To improve the energy-saving effect of thermal kilns, the number and scope of applications of lightweight castables are gradually expanding. From the permanent layer, the insulation layer to the working layer, it extends from the medium and low-temperature areas to the medium and high-temperature areas and transitions from a low-load environment to a high-load environment. At present, the technical performance of lightweight high-aluminum castables used in working layers at medium-low temperatures (<1 200°C) and high temperatures (>1 500°C) has been basically mature. However, the performance of lightweight castables used in the medium and high-temperature range (1 200 ~ 1 500 ℃) needs to be improved. To meet the new requirements for the use of lightweight high-aluminum castables, it is first necessary to understand the impact of the selection and configuration of lightweight aggregates on their performance. RS refractory material manufacturer can provide high-quality refractory lining products for high-temperature industrial furnace linings.
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| Lightweight High Aluminum Castable |
The raw material configuration of traditional lightweight high-aluminum castables mainly uses lightweight aggregates and heavy fine powders. The lightweight aggregate used has larger pore diameters and lower strength, so the thermal conductivity of the lightweight castable is higher. At the same time, the low strength of the aggregate affects the overall strength of the lightweight castable, limiting its use at higher temperatures. Therefore, microporous aggregates and high-strength aggregates are used. The raw materials used mainly include microporous lightweight mullite and complex-phase hollow spheres. High alumina bauxite, floating beads, kyanite, silica micro powder, alumina micro powder, pure calcium aluminate cement, raw bauxite powder, andalusite, pore-forming agent D, pore-forming agent C, etc.
The Choice of Lightweight Aggregates
To meet the construction and high-temperature performance of lightweight castables, lightweight mullite, and complex-phase hollow balls are selected as lightweight aggregates. Multiphase hollow spheres were used to gradually replace lightweight mullite to study the effect on the properties of the castables. The wall thickness of the multiphase hollow spheres is 0.3~0.5 mm, the particle size is 3~7 mm, and its packing density is 0.60 g/cm3. The packing density of microporous mullite is 0.80 g/cm3.
Effect of adding amount of multi-phase hollow spheres on the volume density of castables
When the amount of multiphase hollow spheres increased from 0 to 40%, the bulk density of the sample dropped from 1.86 g/cm3 to 1.68 g/cm3 after baking at 110 °C × 24 h. The bulk density also shows the same trend after high-temperature firing. Since the packing density of the composite hollow spheres is smaller than that of the lightweight mullite aggregate, the bulk density of the castables shows a downward trend as its addition amount increases. That is, the effect of complex-phase hollow balls on reducing the volume density of castables is greater than that of lightweight mullite.
Effect of the Adding Amount of Complex Phase Hollow Balls on the Normal Temperature Compressive Strength of Castables
The changing trend of normal temperature compressive strength of castables after adding different proportions of multi-phase hollow spheres. As the amount of composite hollow balls increases, the normal temperature compressive strength of the castables after baking and high-temperature firing shows an upward trend. Since the strength of the composite hollow sphere, aggregate is higher than that of the lightweight mullite aggregate, and the surface of the composite hollow sphere is dense, its water absorption rate is lower than that of the lightweight mullite aggregate. At the same time, the spherical aggregate is beneficial to improving the fluidity of the castable, reducing the amount of water added to the castable, and is also beneficial to improving the strength of the sample. Therefore, the reinforcing effect of complex hollow spheres on castables is greater than that of light mullite.
Effect of the Adding Amount of Complex Phase Hollow Spheres on Thermal Conductivity of Castables
As the amount of multiphase hollow spheres increases, the thermal conductivity of the sample shows a downward trend. Since the complex-phase hollow balls have a hollow structure, the air is enclosed in the holes, which has a good heat insulation effect. Therefore, the thermal conductivity of the castable decreases after adding complex-phase hollow balls. Since the pore diameter of the multi-phase hollow sphere is larger, the effect of convective heat transfer will increase at high temperatures. As a result, the effect of reducing the thermal conductivity of the castable at 1000°C is not as obvious as that at 700°C.
Microporous lightweight mullite aggregate is beneficial to reducing the thermal conductivity of castables, but its strength is low. Complex-phase hollow spheres are beneficial to improving the strength of castables, but their effect on reducing thermal conductivity is limited. Due to the low density of composite hollow spheres, taking into account the uniform dispersion of different aggregates and taking into account various properties, the appropriate addition amount of both aggregates is 20% to 30%.
To purchase high-quality lightweight high-aluminum castables, please contact Rongsheng Refractory Materials Manufacturer. Our refractory products are of reliable quality and our after-sales service is guaranteed.
