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Discoloration, Contamination

Discoloration, Contamination
Possible Cause Suggested Remedy
Material overheated in injection cylinder a. Decrease melt temperature
b. Decrease overall cycle
c. Residence time in cylinder excessive for shot size – use smaller barrel
d. Decrease nozzle temperature
e. Decrease screw RPM
f. Decrease back pressure
g. Check calibration of cylinder controllers
h. Check barrel and nozzle heater bands and thermocouples
Burned material hanging up in cylinder, nozzle (black specks), or check ring a. Purge injection cylinder
b. Remove and clean nozzle
c. Remove and inspect non-return valve for wear
d. Inspect barrel for cracks or gouges
e. Decrease injection rate
Material oxidized by drying at too high temperature Reduce drying temperature to 180°F (82°C)
Contamination by foreign material a. Keep hopper covered
b. review material handling procedures for virgin and regrind
c. Purge injection cylinder