In the aluminum processing industry, the melting shop is often referred to as the "heart" of operations. However, it is also frequently a major hotspot for scrap generation. Reducing the scrap rate of aluminum billets cannot rely solely on post-production sorting. It requires a deep and comprehensive optimization of the melting process itself.
The following outlines a comprehensive, end-to-end optimization plan—spanning everything from raw material control and melting parameters to refining and impurity removal. This optimization strategy helps to improve the yield of finished aluminum billets at the source. 
Persistently high scrap rates are often attributed to improper raw material ratios or contamination.
Strict Control of Remelt Material Ratios: It is recommended that the proportion of recycled aluminum be kept within 30%. Excessive use of remelt material introduces significant amounts of oxide scale and hydrogen. Leading to defects such as pinholes or slag inclusions in the finished billets.
Pre-treatment: Cold charge materials should undergo pre-treatment to remove surface contaminants such as oil, moisture, and coatings. Moisture is the primary source of hydrogen within the molten bath. Consequently, its removal can directly determine the density and structural integrity of the resulting aluminum billets.
Temperature is the core variable in the melting process. If the temperature is too high, the molten aluminum becomes highly susceptible to hydrogen absorption; conversely. If it is too low, slag removal becomes ineffective, and defects such as "cold shuts" may occur.
Optimal Temperature Range:
The temperature of the molten aluminum must be strictly maintained within the range of 720°C to 750°C.
Dynamic Temperature Adjustment:
Prolonged holding of the molten metal at high temperatures is strictly prohibited. If subsequent processing stages are delayed. The furnace temperature should be lowered or the heating source shut off immediately.
The majority of aluminum billet defects stem from incomplete degassing.
Combined Degassing Method:
Employ a hybrid approach utilizing a combination of "online rotary gas injection with flux powder" and "static box refining."
Rotary Gas Injection:
High-purity argon gas, combined with refining flux powder, is injected via a rotating rotor. This process micro-disperses the gas bubbles, significantly increasing their contact surface area with the molten aluminum and thereby enhancing hydrogen removal efficiency.
Refining Flux Dosage:
The quantity of refining flux used should be precisely metered based on the purity level of the molten aluminum. This practice prevents the formation of salt inclusions—a common defect resulting from the excessive addition of flux.
4.Comparison Table of Key Process Parameters
|
Influencing Factors |
Outdated, Backward Processes |
Optimized Process |
Impact on Reject Rates |
|
Refining Gas |
Standard Industrial Nitrogen |
High-Purity Argon (99.999%) |
Significantly reduces porosity and pinholes |
|
Slag-Metal Separation |
Manual Slag Removal |
Specialized Slagging Agent + Mechanical Stirring |
Minimizes aluminum loss and lowers slag inclusion rates |
|
Filtration Method |
Standard Ceramic Filter Screens |
Dual-Layer Foamed Ceramic Filter Plates |
Intercepts micron-scale non-metallic inclusions |
|
Charging Sequence |
Disorderly Charging |
Large to Small, Heavy to Light |
Enhances thermal efficiency and reduces compositional segregation |
Holding Time :
A settling period is required following the completion of the refining process. It is strongly recommended to ensure a settling time of 15 to 20 minutes for the molten aluminum. This allows fine dross particles to fully float to the surface.
The filtration system serves as the final line of defense before the molten aluminum enters the casting machine.
Upgraded In-Line Filtration: The 30ppi filter plate is upgraded to a dual-stage filtration system.
Launder Sealing: Ensure that the launder is completely sealed. The purpose of this is to minimize secondary oxidation of the molten aluminum during flow.
Furnace-Side Sampling:
Each heat must undergo macrostructure inspection and direct-reading spectroscopic analysis. The purpose of this is to ensure that compositional fluctuations remain within the standard median values.
Operational Standardization:
Operators are strictly prohibited from vigorously agitating the surface of the molten aluminum. This prevents the oxide film from fracturing and becoming entrained within the molten metal.
Summary
Reducing the scrap rate of aluminum billets is not merely a matter of a single technological breakthrough; rather. It constitutes a systemic engineering effort encompassing "raw material purification, precise temperature control, and intensive refining." Through these optimizations, the scrap rate attributable to the smelting process can typically be reduced by 15% to 30%.