Some really good information about sand casting and metal casting!

Sand casting is the most ancient form of metal casting and has been around since ancient Egypt. Sand casting is a method that involves pouring molten metal into a sand mold. Many metal casters prefer using sand casting over many of the other forms of processes because it's cheap and the sand used is readily available.

Many experienced metal casters will continue to use sand casting even though their abilities and resources allow them to use the other metal casting methods like Lost Wax Casting or Investment Casting. Sand casting involves less material and less effort than the other casting methods. Sand casting is a great way for new casters to get into the trade.

In sand casting, the metal caster will create a mold by placing an original in the flask which is filled with sand. The original will be a pattern of what you want to cast. By ramming or vibrating the sand, the caster creates a mold of the original. The casting sand used needs to be able to retain the shape of the mold. Finding the right mixture of sand to water is crucial. Too much water can ruin the mold and possibly destroy it while too little water will create a poor casting. Green sand is a type of casting sand that many prefer since its ability to retain the shape of the mold is far better than normal sand. Green sand usually contains bentonite clay, sand, and water.

After the sand is packed, the pattern or original is removed carefully. Then a series of channels or gates, to carry the molten metal to the cavity, is incorporated. The gating system is generally created by hand, carving away the sand to form the channels. Molten metal is poured into the mold and allowed to cool. The metal caster will then break the mold and dig out the casting.

While sand casting has its benefits the use of green sand can greatly increase the likelihood of a successful casting. Green sand is not really green, the color refers to the damp nature of the sand. Green sand is created by adding water and bentonite to the sand. One of the benefits of using bentonite in green sand is that it makes the sand more permeable which allows more gas to escape.

Metal casters can get the bentonite from a variety of sources like home improvement stores and even from household resources. Many have milled the type of cat litter that clumps since one of the ingredients is bentonite. Remember to work in a well ventilated room or to wear proper face gear when working with bentonite since it will irritate the lungs.

There are several recipes online for green sand but the most common method is experimentation. What you are looking for when mixing the sand, water, and bentonite is a texture that is not wet but damp and will retain its shape when molded.

The type of sand you use to make green sand depends on you and the availability of the sand. Many will use sand that they found out in the wilds of nature and some will buy bags of sand like playground sand. As you cast with green sand you will find out which works best with what metals.

Green sand is growing in popularity as more casters are recognizing the properties of this method. If you have traditionally used regular sand casting, green sand casting will prove to be easier to work with and will produce better casts.

The best part about green sand casting is that is does not cost a lot of money to get into doing it.


A diagram of a typical sand casting mold

Sand Casting Definitions

  • Flask: The frame of the mold
    • Cope: The upper part of the Flask
    • Drag: The bottom part of the flask
    • Pins: Used to assure proper alignment of the cope and drag after the patern is removed.
    • Parting Line: the line where the Cope and Drag come together
  • Mold Cavity: formed when the pattern is embedded in sand in the flask forming an impression of the casting.
  • Gating System: The set of channels through which molten metal flows to the mold cavity
    • Pouring Cup: The flared area where the molten metal is poured
    • Sprue: A vertical channel that guides the molten metal to the runner
    • Runner: a channel through which the melt is supplied to the gates
    • Gates: the channel that carries the molten metal to the mold cavity
    • Riser: or "Feed Head" is a cavity connected to the gating system feeding the casting when it's shrinking.
  • Vents: Used to allow air and gasses that are formed in the cavity to escape
  • Core: Negative forms used to produce cavities within the casting Usually sand-molded, cores are inserted into the casting box after removal of the pattern.

Shakeout: The process of removing the casting from the mold after it has cooled.