Most preform quality problems trace back to a handful of recurring defects. Knowing the likely cause turns a line stoppage into a quick correction.
Calibrated neck-finish gauges in our QC lab, used to check preform neck dimensions. More about our plant →
Short shot / incomplete fill
Usually low injection pressure, cold melt or a blocked gate. First action: check melt temperature and hold pressure before adjusting the mould.
Bubbles & haze
Bubbles point to moisture — verify resin drying (dew point and residence time). Haze often signals crystallinity from excessive heat or slow cooling.
Acetaldehyde (AA) & black specks
High AA comes from over-heating the melt (a flavour risk for water). Black specks indicate degraded material or contamination — purge and inspect the hot runner.
Diagnose faster
Delta’s Defect Diagnosis Advisor covers a 100+ defect library across preforms, bottles and closures, with symptoms, causes, remediation and prevention for each. Browse the full Defect Library.
Frequently asked questions
What causes a short shot (incomplete fill) in a PET preform?
Usually low injection pressure, cold melt or a blocked gate. First check melt temperature and hold pressure before adjusting the mould.
Why does a PET preform have bubbles or haze?
Bubbles point to moisture — verify resin drying (dew point and residence time). Haze often signals crystallinity from excessive heat or slow cooling.
What causes high acetaldehyde or black specks in PET preforms?
High AA comes from over-heating the melt (a flavour risk for water); black specks indicate degraded material or contamination — purge and inspect the feed.
How can I diagnose a PET preform defect quickly?
Use Delta's Defect Diagnosis Advisor — a 100+ defect library across preforms, bottles and closures with symptoms, causes, remediation and prevention.
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