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Weld Lines

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