Factors Affecting the Quality of Impingement Mixed RIM Urethanes

Reaction injection molding of polyurethanes has become an established means of producing highly configured exterior automotive parts. As such, precautions must be taken to assure that RIM urethanes are consistently well mixed, Mixing quality affects cosmetic appearance, physical properties, and performance in the field.

The processing variables for six RIM systems are analyzed and quantified. A procedure to minimize machine set-up time and assure good mixing is given. Three areas are considered-- metering, primary mixing in the mixing chamber, and secondary mixing in the static aftermixer.