The essential elements for a thermoplastic extruder are a tubular barrel, usually electrically heated; a revolving screw, ram or plunger within the barrel; a hopper at one end from which the material to be extruded is fed to the screw, ram or plunger; a die at the opposite end for shaping the extruded mass.
Extruders may be divided into three general types:
* Single Screw Extruder
* Twin or Multiple Screw Extruder
* Ram Extruder
Single screw extruders and twin screw extuders are the most widely used extruders. The screw that is used to push the resin out of the die is the important component of a screw extruder. In the earlier days rubber screw were used but the rubber screw was not able to give enough amount of shear into the polymer. Therefore, screws were designed that would start deeper in the feed and gradually taper shallower in the metering section to apply more work on the polymer as it was going from the feed to the discharge.