Ladle is an essential container in the steelmaking process. With the continuous development of smelting technology, especially the processing of out-of-furnace refining LF and RH, its role has evolved from the simplest receiving molten steel to a furnace that undertakes certain smelting functions. If the molten steel stays in the ladle for a long time, it will inevitably cause the temperature of the molten steel to dissipate, and the ladle lining with high thermal conductivity will cause the heat dissipation loss of the molten steel to increase. The deformation of the ladle shell becomes more serious, and the temperature drop rate of the molten steel increases, causing serious slag hanging nodulation, and cold steel on the ladle wall. Excessive low temperatures may even force the middle package to cut off the flow and final pouring. It not only affects the quality of the cast slab but also reduces the yield of molten steel and increases the production cost. Therefore, thermal insulation ladles are increasingly becoming a need for steel mills. The structural model of thermal insulation ladle refractory materials is usually lightweight insulation panels or nano panels + permanent layer castables + working layer refractory materials. Rongsheng’s long-life thermal insulation refractory castable for ladle furnace lining. Contact Rongsheng to get a free quote.
Lightweight High-Strength Castable for Steel Ladle
The insulation board itself, which plays the most important role in thermal insulation, needs a layer of refractory material to protect it. The material must first protect the insulation material from too much pressure, and secondly, protect the insulation material from exceeding the operating temperature (if it must be below 1000°C), then the ladle Permanent layer castables are such important materials. The ideal permanent layer refractory material for thermal insulation ladles should have good thermal stability, thermal insulation, corrosion resistance, safe and reliable application, complete structure, and long service life. In order to maintain the good thermal insulation performance of the ladle and reduce the temperature drop of the molten steel, the performance evaluation of the new CA6 castable and the lightweight mullite castable was conducted in this work and applied to the ladle, achieving a relatively good comprehensive thermal insulation effect.
Performance comparison of thermal insulation refractory castables for ladles
At present, the permanent layer materials of ladles are mostly ordinary high-aluminum castables, and the main raw material is bauxite. There are the following shortcomings in the use of this refractory castable. First, the thermal conductivity is high, which causes energy loss during use. Second, the refractoriness is low. If the working layer is used abnormally and the molten steel directly contacts the permanent layer, the probability of steel leakage will be greater and the safety factor is low. Third, the volume density is larger and the empty ladle weighs more. Therefore, the special requirements for ladle insulation are not met, and it is necessary to develop new permanent layer castables with excellent comprehensive properties. Performance comparison of new CA6 castable and lightweight mullite castable.
Among them, the CA6 raw material (CaAl12O19, abbreviated as CA6) is the calcium aluminate phase with the highest Al₂O₃ content in the CaO-Al₂O₃ system. Its melting point is 1875℃, its thermal expansion coefficient is 8.0×10-6℃⁻¹, its particle volume density is 2.70g·cm⁻³, and its apparent porosity is 26.8%. The fire resistance of this material is similar to that of plate corundum, but its thermal conductivity is only 1/3 of corundum. It is a new type of high-quality thermal insulation material that has emerged in recent years. CA6 castable is made of CA6 as aggregate, and the matrix part is made of plate-shaped corundum fine powder, alumina powder, and calcium aluminate cement as binding agents. The volume density of spherical lightweight mullite particles is 1.59g·cm⁻³, and the apparent porosity is 38.9%. The lightweight mullite castable is made of microporous M70 spherical lightweight mullite balls as aggregate, and the matrix part is made of plate-like corundum fine powder, alumina powder, and calcium aluminate cement as binding agents to ensure Better resistance to slag erosion to improve the safety of the permanent layer.
The volume density of lightweight mullite castable is 2.17g·cm ⁻³, and its unit weight is 24% lower than the currently used high-aluminum castable. At the same time, the thermal conductivity is reduced by 16%, which can achieve the purpose of lightweight and low thermal conductivity of the ladle. CA6 castable is also 5.6% lighter than ordinary high-aluminum castable, and its thermal conductivity is reduced by 26%.
