Short shot (incomplete fill)
Cause
Low injection pressure, insufficient material, or blocked gate prevents full cavity fill.
Corrective action
Increase injection pressure/speed, check shot size, clear/clean the gate, verify melt temperature.
Diagnosis guide: Short shot (incomplete fill)
What you will see
Part of the preform did not fill: a rounded or missing thread start, support ring or sealing surface, or in severe cases a short body. Affected preforms weigh less than the SKU nominal.
Likely causes
- Shot size or injection pressure too low at the preform plant
- A partly blocked gate or hot-runner nozzle on one cavity
- Melt temperature too low for the melt to fill thin sections
- A blocked cavity vent trapping air at the end of fill
Do this first
STOP receiving. Inspect and weigh 30 preforms from the carton.
How to diagnose it
- Inspect the neck, thread start and support ring of 30 preforms under a magnifier
- Weigh the same 30 preforms on a 0.01 g balance and compare with the SKU spec sheet nominal
- Read the cavity number on every short preform: one cavity repeating points to a blocked gate or vent
- Apply the Go/No-Go neck gauge to the suspect preforms
How to fix it
- Quarantine the lot
- Contact Delta with photos, weights and cavity numbers
- Sort the lot only with Delta's agreement; a short neck finish will not seal