| Bubbles, Voids | |
| Possible Cause | Suggested Remedy |
| Excessive internal shrinkage | a. Increase packing pressure b. Increase injection forward time c. Increase gate thickness d. Minimize, or core out, heavy sections in part design e. Increase feed, ensure cushion f. Replace check valve if cushion cannot be held |
| Melt temperature too high | a. Decrease melt temperature b. Lower back pressure c. Lower screw RPM |
| Moisture in material | a. Review material handling to eliminate moisture pick up b. Dry material prior to moulding c. Utilize hopper dryers d. Review percent of regrind |
| Air entrapment | a. Add mould venting b. Relocate gate c. reduce clamp pressure to allow parting line vents to work |
| Condensation on mould surface | a. Wipe mould surface thoroughly with solvent b. Increase mould temperature |