Mullite Sand
Mullite sand is a type of aluminosilicate refractory material that is widely used in the foundry industry.
Main Chemical Composition:
The primary chemical components of mullite sand are Aluminum Oxide (Al₂O₃) and Silicon Dioxide (SiO₂). The typical chemical composition ranges are: 42% ≤ Al₂O₃ ≤ 47% and 51% ≤ SiO₂ ≤ 53%. It also contains small amounts of Iron Oxide (Fe₂O₃), Alkali Metal Oxides (Na₂O+K₂O), and other trace elements.
Production Process:
Mullite sand is typically produced using minerals rich in aluminosilicate, such as kaolin, hard clay, or muscovite. The process involves crushing the raw materials, mixing them with additives, and pressing them into shape. These shapes are then calcined in a high-temperature furnace at temperatures between 1300°C and 1550°C. After calcination, the product undergoes crushing, screening, magnetic separation to remove iron, and other processes to obtain mullite sand products of various particle sizes.
Particle Size Specifications:
Mullite sand is available in a diverse range of particle sizes. Our main supply includes: 8-16 mesh, 16-30 mesh, 30-60 mesh, 60-80 mesh, and 80-120 mesh. Additionally, we offer finer grades known as mullite powder, such as 200 mesh and 300 mesh.
Performance Characteristics:
High Refractoriness: With a refractoriness of approximately 1750°C, it effectively withstands the high temperatures of molten metal during the casting process, protecting the mold shell from damage.
Excellent Thermal Stability: Mullite sand maintains dimensional stability when subjected to temperature changes. It is resistant to thermal expansion or contraction, ensuring the precision of the castings.
Easy Shakeout Property: After casting, mullite sand can be easily removed (shakeout) from the castings. This reduces the need for subsequent finishing work and improves production efficiency.
High Casting Quality: Using mullite sand as a shell material results in castings with a smooth surface finish. It minimizes casting defects such as sand holes and blowholes, thereby enhancing the overall quality of the castings.
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Specification
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Supper Grade
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Grade 1
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Grade 2
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Al2O3
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44%-45%
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43%-45%
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43%-50%
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SiO2
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50%-53%
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50%-54%
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47%-53%
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Fe2O3
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≤1.0%
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≤1.5%
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≤2.1%
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K2O+Na2O
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≤0.5%
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≤0.6%
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≤0.8%
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CaO
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≤0.4%
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≤0.5%
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≤0.5%
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TiO2
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≤0.3%
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≤0.7%
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≤0.3%
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Xaustic Soda
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≤0.5%
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≤0.5%
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≤0.7%
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Bulk Density
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≥2.5g/cm3
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≥2.5g/cm3
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≥2.45g/cm3
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The core of precision casting is mold shell manufacturing (the process of coating the wax pattern with multiple layers of refractory material to create an outer shell. After the wax pattern melts, a cavity is formed for pouring molten metal). Mullite sand is primarily used as a refractory aggregate in the mold shell and is applied to different layers of the shell, specifically as follows:
1. Surface Shell (Directly Determines the Surface Quality of the Casting)
Function: The surface layer is in direct contact with the casting and must ensure a smooth surface finish (avoiding roughness and pitting) while also withstanding the initial impact of the molten metal.
2. Back Shell (Provides Overall Strength and Breathability)
Function: The back shell is a multi-layered structure outside the surface layer. It supports the overall strength of the mold shell (preventing deformation or collapse during pouring) while ensuring breathability (discharging gases from the cavity and preventing porosity in the casting).
3. Specialized Applications for High-Demand Castings
High-temperature alloy castings: such as aircraft engine turbine blades (pouring temperatures of 1500-1600°C), require the mold shell to withstand extreme temperatures. Mullite sand's high refractoriness can replace the more expensive zircon sand (melting point 2550°C, but expensive), meeting high-temperature resistance requirements while reducing costs.
For reactive metal castings: such as aluminum alloys and magnesium alloys (which are highly reactive and easily react with the SiO₂ in quartz sand to form inclusions), mullite sand's chemical stability can reduce reactivity and prevent the formation of "oxidation inclusions" in the casting.
For large precision castings: such as wind turbine gearbox housings (which can weigh several tons), the mold shell requires higher structural strength. The backing layer formed by mullite sand and binder is high-strength, reducing the risk of mold expansion and collapse.
4. Combination with Other Refractory Materials
In actual production, mullite sand is often used in combination with other materials to optimize mold shell performance:
Combination with zircon sand: zircon sand is used as the surface layer (to ensure a higher surface finish) and mullite sand as the backing layer (to reduce costs). This is suitable for castings with extremely high surface requirements, such as aerospace parts.
Combined with quartz sand: For castings with lower temperature requirements (such as copper alloy, melting point 1083℃), it can partially replace quartz sand and use the low expansion of mullite sand to reduce shell cracks.
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Reference Process For Precision Casting Shell Making
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The general surface slurry, zirconium powder
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325 mesh+silica sol
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Sand: zirconium sand 120 mesh
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Back layer slurry
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325 mesh+silica sol+mullite powder 200 mesh
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Sand: mullite sand 30-60 mesh
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Reinforcement layer
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Mullite powder 200 mesh+silica sol
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Sand: mullite sand 16-30 mesh
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Sealing slurry
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Mullite powder 200 mesh+silica sol
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Shandong Robert New Material Co., Ltd. is located in Zibo City, Shandong Province, China, which is a refractory material production base. We are a modern enterprise that integrates the research and development, production, sales, kiln design and construction, technology, and export refractory materials. We have complete equipment, advanced technology, strong technical strength, excellent product quality, and good reputation. Our factory covers over 200 acres and an annual output of shaped refractory materials is approximately 30000 tons and unshaped refractory materials is 12000 tons.
Our main products of refractory materials include: alkaline refractory materials; aluminum silicon refractory materials; unshaped refractory materials; insulation thermal refractory materials; special refractory materials; functional refractory materials for continuous casting systems.
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