Structural reaction injection-molded SRIM

Structural reaction injection molding (SRIM) maybe considered as a natural evolution ofRIM. It is a very attractive composite manufacturing process for producing large, complex structural parts economically. The basic concepts of the SRIM process are shown in Figure 2.57. A preformed reinforcement is placed in a... 

FIGURE 2.57 Schematic of structural reaction injection molding (SRIM). 

Polyurethanes (PU or PUR) and polyureas are classified as TS resins, but their chemistry is so flexible that they can be formulated different ways. There are moldable solid and expanded TSs, with (RPUR) or without reinforcement, flexible and rigid foams, elastomers and thermoplastic molding compounds. As RPs they are important in reinforced reaction injection molding (RRIM) (Chapter 5) and are also available as reinforced thermoplastic molding compounds. A variant on the process employs a structural preform of the reinforcement that is placed in the mold cavity and is called structural reaction injection molding (SRIM). 

Structural reaction injection molded (SRIM) sandwich panel composites incorporating recycled RRIM granulate have been developed in Europe, comprising two layers of glass reinforcement on either side of a core layer of granulated RRIM. The filling can be composed of either painted or unpainted material and can be preformed to shape before resin injection. 

The first such method was structural reaction injection molding (SRIM), as described above, in which the fiber reinforcement is in the form of a mat, which is usually preformed and laid into the mold before the polyurethane mix is injected from the mixing heads. This, however, introduces the additional operation of preforming the reinforcement, so adding to cost. 

Structural reaction injection molding (SRIM) is usually used to produce stiff composites containing polyester or epoxy matrices. In such techniques, the mold consists of a cavity which can be subjected to vacuum. The fiber reinforcement structure in the form of mats or fabrics is placed into this cavity prior to applying vacuum, followed by injecting the two-component polymer. Vacuum, sometimes in combination with pressure, is used to introduce the polymer into the mold cavity and to force it to penetrate the fiber reinforcement structure and form the polymer matrix. For elastomer composite formation, this molding concept is new. The mold development was made because of the higher viscosity in typical two-component elastomers compared to normal polyester- or epoxy-based rigid matrix polymers. 

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