Reaction injection molding is known as RIM in the manufacturing industry. This process utilizes a mixing process that creates a chemical reaction within the mold to harden the thermoset material. The process is most commonly used for the automotive industry. Two tanks are set up that hold the separated liquid polymers, isocyanate and polyol. Each polymer is piped to a high pressure mixing head. When the heated mold is ready to receive the material the two chemicals are sprayed from the after mixer into the mold. The mixing of both polymers causes a chemical reaction. Inside the mold the mixture expands and then hardens. The mold must stay closed until this reaction is complete. Once complete the cast is removed and taken to be further processed. The chemical reaction forms a light weight ridged foam that can be reinforced with other materials depending on the product being made. There are four types of materials that can be produced from this chemical reaction.
Flexible Foam: This product is sponge like and very durable it is typically used for cushions.
Elastoremic: This product is ridged and has a high impact strength.
Fiber-Enforced (RRIM): This product has glass fiber or mica added to it to create a dense strong material.
Composite (SRIM): Fiber mesh lines the mold before the polymer mixture is added.