Underwater pelletizing machine and method of extruding foamed thermoplastic pellets

A method of extruding foamed thermoplastic plastic pellets, comprises the steps of:

• uniformly mixing thermoplastic material and foaming agent;
• extruding the thermoplastic material mixed with the foaming agent to a high-pressure underwater pelletizing machine;
• forcing high temperature liquid at a high pressure over a cutter to rotate the cutter, said cutter being rotatable about an axis of rotation parallel to or coincident with a flow path of the forced high temperature liquid over the cutter;
• cutting extruded thermoplastic material mixed with the foaming agent into thermoplastic pellets by rotation of the cutter;
• and
• transporting the thermoplastic pellets out of the high-pressure underwater pelletizing machine using the high-temperature liquid in a direction parallel to the axis of rotation of the cutter, said transporting comprising delivering the thermoplastic pellets to a foaming chamber through a pressure drop device connected thereto and cooling the foamed thermoplastic pellets in the foaming chamber, said foaming chamber being connected to the high-pressure underwater pelletizing machine.