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