Extruder melt blockage

Cooling is often provided at the hopper and feed port, to prevent premature melting of the plastic, which can create blockages that interfere with a consistent rate of flow of the plastic into the extruder. 

Once the sample is in place, the piston should be inserted and slowly driven down on top of the sample until a small flow is extruded from the die. This will compress the sample and drive out air bubbles. Usually, by the time the piston is inserted into the barrel the material at the bottom is melted enough to flow, though care should be taken not to overpressure the system. Pushing a small amount of material through the die will help to purge any old material left from previous testing. A pressure spike indicates that the material has filled the pressure tap and no blockage is present. 

---