What is Dross Metal?
Dross is created after melting different types of metals. When metals oxidize in a furnace, they interact with oxides, impurities, oil, and other materials. Dross is the leftover ‘impurities’ in molten metal after oxidation.
Dross occurs more commonly in non-ferrous and low-melting-point metals such as lead, aluminum, zinc, and tin. These metals oxidize more easily than ferrous metals like steel. During the oxidation process, they form a protective oxidized surface layer. These impurities float to the molten metal’s top and can be skimmed from the surface when melted.
The Impact of Dross on Foundries
Removing dross from molten metal is essential because it decreases the overall quality of the final product and can lead to impurities and defects such as porosity. Because dross can cause defects, properly removing, processing, and disposing of it is crucial for foundries to increase profitability. While dross is recyclable, it still costs money and time to reuse. Disposing of it can be challenging as well, making it crucial to minimize it.
Different Types of Dross
There are two types of dross metals: primary and secondary dross. Primary dross forms when metals like aluminum are melted. It comes from the smelting metal and rises to the surface during the melting process.
Secondary dross comes from recycling and remelting scrap metal or old castings. Because it has been processed before, it typically has more contaminants.
Preventing Metallic Dross in Castings
Reducing and managing metal dross in foundries is vital for increasing your bottom line and creating higher-quality castings. Here are a few factors that can potentially reduce the amount of metal dross you get:
- Quality: Higher-quality metals will have less impurities than cheaper ones.
- Temperature: You should control the temperature of your pour and ensure it is consistent and at a specific temperature every time.
- Remelt: Secondary dross that’s being remelted should be in controlled amounts. If more scrap is remelted, there will be a greater amount of oxides and impurities.
- Cleanliness: Furnaces, crucibles, ladles, and all other equipment handling the molten metal should be cleaned regularly based on standard cleaning procedures to keep contamination chances low.
- Degassing: Degassing reduces hydrogen porosity in castings, resulting in less dross in the finalized product. Degassing brings gas bubbles to the surface with the dross, reducing the castings you’ll have to scrap.
How to Remove Dross from Metals
Prevention can mitigate the dross in your metals but may not eliminate it. Thankfully, it can be reclaimed from molten metal in a variety of ways, such as:
- Manual Removal: A hammer and chisel can break the waste off. This method takes a long time and is more dangerous than others.
- Skimming: Dross is skimmed off the top of molten metal using specialized tools such as skimmers or ladles.
- Sand Blasting: Sand blasting equipment can remove dross from metals while polishing it.
- Rotary Equipment: Rotary equipment cleans dross deposits for remelting while breaking down other impurities for recycling or disposal.
Dross Reclamation Equipment: DUCTA-SPRUE®
While other methods of dross reclamation are effective, they can be costly or take longer. Automating dross reclamation can increase workplace safety and efficiency and leave you with cleaner deposits.
General Kinematics’ DUCTA-SPRUE® Dross Reclamation Mill efficiently recovers precious metals from slag and dross. Its rotary action effectively abrades the material to break apart and release dross from valuable metals. It cleans, screens, and separates the dross from precious metals.
Ready to reclaim dross more efficiently? Contact a GK Foundry specialist to get started!
