Reaction Injection Molding RIM Calculator
Polyurethane & thermoset composites: Calculate high-pressure impingement mixing nozzle Reynolds numbers, mixhead pressure drop, and mold filling time vs cream time.
Reactive Stream & Impingement Nozzle
Mixing Hydrodynamics & Injection Pressures
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
How does high-pressure impingement mixing work in Reaction Injection Molding (RIM)?
Unlike traditional injection molding that melts plastic with an extruder screw, RIM pumps liquid reactive monomers (polyol and isocyanate) at ultra-high pressures (150 to 200 bar) through opposing micro-orifices into a tiny mixing chamber. The collision of high-velocity jets (100–150 m/s) generates intense turbulent eddies that disperse the chemicals down to molecular scale within milliseconds.
What is the "cream time" and why does it dictate mold filling speed?
The cream time is the interval from initial mixing until the clear liquid turns milky and begins rapid exothermic polymerization and gas bubble nucleation. In RIM, the entire mold cavity must be filled with low-viscosity liquid before the cream time (typically 2 to 8 seconds); otherwise, expanding foam creates flow lines, voids, and massive mold pressures.
Why must nozzle pressures be closely matched between Component A and B?
If one component has significantly higher pressure than the other, its jet will overpower the opposing stream, pushing past the mixing chamber centerline and even backflowing into the lower-pressure nozzle orifice. This causes localized stoichiometric imbalance, incomplete polymerization, and soft, tacky patches on the finished molding.