Reduce PET Blow Molding Reject Rate: Causes and Solutions for Deformation & Uneven Wall Thickness

High reject rates in blow molding directly increase material costs, lower output, and affect your production profit. For most PET bottle manufacturers, deformation and uneven wall thickness are the two most common defects that cause high scrap rates.

In this post, we explain the real causes and practical solutions to help you reduce rejects quickly and stabilize bottle quality.

1. Bottle Deformation

Common Causes

· Insufficient or uneven cooling of the mold

· Unstable blowing pressure or short blowing time

· Unqualified preform heating

· Improper temperature setting

· Mechanical movement not stable

Effective Solutions

· Optimize mold cooling system and water circulation

· Keep blowing pressure stable and extend blowing time properly

· Use accurate infrared heating to ensure even temperature

· Adjust machine parameters to match preform material

· Choose servo-controlled blow molding machines for stable action

2. Uneven Wall Thickness

Common Causes

· Unbalanced preform heating

· Improper stretch rod position or movement

· Low machine control precision

· Unstable air pressure during blowing

· Mold alignment error

Effective Solutions

· Use independent temperature zones for more even heating

· Adopt precision servo stretch control

· Calibrate stretch rod regularly

· Maintain stable high-pressure air supply

· Ensure accurate mold installation and locking

How ZEGO Machinery Helps You Lower Reject Rate?

All ZEGO fully automatic PET blow molding machines are designed to reduce defects and improve stability:

· High-precision servo drive system for stable stretching and blowing

· Independent infrared heating control for uniform preform temperature

· Optimized cooling design to avoid bottle deformation

· Stable action and low vibration for consistent quality

· Professional parameter guidance to keep reject rate below 0.3%

With ZEGO machines, you produce better bottles, waste less material, and gain higher profit.

If you are struggling with high reject rates, unstable quality, or low production efficiency, ZEGO provides professional turnkey solutions for global customers.

Contact us today and build a more stable and efficient PET bottle production line!