What are the factors that affect the service life of the ladle slide

      The ladle sliding nozzle refractory material is composed of upper and lower nozzle bricks, upper and lower plate bricks and joint mud. The upper slide brick is fixed in the fixed frame of the mechanism. The lower plate brick and the drain brick are installed in the sliding frame, and can be moved back and forth through mechanical operation, so as to achieve the purpose of controlling the amount of injection by controlling the degree of overlap between the upper and lower betting holes. The upper and lower slide bricks are pressed tightly by the tensioning elements of the mechanism, so that the lower slide bricks do not cause gaps between the upper and lower slides during the movement process, so as to prevent the occurrence of steel leakage accidents between the slide plates.

      Since the skateboard is repeatedly subjected to the erosion of molten steel, chemical erosion and strong thermal shock during use, in order to meet the precise flow control function, the skateboard must have high temperature resistance, high strength, good corrosion resistance, good thermal shock resistance, and oxidation resistance. Excellent properties such as high resistance and low creep. It is specifically reflected in the following aspects: (1) It has sufficient strength at high temperature to withstand the static pressure of molten steel; (2) The sliding surface must be very smooth, with a flatness of no more than 0.05mm, so that it can be in tight contact and ensure that the casting process (3) It must be resistant to erosion, corrosion, and good thermal stability, so that it can withstand rapid changes in temperature and the erosion and erosion of molten steel and slag.

Factors Affecting the Service Life of Ladle Sliding Plate

1. Effect of thermal stress and external force

      Before pouring molten steel, the temperature of the skateboard brick is about 200-350°C; after pouring, the temperature of the casting hole of the skateboard rises rapidly to above 1500°C within a few seconds, and the skateboard is subjected to severe thermal shock. Under the action of thermal stress, cracks are inevitable. If it is used in multiple furnaces, it will inevitably undergo repeated thermal shocks, which will easily cause cracks and peeling off on the working surface of the sliding brick. According to Ringery's thermoelastic theory, the initial thermal stress cracking coefficient R can be seen in formula 1. Once a crack is generated, it will continue to expand. The resistance coefficient RST of this crack stress follows Hasslman's theory of fracture mechanics, see formula 2.

formula 1：R=S(1-μ)/Eα

formula 2：RST=[γ(1-μ)/E0α2]1/2

      In the formula: S is the tensile strength; E is the elastic modulus; μ is Poisson's ratio; E0 is the elastic modulus without cracks; α is the thermal expansion coefficient; γ is the fracture energy.

      Equation 1 and Equation 2 show that the greater the initial thermal stress fracture resistance coefficient of the material and the resistance coefficient of crack stress, the smaller the thermal expansion coefficient and elastic modulus of the material, the harder it is for cracks to occur or expand, and the thermal stability of the material the better.

2. The impact of high temperature molten steel and slag erosion, erosion and oxygen burning to clean casting holes

      The erosion, erosion and oxygen burning process of molten steel and slag during the pouring process will cause the diameter of the casting hole of the slide plate to expand, and the melting loss and erosion will cause the casting hole to expand and the refractory material to be lost at the slip mark. Especially when pouring high manganese steel, the manganese in the molten steel reacts with the sliding plate refractory, see formula 3 and formula 4.

formula 3：MnO+SiO₂=MnO·SiO₂

formula 4：MnO+Al₂O₃=MnO·Al₂O₃

      According to the MnO-Al₂O₃-SiO₂ phase diagram, MnO·SiO₂ is a compound with a low melting point. However, no liquid phase is formed, but only a slight increase in the content of MnO in the working zone of the sliding plate, which changes the original structure of the corundum in the sliding plate. When pouring calcium-treated steel, SiO₂ and Al₂O₃ in the slide plate are reduced by calcium in molten steel, and the reactions are shown in formula 5 and formula 6.

formula 5：2[Ca]+SiO₂=2CaO+Si

formula 6：3[Ca]+Al₂O₃=3CaO+2Al

      The produced CaO will react with SiO₂ and Al₂O₃ in refractory materials. According to the CaO-Al₂O₃-SiO₂ phase diagram, the melting point of 2CaO·Al₂O₃·SiO₂ is 1584°C, the melting point of CaO·Al2O3 is 1600°C, and the melting point of 3CaO·Al₂O₃ The melting point of CaO·2Al₂O₃ is 1539°C, the melting point of CaO·Al₂O₃ is 1762°C, and the melting point of 12CaO·7Al₂O₃ is only 1392°C, and it will cause extremely irregular coordination numbers of aluminum and calcium in the slide structure, and there are a large number of structural holes. These low melting points The possibility of the compound turning into a liquid phase within the pouring temperature range is extremely high, and the resulting liquid phase is continuously lost along with the steel flow, which enlarges the casting hole and causes damage to the slide plate. Even if no liquid phase is formed, the formation of these compounds will cause a slight increase in the calcium content of the slide plate working belt, change the structure of the slide plate refractory material, lead to a decline in the performance of the slide plate, and affect its service life.

      During the process of burning oxygen to clean the casting holes, the oxides of iron in molten steel are in direct contact with the nozzle, and diffuse to the inside through pores and cracks, and react with the corundum and mullite phases in the sliding bricks to form silicates with low melting points, see formula 7 and formula 8.

formula 7: 2FeO+SiO₂=2FeO·SiO₂

formula 8：FeO+Al₂O₃=FeO·Al₂O₃

      The melting point of FeO·Al₂O₃ is 1780°C, and a spinel reaction layer is formed around the corundum particles, while the melting point of fayalin 2FeO·SiO₂ is only 1205°C, which exists in a liquid state at the temperature of pouring steel and is continuously lost with the steel flow, making The casting hole expands, causing the slide to be damaged.

3. Effects of sliding resistance, oxidation and slag metal infiltration

      When the skateboard is working, there will be wear and tear between the upper and lower boards due to the friction. In order to ensure no steel leakage, the contact surface of the slides must be very tight, and a specific surface pressure between the slides is required, with a size of 0.5-1.0N/mm2. With the erosion and infiltration of molten steel and slag metal, the friction in the slip mark area increases, causing the slip marks to become rough. When the slide plate adjusts the steel flow, it is easy to generate turbulence, which will also aggravate the wear, and the result is steel infiltration between the slide plates. In addition, when the temperature is not lower than 500°C, the oxidation of carbon will reduce the strength of the material, roughen the surface and increase friction, and in severe cases, steel breakout will also occur.

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