Gilsonite in Foundry Sand: How It Works

Green sand moulding is the most common way to make iron castings. Carbonaceous additives are added to the sand to improve the surface finish of castings, and gilsonite is one of the most effective.

The role of carbon additives

When molten metal is poured into a green sand mould, the additive heats up and releases gases and hydrocarbons. These form a thin layer of lustrous carbon at the mould–metal interface. This layer prevents the metal from wetting and penetrating the sand.

Why gilsonite

• High volatile matter releases plenty of gas
• High lustrous carbon yield
• Low ash and low sulfur compared with many coal dusts
• Lower dosage than traditional sea coal

Benefits for castings

• Smoother surface finish
• Easier shake-out and cleaning
• Fewer burn-on and penetration defects
• Better dimensional accuracy

Typical dosage

0.3–1.0% for iron castings.

What happens at the mould surface

When molten iron at around 1,400 °C meets green sand, the carbon additive heats almost instantly. Volatile hydrocarbons are released and crack in the oxygen-poor atmosphere of the mould. Carbon deposits as a thin, shiny layer on sand grains next to the metal. Molten iron does not wet this layer, so it does not penetrate between sand grains.

Key properties of foundry gilsonite

Practical results foundries look for

Cleaner castings, less shot-blasting, easier shake-out and more stable sand properties.

See our foundry grade gilsonite and read gilsonite vs. sea coal.