In casting aluminum objects, molten aluminum is poured into a mold. One of the techniques for making an aluminum mold is called sand casting. It involves mixing fine sand, some clay, and a small amount of water to make the mixture cohesive. This mixture is called green sand because it is moist, not because it is actually green. The green sand is tamped into a box with a hollow mold shape embedded into it. Molten aluminum is poured into the hollow and allowed to cool. After cooling, the sand is dislodged and the molded aluminum piece is removed.
Sift the sand through the wire mesh into the plastic pan.
Add the water gradually to the sand. Mix the sand and water thoroughly with your hands and the trowel until the water is distributed evenly throughout.
Mix in bentonite powder gradually using your hands and the trowel.
Mull the green sand at least three times. Mulling is stomping on the mixture then fluffing it with the trowel. It is very important that the bentonite is evenly distributed throughout the sand. The consistency should be such that, when you grasp a handful firmly in your fist, it makes a solid clump. If you break the clump, there should be a clean break. If it crumbles, add more clay.
Experiment with different percentages of the ingredients to find out which works best for your purposes.
- Large plastic or metal pan
- 10 lbs. silica or other fine sand
- Fine metal mesh screen
- 1.2 lbs. powdered Bentonite clay
- 12 oz. water
Make sure the sand and clay are clean before starting this procedure. Make your own bentonite clay powder by finely grinding clay kitty litter. Make sure it is the clumping type that contains bentonite. Try different types of sand for different finishes. Remember that the finer the sand the smoother the finish on the molded piece and the better the detail. Keep the green sand in a covered container to keep the water from evaporating before it is used.
Wear a mask when mixing the fine sand and clay. The extremely small particles can be inhaled and cause respiratory problems. Always wear protective clothing, gloves and eyewear when handling molten metal. Never use fireclay instead of bentonite clay. Iron and steel molding requires a green sand mixture moistened by oil instead of water because of the high temperatures necessary for melting them. Do not use water-moistened sand mixtures for iron or steel because the steam buildup can cause an explosion in the mold.