Selection and Application of Castable Refractories for Molten Aluminum Furnaces

  Molten aluminum furnaces are core equipment in the aluminum processing industry, and the selection of their lining castables directly affects furnace service life and production safety. Different parts require specialized castables due to varying degrees of aluminum liquid erosion and high-temperature scouring.

Different key parts of molten aluminum furnaces also require targeted special castables to cope with complex working conditions. 

  Lightweight castables are used for the furnace roof. Since the furnace roof is a suspended structure, it needs to be lightweight while ensuring high-temperature resistance to avoid excessive load on the steel structure. Lightweight castables have a small bulk density (usually ≤1.8g/cm³) and low thermal conductivity, which not only reduce the overall weight of the furnace but also minimize heat loss from the furnace, improving thermal efficiency. Meanwhile, their high-temperature strength can meet the requirement of resisting flue gas scouring on the furnace roof.

  Steel fiber castables are used for furnace doors. Furnace doors are opened and closed frequently, subject to severe temperature fluctuations and mechanical collisions, which easily lead to cracking and spalling. Steel fiber castables mixed with stainless steel fibers can significantly enhance the flexural strength and toughness of the lining, effectively inhibiting crack propagation caused by temperature stress, improving the impact resistance and thermal shock resistance of the furnace door lining, and prolonging its service life.

  Non-stick aluminum castables and anti-seepage castables are used for the furnace bottom. The furnace bottom is in direct contact with aluminum liquid. Non-stick aluminum castables contain special isolation components, which can reduce aluminum liquid adhesion and avoid nodulation affecting the flatness of the furnace bottom. Anti-seepage castables have extremely low porosity and permeability, which can form a dense anti-seepage layer, preventing aluminum liquid and slag from penetrating into the furnace steel structure, and avoiding corrosion and aluminum leakage accidents. Anti-seepage castables are also used on the furnace side walls to block the side aluminum liquid penetration path.

  Slag-resistant castables are used for the aluminum liquid line. The aluminum liquid line is the interface between aluminum liquid and furnace gas, which is most strongly affected by the dual erosion of molten aluminum liquid and slag as well as high-temperature oxidation. Slag-resistant castables contain slag-resistant components such as Cr₂O₃ or SiC, which can react with slag to form low-viscosity slag, reducing slag erosion and penetration into the lining, and ensuring the structural integrity of the furnace wall in key areas.

  Burner port castables are used for burners. The burner area has extremely high temperature and is directly scoured by flames, and also faces corrosion from fuel combustion products. Burner port castables have excellent high-temperature volume stability and thermal shock resistance, which can withstand high-temperature flame scouring above 1600℃, while resisting corrosion from harmful components in combustion flue gas, preventing flame deviation caused by high-temperature damage at the burner part.

  Clay-bonded high-aluminum castables or low-cement high-aluminum castables are mostly used for furnace walls and roofs. Furnace walls mainly bear high-temperature radiation and aluminum liquid splashing scouring. Clay-bonded high-aluminum castables have moderate cost, convenient construction, and good thermal shock stability, which can adapt to frequent furnace temperature fluctuations. The furnace roof is in a suspended state, requiring light weight and high strength. Low-cement high-aluminum castables have high water consumption, low porosity, and higher strength, which can reduce the self-weight of the furnace roof while resisting high-temperature flue gas scouring and molten material dripping erosion.

 Special corundum castables are required for aluminum outlets and launders. These parts are aluminum liquid flow channels, which are most severely scoured and eroded by high-speed aluminum liquid. Corundum castables have an Al₂O₃ content ≥90%, extremely high room temperature and high-temperature strength, and their scouring resistance and erosion resistance are far superior to ordinary castables. They can avoid aluminum leakage accidents caused by damage to the aluminum outlet, ensuring continuous and stable production.

  The construction process of castables must strictly follow the procedures to ensure the lining quality. Firstly, pre-construction preparation: check whether the dimensions of the furnace steel structure meet the design requirements, clean up debris on the base and apply脱模剂 (release agent); at the same time, mix the castables according to the proportion, accurately control the amount of water (or binder) added, and stir for no less than 5 minutes to ensure the slurry is uniform and free of agglomeration. Secondly, casting and forming: use a vibrating rod for layered vibration, with each layer thickness not exceeding 300mm, until the slurry surface bleeds and no bubbles overflow, to avoid defects such as honeycombs and cavities; for complex parts such as aluminum outlets, special molds should be used for shaping. Finally, curing and baking: cure at room temperature for 24-48 hours, and it is strictly forbidden to water or freeze in the early stage; then bake according to the temperature rise curve, slowly heat from room temperature to 200℃ (temperature rise rate ≤50℃/h), the rate can be appropriately increased in the 200-600℃ stage, and keep warm above 600℃ for a period of time to ensure complete discharge of moisture, preventing lining cracking caused by rapid evaporation of moisture during use.