This article describes the factors that affect the service life of the ladle slide.
Key words: steel ladle; slide plate; service life
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 flow by controlling the 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
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 slideboard 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).
R=S(1-μ)/Eα(1)
RST=[γ(1-μ)/E0α2]1/2(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.
Equations (1) and (2) show that the greater the initial thermal stress cracking coefficient and resistance coefficient of cracking stress of the material, the smaller the thermal expansion coefficient and elastic modulus of the material, and the harder it is for cracks to generate or expand. The thermal stability is better.
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 slide plate refractory, see formula (3) and formula (4).
MnO+SiO2=MnO SiO2(3)
MnO+Al2O3=MnO·Al2O3(4)
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).
2[Ca]+SiO2=2CaO+Si(5)
3[Ca]+Al2O3=3CaO+2Al(6)
The generated 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 2Al2O3 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).
2FeO+SiO2=2FeO SiO2(7)
FeO+Al2O3=FeO·Al2O3(8)
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 cast hole expands, resulting in damage to the slide.
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 mark 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.