- molds and plastics  injection troubleshooter -

• Black Specks - plastic injection troubleshooter

• Description:

Small black areas (spots) inside the material, mostly present in transparent resins.

• Causes:
machine · down time too long
· barrel switched off over a long period of time
· poor purging of barrel
· dirty plasticizing unit
· inadequate nozzle
mould · dead edges in gate/ runner system
material · granule impurities
· degradation by other resins
· pick-up of degraded material from cylinder wall during cooling

• Actions:

1st. Purge with an appropriate material in general, or with a universal purging compound like Kapronet. For PC, you can useground acrylic or regrind PC resin; for Ultem resin use regrind Ultem resin or glass-filled PC resin, and so on.
Don’t drop temperature settings while purging.
2nd. check for impurities: use uncontaminated material, do proper housekeeping
3rd. check and adjust melt temperature
4th. check for dead edges: nozzle, back flow valve, gates/runners
5th check for screw wear

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black specks
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