| Weld Lines (Knit Lines) | |
| Possible Cause | Suggested Remedy |
| Melt temperature too low | Increase melt temperature |
| Mould temperature too cold | Increase mould temperature |
| Insufficient pressure at the weld | a. Increase first stage injection pressure b. Increase boost time c. Increase packing pressure d. Increase pack time e. Increase injection speed |
| Entrapped air unable to escape from mould fast enough | a. Increase or provide adequate vents at the weld area b. Decrease injection rate |
| Excessive lubricant on mould surface plugging vents | a. Clean mould surface with solvent b. Use mould release sparingly |
| Distance from gate to weld line too far | a. Relocate or use multiple balanced gates b. Cut overflow tab in mould to improve weld line strength |
| Injection rate too slow | a. Increase injection speed b. Increase first stage injection pressure c. Increase boost time |