← Defect Guide
Black Specks
Dark specks on or inside the part, caused by carbonized resin residue or contamination.
◆ Common Causes
- •Carbonized residue from previous resin/color (incomplete purge)
- •Carbon buildup in screw/barrel/check-ring dead spots
- •Melt temperature or residence time too high (thermal degradation)
- •Contaminated regrind, hopper, or environment
- •Worn screw or barrel
◆ Solutions
- ✓Purge thoroughly (verify over 3–5 shots after a changeover)
- ✓Pull and clean the screw; consider low-dead-space tips
- ✓Lower melt temperature and shorten cycle (reduce residence)
- ✓Keep regrind and hopper clean
- ✓Ensure adequate shot-to-barrel ratio
◆ Resin-Specific Notes
POM
Prone to specks/gas from formaldehyde-type degradation. Minimize residence time.
PVC
Sensitive to thermal degradation. Strict temperature and residence control.
FR Grades
Check flame-retardant decomposition temperature; carbonizes with long residence.
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This content is a field-reference summary. Final judgment requires on-site engineer verification.