Preheating apparatus for an extruder

An apparatus for preheating thermoplastic material prior to entry of the material into an extruder barrel, comprising:

• an elongated housing having a central bore, an inlet adjacent a first end of the housing, and an outlet between the inlet and a second end opposite the first end of the housing, both the inlet and the outlet intersecting the central bore;
• a material flow path beginning at the inlet, continuing through the central bore, and passing from the central bore through the outlet;
• a pair of adjacent, parallel feed screws received within the central bore of the housing for blending the thermoplastic material and advancing it along the material flow path, each feed screw having
• a main body section having a helical flight configured to form a screw channel that is generally U-shared in cross-section and to advance the material from the inlet toward the outlet when the feed screw is rotated,
• an open section having a constant diameter, and
• a terminal section having a helical flight configured to form a screw channel that is generally U-shaped in cross-section and with a lead opposite that of the main body section,
• such that the main body section extends from the inlet to the open section which is adjacent the outlet, and the terminal section extends from the open section to the second end of the housing;
• drive means for rotating the feed screws in the same direction within the central bore;
• and
• means for heating the thermoplastic material to a desired temperature as it is blended and advanced along the material flow path.