Applications of a RIM Process Model

Abstract

Reaction injection molding (RIM) is a relatively new processing technique that is rapidly taking its place alongside the more established plastic processes. During a RIM molding cycle, two highly reactive monomers or prepolymers (in the case of urethanes a diisocyanate and a polyol) are brought into intimate molecular contact by impingement mixing. From the mixing head they flow into the mold and react rapidly to form a solid part. RIM thus combines the polymer synthesis and final shaping into a single operation. Its appeal is clear, most of the polymerization occurs after the reactive mixture is in the desired shape. The low viscosity reactants can be fairly easily mixed and require low pressures to fill the mold. The only way pressures can become large is if the material gels before filling is completed in which case, a short shot occurs.