Jetting (snake marks)
The melt shoots into the cavity like a jet and fills it like a wavy thread without spreading against the wall.
Symptoms
- Wavy, snake-like mark starting at the gate
- Different surface and strength zones
- Dullness near the gate
Tip: Keeping the first stage slow is often enough on its own.
Order of solutions
- Reduce the speed through the gate, then increase it (profiled speed)
- Increase the melt/mold temperature
- Enlarge the gate or turn it towards a wall/protrusion
- Use a fan gate or an impingement surface instead of a direct gate
Likely causes
Process setting
- High speed through the gate
- Low mold and melt temperature
Mold
- No wall opposite the gate direction (opens into a free space)
- Small gate
Part design
- Gate location unsuitable
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Related articles
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.