12 Proven Ways to Reduce Molten Aluminum Dross and Boost Recovery
aluminum castingToday we are rolling up our sleeves and heading into the heart of the foundry to tackle one of the most expensive headaches in the industry: aluminum melting dross. If you have ever looked into a typical reverberatory furnace for melting solid aluminum, you know that what happens on the surface of that melt can make or break your profit margins. To stay competitive, every foundry manager needs to know exactly how to reduce molten aluminum dross before it eats away at their bottom line. When we talk about aluminum recovery, we are really talking about a war against oxidation. Every piece of aluminum scrap fed to a furnace has a very thin skin of aluminum oxide. It doesn’t matter if it’s a heavy ingot or a light turning; that skin is there. When the scrap is heated in a furnace, the higher temperatures cause the skin to grow more rapidly, especially if the scrap is heated in air or an oxidizing environment. If left unchecked, this oxidation leads to massive waste, making it critical to implement strategies that reduce molten aluminum dross during the melting cycle. This guide is designed to help you reduce molten aluminum dross and maximize your aluminum recovery using both common-sense maintenance and advanced chemical strategies. Understanding Aluminum Melting Dross To effectively reduce molten aluminum dross, you first have to understand exactly what it is. When the aluminum melts, the aluminum oxide floats to the surface, forming a second phase known as dross. But it’s not just “trash.” Because of the surface tension of the oxide skin, metallic aluminum is also trapped in the dross from 15% to 80%. Think about that for a second: the primary goal of any foundry is to reduce molten aluminum dross because up to 80% of that “scum” you are skimming off might actually be good, usable metal. Large, heavy-section melt stocks have the largest ratio of mass to surface area and sustain minimal melt loss. However, in-house remelting of clean scrap will increase the melt loss because of the increased surface area, making it even harder to reduce molten aluminum dross. If you want to dive deeper into the basics of melt quality, check out our guide on refining agents. The High Cost of Contamination and Surface Area One of the quickest ways to lose money is by charging “dirty” material, which makes it nearly impossible to reduce molten aluminum dross. For every 1% organics and moisture, 2% melt loss will result. This is why using clean, dry charge materials is rule number one if you want to reduce molten aluminum dross and improve aluminum recovery. Furthermore, the shape of your scrap matters. Charging turnings, borings, and machining chips results in as much as 10% to 15% dross formation. This is due to the massive surface area exposed to the furnace atmosphere. If you are struggling with high scrap rates during die casting machining, the problem likely started right here in the furnace because you didn’t have a plan to reduce molten aluminum dross. The Impact of Temperature on Dross Formation An important factor in your quest to reduce molten aluminum dross is the holding temperature of the melt. You might think a few degrees don’t matter, but the impact of temperature increases of only 25 to 55°C can be quite significant. High temperatures accelerate the oxidation reaction, so keeping a cool melt is the easiest way to reduce molten aluminum dross. Moreover, the thickness of the layer of dross over the melt gives an insulating effect and requires an increase in the firing rate of the burner system. It’s a vicious cycle: the more dross you have, the harder you have to fire the burners, which in turn creates more dross. Therefore, to reduce molten aluminum dross, the thickness of the layer on melter surfaces is most commonly maintained at less than 40 mm to keep the furnace efficient. How to Remove Dross from Aluminum Correctly When it comes time to remove dross from aluminum, you shouldn’t just scrape it out while it’s “wet.” If you do, you are throwing away your profits. Correct application of the proper flux composition results in the physical breaking of a weakly bound oxide layer, which helps reduce molten aluminum dross by entrapping fresh aluminum and returning it to the bath. This allows the metallic liquid alloy droplets to coalesce, which is the “secret sauce” for successful aluminum recovery. You can tell if you are successfully using flux to reduce molten aluminum dross by the look of the material. Metal-rich dross appears bright and shiny, certainly laden with metallic aluminum, whereas treated dross will appear duller and powdery. To remove dross from aluminum effectively, you want that powdery finish. The aluminum content of untreated dross averages 85 to 90%, but furnace treatment can recover approximately half of this amount, significantly boosting your aluminum recovery rates. Ten Common Sense Procedures to Reduce Aluminum Dross The best way to initially deal with dross formation is to minimize it. This can be accomplished by a number of common sense and conscientious maintenance procedures: Advanced Aluminum Recovery Systems Beyond manual skimming, employing a professional dross reclamation system is a total game-changer for high-volume foundries looking to reduce molten aluminum dross. These advanced systems use mechanical action and precise temperature control to “squeeze” the remaining metallic aluminum out of the aluminum melting dross before it has a chance to cool and solidify. By processing the material while it is still hot, you can achieve a much higher level of aluminum recovery than manual methods alone. Additionally, to consistently reduce molten aluminum dross, you must ensure that all thermocouples are in good working order. If your sensors are off, your holding temperature will be inaccurate, and your aluminum melting dross production will skyrocket due to excessive heat. Precise thermal monitoring is the backbone of any strategy to reduce molten aluminum dross. For more information on professional equipment and specialized sourcing, visit China Die Casting Manufacturers. Tool










