This core binder is NOT PURE SODIUM SILICATE, but rather a mixture of sodium silicate and other materials that promote breakdown of the core with heat. This action is necessary to allow the core to be removed from the casting. Pure sodium silicate would form a core that was too hard to be removed. Also a core made from pure sodium silicate would not collapse with the shrinkage that occurs in metal when it solidifies. Without this collapse the metal would be stressed and "Hot Tears" could occur.
Cores are used in sand casting to create hollow cavities in the interior of the part. Sand is mixed with a binder to form a solid "sand core". A core must porous enough to allow gas to escape from the casting, while still blocking the molten metal. It should also be easily removed from the finished casting. Sodium Silicate is used as the binder that "glues" the sand together in cores.
For example, imagine making a cannon. The bore (hollow section) of the cannon can be formed by a core. The hardened sand core goes into the cannon mold so that the molten metal will form the cannon body, but be blocked from filling the center. After the metal cools, the sand core is shaken out of the cannon, leaving the hollow barrel.
There are numerous core binders available, but sodium silicate has a distinct advantage because the cores can be made at room temperature, not baked in ovens like most of the other types. This allows the cores to be made in simple core boxes. A "core box" is used to form the desired shape of the core, such as the cylinder shape of the cannon bore in the above example. Core boxes for sodium silicate cores can be made with materials that would melt while heat curing traditional cores. Examples of materials that can be used to make a core box for sodium silicate are PVC pipe, cardboard, wood or just about anything else that will give the desired shape.
Mix a fine grained sand (try about a 100 mesh to begin with) with 3% to 4% by weight of the sodium silicate. Mixing can be accomplished in a small container by hand for small jobs. Larger batches can be mixed in a muller.
Pack the treated sand into a core box that forms the desired shape. Insert any wires, rods or other support items as required.
To solidify the core, apply CO
The cores will be ready for use immediately after becoming solid.
Here's a link to a you tube video that demonstrates how to do it: http://www.youtube.com/watch?v=BRvFQOVfOlw