In aluminum ingot production, oxidation loss is a key indicator that affects metal recovery rates and production costs. When aluminum is melted at high temperatures, it reacts with oxygen in the air to form aluminum oxide. 
To effectively reduce oxidation loss, it is crucial to prevent such losses as much as possible! This requires systematic control across multiple areas. The following are the core strategies used in the industry to reduce oxidation loss in aluminum ingot production:
Temperature is a key factor affecting the oxidation rate of molten aluminum. As the temperature of molten aluminum rises, the oxidation rate increases exponentially.
Strictly control the melting temperature: The melting point of aluminum is approximately 660°C. During tapping and casting, keep the molten aluminum temperature between 720°C and 760°C.
During this process, you should avoid localized overheating as much as possible. This happens because when the temperature goes above 780°C, the oxide film on molten aluminum changes. It shifts from a dense layer to a porous one. At the same time, this change accelerates the oxidation of the aluminum inside.
Adopt advanced heating and stirring technologies:
Use regenerative burners or natural gas radiant tubes for heating. This reduces direct contact between open flames and the molten aluminum surface.
Replace traditional manual or mechanical stirring with electromagnetic stirring. Electromagnetic stirring facilitates internal circulation of the molten aluminum, preventing damage to the protective oxide film on the surface. This reduces the surface area of the molten aluminum exposed to air.
During smelting, blocking contact between molten aluminum and oxygen is the simplest way to prevent oxidation.
Proper Use of Covering Fluxes: Sprinkle a covering agent made of chloride and fluoride salts on molten aluminum. The flux melts at high temperatures, forming a dense liquid protective layer on the surface of the molten aluminum.
Refined Slagging Operations:
“Dry” Slagging: Before skimming, use a skimming flux to initiate a reaction. This lets the free aluminum fully return to the molten aluminum.
Reducing slag skimming frequency: A thin oxide film on molten aluminum helps protect it. Unless required by the process, frequent slag skimming should be avoided. This prevents the continuous exposure of new molten aluminum surfaces, which would lead to secondary oxidation.
The furnace atmosphere directly determines the severity of oxidation.
Improving furnace sealing: Inspect and maintain the furnace door gaskets regularly. This helps reduce cold air intake into the furnace.
Controlling the combustion atmosphere: Optimize the air-fuel ratio. Use a slightly reducing or neutral combustion atmosphere. This helps minimize leftover oxygen in the furnace.
Due to its large surface area, scrap aluminum is the component most prone to burning loss.
Scrap Aluminum Sorting and Pretreatment: Strictly degrease, remove paint, and dry bundled scrap aluminum and aluminum chips. Residual oil and moisture on the surface decompose at high temperatures, producing large amounts of oxidizing gases that significantly accelerate aluminum oxidation.
Adopt “Dual-Chamber Furnace” or “Bottom-Loading” Processes: For lightweight, thin materials and aluminum chips. It is strictly prohibited to load them directly through the furnace top or door and expose them to open flames. A dual-chamber melting furnace should be used to press thin materials directly into the deep molten aluminum. By using heat stored in the large furnace chamber, these materials melt quickly in molten aluminum. This creates “oxygen-free melting.”
When transferring molten aluminum from the melting furnace to the holding furnace or casting machine. Close attention must be paid to the height difference. If the drop is too great, it will cause violent turbulence and surface agitation, leading to severe “dynamic oxidation.”
Optimizing Traditional Transfer Methods High-drop transfer: Molten aluminum falls directly into the air, forming large amounts of dross.
Horizontal transfer via a flow channel: Design a suitable slope for the channel. This helps molten aluminum flow smoothly. It also reduces turbulence.
Turbulent churning: Disrupts the surface oxide film, causing gases and dross to be drawn into the molten aluminum.
Submerged discharge below the liquid surface. The outlet of the transfer pipe stays below the liquid surface in the receiving vessel at all times.
Conventional gas purging: Uses ordinary air or unpurified gas.
Inert gas protection: Protective covers are placed over the flow channel and transfer point. **Nitrogen or argon** is added to protect the atmosphere.
Conclusions and Lean Management
Reducing oxidation losses in aluminum ingot production is a systematic endeavor. In addition to the technical measures described above, companies should set up a numerical method.
This method should measure aluminum dross weight gain. It should also measure burn-off rates. By introducing automated dross handling systems, operators can recover metallic aluminum from residual dross immediately on-site.
For an aluminum plant producing 10,000 tons, cutting the burn-off rate by 0.5% can save hundreds of thousands. It may even save millions in material costs.
Precise control of the furnace temperature is essential. Careful control of the furnace atmosphere is also important. Standard operating procedures are key. Together, these steps help produce green aluminum ingots with high yield and low consumption.