The screw is the main part for a plastic extruder. The screw is usually contained inside a tight fitting barrel driven by a variable speed motor and gearbox. Plastic extruder is a highly efficient device capable of processing several tons of plastic per hour. The screw is divided into three division the feed section, the compressor and the metering section.
 

The feed section of the screw mechanism in a plastic extruder stores and delivers resin pellets from a gravity fed hopper into the jacketed screw to begin the plastic longitudinal movement. Plastic extruder's Screw threads move the plastic using axial rotation. Within the barrel, heaters help the plastic develop a tack to increase its friction against the barrel wall. Without this friction the plastic could not be conveyed forward and would merely rotate inside the screw.
 

In the transition or melt stage of the plastic extruder, the root diameter of the screw increases while the height of the flight decreases. The resin is melted here because of compression, shearing and heating produced in the barrel of the plastic extruder. Now the melt moves to the metering section, where the screw diameter remains constant. The melted plastic which is under high pressure now is pumped into the plastic extruder die.