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Reaction Injection Molding Companies Take Advantage of Process’s Numerous Benefits

Reaction injection molding companies produce a wide range of parts, including:

  • Corrosion-resistant fittings
  • Bumpers
  • Construction machine covers
  • Fenders

Parts manufactured using RIM molding can be easily painted. End markets range from automotive and construction to appliance, furniture, recreation and sporting goods.

Reaction injection molding is used to create parts that are difficult or impossible to create using injection molding. RIM allows for thick and thin walled parts, encapsulated inners and foamed cores.


RIM molding is accomplished by bringing together two liquid reactants – an isocyanate component and a polyol resin mixture – under high pressure and injecting them into an impinging mixer. The resulting mixture is injected under low pressure into a mold, where it expands and cures.

Because the mixture is flowable before the reaction occurs, reaction injection molding can create intricate parts with detailed surface characteristics.


Reaction injection molding companies can formulate specific resins to meet the end user’s requirements. Materials used in reaction injection molding cover a wide range of thermosets, from structural foams to elastomeric polymers such as:

  • Polyureas
  • Polyisocyanurates
  • Polyesters
  • Polyphenols
  • Polyepoxides
  • Nylon 6


But the material most commonly used by reaction injection molding companies is polyurethane in either a foam or solid state. The advantages of RIM molding polyurethane include:

  • High strength and low weight
  • Heat resistance
  • Thermal insulation
  • Dimensional stability

Compared to traditional injection molding, other advantages of reaction injection molding in general include:

  • Better economies for lower volume production
  • Less expensive tooling
  • Lower energy usage
  • Less required floor space

RIM molding also requires less labor than reaction transfer molding and enables part consolidation when transferring a design from sheet metal.


There are several variations of reaction injection molding. Reinforced reaction injection molding uses reinforcements such as glass fiber or mica to produce strong, rigid parts. Structural reaction injection molding uses fiber meshes as reinforcements.

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