What Is Reaction Injection Molding?

Reaction injection moulding (RIM) is an industrial molding process. An injection molding method that has a chemical reaction during the molding process. The raw material used in this method is not a polymer, but two or more liquid monomers or prepolymers are added to the mixing head in a certain ratio. Mix evenly under pressure, immediately inject into a closed mold, polymerize and solidify in the mold, and shape into a product. Because the raw materials used are liquid, the cavity can be quickly filled with less pressure, so the clamping force and mold cost are reduced, which is especially suitable for producing large-area parts.

Reaction injection moulding (RIM) is an industrial molding process. An injection molding method that has a chemical reaction during the molding process. The raw material used in this method is not a polymer, but two or more liquid monomers or prepolymers are added to the mixing head in a certain ratio. Mix evenly under pressure, immediately inject into a closed mold, polymerize and solidify in the mold, and shape into a product. Because the raw materials used are liquid, the cavity can be quickly filled with less pressure, so the clamping force and mold cost are reduced, which is especially suitable for producing large-area parts.

RIM was first used only for polyurethane materials. With the advancement of process technology, RIM can also be applied to the processing of a variety of materials (such as epoxy, nylon, polyurea, and polycyclopentadiene, etc.). The RIM process for rubber and metal molding is a hot spot of current research. ^[1]

Chinese name

Reaction injection molding

Foreign name

reaction injection moulding

Short name

RIM

Brief introduction

Industrial molding process

Reaction injection molding was developed in the late 1970s. The United States uses reaction injection molding methods to make polyurethane semi-rigid plastic car bumpers, fenders, dashboards, etc. from isocyanates and polyethers. This method has the advantages of low equipment investment and operating costs, beautiful appearance of parts, good impact resistance, and great design flexibility. It developed rapidly in the 1980s. Reaction injection molding can also produce a rigid polyurethane structure foam. In order to further improve the rigidity and strength of the product, when various reinforcing materials are mixed in the raw material, it is called reinforcement reaction injection molding. The product can be used as an automobile body outer panel and an engine hood. Newly developed varieties include epoxy resins, dicyclopentadiene polymers, silicone resins, and interpenetrating polymer networks.

Reaction injection molding requires that the components react immediately after mixing, and the material can be cured to the extent that it can be demoulded. Therefore, special materials and formulations are used, and sometimes the product needs to be heat treated to improve its performance. The key of the molding equipment is the structural design of the mixing head (Figure 2 [mixing head structure]), accurate measurement and transportation of each component. In addition, the temperature control of the raw material storage tank and the mold is also very important.