🔍 Why Do PET Bottles Develop Defects During Blow Molding?
🔍 Why Do PET Bottles Develop Defects During Blow Molding?
Most people see a plastic bottle.
PET engineers see a complex interaction of heat, pressure, stretching, cooling, and material behavior.
When one parameter drifts outside its optimal range, bottle defects begin to appear.
Here are some of the most common PET bottle defects and their engineering causes:
PANELING
Bottle walls collapse inward after production.
Possible causes:
• Uneven wall thickness distribution
• Insufficient material orientation
• Poor vacuum resistance
• Lightweight bottle design exceeding process limits
ROCKER BOTTOM
The bottle does not sit flat and wobbles on the conveyor.
Possible causes:
• Base cooling imbalance
• Stretch timing mismatch
• Uneven crystallization control
• Off-center material distribution
PEARLESCENCE (WHITENING)
White stress marks appear during blowing.
Possible causes:
• Surface overheating
• Cold core temperature
• Over-stretching of PET molecules
• Thermal-pressure imbalance
NECK DEFORMATION
The bottle neck loses dimensional accuracy.
Possible causes:
• Neck overheating during reheating
• Cooling imbalance between cavities
• Stretch rod misalignment
• Neck finish tolerance drift
SHORT SHOT
The bottle fails to fully form.
Possible causes:
• Insufficient blowing pressure
• Improper preform temperature profile
• Air flow restriction
• Transfer timing mismatch
- At BANGEMACHINE, we believe bottle defects should not be treated as isolated problems.
Most defects originate from the interaction between:
• Heating Control
• Servo Stretch Synchronization
• Pressure Curve Stability
• Cooling Balance
• Mold-Machine Compatibility
Stable PET production is not achieved by correcting defects after they appear.
It is achieved by controlling the process before they happen.
What PET bottle defect causes the most trouble in your factory?
