Stringing / gate stringing
Cause
Gate temperature too high or slow gate freeze leaves a string of material at the gate.
Corrective action
Lower gate/tip temperature, optimize hold time, check valve-gate timing and cooling.
Diagnosis guide: Gate stringing (string or tail at the gate)
What you will see
A thin string or tail of PET hangs from the gate point at the base of the preform. Strings can break off as loose PET fibres in the carton, and a long tail can blow into a weak or off-centre base.
Likely causes
- Hot-runner nozzle tip or gate temperature too high at the preform plant
- Valve-gate pin closing late or worn, so the gate does not shut cleanly
- Hold or cooling time too short for the gate to freeze
Do this first
Inspect the gate of 30 preforms and check the carton for loose strings.
How to diagnose it
- Inspect the gate of 30 preforms under a magnifier and measure any tail
- Check the carton and liner for loose PET strings
- Note the cavity numbers of affected preforms
- Blow 10 preforms and inspect the base for an off-centre gate or a weak spot
How to fix it
- Quarantine the lot if strings are loose in the carton (contamination risk on the blow line)
- Contact Delta with photos, tail length and cavity numbers