Casting materials, such as sand, urethane rubber, and plaster of Paris, are used to create sculptures or mechanical parts. Sand casting is the most cost-effective and widely used method, while urethane rubber is durable and used for outdoor applications. Plaster casting allows for multiple casts and is used for non-ferrous metals.
There are many types of casting materials used in the production of sculptures or mechanical parts that can be too complicated to make with another technique. Various types of material in liquid or liquefied form are poured into a casting, or mold, containing an area hollowed out in the shape of the desired part or object, and then allowed to harden into a solid mold shape. One of the oldest types of casting materials is sand which is used to make one large molded object. Urethane rubber is used in the casting process of concrete and other aggregate materials for use in both interior and exterior applications. Gypsum is the main ingredient used for casting materials made from various types of low melting point metals.
Arguably the least complicated and most widely used of all the different casting processes, sand casting allows you to make cast objects at a very low cost. Because the mold is destroyed after each use, this type of casting is ideal for makers who need only a few molded elements. The sand used in sand casting is held together by the use of chemical binders, clay, or certain types of polymerized oils. Sand casting molds are also used for casting very large parts. For example, an entire steel frame for a railroad car, bulldozer, or ship can be made from a single sand casting mold.
Urethane rubber is one of the most durable casting materials and is primarily used for concrete or other aggregate items that will be exposed to the elements. As with casting materials such as plaster, a model is made and urethane rubber is poured or formed around the model. After being allowed to dry, the urethane is then carefully pulled from the model creating a negative shape of the item. After the concrete is poured into the mold, it is subjected to vibrations that push the air bubbles away from the concrete surface, creating a smooth finish that allows the urethane to be easily pulled out. The waterjet concrete process uses rubber molds to create smaller decorative objects such as retaining wall blocks, medallions, cornices, balustrades and pavers.
Similar to sand casting, plaster casting uses the same basic techniques, except plaster of Paris is used instead of sand. In some cases, plaster casting materials allow you to make more than a single cast. A model of the part or object is created by pouring plaster around the part, resulting in a negative mold or plaster casting. The molten metal, or other liquid material, is then poured into the mold to make the final part. The excess plaster is removed by mechanical breakthrough and pressurized water jets. Smelting materials of this type are only capable of handling non-ferrous metals with a low melting point such as copper, aluminum and zinc.
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