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The main products of graphite products for non-ferrous metal industry include: graphite melting crucible, graphite casting crucible, graphite plug rod, graphite oil bath, graphite continuous casting mold, graphite crystallizer, graphite boat, graphite melting pot for welding, graphite rotor for degassing in aluminum industry and so on.
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Graphite rotors are indispensable components in the metal casting industry, particularly for aluminum alloys. Their ability to effectively disperse inert gas and promote degassing leads to significant improvements in casting quality and performance. As the demand for high-quality castings continues to grow, graphite degassing rotors will remain a vital tool for metal casters worldwide.
Graphite rotors, also known as degassing rotors or impellers, are crucial components in the process of removing dissolved gases and impurities from molten metals, especially aluminum alloys. These rotors are designed to effectively disperse inert gas, such as argon or nitrogen, into the molten metal, promoting the formation of gas bubbles that carry dissolved hydrogen and other impurities to the surface for removal.
Molten metals, particularly aluminum, readily dissolve gases like hydrogen during melting and holding. As the metal cools and solidifies, the solubility of these gases decreases. The dissolved gases then precipitate out of the solution, forming gas bubbles within the casting. These gas bubbles can lead to:
Porosity: The presence of gas bubbles creates porosity, weakening the mechanical properties of the casting, such as tensile strength and fatigue resistance.
Surface Defects: Gas bubbles can migrate to the surface of the casting, causing blisters or other surface defects, which can affect the appearance and functionality of the product.
Reduced Density: Porosity reduces the overall density of the casting, affecting its weight and performance.
Therefore, degassing is a critical step in the metal casting process to ensure the production of high-quality, defect-free castings.
Graphite's unique properties make it an excellent material for degassing rotors:
High Temperature Resistance: Molten metals are processed at high temperatures. Graphite can withstand these temperatures without melting, deforming, or significantly degrading, ensuring the rotor maintains its shape and functionality within the molten metal.
Chemical Inertness: Graphite is resistant to chemical attack by most molten metals, particularly aluminum and its alloys. This prevents contamination of the molten metal and extends the lifespan of the rotor.
Machinability: Graphite can be easily machined into complex shapes with precise dimensions, allowing for the creation of rotor designs that optimize gas dispersion and degassing efficiency.
Low Density: Graphite's relatively low density minimizes the load on the degassing equipment and facilitates easier handling and maintenance.
Thermal Shock Resistance: Graphite can withstand rapid temperature changes without cracking or spalling, crucial for immersion in and removal from hot molten metal.
Cost-Effective: Compared to other high-temperature materials, graphite offers a cost-effective solution for manufacturing degassing rotors.
Rotor Design: The rotor design is crucial for efficient gas dispersion. Common designs include:
Bladed Rotors: These rotors have blades that create shear forces in the molten metal, breaking up the inert gas into fine bubbles.
Porous Rotors: These rotors have a porous structure that allows the inert gas to diffuse through the graphite and form fine bubbles directly at the surface.
Combination Rotors: Some rotors combine bladed and porous features to optimize gas dispersion.
Shaft Connection: The rotor is connected to a shaft that drives its rotation. The shaft connection must be strong and secure to withstand the torque generated during degassing.
Gas Injection Ports: Gas injection ports are strategically placed on the rotor to introduce the inert gas into the molten metal.
Balanced Design: The rotor must be properly balanced to minimize vibration and ensure smooth operation during degassing.
Coating (Optional): Some rotors may be coated with a protective layer to further enhance their resistance to erosion and chemical attack.
Immersion: The graphite rotor is lowered into the molten metal bath.
Rotation: The rotor is rotated at a controlled speed, typically ranging from 100 to 500 RPM, depending on the size of the melt and the desired degassing efficiency.
Gas Injection: Inert gas (argon or nitrogen) is injected through the gas injection ports on the rotor.
Bubble Formation: The rotation and rotor design create shear forces in the molten metal, breaking up the inert gas into fine bubbles. Porous rotors generate fine bubbles directly at the surface.
Degassing: These fine bubbles rise to the surface of the molten metal, attracting dissolved hydrogen and other impurities.
Slag Removal: The impurities that accumulate on the surface as slag are removed, leaving behind clean, degassed molten metal.
Improved Casting Quality: Reduces porosity and surface defects, resulting in higher-quality castings with improved mechanical properties.
Increased Mechanical Strength: Higher density castings with reduced porosity exhibit improved tensile strength, yield strength, and fatigue resistance.
Enhanced Corrosion Resistance: Reduced porosity makes the casting less susceptible to corrosion.
Reduced Scrap Rates: Fewer defective castings lead to reduced scrap rates and increased productivity.
Improved Machinability: Degassed castings are easier to machine, reducing tool wear and improving surface finish.
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