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This paper describes the principle of metering and impingement mixing of reaction injection molding (RIM) reactants. Efficient mixing is achieved at turbulent mixing conditions in the mixing chamber. Key factor is the Reynolds' number of the system, depending on the viscosities of the reactants, design, and size of the mixing device, arrangement of nozzles, etc. Mixing conditions are discussed at different ratios of reactants, introduction of additional fluid components to the mixing chamber, mixing of reactants with suspended solid fillers in accordance to reinforced reaction injection molding (RRIM) and lead lag phenomena. The basic requirements for the reactants are outlined for successful processing in accordance to the impingement principle, control of rheology of the initial mixture, effect of air loading, solid fillers, and aftermixing devices. The principles of some RIM and RRIM machines are demonstrated by examples as well as available laboratory RIM and RRIM machines with mold arrangements for the production of specimens under realistic conditions for material development and evaluation, followed by guidelines for aftermixer designs and gate configurations.
urethanes, reinforced reaction injection molding machines, nonreinforced reaction injection molding machines, lead lag phenomena
President, “pta martin sweets” Company, Inc., Louisville, Ky.