| 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 |