A practical guide for extruding PET
Extruding PET (Polyethylene Terephthalate) requires precise temperature control, proper drying, and the right screw speed to ensure high-quality filament or sheet extrusion. Here’s a breakdown of key considerations for your single-screw extruder with three heater bands and variable motor speed:
Drying the PET (Critical Step)
PET is highly hygroscopic, meaning it absorbs moisture from the air. If not properly dried, it will degrade during extrusion, leading to bubbles, brittleness, and poor mechanical properties.
- Pre-dry the PET at 160–180°C (320–356°F) for 4–6 hours in a desiccant dryer with a dew point below -40°C (-40°F).
- If you don’t have a desiccant dryer, an oven at 120°C (248°F) for 8+ hours can work, but it’s less effective.
Recommended Heater Band Temperatures
PET requires a gradual heat profile to prevent degradation:
- Zone 1 (Feed Section): 240–250°C (464–482°F)
- Zone 2 (Compression Section): 260–270°C (500–518°F)
- Zone 3 (Metering Section/Die Zone): 270–280°C (518–536°F)
Make sure the barrel temperature increases gradually from the hopper to the die to avoid premature melting and poor mixing.
Screw Speed & Motor Settings
- Start at 40–60 RPM and adjust based on output quality.
- Too high of an RPM can cause excessive shear stress, leading to thermal degradation.
- Monitor the melt pressure—if it fluctuates too much, adjust speed accordingly.
Die Temperature & Cooling
- Keep the die at 270–280°C to ensure proper flow.
- Use a cooling water bath or air cooling to solidify the extruded PET properly.
Filament Cooling
- Use a water bath at 40–60°C (104–140°F) to cool the extruded filament gradually.