Cold slug mark
Melt that has cooled in the nozzle enters the cavity and creates a ring or a dull zone around the gate.
Symptoms
- Ring or hard zone around the gate
- Solidified plug in the nozzle after the cycle
- Intermittent defect
Tip: If the defect is more pronounced after the machine has stopped and restarted, look at the nozzle temperature.
Order of solutions
- Increase the nozzle temperature
- Review the decompression and the nozzle retraction settings
- In a cold runner mold, add a cold slug well at the end of the runner
- Shorten the nozzle-to-mold contact time
Likely causes
Process setting
- In a long cycle the nozzle freezes while the screw is retracted
Machine
- Nozzle temperature low
- Nozzle-to-mold contact time long, heat is drawn off
- Cooling in the hot runner nozzle
Mold
- No cold slug well (cold runner)
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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.