The process for molding Expanded Polystyrene (EPS) beads is well known. The beads are placed into a closed mold and heated with steam for consolidation at temperatures near the Tg of PS (around 100oC). Expanded Polypropylene beads molding is not as simple since Polypropylene is a semicrystalline material with a Tm around 165oC. Therefore much higher level of steam pressure is necessary to mold Polypropylene expanded beads. However, the service temperature for articles molded from Polypropylene beads is much higher. The expanded beads molding setup at PPI consists of a manually operated molding press, a mold, a small steam generator capable of generating steam at a pressure of 300 psi and associated electronics. The mold, shown in the picture, produces a cubical sample.

The protocol of purging, autoclaving and cooling is extremely important for the production of parts from PP foamed beads. All these operations are controlled from a remote station. Cycle time and the design of the mold are also important factors. Normally a test mold can be made very inexpensively from aluminum.

Part molded from PP foamed beads is being taken out of the mold.


For more information, please contact

Dr. Niloufar Faridi

(973) 596-5665

faridi@polymers-ppi.org