties as carbon, which can improve the material’s ability to resist the erosion of slag and molten steel, and has excellent high temperature stability, good thermal shock stability, and protective oxidation. It is a substitute for carbon Ideal material for composites.
Figure 3 Process of metal plastic phase and transition plastic phase
At present, new metal-oxide composite low-carbon or carbon-free slides such as aluminum-corundum composite carbon-free slides and Al-Si3N4-Al2O3 composite slides have been widely used in ladle flow control and throttling systems, and have achieved good results. Effect. Metal Si, Al, etc. can not only realize plastic molding, but also act as a transitional plastic phase. During high temperature use, a series of gradient reactions occur to form a variety of different reinforcing phases, such as AlON, SiAlON, Al4O4C, Al2OC-AlN, Al4SiC4, etc. , so as to effectively improve the overall performance of the skateboard, and has a good application prospect. The following are the advantages of metal-oxide composite skateboards.
(1) With the plasticity of metals, it can effectively improve the brittleness of inorganic materials;
(2) The non-oxides generated in situ can hinder dislocation movement and crack propagation, and have the effect of diffusion toughening;
(3) No-fire system, low-temperature heat treatment process, which has the advantages of energy saving and environmental protection;
(4) Generate non-oxide reinforcing phase in situ, improve bonding strength, and endow the slide with excellent thermal shock resistance;
(5) Non-oxide has excellent non-wetting properties, and the slide plate has excellent resistance to slag and molten steel erosion;
(6) It does not contain carbon, will not pollute the smelting materials, and is suitable for clean steel production.