Pour the original ladle permanent layer castable B, the new CA6 castable C, and the lightweight mullite castable 3# into crucibles respectively. Add the final converter slag and conduct a slag corrosion resistance test on the crucible under the condition of 1500°C for 3 hours. Observe the resistance to melting loss and penetration of different materials. After completing the test, the crucible was cut open. The erosion status is as follows:
CA6 castable has the best resistance to erosion and penetration, with a large amount of slag remaining in the crucible hole; light mullite castable has the second-best resistance to erosion and penetration. The boundary between ordinary high-aluminum permanent layer casting slag and refractory material is not clear, and the crucible refractory material and slag are melted together. The resistance to penetration is slightly better than the resistance to erosion, indicating that more liquid phases have appeared in the high-aluminum castable at 1500°C. Therefore, the material needs to be improved to improve its high-temperature resistance, which is very important for the safety of the ladle. The micropores of spherical lightweight mullite are beneficial to improve corrosion resistance and permeability, so this lightweight material can also perform better in insulation and corrosion resistance.
Application Comparison
The above three kinds of castables are used for construction and application on 300t steel ladle. The target requirement of the lightweight mullite castable and CA6 castable for the permanent layer of the thermal insulation ladle is to have both good resistance to molten steel erosion and good thermal insulation properties. At the same time, the furnace has good structural integrity and a stable thermal insulation effect during the furnace service process. After three furnace campaigns, the surface conditions of the permanent layer of the steel ladle were different, and cracks of varying degrees appeared in the permanent layer of the steel ladle in the later stages of the furnace campaign. This is related to the thermal shock resistance, strength and damage of the material during the unpacking process. The comprehensive technology of how to reduce the cracking of the permanent layer material of the thermal insulation ladle still needs further in-depth research.
Judging from the average temperatures of each slag line in each furnace, the steel shells of the uninsulated ladle slag lines are all above 320°C, while the average temperatures of the four test slag lines using insulation are below 280°C. Generally, the temperature of the slag line steel shells has dropped. 50～100℃. The temperature drop of the steel shell in the wall part is between 20 and 50°C, which varies slightly depending on the configuration of the insulation material and permanent layer material. The insulation material of the thermal insulation test package remained in good condition during the furnace service period, and the average temperatures of the slag line and wall steel shell were lower than those of ordinary steel ladles, indicating that the permanent layer played a good protective role. In order to ensure safety, the current situation of obvious cracks in the new permanent layer material after two furnace operations still needs to be optimized and improved to ensure that it can be applied to four furnace operations.
In Conclusion
Insulated ladles have become an important technical measure for steel companies to save energy, protect the environment, and improve the quality of steel products. The permanent layer materials of ladles have been given higher requirements. The physical properties such as strength and strength of the developed CA6 castable and lightweight mullite castable meet the application requirements of the permanent layer of the ladle. At the same time, they have better thermal insulation and corrosion resistance than conventional high-aluminum castables and can protect thermal insulation materials. The function ensures that the ladle maintains good heat preservation during the furnace service period. Further in-depth research is needed on the comprehensive technology to reduce the cracking of the permanent layer material of the thermal insulation ladle.
Rongsheng Refractory Castable Manufacturer
Rongsheng refractory castable manufacturer, an environmentally friendly and advanced fully automatic unshaped refractory material production line, provides a reliable guarantee for refractory castable lining materials for high-temperature industrial furnaces. Annual output is 6W tons. Rongsheng Manufacturer can provide high-quality insulation and refractory castable products for ladles, rotary kilns, and non-ferrous smelting furnaces, as well as the design and construction of insulation layer refractory lining materials. The ladle is made of long-life insulation castables and is shipped directly from the manufacturer at a low price. Contact Rongsheng for free details.
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