Refractory for sliding nozzle system
November 19, 2020
It is through the operation mechanism to make the sliding plate slide, make the upper and lower sliding plate hole close and open degree, change the section area of molten steel outflow to achieve the purpose of current control. It is composed of pedestal brick, cast-head brick and skateboard. Our country initially used lower quality products. Sliding plate brick, casting mouth brick water mouth and seat brick are not fired products. The sliding nozzle system has two places to use. First, the flow velocity of molten steel in the ladle to the tundish is controlled under the ladle; second, the flow velocity of molten steel in the tundish to the continuous casting mold is controlled under the tundish to control the casting speed of the continuous casting billet.
With the development of refractory technology, ladle skateboard service life is getting higher and higher, many foreign manufacturers have been widely used to 8 times, China's high quality aluminum zirconium carbon, aluminum carbon skateboard is generally used to 2~4 times. But our country has a lot of small converter, electric furnace steelmaking, these steel mills are still using cheap disposable skateboards. For tundish skateboards, it is generally required to use a continuous runner. That is, generally under 8 times. Many tunics in our country use plug rods for flow control instead of skateboards. For the high quality skateboard, our country needs to improve the product quality, control structure and use method, and we should not be too conservative in use. Aluminum carbon is used for casting of general types of steel. Aluminum zirconium carbon slide machine can meet the requirements. Corundum bricks are generally used for the upper shuikou. Aluminium carbon brick and chrome corundum brick. Their service life is generally in 20~30 times, with low quality service life in less than 10 times to replace. For downspouts, the general service life is replaced with the skateboard.
When the skateboard is used for many times, the strength of the carbon-bonded skateboard will be lost due to the oxidation of the carbon-bonded skateboard under the condition of medium temperature oxidation, which will cause the surface of the skateboard to be pulled or worn, and horseshoe erosion will occur on the sliding surface, which can also lead to the phenomenon that the plug steel and the skateboard are plugged, which is one of the main reasons for skateboard damage; Then there is the thermal shock resistance of the skateboard. Because in the process of use, the skateboard is subjected to strong thermal shock, resulting in great thermal stress, often leading to skateboard crack or burst. In the process of use, the molten steel may flow out along the crack, resulting in steel leakage accident; Another cause of skateboard damage is the erosion and wear of molten steel. The flow rate of molten steel in the orifice of the skateboard is very fast, which causes great erosion to the skateboard. The oxide particles in the slide are washed away, dissolving and washing away the carbon, which causes the slide to widen. Therefore, it is very important to solve the oxidation resistance, wear resistance and improve the erosion resistance of the skateboard. These problems solved the service life will also go up.
For the development of the skateboard, mainly around the above issues. Oxide - metal composite skateboards have now been developed. In the process of burning or using the skateboard, the metal carbonization, oxidation and nitriding reaction occurs, leading to a great increase in strength, so that the moderate temperature antioxidant and wear resistance are significantly improved, the number of times of use increased more than 3 times. Then the development of non - carbon - bonded non - burning skateboard. This kind of slide plate without burning aluminum carbon, the production process is very simple, it does not need to burn, do not need to impregnate treatment. Its performance is as follows: normal temperature compressive strength 120 MPa, volume density 3.17g/cm, apparent porosity 2%, 1000℃, 3h oxidation firing compressive strength 240MPa, 1400℃, 0.5h high temperature bending strength 42MPa (air), 55MPa (carbon embedded).
For some special steel, carbon combined aluminum carbon, aluminum zirconium carbon slide can not meet the requirements of use, its erosion rate will be greatly improved, service life can not meet the requirements of use. This is especially true for tundish skateboards. If the service life of the skateboard is not good, it will lead to the replacement of tundish and a great waste of tundish refractory materials. Now some special steel casting with skateboards are analyzed and introduced.
When aluminum - carbon and aluminum - zirconium - carbon slide casting high oxygen steel erosion quickly, service life decreased significantly, can not meet the requirements of use. The oxygen concentration in high-oxygen steel is very high. It contains high iron oxide and is highly oxidizing. Therefore, when choosing sliding nozzle system refractory, considering the thermal shock resistance and wear resistance, it is necessary to fully consider the product's oxidation resistance and the corrosion of high iron oxide slag caused by the pore expansion, surface roughness and cracking. A large number of studies and applications have proved that aluminum and magnesium spinel carbonates, magnesium spinel carbonates and magnesium carbonates are better.
Aluminum carbon, aluminum zirconium carbon slide plate is not suitable for calcium treatment of steel, aluminum oxide in aluminum carbon, aluminum zirconium carbon slide plate is easy to react with calcium oxide or calcium in steel and form low melting point calcium aluminate phase, resulting in accelerated melting corrosion. The service life of m-MA sintered skateboard used on tundish can reach more than 4 times, while the service life of aluminum-carbon skateboard decreases by more than 25%, thus increasing the consumption of refractory materials for tundish by 25%. The new sliding plate also reduces the index of nonmetallic inclusion resulting in waste products by 70%, which is conducive to improving the quality of steel. Generally speaking, the carbonization impregnation of M-MA skateboard will significantly improve the corrosion resistance. The higher the CONTENT of MgO in the skateboard, the better the corrosion resistance.
It is also worth pointing out that, now the production of ultra-low carbon steel is also increasing, in order to prevent the refractories to carbon liquid steel, and the use of carbon-free skateboard system. Namely the use of sintered rigid jade skateboard, aluminum zirconium skateboard, magnesium aluminum spinel and magnesium skateboard. Further study and improvement of thermal shock resistance equivalence of these materials.