Simulation of Reactive Injection Molding of Polyurethane Foams

In the RIM process of PU foams, shear thinned reacting polymer mixture of adequate isocyanate and polyol group is injected into a mold where after a few seconds the material evolves from a low molecular weight emulsion (through polymerization with the evolution of heat and CO2 gas) to a complex polymer network via chain-linking and polymer entanglement.

Generally, the final structure and attributes of expanding PU foams depends strongly on the evolving material properties of the reactant mixture used in producing them. For instance the mixture viscosity exhibits chemo-rheological behaviour, thus, changing in space and time with the degree of cure and temperature of the foaming system.

Flow Front Development
© Fraunhofer ITWM
Development of the flow front of the foam material in the cylinder after 100 s, 150 s and 200 s: results from simulation (top) and practical tests (bottom).
Temperatur im Zylinder
© Fraunhofer ITWM
Time evolution of the temperature in the cylinder
Vergleich der Drehmomentmessung
© Fraunhofer ITWM
Comparison of the torque measurement (M) of the experiment with the result of our simulation.

Complex Dynamics Predict

In the mathematical framework, this behaviour initiates a coupling between viscosity, degree of polymerization and temperature. With this form of coupling in the state variables it becomes very difficult to estimate associated model parameters analytically. Although the chemistry of reactive blown PU foams has a well documented history, however, obtaining adequate mathematical description of the complex dynamics which occurs in the RIM process still remains an issue of current research.

With the efforts of our collaborators from the Department of Mechanical Engineering in TU Chemnitz who performed all the relevant experimental studies under the MERGE project on light weight structures, we formulate adequate mathematical framework capable of predicting the complex dynamics of the expanding PU foam system. Furthermore, with our in-house robust numerical simulations platform (CoRheoS), we are able to predict the flow behaviour and other physically relevant flow variable necessary for describing the expansion process.

The results from our solution platform provide accurate description of the mass and heat transfer in the expanding foam setup. In addition, the comparison with the available experimental data gives both qualitative and quantitative agreement.

Polyurethane foam expansion in cylindrical tube of 112 [mm] diameter.

Example Projects


RIM Processes of Polyurethane Foams

 In the project FoamInTextil we simulate the foam filling process of Polyurethane foams.