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Common Problems in PET Bottle Blowing and How to Solve Them
The PET bottle blowing industry plays a crucial role in packaging, ensuring the production of high-quality bottles for beverages, pharmaceuticals, and other liquid products. However, manufacturers often encounter various challenges during the PET bottle production. Understanding these problems and their solutions can improve efficiency, reduce waste, and enhance product quality.
In this guide, we’ll explore 8 common PET bottle blowing problems, their causes, and practical solutions to optimize your production process. Whether you operate a PET bottle blowing machine or oversee production, this article will help you troubleshoot issues effectively.
1. Bottom Not Fully Formed (Recessed Feet)
Symptoms:
The bottom profile is unsatisfactory, with partially concave corners.
While it may not affect filling, it reduces bottle stability.
Causes:
Insufficient high-pressure gas.
Low temperature at the bottom corners.
High-pressure blowing time is too short (pre-blowing too long).
Delayed pre-blowing start.
Blocked exhaust holes in the bottom mold.
Solutions:
✔ Increase high-pressure air intake to at least 28 BAR.
✔ Check the high-pressure filter for blockages.
✔ Ensure valves function correctly for pre-blow and high-pressure forming.
✔ Verify pre-blow and high-pressure settings for accuracy.
✔ Optimize pre-blow timing—delayed pre-blow shortens high-pressure cooling time.
✔ Clean exhaust holes in the bottom mold.
✔ Increase heating in the bottom corner area (adjust lamp tubes).
✔ Reduce temperature in thinner sections to redistribute material.
2. Bottle Mouth Expansion (Thread Expansion)
Symptoms:
Threaded area expands, starting from the bottle mouth.
More severe in hot weather, sometimes accompanied by a bursting sound from gas leakage.
Causes:
High furnace cooling water temperature.
Insufficient cooling water flow.
Incorrect cooling plate position.
Poor furnace ventilation.
Improper lamp tube rack adjustment.
Excessive temperature in Zone 1.
Solutions:
✔ Monitor cooling water temperature and flow rate.
✔ Adjust the cooling plate position (1.5mm from preform, 2mm above the support ring).
✔ Improve furnace ventilation (open side doors for better airflow).
✔ Reduce Zone 1 heating percentage or lamp count.
✔ Optimize cooling plate design if necessary.
3. Bent Bottleneck (Crooked Neck)
Symptoms:
Neck tilts to one side.
Threaded area deforms, affecting filling and capping.
Causes:
Mechanical misalignment.
Excessive mold body temperature.
Inconsistent mold cooling.
Uneven material distribution at the neck.
Solutions:
✔ Ensure 0.25mm clearance between the preform and mold.
✔ Check mold cooling flow rate and temperature balance.
✔ Align the blowing nozzle with the mold.
✔ Increase heating in the neck area for better material distribution.
4. Blue Bottom Line (Hot Bottle)
Symptoms:
Pearlescent stripe along the bottom cut line.
Thinner material in affected areas.
Causes:
Excessive pre-blow pressure.
Slow stretching speed.
Early pre-blow air intake.
Solutions:
✔ Check for pre-blow solenoid valve leaks.
✔ Reduce pre-blow pressure.
✔ Inspect the stretching cylinder for air leaks or resistance.
✔ Clean or replace worn seals in the stretching mechanism.
✔ Adjust pre-blow timing.
5. Damaged Bottle Bottom
Symptoms:
Small cracks near the bottom, often near the pouring point.
Causes:
Mechanical stress.
Insufficient preform bottom temperature.
Solutions:
✔ Ensure proper stretching rod clearance (2/3 of preform bottom thickness).
✔ Check extension buffer alignment.
✔ Increase heating at the bottom (adjust lamp tubes).
6. Damaged Bottle Mouth Threads
Symptoms:
Threads are deformed or stretched.
Causes:
Mechanical misalignment during transfer.
Poor nozzle-mold alignment.
Excessive thread area temperature.
Solutions:
✔ Calibrate the transfer arm manipulator.
✔ Use alignment tools for the blow nozzle.
✔ Adjust cooling plate distance and improve ventilation.
7. Excessive Liquid Level Drop After Filling
Symptoms:
Bottle expands excessively after filling.
Causes:
Overheating during blowing, reducing material strength.
Solutions:
✔ Ensure visible pearlescence (optimal stretching).
✔ Avoid overheating—set correct temperature profiles.
8. Bottle Bursting
Symptoms:
Cracks at the bottom or transition areas.
Causes:
Insufficient material stretch.
Wrinkles forming at the bottom.
Uneven bottom thickness.
Low IV (intrinsic viscosity) value.
Solutions:
✔ Optimize stretching (see “Bottom Damage” section).
✔ Ensure uniform material distribution.
✔ Check preform quality if issues persist.
Final Thoughts
Understanding and troubleshooting PET bottle blowing problems ensures smoother production and higher-quality bottles. Regular maintenance of PET bottle blowing machines, proper temperature control, and material handling are key to minimizing defects.
By implementing these solutions, manufacturers can reduce waste, improve efficiency, and meet industry standards. For more insights into the PET bottle blowing industry, stay updated with the latest technical guides and best practices.
