Green Sand Casting Step by Step and the Role of Gilsonite

Green sand casting is the most widely used metal casting method in the world. “Green” means the sand is moist, not that it is coloured. Here is how the process works and where gilsonite fits.

1. Sand preparation

Silica sand is mixed in a muller with bentonite clay, water and a carbonaceous additive such as gilsonite. The mixture must have the right moisture, strength and permeability.

2. Moulding

Sand is compacted around a pattern in a two-part flask (cope and drag). The pattern is removed, leaving a cavity in the shape of the part.

3. Cores

If the part has internal cavities, sand cores are placed in the mould.

4. Pouring

Molten metal is poured into the mould through a gating system. At this moment gilsonite releases gases and forms lustrous carbon, protecting the sand surface.

5. Cooling and shake-out

After solidification, the mould is broken on a shake-out grid. Good carbon additives make the sand fall away cleanly.

6. Cleaning and finishing

Gates and risers are removed, and the casting is shot-blasted and ground.

7. Sand reclamation

Most sand is cooled, screened and returned to the muller with fresh additives.

Typical green sand composition

Why green sand is popular

It is reusable, fast and inexpensive, and suits high-volume production of iron castings from small parts to large housings.

Where problems usually start

Most green sand defects trace back to sand control: moisture, clay activity, compactability and carbon level. A stable sand system is the foundation of good castings.

Our foundry grade gilsonite improves surface finish and shake-out. Read gilsonite in foundry sand.