Page 474 - Injection Molding Advanced Troubleshooting Guide
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474 47 Weld Lines
Figure 47.3 Magnified weld line
Verify melt temperature against the documented process as well as against the
supplier-recommended settings. If melt temperature is off, verify that the various
settings that contribute to melt temperature are set correctly. The key items to
check relative to melt temperature include:
Screw recovery speed
Back pressure
Barrel temperatures
Residence time
Screw design (only changes if the screw was replaced or the job was moved to
another machine)
If any of the above conditions have changed when compared to the documented
process make the required correction.
47.3.1.3 Molding Process: Second-Stage Pressure
It is important to provide adequate pack pressure at weld lines. Higher pack pres-
sures will force the material at the weld line to co-mingle and provide stronger
bonds between the plastic at the weld line. Fully packed-out parts will provide
stronger weld lines.
