Casting resins are pourable plastic or elastomer compounds that are used to cast parts, make molds, or form structures in place. They are mixed with a hardener, catalyst, or activator and then poured into the sprue of open molds. Moldmaking applications for these resins include their use with semiconductors; generators and motors; coils and transformers; and switches and circuit breakers.

Types of Casting Resins

There are different material types for casting resins which define a resins properties and applications.

Composites are types of resins made from two or more constituent materials with significantly different physical or chemical properties. One of these constituents is generally a strengthening phase, reinforcement fibers, toughening phase, or other specialty fillers that provide unique properties.

Elastomers and rubber materials are characterized by their high degree of flexibility and elasticity (high reversible elongation). They are based on a variety of different chemicals, including silicone, polyurethane, chloroprene, butyl, polybutadiene, neoprene, natural rubber or isoprene, and other synthetic rubber or compounds. 

Thermoplastic are polymers that turn to liquid when heated and turn solid when cooled. They can be repeatedly remelted and remolded, allowing parts and scraps to be reprocessed. In most cases they are also very recyclable. 

Thermoset or thermosetting plastics are polymer materials that have been irreversibly cured. They are generally stronger than thermoplastics due to the polymer cross-linking and are better suited for high-temperature applications (below their decomposition points). They tend to be more brittle than thermoplastics and many cannot be recycled due to irreversibility.

Two-Part Casting Resins

Two-part casting resins are supplied as spray-on foams, pourable foams, and froth packs. Most consist of A+B systems where A is the resin and B is the catalyst or hardener. To start the curing process, these components are mixed either manually or mechanically. Some multi-component systems are designed for sealing, and consist of two or more resins or a resin and an activator or catalyst, hardener, or cross-linker. When combined, these components react and cure to create a polymerized compound or bond. Although two-part casting resins are suitable for many applications, they require proper mixing and balancing of the A+B mixture. If the mixture is unbalanced, the resin may fail to cure or remain tacky after curing. Problems may also arise if a workpiece is cured in an environment where the temperature is too cold.

Clear Casting Resins

Clear casting resins are optically-clear products that are used mainly in specimen making and preservation. The specimen must be dried thoroughly and kept warm for proper embedding. In some cases, the application of a polyurethane sealant is necessary to prevent the ingress of moisture, which can interfere with the curing process. Clear polyester casting resins are sometimes used in place of liquid acrylic resins.

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Ellsworth Adhesives