Splay (silver streaks)
Fine silvery streaks on the part surface in the flow direction.
Symptoms
- Silvery streaks starting at the gate and extending in the flow direction
- Foaming or bubbling purge shot
- Dull and broken lines on the surface
Tip: If the streaks are in the same place and the same shape in every cycle, it is moisture; if they are random, it is air or shear heat.
Order of solutions
- Make an air shot (purge) and check for foaming
- Dry the material under the conditions in the data sheet; check the dryer dew point
- Reduce the melt temperature and the residence time
- Reduce the decompression
- Clean the barrel; purge out the degraded material
Likely causes
Process setting
- Melt temperature too high or residence time too long (degradation)
- Too much decompression (suck-back); air is drawn in
- Back pressure too low, screw speed too high (shear heat)
Raw material
- Material is moist (PA, PC, PET, ABS, PBT)
- Regrind is moist or degraded
- Volatile additive or pigment
Machine
- Dryer faulty or dew point insufficient
- Dead spot in the screw/barrel, degraded material
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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.