Non Isothermal Flow Dynamics and Viscous Heat Generation in Polymer Melt Extrusion
Non-isothermal viscous dissipation drives core melt temperature spikes that cause extrudate defects if die land geometry is not scaled to shear rates.
Screw Metering Zone
Meaning
Functional sections located at the discharge end of an extrusion screw regulate the final flow and pressure of the material. The screw metering zone has a constant, shallow flight depth that ensures a consistent volume of plastic is delivered to the die. It acts as a pump that smooths out any pulsations coming from the earlier melting stages.
Volume Control
The dimensions of the flights in this area determine the pumping capacity of the extruder. Within the screw metering zone, the material is fully melted and pressurized to overcome the resistance of the downstream tooling. A deeper flight in this section increases the output but may reduce the stability of the flow.
Pressure Stability
Maintaining a constant force at the die entrance is necessary for achieving uniform product dimensions. The screw metering zone creates a seal that prevents the high pressure at the die from leaking back into the melting section. This stability is the primary indicator of the machine’s capability to produce high-quality goods.
Mechanical Load
High pressures in this final section put a heavy strain on the thrust bearings and the motor of the extruder. Monitoring the torque required to turn the screw metering zone helps identify if the material is too cold or if the die is restricted. Excessive load can lead to mechanical failure and unplanned downtime in a production facility.