During PET sheet production, many common defects affect surface quality, thickness consistency and yield rate. Most PET sheet extrusion problems come from improper drying, unstable temperature, roller parameters and raw material issues.
1. Sheet Bubbles & Air Holes
Problem Cause
- PET material moisture is too high
- Insufficient drying or uneven drying temperature
- Recycled PET flakes contain residual water
Solutions
- Extend drying time and stabilize dehumidifier temperature
- Check dryer air flow and filter regularly
- Control moisture rate before feeding materials
2. Uneven Sheet Thickness
Problem Cause
- Unbalanced T-die gap
- Unstable extruder output speed
- Three-roll calender pressure unbalanced
Solutions
- Fine-tune T-die temperature and gap uniformity
- Stabilize screw speed and feeding quantity
- Calibrate three-roll pressure and parallelism
3. Sheet Surface Scratches & Streaks
Problem Cause
- Dirty die or scratched roller surface
- Impurities in PET melt
- Damaged screen mesh
Solutions
- Clean T-die and replace screen filter regularly
- Polish roller surface to keep smooth
- Control raw material purity
4. Sheet Warping & Curling
Problem Cause
- Uneven cooling temperature on upper and lower rollers
- Too fast haul-off speed
- Internal stress caused by improper temperature setting
Solutions
- Balance three-roll temperature difference
- Match extrusion speed with haul-off speed
- Slow down cooling speed properly to release stress
5. Low Sheet Transparency & Haze
Problem Cause
- Overheating or insufficient plasticization
- Poor raw material quality
- Aging screw and barrel
Solutions
- Optimize extrusion temperature profile
- Use high-quality PET resin or qualified recycled flakes
- Check and replace worn screw and barrel parts
6. Sheet Edge Cracking
Problem Cause
- Low edge temperature
- Excessive tension during winding
- Unstable die edge flow
Solutions
- Adjust die edge heating zone
- Stabilize winding tension
- Optimize melt flow balance
Conclusion
Most PET sheet extrusion problems are caused by moisture, temperature instability, equipment calibration and raw material quality. Standard operation and regular machine maintenance can greatly reduce defects and improve production yield.
We provide high-stability PET sheet extrusion lines and professional technical guidance. Contact us for more solution support!
Hot Tags: apet/petg/pet mono or multi layer sheet production line, China apet/petg/pet mono or multi layer sheet production line manufacturers, suppliers, factory, Pvc Sheet Line, Pe Sheet Making Machine, Pe Thick Sheet Extrusion Line, Pp Sheet Extrusion Line, Pmma Sheet Extrusion Machine, Polyethylene Plastic Liner