EPP is short for Expanded polypropylene, The purpose of EPP pre-expansion is to produce expandable polypropylene particles to the desired density. During pre-expansion, the EPP resins are fed to a vessel containing an agitator and controlled steam and air supplies, this vessel is called EPP Pre-expander. The diameter of the particles increases while the density of the resin decreases. After exiting from the pre-expander, the expanded beads will flow through a dryer to remove moisture, and then go to aging silo.