Uneven wall thickness
Cause
Poor preform temperature profile or stretch-blow timing gives thin/thick zones.
Corrective action
Optimize preform heating profile, adjust pre-blow timing/pressure, verify stretch rod speed.
Diagnosis guide: Uneven wall thickness — body has thin and thick zones
What you will see
Wall thickness varies by more than ±15% across the body when measured around the circumference or top-to-bottom. Cross-section shows clearly asymmetric distribution. Causes top-load and burst failures.
Likely causes
- Asymmetric heating across preform — one side hotter than other
- Lamp output uneven (some lamps decayed)
- Preform off-center in oven — closer to lamps on one side
- Pre-blow valve flow rate uneven
- Mold not parallel — bottle stretches off-axis
Do this first
Measure 4-point wall thickness on 10 sample bottles, identify pattern (front-back, top-bottom, around circumference).
How to diagnose it
- Cut bottle horizontally at body midpoint; measure wall at 0°, 90°, 180°, 270°
- Tabulate by cavity number to see if pattern is cavity-specific or systemic
- Inspect preform feeding orientation in oven
- Check pre-blow valve flow rates with manometer per cavity
How to fix it
- Replace all lamps showing >15% output deviation
- Re-center preform feeding rails so preforms stay axisymmetric in oven
- Balance pre-blow flow per cavity using flow valves
- Inspect mold for parallel alignment; correct if off