Dross

Definition - What does Dross mean?

Dross is a waste product taken off molten metal during smelting, essentially metallic in character. It must be eliminated and processed separately or discarded in a safe place. It may also be dangerous and/or poisonous depending on the context of the usage.

Dross is inherent to nonferrous metal casting operations. It is very important because the profitability of a nonferrous operation is affected by the amount of dross generated at the facility and the way that dross is handled.

Corrosionpedia explains Dross

Dross forms on the surface of metals which have low melting points, such as:

  • Tin
  • Lead
  • Zinc
  • Aluminum

As metal is melted, it oxidizes, forming a layer of scum and impurities which float to the surface as the metal heats up. This dross can be skimmed from the metal so that the refined product is more pure, ensuring a reliable performance when it is cast or worked. With some metals, the amount of dross generated can be very high, as much as 50% of the metal, and this can drive the cost of the metal up significantly.

Dross sometimes poses a risk to human health and can cause problems in refineries and forges, as it may off-gas dangerously when heated.

Dross is a solid which is distinguished from slag, which is a liquid. Dross product is not entirely waste material; aluminum dross, for example, can be recycled and is used in secondary steel making for slag deoxidation.

The best way to reduce the occurrence of dross is to stop its formation through good casting procedures and practices.

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