Nozzle drool and stringing
Drooling and strings form at the nozzle or at the hot runner gate.
Symptoms
- String at the gate while the mold opens
- Melt drop at the nozzle tip
- Fine string residue on the part
Tip: If you increase the decompression too much, splay (air) appears; find the balance by trial.
Order of solutions
- Increase the decompression (do not overdo it, it draws in air)
- Reduce the nozzle and hot runner temperature
- Shorten the nozzle and mold contact time
- Use a valve-gated hot runner or a nozzle shut-off
Likely causes
Process setting
- Decompression (suck-back) insufficient
- Nozzle or hot runner temperature too high
- Melt viscosity too low
Machine
- Nozzle shut-off not working
Mold
- Hot runner gate temperature high, open-tip gate
- Valve gate delay
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Other defects
Short shot (incomplete fill)
The cavity does not fill completely; the farthest or thinnest area of the part stays incomplete.
Flash
Plastic escapes through the parting line or around the ejector pins.
Sink mark
A dent on the surface opposite a thick section; the surface is drawn inwards.
Void (internal vacuum void)
Internal cavity in a thick section of the part; the outer surface may look perfect.