RIM Casting Company, Reaction Injection Molding

Reaction Injection Molding (RIM)

Reaction Injection Molding (RIM) produces parts with complicated detail that are dimension-ally stable, chemically resistant, physically tough, and wear resistant. This process is an good choice for larger plastic parts produced in short run or low volume production quantities.

The process takes its name from a chemical reaction that occurs within the tool. The plastics used are thermosets, either polyurethanes or foamed polyurethanes. The two components that produce the polyurethane are mixed just prior to injection into the tool. With the low viscosity and low injection pressures, large, complex parts can be produced economically in low quantities.

Considerable design freedom is possible, including thick and thin wall sections that are not good for injection molding, due to the uniform shrink characteristics. Foamed polyurethanes are natural thermal and acoustic insulators. Excellent flowability allows for the encapsulation of a variety of inserts.

Reaction injection molding is used in many industries for many types of parts. While bumpers for vehicles are produced in this process, most applications are for large, complex parts produced in quantities less than 5,000 units. Examples include panels for electrical equipment, enclosures for medical devices, and housings for computer and telecommunications equipment.

If you think that your next project may benefit from Reaction Injection Molding, contact us to learn the advantages and differences when compared to other plastic molding processes.

For detailed specifications, view a technical data sheet for Reaction Injection Molding.

The Reaction Makes All the Difference

Reaction injection molding and plastic injection molding have almost the same name, so even experienced engineers and designers might think they are the same. But “reaction” signals a big difference.

Unlike plastic injection molding, RIM molding techniques utilize low-viscosity liquid polymers in thermoset – not thermoplastic or thermoforming – processes. Through a variety of chemical reactions, these polymers expand, thicken, and harden only after they’re injected into the heated mold, accommodating much more intricate designs than ordinary plastic injection molding.

Raw materials and reaction injection molding techniques can be selected and even customized to precisely deliver desired weight, strength, density, and hardness characteristics. The result is large polyurethane parts with a much lighter weight than those created by more commonplace processes.

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