Resin Casting is the process of using a mold or similar means to form a solidifying resin into a desired shape. The resin must then be left alone to until it is solid. This process may be employed commonly in model-making or in situations where a customized or unique item is needed, such as in dentistry or antique car restoration.
Many modern applications involve mixing separate liquids that slowly solidify when combined, allowing a limited time in which the substance can be poured into a mold before it hardens. This process is referred to as “curing,” and may also be achieved through heating and then cooling the resin or by irradiating it. All methods of curing are intended to be irreversible, and the process results in a chemical change within the resin, usually the conversion of monomers into polymers.
The process of resin casting may share traits with the casting of other materials, but several features set the processes apart. Unlike metals or some petroleum-based plastics, resin castings cannot simply be reheated and recast, though this does not mean they are immune to melting. In most resin casting, monomers — single molecules or atoms capable of combining with similar monomers — form into completely new compounds called polymers.
The castings made from polymerizing chemicals include separate liquids that harden when combined. This format can allow for simple, repeatably-consistent production of pieces with very few tools. Most polymer reactions require little or no outside heat, making them particularly well-suited to home workshops or small-scale production.
Dental composite is a form of resin casting commonly used in modern dentistry to repair cavities. The chemicals involved may be separate monomers that react to form a polymer when combined, or the curing may be initiated by a chemical in the mixture that is sensitive to light or heat. In the latter case, once the dental composite is in place and properly formed, heat or a specific wavelength of light is applied. The chemical reaction may encourage the bonding of the composite with the tooth as well, and some modern composites may create a finished surface comparable in strength and durability to the original tooth enamel.
The molding of the resin may be accomplished in a number of ways. In modeling or car restoration, a mold may be carved by hand or cast from an existing item to be copied. The resin casting in dental composite takes place in the patient’s mouth, where the dentist manipulates the resin into a desired shape before it is cured. To create a cylindrical object, such as a drum or pipe, the resin may be spun inside a hollow tube that then acts as a mold. Sheets of hardened resin may also be created using moving belts or chemical baths, with the resin curing on the surface.