Sticking / drag marks
The part is hard to eject; scuffs or scratches form on the surface during ejection.
Symptoms
- Lines in the ejection direction
- Part stays stuck to a mold half
- Deformation during ejection
Tip: If sticking occurs on one half only, look at the temperature difference between the mold halves.
Order of solutions
- Reduce the holding pressure and time
- Increase the cooling time
- Reduce the mold temperature
- Check the draft angle and the polish
- Air ejection or mold release agent
Likely causes
Process setting
- Too much holding, the part is clamped in the mold
- Cooling insufficient (part is soft)
- Mold too hot
Raw material
- No mold release agent or too much of it
Mold
- Draft insufficient, surface rough
- Vacuum effect
- Surface damage (notches, worn coating)
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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.