| Problem |
 |
Possible Cause |
|
Possible Solution |
|
| Rough Surface |
|
Melt too cold |
|
Increase barrel temperature |
|
|
|
|
|
Increase die temperature |
|
|
|
Heaters not working |
|
Check thermocouples and heater bands |
|
|
|
Melt not mixed |
|
Use higher compression ratio screw or screw with mixing section |
|
|
|
Die design |
|
Decrease land length |
|
| Uneven Cross Section |
|
Surging |
|
Decrease extrusion rate |
|
|
|
|
|
Use screw with longer feed or metering section |
|
|
|
|
|
Use screen pack to increase back pressure |
|
|
|
|
|
Decrease die temperature |
|
| Black Specks / Undispersed Lumps |
|
Contamination |
|
Purge with low melt flow PP or HDPE |
|
|
|
|
|
Check the colour concentrate is based on PS,PP or PE - not PVC |
|
| Odor / Yellowing |
|
Melt too hot |
|
Decrease die and barrel temperature |
|
|
|
|
|
Decrease screw speed and back pressure |
|
| Voids |
|
Moisture |
|
Dry pellets |
|
|
|
|
|
If using vacuum check that vent is unplugged |
|
| High Extruder pressure / Low Throughput |
|
Melt too cold |
|
Increase extruder temperature |
|
|
|
|
|
Increase die temperature |
|
|
|
Clogged screen pack |
|
Clean/Replace |
|
|
|
Heaters not working |
|
Check thermocouples and heater bands |
|
