Flow marks
Gloss differences in the form of waves or rings on the surface.
Symptoms
- Rings around the gate
- Wavy, record-groove-like lines on the surface
Tip: Fast and hot filling is usually the shortest way to get rid of flow marks.
Order of solutions
- Increase the melt and mold temperature
- Increase the speed (so that it fills before the front cools down)
- Increase the holding pressure
- Enlarge the gate or add radii at the transitions
Likely causes
Process setting
- Melt front is cooling down (low temperature or low speed)
- Insufficient holding disturbs the contact of the surface with the mold
Mold
- Gate cross-section small
- Mold surface too cold
Part design
- Wall thickness difference (abrupt transition)
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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.