Why Is First Refining Necessary?
First refining of aluminum melt is a technical measure adopted according to the characteristics of liquid primary aluminum. Liquid primary aluminum usually contains a relatively high amount of gases such as hydrogen, as well as non-metallic inclusions such as aluminum oxide. In other words, when liquid primary aluminum is used as the main raw material, its initial cleanliness is relatively low. Refining only after remelting aluminum ingots cannot fully meet product quality requirements.
The purpose of first refining is to remove part of the oxide inclusions, gases, and metallic sodium from the liquid aluminum. In practice, first refining is a pretreatment process for liquid primary aluminum. It creates favorable conditions for the refining treatment before casting, helping the final product meet quality requirements.
According to joint research by Northeast Light Alloy Processing Plant and Fushun Aluminum Plant, electrolytic liquid primary aluminum should first be pretreated with flux to ensure the final refining effect. This pretreatment is known as first refining. The research also set a specific requirement: after treatment, the gas content should not exceed 0.24 mL/100 g Al.
When producing remelted aluminum ingots, only first refining is required, and second refining is generally unnecessary. From the perspective of improving the overall technical level of the aluminum industry, first refining of liquid primary aluminum used for remelted ingots is very necessary. It can improve the cleanliness of remelted aluminum ingots and create favorable conditions for improving product quality in subsequent production processes.
Where Is First Refining Carried Out?
In the early stage, chlorine gas was used as the refining agent. The open transfer ladle was moved into a specially designed chlorination room, where refining was carried out directly inside the ladle. After refining, the aluminum melt was poured from the ladle into the mixing furnace.
Under this method, the melt temperature during refining was difficult to control accurately. During transfer, the aluminum melt was also more likely to oxidize and absorb gas, so the refining effect was affected to some extent.
At present, first refining is usually carried out in a holding furnace or mixing furnace. When producing remelted aluminum ingots, first refining can be performed after the charging operation is completed. This avoids transferring the refined aluminum melt again. The aluminum melt remains more stable, and the refining temperature can be controlled more accurately, which helps maintain a good refining effect.
In aluminum alloy production, when a combined melting furnace and holding furnace process is used without external furnace refining, first refining is carried out in the melting furnace, while second refining is carried out in the holding furnace. If melting and settling are completed in the same furnace, first refining is also carried out directly inside the furnace.
Some producers also recommend installing a large-aperture filter plate at the aluminum inlet of the mixing furnace or holding furnace. This allows liquid primary aluminum to be pretreated before entering the furnace, helping remove large flaky oxide inclusions from the melt.
